Source: Chapter 28 Part 2, Anatomy and Physiology (University of Florida)
Tags: female hormones, GnRH, FSH, LH, oestrogen, progesterone, hCG, uterine cycle, menstrual cycle, ovulation, menopause, contraception, LARC, IUD, pelvic inflammatory disease, STI, sexually transmitted infection
Difficulty: Intermediate | Prerequisites: Part 1 of these notes (oogenesis, follicle stages, reproductive anatomy); basic endocrine system concepts (hypothalamus–anterior pituitary axis)
This set of notes covers the hormonal machinery that drives the monthly reproductive cycle, from puberty through menopause, and then rounds out the chapter with contraception methods and common sexually transmitted infections. The hormonal content is where most students struggle, because it involves feedback loops: hormones that stimulate their own inhibitors, and a single hormone (oestrogen) that switches from negative to positive feedback depending on its concentration. If you understand the four key hormones (GnRH, FSH, LH, and progesterone) and what each one does at each phase, the rest of the cycle falls into place. The contraception and STI material is more straightforward but still appears on exams.
GnRH from the hypothalamus drives FSH and LH release, which in turn control follicle growth, ovulation, and corpus luteum function. The uterine cycle has three phases (menses, proliferative, secretory) synchronised to the ovarian cycle by oestrogen and progesterone. Menopause occurs when the ovaries stop responding to these signals. Contraception methods range from long-acting reversible options to permanent sterilisation, and several STIs (PID, trichomoniasis, herpes, syphilis, HIV/AIDS) are commonly tested.
GnRH (gonadotropin-releasing hormone)
A hypothalamic hormone that stimulates the anterior pituitary to release FSH and LH. Think of it as the master switch for the entire reproductive hormone cascade. Rising GnRH at puberty is what initiates the first menstrual cycles.
FSH (follicle-stimulating hormone)
An anterior pituitary hormone that stimulates ovarian follicle growth and promotes oestrogen secretion by the granulosa cells. In simple terms, FSH is the signal that tells a batch of follicles to start maturing each month.
LH (luteinising hormone)
An anterior pituitary hormone whose mid-cycle surge triggers ovulation (around day 14). After ovulation, LH supports the formation and function of the corpus luteum. The LH surge is the single most important hormonal event in the cycle for exam purposes.
Oestrogen
Produced mainly by the granulosa cells of developing follicles (and later by the corpus luteum and placenta). It rebuilds the endometrial lining during the proliferative phase, drives secondary sex characteristic development, and, at high concentrations just before ovulation, triggers the LH surge through positive feedback. In simple terms, oestrogen builds things up: the endometrium, breast tissue, and the signal for ovulation.
Progesterone
Produced primarily by the corpus luteum after ovulation. It thickens the endometrium further, makes it secretory (ready for implantation), and inhibits LH and FSH to prevent a second ovulation. Think of progesterone as the hormone that says, "Hold steady and prepare for a possible pregnancy."
hCG (human chorionic gonadotropin)
A hormone produced by the developing embryo (specifically the trophoblast/placenta) that maintains the corpus luteum past its normal lifespan, keeping progesterone levels high. It is the hormone detected by pregnancy tests.
Menses (menstrual phase)
Days 1 to 4 (approximately) of the uterine cycle. The functional layer of the endometrium is shed because progesterone and oestrogen levels have dropped.
Proliferative phase
Days 5 to 14 (approximately). Rising oestrogen from developing follicles stimulates the endometrium to rebuild its functional layer.
Secretory phase
Days 15 to 28 (approximately). Progesterone from the corpus luteum causes the endometrium to thicken further and secrete nutrients, preparing for possible implantation.
Menopause
The permanent cessation of menstrual cycles, typically occurring in the late 40s to early 50s. The ovaries stop responding to FSH and LH, so oestrogen and progesterone levels fall, while FSH and LH levels rise (because negative feedback is lost).
LARC (long-acting reversible contraceptives)
Contraceptive methods that provide extended protection without daily action: intrauterine devices (IUDs) and subdermal implants.
Pelvic inflammatory disease (PID)
A serious bacterial infection of the upper reproductive tract (uterus, uterine tubes, ovaries), often caused by untreated STIs such as chlamydia or gonorrhoea. Can lead to scarring, chronic pain, and infertility.
Female puberty begins when the hypothalamus increases its pulsatile release of GnRH.
GnRH stimulates the anterior pituitary to secrete FSH and LH.
