🔬 Reproductive Systems
Study male and female reproductive anatomy for CUET Agriculture. Spermatogenesis, oogenesis, menstrual cycle and hormonal regulation covered.
Male Reproductive System
The male reproductive system is designed for the continuous production, storage, and delivery of spermatozoa (sperm), along with the synthesis of male sex hormones (androgens).
Testes
The testes are the primary male sex organs — they perform the dual function of producing sperm (exocrine) and secreting testosterone (endocrine).
- Paired, oval organs located in the scrotum, a pouch of skin that hangs outside the abdominal cavity
- The scrotum maintains the testicular temperature at 2–2.5°C lower than normal body temperature (37°C). This lower temperature is essential for spermatogenesis — sperm production is severely impaired at body temperature. This is why the testes descend into the scrotum before birth; failure to descend (cryptorchidism) can lead to infertility.
- Each testis measures approximately 4–5 cm long, 2–3 cm wide, weighing ~10–15 g
- Each testis is covered by three protective layers:
- Tunica vaginalis (outermost) — a serous membrane derived from the peritoneum
- Tunica albuginea (middle) — a tough, dense white fibrous capsule that gives the testis its shape and extends inward as septa to divide it into lobules
- Tunica vasculosa (innermost) — a highly vascular layer that nourishes the testis
- Each testis contains approximately ~250 lobules, and each lobule houses 1–3 highly coiled seminiferous tubules (total length of all tubules in both testes can exceed 250 metres)
Seminiferous Tubules
The seminiferous tubules are the site of sperm production — this is where spermatogenesis occurs:
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Male Reproductive System
The male reproductive system is designed for the continuous production, storage, and delivery of spermatozoa (sperm), along with the synthesis of male sex hormones (androgens).
Testes
The testes are the primary male sex organs — they perform the dual function of producing sperm (exocrine) and secreting testosterone (endocrine).
- Paired, oval organs located in the scrotum, a pouch of skin that hangs outside the abdominal cavity
- The scrotum maintains the testicular temperature at 2–2.5°C lower than normal body temperature (37°C). This lower temperature is essential for spermatogenesis — sperm production is severely impaired at body temperature. This is why the testes descend into the scrotum before birth; failure to descend (cryptorchidism) can lead to infertility.
- Each testis measures approximately 4–5 cm long, 2–3 cm wide, weighing ~10–15 g
- Each testis is covered by three protective layers:
- Tunica vaginalis (outermost) — a serous membrane derived from the peritoneum
- Tunica albuginea (middle) — a tough, dense white fibrous capsule that gives the testis its shape and extends inward as septa to divide it into lobules
- Tunica vasculosa (innermost) — a highly vascular layer that nourishes the testis
- Each testis contains approximately ~250 lobules, and each lobule houses 1–3 highly coiled seminiferous tubules (total length of all tubules in both testes can exceed 250 metres)
Seminiferous Tubules
The seminiferous tubules are the site of sperm production — this is where spermatogenesis occurs:
- Lined by two types of cells working together:
- Spermatogonia (male germ cells) — these are the stem cells of the male germline. They undergo the complex process of spermatogenesis to eventually produce mature spermatozoa.
- Sertoli cells (also called sustentacular or nurse cells) — large, supportive cells that extend from the basement membrane to the lumen. They perform multiple vital functions:
- Provide nutrition and physical support to developing sperm
- Produce inhibin (a hormone that provides negative feedback to the pituitary, reducing FSH secretion)
- Secrete ABP (Androgen Binding Protein) — concentrates testosterone within the tubules to maintain the high local testosterone level needed for spermatogenesis
- Form the blood-testis barrier (tight junctions between adjacent Sertoli cells create a protected microenvironment, shielding developing sperm from the immune system — this is important because sperm, produced after puberty, would be recognized as "foreign" by the immune system)
Interstitial Cells (Leydig Cells)
- Located in the connective tissue between seminiferous tubules (hence "interstitial")
- Their primary function is to secrete testosterone, the principal male sex hormone (androgen)
- Testosterone drives the development of male secondary sexual characteristics (facial hair, deep voice, muscle mass), maintains spermatogenesis, and influences libido
- Leydig cells are stimulated by LH (Luteinizing Hormone) from the anterior pituitary. In males, LH is sometimes called ICSH (Interstitial Cell Stimulating Hormone) for this reason.
