📋 Index
- The Male Reproductive System
- The Female Reproductive System
- Gametogenesis — Spermatogenesis
- Gametogenesis — Oogenesis
- Structure of a Sperm and Ovum
- The Menstrual Cycle
- Fertilisation and Implantation
- Pregnancy and Embryonic Development
- Parturition and Lactation
- Important Diagrams & Labels
- NCERT Questions & Solutions
1. The Male Reproductive System MOST IMP
Male Reproductive System: Consists of a pair of testes, accessory ducts, accessory glands and external genitalia. Its function is to produce male gametes (sperms) and transfer them to the female reproductive tract.
(A) Testes (Primary Male Sex Organ)
- Location: Present outside the abdominal cavity within a pouch called scrotum
- Scrotum: Skin-covered sac that maintains temperature 2–2.5°C lower than body temperature (essential for sperm formation)
- Structure: Each testis has about 250 compartments called testicular lobules
- Each lobule contains 1–3 highly coiled seminiferous tubules
- Seminiferous tubules are lined by male germ cells (spermatogonia) and Sertoli cells
- Regions outside seminiferous tubules contain Leydig cells (interstitial cells) which secrete testosterone
Sertoli Cells: Provide nutrition to germ cells. Form blood-testis barrier. Secrete inhibin and androgen-binding protein (ABP).
Leydig Cells: Secrete androgens (mainly testosterone). Stimulated by LH (ICSH).
Leydig Cells: Secrete androgens (mainly testosterone). Stimulated by LH (ICSH).
(B) Accessory Ducts
| Duct | Description | Function |
|---|---|---|
| Rete testis | Network of tubules in testis | Collects sperm from seminiferous tubules |
| Vasa efferentia | 12–20 fine tubules | Carry sperm from rete testis to epididymis |
| Epididymis | Highly coiled tube on posterior surface of testis | Stores sperm; sperm mature and gain motility here |
| Vas deferens | Long muscular tube from epididymis to urethra | Transports sperm during ejaculation |
| Ejaculatory duct | Formed by union of vas deferens and duct of seminal vesicle | Opens into urethra |
| Urethra | Common passage for urine and semen | Transports semen out of body |
(C) Accessory Glands
- Seminal Vesicles (1 pair): Secrete seminal plasma rich in fructose, calcium, prostaglandins. Fructose provides energy for sperm motility.
- Prostate Gland: Single gland surrounding urethra. Secretes alkaline fluid (neutralizes acidic vagina), citric acid, enzymes, lipids.
- Bulbourethral Glands (Cowper’s glands): Pair of small glands. Secrete mucus-rich fluid that lubricates penis and neutralizes urethra.
Semen = Sperm (from testes) + Seminal Plasma (from seminal vesicles, prostate, bulbourethral glands)
Sperm count: 200–300 million per ejaculate | pH: 7.2–7.7 (alkaline)
(D) External Genitalia — Penis
- Male copulatory organ made of erectile tissue
- Corpora cavernosa: Two dorsal columns of erectile tissue
- Corpus spongiosum: One ventral column surrounding urethra, expands to form glans penis
- Covering fold of skin = foreskin (prepuce)
ADD_YOUR_DIAGRAM(eg: L.S. of male reproductive system showing testis in scrotum, epididymis, vas deferens, seminal vesicle, prostate, bulbourethral gland, penis, urethra)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: T.S. of seminiferous tubule showing Sertoli cells, spermatogonia, primary spermatocytes, spermatids, Leydig cells in interstitial space)_LINK_HERE
2. The Female Reproductive System MOST IMP
Female Reproductive System: Consists of a pair of ovaries, a pair of oviducts (fallopian tubes), uterus, cervix, vagina and external genitalia. Functions include production of female gametes (ova), reception of sperm, fertilisation, gestation and childbirth.
(A) Ovaries (Primary Female Sex Organ)
- Location: Small, oval-shaped, located in lower abdomen (pelvic region), one on each side of uterus
- Structure: Outer cortex and inner medulla
- Cortex: Contains ovarian follicles at various stages of development
- Medulla: Contains blood vessels, lymph vessels, nerve fibres
- Attached to uterus by ovarian ligament and to pelvic wall by mesovarium
- Produce ova and secrete estrogen and progesterone
Ovarian Follicle Development
- Primordial follicle: Primary oocyte surrounded by single layer of flattened follicular cells
- Primary follicle: Follicular cells become cuboidal, proliferate to form stratified granulosa cells
- Secondary follicle: Fluid-filled cavity antrum begins to form; theca layer develops
- Tertiary (Graafian) follicle: Large fluid-filled antrum; primary oocyte completes meiosis-I to form secondary oocyte + first polar body; secondary oocyte is surrounded by zona pellucida and layer of follicular cells called corona radiata
- Corpus luteum: After ovulation, ruptured follicle transforms into yellow endocrine structure that secretes progesterone
- Corpus albicans: Degenerated corpus luteum (white scar tissue) if pregnancy does not occur
Graafian Follicle: Mature follicle ready for ovulation. Contains secondary oocyte arrested at metaphase-II. Ovulation releases secondary oocyte (not mature ovum).
(B) Oviducts (Fallopian Tubes)
- Paired, 10–12 cm long, extend from ovary to uterus
- Parts (from ovarian end):
- Infundibulum: Funnel-shaped, fringed with finger-like projections called fimbriae (help collect ovum)
- Ampulla: Widest part; site of fertilisation
- Isthmus: Narrow part connecting to uterus
- Uterine part: Passes through uterine wall
(C) Uterus (Womb)
- Pear-shaped, thick-walled muscular organ
- Parts:
- Fundus: Dome-shaped upper part above openings of fallopian tubes
- Body: Main central part
- Cervix: Narrow lower part opening into vagina
- External os: Opening into vagina
- Internal os: Opening into uterine cavity
- Three layers of uterine wall:
- Perimetrium: Outer thin membranous layer (visceral peritoneum)
- Myometrium: Thick middle layer of smooth muscle; contracts during parturition
- Endometrium: Inner glandular lining; undergoes cyclic changes during menstrual cycle; site of implantation
(D) Vagina and External Genitalia
- Vagina: Muscular, tubular copulatory organ; receives semen; birth canal
- Vulva: External genitalia including:
- Mons pubis: Cushion of fatty tissue covered by skin and hair
- Labia majora: Large fleshy folds of skin
- Labia minora: Inner folds surrounding vaginal and urethral openings
- Clitoris: Small erectile tissue at upper junction of labia minora
- Hymen: Membrane partially covering vaginal opening (may rupture during first coitus or other physical activities)
ADD_YOUR_DIAGRAM(eg: L.S. of female reproductive system showing ovary, ovarian follicles, oviduct/fallopian tube with infundibulum and fimbriae, uterus with fundus body cervix, vagina)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: Section of ovary showing stages of follicular development – primordial, primary, secondary, Graafian follicle, corpus luteum, corpus albicans)_LINK_HERE
3. Gametogenesis — Spermatogenesis 5 MARKS
Spermatogenesis: Process of formation of spermatozoa from immature male germ cells (spermatogonia) in the seminiferous tubules of testes. It begins at puberty and continues throughout life.
Stages of Spermatogenesis
Step 1 — Multiplication Phase:
Spermatogonia (2n, diploid) present on inner lining of seminiferous tubules divide by mitosis to form more spermatogonia. Some spermatogonia stop dividing and grow to form primary spermatocytes (2n).
