The trick that makes PHS 220 reproductive physiology click is realising that the male and female systems are built on the same blueprint. In both sexes one command line, the hypothalamo-pituitary-gonadal axis, runs the whole show: the hypothalamus releases GnRH in pulses, the pituitary answers with LH and FSH, and the gonads make sex steroids and gametes while feeding signals back to keep the loop balanced. Learn that shared logic once and the differences between the sexes become easy variations on a theme rather than two unrelated lists to cram. This page is a student-written study companion for the reproductive block of PHS 220 Physiology, the compulsory second-semester course for ABUAD 200 Level Pharmacy students.
This guide covers both sexes in one place: the shared principles of the reproductive axis, female anatomy and the menstrual cycle, oogenesis, pregnancy and menopause, then male anatomy, testosterone and spermatogenesis, and male sexual function. The summaries below turn the syllabus into plain-English notes, with original practice questions and worked answers so you can check that each idea has stuck, and callout boxes for the high-yield mechanisms and clinical correlates examiners like to test. The full illustrated workbook, with every comparison table and labelled diagram, sits in the reader at the end of this page as a free bonus to the notes here.
- Course: PHS 220 – Physiology (Reproductive block)
- College / Department: College of Medicine and Health Sciences – Department of Physiology
- Level / Semester: 200 Level, Second Semester
- Topics covered: Shared principles of the hypothalamo-pituitary-gonadal axis, female anatomy and the HPO axis, female hormones and the menstrual cycle, oogenesis, pregnancy and menopause, male anatomy and the HPG axis, testosterone and spermatogenesis, and male sexual function with clinical correlates
- Best for: Continuous assessment + second-semester exam revision
Topics Covered in the PHS 220 Reproductive Block
1. Reproductive Physiology: Shared Principles
Male and female reproduction share one control axis, and reading the two sexes side by side makes the design obvious. The hypothalamus releases gonadotropin-releasing hormone in discrete pulses, the anterior pituitary responds with luteinising hormone and follicle-stimulating hormone, and the gonads respond with steroids and gametes. Two rules do most of the work. First, GnRH must be pulsatile: discrete pulses keep the pituitary responsive, while continuous GnRH paradoxically switches LH and FSH off, which is exactly how GnRH agonist drugs are used to suppress the axis in prostate cancer, endometriosis and assisted reproduction. Second, the two gonadotropins have consistent jobs: LH acts on the steroid-producing cells (theca in the ovary, Leydig in the testis) and FSH acts on the gamete-support cells (granulosa in the ovary, Sertoli in the testis).
The differences then fall into place. In the female the axis is called the HPO axis, LH targets theca cells to supply androgen substrate, FSH targets granulosa cells to make oestradiol, the dominant steroid shifts from oestradiol to progesterone across the cycle, and gamete output is cyclical, releasing one oocyte per cycle. In the male the axis is the HPG axis, LH drives Leydig cells to make testosterone, FSH supports Sertoli cells, testosterone is the dominant steroid, and gamete output is continuous. In both sexes inhibin B is the selective brake on FSH. Exam tip: make a two-column table with the female and male versions of each element on the same row, because most "compare the sexes" questions are answered directly from that layout, and it fixes the LH-theca-Leydig and FSH-granulosa-Sertoli pairings in one glance.
2. Female Anatomy and the HPO Axis
The female reproductive system prepares monthly for fertilisation, supports gestation and delivers offspring, working from menarche to menopause. The ovaries carry out oogenesis and make oestrogen, progesterone, androgens and inhibin; the fallopian tubes transport the ovum and are the usual site of fertilisation in the ampulla; the uterus houses implantation and menstruation; the cervix controls access with a mucus plug and dilates in labour; and the acidic vagina serves as the birth canal. The HPO axis controls all of this through GnRH, released from the arcuate nucleus by the KNDy (kisspeptin) neuron network. A key detail is that GnRH pulse frequency shapes the output: fast pulses favour LH and slow pulses favour FSH, and stress raises opioid tone that slows GnRH and disrupts cycles.
Two mechanisms are worth locking in. The first is the two-cell, two-gonadotropin model of oestradiol synthesis: LH drives theca cells to make androgens, those androgens diffuse to the granulosa cells, and FSH there has switched on aromatase to convert them into oestradiol, so neither cell can make oestradiol alone. The second is the switch in feedback. For most of the cycle oestradiol exerts negative feedback and keeps LH and FSH low, but once it stays high for a day and a half or more, it flips to positive feedback and triggers the LH surge. Progesterone in the luteal phase gives negative feedback and slows GnRH, while inhibin selectively suppresses FSH. Exam tip: the single most examined idea here is that the same hormone, oestradiol, does opposite things at different levels and durations, so tie "low and brief equals negative feedback, high and sustained equals positive feedback and the surge" firmly together.