Male Accessory Ducts
After production in the seminiferous tubules, sperm travel through a series of ducts that progressively store, mature, and transport them:
| Structure | Function |
|---|---|
| Rete testis | A network of tubules that collects sperm from the seminiferous tubules at the back of each testis |
| Vasa efferentia | ~12–20 small ductules that carry sperm from the rete testis to the epididymis; their ciliated lining helps propel sperm |
| Epididymis | A remarkably long (~6 m) tightly coiled tube along the posterior surface of the testis. Sperm spend 12–21 days here undergoing maturation — they gain the ability to swim (motility) and to fertilize. The epididymis also serves as a storage site. |
| Vas deferens (ductus deferens) | ~30 cm long muscular tube. Carries sperm from the epididymis upward through the inguinal canal into the pelvic cavity, where it joins the duct of the seminal vesicle to form the ejaculatory duct. Its thick muscular wall enables peristaltic contractions during ejaculation. |
| Ejaculatory duct | A short duct formed by the union of the vas deferens and the duct of the seminal vesicle. It passes through the prostate gland and opens into the prostatic urethra. |
| Urethra | The common passage for both urine and semen. In males, it has three parts: prostatic (through prostate), membranous (through pelvic floor), and penile/spongy (through penis). Opens at the tip of the penis. |
NOTE
Vasectomy, a common method of male sterilization, involves cutting and sealing the vas deferens bilaterally. This prevents sperm from reaching the semen while leaving hormone production and sexual function unaffected.
Male Accessory Glands
Three sets of glands contribute their secretions to form semen (seminal fluid = sperm + glandular secretions). Normal semen volume per ejaculation is 2–5 ml, containing 200–300 million sperm.
| Gland | Secretion | Function |
|---|---|---|
| Seminal vesicles (paired) | Contribute ~60% of semen volume | Secrete a viscous, alkaline fluid rich in fructose (the primary energy source for sperm motility), prostaglandins (stimulate female tract contractions to aid sperm transport), and fibrinogen (coagulates semen temporarily after ejaculation) |
| Prostate gland (single, walnut-sized) | Contributes ~20–30% of semen | Secretes a slightly alkaline, milky fluid containing citric acid, acid phosphatase (a clinical marker — elevated PSA indicates prostate issues), and lipids. The alkalinity helps neutralize the acidic environment of the vagina, protecting sperm. |
| Bulbourethral / Cowper's glands (paired, pea-sized) | Pre-ejaculatory fluid | Secrete a clear, mucus-like fluid during sexual arousal that lubricates the urethra and neutralizes residual urinary acidity before ejaculation |
Penis
The penis is the male copulatory organ, designed for delivering semen into the female reproductive tract:
- Made of 3 cylindrical bodies of erectile tissue:
- 2 corpora cavernosa (dorsal, side by side) — larger, primary erectile bodies
- 1 corpus spongiosum (ventral) — surrounds and protects the urethra as it passes through the penis
- The tip is enlarged as the glans penis, a highly sensitive structure covered by the prepuce (foreskin), which may be removed by circumcision
- During sexual arousal, the erectile tissue fills with blood (arterial inflow increases, venous outflow is compressed), causing erection
Spermatogenesis
Spermatogenesis is the process of formation of spermatozoa from spermatogonia. It is a continuous process that begins at puberty and continues throughout life. The entire process takes 65–74 days in humans and occurs within the seminiferous tubules under the influence of FSH, LH, and testosterone.
