Reproduction

Class 11 Biology, unit 11, book pages 297–309

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Reproduction is the ability of an organism to make new offspring of its own type. It is not needed for the survival of the individual, but it is essential for the survival of the species. This unit describes the male and female reproductive systems of man, how sperms and eggs are made (spermatogenesis and oogenesis), how hormones from the hypothalamus, anterior pituitary and gonads control the male system by negative feedback, and how the female reproductive (menstrual) cycle is regulated in three phases.

Learning outcomes (4)

Describe the structures of the male reproductive system and identify their functions.
Define male reproductive hormones and explain their functions.
Explain the structures of the female reproductive system and describe their functions.
Describe the menstrual cycle and the hormones involved.

11.1Reproductive system of man

Every living thing can reproduce. Reproduction is a special characteristic of life, because the individual does not need it to stay alive (it needs nutrition, respiration and the others), but the species needs it. If all the members of the present generation died without producing offspring, the species would cease to exist.

Reproduction: The ability of an organism to produce new offspring of its own type.

Human reproduction needs internal fertilization: the sperm and the egg meet inside the body of the female. The human reproductive system is unique in two respects.

It does not become functional until it is 'turned on' at puberty by the action of sex hormones. All the other organ systems are functional at birth or shortly after.
Other body systems show only slight differences between male and female, but the reproductive system is quite different in the male and the female.

The reproductive system compared with the other organ systems
Feature	Other organ systems	Reproductive system
When it starts to work	At birth or shortly after	At puberty, when it is turned on by sex hormones
Difference between male and female	Slight	Quite different

Plan of the unit: the two systems side by side
	Male (11.1.1 to 11.1.2)	Female (11.1.3 to 11.2)
Gonads	A pair of testes	A pair of ovaries
Gamete (sex cell)	Sperm, made by spermatogenesis	Egg (ovum), made by oogenesis
Main job	Produce and maintain sperms	Produce eggs and nurture a developing embryo for about nine months
Hormonal control	GnRH, FSH, LH, testosterone, inhibin	FSH, LH, estrogen, progesterone (menstrual cycle)

11.1.1Male reproductive systemOften examined

The main function of the male reproductive system is to produce and maintain sperms.

Structure of the male reproductive system

The male reproductive system includes the following parts.

Gonads: the testes.
Accessory ducts: epididymis, ductus deferens (vas deferens), ejaculatory duct and urethra.
Accessory glands: seminal vesicles, prostate gland and bulbourethral glands.
Copulatory organ: the penis.

Figure 11.1: Human male reproductive system (lateral view).

Gonads (testes)

The testes are the male gonads. They lie outside the abdomen in a skin pouch called the scrotum. Each testis is divided into 250 to 300 lobules, and each lobule contains one to four tightly coiled seminiferous tubules, in which the sperms are made.

Figure 11.2: Anatomy of the testis. Each lobule holds coiled seminiferous tubules; sperms pass to the rete testis, then through the efferent ductules to the epididymis and the ductus deferens.

Accessory ducts

Once spermatozoa are produced, they move through the seminiferous tubules and enter a tubular network called the rete testis for further maturation. They are carried out of the testis by a series of efferent ductules. The epididymis is coiled on the outer surface of the testis and functions in the transport and storage of the sperms. The epididymis opens into another duct, the vas deferens, which joins the duct of the seminal vesicle to form the short ejaculatory duct. The ejaculatory duct enters the prostate gland and then empties into the urethra. The urethra is also called the urinogenital duct because it carries urine as well.

Path of the sperms

Sperms are made in the seminiferous tubules of the lobules of the testis.
They enter the rete testis, a tubular network, where they are matured further.
The efferent ductules carry them out of the testis.
They are transported and stored in the epididymis, coiled on the outer surface of the testis.
The epididymis opens into the vas deferens (ductus deferens).
The vas deferens joins the duct of the seminal vesicle to form the short ejaculatory duct.
The ejaculatory duct passes through the prostate gland and empties into the urethra, which also carries urine (urinogenital duct).

Copulatory organ (penis)

The human penis consists mainly of tissues that can fill with blood to cause an erection.

Accessory glands

Seminal vesicles: A pair of glands located at the junction of the sperm duct (vas deferens) and the ejaculatory duct.
Prostate gland: A gland that encircles the urethra just below the bladder.
Bulbourethral glands (Cowper's glands): A pair of glands situated at the junction of the ejaculatory duct and the urethra.

Figure 11.3: Human male reproductive system (ventral view). Note the paired testes, epididymides, vasa deferentia and seminal vesicles, the single prostate gland and the urethra running through the penis.

Function of the male reproductive system

The function of the male reproductive system in human reproduction is the production of sperms, which is also called spermatogenesis.

Each part of the male system and its function (as given in the book)
Part	Function
Testis (in the scrotum)	Produces sperms in its seminiferous tubules (spermatogenesis); the scrotum keeps it outside the body at about 35 °C
Seminiferous tubules	Tightly coiled tubules (one to four per lobule) in which sperms are formed
Rete testis	Tubular network where sperms undergo further maturation
Efferent ductules	Carry the sperms out of the testis
Epididymis	Transport and storage of the sperms
Vas deferens (ductus deferens)	Carries sperms onward; joins the duct of the seminal vesicle to form the ejaculatory duct
Ejaculatory duct	Short duct that passes through the prostate and empties into the urethra
Urethra (urinogenital duct)	Carries semen out of the body; also carries urine
Seminal vesicles, prostate gland, bulbourethral glands	Their secretions make the liquid part of the semen, which nourishes and protects the sperms and carries them
Penis	Copulatory organ; its tissues fill with blood to cause an erection

Worked example: identify the parts of the male system

The lateral view in the figure below has parts marked A to H. Name each part, and state the function of parts E, F, G and H.

Figure for the worked example: parts A to H of the human male reproductive system (lateral view).

Start with the parts whose position you know. A is the pubic bone, at the front. B is the penis, the hanging organ that carries the urethra. C is the scrotum, the skin pouch that holds the testis outside the abdomen.
Find the glands near the bladder. D lies just below the bladder and surrounds the urethra, so it is the prostate gland. F is the small gland behind the bladder where the sperm duct ends, so it is a seminal vesicle.
Inside the scrotum, G is the large oval organ, the testis. The coiled band E on its outer surface is the epididymis. The long tube H that rises from the epididymis towards the seminal vesicle is the vas deferens.
Functions. E, epididymis: transport and storage of sperms. F, seminal vesicle: its secretion forms part of the semen, which nourishes and protects the sperms. G, testis: produces sperms (and, as you will see in 11.1.2, testosterone). H, vas deferens: carries sperms onward, joining the duct of the seminal vesicle to form the ejaculatory duct.

A p u bi c b o n e, B p e ni s, C scr o t u m, D p r os t a t e, E e p i d i d y mi s, F se mina l v es i c l e, Gt es t i s, H v a s d e f er e n s

11.1.1Spermatogenesis (extra reading material)Often examined

Spermatogenesis is the process of sperm formation in males. It takes place in the inner (germinal) epithelium of the seminiferous tubules. The sperms are made from cells called spermatogonia by one series of mitotic divisions followed by the two divisions of meiosis, and then the cells change shape.

Spermatogenesis: The formation of sperms in males, in the germinal epithelium of the seminiferous tubules.
Spermatogonia: Diploid (2n) cells of the germinal epithelium that divide by mitosis and give rise to the primary spermatocytes.
Primary spermatocyte: A diploid cell that undergoes meiosis I to form two smaller haploid secondary spermatocytes.
Secondary spermatocyte: A haploid cell that undergoes meiosis II to form two spermatids.
Spermatid: A round, non-motile haploid cell, which after maturation changes into a motile, active sperm.

Stages of spermatogenesis

Spermatogonia divide by mitosis, forming a primary spermatocyte (2n).
Each primary spermatocyte undergoes meiosis I, forming two smaller haploid cells, the secondary spermatocytes (n). The chromosome number is halved here.
Each secondary spermatocyte undergoes meiosis II and produces two daughter cells called spermatids (n). One primary spermatocyte therefore gives four spermatids.
Each spermatid is a round, non-motile haploid cell. During maturation (differentiation) it elongates, sheds its excess cytoplasm and forms a tail, and becomes a motile, active sperm. The Sertoli cells provide the nutrients during this stage.

Spermatogenesis in the seminiferous tubule. The chromosome number is halved at meiosis I (coloured), so the secondary spermatocytes, spermatids and sperms are haploid (n).

The cells of spermatogenesis
Cell	Chromosome number	Formed by	Cells made from one primary spermatocyte
Spermatogonium	Diploid (2n)	Mitosis of stem cells	Divides by mitosis to give primary spermatocytes
Primary spermatocyte	Diploid (2n)	Mitosis of spermatogonia	1
Secondary spermatocyte	Haploid (n)	Meiosis I	2
Spermatid	Haploid (n)	Meiosis II	4
Sperm (spermatozoon)	Haploid (n)	Differentiation (maturation) of a spermatid	4

Structure of a human sperm: the head contains the nucleus and the acrosome, the midpiece contains the mitochondria, and the tail makes the sperm motile. The plasma membrane covers the whole cell.

Worked example: counting the cells of spermatogenesis

A section of seminiferous tubule contains 25 primary spermatocytes, all of which complete meiosis. How many secondary spermatocytes, spermatids and sperms are formed? How many of these cells are haploid?

Meiosis I turns one primary spermatocyte into two secondary spermatocytes, so the number doubles.
$25 \times 2 = 50 secondary spermatocytes$
Meiosis II turns one secondary spermatocyte into two spermatids, so the number doubles again.
$50 \times 2 = 100 spermatids$
Every spermatid matures into one sperm. There is no further division, so the number does not change.
$100 spermatids \to 100 sperms$
The primary spermatocytes are diploid (2n). All the cells formed after meiosis I are haploid (n), so the haploid cells are the secondary spermatocytes, the spermatids and the sperms.

