Subtopics - Human Reproduction (NEET)
From gamete formation through fertilization, embryonic development, placentation, and parturition: the complete biology of human reproduction for NEET mastery.
1) Male Reproductive System
The male reproductive system comprises the scrotum housing a pair of testes, a duct system (vasa efferentia, epididymis, vasa deferentia, ejaculatory ducts, urethra), the penis as the copulatory organ, and accessory sex glands (seminal vesicles, prostate gland, Cowper's glands). Each testis contains about 750 seminiferous tubules lined by germinal epithelium with spermatogenic cells and Sertoli cells (nurse cells providing nutrition), while Leydig cells in the interstitium secrete testosterone. The testes are covered by tunica vaginalis, tunica albuginea, and tunica vasculosa. Septa from tunica albuginea divide the testis into 200-300 lobules. The epididymis (6 metres long) stores sperms temporarily and is divided into caput, corpus, and cauda regions. Seminal vesicles contribute 60% of semen volume rich in fructose and prostaglandins, prostate gland adds 25% with citric acid, calcium, and fibrinolysin, while Cowper's glands secrete alkaline mucus for lubrication. The penis contains two dorsally placed corpora cavernosa and one ventral corpus spongiosum enclosing the urethra. Semen is milky, viscous, alkaline (pH 7.2-7.7) with 50-150 million sperm per ml, and a normal ejaculate measures about 3.5 ml.
2) Hormonal Control and Puberty
Hormonal regulation of male reproduction involves the hypothalamic-pituitary-gonadal axis: hypothalamus releases GnRH, anterior pituitary secretes FSH (controls seminiferous tubules and spermatogenesis) and ICSH/LH (stimulates Leydig cells to produce testosterone). Testosterone triggers puberty in males, causing enlargement of penis and scrotum, broadening of shoulders, growth of body and facial hair, deepening of voice due to larynx enlargement, and increased musculature. In females, FSH promotes growth of ovarian follicles from primary to Graafian follicle stage, while LH regulates ovulation and corpus luteum formation. Estrogen (from follicular cells) controls growth and maturation of secondary sex organs and characters: breast development, broadening of pelvis, growth of pubic and axillary hair, and initiation of menstruation. Progesterone from corpus luteum suspends ovulation during pregnancy, promotes implantation, and supports foetal development. Relaxin from corpus luteum broadens the pelvis at the end of pregnancy for parturition.
3) Female Reproductive System
The female reproductive system consists of paired ovaries, paired fallopian tubes (oviducts), uterus, vagina, external genitalia (vulva), and mammary glands. Ovaries are almond-shaped (3 cm long), with an outer cortex containing follicles and inner medulla, covered by tunica albuginea and germinal epithelium. Fallopian tubes (12 cm) develop from mullerian ducts and have four regions: infundibulum (funnel-shaped with fimbriae), ampulla (site of fertilization, wide and tortuous), isthmus (narrow, thick-walled), and uterine part. The uterus is pyriform, 7.5 cm long, with three layers: perimetrium, myometrium, and endometrium (highly vascular with ciliated columnar epithelium). The uterine cavity can expand 500 times during pregnancy (10 to 5000 cubic cm). Types of uterus include duplex (rat), bipartite (carnivores), bicornuate (rabbit), and simplex (man). Vagina (10 cm) has non-keratinised stratified squamous epithelium with glycogen producing organic acid via Lactobacillus (Doderlein's Bacillus). External genitalia include labia majora, labia minora, clitoris (homologous to penis), vestibule, and hymen. Bartholin's glands secrete alkaline lubricant. Mammary glands are modified sweat glands with lactiferous ducts opening on nipples, controlled by prolactin for secretion and oxytocin for ejection.