Stages
| Stage | Process | Result |
|---|---|---|
| A. Multiplicative phase | Spermatogonia (2n = 46) divide repeatedly by mitosis to increase their numbers | Primary spermatocytes (2n) |
| B. Growth phase | Primary spermatocytes increase in size, accumulating nutrients and organelles | Enlarged primary spermatocytes |
| C. Maturation phase I | Meiosis I (reductional division) — chromosome number is halved | 2 Secondary spermatocytes (n = 23) |
| D. Maturation phase II | Meiosis II (equational division) | 4 Spermatids (n = 23) |
| E. Spermiogenesis | Spermatids undergo dramatic transformation — nucleus condenses, acrosome forms from Golgi, mitochondria arrange into sheath, tail develops | 4 Spermatozoa (n) |
| F. Spermiation | Release of mature spermatozoa from Sertoli cells into the lumen of the seminiferous tubule | Free spermatozoa |
IMPORTANT
Key difference: 1 primary spermatocyte produces 4 functional spermatozoa (all four are viable). Compare this with oogenesis, where 1 primary oocyte produces only 1 functional ovum + 3 polar bodies.
Hormonal Control of Spermatogenesis
Spermatogenesis is regulated by a hormonal axis involving the hypothalamus, anterior pituitary, and the testes (the HPG axis — Hypothalamic-Pituitary-Gonadal axis):
| Hormone | Source | Function |
|---|---|---|
| GnRH | Hypothalamus | Released in pulses; stimulates the anterior pituitary to release FSH and LH |
| FSH | Anterior pituitary | Acts on Sertoli cells → stimulates spermatogenesis by promoting sperm cell maturation and providing nutritional support |
| LH (ICSH) | Anterior pituitary | Acts on Leydig cells → stimulates testosterone production |
| Testosterone | Leydig cells (testes) | Essential for spermatogenesis (maintains the process within seminiferous tubules), development of male secondary sexual characters (beard, deep voice, muscle mass), and maintenance of accessory reproductive organs |
| Inhibin | Sertoli cells | Provides negative feedback — inhibits FSH secretion from the anterior pituitary when sperm count is adequate, creating a self-regulating system |
Structure of a Spermatozoon
A mature human sperm is a highly specialized cell, stripped down to the bare essentials for reaching and fertilizing the ovum. It is approximately 60 μm long with 3 distinct parts:
-
Head (~5 μm)
- Contains the nucleus with haploid, highly condensed chromatin (paternal genetic material)
- The anterior tip is covered by the acrosome — a cap-like structure derived from the Golgi apparatus. It contains powerful enzymes: hyaluronidase (dissolves the hyaluronic acid matrix holding together the cells of the corona radiata) and acrosin (a protease that digests the zona pellucida of the ovum). These enzymes are essential for sperm penetration during fertilization.
-
Middle piece (~5 μm)
- Contains mitochondria arranged in a tight spiral forming the mitochondrial sheath — these provide the ATP energy needed for the tail's whip-like movement
- Also contains the proximal centriole (plays a role in the first cleavage division of the zygote after fertilization) and distal centriole (gives rise to the axial filament of the tail)
-
Tail (~50 μm)
- The longest part of the sperm — a flagellum responsible for motility
- Contains an axial filament (axoneme) with the characteristic 9+2 microtubule arrangement (9 outer doublets + 2 central singlets — the same arrangement found in all eukaryotic cilia and flagella)
- The tail beats in a wave-like motion, propelling the sperm at about 1–3 mm per minute through the female reproductive tract
Female Reproductive System
Ovaries
The ovaries are the primary female sex organs — they produce ova (eggs) and secrete the female sex hormones estrogen and progesterone.
- Paired, almond-shaped organs located in the pelvic cavity, one on each side of the uterus, held in place by ligaments (ovarian ligament, suspensory ligament)
- Size: approximately 3 cm x 2 cm x 1 cm — small but remarkably productive
- Each ovary has two distinct regions:
- Cortex (outer region): contains ovarian follicles at various stages of development — from tiny primordial follicles to large, mature Graafian follicles
- Medulla (inner region): connective tissue with blood vessels, lymphatics, and nerves that supply the ovary
- Covered by germinal epithelium (simple cuboidal epithelium on the surface — despite its name, this layer does NOT actually give rise to germ cells) and tunica albuginea (a fibrous capsule beneath the epithelium)
Follicle Development
Follicle development is a long, multi-stage process. Women are born with all the follicles they will ever have (~2 million at birth, declining to ~400,000 at puberty). Only about 400 follicles will complete maturation and ovulate during a woman's reproductive lifetime.