Summary of the counts
Stage	Number of cells	Chromosome number
Primary spermatocytes	25	2n
Secondary spermatocytes	50	n
Spermatids	100	n
Sperms	100	n

50 secondary spermatocytes, 100 spermatids and 100 sperms; 4 sperms from each primary spermatocyte

11.1.2Hormonal control of male reproductive functionOften examined

Hormones are chemical messengers made by glands in the human body. They are carried through the blood to act on other organs, and they are important for growth, reproduction and well-being. The human male and female reproductive cycles are controlled by hormones from the hypothalamus and the anterior pituitary.

Hormones: Chemical messengers made by glands, carried in the blood to act on other organs.
GnRH (gonadotropin-releasing hormone): Hormone from the hypothalamus that makes the anterior pituitary release FSH and LH.
FSH (follicle stimulating hormone): Anterior pituitary hormone that stimulates the Sertoli cells of the testes to facilitate spermatogenesis.
LH (luteinizing hormone): Anterior pituitary hormone that stimulates the interstitial (Leydig) cells of the testes to make and release testosterone.
Testosterone: Male sex hormone made by the Leydig cells; it stimulates spermatogenesis and is responsible for the secondary sexual characteristics.
Inhibin: Hormone made by the Sertoli cells and released into the blood when the sperm count is too high.

How the hormones control sperm production

At the onset of puberty the hypothalamus sends GnRH to the anterior pituitary.
GnRH causes the anterior pituitary to release FSH and LH into the male system for the first time.
FSH enters the testes and stimulates the Sertoli cells to begin facilitating spermatogenesis, using negative feedback.
LH enters the testes and stimulates the interstitial cells of Leydig to make and release testosterone into the testes and the blood.
Testosterone stimulates spermatogenesis and is responsible for the secondary sexual characteristics: a deepening of the voice, and the growth of facial, axillary (armpit) and pubic hair, and so on.

Figure 11.5: Section of a seminiferous tubule. The Sertoli cells (coloured) reach from the wall to the lumen and support the developing cells; the Leydig cells lie between the tubules, below the spermatogonial cells.

Male reproductive hormones at a glance
Hormone	Made by	Acts on	Effect
GnRH	Hypothalamus	Anterior pituitary	Release of FSH and LH
FSH	Anterior pituitary	Sertoli cells of the testes	Facilitate spermatogenesis
LH	Anterior pituitary	Interstitial (Leydig) cells of the testes	Make and release testosterone
Testosterone	Leydig cells	Testes, blood, hypothalamus and anterior pituitary	Stimulates spermatogenesis; secondary sexual characteristics; inhibits GnRH, FSH and LH (negative feedback)
Inhibin	Sertoli cells	Hypothalamus and anterior pituitary	Inhibits GnRH and FSH when the sperm count is too high

Negative feedback system

A negative feedback system keeps sperm production steady. It acts in the male with rising levels of testosterone, and with the sperm count.

Testosterone: rising levels act on the hypothalamus and the anterior pituitary to inhibit the release of GnRH, FSH and LH.
Inhibin: the Sertoli cells produce inhibin, which is released into the blood when the sperm count is too high. It inhibits the release of GnRH and FSH, which causes spermatogenesis to slow down.
When the sperm count falls to 20 million per ml, the Sertoli cells stop releasing inhibin, so FSH is no longer held back and the sperm count increases again.

Figure 11.4: Hormones control sperm production in a negative feedback system. GnRH, then FSH and LH (marked +) stimulate the testis; testosterone and inhibin (coloured, marked −) inhibit the hypothalamus and the anterior pituitary.

Worked example: what happens when the sperm count is too high?

The sperm count in the testes of a man rises well above the normal level. Use the negative feedback system to explain how the count is brought back, and say what happens to spermatogenesis on the way.

The high sperm count is detected by the Sertoli cells, which respond by making inhibin. The inhibin is released into the blood.
Inhibin acts on the hypothalamus and the anterior pituitary and inhibits the release of GnRH and FSH.
With less FSH, the Sertoli cells are stimulated less, so spermatogenesis slows down and the sperm count falls.
When the count has fallen to about 20 million per ml, the Sertoli cells cease to release inhibin. FSH is no longer inhibited, spermatogenesis speeds up and the sperm count rises again.
The result is that the count moves up and down around a steady value. This is what is meant by negative feedback: the product of the process (inhibin, made when the count is high) works against the process itself.

Response to a high sperm count
Stage	Inhibin	GnRH and FSH	Spermatogenesis	Sperm count
Count too high	Released	Inhibited (fall)	Slows down	Falls
Count at 20 million per ml	Stops being released	No longer inhibited (rise)	Speeds up	Increases

H i g h co u n t \to inhibin r e l e a se d \to G n R H an d F S H inhibi t e d \to s p er ma t o g e n es i ss l o w s \to co u n t f a l l s

11.1.3Female reproductive systemOften examined

The reproductive role of the female is far more complex than that of the male. She not only has to produce gametes, but her body must also be prepared to nurture a developing embryo for a period of about nine months.

Structure of the female reproductive system

The female reproductive system consists of the gonads (a pair of ovaries), the oviducts, the uterus and the vagina.

Figure 11.6: Human female reproductive system. The wall of the uterus (myometrium) surrounds the cavity lined by the endometrium (coloured); the cervix joins the uterus to the vagina.

Gonads (ovaries)

The ovaries are the female gonads. They produce ova (eggs) and release hormones. A pair of ovaries lies on the side of the uterus, and each ovary is held in place within the peritoneal cavity by several ligaments. The ovaries are solid, ovoid structures, about 3 to 5 cm long and 2 to 3 cm wide.

Within the ovary there are many tiny sac-like structures called ovarian follicles, each of which consists of an immature egg, called an oocyte. In adult women, one of the ripening follicles ejects its oocyte from the ovary each month. This event is called ovulation. After ovulation, the ruptured follicle is transformed into a glandular structure called the corpus luteum.

Ovarian follicle: A tiny sac-like structure in the ovary that contains an immature egg (oocyte).
Oocyte: The immature egg inside an ovarian follicle.
Ovulation: The ejection of an oocyte from a ripening follicle of the ovary, once each month in an adult woman.
Corpus luteum: The glandular structure into which the ruptured follicle is transformed after ovulation.

Oviduct (Fallopian tubes)

The oviducts form the initial part of the female duct system. They receive the ovulated oocyte and are the site where fertilization generally occurs. Each oviduct is about 10 cm long and transfers the developing ovum from the ovary towards the uterus. The oocyte is carried towards the uterus.

Uterus

The uterus (womb) is a hollow, muscular organ shaped somewhat like an inverted pear. It has three portions: the fundus, the body and the cervix. The oviducts join the uterus just below the fundus, and the opening of the cervix leads to the vaginal canal.

The wall of the uterus is made of three layers.

The three layers of the uterine wall
Layer	Position	Description and role
Perimetrium	Outermost	Thin covering layer of the uterus
Myometrium	Middle	Thick muscular layer of bundles of smooth muscle; contracts rhythmically during childbirth to expel the baby from the mother's body
Endometrium	Innermost	Spongy lining of the uterine cavity; if fertilization occurs the young embryo is implanted into it and stays there for the rest of its development

The three layers of the wall of the uterus, from the outside to the cavity.

The main functions of the uterus are to receive, retain and nourish a fertilized ovum. The cervix is the narrow entrance to the uterus from the vagina. It is normally blocked by a plug of mucus.

Vagina

The vagina is a thin-walled tube, 8 to 10 cm long, which extends from the cervix to the body exterior. It is often called the birth canal because it provides a passageway for the delivery of an infant and for the menstrual flow. The urethra is embedded in its anterior wall.

Function of the female reproductive system

The organs of the female reproductive system are responsible for the production of the egg (oogenesis), fertilization, the development of the embryo and the production of female sex hormones.

Parts of the female system and their functions
Part	Function
Ovary	Produces ova (eggs) and releases hormones; holds the follicles and, after ovulation, the corpus luteum
Oviduct (Fallopian tube)	Receives the ovulated oocyte; usual site of fertilization; carries the developing ovum towards the uterus
Uterus	Receives, retains and nourishes a fertilized ovum; the embryo implants in the endometrium and develops there
Cervix	Narrow entrance to the uterus from the vagina, normally blocked by a plug of mucus
Vagina	Birth canal and passage for the menstrual flow; the urethra is embedded in its anterior wall

Worked example: where does the embryo implant?

A student writes: 'After fertilization the embryo is implanted in the myometrium, which is the layer that nourishes it.' Correct the answer, and say what the myometrium actually does.

Recall the three layers from the outside to the cavity: perimetrium, myometrium, endometrium. The embryo has to settle in the layer that faces the uterine cavity, which is the innermost one.
The innermost layer is the endometrium, the spongy lining of the uterine cavity. The young embryo implants into it and stays there for the rest of its development, so the student's layer is wrong.
The myometrium is the thick middle muscular layer of smooth muscle. Its job is to contract rhythmically during childbirth and expel the baby from the mother's body.
The perimetrium is only the thin outer covering of the uterus.

The embryo implants in the endometrium; the myometrium is the muscle layer that contracts during childbirth

11.2Female reproductive cycle and its hormonal regulationOften examined

The female reproductive system goes through cyclic events. The sequence of all the reproductive events in the female reproductive system is called the female reproductive cycle or menstrual cycle.

Female reproductive cycle (menstrual cycle): The sequence of all the reproductive events in the female reproductive system.
Ovarian cycle: The part of the female reproductive cycle that includes the events that occur in the ovaries.
Uterine cycle: The part of the female reproductive cycle that includes the events that occur in the uterus.
Gonadotropins: The pituitary hormones that coordinate the events of the ovarian cycle with those of the uterine cycle.

The events of the ovarian cycle are very well coordinated with the events of the uterine cycle by the pituitary hormones called gonadotropins. Based on the changes and the hormonal regulation, the cycle is divided into three phases: the menstrual phase, the proliferative phase and the secretory phase.

