Human ReproductionClass 12 Biology Important Points

The male reproductive system includes a pair of testes located in the scrotum for spermatogenesis at a lower temperature ($2-2.5^{\circ}\text{C}$ below body temp), accessory ducts, glands, and the external genitalia.

Spermatogenesis is the process where diploid spermatogonia in the testes undergo meiosis to produce haploid spermatozoa (sperms). This process begins at puberty and continues throughout life.

Sertoli cells provide nutrition to developing sperm cells within the seminiferous tubules. Leydig cells, located in the interstitial spaces, produce and secrete androgens, primarily testosterone.

The female system includes a pair of ovaries that produce the ovum and hormones, a pair of oviducts (fallopian tubes), the uterus, cervix, vagina, and external genitalia. These are supported by mammary glands.

Oogenesis begins in the fetal stage, forming primary oocytes arrested in meiosis I. After puberty, a secondary oocyte is formed and arrested in meiosis II, which completes only upon fertilization.

A sperm is a microscopic structure with a head containing the haploid nucleus and an acrosome for fertilization, a middle piece with mitochondria for energy, and a tail for motility.

This is the reproductive cycle in female primates, lasting about 28 days. It consists of the menstrual phase (bleeding), follicular phase (follicle growth), ovulation (egg release), and luteal phase (corpus luteum activity).

The cycle is regulated by gonadotropins (FSH and LH) from the pituitary and ovarian hormones (estrogen and progesterone). A rapid secretion of LH (LH surge) around day 14 induces ovulation.

After ovulation, the remaining part of the Graafian follicle transforms into the corpus luteum. It secretes large amounts of progesterone, which is essential for maintaining the uterine endometrium for pregnancy.

Fertilisation is the fusion of a sperm with an ovum, occurring in the ampullary region of the fallopian tube. This process results in the formation of a single diploid cell called a zygote.

The zygote undergoes rapid mitotic divisions, called cleavage, to form a blastocyst. The blastocyst then embeds itself into the endometrium of the uterus, a process known as implantation.

The placenta is the connection between the developing embryo and the mother, facilitating the supply of oxygen and nutrients and removal of wastes. It also acts as an endocrine gland, producing hormones like hCG and hPL.

After implantation, the inner cell mass of the blastocyst differentiates into three primary germ layers: ectoderm, mesoderm, and endoderm. These layers give rise to all the tissues and organs of the body.

Parturition is the expulsion of the fully developed foetus from the uterus. It is induced by a complex neuroendocrine mechanism involving signals from the foetus and placenta, and the hormone oxytocin.

Lactation is the production of milk by the mammary glands following childbirth. The initial milk, called colostrum, is rich in antibodies and provides essential passive immunity to the newborn.

The sex of an individual is determined at fertilization by the type of sperm. A sperm carrying an X chromosome results in a female (XX), while a sperm carrying a Y chromosome results in a male (XY).