Spermatogonia (2n, diploid) present on inner lining of seminiferous tubules divide by mitosis to form more spermatogonia. Some spermatogonia stop dividing and grow to form primary spermatocytes (2n).
Step 2 — Growth Phase:
Primary spermatocytes grow in size, accumulate nutrients, and prepare for meiosis.
Primary spermatocytes grow in size, accumulate nutrients, and prepare for meiosis.
Step 3 — Maturation Phase (Meiosis):
Each primary spermatocyte (2n) undergoes meiosis-I to form two secondary spermatocytes (n).
Each secondary spermatocyte undergoes meiosis-II to form two spermatids (n).
Thus, 1 primary spermatocyte → 4 spermatids.
Each primary spermatocyte (2n) undergoes meiosis-I to form two secondary spermatocytes (n).
Each secondary spermatocyte undergoes meiosis-II to form two spermatids (n).
Thus, 1 primary spermatocyte → 4 spermatids.
Step 4 — Spermiogenesis:
Spermatids undergo structural transformation to become spermatozoa (sperm). No division occurs. Changes include:
Spermatids undergo structural transformation to become spermatozoa (sperm). No division occurs. Changes include:
- Nucleus condenses and moves to head region
- Golgi body forms acrosome at anterior end
- Centrioles form neck and tail (flagellum)
- Mitochondria concentrate in middle piece
- Most cytoplasm is shed as residual bodies (phagocytosed by Sertoli cells)
1 Spermatogonium (2n) → 1 Primary Spermatocyte (2n) → 2 Secondary Spermatocytes (n) → 4 Spermatids (n) → 4 Sperms (n)
Duration: ~64–74 days | Millions of sperms produced daily
Hormonal Control of Spermatogenesis
| Hormone | Source | Action |
|---|---|---|
| GnRH | Hypothalamus | Stimulates anterior pituitary to release FSH and LH |
| FSH | Anterior Pituitary | Acts on Sertoli cells; stimulates spermatogenesis and secretion of ABP and inhibin |
| LH (ICSH) | Anterior Pituitary | Acts on Leydig cells; stimulates testosterone secretion |
| Testosterone | Leydig cells | Stimulates spermatogenesis, development of secondary sexual characters, libido |
| Inhibin | Sertoli cells | Negative feedback on FSH secretion |
ABP (Androgen Binding Protein): Secreted by Sertoli cells under FSH stimulation. Binds testosterone and keeps its concentration high in seminiferous tubules — essential for spermatogenesis.
ADD_YOUR_DIAGRAM(eg: Stages of spermatogenesis – spermatogonia, primary spermatocyte, secondary spermatocyte, spermatid, sperm; with meiosis I and II labeled)_LINK_HERE
4. Gametogenesis — Oogenesis 5 MARKS
Oogenesis: Process of formation of mature female gametes (ova) from oogonia in the ovary. It begins during fetal development, arrests at birth, resumes at puberty, and completes at fertilisation.
Stages of Oogenesis
Step 1 — Multiplication Phase (Fetal stage):
Oogonia (2n) are formed in fetal ovary by mitosis. They multiply and enter prophase-I of meiosis to form primary oocytes (2n). By 20th week of fetal development, all oogonia are converted to primary oocytes.
Oogonia (2n) are formed in fetal ovary by mitosis. They multiply and enter prophase-I of meiosis to form primary oocytes (2n). By 20th week of fetal development, all oogonia are converted to primary oocytes.
Step 2 — Growth Phase:
Primary oocytes remain arrested at diplotene stage of prophase-I (suspended state) from birth until puberty. They are surrounded by a layer of granulosa cells = primary follicle.
Primary oocytes remain arrested at diplotene stage of prophase-I (suspended state) from birth until puberty. They are surrounded by a layer of granulosa cells = primary follicle.
Step 3 — Maturation Phase (After Puberty):
Each menstrual cycle, some primary oocytes complete meiosis-I just before ovulation, forming:
Each menstrual cycle, some primary oocytes complete meiosis-I just before ovulation, forming:
- Secondary oocyte (n) — large, receives most cytoplasm
- First polar body (n) — small, degenerates
Step 4 — Completion at Fertilisation:
Secondary oocyte completes meiosis-II only when sperm enters it. This forms:
Secondary oocyte completes meiosis-II only when sperm enters it. This forms:
- Functional Ovum (n) — large cell
- Second polar body (n) — small, degenerates
1 Oogonium (2n) → 1 Primary Oocyte (2n) → 1 Secondary Oocyte (n) + 1 Polar Body (n) → 1 Ovum (n) + 2–3 Polar Bodies (n)
Result: 1 functional ovum + 2–3 polar bodies (degenerate). Polar bodies are small and cytoplasm-deficient.
Key Differences: Spermatogenesis vs Oogenesis
| Feature | Spermatogenesis | Oogenesis |
|---|---|---|
| Site | Seminiferous tubules of testes | Ovarian follicles of ovary |
| Starts at | Puberty | Fetal stage (before birth) |
| Completes at | Within testes | In fallopian tube (at fertilisation) |
| Products | 4 functional sperms | 1 functional ovum + polar bodies |
| Cytoplasm distribution | Equal | Unequal (ovum gets most) |
| Nature of gametes | Motile, small | Non-motile, large, nutrient-rich |
| Arrest phases | No arrest | Arrested at diplotene (birth to puberty) and metaphase-II (ovulation to fertilisation) |
Exam Point: Primary oocytes are formed before birth and remain arrested for 12–50 years. This long arrest makes them susceptible to chromosomal abnormalities (e.g., Down syndrome with advancing maternal age).
ADD_YOUR_DIAGRAM(eg: Stages of oogenesis – oogonia, primary oocyte arrested at diplotene, completion of meiosis I before ovulation forming secondary oocyte + polar body, completion of meiosis II at fertilisation forming ovum + second polar body)_LINK_HERE
5. Structure of a Sperm and Ovum IMPORTANT
Structure of Human Sperm
- Length: ~60 μm; microscopic, motile
- Four parts:
- Head: Flattened, contains condensed nucleus (haploid) and anterior cap-like acrosome
- Acrosome contains hydrolytic enzymes (hyaluronidase, acrosin) that help sperm penetrate ovum
- Derived from Golgi body
- Neck: Contains proximal and distal centrioles
- Distal centriole gives rise to axial filament of tail
- Middle Piece: Contains mitochondria arranged spirally
- Produces ATP for tail movement
- Contains axial filament (9+2 microtubule arrangement)
- Tail: Long, slender, flagellum-like
- Propels sperm forward
- 9+2 microtubule arrangement (typical eukaryotic flagellum)
- Head: Flattened, contains condensed nucleus (haploid) and anterior cap-like acrosome
Enzymes in Acrosome: Hyaluronidase dissolves hyaluronic acid between corona radiata cells. Acrosin dissolves zona pellucida. Together they enable sperm penetration.