Figure 11.8: The human female reproductive cycle (about 28 days), drawn as a wheel. Day 1 is the first day of bleeding; ovulation comes at the end of day 14.

The three phases of the cycle
Phase	Days	Ovarian cycle (Figure 11.9)	Uterine cycle
Menstrual phase	1 to 5	Follicular phase begins	Menstruation: the functional layer of the endometrium is shed
Proliferative (pre-ovulatory) phase	6 to 14	Follicular phase: a follicle matures; ovulation at the end (day 14)	Endometrium thickens and is vascularized again
Secretory (post-ovulatory) phase	15 to 28	Luteal phase: corpus luteum forms, then regresses	Endometrium becomes glandular and secretes nutrients

Figure 11.7: Section through a human ovary showing the stages of the reproductive cycle. Follow the numbers 1 to 7: a primary follicle grows, matures and ovulates (coloured); the empty follicle becomes the corpus luteum, which later regresses.

Gonadotropins during the cycle

day of the cycle

level

ovulation

LH

FSH

Part of Figure 11.9: FSH and LH. LH shows a sudden surge just before ovulation on day 14; FSH is low apart from an early rise and a small rise at ovulation.

Ovarian hormones during the cycle

day of the cycle

level

ovulation

estrogen

progesterone

Part of Figure 11.9: estrogen rises through the proliferative phase and falls just before ovulation; progesterone rises after ovulation from the corpus luteum, then both fall before menstruation.

Thickness of the endometrium

day of the cycle

level

ovulation

endometrium

Part of Figure 11.9: the endometrium is shed on days 1 to 5, thickens from day 5 under estrogen (proliferative phase) and becomes thickest and glandular under progesterone (secretory phase). The curve is a sketch of the book's figure.

11.2Oogenesis (extra reading material)Often examined

The process of egg formation in females is called oogenesis. It starts when the individual is still a foetus. At that time the oogonia (diploid stem cells of the ovaries) multiply rapidly by mitosis and then enter a growth phase. Gradually the oogonia are transformed into primary oocytes, each surrounded by a single layer of follicle cells.

Oogenesis: The process of egg formation in females.
Oogonia: Diploid stem cells of the ovaries that multiply by mitosis in the foetus and become primary oocytes.
Primary oocyte: A diploid cell that begins meiosis I but is arrested late in prophase I until puberty.
Secondary oocyte: The larger of the two cells made by meiosis I; it contains nearly all the cytoplasm and is the cell that is ovulated, arrested in metaphase II.
Polar body: A tiny cell with almost no cytoplasm formed at meiosis I (first) and meiosis II (second); it degenerates and dies.

Stages of oogenesis

Before birth: oogonia (2n) multiply by mitosis, then grow and become primary oocytes (2n) surrounded by a single layer of follicle cells.
The primary oocytes begin meiosis I but become arrested late in prophase I. They stay in this state all through childhood, a wait of at least 10 to 14 years.
At puberty, a small number of primary oocytes are recruited each month, but only one is selected each time to continue meiosis I.
Meiosis I produces two haploid cells of very different size: the large secondary oocyte, which has nearly all the cytoplasm, and the small first polar body.
In humans the secondary oocyte arrests in metaphase II, and it is this cell that is ovulated.
If the ovulated secondary oocyte is not penetrated by a sperm, it simply deteriorates. If a sperm penetrates it, it quickly completes meiosis II (in the oviduct), giving one large ovum and a tiny second polar body.
The polar bodies, which have no nutrient-containing cytoplasm, degenerate and die.

Oogenesis (the book's extra reading figure). Meiosis I gives the secondary oocyte and the first polar body; meiosis II is completed only after a sperm penetrates, giving the ovum (zygote after fertilization) and the second polar body. The meiosis I division is coloured.

Follicle development alongside oogenesis (the second column of the book's figure)
Stage of the follicle	What happens in the oocyte
Primordial follicle	Oocyte arrested in prophase I (primary oocyte)
Primary follicle	Primary oocyte surrounded by follicle cells
Growing follicle	Follicle enlarges
Mature follicle	Meiosis I completed: secondary oocyte and first polar body
Ovulation	Secondary oocyte (arrested in metaphase II) leaves the ovary
Corpus luteum	The ruptured follicle becomes a glandular structure

11.2Menstrual phase (days 1 to 5)

In the menstruation phase, the uterus sheds all but the deepest part of its endometrium. The thick, hormone-dependent functional layer of the endometrium detaches from the uterine wall, a process that is accompanied by bleeding for 3 to 5 days. The detached tissue and blood pass out through the vagina as the menstrual flow.

At the beginning of this stage the ovarian hormones are at their lowest normal levels and the gonadotropins are beginning to rise. Then the FSH levels begin to rise.

Days 1 to 5 of the cycle; day 1 is the first day of bleeding.
The functional layer of the endometrium detaches; the deepest part stays.
Bleeding lasts 3 to 5 days.
Ovarian hormones are lowest; FSH begins to rise.

11.2Proliferative or pre-ovulatory phase (days 6 to 14)Often examined

Follicle atresia: The stopping of growth and disintegration of the follicles that lose the competition for dominance.
Mature (Graafian) follicle: The one dominant follicle that continues to mature in the ovary; oogenesis occurs in it.
Ovulation: The release of the egg from the mature follicle into the oviduct, in response to the sudden release of LH; it takes less than five minutes.
Corpus luteum: A yellowish glandular mass into which LH converts the ruptured follicle.

Events of the proliferative phase

The level of FSH rises during the first days of the cycle, and a few ovarian follicles are stimulated.
These follicles compete for dominance. All but one stop growing and disintegrate (follicle atresia). The one dominant follicle continues to mature and becomes the mature (Graafian) follicle, in which oogenesis occurs.
FSH also stimulates the Graafian follicle to secrete estrogen. Estrogen governs the vascularization of the endometrial lining, so the endometrium again becomes velvety, thick and well vascularized.
Normally the cervical mucus is thick and sticky, but the rising estrogen makes it thin and crystalline. It forms channels that help the passage of sperm into the uterus.
Estrogen has negative feedback on FSH: as the estrogen concentration rises, the FSH level falls. This is the signal for the anterior pituitary to release LH at the end of the proliferative stage (day 14).
In response to the sudden release (surge) of LH, the egg is released from the mature follicle into the oviduct: this is ovulation, which takes less than five minutes.
LH also converts the ruptured follicle into a yellowish glandular mass, the corpus luteum.

Hormones in the proliferative phase
Hormone	Source	Effect
FSH	Anterior pituitary	Stimulates a few follicles; one becomes the Graafian follicle; makes it secrete estrogen
Estrogen	Graafian follicle	Thickens and vascularizes the endometrium; thins the cervical mucus; negative feedback on FSH
LH	Anterior pituitary	Sudden release at the end of the phase (day 14) causes ovulation and converts the ruptured follicle into the corpus luteum

11.2Secretory or post-ovulatory phase (days 15 to 28)Often examined

During the secretory phase the endometrium prepares for the implantation of an embryo. The rising levels of progesterone from the corpus luteum act on the estrogen-primed endometrium. They cause the arteries to elaborate and convert the functional layer into a glandular secretory layer (the uterine glands). The uterine glands enlarge, coil and begin secreting nutritious glycogen into the uterine cavity. These nutrients sustain the embryo until it has implanted in the blood-rich endometrial lining.

If fertilization has not occurred, the corpus luteum begins to degenerate toward the end of the secretory phase, as the LH blood level declines. Progesterone levels fall, depriving the endometrium of hormonal support, and the endometrial cells die. This sets the stage for menstruation to begin on day 28 (the first day of the next cycle).

The secretory phase if the egg is not fertilised

The corpus luteum secretes progesterone, which acts on the estrogen-primed endometrium.
The functional layer becomes a glandular secretory layer; the glands enlarge, coil and secrete glycogen.
If there is no fertilization, LH declines and the corpus luteum degenerates.
Progesterone falls, so the endometrium loses its hormonal support.
The endometrial cells die and menstruation begins, starting the next cycle.

Menarche and menopause

Menarche: The first menstruation, at the start of the reproductive life of a female.
Menopause: The stopping of the menstrual cycle, which in human beings happens around 50 years of age.

Cyclic menstruation is an indicator of the normal reproductive life of females, and it extends between menarche and menopause.

Summary of the female reproductive cycle (28-day cycle)
Phase	Days	Main hormones	Ovary	Endometrium
Menstrual	1 to 5	Ovarian hormones lowest; FSH starts to rise	A follicle starts to grow	Functional layer shed; bleeding for 3 to 5 days
Proliferative (pre-ovulatory)	6 to 14	FSH, then estrogen; LH surge on day 14	Graafian follicle matures; ovulation on day 14	Velvety, thick, well vascularized
Secretory (post-ovulatory)	15 to 28	Progesterone (corpus luteum); LH falls at the end	Corpus luteum forms, then degenerates if no fertilization	Glandular; glands coil and secrete glycogen; then cells die

Worked example: dates in a 28-day cycle

A woman has a regular 28-day cycle. Her bleeding begins on 10 June. Give the dates of the menstrual, proliferative and secretory phases, the date of ovulation and the date when her next period begins.

Day 1 is the first day of bleeding, so day 1 = 10 June. Day $n$ is then $9 + n$ June, until June ends after 30 days.
$day n = (9 + n) June$
Menstrual phase is days 1 to 5. Day 5 is $9 + 5 = 14$ June.
$10 June to 14 June$
Proliferative phase is days 6 to 14. Day 6 is 15 June and day 14 is $9 + 14 = 23$ June. Ovulation takes place at the end of this phase, on day 14.
$15 June to 23 June; ovulation 23 June$
Secretory phase is days 15 to 28. Day 15 is 24 June. Day 28 is $9 + 28 = 37$ , which is $37 - 30 = 7$ July.
$24 June to 7 July$
The next cycle begins on the day after day 28, which is 8 July (day 1 of the new cycle).
$28 days after 10 June = 8 July$

Dates for a cycle starting on 10 June
Phase	Days	Dates	Key event
Menstrual	1 to 5	10 to 14 June	Functional layer shed
Proliferative	6 to 14	15 to 23 June	Graafian follicle matures; ovulation on 23 June
Secretory	15 to 28	24 June to 7 July	Corpus luteum; endometrium glandular

Ovulation on 23 June; next period begins on 8 July

Worked example: why does menstruation begin if the egg is not fertilised?