| Stage | Features |
|---|---|
| Primordial follicle | The earliest stage: a primary oocyte (arrested in prophase I of meiosis since fetal life) surrounded by a single layer of flat granulosa cells. Most follicles remain in this dormant state. |
| Primary follicle | Activation begins: granulosa cells become cuboidal and multiply. The zona pellucida — a thick glycoprotein layer — forms between the oocyte and the granulosa cells. This layer plays a crucial role in fertilization. |
| Secondary follicle | Multiple layers of granulosa cells accumulate. Two theca layers form from surrounding stromal cells: theca interna (secretes androgens that are converted to estrogen by granulosa cells) and theca externa (structural support). |
| Tertiary / Antral follicle | A fluid-filled cavity called the antrum appears within the granulosa cell layers, filled with follicular fluid rich in estrogen |
| Graafian follicle | The fully mature follicle, ready for ovulation. The oocyte sits on a mound of granulosa cells called the cumulus oophorus. It bulges from the ovarian surface. At ovulation, the follicle wall ruptures and the secondary oocyte (surrounded by the corona radiata) is released. |
Other Female Reproductive Organs
| Organ | Features |
|---|---|
| Fallopian tubes / Oviducts | Paired tubes, each ~12 cm long, connecting the ovary to the uterus. Four regions: Infundibulum (funnel-shaped opening near ovary with finger-like fimbriae that sweep the released ovum into the tube) → Ampulla (widest part — the site of fertilization) → Isthmus (narrow, thick-walled segment) → Uterine part (passes through the uterine wall). Ciliated epithelium and peristalsis move the ovum toward the uterus. |
| Uterus | A pear-shaped, muscular organ, approximately ~7.5 cm long. Its wall has 3 layers: Perimetrium (outer serous layer), Myometrium (middle — the thickest layer, composed of smooth muscle that contracts powerfully during labor), Endometrium (inner glandular layer, richly vascularised — this is the layer that thickens each month in preparation for implantation and is shed during menstruation). |
| Cervix | The lower, narrow neck of the uterus that protrudes into the vagina. Its opening into the vagina is called the external os. The cervical canal secretes mucus that changes consistency during the menstrual cycle — thin and watery at ovulation (facilitating sperm entry) and thick at other times (forming a plug). |
| Vagina | A muscular, elastic canal approximately 7–10 cm long. Serves as the birth canal during delivery and receives the penis during copulation. Its acidic environment (pH ~3.8–4.5, maintained by Lactobacillus bacteria) protects against infections. |
| Vulva | The external genitalia, comprising: mons pubis (fatty pad over the pubic bone), labia majora (outer fleshy folds), labia minora (inner thin folds), clitoris (highly sensitive erectile organ, homologous to the penis), vestibule (space between labia minora containing the urethral and vaginal openings), and hymen (thin membrane partially covering the vaginal opening). |
| Bartholin's glands | Paired glands located at the vaginal opening; homologous to Cowper's glands in males. Secrete mucus for lubrication during sexual arousal. |
Mammary Glands
The mammary glands are modified sweat glands (apocrine type) that are functionally part of the reproductive system, designed to nourish the newborn:
- Each breast contains 15–20 mammary lobes, each with clusters of alveoli (milk-secreting cells)
- The milk pathway: Alveoli (milk production) → mammary tubules → mammary duct → mammary ampulla (temporary storage sinus) → lactiferous duct → opens at the nipple
- Areola: the pigmented circular area surrounding the nipple, which darkens during pregnancy. It contains small sebaceous glands (Montgomery's glands) that lubricate the nipple during breastfeeding.
