Wednesday 11 July 2012

SEMEN PHYSIOLOGY

SEMEN PHYSIOLOGY
Depending on the species, spermatozoa can fertilize ova externally or internally. In outside fertilization, the spermatozoa fertilize the ova directly, outside of the female's sexual organs. Female fish, for example, spawn ova in to their aquatic surroundings, where they are fertilized by the semen of the male fish.

In the coursework of internal fertilization, however, fertilization occurs inside the female's sexual organs. Internal fertilization takes place after insemination of a female by a male through copulation. In low vertebrates (amphibians, reptiles, birds & monotreme mammals), copulation is achieved through the physical mating of the cloaca of the female & male. In marsupial & placental mammals, copulation occurs through the vagina.



HUMAN SEMEN COMPOSITION
During the process of ejaculation, sperm passes through the ejaculatory ducts and mixes with fluids from the seminal vesicles, the prostate, and the bulbourethral glands to form the semen.

The seminal vesicles produce a yellowish sticky liquid rich in fructose and other substances that makes up about 70% of human semen.

Sertoli cells, which nurture and support developing spermatocytes, secrete a liquid in to seminiferous tubules that helps transport sperm to the genital ducts. The ductuli efferentes possess cuboidal cells with microvilli and lysosomal granules that alter the semen by reabsorbing some liquid.

The prostatic secretion, influenced by dihydrotestosterone, is a whitish (sometimes clear), narrow liquid containing proteolytic enzymes, citric acid, acid phosphatase and lipids.

Seminal plasma of humans contains a complex range of organic and inorganic constituents.

One time the semen enters the ductus epididymis the principle cells, which contain pinocytotic vessels indicating liquid reabsorption, secrete glycerophosphocholine which most likely inhibits premature capacitation. The accessory genital ducts, the seminal vesicle, prostate glands, and the bulbourethral glands, produce most of the seminal liquid.

The normal surroundings of the vagina is a hostile for sperm cells, as it is acidic (from the native microflora producing lactic acid), sticky, and patrolled by immune cells.

The seminal plasma provides a nutritive and protective medium for the spermatozoa in the coursework of their journey through the female reproductive tract.

The parts in the seminal plasma try to compensate for this hostile surroundings. Basic amines such as putrescine, spermine, spermidine and cadaverine are responsible for the smell and flavor of semen.

These alkaline bases counteract the acidic surroundings of the vaginal canal, and protect DNA inside the sperm from acidic denaturation.

A 1992 World Health Organization document described normal human semen as having a volume of two ml or greater, pH of 7.2 to 8.0, sperm concentration of 20x106 spermatozoa/ml or more, sperm count of 40x106 spermatozoa per ejaculate or more, & motility of 50% or more with forward progression (categories a & b) of 25% or more with fast progression (section a) within 60 minutes of ejaculation.

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