Structure of Human Ovum
- Non-motile, spherical, ~100 μm in diameter (largest human cell)
- Surrounded by:
- Zona pellucida: Thick, transparent glycoprotein layer secreted by ovum itself
- Corona radiata: Layer of follicular cells attached to zona pellucida (from Graafian follicle)
- Cytoplasm: Rich in nutrients (yolk), contains cortical granules beneath plasma membrane
- Nucleus: Haploid, called female pronucleus after fertilisation
- Polar body: May be seen near ovum (result of meiotic divisions)
ADD_YOUR_DIAGRAM(eg: Structure of human sperm showing head with acrosome and nucleus, neck with centrioles, middle piece with mitochondria, tail with 9+2 arrangement)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: Structure of human ovum showing nucleus, cytoplasm, zona pellucida, corona radiata, polar body)_LINK_HERE
6. The Menstrual Cycle 5 MARKS
Menstrual Cycle: Cyclic series of changes in the reproductive tract of human females. It repeats every 28 days (range 21–35 days) from puberty (menarche) to menopause. It involves changes in ovaries (ovarian cycle) and uterus (uterine cycle).
Phases of Menstrual Cycle
(A) Menstrual Phase (Day 1–5)
- Also called bleeding phase
- Endometrium breaks down; blood, mucus, endometrial cells discharged through vagina = menstruation/menses
- Loss of 50–100 ml blood
- Caused by low levels of estrogen and progesterone (due to degeneration of corpus luteum)
- Ovarian event: Corpus luteum of previous cycle degenerates into corpus albicans
(B) Follicular / Proliferative Phase (Day 6–14)
- Endometrium regenerates and proliferates; uterine glands develop; blood vessels increase
- Endometrium thickens to 4–6 mm
- Ovarian event: Primary follicles develop into Graafian follicles under FSH stimulation
- Estrogen secretion increases, which stimulates endometrial proliferation and inhibits FSH (negative feedback)
- High estrogen causes LH surge on 14th day (positive feedback)
(C) Ovulatory Phase (Day 14)
- LH surge triggers rupture of Graafian follicle and release of secondary oocyte (ovum)
- Ovulation occurs
- Secondary oocyte is arrested at metaphase-II
- Fimbriae of infundibulum help direct ovum into fallopian tube
(D) Luteal / Secretory Phase (Day 15–28)
- Ruptured follicle transforms into corpus luteum under LH influence
- Corpus luteum secretes large amounts of progesterone and some estrogen
- Progesterone:
- Makes endometrium thick, vascular and glandular (secretory) — ready for implantation
- Inhibits contraction of uterus
- Inhibits development of new follicles (negative feedback on FSH and LH)
- If fertilisation occurs: Corpus luteum persists (stimulated by hCG from embryo) and secretes progesterone throughout pregnancy
- If fertilisation does NOT occur: Corpus luteum degenerates into corpus albicans by day 24–25; progesterone and estrogen levels fall; endometrium breaks down; next menstrual cycle begins
Menstrual Cycle = Ovarian Cycle (follicular phase + ovulation + luteal phase) + Uterine Cycle (menstrual + proliferative + secretory phase)
Average duration: 28 days | Menarche: 10–14 years | Menopause: 45–50 years
Hormonal Regulation (Hypothalamic-Pituitary-Ovarian Axis)
| Hormone | Source | Phase Peak | Function |
|---|---|---|---|
| GnRH | Hypothalamus | Pulsatile release | Stimulates FSH and LH release |
| FSH | Anterior Pituitary | Early follicular phase | Follicular development, estrogen secretion |
| LH | Anterior Pituitary | Mid-cycle surge (Day 14) | Ovulation, corpus luteum formation |
| Estrogen | Developing follicle | Late follicular phase | Endometrial proliferation, LH surge trigger |
| Progesterone | Corpus luteum | Luteal phase | Maintains endometrium, inhibits uterine contraction |
Exam Point: LH surge is the trigger for ovulation. Without LH surge, ovulation does not occur. This is the basis of contraceptive pills (inhibit LH surge).
ADD_YOUR_DIAGRAM(eg: Menstrual cycle graph showing hormone levels – FSH, LH, estrogen, progesterone across 28 days with phases marked – menstrual, follicular, ovulatory, luteal)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: Cyclic changes in ovary and uterus showing follicular development, ovulation, corpus luteum formation, endometrial changes)_LINK_HERE
7. Fertilisation and Implantation MOST IMP
Fertilisation
Fertilisation: Fusion of sperm and ovum to form a diploid zygote. It restores the chromosome number (46) and initiates embryonic development.
Events Leading to Fertilisation
- Ejaculation: ~200–300 million sperms deposited in vagina near cervix
- Sperm transport: Sperms swim through cervix → uterus → fallopian tube. Only ~100 sperms reach ampulla.
- Capacitation: Sperms undergo functional maturation in female reproductive tract (acquire motility and ability to fertilise). Takes ~5–6 hours.
Process of Fertilisation (at Ampullary-Isthmic Junction)
Step 1 — Corona Radiata Penetration:
Sperm releases hyaluronidase enzyme from acrosome to separate cells of corona radiata.
Sperm releases hyaluronidase enzyme from acrosome to separate cells of corona radiata.
Step 2 — Acrosome Reaction:
Sperm head binds to ZP3 receptors on zona pellucida. Acrosome releases enzymes (acrosin) to digest zona pellucida. Membrane of sperm head fuses with ovum plasma membrane.
Sperm head binds to ZP3 receptors on zona pellucida. Acrosome releases enzymes (acrosin) to digest zona pellucida. Membrane of sperm head fuses with ovum plasma membrane.
Step 3 — Fusion and Entry:
Sperm head (with nucleus) enters ovum cytoplasm. Tail and middle piece are left outside and degenerate.
Sperm head (with nucleus) enters ovum cytoplasm. Tail and middle piece are left outside and degenerate.
Step 4 — Cortical Reaction / Block to Polyspermy:
Entry of sperm triggers release of enzymes from cortical granules of ovum. These enzymes harden zona pellucida and destroy ZP3 receptors, preventing entry of other sperms. This ensures monospermy (only one sperm fertilises).
Entry of sperm triggers release of enzymes from cortical granules of ovum. These enzymes harden zona pellucida and destroy ZP3 receptors, preventing entry of other sperms. This ensures monospermy (only one sperm fertilises).
Step 5 — Completion of Meiosis-II:
Sperm entry stimulates secondary oocyte to complete meiosis-II, forming:
Sperm entry stimulates secondary oocyte to complete meiosis-II, forming:
- Mature ovum (n) with female pronucleus
- Second polar body (degenerates)
Step 6 — Syngamy:
Male pronucleus (from sperm) and female pronucleus (from ovum) fuse. Chromosomes intermix. Zygote (2n) is formed with 46 chromosomes.
Male pronucleus (from sperm) and female pronucleus (from ovum) fuse. Chromosomes intermix. Zygote (2n) is formed with 46 chromosomes.
Secondary Oocyte (n, 23 chromosomes) + Sperm (n, 23 chromosomes) → Zygote (2n, 46 chromosomes)
Site: Ampullary-isthmic junction of fallopian tube | Time after ovulation: 12–24 hours
Cleavage and Blastocyst Formation
- Cleavage: Rapid mitotic divisions of zygote without growth in size. Cells formed = blastomeres.
