Human Reproduction NEET Notes 2027: Key Points and PDF

Human Reproduction is Chapter 2 of NCERT Class 12 Biology and part of Unit 6, Reproduction, of the NEET UG syllabus. These notes cover the male and female reproductive systems, spermatogenesis and oogenesis, sperm structure, the menstrual cycle, fertilisation, implantation, pregnancy, placenta, parturition and lactation, with comparison tables and a free notes PDF.

Human Reproduction NEET Notes

Section-wise key points from NCERT Chapter 2, comparison tables, high-yield facts and common mistakes for NEET 2027 revision.

Human Reproduction at a Glance

The topic list follows the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025, which stays the reference until the 2027 syllabus is out. The full list is on the NEET syllabus page.

What are the main events of human reproduction?

Humans are sexually reproducing and viviparous, and the reproductive events begin after puberty.

• Sequence: gametogenesis → insemination → fertilisation (zygote) → blastocyst formation → implantation → gestation → parturition.
• Sperm formation continues even in old men, but formation of ovum ceases in women around the age of fifty years.

Male Reproductive System

The male reproductive system lies in the pelvis region and includes a pair of testes, accessory ducts, glands and the external genitalia.

• Testes lie outside the abdominal cavity in the scrotum, which keeps them 2-2.5 °C below body temperature, as needed for spermatogenesis.
• Each adult testis is oval, about 4-5 cm long and 2-3 cm wide, with about 250 testicular lobules; each lobule has one to three highly coiled seminiferous tubules.
• Seminiferous tubules are lined by male germ cells (spermatogonia), which form sperms by meiosis, and Sertoli cells, which nourish the germ cells.
• Interstitial spaces outside the tubules contain blood vessels, immunologically competent cells and Leydig (interstitial) cells, which secrete androgens.

• Seminal plasma (secretions of the accessory glands) is rich in fructose, calcium and certain enzymes.

Female Reproductive System

The female system has a pair of ovaries, a pair of oviducts, the uterus, cervix, vagina and external genitalia in the pelvic region, together with a pair of mammary glands.

• Ovaries are the primary female sex organs, producing the ovum and steroid (ovarian) hormones. Each is about 2-4 cm long, held to the pelvic wall and uterus by ligaments.
• The ovary is covered by thin epithelium enclosing the ovarian stroma, which has a peripheral cortex and an inner medulla.
• Each fallopian tube (oviduct) is about 10-12 cm long: funnel-shaped infundibulum with finger-like fimbriae that collect the ovum, then the wider ampulla, then the narrow isthmus that joins the uterus.
• The uterus (womb) is single, shaped like an inverted pear and held by ligaments; it opens into the vagina through the narrow cervix. The cervical canal and vagina form the birth canal.
• External genitalia: mons pubis, labia majora, labia minora, hymen and clitoris. The presence or absence of the hymen is not a reliable indicator of virginity or sexual experience.

Mammary Glands

• Each breast has 15-20 mammary lobes containing clusters of alveoli, whose cells secrete milk into their lumens.
• Milk path: alveoli → mammary tubules → mammary duct → mammary ampulla → lactiferous duct → nipple.

Gametogenesis: Spermatogenesis and Oogenesis

Gametogenesis is the formation of sperms in the testis and ovum in the ovary.

Spermatogenesis

• After spermiogenesis, sperm heads embed in Sertoli cells and are released from the tubules by spermiation.
• Spermatogenesis starts at puberty with a rise in GnRH (hypothalamus), which makes the anterior pituitary secrete LH and FSH.
• LH acts on Leydig cells to release androgens, which stimulate spermatogenesis. FSH acts on Sertoli cells, which secrete factors that help spermiogenesis.

Structure of a Sperm

• Head, neck, middle piece and tail, all enclosed by a plasma membrane.
• Head: elongated haploid nucleus capped by the acrosome, filled with enzymes that help fertilisation.
• Middle piece: numerous mitochondria that give energy for tail movement.
• A man ejaculates about 200-300 million sperms; for normal fertility at least 60 per cent must have normal shape and size and at least 40 per cent must show vigorous motility.
• Secretions of the epididymis, vas deferens, seminal vesicle and prostate are essential for sperm maturation and motility. Seminal plasma plus sperms = semen.

Oogenesis

• Begins during embryonic development: a couple of million oogonia form in each fetal ovary, and none are added after birth.
• Oogonia enter prophase I of meiosis and are arrested there as primary oocytes; each is surrounded by granulosa cells to form a primary follicle.
• Many follicles degenerate between birth and puberty, so only 60,000-80,000 primary follicles remain in each ovary at puberty.
• Secondary follicle: more granulosa layers and a new theca. Tertiary follicle: fluid-filled antrum, with theca interna and theca externa.
• In the tertiary follicle the primary oocyte completes meiosis I unequally, giving a large haploid secondary oocyte and a tiny first polar body.
• The tertiary follicle becomes the Graafian follicle; the secondary oocyte forms the zona pellucida and is released at ovulation.

Menstrual Cycle: Phases and Hormones

The reproductive cycle of female primates is the menstrual cycle. It repeats about every 28/29 days, with one ovum released in the middle of each cycle.