3. Female Hormones and the Menstrual Cycle
Three oestrogens matter at different stages of life: oestradiol dominates the reproductive years, oestrone takes over after menopause, and oestriol is the oestrogen of pregnancy. Oestradiol proliferates the endometrium, thins cervical mucus at ovulation, protects bone by inhibiting osteoclasts, and is cardioprotective before menopause, but it also raises binding globulins and clotting factors, which is the basis of the thrombosis risk with exogenous oestrogen. Progesterone is the hormone of the luteal phase: it converts the proliferative endometrium into a secretory, implantation-ready lining, keeps the myometrium quiet, thickens cervical mucus, and raises basal body temperature by a few tenths of a degree, which is why a rise in temperature marks ovulation and a day-21 progesterone confirms it happened. Prolactin, unusually, is under tonic inhibition by dopamine, so dopamine-blocking drugs and prolactinomas raise it and cause amenorrhoea and galactorrhoea.
The menstrual cycle averages 28 days and divides into menstruation, the follicular (proliferative) phase, ovulation, and the luteal (secretory) phase. In the follicular phase rising FSH selects a dominant follicle and oestradiol climbs; at mid-cycle the sustained high oestradiol triggers the LH surge, which resumes meiosis in the oocyte, digests and ruptures the follicle wall, and luteinises the granulosa cells into a corpus luteum. The luteal phase is then dominated by progesterone from that corpus luteum, which prepares the endometrium and lasts about 14 days unless a pregnancy rescues it. If there is no pregnancy the corpus luteum degenerates, progesterone falls, and the lining is shed. Exam tip: anchor the cycle on day 14. Everything before it is FSH-driven follicle growth with rising oestradiol, the surge is the pivot, and everything after it is progesterone-driven secretory change, so a question about any day can be placed relative to ovulation.
4. Oogenesis, Pregnancy and Menopause
Oogenesis runs on a very different clock from sperm production. The full stock of oogonia is made in fetal life and peaks at six to seven million around 20 weeks, then falls by atresia so that only a few hundred thousand primordial follicles remain at puberty and only a few hundred ever ovulate. The primary oocyte enters meiosis I in fetal life and then arrests in prophase for years, completing meiosis I only at ovulation and arresting again at metaphase II until a sperm arrives. Fertilisation happens in the ampulla within a day of ovulation, the cortical reaction blocks a second sperm, and by day five a blastocyst forms and implants over days six to ten. The trophoblast then secretes hCG, which rescues the corpus luteum so progesterone keeps the pregnancy going.
Pregnancy is a hormonal relay. Early on the corpus luteum supplies the progesterone, but from about weeks eight to ten the placenta takes over as the dominant source, the luteo-placental shift, which is why a failing corpus luteum matters most in the first trimester. hCG rescues the corpus luteum and stimulates the fetus, human placental lactogen raises maternal glucose for the fetus, progesterone keeps the uterus quiet, and oestriol drives uterine and breast growth. Menopause is the mirror image at the other end of life: the follicles run out, oestradiol falls by around 90%, and the loss of feedback lets FSH rise, which is the diagnostic marker. The consequences of low oestrogen (hot flushes, vaginal atrophy, rapid bone loss and rising cardiovascular risk) all follow from that single fall. Exam tip: hCG is the highest-yield hormone here, so be able to state its job (rescuing the corpus luteum), its source (the syncytiotrophoblast) and its clinical use (the basis of pregnancy tests) in one line.
5. Male Anatomy and the HPG Axis
The male system is built for continuous gamete production. The testes sit in the scrotum a few degrees below core temperature, which spermatogenesis needs, and make both sperm and testosterone. Sperm mature and are stored in the epididymis, travel through the vas deferens (the structure cut in a vasectomy), and are mixed with fluid from the seminal vesicles (about 60% of semen, rich in fructose) and the prostate (about a third, providing PSA and zinc) to form semen. The spermatic cord carries the vas, the testicular artery and the pampiniform venous plexus, and that plexus is important physiologically because it cools arterial blood by counter-current exchange. When it becomes dilated (a varicocele) the cooling fails, testicular temperature rises, and fertility can suffer.
The HPG axis in the male runs the same three levels as in the female. Pulsatile GnRH drives LH and FSH; LH stimulates Leydig cells to make testosterone, and FSH supports the Sertoli cells and raises androgen-binding protein and inhibin B. Feedback then closes the loop: testosterone gives long-loop negative feedback on both the hypothalamus and pituitary, while inhibin B from the Sertoli cells selectively suppresses FSH. Exam tip: keep the two feedback signals separate, because testosterone suppresses LH while inhibin B suppresses FSH, and questions often test whether you can predict what happens to each gonadotropin when only one arm of feedback is lost.