- Morula: Solid ball of 8–16 blastomeres (reaches uterus 3–4 days after fertilisation)
- Blastula / Blastocyst: Morula develops fluid-filled cavity called blastocoel
- Trophoblast: Outer layer of cells; forms embryonic part of placenta
- Inner Cell Mass (ICM): Cluster of cells inside; forms embryo proper
- Blastocoel: Fluid-filled cavity
Implantation
- Definition: Attachment and embedding of blastocyst into the endometrium of uterus
- Time: 6–7 days after fertilisation
- Process: Trophoblast cells secrete enzymes that digest endometrial tissue, allowing blastocyst to bury itself
- Site: Usually upper, posterior wall of uterus
- Endometrium at implantation site becomes thick and vascular = decidua
- Trophoblast differentiates into:
- Cytotrophoblast: Inner cellular layer
- Syncytiotrophoblast: Outer multinucleate layer (invades endometrium, forms chorionic villi)
Ectopic Pregnancy: If blastocyst implants outside uterus (usually in fallopian tube). Dangerous, requires medical intervention.
ADD_YOUR_DIAGRAM(eg: Fertilisation – sperm penetrating corona radiata, acrosome reaction, fusion with ovum, cortical reaction, formation of zygote)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: Cleavage stages – zygote, 2-cell, 4-cell, 8-cell morula, blastocyst showing trophoblast, inner cell mass, blastocoel)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: Implantation of blastocyst in uterine endometrium showing trophoblast, syncytiotrophoblast, cytotrophoblast, decidua)_LINK_HERE
8. Pregnancy and Embryonic Development 5 MARKS
Placenta
Placenta: Temporary organ that connects developing embryo to uterine wall. It facilitates nutrient supply, gas exchange, waste removal and hormone secretion. Formed from maternal endometrium and fetal chorion.
- Structure:
- Chorionic villi: Finger-like projections from trophoblast (fetal part) that invade endometrial tissue
- Maternal blood sinuses: Spaces filled with maternal blood surrounding chorionic villi
- Placental barrier separates maternal and fetal blood (they do NOT mix)
- Exchange occurs by diffusion across placental membrane
- Functions:
- Respiratory: O2 from mother to fetus; CO2 from fetus to mother
- Nutritive: Glucose, amino acids, fatty acids, vitamins, minerals pass to fetus
- Excretory: Urea, uric acid, creatinine removed from fetal blood
- Barrier: Prevents some pathogens and drugs from reaching fetus (not all)
- Endocrine: Secretes hormones essential for pregnancy maintenance
Hormones Secreted by Placenta
| Hormone | Function |
|---|---|
| hCG (human Chorionic Gonadotropin) | Detected in urine for pregnancy test; maintains corpus luteum in early pregnancy; stimulates progesterone secretion |
| hPL (human Placental Lactogen) | Develops mammary glands; metabolic adjustment of mother for fetal nutrition |
| Estrogen | Supports pregnancy, uterine growth, mammary gland development |
| Progesterone | Maintains endometrium, prevents uterine contraction, suppresses ovulation |
| Relaxin | Softens cervix, relaxes pelvic ligaments for childbirth |
Pregnancy Test: Based on detection of hCG in urine. hCG appears in blood/urine within 6–8 days after fertilisation. Home pregnancy test kits detect hCG.
Embryonic Development (First Trimester)
Gastrulation (3rd week)
- Inner cell mass differentiates into embryonic disc with two layers:
- Ectoderm: Outer layer
- Endoderm: Inner layer
- Later, mesoderm forms between them
- These three germ layers form all tissues and organs:
| Germ Layer | Structures Formed |
|---|---|
| Ectoderm | Skin epidermis, hair, nails, sweat glands, nervous system (brain, spinal cord, nerves), lens of eye, inner ear, enamel of teeth |
| Mesoderm | Muscles, bones, cartilage, blood, heart, kidneys, gonads, dermis of skin, notochord, connective tissues |
| Endoderm | Lining of gut, respiratory tract, liver, pancreas, thyroid, urinary bladder, thymus, tonsils |
Key Developmental Milestones
| Time | Development |
|---|---|
| Week 1 | Fertilisation, cleavage, blastocyst formation, implantation |
| Week 2 | Embryonic disc formed; amnion and yolk sac develop |
| Week 3 | Gastrulation; three germ layers formed; notochord develops; neural plate forms |
| Week 4 | Heart begins to beat; limb buds appear; neural tube closes |
| Week 8 | Major organs formed; called fetus now; external genitalia begin to differentiate |
| Week 12 | Fingers and toes formed; nails develop; eyelids fuse |
| Week 24 | Hair on head; eyelashes; eyebrows; viable outside with intensive care |
| Week 36–40 | Full term; lanugo (fine hair) shed; vernix caseosa (waxy coating); ready for birth |
Extra-Embryonic Membranes
- Amnion: Thin membrane surrounding embryo; filled with amniotic fluid
- Amniotic fluid: Shock absorber, maintains temperature, allows fetal movement, prevents adhesion
- Chorion: Outermost membrane; forms chorionic villi and fetal part of placenta
- Yolk Sac: Early nutrition; site of blood cell formation; contributes to gut
- Allantois: Contributes to umbilical cord blood vessels and urinary bladder
Umbilical Cord
- Connects fetal abdomen to placenta
- Contains:
- 2 umbilical arteries (carry deoxygenated blood from fetus to placenta)
- 1 umbilical vein (carries oxygenated blood from placenta to fetus)
- Wharton’s jelly (connective tissue)
Exam Point: Umbilical arteries carry deoxygenated blood (exception to rule). Pulmonary artery also carries deoxygenated blood. Umbilical vein carries oxygenated blood.
ADD_YOUR_DIAGRAM(eg: Structure of placenta showing chorionic villi, maternal blood sinuses, umbilical cord, placental barrier)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: Human embryo showing extra-embryonic membranes – amnion, chorion, yolk sac, allantois, umbilical cord)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: Fate of three germ layers – ectoderm, mesoderm, endoderm with examples of organs derived from each)_LINK_HERE
9. Parturition and Lactation IMPORTANT
Parturition (Childbirth)
Parturition: Process of delivery of the fully developed fetus from the uterus at the end of gestation period (~9 months / 280 days). It involves strong contractions of myometrium.
Hormonal Control of Parturition
- Estrogen: Increases near end of pregnancy; stimulates uterine contractions, increases oxytocin receptors on myometrium
- Oxytocin: Secreted by posterior pituitary (and placenta). Stimulates powerful uterine contractions (positive feedback loop: contractions stimulate more oxytocin release)
- Relaxin: Softens cervix, relaxes pelvic ligaments
- Cortisol: From fetal adrenal gland; stimulates estrogen and prostaglandin secretion
- Prostaglandins: From placenta and uterus; stimulate uterine contractions and cervical dilation
Stages of Parturition
| Stage | Name | Events | Duration |
|---|---|---|---|
| 1st | Dilation | Cervix dilates; amnion ruptures (“water breaks”); regular contractions begin | 6–12 hours (longer in first pregnancy) |
| 2nd | Expulsion | Strong contractions push fetus through birth canal; head emerges first (crowning); baby delivered | 20 min – 1 hour |
| 3rd | Afterbirth | Placenta and umbilical cord expelled; uterus contracts to prevent bleeding | 10–45 min |
Gestation Period: Average 280 days (40 weeks / 9 months) from first day of last menstrual period (LMP). Actual embryonic age is ~266 days (38 weeks) from fertilisation.
Lactation
Lactation: Production and secretion of milk by mammary glands to nourish the newborn. It is initiated after childbirth and maintained by hormonal stimulation.