4) Reproductive Cycle
The reproductive cycle in female mammals is of two types: oestrous cycle (found in all mammals except primates, with oestrus or heat period allowing copulation and pregnancy, followed by anoestrus or quiescence) and menstrual cycle (found only in primates except new world monkeys, averaging 28 days). The menstrual cycle has four phases: (1) Menstrual phase (days 1-4): unfertilised ovum, ruptured endometrium, about 40 ml blood discharged; (2) Follicular/proliferative phase (days 5-13): FSH stimulates primary follicle to Graafian follicle, follicular cells secrete estrogen; (3) Ovulatory phase (day 14): LH surge causes Graafian follicle rupture, secondary oocyte released with zona pellucida and corona radiata; (4) Luteal/secretory phase (days 15-28): empty Graafian follicle becomes corpus luteum secreting progesterone peaking around day 22. If fertilisation occurs, trophoblast secretes hCG maintaining corpus luteum; by 16th week placenta produces sufficient progesterone. Absence of menstrual bleeding is earliest sign of pregnancy. Menopause occurs between ages 45-55 (average 52) when ovulation and menstruation cease due to declining estrogen levels.
5) Gametogenesis
Gametogenesis is the formation of haploid gametes from diploid germ cells, stimulated by FSH and requiring vitamins A and E. Spermatogenesis occurs continuously in seminiferous tubules from puberty: primordial germ cells (from yolk sac endoderm) undergo mitosis forming spermatogonia (multiplication phase), growth to primary spermatocytes (growth phase), meiosis-I to secondary spermatocytes then meiosis-II to spermatids (maturation phase), and spermiogenesis transforming round spermatids into motile sperms. Sperm has three parts: head (nucleus + acrosome from Golgi with hyaluronidase and acrosin), middle piece (energy chamber with mitochondrial nebenkern sheath, 9+2 axoneme, ring centriole), and tail (main piece + end piece). Oogenesis begins before birth but completes only after fertilisation: oogonia multiply by mitosis, grow into primary oocytes (vitellogenesis), undergo meiosis-I after puberty to form secondary oocyte and first polar body, then meiosis-II halts at metaphase-II until fertilisation. One oogonium produces one functional ovum and 2-3 polar bodies. Human ovum is microlecithal (100 micrometres) with egg envelopes: vitelline membrane, zona pellucida, and corona radiata.
6) Types of Eggs
Eggs are classified on three bases. By yolk amount and distribution: alecithal/microlecithal with uniform yolk (human, Amphioxus, sea urchin), mesolecithal/telolecithal with moderate yolk concentrated basally (amphibians, lungfish), polylecithal/megalecithal with large yolk at vegetal pole (reptiles, birds, prototherian mammals), and centrolecithal with central yolk (insects). By fate: determinate/mosaic eggs (each blastomere has fixed fate, invertebrates except echinoderms) and indeterminate/regulative eggs (fate not predetermined, echinoderms and vertebrates). By shell: cleidoic (hard-shelled for terrestrial life, reptiles, birds, insects) and non-cleidoic (without hard shell, aquatic oviparous animals and all viviparous mammals). Egg membranes classified as primary (vitelline membrane, secreted by ovum), secondary (corona radiata, zona pellucida, secreted by ovary), and tertiary (jelly coat of frog, albumen and shell of bird egg, secreted by uterus or oviduct).
7) Fertilization
Fertilisation is the fusion of haploid spermatozoan and ovum to form a diploid zygote, normally occurring in the ampulla of the fallopian tube. The process involves four major steps: (1) Approach of sperm to ovum: of 400 million sperms in an ejaculate, only about 100 reach the tube, aided by uterine aspiration and tubal peristalsis; capacitation (physiological maturation of sperm by acrosome membrane breakdown) takes 5-6 hours in the female genital tract. (2) Penetration of sperm: fertilizin-antifertilizin interaction causes species-specific sperm-egg agglutination; acrosomal reaction releases sperm lysins (hyaluronidase dissolving corona radiata, acrosin dissolving zona pellucida). (3) Cortical reaction: prevents polyspermy by cortical granule release, lifting the vitelline membrane into the fertilisation membrane. (4) Fusion of gametic nuclei: sperm entry triggers completion of meiosis-II in the secondary oocyte; male and female pronuclei fuse (karyogamy) restoring the diploid chromosome number. Fertilisation types include external/internal, monospermic/polyspermic, and self/cross fertilisation.