6. Testosterone and Spermatogenesis
Testosterone is a steroid made from cholesterol in the Leydig cells, with LH driving the rate-limiting transport of cholesterol into the mitochondria. In the blood most of it is bound (tightly to SHBG, loosely to albumin) and only a small free fraction is active, so anything that changes SHBG changes the amount of usable hormone. Testosterone is not always the final actor. In many target tissues it is converted by 5-alpha-reductase into the more potent DHT, which drives prostate growth, male-pattern baldness and virilisation of the external genitalia, and is the target of drugs such as finasteride. In other tissues it is converted by aromatase into oestradiol, which is essential for male bone density and for feedback. Across life testosterone builds the Wolffian ducts in the embryo, drives puberty, and in the adult maintains spermatogenesis, libido, muscle and bone.
Spermatogenesis turns diploid spermatogonia into haploid sperm in the seminiferous tubules over about 74 days, running continuously from puberty. Spermatogonia amplify by mitosis, primary spermatocytes go through the long meiosis I, secondary spermatocytes quickly finish meiosis II, and the resulting spermatids remodel into sperm during spermiogenesis, growing an acrosome and a tail and shedding cytoplasm before being released. The Sertoli cells are the nurse cells that make it all possible: their tight junctions form the blood-testis barrier that protects developing sperm from the immune system, they feed the germ cells, and they secrete inhibin B and androgen-binding protein. A sperm ends up with a head carrying enzymes to penetrate the egg, a mitochondria-packed midpiece for energy, and a flagellar tail, and it only becomes fully functional after capacitation in the female tract. Exam tip: learn the Sertoli cell as a single multi-tasking "nurse" (barrier, nutrition, hormone secretion), because grouping its jobs under one role is far easier to recall than four separate facts.
7. Male Sexual Function and Clinical Correlates
Erection and ejaculation are controlled by different arms of the nervous system, which is a favourite exam point. Erection is a parasympathetic, vascular event: sexual stimulation releases nitric oxide, which raises cGMP, relaxes the cavernosal smooth muscle so the sinusoids fill with blood, and the swelling compresses the veins to trap it. This is exactly why PDE5 inhibitors such as sildenafil work, because they stop cGMP being broken down. Emission and ejaculation, by contrast, are driven by the sympathetic and somatic systems, and detumescence afterwards is sympathetic. A simple way to remember the sequence is "point and shoot": the Parasympathetic system produces the erection (point) and the Sympathetic system drives emission and ejaculation (shoot).
Male hypogonadism is read the same way as any endocrine axis, using the gonadotropins to localise the lesion. Primary (testicular) failure raises LH and FSH because feedback is lost, as in Klinefelter syndrome or mumps orchitis, while secondary (pituitary or hypothalamic) failure lowers or fails to raise them, as in Kallmann syndrome or anabolic steroid abuse. The features of low testosterone in an adult (reduced libido, erectile dysfunction, loss of muscle, more central fat, low mood and osteoporosis) follow logically from losing the hormone's normal actions. Finally, a vasectomy blocks sperm delivery without touching the Leydig cells or the axis, so LH, FSH and testosterone are unchanged and semen volume barely alters, because most fluid comes from the prostate and seminal vesicles. Exam tip: use "point and shoot" for the neural control, and treat every hypogonadism question as a localisation exercise, high gonadotropins mean the testis has failed, low gonadotropins mean the problem is above it.
Sample Practice Questions (With Answers)
Here are a few representative questions across the reproductive block, written in our own words, with the reasoning explained so you understand the why, not just the result:
Q1. GnRH agonists are used to switch the reproductive axis off, yet GnRH is the hormone that normally turns it on. How does giving more of it suppress the axis?
Answer: The axis depends on GnRH being pulsatile, not merely present. Discrete pulses keep the pituitary gonadotrophs sensitive, so LH and FSH are released normally. A GnRH agonist given continuously floods the receptors without a pulse pattern, which down-regulates and desensitises them, so after an initial flare LH and FSH fall and the gonads go quiet. It is the loss of pulsatility, not a lack of hormone, that shuts the system down, which is why agonists treat prostate cancer and endometriosis.
Q2. Why does oestradiol suppress LH for most of the cycle but trigger a massive LH surge at mid-cycle?
Answer: Because oestradiol's effect depends on its level and how long it is sustained. At the low to moderate concentrations present through most of the cycle it exerts negative feedback and keeps LH and FSH down. As the dominant follicle matures, oestradiol climbs and stays high for a day and a half or more, and at that point feedback flips from negative to positive: GnRH receptors up-regulate and the pituitary releases an explosive LH surge that causes ovulation. The same hormone, read at a different level and duration, produces the opposite response.
