Revision: Class 12 >> Human Reproduction NEET (UG) Human Reproduction

Puberty is the process of physical and hormonal changes by which a child’s body matures into an adult body capable of sexual reproduction to enable fertilization.

Reproduction is a process that results in the formation of new individuals of the same kind, though usually with slight genetic, structural and physiological variations.

Hernia is an abnormal condition that is caused when the intestine, due to the pressure in the abdomen, bulges into the scrotum through the inguinal canal.

The process of expulsion of semen from the urethra is called ejaculation.

Spermatogenesis is the process of formation and development of sperm cells (spermatozoa) in the testes from spermatogonial stem cells through mitosis and meiosis.

The secretion of glands with spermatozoa is a whitish viscous fluid known as seminal fluid or semen.

The opening of the vagina in young females is partially closed by a thin membrane called the hymen (or virgin knot).

Gametogenesis is the process of formation of gametes i.e., sperms and ovary from the primary sex organs in all sexually reproducing organisms. Meiosis plays the most significant role in the process of gametogenesis.

Spermiation is the process of releasing mature spermatozoa. In this, spermatozoa are shed into the lumen of the seminiferous tubule for transport.

After spermiogenesis, sperm heads become embeded in sertoli cells from which they obtain their nutrition and finally get released into the lumen of seminiferous tubules. This process of release of mature sperms from sertoli cells is called spermiation.

Gametogenesis is the process by which male and female primary sex organs produce gametes (sperms and ova).

Gametogenesis is the process by which male and female gametes are formed from germinal cells in the gonads through a series of developmental stages.

Spermiogenesis is the process of transforming spermatids into mature, flagellated spermatozoa (sperms).

The process of transformation of a circular spermatid to a spermatozoon is called spermiogenesis.

Formation of haploid sperms (male gametes) from diploid spermatogonia (sperm mother cells) is called spermatogenesis.

The formation of ova in the ovary from primordial germinal cells is said to be oogenesis.

The rhythmic series of changes in the sex organs throughout the reproductive life of a female primate (e.g., monkeys, apes, and human beings) from puberty to menopause is called the menstrual cycle (L. mensis = month, lunar month).

It is the stage when a girl menstruates for the first time.

The release of the ovum from the ovary is called ovulation.

The fusion of the male gamete (sperm) and female gamete (ovum) to form a zygote is called fertilisation.

or

Formation of zygote by union of sperm and ovum is called as fertilization.

The formation of a zygote by the union of male and female gametes is known as fertilization.

The process of the blastocyst embedding itself into the endometrial lining of the uterus about 5–7 days after ovulation is called implantation.

or

The process of fixing of the blastocyst to the wall of the uterus/endometrium is termed implantation.

Placenta is a temporary organ formed during pregnancy that connects the foetus to the uterine wall and allows exchange of nutrients, gases and wastes between the mother and the foetus.

Gastrulation is the early developmental process in which the embryo changes from a single-layered blastula into a three-layered structure called the gastrula.

After nine months of pregnancy, the fully developed foetus is ready for delivery. The process of childbirth is called parturition.

or

Parturition is the act of expelling the full term foetus from the mother's uterus at the end of gestation.

The term lactation refers to the secretion and ejection of milk by the mammary glands.

1. Human reproductive organs are divided into primary (gonads) and accessory parts.
2. Primary gonads: Testes in males produce sperms; ovaries in females produce eggs.
3. Accessory organs include ducts and glands that aid in fertilisation and embryo development.
4. Secondary sexual characters (e.g., beard, breasts) are not reproductive parts, as they do not directly participate in reproduction.

• The male reproductive system is located in the pelvic region and includes testes, accessory ducts, accessory glands, and external genitalia (penis and scrotum).
• Testes are the primary sex organs present in the scrotum; they contain seminiferous tubules where sperm are produced, while Leydig cells secrete testosterone, and Sertoli cells provide nourishment.
• Accessory ducts—rete testis → vasa efferentia → epididymis → vas deferens → ejaculatory duct → urethra—help in storage, maturation, and transport of sperm.
• Accessory glands—seminal vesicles, prostate gland, and bulbourethral glands—add secretions like fructose, enzymes, and mucus, which nourish sperms and aid in their movement.
• The penis acts as the external genital organ, containing the urethra, and helps in the transfer of sperm during ejaculation.

