Wednesday, January 14, 2009

Know the Mechanism of Reproduction in Humans

Reproduction in humans occurs only by sexual methods.

The gametes in human reproduction are the sperm and egg. Sperms are the male gametes and egg is the female gamete. Both are produced after meiosis and therefore are haploid. Humans are unisexual and thus male and female gametes are produced in separate individuals. Humans have a pair of primary reproductive organs; sperm-producing testes in males and egg-producing ovaries in females, along with accessory ducts and glands. Testes and ovaries also produce hormones that influence reproductive functions and secondary sexual traits.

The hormones testosterone, LH (luteinizing hormone), and FSH, (follicle stimulating hormone) control sperm production. The hormones estrogen, progesterone, FSH, and LH control egg maturation and release, as well as changes in the lining of the uterus, the endometrium. The testis is an ovoid-shaped gland consisting of coiled tubules called seminiferous tubules. The testes are placed in a scrotal sac outside the abdominal cavity. The male gametes or sperms are produced in seminiferous tubules by a complex process called spermatogenesis. Sperm produced in the testes are carried to the copulating organ, the penis via epididymis (stores sperm until they have matured) and vas deference. Vas deference is a straight tube, which along with spermatic artery and vein, forms the spermatic cord. Seminal vesicle, prostate gland, Cowper's gland, etc. are the accessory parts present along with male genital organs.

The female reproductive organs consist of ovaries and fallopian tubes. Ovaries produce the female gamete ovum (egg) and fallopian tubes are a pair of ducts, one from each ovary, that catches the ovum released at ovulation each month. This tube carries the egg and houses the fertilized egg through its embryonic development and is lined with smooth muscle, which contracts, moving the ovum toward the uterus. The fertilization of ovum with sperm usually occurs in this tube and the initial development of resulting zygote into an embryo also occurs here. The uterus is lined with endometrium; this is where the embryo implants and completes its development the cervix is the muscular ring at the mouth of the uterus and the vagina is a thin-walled chamber into which sperm are directly deposited during intercourse. The urethra is part of the female urinary tract, but not part of the female reproductive tract, unlike males. The production of sperm is a continuous process starting from puberty and lasting throughout life in males. But in females the production of female gamete or the egg is a cyclic process with a periodicity of about 28 days. During these periods there is a great change in the structure and function of the entire reproductive system. At birth, the female has about 2 million primary oocytes, which give rise to what will become a mature egg, or ovum. Unlike the male, no more primary oocytes or cells that will give rise to a mature gamete are produced after a female is born. At birth the primary oocytes are in a resting state and will not develop any further until they are triggered by the hormone FSH released from the pituitary, at which point a few at a time will resume meiosis. Only 400 of the original 2 million primary oocytes actually develop into mature eggs.

During copulation sperm is deposited near the cervix in the vagina. These sperms are motile and active for some times-at least for three days. They move toward the fallopian tubes where they may come in contact with the egg cell. During fertilization, the sperm cell injects its nucleus into the cytoplasm of the oocyte and fertilization takes place. Only one sperm can fertilize an egg and further fusion with sperm is prevented. By fertilization the diploid number of chromosomes is restored in the fertilized egg, which is known as the zygote. The zygote starts its development in the fallopian tube and continues its development in the uterus.

Tags: Bio Technology, Bio Genetics, Human Reproduction

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