Q3. A woman is 8 weeks pregnant. Which structure is maintaining the pregnancy hormonally at this point, and how will that change over the next few weeks?
Answer: At 8 weeks the corpus luteum is still the dominant source of progesterone, kept alive by hCG from the trophoblast. Over the next few weeks the luteo-placental shift occurs: from roughly weeks 8 to 10 the placenta takes over as the main progesterone producer, and the corpus luteum is no longer essential. This is why a problem with the corpus luteum threatens a pregnancy most in the first trimester, before the placenta has assumed the role.
Q4. Two men both have low testosterone. One has high LH and FSH, the other has low LH and FSH. What does this tell you about where each problem lies?
Answer: Use the gonadotropins to localise the lesion. High LH and FSH with low testosterone means the testis itself has failed (primary, hypergonadotrophic hypogonadism); the pituitary is working and pushing hard because feedback is lost, as in Klinefelter syndrome or mumps orchitis. Low LH and FSH with low testosterone means the drive from above has failed (secondary, hypogonadotrophic hypogonadism), as in Kallmann syndrome, hyperprolactinaemia or anabolic steroid use. The gonadotropin level, not the testosterone, points to the site.
Q5. After a vasectomy, a man's testosterone, LH and FSH are unchanged and his semen volume is almost the same. Explain why.
Answer: A vasectomy divides the vas deferens, which only blocks the delivery of sperm. It does not touch the Leydig cells that make testosterone or the HPG axis that controls them, so testosterone, LH and FSH all stay normal. Semen volume barely changes because sperm contribute very little fluid; most of the ejaculate comes from the seminal vesicles and prostate, whose ducts are untouched. The man becomes infertile once tests confirm no sperm remain, usually after about three months.
How to Study the Reproductive Block Effectively
- Build one master table comparing the sexes element by element (axis name, LH target, FSH target, dominant steroid, gamete pattern), because most compare-and-contrast questions come straight off it.
- Fix the two-cell, two-gonadotropin model of oestradiol, since it explains why losing either FSH or LH lowers oestrogen.
- Learn the menstrual cycle around day 14: FSH-driven growth and rising oestradiol before it, the LH surge as the pivot, progesterone-driven secretory change after it.
- Tie oestradiol's dual feedback together as a single rule (low and brief suppresses, high and sustained triggers the surge), because it is the most tested idea in the block.
- Use "point and shoot" for erection versus ejaculation, and treat hypogonadism as a localisation exercise driven by the gonadotropin level.
- Read the topic summaries here to build the framework, then work through the full illustrated workbook in the reader below and attempt the practice questions from memory before your class test.
Download the Full PHS 220 Reproductive Study Guide
The notes above stand on their own, but if you want the complete reproductive block in one place, the full PHS 220 Reproductive Physiology illustrated study guide is loaded in the reader just below, with the male-versus-female comparison tables, the menstrual cycle phase by phase, the hormones of pregnancy, and the labelled callout boxes for the key mechanisms and clinical correlates. Read it right here on the page, or save a copy so you can keep drilling the axis, the cycle and the clinical patterns offline in the days before your test.
Frequently Asked Questions
Is this PHS 220 reproductive material free?
Yes, completely. There is no fee, sign-up, or paywall anywhere on this page. The reproductive notes, practice questions, and the downloadable study guide are open to any student who needs a hand with the physiology of the male and female reproductive systems.
Does this guide cover both the male and female systems?
Yes. This single guide covers both sexes in one place, starting from the shared reproductive axis and then working through female anatomy, the menstrual cycle, oogenesis, pregnancy and menopause, and male anatomy, testosterone, spermatogenesis and sexual function. That is why it replaces the separate male and female topic pages that used to stand alone.
What is the fastest way to revise the reproductive block before a test?
Work from the comparison table and the cycle. Reproduce the male-versus-female table from memory, sketch the menstrual cycle around ovulation on day 14, and rehearse the feedback rules for oestradiol and the gonadotropins. Then attempt the practice questions above from memory, because active recall is close to how the course is examined.
Will these exact questions appear in my exam?
No. This is an original revision set written from scratch to rehearse the reasoning and the phrasing, not a forecast of what your lecturer will set. Use it to practise, then sit your test on the specimens, diagrams and outline your own course actually covers.
About this resource: All summaries, explanations, study tips, and practice questions on this page were written, paraphrased, and adapted by the EverythingABUAD student team to support exam revision. This is an original study aid, not an official ABUAD document, and it is not a prediction of any future exam. Always cross-check with your lecturer's current course outline.
Written by the Everything ABUAD Team
Current students at Afe Babalola University, Ado-Ekiti. Guides are checked against the official ABUAD portal and campus notices, and confirmed with department and course reps before publishing.