8) Cleavage, Implantation, and Gastrulation
Cleavage is a series of rapid mitotic divisions of the zygote forming a blastula, characterised by shorter interphase, no growth between divisions, decreasing cell size, and increasing nuclear-cytoplasmic ratio. Cleavage planes include meridional, vertical, equatorial, and latitudinal. Patterns include radial (sea urchin, Amphioxus), spiral (annelids, molluscs), bilateral (tunicates), and rotational (mammals). Types based on yolk: holoblastic (complete cleavage in microlecithal and mesolecithal eggs) and meroblastic (incomplete, in polylecithal and centrolecithal eggs). Implantation is the attachment of the blastocyst to the uterine endometrium. Gastrulation involves mass migration of cells from blastula surface to interior, forming three germ layers: ectoderm (epidermis, nervous system, eye lens), mesoderm (dermis, muscle, skeleton, circulatory system, kidneys, gonads), and endoderm (gut lining, liver, pancreas, lungs, thyroid). Gastrulation mechanisms include invagination, involution, ingression, and delamination. Neurulation follows, establishing the neural plate and beginning organogenesis.
9) Extra-embryonic Membranes and Placenta
Four extra-embryonic membranes form in amniotes: yolk sac (outer mesoderm + inner endoderm, vestigial in humans, blood cell formation site until week 6), amnion (outer mesoderm + inner ectoderm, amniotic fluid cushions and protects embryo), allantois (mesoderm + endoderm from hindgut, stores uric acid in reptiles/birds, provides vasculature in mammals), and chorion (outermost, ectoderm + somatic mesoderm, forms placenta in primates). Placenta is a temporary connection between foetal and maternal tissues for nutrition, respiration, and excretion. Human placenta is chorionic (formed only by chorion), haemochorial (three foetal layers, maternal blood directly contacts chorionic villi), metadiscoidal (villi restricted to one disc), and deciduous. Classification: by foetal membrane (yolk sac in marsupials, allantoic in most eutherians, chorionic in primates); histologically (epitheliochorial, syndesmochorial, endotheliochorial, haemochorial, haemoendothelial); by villi distribution (diffuse, cotyledonary, zonary, discoidal, metadiscoidal). Placenta serves as nutritive, respiratory, and excretory organ but also acts as a barrier, though AIDS virus, syphilis bacteria, nicotine, and addictive drugs can cross it.
10) Gestation, Parturition, and Lactation
Gestation period is the duration between fertilisation and parturition, approximately 270-290 days in humans. Parturition involves expulsion of the fully formed foetus after gestation, triggered by signals from the foetus and placenta inducing foetal ejection reflex. Oxytocin from neurohypophysis causes uterine contractions, while the shift in estrogen-to-progesterone ratio increases uterine contractility towards the end of pregnancy. The foetal pituitary and adrenal glands also secrete oxytocin and cortisol respectively as possible uterine stimulants. Lactation is milk production by mammary glands following parturition, controlled by prolactin (anterior pituitary) whose secretion increases steadily from the fifth week of pregnancy. Prolactin is tonically inhibited by prolactin inhibitory hormone (PIH) from hypothalamus. Colostrum is the initial fluid secreted, containing same protein and lactose concentrations as milk but almost no fat. Milk composition: water 88.5%, lactose 6.8%, fat 3.3%, casein 0.9%, lactalbumin and other proteins 0.4%, with low iron and vitamin C content.
Human Reproduction Download Notes & Weightage Plan
For each topic in the Human Reproduction chapter below, you get (2) the exact resources to download and how to use them, and (3) a simple importance & time plan so NEET students know what to do first and what to revise last.
Covers anatomy of testes, accessory ducts (epididymis, vas deferens, ejaculatory ducts), accessory glands (seminal vesicles, prostate, Cowper's), penis structure, and semen composition.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: NEET asks which gland secretes fructose (seminal vesicle), function of Sertoli cells vs Leydig cells, site of sperm storage (epididymis), and semen pH and composition.
- High-risk Area: Confusing Sertoli cells (inside seminiferous tubules, support/nutrition) with Leydig cells (outside in interstitium, testosterone secretion). Also confusing vasa efferentia (12-20, rete testis to caput epididymis) with vasa deferentia (2, cauda epididymis to ejaculatory duct).