Oogenesis
Oogenesis is the process of formation of ova (eggs) from oogonia in the ovary. Unlike spermatogenesis, which is continuous, oogenesis is discontinuous — it begins in fetal life, pauses for years, and is only completed if and when fertilization occurs.
Three Phases
| Phase | Details |
|---|---|
| Multiplicative phase | Oogonia (2n) multiply rapidly by mitosis in the fetal ovary (during months 3–7 of fetal development). By birth, approximately ~2 million oogonia are present, but most degenerate (atresia). By puberty, only about 400,000 remain. |
| Growth phase | Oogonia enter meiosis and become primary oocytes (2n). However, they are arrested in prophase I (specifically the diplotene stage) — and can remain in this arrested state for decades (from fetal life until ovulation, which may be 12–50 years later). The primary oocyte grows significantly in size, accumulating organelles, nutrients, and mRNA. |
| Maturation phase | Meiosis I is completed just before ovulation — produces 1 large secondary oocyte (n) + 1 small first polar body (the cytoplasm divides unequally to preserve nutrients in the oocyte). Meiosis II begins but is arrested at metaphase II — it is completed only if fertilization occurs → produces 1 ovum (n) + 2nd polar body. |
IMPORTANT
Key outcome: 1 primary oocyte → 1 functional ovum + 3 polar bodies (all three polar bodies degenerate). The unequal cytoplasmic division ensures that the single ovum receives virtually all the cytoplasm, organelles, and nutrients needed to support early embryonic development.
Spermatogenesis vs Oogenesis
| Feature | Spermatogenesis | Oogenesis |
|---|---|---|
| Occurs in | Testes (seminiferous tubules) | Ovary |
| Starts at | Puberty | Fetal life (arrested until puberty) |
| Duration | 65–74 days (continuous production) | Years (discontinuous, with prolonged arrested stages) |
| Functional gametes | 4 spermatozoa per primary spermatocyte | 1 ovum per primary oocyte |
| Unequal division | No — all 4 cells are equal in size | Yes — polar bodies receive minimal cytoplasm |
| Completion | Completed entirely within the testis | Completed only after fertilization (meiosis II finishes upon sperm entry) |
| Continues until | Old age (~lifelong) | Menopause (~50 years) |
Menstrual Cycle
The menstrual cycle is a monthly reproductive cycle that prepares the female body for potential pregnancy. It involves coordinated hormonal changes in the hypothalamus, pituitary, ovaries, and uterus.
- Occurs in primate females (humans, apes, monkeys) — other mammals have an estrous cycle instead (no menstrual bleeding)
- Average duration: ~28 days (normal range: 21–35 days)
- Menarche: the first menstruation, typically occurring between 10–15 years of age
- Menopause: the permanent cessation of menstruation, typically between 45–55 years of age
Phases of Menstrual Cycle
| Phase | Days | Hormonal Changes | Ovarian Changes | Uterine Changes |
|---|---|---|---|---|
| Menstrual phase | 1–5 | Estrogen and progesterone are at their lowest levels (corpus luteum has degenerated) | Corpus luteum has fully degenerated into corpus albicans | Endometrium sheds — the functional layer breaks down, causing menstrual bleeding (~50–80 ml blood loss) |
| Follicular / Proliferative phase | 6–13 | FSH rises → stimulates follicle development → growing follicle produces increasing estrogen | Follicle development progresses: primary → secondary → tertiary → Graafian follicle | Estrogen stimulates endometrium to regenerate and thicken — new blood vessels, glands, and tissue layers form |
| Ovulation | Day 14 | A sharp LH surge (accompanied by an FSH peak), triggered by the high estrogen levels from the mature follicle (positive feedback) | Graafian follicle ruptures; secondary oocyte (surrounded by corona radiata) is released into the peritoneal cavity and swept into the fallopian tube by fimbriae | — |
| Luteal / Secretory phase | 15–28 | LH supports the formation and function of the corpus luteum → progesterone rises sharply (with some estrogen) | Corpus luteum forms from the collapsed follicle and actively secretes progesterone and estrogen | Progesterone transforms the endometrium: it becomes highly vascular and glandular (secretory), producing glycogen-rich secretions — ready for implantation of a blastocyst |
What happens next depends on fertilization:
- If fertilization occurs: the embryo implants in the endometrium and begins secreting hCG, which maintains the corpus luteum → progesterone production continues → no menstruation → pregnancy begins
- If no fertilization: the corpus luteum degenerates after ~14 days → becomes the corpus albicans (scar tissue) → progesterone and estrogen levels plummet → the thickened endometrium can no longer be maintained → it sheds → menstruation begins → the cycle restarts
What is the LH surge and why is it important?
