Reproductive System — revision sheet

The reproductive system produces haploid gametes, delivers them so that fertilisation can occur, and — in females — supports the embryo and fetus through pregnancy, birth and lactation. Its gonads are also endocrine glands whose sex steroids shape sexual development and influence almost every tissue.

Testis: ≈4–5 × 3 × 2.5 cm; volume ≈15–25 mL; ≈2–3 °C below core temperatureSpermatogenesis: ≈64–74 days, plus ≈1–2 weeks of epididymal transitSemen lower reference limits (WHO 2021): 1.4 mL · 16 million/mL · 39 million total · 30 % progressive motility · 4 % normal formsOvarian oocyte pool: ≈6–7 million (20 weeks gestation) → ≈1–2 million (birth) → ≈300 000–400 000 (menarche) → ≈1000 (menopause)Oocytes ovulated in a lifetime: ≈400–500Menstrual cycle: Mean ≈28 days (normal 24–38); menses ≤8 days; luteal phase ≈14 daysFertile window: ≈6 days: sperm survive ≈5 days, oocyte ≈12–24 hUterus (nulliparous): ≈7.5 × 5 × 2.5 cm; ≈1 kg at termUterine tube: ≈10–12 cm; fertilisation in the ampullaImplantation: Begins ≈day 6–7 after fertilisation; complete by ≈day 10–12Term placenta: ≈500 g, ≈20 cm diameter, ≈2–3 cm thickPregnancy: ≈40 weeks (280 days) from the last menstrual period; term 37–42 weeksMenopause: Median ≈51 years; premature ovarian insufficiency <40 years

Male — testis & spermatogenesis

Testis Organ: The paired male gonad, suspended in the scrotum by the spermatic cord, which produces spermatozoa in its seminiferous tubules and secretes testosterone from its interstitial Leydig cells.
Seminiferous tubules Organ part: Highly coiled tubules that make up ≈80–90 % of the testis, lined by a stratified epithelium of Sertoli cells and developing germ cells in which spermatogenesis takes place.
Sertoli cell Cell: Tall supporting cells of the seminiferous epithelium that nourish and protect developing germ cells, form the blood–testis barrier, and mediate the effects of FSH and testosterone on spermatogenesis.
Leydig cell Cell: Steroid-secreting cells lying in clusters between the seminiferous tubules that produce testosterone in response to LH.
Spermatogenesis Cell process: The ≈64–74-day process in the seminiferous tubules by which diploid spermatogonia generate haploid spermatozoa through mitosis, meiosis and spermiogenesis.
Spermatozoon Cell: The motile male gamete (≈55–60 µm long): a haploid head capped by the acrosome, a mitochondria-packed midpiece and a long flagellum, specialised to reach and fertilise the oocyte.

Male — ducts & accessory glands

Epididymis Duct: A comma-shaped structure on the posterior border of the testis, formed by a single tightly coiled duct about 6 m long, in which sperm mature, gain motility and are stored.
Ductus deferens (vas deferens) Duct: A thick-walled muscular tube ≈45 cm long that carries sperm from the tail of the epididymis, through the spermatic cord and inguinal canal, over the ureter, to join the seminal vesicle duct as the ejaculatory duct.
Spermatic cord Region: The bundle of structures — ductus deferens, vessels, nerves and lymphatics — that runs from the deep inguinal ring through the inguinal canal to the testis, wrapped in three fascial coverings derived from the abdominal wall.
Seminal vesicle (seminal gland) Gland: Paired coiled tubular glands (≈5 cm) on the posterior surface of the bladder that secrete about 60–70 % of the volume of semen — an alkaline, fructose-rich, coagulable fluid.
Ejaculatory duct Duct: A paired, ≈2 cm duct formed by the union of the ductus deferens and the seminal vesicle duct that passes through the prostate to open into the prostatic urethra on the seminal colliculus.
Prostate Gland: A walnut-sized fibromuscular gland (≈20 g) surrounding the prostatic urethra below the bladder that adds a thin, milky, PSA- and citrate-rich secretion (≈20–30 % of semen); it is the site of benign prostatic hyperplasia and prostate cancer.
Bulbourethral gland (Cowper gland) Gland: Paired pea-sized glands beside the membranous urethra in the deep perineal pouch whose ducts open into the proximal spongy urethra; they secrete a clear mucus (pre-ejaculate) during sexual arousal.
Semen Fluid: The ejaculated mixture of spermatozoa (<5 % of volume) and secretions of the seminal vesicles, prostate and bulbourethral glands that transports, nourishes and protects sperm.

