Definition of  Semen

The fluid of a man’s ejaculation. In a fertile man about 5 percent of the semen content is sperm; in a man who has had a vasectomy semen does not contain sperm.

The seminal vesicles and the prostate gland produce the milky fluid of semen, which is primarily a water base that contains proteins, sugars (notably fructose and some glucose), lipids (fatty acids), electrolytes, and prostaglandins.

The bulbourethral glands, also called Cowper’s glands, add a gelatinous secretion to the semen that thickens it. Semen may flow back into the bladder rather than out of the penis (retrograde ejaculation) in a man with a prostatectomy (surgery to remove the prostate gland).

The electrolytes protect sperm on their journey through the vagina and into the uterus. The sugars, particularly fructose, and lipids provide nutrition for the sperm. Vaginal secretions are highly acidic and deadly to sperm. The thickness of semen helps contain and insulate sperm as they travel through the vagina, though the semen thins by the time it reaches the uterus to release the sperm.

The electrolytes in semen make it highly alkaline, helping neutralize the vaginal environment to improve sperm survival. Prostaglandins help suppress the immune response, the natural reaction of the woman’s immune system to the presence of the sperm. The semen also has the ability to carry various pathogens such as viruses and bacteria that can spread sexually transmitted diseases (stds).

Semen Analysis

Semen analysis is a laboratory examination of a semen sample to measure the concentrations of its ingredients and the number and characteristics of the sperm.

Alcohol consumption, cigarette smoking, and frequency of ejaculation are among the factors that influence the volume and content of semen.

semen volume1.5 to 6.5 milliliters
sperm count20 to 250 million per milliliter
pH7.1 to 8.0
fructose30 milligrams per milliliter


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