FSH drives follicle development and oestrogen production; rising oestrogen triggers the development of secondary sex characteristics (breast development, fat distribution, pubic hair) and eventually the first menstrual cycle (menarche).
FSH: stimulates follicle growth; promotes oestrogen secretion by granulosa cells.
LH: mid-cycle surge triggers ovulation (around day 14); supports corpus luteum formation and progesterone secretion after ovulation.
Oestrogen: rebuilds endometrium during the proliferative phase; at high levels, exerts positive feedback on the anterior pituitary to cause the LH surge; at lower levels earlier in the cycle, exerts negative feedback.
Progesterone: maintains and further develops the endometrium during the secretory phase; inhibits GnRH, FSH, and LH after ovulation (negative feedback), preventing additional follicle recruitment.
Menses (days 1 to 4): progesterone and oestrogen levels drop because the corpus luteum has degenerated. Without hormonal support, the spiral arteries of the functional layer constrict, the tissue becomes ischaemic, and the functional layer is shed as menstrual flow.
Proliferative phase (days 5 to 14): rising oestrogen from developing ovarian follicles stimulates the endometrium to regenerate its functional layer. Glands elongate, spiral arteries regrow, and the lining thickens.
Secretory phase (days 15 to 28): after ovulation, the corpus luteum produces progesterone (and some oestrogen). The endometrium becomes oedematous and secretory, producing glycogen-rich fluid to nourish a potential embryo. If no implantation occurs, the corpus luteum degenerates, hormone levels fall, and the cycle resets to menses.
Fertilisation occurs in the ampulla of the uterine tube.
If fertilisation occurs, the developing embryo produces hCG, which maintains the corpus luteum and its progesterone output beyond the normal two-week window.
hCG is the hormone detected by both urine and blood pregnancy tests. Its levels rise rapidly in early pregnancy.
Defined as the permanent cessation of menstrual cycles (clinically confirmed after 12 consecutive months without a period).
The ovaries become less responsive to FSH and LH, so oestrogen and progesterone production declines.
Because oestrogen no longer provides negative feedback, FSH and LH levels are elevated in menopause. This is a commonly tested detail.
Symptoms include hot flashes, night sweats, mood changes, irritability, fatigue, and vaginal dryness.
LARC (long-acting reversible contraceptives): IUDs (hormonal or copper) and subdermal implants. Highest effectiveness rates with minimal user effort.
Barrier methods: condoms and diaphragms. They physically prevent sperm from reaching the oocyte. Condoms also reduce STI transmission.
Emergency contraception: Plan B (levonorgestrel pill) or a copper IUD inserted shortly after unprotected intercourse. These are not intended as routine contraception.
Permanent methods: tubal ligation (female) or vasectomy (male). Considered irreversible for practical purposes.
Pelvic inflammatory disease (PID): a bacterial infection of the upper genital tract, often secondary to chlamydia or gonorrhoea. Major risk factor for infertility due to tubal scarring.
Trichomoniasis: caused by the protozoan Trichomonas vaginalis. Presents with foul-smelling discharge, more common in females. Treatable with antibiotics (metronidazole).
Genital herpes: caused by herpes simplex virus type 2 (HSV-2). Produces painful blisters. Managed but not cured with antiviral medication.
Syphilis: caused by the bacterium Treponema pallidum. Progresses through stages (primary, secondary, latent, tertiary) if untreated. Curable with antibiotics (penicillin).
HIV/AIDS: human immunodeficiency virus destroys CD4+ T cells, progressively disabling the immune system. The late stage of HIV infection is called AIDS (acquired immunodeficiency syndrome).
Oral contraceptive pills work by supplying exogenous oestrogen and progesterone, which maintain negative feedback on FSH and LH and prevent the LH surge needed for ovulation. Understanding this feedback loop is not just an exam topic; it is the pharmacological basis of hormonal birth control.
Pregnancy tests, whether the home urine strip or a clinical blood draw, detect hCG. The test becomes positive roughly 10 to 14 days after fertilisation, when hCG levels are high enough to register.
Students often confuse what happens to FSH and LH levels in menopause. Because oestrogen drops, negative feedback is lost, so FSH and LH go up, not down. The ovaries are not responding, but the pituitary is still trying.
The proliferative phase is sometimes confused with the secretory phase. A helpful mnemonic: "proliferative" means cells are proliferating (rebuilding), driven by oestrogen. "Secretory" means glands are secreting, driven by progesterone.