Male — external genitalia

Scrotum Organ: A pouch of thin, pigmented skin and smooth muscle (dartos) divided by a septum into two compartments, each housing a testis, epididymis and the lower spermatic cord at a temperature a few degrees below the core.
Penis Organ: The male copulatory organ and the conduit for urine and semen, built from three cylinders of erectile tissue — two corpora cavernosa and the corpus spongiosum around the urethra — that become rigid when engorged with blood.
Corpus cavernosum of penis Organ part: The paired dorsal cylinders of erectile tissue of the penis, encased in thick tunica albuginea, whose filling with arterial blood produces the rigidity of erection.
Corpus spongiosum Organ part: The single ventral erectile body of the penis that surrounds the spongy urethra, expanding proximally into the bulb and distally into the glans; its thin tunica keeps the urethra open during erection.

Female — ovary & oogenesis

Ovary Organ: The paired almond-shaped female gonad on the lateral pelvic wall that stores the finite supply of oocytes, releases one at ovulation each cycle, and secretes estrogens, progesterone, inhibin and androgens.
Ovarian follicle Organ part: The functional unit of the ovary: an oocyte surrounded by granulosa (and later theca) cells, which develops from the primordial stage to a mature (Graafian) follicle that ruptures at ovulation.
Corpus luteum Organ part: A temporary endocrine gland formed from the ruptured follicle after ovulation that secretes progesterone, estradiol and inhibin A for ≈14 days — or for ≈7–9 weeks if rescued by hCG in pregnancy.
Oocyte Cell: The female gamete — one of the largest human cells (≈100–120 µm) — ovulated as a secondary oocyte arrested in metaphase II, enclosed in the zona pellucida and corona radiata, and viable for only ≈12–24 hours.
Oogenesis Cell process: The production of female gametes, which begins before birth, pauses in prophase I for years to decades, resumes at each ovulation and completes only at fertilisation, yielding one oocyte and polar bodies from each primary oocyte.
Ovarian cycle Physiological process: The ≈28-day sequence of follicle growth (follicular phase), ovulation and corpus luteum function (luteal phase) driven by the hypothalamic–pituitary–ovarian axis, which in turn drives the uterine cycle.

Female — uterine tubes & uterus

Uterine tube (fallopian tube) Organ: A paired muscular tube ≈10–12 cm long running in the upper edge of the broad ligament from the uterus to the ovary, which captures the ovulated oocyte, is the site of fertilisation, and transports the early embryo to the uterus.
Uterus Organ: A thick-walled, pear-shaped muscular organ in the lesser pelvis (≈7.5 × 5 × 2.5 cm) in which the embryo implants and the fetus develops; its endometrium cycles monthly and its myometrium expels the fetus at birth.
Endometrium Tissue: The glandular mucosa lining the uterine cavity, whose superficial functional layer is rebuilt by estrogen, prepared for implantation by progesterone and shed at menstruation, while the deep basal layer regenerates it.
Myometrium Tissue: The thick smooth-muscle middle layer of the uterine wall, which hypertrophies enormously in pregnancy, remains quiet under progesterone, contracts powerfully in labour and clamps its own blood vessels after delivery.
Perimetrium Membrane: The outer serous coat of the uterus — visceral peritoneum with a thin layer of connective tissue — continuous laterally with the broad ligament and reflected onto the bladder and rectum.
Cervix Organ part: The narrow lower third of the uterus (≈2.5–3 cm), mostly dense connective tissue, that projects into the vagina; its mucus gates sperm entry, its canal stays closed in pregnancy, and its transformation zone is the site of cervical cancer.
Uterine (menstrual) cycle Physiological process: The cyclic, hormone-driven changes of the endometrium — menstrual, proliferative and secretory phases — that prepare it each month for implantation and shed it when pregnancy does not occur.

Female — ligaments & support

Broad ligament Ligament: A double fold of peritoneum draped over the uterus and uterine tubes, extending from the sides of the uterus to the lateral pelvic walls; it carries the uterine vessels and encloses the tubes, ovarian and round ligaments.
Round ligament of uterus Ligament: A fibromuscular cord ≈10–12 cm long running from the uterotubal junction through the inguinal canal to the labium majus; with the ovarian ligament, it is the female remnant of the gubernaculum.
Ovarian ligament (proper ligament of ovary) Ligament: A short fibromuscular cord within the broad ligament connecting the uterine (lower) pole of the ovary to the lateral wall of the uterus just below the uterine tube.
Suspensory ligament of ovary Ligament: A peritoneal fold extending from the tubal (upper) pole of the ovary to the lateral pelvic wall over the external iliac vessels, conveying the ovarian artery, vein, lymphatics and nerves.

Female — vagina & external genitalia

Vagina Organ: A distensible fibromuscular tube ≈7–9 cm long extending upward and backward from the vestibule to the cervix; it receives the penis, conveys menstrual flow and forms the lower birth canal.
Vulva Region: The external female genitalia — mons pubis, labia majora and minora, clitoris, vestibule with the urethral and vaginal openings, vestibular bulbs and glands — which protect the urogenital openings and function in sexual arousal.
Clitoris Organ: An erectile organ — homologue of the penis — with a small visible glans and a larger internal body and crura; densely innervated, it is the principal organ of female sexual sensation.
Greater vestibular gland (Bartholin gland) Gland: Paired pea-sized mucous glands posterolateral to the vaginal orifice whose ducts open into the vestibule at about 4 and 8 o'clock, providing lubrication during sexual arousal; homologue of the bulbourethral glands.