The **LH surge** is a dramatic spike in LH levels that occurs around day 12–13, peaking on day 14. It is triggered by the high estrogen levels produced by the mature Graafian follicle — uniquely, high estrogen at this point switches from negative feedback to **positive feedback** on the pituitary, causing a massive release of stored LH. The LH surge triggers: (1) completion of meiosis I in the primary oocyte, (2) rupture of the Graafian follicle (ovulation), and (3) conversion of the ruptured follicle into the corpus luteum. Home ovulation prediction kits detect this LH surge in urine.Puberty Changes
Puberty is the transition period during which a child develops secondary sexual characteristics and becomes capable of reproduction. It is triggered by the reactivation of the HPG axis (hypothalamic-pituitary-gonadal axis) after childhood dormancy.
| Feature | Males | Females |
|---|---|---|
| Age of onset | 13–15 years | 10–14 years (generally 1–2 years earlier than males) |
| Growth spurt | Later onset but continues longer; greater final height and muscle mass | Earlier onset but shorter duration |
| Voice | Deepens significantly (larynx enlarges under testosterone influence → longer vocal cords) | Remains higher pitched (smaller larynx) |
| Hair growth | Facial hair (beard, moustache), axillary, pubic, and body hair | Axillary and pubic hair (no significant facial hair) |
| Body shape | Broader shoulders, increased muscle mass, narrower hips | Wider hips (for childbearing), breast development, more subcutaneous fat |
| Gonads | Testes enlarge; spermatogenesis begins | Ovaries enlarge; menarche (first menstruation) |
| Hormones | Testosterone rises dramatically | Estrogen rises dramatically |
| Skin | Acne common (sebaceous glands become more active under androgen influence) | Acne possible but generally less severe |
Homologous Organs (Male–Female)
During early embryonic development (first 6–7 weeks), male and female embryos are anatomically identical. The same embryonic structures differentiate into different organs depending on whether testosterone (male) or estrogen (female) predominates. These developmentally equivalent structures are called homologous organs:
| Male Structure | Female Homologue |
|---|---|
| Testes | Ovaries |
| Penis | Clitoris |
| Scrotum | Labia majora |
| Cowper's glands | Bartholin's glands |
| Prostate gland | Skene's glands (paraurethral glands) |
| Prepuce (foreskin) | Clitoral hood |
NOTE
Homologous organs share the same embryonic origin but differ in adult structure and function. This is different from analogous organs, which have similar function but different embryonic origins.