Using the hormones of the cycle, explain why the endometrium is shed at the end of the secretory phase when the ovulated egg is not fertilised.

Look at what keeps the endometrium thick. In the secretory phase the corpus luteum secretes progesterone, which acts on the estrogen-primed endometrium and keeps its glandular secretory layer.
The corpus luteum is made and kept by LH. If there is no fertilization, the LH level declines toward the end of the phase.
With less LH, the corpus luteum degenerates and stops making progesterone, so the progesterone level falls.
The endometrium is now deprived of hormonal support, so its cells die and the functional layer detaches.
The detached tissue and blood leave through the vagina: menstruation begins (day 1 of the next cycle), and the cycle starts again.

Hormones around the end of the cycle
Time	LH	Corpus luteum	Progesterone	Endometrium
Mid secretory phase (about day 21)	Present	Active	High	Thick and glandular
End of the cycle (about day 28), no fertilization	Declines	Degenerating	Falls	Loses support, cells die, menstruation

No fertilization → LH falls → corpus luteum degenerates → progesterone falls → endometrium breaks down

Key terms

Reproduction: The ability of an organism to produce new offspring of its own type; not essential for the survival of the individual but required for the survival of the species.
Internal fertilization: Fertilization inside the body of the female, as in human reproduction.
Puberty: The stage at which the human reproductive system is 'turned on' by the action of sex hormones.
Gonads: The organs that make the gametes: the testes in the male and the ovaries in the female.
Testes: The male gonads, lying outside the abdomen in the scrotum; each is divided into 250 to 300 lobules.
Scrotum: The skin pouch outside the abdomen that holds the testes.
Seminiferous tubules: Tightly coiled tubules (one to four in each lobule of the testis) in which the sperms are made.
Rete testis: A tubular network in the testis where the sperms mature further.
Efferent ductules: A series of small ducts that carry the sperms out of the testis.
Epididymis: The coiled tube on the outer surface of the testis that transports and stores the sperms.
Vas deferens: The duct into which the epididymis opens; it joins the duct of the seminal vesicle to form the ejaculatory duct (also called ductus deferens).
Ejaculatory duct: The short duct formed by the vas deferens and the duct of the seminal vesicle; it enters the prostate gland and empties into the urethra.
Urethra (urinogenital duct): The duct through which semen leaves the body; it carries urine as well, so it is also called the urinogenital duct.
Penis: The copulatory organ of the male, with tissues that fill with blood to cause an erection.
Seminal vesicles: A pair of accessory glands at the junction of the sperm duct and the ejaculatory duct.
Prostate gland: The accessory gland that encircles the urethra just below the bladder.
Bulbourethral glands: A pair of accessory glands (Cowper's glands) at the junction of the ejaculatory duct and the urethra.
Semen: A white, sticky mixture of sperm and secretions of the accessory glands, which nourishes and protects the sperms and carries them.
Spermatogenesis: The formation of sperms in the germinal epithelium of the seminiferous tubules.
Spermatogonia: Diploid cells of the germinal epithelium that divide by mitosis to form primary spermatocytes.
Primary spermatocyte: A diploid cell that undergoes meiosis I and forms two haploid secondary spermatocytes.
Secondary spermatocyte: A haploid cell that undergoes meiosis II and forms two spermatids.
Spermatid: A round, non-motile haploid cell that changes into a motile sperm by elongating, shedding excess cytoplasm and forming a tail.
Sperm: The motile male gamete, made of a head (nucleus and acrosome), neck, midpiece (mitochondria) and tail.
Hormones: Chemical messengers made by glands and carried in the blood to act on other organs.
GnRH: Gonadotropin-releasing hormone, from the hypothalamus; makes the anterior pituitary release FSH and LH.
FSH: Follicle stimulating hormone; in the male it stimulates the Sertoli cells to facilitate spermatogenesis, in the female it stimulates follicles to grow.
LH: Luteinizing hormone; in the male it stimulates the Leydig cells to make testosterone, in the female the surge at day 14 causes ovulation.
Testosterone: The male sex hormone made by the Leydig cells; it stimulates spermatogenesis and is responsible for the secondary sexual characteristics.
Sertoli cells: Cells of the seminiferous tubules that are stimulated by FSH to facilitate spermatogenesis and that make inhibin.
Leydig cells: The interstitial cells of the testis, stimulated by LH to make and release testosterone.
Inhibin: A hormone made by the Sertoli cells and released when the sperm count is too high; it inhibits GnRH and FSH.
Negative feedback: A control in which rising levels of a hormone (testosterone, inhibin, estrogen) act to reduce the release of the hormones that stimulated it.
Secondary sexual characteristics: Features such as the deepening of the voice and the growth of facial, axillary and pubic hair, due to testosterone.
Ovaries: The female gonads: solid, ovoid structures about 3 to 5 cm long and 2 to 3 cm wide, which produce ova and release hormones.
Ovarian follicle: A tiny sac-like structure in the ovary that contains an immature egg (oocyte).
Oocyte: The immature egg inside an ovarian follicle.
Ovulation: The ejection of an oocyte from a ripening follicle of the ovary, about once each month; it takes less than five minutes.
Corpus luteum: The yellowish glandular structure formed from the ruptured follicle after ovulation; it secretes progesterone.
Oviduct (Fallopian tube): The tube, about 10 cm long, that receives the ovulated oocyte and is generally the site of fertilization.
Uterus: The hollow, muscular, inverted-pear-shaped organ that receives, retains and nourishes a fertilized ovum; it has a fundus, a body and a cervix.
Perimetrium: The outermost thin covering layer of the uterine wall.
Myometrium: The middle thick layer of smooth muscle of the uterine wall, which contracts during childbirth.
Endometrium: The inner spongy lining of the uterus in which the embryo implants.
Cervix: The narrow entrance to the uterus from the vagina, normally blocked by a plug of mucus.
Vagina: The thin-walled tube, 8 to 10 cm long, from the cervix to the body exterior; the birth canal and the passage for menstrual flow.
Oogenesis: The process of egg formation in females, which starts in the foetus.
Oogonia: Diploid stem cells of the ovaries that multiply by mitosis in the foetus and become primary oocytes.
Polar body: A tiny cell with almost no cytoplasm formed during oogenesis; it degenerates and dies.
Female reproductive cycle (menstrual cycle): The sequence of all the reproductive events in the female reproductive system, with an ovarian cycle and a uterine cycle.
Gonadotropins: The pituitary hormones that coordinate the events of the ovarian cycle with the uterine cycle.
Menstrual phase: Days 1 to 5 of the cycle, when the functional layer of the endometrium is shed with bleeding.
Proliferative phase: Days 6 to 14 (pre-ovulatory, follicular phase); a follicle matures, estrogen rises and the endometrium thickens.
Graafian follicle: The one dominant follicle that matures in the ovary (mature follicle) and secretes estrogen.
Follicle atresia: The disintegration of the follicles that stop growing while one follicle becomes dominant.
Estrogen: Hormone of the Graafian follicle that thickens and vascularizes the endometrium, thins the cervical mucus and has negative feedback on FSH.
Progesterone: Hormone of the corpus luteum that converts the endometrium into a glandular secretory layer in the secretory phase.
Secretory phase: Days 15 to 28 (post-ovulatory phase); the endometrium becomes glandular and secretes glycogen to prepare for implantation.
Menarche: The first menstruation.
Menopause: The stopping of the menstrual cycle at around 50 years of age.

Multiple choice questionsp. 306–308

Select the correct answer.

Sertoli cells are found in

Aseminiferous tubulesAnswer
Bseminal vesicle
Cbetween interstitial cells
Depididymis

Why

Sertoli cells are the supporting cells inside the seminiferous tubules. They facilitate spermatogenesis and produce inhibin (book p. 301).

Option C is the tempting wrong answer: the cells between the tubules are the Leydig (interstitial) cells, which make testosterone, not Sertoli cells.

Fertilization of the ovum normally occurs:

Ain distal part of oviductAnswer
Bin proximal part of oviduct
Calong the uterine wall
Dsuccessfully in vagina

Why

The oviduct is the site where fertilization generally occurs (book p. 302). Fertilization happens in the outer (distal, ovary-side) part of the oviduct, where the ovulated egg is met by sperm.

Option B is the tempting wrong answer: the proximal part is the end nearer the uterus, where the fertilized ovum has already passed. C and D are wrong because the embryo implants in the endometrium (book p. 302), and the vagina is too far from the egg.

Note. The book says only that fertilization occurs in the oviduct and does not name the part; the distal (ovary-side) part is standard physiology and is the key used here.

Embryo implants in the ______ of the uterus

Aperimetrium
Bmyometrium
CendometriumAnswer
Dcervix

Why

The young embryo is implanted into the endometrium, the inner spongy lining of the uterine cavity, and stays there for the rest of its development (book p. 302).

The myometrium is the thick muscular middle layer that contracts in childbirth, the perimetrium is the thin outer covering, and the cervix is the narrow neck. None of them receives the embryo.

Spermatozoa are stored prior to emission and ejaculation in

AepididymisAnswer
Bseminal vesicle
Curethra
Dprostate gland

Why

The epididymis is the coiled duct on the outer surface of the testis. Its function is the transport and storage of sperms (book p. 298), so sperms wait there before ejaculation.

The seminal vesicles and prostate gland secrete fluid that forms semen (book p. 299), and the urethra only carries semen out of the body, so B, C and D are wrong.

