Human Reproduction

Reproductive organs
Humans reproduce by the process of sexual reproduction. Sexual reproduction is a characteristic feature of human beings by which they produce offspring for the survival of their species, and pass on traits from one generation to the next.

The male reproductive system consists of a pair of testes, the male sex accessory ducts and the accessory glands and external genitalia.

Each testis is made up of about 250 compartments called testicular lobules. Eachlobule contains one to three highly coiled seminiferous tubules. Eachseminiferous tubule is lined by spermatogonia and Sertoli cells.
During sperm formation the spermatogonia undergo meiotic divisions, while Sertoli cells provide nutrition to the dividing germ cells.
Sperm on leaving testis go past the following glands: Seminal vesicles, Prostate glands and Cowper's glands.
Seminal vesicles are situated on either side of the urethra, just above prostate gland.
Prostate glands are situated just below the urinary bladder. Cowper’s glands are pair of small glands that are connected to the urethra.
The male external genitalia is called penis.
The female reproductive system is made up of a pair of ovaries, a pairof oviducts, a uterus, a vagina, external genitalia, and a pair ofmammary glands.
The ovaries produce the female gamete called ovum.Some steroid hormones called ovarian hormones are also produced in the ovaries. The female accessory duct consists of the oviducts, uterusand vagina.
Ovaries are two in number, on either side of uterus. Millions of eggs are stored in each ovary at birth. At puberty, only one egg ripens each month.Ovary secretes hormones estrogen and progesterone which are involved in the onset of menstrual cycle. Mammary glands produce milk for the sustenance of the young.

Gametogenesis and fertilization
In males, gametogenesis occurs in testes and is termed as spermatogenesis. In females, gametogenesis occurs in ovaries and is termed as oogenesis.
The process of formation of sperm is called spermatogenesis. It begins at puberty in males.The Leydig cells present outside the seminiferous tubules synthesise and secrete testicular hormones called androgens.Androgens stimulate the process of spermatogenesis.

A human sperm consists of: a head, neck, a middle piece and tail.
The process offormation of mature female gametes is called oogenesis. It is initiated during embryonic stage.
Thereproductive cycle in female is called menstrual cycle.Fertilisation is the process of fusion of sperm and ovum in fallopian tubes.
During fertilisation, the sperm fertilises the ovum leading to formation of adiploid zygote. After fertilization, the zygote undergoes repeated mitoticdivision to form a blastocyst. The blastocysts when gets implanted in the uterus, it results in pregnancy. Embryo receives food and oxygen from the mother through placenta.
The process of childbirth is called parturition. It is induced by a complex neuroendocrine mechanism involving cortisol,estrogens and oxytocin.

Lactation is the process of secretion of milk from mammary glands after childbirth. The secretion of milk is stimulated by the hormone prolactin.

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