Structure of Mammary Glands
- Modified sweat glands present in chest region
- Contains 15–20 lobes of glandular tissue
- Each lobe has smaller lobules containing alveoli (milk-secreting cells)
- Alveoli drain into lactiferous ducts → lactiferous sinuses → nipple
- Dark area around nipple = areola (contains sebaceous glands)
Hormonal Control of Lactation
| Hormone | Source | Function |
|---|---|---|
| Prolactin (PRL) | Anterior Pituitary | Stimulates milk production (synthesis) in alveolar cells; levels rise during pregnancy but progesterone inhibits its action |
| Oxytocin | Posterior Pituitary | Milk ejection reflex (let-down reflex); causes contraction of myoepithelial cells around alveoli, squeezing milk into ducts |
| Progesterone | Placenta / Corpus luteum | During pregnancy, inhibits prolactin action on mammary glands; after delivery, levels drop, allowing lactation |
| hPL | Placenta | Prepares mammary glands during pregnancy |
Colostrum
- First milk produced during initial 2–3 days after delivery
- Yellowish, thick, rich in proteins (lactalbumin, lactoglobulin)
- Contains IgA antibodies (passive immunity for newborn)
- Rich in minerals and vitamins; low in fat
- Essential for newborn’s immune protection and gut development
Exam Point: Colostrum provides natural passive immunity (IgA). Breast milk is ideal food for infant — contains all nutrients, antibodies, and growth factors. WHO recommends exclusive breastfeeding for first 6 months.
ADD_YOUR_DIAGRAM(eg: Stages of parturition – dilation, expulsion, afterbirth showing fetal position and uterine contractions)_LINK_HERE
ADD_YOUR_DIAGRAM(eg: L.S. of mammary gland showing lobes, lobules, alveoli, lactiferous ducts, lactiferous sinus, nipple, areola)_LINK_HERE
10. Important Diagrams & Labels DIAGRAM BASED
These diagrams are frequently asked in board exams. Practice labeling them perfectly.
Must-Know Diagrams
- L.S. of Male Reproductive System — Testis, epididymis, vas deferens, seminal vesicle, prostate, bulbourethral gland, penis, urethra, scrotum
- T.S. of Seminiferous Tubule — Sertoli cells, spermatogonia, primary spermatocytes, spermatids, sperms, Leydig cells
- L.S. of Female Reproductive System — Ovary, ovarian follicles, fallopian tube (infundibulum, fimbriae, ampulla, isthmus), uterus (fundus, body, cervix), vagina
- Section of Ovary — Primordial, primary, secondary, Graafian follicles, corpus luteum, corpus albicans, stroma
- Stages of Spermatogenesis — Spermatogonia, primary spermatocyte, secondary spermatocyte, spermatid, sperm
- Stages of Oogenesis — Oogonia, primary oocyte, secondary oocyte, ovum, polar bodies
- Structure of Sperm — Head (acrosome, nucleus), neck, middle piece (mitochondria), tail
- Structure of Ovum — Nucleus, cytoplasm, zona pellucida, corona radiata
- Menstrual Cycle Graph — Hormone levels (FSH, LH, estrogen, progesterone) across 28 days with phases
- Fertilisation — Sperm penetrating ovum, acrosome reaction, cortical reaction, zygote formation
- Blastocyst and Implantation — Trophoblast, inner cell mass, blastocoel, embedding in endometrium
- Structure of Placenta — Chorionic villi, maternal blood sinuses, umbilical cord
- Extra-embryonic Membranes — Amnion, chorion, yolk sac, allantois
- L.S. of Mammary Gland — Lobes, lobules, alveoli, lactiferous ducts, nipple
Labeling Tips:
• Use pencil for diagrams in exam
• Draw proportionate sizes (ovum larger than sperm)
• Label with straight leader lines (leader lines)
• Write labels on right side, aligned horizontally
• Diagrams carry 3–5 marks — practice all 14 diagrams
• Use pencil for diagrams in exam
• Draw proportionate sizes (ovum larger than sperm)
• Label with straight leader lines (leader lines)
• Write labels on right side, aligned horizontally
• Diagrams carry 3–5 marks — practice all 14 diagrams
11. NCERT Questions & Solutions EXAM PATTERN
Q1. Fill in the blanks: (a) Humans reproduce __________ (asexually/sexually). (b) Humans are __________ (oviparous/viviparous/ovoviviparous). (c) Fertilisation is __________ in humans (external/internal). (d) Male and female gametes are __________ (diploid/haploid). (e) Zygote is __________ (diploid/haploid). (f) The process of release of ovum from mature Graafian follicle is called __________. (g) Ovulation is induced by a hormone called __________. (h) The fusion of male and female gametes is called __________. (i) Fertilisation takes place in __________. (j) Zygote divides to form __________ which is implanted in uterus. (k) The structure which provides vascular connection between fetus and uterus is called __________.
(a) sexually
(b) viviparous
(c) internal
(d) haploid
(e) diploid
(f) ovulation
(g) luteinizing hormone (LH)
(h) fertilisation
(i) ampullary-isthmic junction of fallopian tube
(j) blastocyst
(k) placenta
(b) viviparous
(c) internal
(d) haploid
(e) diploid
(f) ovulation
(g) luteinizing hormone (LH)
(h) fertilisation
(i) ampullary-isthmic junction of fallopian tube
(j) blastocyst
(k) placenta
Tip: Remember basic definitions. Viviparous = give birth to young ones. Oviparous = lay eggs.
Q2. Draw a labelled diagram of male reproductive system.
Key Labels to include:
1. Testis (inside scrotum)
2. Epididymis
3. Vas deferens
4. Seminal vesicle
5. Ejaculatory duct
6. Prostate gland
7. Bulbourethral gland (Cowper’s gland)
8. Urethra
9. Penis (with glans and foreskin)
10. Scrotum
Additional: Urinary bladder, rectum (for anatomical position)
1. Testis (inside scrotum)
2. Epididymis
3. Vas deferens
4. Seminal vesicle
5. Ejaculatory duct
6. Prostate gland
7. Bulbourethral gland (Cowper’s gland)
8. Urethra
9. Penis (with glans and foreskin)
10. Scrotum
Additional: Urinary bladder, rectum (for anatomical position)
Tip: Draw testis and penis on left side. Show accessory glands behind bladder. Use straight leader lines.
Q3. Draw a labelled diagram of female reproductive system.
Key Labels to include:
1. Ovary
2. Oviduct / Fallopian tube (infundibulum with fimbriae, ampulla, isthmus)
3. Uterus (fundus, body, cervix with external and internal os)
4. Vagina
5. Cervical canal
6. Vulva / External genitalia
Additional: Urinary bladder, urethra, rectum, pelvic region
1. Ovary
2. Oviduct / Fallopian tube (infundibulum with fimbriae, ampulla, isthmus)
3. Uterus (fundus, body, cervix with external and internal os)
4. Vagina
5. Cervical canal
6. Vulva / External genitalia
Additional: Urinary bladder, urethra, rectum, pelvic region
Tip: Show both ovaries and both fallopian tubes. Label fimbriae clearly — they are frequently asked.