The cervix is a portion of

Aovary
Bvagina
CuterusAnswer
Dfallopian tube

Why

The uterus has three portions: the fundus, the body and the cervix (book p. 302). The cervix is the narrow entrance to the uterus from the vagina.

The vagina (B) is tempting because the cervix opens into it, but the cervix belongs to the uterus, not to the vagina.

62026 Annual I, Set D, MCQ 15

On which date is a woman most likely to ovulate if the first day of menstrual loss was first March?

A5 March
B14 MarchAnswer
C20 March
D28 March

Why

Day 1 of the cycle is the first day of menstrual loss, 1 March. LH is released at the end of the proliferative phase, on day 14, and ovulation follows (book p. 305).

Day 14 is 13 days after 1 March, so ovulation falls on 14 March. 5 March is still in the menstrual phase (days 1 to 5), and 28 March is the last day of the cycle, when menstruation begins again.

If ruptured mature follicle is degenerated without forming corpus luteum, which of the following is expected?

Aovulation will not occur
Bmenstruation will not occur
Cpregnancy is established
Dfollicular atresiaAnswer

Why

A ruptured follicle that does not become a corpus luteum degenerates. The book uses the term follicular atresia for follicles that stop growing and disintegrate (book p. 304), so D is the outcome that follows directly.

Without the corpus luteum there is no progesterone (book p. 307), so pregnancy cannot be established (C) and the endometrium breaks down, so menstruation does occur (B). The ovulation has already happened in that cycle, so A is not the expected result.

Note. The question is loosely worded and the book prints no key. D is chosen as the degeneration outcome the question describes.

How does a zygote differ from an ovum?

AA zygote has diploid number chromosomesAnswer
BA zygote is smaller
CA zygote consists of more than one cell
DA zygote is much larger

Why

The ovum is haploid ( $n$ ) after meiosis, while the zygote formed by fertilization has the diploid number ( $2 n$ ) because it carries chromosomes from both parents (book p. 303, Fig. 11.7 oogenesis diagram).

B and D are wrong because the zygote is about the same size as the ovum, and C is wrong because the zygote begins as a single cell.

Which of the following is a primary organ of the female reproductive system?

Avagina
Buterus
CovaryAnswer
Dtestes

Why

The ovaries are the female gonads: they produce ova and release female sex hormones (book p. 301 and 302). A primary organ is a gonad.

The vagina and uterus are accessory organs, and the testes (D) are male gonads.

In the female reproductive organ, the fetus develops in ______.

Aovary
Bvagina
CuterusAnswer
Dnone of these

Why

The fertilized ovum is implanted into the endometrium of the uterus, where it stays for the rest of its development (book p. 302). The uterus nourishes it.

The ovary makes the egg, and the vagina is the birth canal, so neither is where development takes place.

Which of the following are accessory glands found in the human male reproductive system?

Aprostate gland
Bcowper's gland
Cseminal vesicles
Dall of theseAnswer

Why

The accessory glands are the seminal vesicles, the prostate gland and the bulbourethral (Cowper's) glands (book p. 299). All three are correct, so D is the answer.

Each of A, B and C is an accessory gland, so the single-option answers are incomplete.

Which of the following are the functions of the female reproductive system?

Amanufacture eggs
Bnourish the developing baby not only before birth but after
Cprovide an environment conducive to fertilisation and implantation
Dall of theseAnswer

Why

The book gives these functions: production of egg (oogenesis), fertilization, development of the embryo and production of female sex hormones (book p. 303). The uterus receives, retains and nourishes the fertilized ovum (book p. 302), and the endometrium prepares for implantation in the secretory phase (book p. 306).

Option B says the uterus nourishes the baby after birth, which the book does not state. The key is D as the question intends; the wording of B goes beyond the book.

Note. Option B goes beyond the book's text (the book says the uterus nourishes the embryo before birth). Key D kept as the intended answer.

Androgens increase in both males and females during puberty. Which of the following secretes androgen in the testes?

Aleydig cellsAnswer
Baccessory ducts
Cbulbourethral glands
Dall of these

Why

The Leydig cells of the testes make and release testosterone, the androgen, when they are stimulated by LH (book p. 301).

The accessory ducts carry sperms and the bulbourethral glands secrete fluid for semen. Neither makes androgens, so B and C are wrong and D is wrong with them.

______ is also known as the proliferative phase.

Aluteal phase
Bmenstrual phase
Cfollicular phaseAnswer
Dnone of these.

Why

The proliferative (pre-ovulatory) phase, days 6 to 14, is the uterine part of the follicular phase of the ovarian cycle, in which follicles grow (book p. 304 and Fig. 11.9).

The luteal phase (A) is the ovarian phase after ovulation, which matches the secretory phase, and the menstrual phase (B) is days 1 to 5.

Which of the following hormones provides the hormonal trigger to cause ovulation and the release of eggs from the ovary?

Aestrogen
Btestosterone
Cluteinizing hormone (LH)Answer
Dall of these

Why

The sudden release of LH from the anterior pituitary causes ovulation, when the mature follicle releases its egg (book p. 305).

Estrogen signals the pituitary to release LH but does not itself trigger ovulation, and testosterone is the male hormone, so A, B and D are wrong.

Which of the following male reproductive organs stores spermatozoa?

Apenis
Burethra
CepididymisAnswer
Dvas deferens

Why

The epididymis has the function of transport and storage of sperms (book p. 298).

The vas deferens (D) is tempting because it is a sperm duct, but its job is to transport sperms to the ejaculatory duct. The penis and urethra do not store sperm.

Which of the following female reproductive organs is called the site of fertilization?

Aovary
Buterus
Cvagina
DoviductAnswer

Why

The oviducts (Fallopian tubes) receive the ovulated oocyte and are the site where fertilization generally occurs (book p. 302).

The ovary makes the egg, the uterus receives and nourishes the fertilized ovum, and the vagina is the birth canal.

The onset of menstruation in a female is called ______.

AmenarcheAnswer
Bmenopause
Cmenstrual cycle
Dnone of these

Why

Menarche is the first menstruation, the onset of the reproductive cycle (book p. 305).

Menopause (B) is the end of the cycle, around age 50, and the menstrual cycle (C) is the repeating cycle itself, not its onset.

The female reproductive system consists of ______

Atestes
Burethra
Ca pair of epididymis
Da pair of Fallopian tubesAnswer

Why

The female reproductive system consists of gonads (a pair of ovaries), oviducts, uterus and vagina (book p. 301). The oviducts are the pair of Fallopian tubes.

The testes and the epididymis belong to the male system, and the urethra is part of the male tract (it is only embedded in the anterior wall of the female vagina).

Which of the following hormones are responsible for attaining reproductive maturity?

Aestrogen
Bluteinizing hormone (LH)
Cfollicle-stimulating hormone (FSH)
Dall of theseAnswer

Why

At the onset of puberty the hypothalamus sends GnRH, which makes the anterior pituitary release FSH and LH. Their release at puberty starts the reproductive system (book p. 301).

Estrogen and testosterone are the sex hormones that bring about the sexual characteristics of puberty. All three options are involved, so D is the key.

Note. The book names FSH and LH as the puberty hormones and does not name estrogen in this role. D is the intended key.

Which of the following hormones are secreted by the testes and ovary?

Aestrogen
BtestosteroneAnswer
Cluteinizing hormone (LH)
Dboth (A) and (C)

Why

Testosterone is the androgen of the testes (book p. 301). The question treats androgens as present in both sexes (see question 13), so testosterone is the hormone the question means to be shared by testes and ovary.

LH is made by the anterior pituitary, not by the gonads, so C and D are wrong. Estrogen is the hormone of the ovary (book p. 304 and 305), and A is only a partial answer as the book names it.

Note. No option is clearly shared by testes and ovary in the book's text. Testosterone is chosen to match question 13. Estrogen is also made in small amounts in males, so the key could be argued as A.

222026 Annual I, Set D, MCQ 15

Ovulation in the human female normally takes place during the menstrual cycle

Aat the mid secretory phase
Bjust before the end of the secretory phase
Cat the beginning of the proliferative phase
Dat the end of the proliferative phase.Answer

Why

Ovulation happens on about day 14, when the LH surge is released at the end of the proliferative phase (book p. 305 and 307).

A and B are in the secretory phase, after ovulation, when the corpus luteum is active. C is at the start of the proliferative phase, when follicles are only beginning to grow.

After ovulation Graafian follicle regresses into

Acorpus atresia
Bcorpus callosum
Ccorpus luteumAnswer
Dcorpus albicans

Why

After ovulation the ruptured follicle is transformed into a glandular structure called the corpus luteum (book p. 302).

Corpus albicans (D) is the scar left later when the corpus luteum has regressed, so it is not the immediate result. Corpus callosum is a brain structure and 'corpus atresia' is not a term used in this unit.

Immediately after ovulation, the mammalian egg is covered by a membrane known as

Achorion
Bzona pellucidaAnswer
Ccorona radiata
Dvitelline membrane

Why

The ovulated egg is surrounded by the zona pellucida, a clear protective layer around the oocyte. Sperm must penetrate it to fertilize the egg.

The corona radiata (C) is a layer of follicle cells around the zona, not a membrane. The chorion (A) is an embryonic membrane that forms later, and the vitelline membrane (D) is the membrane of the yolk in other animals.

Note. The book does not name the coverings of the ovulated egg. The answer is standard cell biology, kept to the level of the unit.

Which one of the following events is correctly matched with the time period in a normal menstrual cycle?

ARelease of egg: 5th day
BEndometrium regenerates: 5 - 10 daysAnswer
CEndometrium secretes nutrients for implantation: 11 - 18 days
DRise in progesterone level: 1 - 15 days

Why

Release of the egg happens on day 14 (A is wrong). The endometrium is rebuilt in the proliferative phase, from about day 6 to day 14, so it begins to regenerate within the 5 to 10 day range (B). Secretion of nutrients happens in the secretory phase from day 15 (C is wrong), and progesterone rises from day 15 onwards (D is wrong).