- Best Practice Style: Create a comparison table of all three accessory glands with their secretion, percentage contribution, pH, and key chemicals. Label a cross-section diagram of seminiferous tubule showing cell types.
Hormonal Control and Reproductive Cycles
Covers hormonal regulation of male and female reproductive systems, the four phases of the menstrual cycle with hormonal control, oestrous vs menstrual cycles, and menopause.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: NEET repeatedly tests: which phase of menstrual cycle is driven by which hormone, what LH surge triggers (ovulation on day 14), role of corpus luteum, hCG function in early pregnancy, and what menopause is caused by (estrogen decline).
- High-risk Area: Confusing follicular phase (FSH-driven, pre-ovulatory) with luteal phase (progesterone-driven, post-ovulatory). Also confusing oestrous cycle (no bleeding, anoestrus between cycles) with menstrual cycle (bleeding occurs, only in primates). Students forget that new world monkeys have oestrous cycle, not menstrual.
- Best Practice Style: The menstrual cycle diagram with hormone curves is the single most important visual in this chapter. Practice drawing it repeatedly until it becomes automatic. Solve previous year questions on cycle phase identification.
Covers spermatogenesis (three phases + spermiogenesis), oogenesis (three phases with interrupted meiosis), sperm and ovum structure, and key differences between the two processes.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: NEET tests: number of sperms from one primary spermatocyte (4), which enzymes in acrosome (hyaluronidase + acrosin), when does meiosis-II complete in oogenesis (only after fertilisation), function of middle piece (energy from mitochondria).
- High-risk Area: The biggest trap is timing of meiosis completion in oogenesis: meiosis-I completes at puberty (not at birth), and meiosis-II completes only after fertilisation (not at ovulation). Students also confuse acrosome origin (Golgi complex) with middle piece origin (mitochondria).
- Best Practice Style: Master the comparison table and sperm diagram. Create a timeline of oogenesis from foetal life through puberty to fertilisation showing exactly when each meiotic division starts and stops.
Covers the four steps of fertilisation (sperm approach, penetration, cortical reaction, pronuclear fusion), significance of fertilisation, cleavage types (holoblastic, meroblastic), and cleavage patterns.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: NEET asks: site of fertilisation (ampulla), what is capacitation, role of cortical reaction (polyspermy block), which enzyme dissolves zona pellucida (acrosin), and holoblastic vs meroblastic cleavage.
- High-risk Area: Students confuse the fertilisation site (ampulla) with the implantation site (endometrium). Also confusing hyaluronidase (dissolves intercellular cement of corona radiata) with acrosin (dissolves zona pellucida). These are tested as separate enzymes with distinct targets.
- Best Practice Style: Create enzyme-target pairs: hyaluronidase = corona radiata, acrosin = zona pellucida. Practise elimination-based MCQs on fertilisation steps.
Embryonic Development, Placenta, and Parturition
Covers gastrulation and germ layer formation, extra-embryonic membranes, placenta classification (by foetal membrane, histology, and villi distribution), gestation period, parturition, and lactation.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: NEET asks: which germ layer gives rise to kidney (mesoderm), type of human placenta (haemochorial), function of amnion (cushioning), role of oxytocin in parturition, and what colostrum contains.
- High-risk Area: Students confuse kidney origin (mesoderm) with liver origin (endoderm). The histological sequence of placenta types (epitheliochorial, syndesmochorial, endotheliochorial, haemochorial, haemoendothelial) and their examples are frequently mixed up.
- Best Practice Style: Create a master classification table for placenta types. Use mnemonic for histological types: Every Student Enters Hard Exams (Epithelio, Syndesmo, Endothelio, Haemo-chorial, Haemo-endothelial). Practise germ layer origin questions extensively.
Human Reproduction Chapter NEET Traps & Common Mistakes (Topic-Wise)
Each subtopic below is of the Human Reproduction chapter and shows what NEET students usually do wrong in NEET examination, a short example of the mistake, and how NEET frames the question to trick you with close options are given below.
Mistake Snapshot (What Students Do Wrong)
- Fertilisation site confusion: Fertilisation occurs in the ampulla of the fallopian tube, NOT in the uterus. Implantation occurs in the endometrium of the uterus. Students frequently confuse these two distinct anatomical sites.