• Menarche is the first menstruation at puberty; menopause is the end of cycles around 50 years.
• Menstruation occurs only if the ovum is not fertilised. Lack of menstruation may indicate pregnancy but can also be caused by stress or poor health.
• During pregnancy all events of the cycle stop. Without fertilisation, the corpus luteum degenerates and the endometrium disintegrates.
• Menstrual hygiene in NCERT: change sanitary napkins or clean homemade pads every 4-5 hours as needed and dispose of them properly.

Fertilisation and Implantation

Fertilisation, the fusion of a sperm with an ovum, takes place in the ampullary region of the fallopian tube.

• Semen is released into the vagina (insemination); sperms pass through the cervix and uterus to the ampulla. Ovum and sperms must reach the ampulla at the same time.
• A sperm contacting the zona pellucida induces membrane changes that block other sperms, so only one sperm fertilises the ovum.
• Acrosome secretions help the sperm enter; this triggers the unequal meiosis II, giving a second polar body and a haploid ovum (ootid). The haploid nuclei fuse to form a diploid zygote.
• Sex is decided at fertilisation: all ova carry X; 50 per cent of sperms carry X and 50 per cent carry Y. XX gives a girl and XY a boy, so the father’s sperm decides the sex of the baby.

Pregnancy, Placenta and Embryonic Development

After implantation, chorionic villi on the trophoblast interdigitate with uterine tissue to form the placenta, the structural and functional unit between foetus and mother.

• The placenta supplies oxygen and nutrients, removes carbon dioxide and wastes, and connects to the embryo through the umbilical cord.
• Placental hormones: hCG, hPL, estrogens and progestogens. Relaxin is secreted by the ovary in the later phase of pregnancy. hCG, hPL and relaxin are produced only during pregnancy.
• Estrogens, progestogens, cortisol, prolactin and thyroxine also rise several-fold in maternal blood.
• The inner cell mass forms ectoderm, endoderm and then mesoderm, which give rise to all adult tissues; it also contains stem cells.

Parturition and Lactation

Parturition (childbirth) after a gestation period of about 9 months is induced by a complex neuroendocrine mechanism involving cortisol, estrogens and oxytocin.

• Signals from the fully developed foetus and placenta cause mild uterine contractions, the foetal ejection reflex.
• This releases oxytocin from the maternal pituitary; oxytocin causes stronger contractions, which release more oxytocin, until the baby is expelled through the birth canal. The placenta is expelled soon after.
• Mammary glands differentiate during pregnancy and produce milk towards its end (lactation).
• Colostrum, the milk of the first few days, contains antibodies essential for resistance in the new-born.

Most-asked Facts for NEET: Human Reproduction

Revise these one-line facts from the NCERT chapter just before the exam.

• Testes are kept 2-2.5 °C below body temperature by the scrotum.
• Each testis has about 250 lobules with one to three seminiferous tubules each.
• Sertoli cells nourish germ cells; Leydig cells secrete androgens.
• Seminal plasma is rich in fructose, calcium and certain enzymes.
• Fallopian tube: infundibulum (fimbriae) → ampulla → isthmus; about 10-12 cm long.
• Uterine wall: perimetrium, myometrium, endometrium.
• Each breast has 15-20 mammary lobes.
• Spermatogonia and primary spermatocytes have 46 chromosomes; secondary spermatocytes and spermatids have 23.
• LH acts on Leydig cells; FSH acts on Sertoli cells.
• Sperm count per ejaculation: 200-300 million; at least 60% normal shape and 40% vigorous motility for normal fertility.
• 60,000-80,000 primary follicles remain in each ovary at puberty.
• Antrum appears in the tertiary follicle; zona pellucida forms around the secondary oocyte.
• Ovulation is induced by the LH surge around day 14.
• Corpus luteum secretes progesterone, which maintains the endometrium.
• Fertilisation occurs in the ampullary region of the fallopian tube.
• Morula has 8-16 blastomeres; blastocyst has trophoblast and inner cell mass.
• hCG, hPL and relaxin are produced only during pregnancy.
• Heart forms after one month; first foetal movements in the fifth month.

Common Mistakes to Avoid

Watch for these mix-ups when you answer questions on this chapter.

• Saying Sertoli cells secrete androgens. Leydig (interstitial) cells do; Sertoli cells nourish germ cells.
• Placing Leydig cells in the ovary. They are in the interstitial spaces of the testis.
• Saying the ovum is fully haploid at ovulation after both meiotic divisions. The secondary oocyte is released; meiosis II completes only when a sperm enters.
• Writing that oogenesis starts at puberty. It starts during embryonic development.
• Saying fertilisation happens in the uterus. It happens in the ampullary region of the fallopian tube.
• Calling the endometrium the muscular layer. The myometrium is the smooth muscle layer; the endometrium is glandular.
• Attributing ovulation to FSH alone. The LH surge induces rupture of the Graafian follicle.
• Saying the mother decides the sex of the baby. The sperm (X or Y) decides it.
• Saying relaxin is made by the placenta. NCERT says the ovary secretes relaxin in the later phase of pregnancy.
• Thinking spermatogenesis divisions are unequal. Unequal divisions and polar bodies belong to oogenesis.

Human Reproduction Notes PDF and Related Pages

Download the AglaSem notes for Human Reproduction (key notes and important questions with answers) free: View PDF

• All chapters: NEET Biology notes
• Full topic list: NEET syllabus
• Practice: NEET question papers
• Source text: NCERT Chapter 2 (NCERT, Class 12 Biology)

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