Semen is the fluid that is ejaculated at the time of orgasm.

The average volume of semen per ejaculate is 2.5 to 3.5 mL (after several days of continence).

There is a rapid decline in the volume of semen and the sperm count with repeated ejaculation.

The semen contains sperms and secretions from the prostate, seminal vesicles, urethral  and Cowper’s glands .

There are normally 100 million sperms per mL of semen.

It is important to note that almost all men with sperm counts under 20 million/mL are sterile. 50% of men with sperm counts of 20 -40 million are also sterile.

There is a very high concentration of prostaglandins in the semen and their functions in semen are not fully understood.

Motility of Sperms:

Human sperms move at the speed of about 3mm/ min through the female genital tract. Therefore sperms reach the uterine tubes about 30 to 60 minutes after copulation.

Summary of the Composition of Normal Human Semen

Colour: White, opalescent

Specific gravity: 1.028

pH: 7.35-7.50

Sperm count: Average about 100 million/mL, with fewer than 20% abnormal forms.

Other components:

From seminal vesicles (constitutes 60% of total volume):

Fructose (1.5-6.5 mg/ml)

Phosphorylcholine

Ergothioneine

Ascorbic acid

Flavins

Prostaglandins

From Prostate( Constitutes 20% of total volume):

Spermine

Citric acid

Cholesterol and phospholipids

Fibrinolysin and fibrinogenase

Zinc

Acid Phosphatase.

Buffers:

Phosphate

Bicarbonate

Component that cannot be classified above:

Hyaluronidase

References:

Pages 412 to 414 Chapter 23, The Gonads; Development and Function of the Reproductive System. Review of Medical Physiology 20th Edition by William F Ganong.

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