- Ampulla vs isthmus confusion: The ampulla is the wide, tortuous, thin-walled major part of the fallopian tube where fertilisation occurs. The isthmus is the narrow, thick-walled part that follows. Students select isthmus when asked about the fertilisation site.
- Infundibulum role misidentified: The infundibulum with its fimbriae catches the ovulated egg but is not the fertilisation site. Fertilisation happens in the ampulla, the next region from the infundibulum. Students confuse egg reception with fertilisation.
A NEET question asks: Where does fertilisation normally occur in the human female? Students who recall that the fimbriae catch the egg select infundibulum, but the correct answer is ampulla of the fallopian tube, which is the next region from the infundibulum.
How NEET Frames The Trap
NEET offers options including uterus, cervix, infundibulum, and ampulla. The question tests whether students know the precise location within the fallopian tube, not just that it occurs in the oviduct.
Q. In human females, fertilisation of the ovum by sperm normally occurs in the:
A. Uterine cavity B. Isthmus of the fallopian tube C. Ampulla of the fallopian tube D. Infundibulum of the fallopian tube
Trick: Option (c) Ampulla of the fallopian tube is correct. The infundibulum catches the ovulated egg via fimbriae, but the actual fusion of sperm and egg occurs in the ampulla, which is the next wider region of the oviduct. The uterus is the site of implantation, not fertilisation.
Mistake Snapshot (What Students Do Wrong)
- Location and function swap: Sertoli cells are INSIDE seminiferous tubules and provide nutrition (nurse cells) and secrete inhibin. Leydig cells are OUTSIDE in the interstitium and secrete testosterone. Students swap their locations and functions.
- Inhibin source confusion: Inhibin is secreted by Sertoli cells, not Leydig cells. It provides negative feedback to suppress FSH secretion. Students attribute inhibin to Leydig cells because they associate all testicular hormones with the same cell type.
- FSH target vs LH target: FSH acts on Sertoli cells to support spermatogenesis. LH (ICSH) acts on Leydig cells to stimulate testosterone production. Students reverse the hormone-target cell pairing.
A question asks which cells secrete testosterone. Students who confuse Sertoli with Leydig select Sertoli cells. The correct answer is Leydig cells (interstitial cells) located between the seminiferous tubules.
How NEET Frames The Trap
NEET presents options with Sertoli cells and Leydig cells for questions about testosterone secretion, inhibin secretion, or FSH/LH targets. The trick is in pairing the correct cell type with its specific function and location.
Q. Which cells in the testis secrete inhibin and are regulated by FSH?
A. Leydig cells B. Sertoli cells C. Spermatogonia D. Primary spermatocytes
Trick: Option (b) Sertoli cells is correct. Sertoli cells (nurse cells) are located inside seminiferous tubules, regulated by FSH, and secrete inhibin for negative feedback. Leydig cells are in the interstitium, regulated by LH/ICSH, and secrete testosterone. Mixing the two is one of the most common NEET errors in this chapter.
Mistake Snapshot (What Students Do Wrong)
- When meiosis-I completes in oogenesis: Meiosis-I begins in foetal life but halts at prophase-I. It resumes and completes only at puberty, producing a secondary oocyte and a first polar body. Students wrongly state meiosis-I completes before birth.
- When meiosis-II completes: The secondary oocyte starts meiosis-II but halts at metaphase-II. It completes ONLY after fertilisation by a sperm, not at the time of ovulation. Students incorrectly assume meiosis-II is complete at ovulation.
- State of egg at ovulation: The egg ovulated is a secondary oocyte arrested at metaphase-II, NOT a mature ovum. It becomes a true ovum only after sperm entry triggers completion of meiosis-II. Students call the ovulated cell an ovum.
NEET asks: At what stage is the human egg at the time of ovulation? Students select mature ovum or primary oocyte. The correct answer is secondary oocyte arrested at metaphase-II.
How NEET Frames The Trap
NEET exploits the multi-step, multi-year timeline of oogenesis. Questions test precisely which meiotic division is complete, in progress, or arrested at specific life stages (birth, puberty, ovulation, fertilisation).
