PHY2011 Final: PHY2011

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Producing sperm: spermatogenesis
In humans, this process takes ~64-72 days to complete (spermatogonia à sperm)
Requires testosterone and FSH (follicle stimulating hormone)
o Receptors are in the Sertoli cells that support the spermatogenic cells
o No receptors for T or FSH on the germ cells
Can be divided into phases
i. Spermatogonial phase (mitosis)
ii. Spermatocyte phase (meiosis)
iii. Spermatid phase (spermiogenesis)
Spermatocyte phase (meiosis)
During meiosis two divisions occur (meiosis I & II)
Primary spermatocytes initially replicate their DNA, then enter meiosis I
Homologous chromosomes then pair up & closely aligned parts of chromosomes are exchanged
Each primary spermatocyte divides to form two secondary spermatocytes
Secondary spermatocytes then rapidly undergo meiosis II
Spermatids do not divide, instead of mature into spermatozoa via by spermiogenesis
Spermatogenic cycle: mouse
Spermatogenic cycle: rat
Spermatogenic wave duration
Species
Spermatogenesis (d)
Seminif. Epithel. Cycle (d)
Human
64
16
Cattle
54
13.5
Rat
48
12.9
Mouse
34
8.6
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Document Summary

3 major regions: head: genetic region; nucleus and helmet-like acrosome containing hydrolytic enzymes that enable the sperm to penetrate an egg, midpiece: metabolic region; mitochondria, tail: locomotor region; flagellum. Final stage of spermatogenesis(cid:0) no cell division involved (cid:0) Key events: formation of the acrosome, nuclear changes, development of flagellum, reorganisation of organelles, cytoplasm largely discarded (residual body) (cid:0, spermatozoa released from sertoli cell, process of spermiation, released spermatozoa remain non-motile. Oogenesis: occurs in the ovary, unlike men who can continually make new germ cells (sperm) from adolescence onwards. Lecture objectives: describe the steps involved in fertilisation, describe the structure and functions of the placenta and the amniotic fluid, understand hormonal control of pregnancy and maternal adaptations, describe the hormonal control of lactation. Initially we have the ovulated egg (surrounded with zona pellucida and corona radiate granulosa cells released when sperm interacts) Binding: sperm"s membrane binds to the oocyte"s sperm-binding receptors.