Spermatogenesis

Spermatogenesis refers to the creation, or genesis, of spermatozoa, which occurs in the male gonads. Sperm cells develop initially from germ stem cells known as spermatogonia. As these differentiate they go through the following stages:

Related Topics:
Spermatozoa - Male - Gonad - Spermatogonia

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• spermatocytogenesis (creation of spermatocytes):
• mitosis of spermatogonia into primary spermatocytes
• meiosis of primary spermatocytes into haploid secondary spermatocytes
• spermatidogenesis (creation of spermatids through mitosis of secondary spermatocytes)
• spermiogenesis (creation of spermatozoa through further development of spermatids).

The female counterpart to spermatogenesis is oogenesis.

Related Topics:
Female - Oogenesis

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The process of spermatogenesis is highly regulated via hormonal messengers and also the cell-cell communication between the developing germ cells (sperm cells) and the nurse-like Sertoli cells.

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The Sertoli cell is essential for spermatogenesis as it provides support for the developing sperm cells - moving them towards the lumen of the seminiferous tubule as they develop until maturity when they are released. The Sertoli cell also reduces motility and capacitation(initiation of the acrosome reaction) of the sperm cells so viability is maintained.

Related Topics:
Sertoli cell - Lumen - Seminiferous tubule - Capacitation

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Spermatozoa are produced in seminiferous tubules in the testes. They start off as spermatogonia, undergoing mitosis becoming a type A spermatogonium or a type B spermatogonium.

Related Topics:
Seminiferous tubule - Testes - Spermatogonia - Mitosis

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Type B spermatogonia become primary spermatocytes. Primary spermatocytes go through a meiotic division to become secondary spermatocytes, which undergo another mit-otic division to become spermatids. Type A spermatogonia stay as spermatogonia, and do not change. They act as stem cells and will divide again producing more Type A and B cells.

Related Topics:
Meiotic - Spermatid - Stem cell

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The primary spermatocytes contain twice the DNA of a normal body cell (2 × 2N). Each primary spermatocyte divides into two secondary spermatocytes containing two sets of chromosomes (2 × 1N).

Related Topics:
DNA - Chromosome

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The secondary spermatocytes then divide into two spermatids, each containing just one set of chromosomes (1N), half the DNA needed to make a human being. (The other half will come from the ovum at fertilisation).

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The spermatids at this point are still round cells. During the process called spermiogenesis the sperm extrude tails, repackage DNA into a head, cap the head with a lysosome-like acrosome and construct an energy transducing neck region of tightly packed mitochondria to finally become mature testicular spermatozoa. They are then released into the lumen of the seminiferous tubule and travel with fluid from the testis into the epididymis for further maturation processes.

Related Topics:
Acrosome - Mitochondria - Epididymis

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Morphological, physiological, and biochemical changes are among the maturation steps the sperm undergoes in the epididymis. During migration through the epididymis the sperm sheds excess cytoplasm, released as the cytoplasmic droplet. In transit, it also gains the capacity for motility. Finally, while traversing the epididymis the sperm's source of energy gradually changes from primarily glycolysis to oxidative respiration. By the time the mature sperm exits the epididymis, it is streamlined, motile, and has sufficient energy to draw near to an ovum and fertilize it.

Related Topics:
Cytoplasm - Glycolysis - Oxidative respiration

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See also: folliculogenesis

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