Q4. Write the functions of the following: (a) Corpus luteum (b) Endometrium (c) Acrosome (d) Sperm tail (e) Fimbriae
(a) Corpus luteum:
• Formed from ruptured Graafian follicle after ovulation
• Secretes progesterone and estrogen
• Maintains endometrium for implantation
• If pregnancy occurs, persists and secretes hormones; if not, degenerates into corpus albicans
(b) Endometrium:
• Inner glandular lining of uterus
• Undergoes cyclic changes during menstrual cycle (proliferation and secretion)
• Site of implantation of blastocyst
• Forms maternal part of placenta
(c) Acrosome:
• Cap-like structure at anterior end of sperm head
• Contains hydrolytic enzymes (hyaluronidase, acrosin)
• Helps sperm penetrate corona radiata and zona pellucida of ovum
(d) Sperm tail:
• Long, flagellum-like structure
• Propels sperm forward through female reproductive tract
• Contains 9+2 microtubule arrangement (axoneme)
(e) Fimbriae:
• Finger-like projections at ovarian end of infundibulum
• Help in collection of ovum after ovulation
• Guide ovum into fallopian tube
• Formed from ruptured Graafian follicle after ovulation
• Secretes progesterone and estrogen
• Maintains endometrium for implantation
• If pregnancy occurs, persists and secretes hormones; if not, degenerates into corpus albicans
(b) Endometrium:
• Inner glandular lining of uterus
• Undergoes cyclic changes during menstrual cycle (proliferation and secretion)
• Site of implantation of blastocyst
• Forms maternal part of placenta
(c) Acrosome:
• Cap-like structure at anterior end of sperm head
• Contains hydrolytic enzymes (hyaluronidase, acrosin)
• Helps sperm penetrate corona radiata and zona pellucida of ovum
(d) Sperm tail:
• Long, flagellum-like structure
• Propels sperm forward through female reproductive tract
• Contains 9+2 microtubule arrangement (axoneme)
(e) Fimbriae:
• Finger-like projections at ovarian end of infundibulum
• Help in collection of ovum after ovulation
• Guide ovum into fallopian tube
Tip: Write at least 2 points for each. Acrosome enzymes are frequently asked in MCQs.
Q5. Describe the structure of a seminiferous tubule.
Structure:
• Seminiferous tubules are highly coiled tubes present in testicular lobules
• Lined by two types of cells on basement membrane:
1. Male Germ Cells (Spermatogenic cells):
• Spermatogonia: Stem cells on basement membrane (diploid)
• Primary spermatocytes: Large cells undergoing meiosis-I
• Secondary spermatocytes: Smaller, haploid, undergo meiosis-II
• Spermatids: Round cells near lumen, transform into sperms
• Spermatozoa: Mature sperms released into lumen
2. Sertoli Cells (Nurse cells):
• Tall columnar cells extending from basement membrane to lumen
• Provide nutrition to developing germ cells
• Form blood-testis barrier
• Secrete inhibin and androgen-binding protein (ABP)
• Phagocytose residual bodies during spermiogenesis
Interstitial tissue (outside tubules):
• Contains Leydig cells (interstitial cells) that secrete testosterone
• Seminiferous tubules are highly coiled tubes present in testicular lobules
• Lined by two types of cells on basement membrane:
1. Male Germ Cells (Spermatogenic cells):
• Spermatogonia: Stem cells on basement membrane (diploid)
• Primary spermatocytes: Large cells undergoing meiosis-I
• Secondary spermatocytes: Smaller, haploid, undergo meiosis-II
• Spermatids: Round cells near lumen, transform into sperms
• Spermatozoa: Mature sperms released into lumen
2. Sertoli Cells (Nurse cells):
• Tall columnar cells extending from basement membrane to lumen
• Provide nutrition to developing germ cells
• Form blood-testis barrier
• Secrete inhibin and androgen-binding protein (ABP)
• Phagocytose residual bodies during spermiogenesis
Interstitial tissue (outside tubules):
• Contains Leydig cells (interstitial cells) that secrete testosterone
Tip: Draw T.S. showing germ cells in layers (spermatogonia at base, sperms in lumen) and Sertoli cells between them.
Q6. What is spermatogenesis? Briefly describe the process of spermatogenesis.
Spermatogenesis is the process of formation of sperms from immature male germ cells (spermatogonia) in the seminiferous tubules of testes. It begins at puberty and involves four phases:
1. Multiplication Phase: Spermatogonia (2n) divide by mitosis. Some grow to form primary spermatocytes (2n).
2. Growth Phase: Primary spermatocytes grow in size and accumulate nutrients.
3. Maturation Phase: Each primary spermatocyte undergoes meiosis-I to form 2 secondary spermatocytes (n). Each secondary spermatocyte undergoes meiosis-II to form 2 spermatids (n). Thus, 1 primary spermatocyte produces 4 spermatids.
4. Spermiogenesis: Spermatids transform into spermatozoa. The nucleus condenses to form head, Golgi body forms acrosome, centrioles form neck and tail, mitochondria gather in middle piece. Excess cytoplasm is shed.
Hormonal control: GnRH → FSH and LH → FSH acts on Sertoli cells; LH acts on Leydig cells to produce testosterone → testosterone stimulates spermatogenesis.
1. Multiplication Phase: Spermatogonia (2n) divide by mitosis. Some grow to form primary spermatocytes (2n).
2. Growth Phase: Primary spermatocytes grow in size and accumulate nutrients.
3. Maturation Phase: Each primary spermatocyte undergoes meiosis-I to form 2 secondary spermatocytes (n). Each secondary spermatocyte undergoes meiosis-II to form 2 spermatids (n). Thus, 1 primary spermatocyte produces 4 spermatids.
4. Spermiogenesis: Spermatids transform into spermatozoa. The nucleus condenses to form head, Golgi body forms acrosome, centrioles form neck and tail, mitochondria gather in middle piece. Excess cytoplasm is shed.
Hormonal control: GnRH → FSH and LH → FSH acts on Sertoli cells; LH acts on Leydig cells to produce testosterone → testosterone stimulates spermatogenesis.
Tip: Mention all 4 phases clearly. Spermiogenesis is transformation, not division. Hormonal control adds value.
Q7. Name the hormones involved in regulation of spermatogenesis.
1. GnRH (Gonadotropin Releasing Hormone): From hypothalamus; stimulates anterior pituitary to release FSH and LH.
2. FSH (Follicle Stimulating Hormone): From anterior pituitary; acts on Sertoli cells to stimulate spermatogenesis and secretion of ABP and inhibin.
3. LH (Luteinizing Hormone) / ICSH (Interstitial Cell Stimulating Hormone): From anterior pituitary; acts on Leydig cells to stimulate testosterone secretion.
4. Testosterone: From Leydig cells; stimulates spermatogenesis and development of secondary sexual characters.
5. Inhibin: From Sertoli cells; provides negative feedback to pituitary to decrease FSH secretion when sperm count is high.
2. FSH (Follicle Stimulating Hormone): From anterior pituitary; acts on Sertoli cells to stimulate spermatogenesis and secretion of ABP and inhibin.
3. LH (Luteinizing Hormone) / ICSH (Interstitial Cell Stimulating Hormone): From anterior pituitary; acts on Leydig cells to stimulate testosterone secretion.
4. Testosterone: From Leydig cells; stimulates spermatogenesis and development of secondary sexual characters.
5. Inhibin: From Sertoli cells; provides negative feedback to pituitary to decrease FSH secretion when sperm count is high.
Tip: Remember the hypothalamic-pituitary-testis axis. Inhibin is often forgotten but important.
Q8. Define spermiogenesis and spermiation.