Breast

Mammary gland (breast) Gland: A modified apocrine sweat gland in the subcutaneous tissue of the anterior chest wall, organised into 15–20 lobes drained by lactiferous ducts that open on the nipple; it produces milk and drains lymph chiefly to the axillary nodes.
Lactation Physiological process: The synthesis and ejection of milk by the mammary gland after childbirth, triggered by the postpartum fall in progesterone and maintained by suckling through the prolactin (synthesis) and oxytocin (ejection) reflexes.

Fertilisation & pregnancy

Fertilisation Physiological process: The fusion of a spermatozoon with a secondary oocyte, usually in the ampulla of the uterine tube within a day of ovulation, which restores the diploid chromosome number, determines genetic sex and initiates embryonic development.
Zygote Cell: The single diploid, totipotent cell formed at fertilisation, which begins cleavage divisions inside the zona pellucida as it is carried along the uterine tube.
Morula Physiological process: A solid ball of ≈12–32 blastomeres ("mulberry") formed ≈3–4 days after fertilisation, in which compaction separates inner from outer cells; it enters the uterine cavity at about day 4.
Blastocyst Physiological process: The fluid-filled stage of the early embryo (day 4–5), consisting of an outer trophoblast that will form the placenta and an inner cell mass that will form the embryo; it hatches from the zona pellucida and implants.
Implantation Physiological process: The embedding of the blastocyst into the receptive endometrium, beginning ≈6–7 days after fertilisation and complete by ≈day 10–12, usually in the upper posterior wall of the uterine body.
Placenta Organ: A temporary discoid organ (≈500 g at term) formed from the chorion frondosum and the decidua basalis that exchanges gases, nutrients and wastes between maternal and fetal blood and secretes the hormones of pregnancy.
Umbilical cord Organ: The cord (≈50–60 cm at term) linking fetus and placenta, containing two umbilical arteries and one umbilical vein embedded in protective Wharton's jelly and covered by amnion.
Pregnancy Physiological process: The ≈40-week period (from the last menstrual period) during which the conceptus develops within the uterus, divided into three trimesters and accompanied by extensive maternal physiological adaptation.
Parturition (labour and birth) Physiological process: The process of giving birth: regular uterine contractions progressively efface and dilate the cervix (first stage), expel the baby (second stage) and deliver the placenta (third stage), driven by a positive-feedback loop of oxytocin and prostaglandins.

Life stages

Puberty Physiological process: The transition to reproductive maturity, triggered by reactivation of pulsatile GnRH secretion, during which secondary sexual characteristics develop, a growth spurt occurs and gametogenesis begins.
Menopause Physiological process: The permanent cessation of menstruation caused by depletion of ovarian follicles, diagnosed after 12 months of amenorrhoea (median age ≈51), with falling estradiol and rising FSH.

Mnemonics

Path of sperm: SEVEN UP: Seminiferous tubules → Epididymis → Vas (ductus) deferens → Ejaculatory duct → (Nothing) → Urethra → Penis.
Autonomic control of the male sexual response: Point, Squeeze and Shoot: Parasympathetic → erection (Point); Sympathetic → emission (Squeeze); Somatic (pudendal) → ejaculation (Shoot).
Water under the bridge: The ureter passes under the uterine artery (≈2 cm lateral to the cervix) in women and under the ductus deferens in men — a classic site of ureteric injury in hysterectomy.
Parts of the uterine tube (lateral → medial): I Am In: Infundibulum (fimbriae) → Ampulla (fertilisation, ectopic) → Isthmus (ligation) → Intramural (uterine) part.
Contents of the spermatic cord — rule of threes: 3 arteries (testicular, cremasteric, artery to ductus deferens), 3 veins (pampiniform plexus, cremasteric vein, vein of ductus), 3 nerves (genital branch of genitofemoral, sympathetic testicular plexus; ilioinguinal runs alongside, outside the cord), 3 other (ductus deferens, lymphatics, processus vaginalis remnant). 3 coverings: external spermatic fascia, cremasteric muscle and fascia, internal spermatic fascia.
Prostate zones: Peripheral = Palpable and Prostate cancer (≈70 %); Transition = Too big (BPH); Central = surrounds the ejaculatory Channels.
Causes of postpartum haemorrhage: 4 Ts: Tone (uterine atony — commonest), Trauma (tears), Tissue (retained placenta), Thrombin (coagulopathy).

From the Corpus anatomy atlas — for education only.