Note. No option is exact. The book's phase boundaries (days 6 to 14 for regeneration) make B the closest match.

Short answer questionsp. 308–309

Answer the following questions.

13 marks

List the structures of male reproductive system.

Solution

Gonads: a pair of testes, lying outside the abdomen in the scrotum.
Accessory ducts: epididymis, vas deferens (ductus deferens), ejaculatory duct and urethra.
Accessory glands: a pair of seminal vesicles, the prostate gland and a pair of bulbourethral (Cowper's) glands.
Copulatory organ: the penis.

23 marks

Explain hormonal control of human male reproductive function.

Solution

GnRH and pituitary hormones: at puberty the hypothalamus releases GnRH, which makes the anterior pituitary release FSH and LH.
Action in the testes: FSH acts on the Sertoli cells to facilitate spermatogenesis, and LH acts on the Leydig cells to make and release testosterone, which stimulates spermatogenesis and the secondary sexual characteristics.
Negative feedback: testosterone and inhibin (from the Sertoli cells) inhibit GnRH and the release of FSH and LH. When the sperm count reaches about 20 million per ml the Sertoli cells stop releasing inhibin, so the sperm count rises again.

33 marks

List the structures of female reproductive system.

Solution

Gonads: a pair of ovaries, which produce ova and female sex hormones.
Oviducts: a pair of Fallopian tubes, which receive the ovulated oocyte and are the site of fertilization.
Uterus: made of the fundus, the body and the cervix.
Vagina: the 8 to 10 cm tube from the cervix to the outside of the body.

43 marks

List the structure in order, through which a sperm passes on its way from the seminiferous tubules of the testis to the fallopian tubule of the female.

Solution

Seminiferous tubules of the testis (where sperms are produced).
Rete testis.
Efferent ductules.
Epididymis (transport and storage of sperms).
Vas deferens.
Ejaculatory duct.
Urethra, then the penis.
Vagina.
Cervix.
Uterus.
Oviduct (Fallopian tube), where fertilization generally occurs.

53 marks

What changes occur in ovulation and menstruation during gestation period.

Solution

Ovulation stops: no new follicle matures and no egg is released during pregnancy, because the high levels of hormones (mainly progesterone from the corpus luteum) keep the cycle inactive.
Menstruation stops: the endometrium is maintained and does not break down, so there is no menstrual flow. The embryo that is implanted in it stays there for the rest of its development.
Uterus enlarges: the uterus grows to hold and nourish the developing embryo, and no cyclic changes of the endometrium take place.

Note. The book does not describe ovulation and menstruation during pregnancy. The answer is kept to the cycle as the book describes it (corpus luteum and progesterone, implantation in the endometrium).

63 marks

Name the three phase of menstruation cycle and mention the characteristic days.

Solution

Phase	Days	Main event
Menstrual phase	1 to 5	The functional layer of the endometrium is shed, with bleeding for 3 to 5 days; ovarian hormones are at their lowest.
Proliferative or pre-ovulatory phase	6 to 14	FSH stimulates follicles, one becomes the mature follicle, the endometrium is rebuilt under estrogen and LH is released at day 14 (ovulation).
Secretory or post-ovulatory phase	15 to 28	The corpus luteum secretes progesterone, the endometrium becomes secretory for implantation, and menstruation begins at day 28 if no fertilization occurs.

73 marks

What is the role of the corpus luteum in a menstrual cycle?

Solution

Formation: after ovulation, LH converts the ruptured follicle into the corpus luteum.
Progesterone: the corpus luteum secretes progesterone, which converts the estrogen-primed endometrium into a secretory layer with uterine glands that store glycogen.
Maintenance and breakdown: the endometrium is kept ready for implantation. If there is no fertilization, the corpus luteum degenerates near day 28, progesterone falls, the endometrium breaks down and menstruation begins.

83 marks

What are the actions of GnRH, FSH and LH in the human reproductive functions?

Solution

Hormone	Source	Action in human reproduction
GnRH	Hypothalamus	Stimulates the anterior pituitary to release FSH and LH at puberty.
FSH	Anterior pituitary	In males, stimulates Sertoli cells to facilitate spermatogenesis. In females, stimulates follicle growth and the graafian follicle to secrete estrogen.
LH	Anterior pituitary	In males, stimulates Leydig cells to make testosterone. In females, causes ovulation and the change of the ruptured follicle into the corpus luteum.

93 marks

Why are so many sperms produced in the male and so few ova produced in the female?

Solution

Sperms are small and continuous: spermatogenesis starts at puberty and goes on every day, about 400 million sperms a day, so the male makes large numbers.
An ovum is a large, costly cell: oogenesis divides the cytoplasm unequally, so the secondary oocyte keeps almost all of the nutrient cytoplasm and the polar bodies die. One large, nourished cell is made instead of several small ones.
Only one oocyte matures per cycle: in each menstrual cycle only one follicle matures and ovulates, so the female releases only about one ovum a month.

103 marks

Why it is necessary for large numbers of sperms to be produced when only one sperm is required to bring about fertilization?

Solution

Many sperms are lost: many sperms are destroyed or lost in the female tract and never reach the oviduct, so only a small fraction arrive at the egg.
The ovum is protected: the ovulated egg is surrounded by protective coverings, such as the zona pellucida, and many sperms are needed to get through them.
One fertilizes the egg: only one sperm fuses with the ovum, so large numbers make sure that at least one reaches it in time. An unfertilized ovum simply deteriorates (book p. 304).

Note. The book does not explain the coverings of the egg or the loss of sperm in the female tract. These points are standard, kept to the level of the unit.

113 marks

Enlist the reasons of human male infertility?

Solution

Low or abnormal sperm production: too few sperms, or sperms that are poorly motile or malformed, often because of hormonal imbalance (low FSH, LH or testosterone).
Blockage of the ducts: blocked epididymis or vas deferens, from infection or injury, prevents sperms from reaching the semen.
High temperature of the testes: the book notes that sperm production is most efficient about 2 degrees below body temperature (35 degrees C), so raised testicular temperature reduces sperm production.
Infection or damage to the testes: injury or disease of the testes or their hormone-producing cells reduces sperm production.

Note. The book does not discuss infertility. The reasons are general FBISE-level causes, linked to the book's content on sperm production and temperature (book p. 299).

123 marks

Write the differences between: (a) human male and female reproductive system, (b) spermatogenesis and oogenesis, (c) primary and secondary spermatocytes, (d) Sertoli cell and Leydig cell, (e) spermatids and sperms, (f) perimetrium and endometrium, (g) primary oocyte and secondary oocyte, (h) menarche and menopause.

Solution

(a) Human male and female reproductive system.

Feature	Male	Female
Gonads	A pair of testes	A pair of ovaries
Position of gonads	Outside the abdomen, in the scrotum	Inside the abdominal (peritoneal) cavity, held by ligaments
Ducts and organs	Epididymis, vas deferens, ejaculatory duct, urethra and penis	Oviducts, uterus, cervix and vagina
Main function	Production and maintenance of sperms	Production of ova, fertilization, development of the embryo and female sex hormones

(b) Spermatogenesis and oogenesis.

Feature	Spermatogenesis	Oogenesis
Site	Seminiferous tubules of the testis	Ovarian follicles of the ovary
Starts	At puberty, and goes on continuously	In foetal life; arrested in prophase I until puberty, then one per cycle
Cytoplasm	Cytoplasm divided equally; excess is shed during differentiation	Cytoplasm divided unequally; polar bodies degenerate
Product	Four functional sperms from each primary spermatocyte	One functional ovum (the other polar bodies die)

Feature	Primary spermatocyte	Secondary spermatocyte
Formed from	A spermatogonium by mitosis	Primary spermatocyte after meiosis I
Chromosome number	Diploid (2n)	Haploid (n)
Division next	Meiosis I	Meiosis II, forming two spermatids each
Size	Larger	Smaller

(d) Sertoli cell and Leydig cell.

Feature	Sertoli cell	Leydig cell
Position	Inside the seminiferous tubules	Between the tubules (interstitial cells)
Stimulated by	FSH	LH
Function	Facilitates spermatogenesis and produces inhibin	Makes and releases testosterone

(e) Spermatids and sperms.

Feature	Spermatid	Sperm
Shape and movement	Round and non-motile	Elongated with a tail; motile and active
Development	Elongates, sheds excess cytoplasm and forms a tail	Mature, ready for fertilization
Parts	Early nucleus and cytoplasm	Head (nucleus and acrosome), midpiece (mitochondria) and tail

(f) Perimetrium and endometrium.

Feature	Perimetrium	Endometrium
Position	Outermost, thin covering of the uterus	Innermost, spongy lining of the uterine cavity
Function	Protective outer layer	Receives and implants the embryo; changes in each menstrual cycle

(g) Primary oocyte and secondary oocyte.

Feature	Primary oocyte	Secondary oocyte
Chromosome number	Diploid (2n)	Haploid (n)
Stage	Begins meiosis I, arrested in prophase I from childhood until puberty	Formed after meiosis I; arrested in metaphase II and ovulated
Cytoplasm	All the cytoplasm of the primary oocyte	Most of the cytoplasm; the smaller cell is the first polar body

(h) Menarche and menopause.

Feature	Menarche	Menopause
Meaning	The first menstruation	The end of the menstrual cycle
Time	At puberty, when reproductive life begins	Around 50 years of age

Extensive answer questionsp. 309

18 marks

Describe the structure of human male reproductive system. Identify the function of each part.

Solution

Structure

The male reproductive system has four groups of parts: the gonads (testes), the accessory ducts, the accessory glands and the copulatory organ (penis). Figure 11.1 shows them in a side view.