Many students assume the LH surge causes oestrogen to rise. It is the reverse: rising oestrogen (positive feedback) causes the LH surge, and the LH surge then triggers ovulation.
Emergency contraception is sometimes mistakenly called an "abortion pill." Plan B prevents or delays ovulation; it does not terminate an established pregnancy.
⚠️ Be able to name the dominant hormone of each uterine cycle phase: oestrogen for the proliferative phase, progesterone for the secretory phase.
⚠️ The positive feedback loop (high oestrogen triggers the LH surge) is a favourite exam question because it is an exception to the usual negative feedback pattern.
⚠️ Know that hCG maintains the corpus luteum and is the pregnancy test hormone. These two facts often appear as a single multi-part question.
⚠️ FSH and LH are elevated (not low) in menopause. This catches many students.
⚠️ PID and its link to infertility is a commonly tested clinical application.
⚠️ Be ready to classify contraceptive methods into categories: LARC, barrier, emergency, and permanent.
True or false: Progesterone is the dominant hormone during the proliferative phase of the uterine cycle.
Fill in the blank: The __________ surge around day 14 triggers ovulation.
True or false: In menopause, FSH and LH levels decrease because the ovaries are no longer functioning.
Fill in the blank: The hormone detected by pregnancy tests is __________.
True or false: Plan B (emergency contraception) works by terminating an implanted embryo.
Answers: 1. False (oestrogen is dominant during the proliferative phase; progesterone dominates the secretory phase). 2. LH. 3. False (FSH and LH levels rise because negative feedback from oestrogen is lost). 4. hCG. 5. False (it prevents or delays ovulation).
Q: Explain the hormonal feedback loop that leads to the LH surge and ovulation.
A: During the late proliferative phase, maturing follicles produce increasingly high levels of oestrogen. When oestrogen reaches a sustained high threshold, it switches from negative to positive feedback on the anterior pituitary, causing a sharp spike in LH secretion (the LH surge). This surge triggers the Graafian follicle to rupture and release the secondary oocyte, which is ovulation.
Q: What are the three phases of the uterine cycle, and what drives each one hormonally?
A: Menses (days 1 to 4) occurs when oestrogen and progesterone drop following corpus luteum degeneration, causing the functional endometrial layer to shed. The proliferative phase (days 5 to 14) is driven by rising oestrogen, which rebuilds the endometrium. The secretory phase (days 15 to 28) is driven by progesterone from the corpus luteum, which prepares the endometrium for implantation.
Q: How does hCG prevent menstruation in early pregnancy?
A: hCG, produced by the trophoblast of the implanting embryo, maintains the corpus luteum beyond its normal lifespan. The corpus luteum continues secreting progesterone (and oestrogen), which keeps the endometrium intact and prevents the hormonal drop that would trigger menses.
Q: Why are FSH and LH levels elevated in menopause rather than low?
A: The ovaries become unresponsive to FSH and LH, so oestrogen and progesterone production declines. Because oestrogen normally provides negative feedback to the hypothalamus and anterior pituitary, its absence removes the brake on GnRH, FSH, and LH secretion, causing their levels to rise.
Q: Distinguish between LARC and barrier methods of contraception, giving one example of each.
A: LARC (long-acting reversible contraceptives) provide extended protection with minimal user involvement; examples include IUDs and subdermal implants. Barrier methods physically block sperm from reaching the oocyte and require use at each act of intercourse; examples include condoms and diaphragms.
Q: What is pelvic inflammatory disease, and why is it clinically significant?
A: PID is a bacterial infection of the upper female reproductive tract (uterus, uterine tubes, ovaries), commonly caused by sexually transmitted bacteria such as Chlamydia trachomatis or Neisseria gonorrhoeae. It is clinically significant because it can cause scarring of the uterine tubes, leading to chronic pelvic pain, ectopic pregnancy, and infertility.
The hormonal feedback loops here tie directly into the broader endocrine system material from earlier in the course, particularly the hypothalamic–pituitary axis. If you studied the male reproductive system (Chapter 28 Part 1), you will notice parallels: GnRH drives both FSH and LH in males as well, but the downstream targets and feedback molecules differ (testosterone and inhibin in males versus oestrogen and progesterone in females). The STI content connects to microbiology and immunology, especially the distinction between bacterial infections (treatable with antibiotics) and viral infections (managed but not cured).
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