Spermiogenesis: The process of transformation of non-motile, round spermatids into motile, elongated spermatozoa (sperms). It involves no cell division. Changes include condensation of nucleus, formation of acrosome, development of tail, and shedding of excess cytoplasm.
Spermiation: The process of release of mature sperms from the seminiferous tubules into the lumen. Sertoli cells help in this release.
Spermiation: The process of release of mature sperms from the seminiferous tubules into the lumen. Sertoli cells help in this release.
Tip: Spermiogenesis = structural transformation. Spermiation = release. Don’t confuse with spermatogenesis.
Q9. Draw a labelled diagram of sperm.
Parts to label:
1. Head: Contains condensed nucleus (haploid) and anterior acrosome
2. Acrosome: Cap-like structure with enzymes (hyaluronidase, acrosin)
3. Neck: Contains proximal and distal centrioles
4. Middle piece: Contains mitochondria (spirally arranged) for ATP production
5. Tail: Long flagellum for propulsion; 9+2 microtubule arrangement
Show head as flattened oval, middle piece short and thick, tail long and thin.
1. Head: Contains condensed nucleus (haploid) and anterior acrosome
2. Acrosome: Cap-like structure with enzymes (hyaluronidase, acrosin)
3. Neck: Contains proximal and distal centrioles
4. Middle piece: Contains mitochondria (spirally arranged) for ATP production
5. Tail: Long flagellum for propulsion; 9+2 microtubule arrangement
Show head as flattened oval, middle piece short and thick, tail long and thin.
Tip: Acrosome is at the tip. Mitochondria in middle piece provide energy. Tail has 9+2 arrangement.
Q10. What are the major functions of male accessory ducts and glands?
Accessory Ducts:
• Rete testis: Collects sperm from seminiferous tubules
• Vasa efferentia: Transport sperm from rete testis to epididymis
• Epididymis: Stores sperm; sperm mature and gain motility here
• Vas deferens: Conducts sperm from epididymis to ejaculatory duct during ejaculation
• Ejaculatory duct: Receives sperm and seminal fluid; opens into urethra
Accessory Glands:
• Seminal vesicles: Secrete alkaline fructose-rich fluid (60% of semen volume); fructose nourishes sperm; prostaglandins stimulate uterine contractions
• Prostate gland: Secretes alkaline fluid with citric acid, enzymes, lipids (20–30% of semen); neutralizes acidic vaginal pH and urethra
• Bulbourethral glands: Secrete mucus-rich fluid that lubricates penis and neutralizes acidic urine residue in urethra
Overall function: Formation of seminal plasma, nourishment of sperm, neutralization of acidity, lubrication, and transport of sperm.
• Rete testis: Collects sperm from seminiferous tubules
• Vasa efferentia: Transport sperm from rete testis to epididymis
• Epididymis: Stores sperm; sperm mature and gain motility here
• Vas deferens: Conducts sperm from epididymis to ejaculatory duct during ejaculation
• Ejaculatory duct: Receives sperm and seminal fluid; opens into urethra
Accessory Glands:
• Seminal vesicles: Secrete alkaline fructose-rich fluid (60% of semen volume); fructose nourishes sperm; prostaglandins stimulate uterine contractions
• Prostate gland: Secretes alkaline fluid with citric acid, enzymes, lipids (20–30% of semen); neutralizes acidic vaginal pH and urethra
• Bulbourethral glands: Secrete mucus-rich fluid that lubricates penis and neutralizes acidic urine residue in urethra
Overall function: Formation of seminal plasma, nourishment of sperm, neutralization of acidity, lubrication, and transport of sperm.
Tip: Mention percentage contributions if possible. Seminal vesicles = 60%, Prostate = 25%, Bulbourethral = small amount.
Q11. What is oogenesis? Give a brief account of oogenesis.
Oogenesis is the process of formation of a mature female gamete (ovum) from oogonia in the ovary. It involves three phases:
1. Multiplication Phase: During fetal development, oogonia (2n) divide by mitosis to form millions of oogonia. They enter prophase-I of meiosis and become primary oocytes. By 5th month of fetal life, all oogonia are converted to primary oocytes.
2. Growth Phase: Primary oocytes remain arrested at diplotene stage of prophase-I from birth until puberty. They are surrounded by granulosa cells forming primary follicles.
3. Maturation Phase: After puberty, during each menstrual cycle, a primary oocyte completes meiosis-I just before ovulation to form a large secondary oocyte (n) and a small first polar body (n). The secondary oocyte begins meiosis-II but arrests at metaphase-II. It is released during ovulation.
Completion: Secondary oocyte completes meiosis-II only when a sperm enters it. This produces a functional ovum (n) and a second polar body (n). The first polar body may also divide.
Result: 1 functional ovum + 2–3 polar bodies (degenerate).
1. Multiplication Phase: During fetal development, oogonia (2n) divide by mitosis to form millions of oogonia. They enter prophase-I of meiosis and become primary oocytes. By 5th month of fetal life, all oogonia are converted to primary oocytes.
2. Growth Phase: Primary oocytes remain arrested at diplotene stage of prophase-I from birth until puberty. They are surrounded by granulosa cells forming primary follicles.
3. Maturation Phase: After puberty, during each menstrual cycle, a primary oocyte completes meiosis-I just before ovulation to form a large secondary oocyte (n) and a small first polar body (n). The secondary oocyte begins meiosis-II but arrests at metaphase-II. It is released during ovulation.
Completion: Secondary oocyte completes meiosis-II only when a sperm enters it. This produces a functional ovum (n) and a second polar body (n). The first polar body may also divide.
Result: 1 functional ovum + 2–3 polar bodies (degenerate).
Tip: Emphasize the two arrests (diplotene and metaphase-II). Mention that ovulation releases secondary oocyte, not mature ovum.
Q12. Draw a labelled diagram of a Graafian follicle.
Labels to include:
1. Primary oocyte (arrested at prophase-I, then completes meiosis-I)
2. Secondary oocyte (formed after meiosis-I, arrested at metaphase-II)
3. Zona pellucida (glycoprotein layer around oocyte)
4. Corona radiata (layer of follicular cells attached to zona pellucida)
5. Cumulus oophorus (mass of granulosa cells attached to oocyte)
6. Antrum (fluid-filled cavity)
7. Granulosa cells (follicular cells lining antrum)
8. Theca interna (inner vascular layer, secretes estrogen)
9. Theca externa (outer fibrous layer)
10. Membrane granulosa (granulosa cell layer)
1. Primary oocyte (arrested at prophase-I, then completes meiosis-I)
2. Secondary oocyte (formed after meiosis-I, arrested at metaphase-II)
3. Zona pellucida (glycoprotein layer around oocyte)
4. Corona radiata (layer of follicular cells attached to zona pellucida)
5. Cumulus oophorus (mass of granulosa cells attached to oocyte)
6. Antrum (fluid-filled cavity)
7. Granulosa cells (follicular cells lining antrum)
8. Theca interna (inner vascular layer, secretes estrogen)
9. Theca externa (outer fibrous layer)
10. Membrane granulosa (granulosa cell layer)
Tip: Show large antrum clearly. Corona radiata and zona pellucida are frequently asked labels.
Q13. Name the functions of placenta.
1. Respiratory function: Supplies O2 to fetus and removes CO2 from fetal blood.
2. Nutritive function: Transfers glucose, amino acids, fatty acids, vitamins, minerals and water from maternal blood to fetal blood.