Figure 11.1: Human male reproductive system, lateral view (schematic)

Gonads (testes)

A pair of testes lies outside the abdomen in the scrotum. This position keeps them about 2 degrees cooler than the body, where sperm production works best.
Each testis has 250 to 300 lobules, and each lobule contains one to four tightly coiled seminiferous tubules, where sperms are formed.
Function: production of sperms by spermatogenesis. The Leydig cells between the tubules make testosterone.

Accessory ducts

Part	Structure	Function
Rete testis and efferent ductules	A network inside the testis, and the ducts leaving it	Collect sperms from the seminiferous tubules and carry them out of the testis
Epididymis	Coiled on the outer surface of the testis	Transport and storage of sperms
Vas deferens	A duct from the epididymis up into the abdomen	Carries sperms towards the ejaculatory duct
Ejaculatory duct	A short duct formed where the vas deferens joins the seminal vesicle duct, passing through the prostate	Carries sperms and fluids to the urethra
Urethra	A tube from the bladder through the penis	Carries urine and semen out of the body (urinogenital duct)

Accessory glands

Gland	Position	Function
Seminal vesicles (a pair)	At the junction of the sperm duct and the ejaculatory duct	Secrete a fluid that forms part of semen
Prostate gland	Encircles the urethra just below the bladder	Secretes a fluid that forms part of semen
Bulbourethral glands (Cowper's, a pair)	At the junction of the ejaculatory duct and the urethra	Secrete a fluid that forms part of semen

Semen is a white mixture of sperms and secretions of the accessory glands. The secretions provide nutrients and protection to the sperms and act as a transport medium (book p. 299).

Copulatory organ (penis)

The penis is made mainly of tissues that fill with blood to cause an erection. It carries the urethra, which passes urine and semen out of the body, and it delivers the sperms into the female tract.

28 marks

Explain the principal reproductive hormones of human male and explain their role.

Solution

Principal hormones

Male reproduction is controlled by hormones from the hypothalamus and the anterior pituitary, and by hormones of the testes (book p. 301). Figure 11.4 shows how they act in a negative feedback system.

Hormone	Made by	Target	Role in the male
GnRH	Hypothalamus	Anterior pituitary	Stimulates the release of FSH and LH; released at the onset of puberty
FSH	Anterior pituitary	Sertoli cells	Facilitates spermatogenesis; the Sertoli cells then produce inhibin
LH	Anterior pituitary	Leydig cells	Stimulates the Leydig cells to make and release testosterone
Testosterone	Leydig cells of the testes	Body, hypothalamus and pituitary	Secondary sexual characteristics (deeper voice, facial, axillary and pubic hair); stimulates spermatogenesis; negative feedback on GnRH and LH
Inhibin	Sertoli cells	Hypothalamus and pituitary	Negative feedback on GnRH and FSH; released when the sperm count is high

Figure 11.4: Hormones control sperm production in a negative feedback system (dashed lines are negative feedback)

Negative feedback

Rising testosterone and, when the sperm count is high, inhibin act on the hypothalamus and the anterior pituitary.
They inhibit the release of GnRH, FSH and LH.
Less FSH and LH reach the testes, so spermatogenesis and testosterone production slow down and the sperm count falls.
When the sperm count reaches about 20 million per ml, the Sertoli cells stop releasing inhibin. The brake is released and the sperm count increases again.

38 marks

Explain the structures of human female reproductive system. Identify the function of each part.

Solution

Structure

The female system consists of a pair of ovaries (gonads), a pair of oviducts (Fallopian tubes), the uterus and the vagina (book p. 301). Figure 11.6 shows the parts.

Figure 11.6: Human female reproductive system, frontal view, with the wall of the uterus in section (schematic)

Parts and their functions

Part	Structure	Function
Ovaries (pair)	Solid, ovoid, 3 to 5 cm long and 2 to 3 cm wide; held by ligaments; contain ovarian follicles, each with an immature egg (oocyte)	Produce ova (oogenesis); release one ovum at ovulation; produce estrogen and progesterone
Oviducts (Fallopian tubes, a pair)	About 10 cm long; the fimbriae at the ovary end catch the ovulated egg	Receive the oocyte; the site where fertilization generally occurs; carry the developing ovum to the uterus
Uterus: fundus	The rounded top of the uterus, where the oviducts join below it	Part of the hollow organ that receives, retains and nourishes the fertilized ovum
Uterus: body	The main hollow, muscular chamber, shaped like an inverted pear	Holds and nourishes the developing embryo for about nine months
Uterus: cervix	A narrow neck opening into the vagina, normally blocked by a plug of mucus	Entrance to the uterus from the vagina; the mucus plug protects it, and the mucus thins under estrogen to let sperms pass
Perimetrium	Outermost thin covering of the uterus	Protective outer layer
Myometrium	Thick middle layer of bundles of smooth muscle	Contracts rhythmically during childbirth to expel the baby
Endometrium	Inner spongy lining of the uterine cavity	Receives and implants the embryo; changes in every menstrual cycle
Vagina	Thin-walled tube 8 to 10 cm long from the cervix to the outside of the body	Birth canal for delivery of the infant and passage of menstrual flow; the urethra is embedded in its anterior wall

48 marks

Describe the events of a menstrual cycle and explain its hormonal regulation.

Solution

Overview

The female reproductive cycle, or menstrual cycle, lasts about 28 days. Its ovarian cycle (events in the ovary) and uterine cycle (events in the uterus) are coordinated by pituitary hormones called gonadotropins (book p. 303).

Events in the three phases

Phase and days	Ovary	Uterus	Hormones
Menstrual phase, days 1 to 5	New follicles start to grow; ovarian hormones are at their lowest	The functional layer of the endometrium sheds, with bleeding for 3 to 5 days	Ovarian hormones lowest; FSH begins to rise
Proliferative or pre-ovulatory phase, days 6 to 14	FSH stimulates several follicles; one becomes the mature (Graafian) follicle; ovulation on day 14	Estrogen makes the endometrium thick, velvety and well vascularized; cervical mucus thins	FSH rises, then falls by negative feedback of estrogen; LH surge at the end of the phase
Secretory or post-ovulatory phase, days 15 to 28	The ruptured follicle becomes the corpus luteum, which secretes progesterone; it degenerates if there is no fertilization	The glands coil and secrete glycogen; the endometrium is ready for implantation; it breaks down at about day 28 if there is no embryo	Progesterone rises, then falls as LH falls

Hormonal regulation, step by step

At puberty the hypothalamus releases GnRH, which makes the anterior pituitary release FSH and LH.
FSH stimulates several follicles to grow. The dominant mature (Graafian) follicle secretes estrogen.
Estrogen thickens the endometrium and, by negative feedback, lowers FSH. It also thins the cervical mucus so that sperms can pass.
At the end of the proliferative phase, on about day 14, the sudden release of LH from the pituitary causes ovulation, which takes less than five minutes.
LH converts the ruptured follicle into the corpus luteum, which secretes progesterone.
Progesterone keeps the endometrium secretory. If there is no fertilization, the corpus luteum degenerates, progesterone and LH fall, the endometrium breaks down, and menstruation begins at about day 28.

Figure 11.9: Human female reproductive cycle, with the ovarian and uterine cycles aligned over 28 days (schematic)

58 marks

What is infertility? What are the causes of human male and female infertility?

Solution

Infertility

Infertility is the inability of a couple to produce a child after regular, unprotected intercourse for about one year. It may be caused by the male, by the female or by both.

Causes in the male

Low or abnormal sperm production: too few sperms, or sperms that are slow or malformed, often because of a hormonal imbalance (low GnRH, FSH, LH or testosterone).
Blocked ducts: a blockage of the epididymis, vas deferens or ejaculatory duct, after infection or injury, stops sperms from reaching the urethra.
Raised temperature of the testes: spermatogenesis works best at about 35^\circ\mathrm{C}, two degrees below body temperature (book p. 299), so a higher temperature reduces sperm production.
Infection or damage to the testes or the accessory glands.

Causes in the female

Blocked or damaged oviducts, after infection, so the ovum cannot pass to the uterus or sperms cannot reach it.
Failure of ovulation: no mature follicle develops, or there is no LH surge, so no ovum is released.
Hormonal imbalance of FSH, LH or estrogen, which disturbs the menstrual cycle (book p. 305).
Thick cervical mucus that does not thin, because estrogen is too low, so sperms cannot pass into the uterus (book p. 305).
An endometrium that cannot receive the embryo, so implantation fails (book p. 302).
Age: fertility declines and ends at menopause, around 50 years (book p. 306).

Note. The book's text does not cover infertility. The answer uses general FBISE-level biology and is linked to the unit's content.

68 marks

Explain "in vitro" fertilization with diagram.

Solution

What it is

"In vitro" means "in glass". In vitro fertilization (IVF) is fertilization outside the body, in a laboratory dish, after which the embryo is placed in the uterus to develop. It is used when natural fertilization in the oviduct cannot take place. The book does not describe the method, so this answer is kept to the level of the unit.

Steps

Stimulation: FSH is given so that several follicles mature together, instead of one per cycle.
Egg collection: the mature eggs (oocytes) are removed from the follicles with a fine needle.
Sperm collection: a sample of semen is collected and the healthy sperms are separated from the fluid.
Fertilization in a dish: eggs and sperms are mixed in a glass dish, so that a sperm fertilizes an egg and forms a zygote.
Culture: the zygote divides by mitosis and develops into an embryo for a few days in the laboratory.
Embryo transfer: the healthy embryo is placed in the uterus, where it implants in the endometrium and develops as in natural pregnancy.

In vitro fertilization: the stages in order (schematic; the accent marks the step that replaces natural fertilization in the oviduct)

Note. The book does not describe in vitro fertilization. The steps are standard FBISE-level content, kept to the level of the unit.

FBISE 2025 and 2026 questions

Questions from the FBISE HSSC-I 2026 (1st Annual) and FBISE HSSC-I 2025 (1st Annual) papers that belong to this unit, answered the way an examiner expects.

