Human Reproduction

1. Chapter at a glance

• Humans are sexually reproducing and viviparous; reproductive events are gametogenesis, insemination, fertilisation, implantation, gestation and parturition.
• Male reproductive system includes testes in scrotum (2–2.5 °C lower than body temperature), seminiferous tubules lined by spermatogonia and Sertoli cells, Leydig cells secreting androgens, accessory ducts (rete testis, vasa efferentia, epididymis, vas deferens) and glands (seminal vesicles, prostate, bulbourethral glands).
• Female reproductive system includes ovaries producing ova and ovarian hormones, oviducts (infundibulum with fimbriae, ampulla, isthmus), uterus (perimetrium, myometrium, endometrium) and accessory structures.
• Spermatogenesis begins at puberty; diploid spermatogonia (46 chromosomes) form haploid spermatids (23 chromosomes) via meiosis, followed by spermiogenesis and spermiation.
• Oogenesis starts in fetal life; primary oocytes arrest in prophase-I; at puberty ~60 000–80 000 primary follicles remain; tertiary/Graafian follicle releases secondary oocyte at ovulation.
• Menstrual cycle (average 28/29 days) comprises menstrual, follicular, ovulatory and luteal phases; cyclic changes driven by pituitary (LH, FSH) and ovarian hormones; ceases at menopause (~50 years).
• Fertilisation occurs in ampullary region of fallopian tube; zygote undergoes cleavage to morula then blastocyst; implantation in endometrium establishes pregnancy.
• Parturition (after ~9 months gestation) is induced by foetal ejection reflex and oxytocin; lactation begins with colostrum secretion containing antibodies.

2. Definitions and laws

• “The process of formation of a mature female gamete is called oogenesis.”
• “The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called menstrual cycle.”
• “The first menstruation begins at puberty and is called menarche.”
• “The process of fusion of a sperm with an ovum is called fertilisation.”
• “The process of delivery of the foetus (childbirth) is called parturition.”
• “The milk produced during the initial few days of lactation is called colostrum.”
• “Humans are sexually reproducing and viviparous.”
• “The average duration of human pregnancy is about 9 months which is called the gestation period.”

(No numerical formulas or SI units appear in the chapter.)

3. Important diagrams and activities

• Figure 2.1(a) & (b): Diagrammatic sectional view of male pelvis and reproductive system – shows location of testes in scrotum, accessory ducts and glands.
• Figure 2.2: Diagrammatic sectional view of seminiferous tubule – illustrates spermatogonia, Sertoli cells and Leydig cells.
• Figure 2.3(a) & (b): Female pelvis and reproductive system – shows ovaries, fallopian tube regions, uterus layers and external genitalia.
• Figure 2.4: Diagrammatic sectional view of mammary gland – demonstrates alveoli, ducts and lactiferous duct.
• Figure 2.5: Enlarged sectional view of seminiferous tubule – shows stages of spermatogenesis.
• Figure 2.6: Structure of a sperm – labels head (acrosome, nucleus), neck, middle piece (mitochondria) and tail.
• Figure 2.7: Diagrammatic section view of ovary – shows ovarian follicles at different stages.
• Figure 2.8: Schematic representation of spermatogenesis and oogenesis – compares chromosome number and meiotic divisions.
• Figure 2.9: Diagrammatic presentation of events during menstrual cycle – correlates hormone levels with ovarian and uterine changes.
• Figure 2.10: Ovum surrounded by few sperms – shows zona pellucida and acrosome reaction.
• Figure 2.11: Transport of ovum, fertilisation and passage of embryo – illustrates cleavage, morula, blastocyst and implantation.
• Figure 2.12: Human foetus within the uterus – shows placenta, chorionic villi and umbilical cord.

4. Common misconceptions and exam pitfalls

• Sex of the baby is determined by the father (XY sperm), not the mother; many students incorrectly state the opposite.
• Hymen presence/absence is not a reliable indicator of virginity or sexual experience.
• Spermatogenesis continues throughout life in males, whereas oogenesis ceases around age 50 (menopause).
• Only one ovum is released per menstrual cycle; identical twins arise from one zygote, fraternal twins from two.
• Fertilisation occurs in the ampullary region, not the uterus; implantation follows blastocyst formation.
• Corpus luteum secretes progesterone for endometrial maintenance; its degeneration causes menstruation if no fertilisation occurs.
• Placenta produces hCG, hPL, estrogens, progestogens and relaxin only during pregnancy.

5. Formula sheet

No mathematical formulas, equations or quantitative relations are present in the chapter.