Summary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| Male — Testes | Primary sex organs; paired, located in scrotum (2–3°C below body temperature for spermatogenesis) Each testis has ~250 lobules, each containing 1–3 seminiferous tubules Seminiferous tubules: site of sperm production; lined with Sertoli cells (nourish sperm, secrete inhibin) and spermatogonia |
| Leydig Cells (Interstitial Cells) | Located between seminiferous tubules Secrete testosterone (primary male sex hormone) Stimulated by LH (ICSH) from anterior pituitary |
| Male Accessory Ducts | Rete testis → vasa efferentia (12–20 ducts) → epididymis (sperm maturation + storage, ~6 m long) → vas deferens → ejaculatory duct → urethra |
| Male Accessory Glands | Seminal vesicles (1 pair): secrete ~60% of semen volume (fructose for sperm energy, prostaglandins) Prostate gland (single): secretes ~30% (slightly alkaline, contains citric acid, acid phosphatase, PSA) Bulbourethral/Cowper's glands (1 pair): secrete pre-ejaculatory fluid (lubricant, neutralises urethral acidity) |
| Semen | Volume: 2–5 ml per ejaculation Sperm count: ~200–300 million per ejaculation Normal count: >15 million/ml (WHO); <15 million/ml = oligospermia |
| Spermatogenesis | Location: seminiferous tubules Duration: ~65–74 days Spermatogonium (2n) → mitosis → primary spermatocyte (2n) → Meiosis I → secondary spermatocytes (n) → Meiosis II → spermatids (n) → spermiogenesis → spermatozoa Starts at puberty, continues throughout life |
| Hormonal Control (Male HPG Axis) | Hypothalamus → GnRH → anterior pituitary → FSH (stimulates Sertoli cells → spermatogenesis) + LH/ICSH (stimulates Leydig cells → testosterone) Negative feedback: testosterone inhibits GnRH and LH; inhibin (from Sertoli cells) inhibits FSH |
| Sperm Structure | Head: acrosome (enzymes for egg penetration) + haploid nucleus Neck/Middle piece: contains mitochondria (spiral, provide energy for motility) + centriole Tail: flagellum for motility Total length: ~60 μm |
| Female — Ovaries | Primary sex organs; paired, almond-shaped, located in pelvic cavity Produce ova (eggs) + secrete estrogen and progesterone Ovarian cortex: contains follicles at various stages Ovarian medulla: blood vessels and nerves |
| Follicle Development | Primordial follicles (~2 million at birth, ~60,000–80,000 at puberty) → primary follicle → secondary follicle (antrum forms) → Graafian follicle (mature, ready for ovulation) Only ~400 follicles ovulate in a lifetime After ovulation: empty follicle → corpus luteum (secretes progesterone) → corpus albicans (if no pregnancy) |
| Fallopian Tubes (Oviducts) | ~12 cm long; regions: infundibulum (funnel-shaped, with fimbriae that catch the ovum) → ampulla (widest, site of fertilization) → isthmus (narrow) → connects to uterus Lined with ciliated epithelium (moves ovum toward uterus) |
| Uterus | Pear-shaped, ~7.5 cm long Regions: fundus (dome-shaped top), body (main), cervix (narrow lower, opens into vagina) Wall layers: perimetrium (outer), myometrium (thick smooth muscle, contracts during labor), endometrium (inner, shed during menstruation, site of implantation) |
| Mammary Glands | Each breast has 15–20 lobes of glandular tissue, each with alveoli (milk-secreting) Alveoli → mammary tubules → mammary ducts → mammary ampulla → lactiferous duct → opens at nipple Development: stimulated by estrogen (duct growth) and progesterone (alveolar growth) |
| Oogenesis | Begins in foetal life (unlike spermatogenesis) Oogonium (2n) → mitosis → primary oocyte (2n) → arrested in Prophase I (diplotene) at birth At puberty: Meiosis I completes → secondary oocyte (n) + 1st polar body → arrested in Metaphase II Meiosis II completes only if fertilization occurs → ovum (n) + 2nd polar body |
| Menstrual Cycle | Duration: ~28 days (range 21–35); controlled by hormones Menstrual phase (days 1–5): endometrium shed, bleeding Follicular/Proliferative phase (days 6–13): FSH → follicle growth → estrogen → endometrium rebuilds Ovulation (day 14): LH surge → Graafian follicle ruptures → secondary oocyte released Luteal/Secretory phase (days 15–28): corpus luteum → progesterone → endometrium thickens + becomes secretory If no fertilization: corpus luteum degenerates → progesterone drops → menstruation |
| Puberty | Males: 13–15 years; females: 10–14 years (earlier) Triggered by GnRH from hypothalamus → FSH + LH → gonadal hormones Menarche: first menstruation; Menopause: cessation of menstruation (~45–55 years) |
| Homologous Organs | Testes ↔ Ovaries, Penis ↔ Clitoris, Scrotum ↔ Labia majora, Cowper's glands ↔ Bartholin's glands, Prostate ↔ Skene's glands |
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