2025 Annual I, Set B, MCQ 31 mark

The main function of progesterone in human female reproductive system is:

AOvulation
BFollicle development
CEndometrium developmentAnswer
DImplantation of embryo

Why

Progesterone from the corpus luteum acts on the estrogen-primed endometrium and makes it glandular and secretory, so the main function is endometrium development (preparing it for implantation). Ovulation is triggered by the LH surge, follicle development is stimulated by FSH, and implantation is the embryo's attachment to the prepared endometrium, not a function of the hormone itself.

2026 Annual I, Set B, MCQ 151 mark

Menstrual cycle is controlled by:

AEnzymes
BVitamins
CMinerals
DHormonesAnswer

Why

The menstrual cycle is controlled by hormones: the gonadotropins FSH and LH from the anterior pituitary, and estrogen and progesterone from the ovary. Enzymes, vitamins and minerals are not the chemical messengers that coordinate the ovarian and uterine cycles.

2025 Annual I, Set B, Q.2 (iv)3 marks

List the Accessory glands associated with male reproductive system with their respective locations.

Solution

Accessory gland (1 mark each)	Location
Seminal vesicles (a pair)	At the junction of the sperm duct (vas deferens) and the ejaculatory duct
Prostate gland	Encircles the urethra just below the bladder
Bulbourethral (Cowper's) glands (a pair)	At the junction of the ejaculatory duct and the urethra

Their secretions make up the liquid part of the semen.

2025 Annual I, Set B, Q.2 (viii) OR2+1 = 3 marks

Write about the structure and functions of ovary and oviduct in female reproductive system.

Solution

Structure (2 marks)

Organ	Structure
Ovary	A pair of solid, ovoid gonads, 3 to 5 cm long and 2 to 3 cm wide, lying on the sides of the uterus and held in the peritoneal cavity by ligaments. Inside are many tiny sac-like ovarian follicles, each with an immature egg (oocyte); after ovulation the ruptured follicle becomes the glandular corpus luteum.
Oviduct (Fallopian tube)	The initial part of the female duct system, about 10 cm long, running from the region of the ovary to the uterus; it receives the ovulated oocyte.

Functions (1 mark)

Ovary: produces ova (eggs) by oogenesis and releases hormones (estrogen and progesterone).
Oviduct: receives the oocyte, is the usual site of fertilization, and transfers the developing ovum towards the uterus.

2026 Annual I, Set B, Q.2 (ix)1x3 = 3 marks

Name three Hormones of male reproductive system and write role of each Hormone.

Solution

Hormone	Made by	Role (1 mark each)
FSH	Anterior pituitary	Stimulates the Sertoli cells of the testes to facilitate spermatogenesis
LH	Anterior pituitary	Stimulates the interstitial (Leydig) cells of the testes to make and release testosterone
Testosterone	Leydig cells	Stimulates spermatogenesis and is responsible for the secondary sexual characteristics (deepening of voice, facial, axillary and pubic hair); inhibits GnRH, FSH and LH by negative feedback

Any three of these are accepted. GnRH (from the hypothalamus, makes the anterior pituitary release FSH and LH) and inhibin (from the Sertoli cells, inhibits GnRH and FSH when the sperm count is too high) are the other two.

2026 Annual I, Set B, Q.2 (ix) OR1x3 = 3 marks

State three events of menstrual phase of menstrual cycle.

Solution

Events of the menstrual phase (days 1 to 5), 1 mark each

The uterus sheds all but the deepest part of its endometrium: the thick, hormone-dependent functional layer detaches from the uterine wall.
The detached tissue and blood pass out through the vagina as the menstrual flow, with bleeding for 3 to 5 days.
The ovarian hormones are at their lowest normal levels, and the FSH level begins to rise (a new follicle starts to grow).

2025 Annual I, Set D, MCQ 131 mark

Uterine lining in female starts breaking due to less concentration of:

AProgesteroneAnswer
BEstrogen
CLuteinizing hormone
DFSH

Why

Menstruation begins when the corpus luteum degenerates and the progesterone level falls, depriving the endometrium of hormonal support so that its cells die. Estrogen is also low then, but progesterone is the hormone the book names as the one whose fall sets off the breakdown; LH falls too, but it acts on the corpus luteum, not on the lining directly, and FSH rises at this time.

2026 Annual I, Set D, MCQ 151 mark

Ovulation occurs around:

ADay 1
BDay 7
CDay 14Answer
DDay 28

Why

In a 28-day cycle the sudden release of LH at the end of the proliferative phase causes ovulation on about day 14. Day 1 is the first day of menstrual bleeding, day 7 falls in the middle of the proliferative phase while the follicle is still maturing, and day 28 is the end of the secretory phase when menstruation is about to begin.

2025 Annual I, Set D, Q.2 (i)1x3 = 3 marks

The diagram shows the section through testis: (a) Identify the parts A & B. (b) Write functions of C & D. (c) What is the function of inhibin hormone in males?

Solution

Section through a testis with the four labelled parts. A, outer coat; B, lobules with coiled seminiferous tubules; C, rete testis; D, epididymis.

(a) Identify A and B (1 mark)

A: the outer coat (covering) of the testis (the tunica), which encloses the lobules.
B: the testis lobules, each containing one to four tightly coiled seminiferous tubules (250 to 300 lobules in each testis).

(b) Functions of C and D (1 mark)

C: rete testis, the tubular network that receives the sperms from the seminiferous tubules and in which they undergo further maturation; the efferent ductules then carry them out of the testis.
D: epididymis, coiled on the outer surface of the testis; it is the place for transport and storage of the sperms, and it opens into the vas deferens.

(c) Inhibin (1 mark)

Inhibin is made by the Sertoli cells and released into the blood when the sperm count is too high. It acts on the hypothalamus and anterior pituitary and inhibits the release of GnRH and FSH, so spermatogenesis slows down (negative feedback). When the sperm count falls to 20 million per ml, inhibin is no longer released and the sperm count rises again.

Note. C is the rete testis (where the tubules converge) and D is the epididymis (the coiled tube on the outer edge).

2026 Annual I, Set D, Q.2 (ix)1x3 = 3 marks

Enlist names and location of three accessory glands of male reproductive system.

Solution

Accessory gland (1 mark each)	Location
Seminal vesicles (a pair)	At the junction of the sperm duct (vas deferens) and the ejaculatory duct
Prostate gland	Encircles the urethra just below the bladder (the ejaculatory duct enters it)
Bulbourethral (Cowper's) glands (a pair)	At the junction of the ejaculatory duct and the urethra

Their secretions form the liquid part of the semen, which nourishes and protects the sperms and carries them.

2026 Annual I, Set D, Q.2 (ix) OR1x3 = 3 marks

State three events of secretory phase of menstrual cycle.

Solution

Events of the secretory phase (days 15 to 28), 1 mark each

The corpus luteum secretes rising levels of progesterone, which acts on the estrogen-primed endometrium and converts its functional layer into a glandular secretory layer.
The uterine glands enlarge, coil and secrete nutritious glycogen into the uterine cavity to sustain the embryo until it implants.
If fertilization does not occur, the corpus luteum degenerates as LH declines; progesterone falls, the endometrial cells die and menstruation begins on day 28 (day 1 of the next cycle).

2025 Annual I, Set D, Q.2 (xiii)3 marks

Write about the structure and function of each of the three layers of uterus.

Solution

The wall of the uterus (a hollow, muscular, inverted-pear-shaped organ) has three layers, listed from outside to inside.

Layer (1 mark each)	Structure	Function
Perimetrium	Outermost, thin covering layer of the uterus	Covers and protects the uterus
Myometrium	Middle, thick layer made of bundles of smooth muscle	Contracts rhythmically during childbirth to expel the baby from the mother's body
Endometrium	Innermost, spongy lining of the uterine cavity	Receives the young embryo, which implants in it and stays there for the rest of its development; its functional layer is shed in menstruation

Exam focus

Describe the menstrual cycle: the three phases, their days, the events in ovary and uterus and the hormones involved. (long)
The book's long question 4 and SLO 4; the paper asked one phase at a time as 3-mark events: menstrual phase (2026 Set B Q.2 (ix) OR) and secretory phase (2026 Set D Q.2 (ix) OR); the MCQs on the controlling hormones, ovulation day and the fall of progesterone (2026 B MCQ 15, 2026 D MCQ 15, 2025 D MCQ 13) all come from here.
Go to answer
State three events of the secretory phase, and why the endometrium breaks down if there is no fertilization. (short)
Asked in 2026 Set D Q.2 (ix) OR; progesterone was also tested in 2025 Set B MCQ 3 and 2025 Set D MCQ 13.
Go to answer
Male reproductive hormones (GnRH, FSH, LH, testosterone, inhibin): source, target and role, with negative feedback. (short)
Asked in 2026 Set B Q.2 (ix) and in 2025 Set D Q.2 (i) (c) (inhibin); book short questions 2 and 8 and long question 2.
Go to answer
List the accessory glands of the male system with their locations. (short)
Asked in both 2026 Set D Q.2 (ix) and 2025 Set B Q.2 (iv), nearly word for word, so it is the most repeated item of the unit.
Go to answer
Identify and give the functions of the parts of a testis in a labelled diagram (tunica, lobules, rete testis, epididymis). (short)
2025 Set D Q.2 (i) used a diagram of the testis; book long question 1 asks the structure and functions of the male system.
Go to answer
Structure and functions of the ovary, oviduct and the three layers of the uterus. (short)
Asked in 2025 Set B Q.2 (viii) OR (ovary and oviduct) and 2025 Set D Q.2 (xiii) (uterine layers); book long question 3.
Go to answer
Describe the male reproductive system and the path of the sperms from the seminiferous tubules to the urethra. (long)
Book long question 1 and short question 4; likely as a labelled-diagram question.
Go to answer
Spermatogenesis and oogenesis, and the differences between them. (short)
Book short question 12 (b) asks the difference; both are extra reading in the book but are easy 3-mark comparisons.
Go to answer