4.2 Getting the spermatozoa ready

The seminal plasma

The seminal plasma mediates the chemical function of the ejaculate.The mixing together of the various glandular fractions leads to a coagulation of the fresh ejaculate in the rear vaginal cavity within a minute. In this way a deposit of spermatozoa is formed in the vagina. After about 15-20 minutes the coagulated ejaculate becomes a fluid again.

Due to its slight alkalinity (light alkaline buffer) it is also responsible for creating a milieu beneficial for the spermatozoa in a vaginal surrounding that is normally maintained acidic.

The seminal plasma has to fulfill the following tasks:
  • Creation of an alkaline buffered milieu in the vagina
  • Coagulation of the ejaculate and creating a sperm deposit in the vagina
  • Coating the sperm cells with capacitation inhibitors
  • Activation and augmenting the motility of the sperm cells
  • Supplying nutrients for the sperm cells
  • Fluidizing the ejaculate after 15-20 minutes

The secretions of the seminal gland contribute the main portion of the seminal plasma.

The seminal gland's secretion contains various proteins and fructose as energy suppliers for sperm motility and is also responsible for making the largest proportion of the alkaline buffer.
The prostate secretion contains protease for fluidizing the ejaculate, which supports the motility and the further maturation of the spermatozoa.

The exact composition of the seminal plasma can be taken from the following table.

Composition of the seminal plasma
Amount 2-6 ml
pH value 7-8 (light alkaline buffer)
Seminal gland secretion 75% of the volume, alkaline fructose-rich secretion (1.5-6.5 mg/ml fructose), phosphorylcholine, ascorbic acid
Prostate secretion 20%-25% of the volume, biogenic amine (spermidine, spermine), citric acid, cholesterol, phospholipids, protease to fluidize the ejaculate (fibrinolysin, fibrinogenase)
Further components Phosphate and bicarbonate as buffer, prostaglandin, hyaluronidase, cell detritus from Sertoli's cells, cells from preliminary stages of the spermiogenesis, lymphocytes.

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