• Includes — Ovaries, Fallopian tubes, Uterus, Cervix, Vagina, External genitalia, Bartholin's glands, Mammary glands — all in the pelvic region.
• Ovaries — outer cortex (follicles) + inner medulla; produce ova and ovarian hormones; release one ovum monthly after puberty.
• Fallopian tube — 3 parts: Infundibulum (fimbriae collect ovum) → Ampulla (site of fertilisation) → Isthmus (connects to uterus); cilia push egg towards uterus.
• Uterus — 3 layers: Perimetrium (outer), Myometrium (muscular), Endometrium (inner, menstrual changes); opens into vagina via cervix (birth canal).
• Zygote implants in the endometrium; the placenta connects the embryo to the mother for nutrient and waste exchange till birth.
• External genitalia — Mons pubis, Labia majora, Labia minora, Hymen, Clitoris. Bartholin's glands provide lubrication.
• Mammary glands — produce milk for newborn. Puberty begins at 10–14 years in females.

• The menstrual cycle is a series of monthly changes in females of reproductive age.
• The beginning of the cycle is called menarche, and its permanent stop is called menopause (around 45–50 years).
• It occurs mainly in primates, including humans, and involves changes in the ovaries and uterus.
• The cycle is controlled by hormones (gonadotropins and ovarian hormones) and repeats every ~28 days.
• In the middle of the cycle, ovulation occurs, where an egg is released from one of the ovaries.

• Fertilisation in humans is the fusion of male and female gametes (sperm and ovum) and is an internal process occurring in the oviduct, leading to the formation of a diploid zygote.
• During copulation, millions of sperms are released into the vagina, but only one sperm reaches the ovum due to selection and protective barriers around the egg.
• Before fertilisation, sperm undergo capacitation and move towards the ovum; interaction between sperm and egg involves recognition molecules like fertilizin (ovum) and antifertilizin (sperm).
• The sperm’s acrosome releases enzymes that help digest the egg coverings (corona radiata and zona pellucida), allowing sperm entry through the membrane.
• After entry, the sperm nucleus and the ovum nucleus fuse (syngamy), forming a zygote (2n); this process restores the diploid chromosome number (46 in humans).
• Fertilisation triggers completion of meiosis II in the oocyte, formation of the second polar body, and formation of the female pronucleus and male pronucleus.
• In humans, sperm carry 22+X or 22+Y chromosomes, while ova carry 22+X only, determining the genetic sex of the offspring.

• Placenta is formed after implantation and helps in exchange of nutrients, oxygen and wastes between mother and foetus.
• Three germ layers (ectoderm, mesoderm and endoderm) are formed, which develop into all body organs.
• Hormones like hCG, progesterone and estrogen increase to support pregnancy and foetal growth.
• Foetal development occurs gradually, and by nine months the foetus is fully developed and ready for birth.

• Parturition is the process of childbirth, i.e., the delivery of the foetus at the end of the gestation period.
• It is controlled by a neuro-endocrine mechanism involving signals from the fully developed foetus and placenta.
• Foetal signals trigger uterine contractions known as the foetal-ejection reflex (labour pain).
• Hormones like ACTH and corticosteroids from the foetus stimulate the release of oxytocin from the mother’s pituitary gland.
• Parturition occurs in three stages: dilation, expulsion of the baby, and after birth (placenta removal).

• Lactation is the process by which mammary glands produce milk at the end of pregnancy, under the influence of the hormone Prolactin.
• The first milk secreted soon after childbirth is called Colostrum — it is sticky, yellowish and rich in proteins, lactose and antibodies (IgA); fat content is low.
• Antibodies (especially IgA) in colostrum provide passive immunity to the newborn when its own immune system is not yet fully developed.
• Lactation helps the mother in feeding and nourishing the newborn baby, providing all essential nutrients required in early life.