Q. At the time of ovulation in human females, the oocyte released is at the stage of:
A. Primary oocyte in prophase-I B. Secondary oocyte in metaphase-II C. Mature ovum after completion of meiosis-II D. Secondary oocyte in anaphase-II
Trick: Option (b) Secondary oocyte in metaphase-II is correct. Meiosis-I is completed just before ovulation, converting the primary oocyte into a secondary oocyte and first polar body. The secondary oocyte immediately begins meiosis-II but arrests at metaphase-II. Meiosis-II completes only upon sperm penetration during fertilisation. The ovulated cell is therefore NOT a mature ovum.
Mistake Snapshot (What Students Do Wrong)
- Hyaluronidase target confusion: Hyaluronidase dissolves the hyaluronic acid in intercellular spaces holding corona radiata cells together. It does NOT dissolve zona pellucida. Students swap the enzyme-target pairing.
- Acrosin function misattributed: Acrosin is the enzyme that specifically dissolves the zona pellucida. Students attribute zona pellucida dissolution to hyaluronidase or use a generic term, missing the specific enzyme.
- Acrosome origin: The acrosome is derived from the Golgi complex during spermiogenesis. Students sometimes attribute it to mitochondria (which form the middle piece) or endoplasmic reticulum.
A question asks: Which enzyme released from the acrosome dissolves the zona pellucida during fertilisation? Options include hyaluronidase and acrosin. Students who remember hyaluronidase from general biology select it, but acrosin is the specific enzyme for zona pellucida.
How NEET Frames The Trap
NEET tests specific enzyme-target pairs. The question may ask about corona radiata (hyaluronidase) or zona pellucida (acrosin). Getting the pairing backwards is the most common error.
Q. During fertilisation, the enzyme responsible for dissolving the zona pellucida of the ovum is:
A. Hyaluronidase B. Acrosin C. Corona penetrating enzyme D. Lysozyme
Trick: Option (b) Acrosin is correct. Hyaluronidase dissolves the hyaluronic acid holding corona radiata cells together (outer layer). Acrosin specifically dissolves the zona pellucida (middle glycoprotein layer). Corona penetrating enzyme helps traverse corona radiata but does not dissolve zona pellucida. Students who do not distinguish between these three acrosomal enzymes and their specific targets commonly select hyaluronidase.
Mistake Snapshot (What Students Do Wrong)
- Human placenta histological type: Human placenta is haemochorial (maternal blood directly bathes foetal chorionic villi, with three foetal layers remaining). Students confuse this with haemoendothelial (rat, rabbit, where only foetal capillary endothelium separates bloods) or endotheliochorial (dog, cat).
- Chorionic vs allantoic placenta: Human placenta is chorionic (formed only by chorion; allantois remains small). Most other eutherians have allantoic placenta. Students generalise the allantoic type to all mammals including primates.
- Deciduous vs non-deciduous confusion: Human placenta is deciduous (maternal tissue is shed at birth with bleeding). In non-deciduous placentae (pig, horse), villi withdraw without tissue damage. Students confuse the two terms.
NEET asks: What type of placenta is found in humans? Options include allantoic, chorionic, epitheliochorial, and haemochorial. Students must recognise that multiple classifications apply: human placenta is chorionic (by membrane), haemochorial (by histology), and metadiscoidal (by villi distribution).
How NEET Frames The Trap
Questions may ask about one specific classification axis (histological type, membrane type, or villi type), and the options mix categories. Students must identify which classification system the question targets.
Q. The histological type of placenta found in humans is:
A. Epitheliochorial B. Syndesmochorial C. Endotheliochorial D. Haemochorial
Trick: Option (d) Haemochorial is correct. In haemochorial placenta, three maternal barriers are absent (uterine epithelium, connective tissue, and endothelium of maternal blood vessels), so maternal blood directly contacts the foetal chorionic villi with only three foetal layers remaining. Epitheliochorial has all six barriers (horse, pig). Syndesmochorial lacks uterine epithelium (cow, sheep). Endotheliochorial retains four barriers (dog, cat).