3. Excretory function: Removes nitrogenous wastes (urea, uric acid, creatinine) from fetus to maternal blood.
4. Protective/Barrier function: Acts as selective barrier. Prevents some pathogens and drugs from reaching fetus, though not all (e.g., HIV, rubella virus, alcohol, some drugs can cross).
5. Endocrine function: Secretes hormones essential for pregnancy:
• hCG (human Chorionic Gonadotropin) — maintains corpus luteum, detected in pregnancy tests
• hPL (human Placental Lactogen) — metabolic adjustments, mammary development
• Estrogen and Progesterone — maintain pregnancy, develop mammary glands
• Relaxin — softens cervix, relaxes pelvic ligaments
6. Storage function: Stores some nutrients (glycogen, iron, calcium) for short periods.
2. Nutritive function: Transfers glucose, amino acids, fatty acids, vitamins, minerals and water from maternal blood to fetal blood.
3. Excretory function: Removes nitrogenous wastes (urea, uric acid, creatinine) from fetus to maternal blood.
4. Protective/Barrier function: Acts as selective barrier. Prevents some pathogens and drugs from reaching fetus, though not all (e.g., HIV, rubella virus, alcohol, some drugs can cross).
5. Endocrine function: Secretes hormones essential for pregnancy:
• hCG (human Chorionic Gonadotropin) — maintains corpus luteum, detected in pregnancy tests
• hPL (human Placental Lactogen) — metabolic adjustments, mammary development
• Estrogen and Progesterone — maintain pregnancy, develop mammary glands
• Relaxin — softens cervix, relaxes pelvic ligaments
6. Storage function: Stores some nutrients (glycogen, iron, calcium) for short periods.
Tip: Write at least 5 functions. Endocrine function is most important — mention specific hormones.
Q14. What is menstrual cycle? Which hormones regulate menstrual cycle?
Menstrual cycle is the cyclic series of changes in the reproductive system of human females that repeats approximately every 28 days. It involves coordinated changes in the ovary (ovarian cycle) and uterus (uterine cycle).
Phases:
• Menstrual phase (Day 1–5): Shedding of endometrium
• Follicular/Proliferative phase (Day 6–14): Endometrium regenerates; follicles develop
• Ovulatory phase (Day 14): Release of secondary oocyte
• Luteal/Secretory phase (Day 15–28): Corpus luteum forms; endometrium becomes secretory
Hormones regulating menstrual cycle:
• GnRH (Hypothalamus) — stimulates FSH and LH
• FSH (Anterior Pituitary) — follicular development
• LH (Anterior Pituitary) — ovulation, corpus luteum formation
• Estrogen (Developing follicle) — endometrial proliferation, LH surge
• Progesterone (Corpus luteum) — maintains endometrium, inhibits contraction
Phases:
• Menstrual phase (Day 1–5): Shedding of endometrium
• Follicular/Proliferative phase (Day 6–14): Endometrium regenerates; follicles develop
• Ovulatory phase (Day 14): Release of secondary oocyte
• Luteal/Secretory phase (Day 15–28): Corpus luteum forms; endometrium becomes secretory
Hormones regulating menstrual cycle:
• GnRH (Hypothalamus) — stimulates FSH and LH
• FSH (Anterior Pituitary) — follicular development
• LH (Anterior Pituitary) — ovulation, corpus luteum formation
• Estrogen (Developing follicle) — endometrial proliferation, LH surge
• Progesterone (Corpus luteum) — maintains endometrium, inhibits contraction
Tip: Draw the hormone graph for full marks. Mention both ovarian and uterine events.
Q15. What is parturition? Which hormones are involved in induction of parturition?
Parturition is the process of delivery of a fully developed fetus from the mother’s uterus at the end of gestation period (about 280 days). It involves strong, rhythmic contractions of the myometrium (uterine muscles).
Hormones involved:
• Estrogen: Increases near term; increases sensitivity of myometrium to oxytocin; stimulates prostaglandin synthesis
• Oxytocin: From posterior pituitary; stimulates powerful uterine contractions; positive feedback (contractions stimulate more oxytocin release)
• Relaxin: Softens cervix, relaxes pelvic ligaments and pubic symphysis
• Cortisol: From fetal adrenal cortex; stimulates estrogen and prostaglandin production
• Prostaglandins: From placenta and uterus; stimulate uterine contractions and cervical dilation
Hormones involved:
• Estrogen: Increases near term; increases sensitivity of myometrium to oxytocin; stimulates prostaglandin synthesis
• Oxytocin: From posterior pituitary; stimulates powerful uterine contractions; positive feedback (contractions stimulate more oxytocin release)
• Relaxin: Softens cervix, relaxes pelvic ligaments and pubic symphysis
• Cortisol: From fetal adrenal cortex; stimulates estrogen and prostaglandin production
• Prostaglandins: From placenta and uterus; stimulate uterine contractions and cervical dilation
Tip: Mention the positive feedback of oxytocin. Cortisol from fetal side is important — fetus signals readiness for birth.
Q16. In our society, women are often blamed for giving birth to daughters. Can you explain why this is incorrect?
This belief is completely incorrect and unscientific. The sex of a child is determined by the father’s sperm, not the mother’s egg.
Scientific explanation:
• Human females have XX sex chromosomes; they can produce only one type of egg carrying X chromosome.
• Human males have XY sex chromosomes; they produce two types of sperms in equal proportion:
• 50% sperms carry X chromosome
• 50% sperms carry Y chromosome
• If an X-bearing sperm fertilises the egg (X), the zygote is XX → female child.
• If a Y-bearing sperm fertilises the egg (X), the zygote is XY → male child.
Therefore, the father determines the sex of the child depending on which type of sperm fertilises the egg. Blaming the mother is biologically wrong and socially unjust.
Scientific explanation:
• Human females have XX sex chromosomes; they can produce only one type of egg carrying X chromosome.
• Human males have XY sex chromosomes; they produce two types of sperms in equal proportion:
• 50% sperms carry X chromosome
• 50% sperms carry Y chromosome
• If an X-bearing sperm fertilises the egg (X), the zygote is XX → female child.
• If a Y-bearing sperm fertilises the egg (X), the zygote is XY → male child.
Therefore, the father determines the sex of the child depending on which type of sperm fertilises the egg. Blaming the mother is biologically wrong and socially unjust.
Tip: This is a value-based question. Explain chromosome mechanism clearly. Emphasize that mother contributes only X.
🎯 Exam Writing Tips
- ✅ Draw diagrams with pencil — they carry 3–5 marks
- ✅ Label all parts with straight leader lines on right side
- ✅ Spermatogenesis = 4 phases; Oogenesis = 3 phases + completion at fertilisation
- ✅ Remember two arrests in oogenesis: diplotene (birth to puberty) and metaphase-II (ovulation to fertilisation)
- ✅ LH surge triggers ovulation — basis of contraceptive pills
- ✅ Fertilisation occurs at ampullary-isthmic junction
- ✅ Implantation occurs 6–7 days after fertilisation
- ✅ Placenta secretes hCG, hPL, estrogen, progesterone, relaxin
- ✅ Colostrum contains IgA antibodies — passive immunity
- ✅ Father determines sex of child (X or Y sperm)
- ✅ Umbilical arteries carry deoxygenated blood (exception!)
All the best for your exams! 🧬
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