Semen Physiology Notes

Semen

Nature Of Semen

Semen is a white or grey fluid that contains spermatozoa (sperms). It is the collection of fluids from the testes, seminal vesicles, prostate gland, and bulbourethral glands. Semen is discharged during sexual act and the process of discharge of semen is called ejaculation.

• Testes contribute sperm. The prostate secretion gives a milky appearance to semen. And, the secretions from seminal vesicles and bulbourethral glands provide mucoid consistency to semen.
• At the time of ejaculation, human semen is liquid in nature. Immediately, it coagulates and after some time it undergoes a secondary liquefaction.

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• The fibrinogen secreted from the seminal vesicle is converted into a weak coagulum by the clotting enzymes secreted from the prostate gland.
• The coagulum is liquefied after about 30 minutes, as it is lysed by fibrinolysin. Fibrinolysin is the activated form of fibrinolysin produced in the prostate gland. When semen is ejaculated, the sperms are nonmotile due to the viscosity of the coagulum. When the coagulum dissolves, the sperms become motile.

Properties Of Semen

1. Specific gravity: 1.028
2. Volume : 2-6 mL per ejaculation
3. Reaction: It is alkaline with a pH of 7.5. The alkalinity is due to the secretions from the prostate gland.

Composition Of Semen

Semen contains 10% sperms and 90% of fluid part which is called seminal plasma. The seminal plasma contains the products from the seminal vesicle and prostate gland. It also has a small amount of secretions from the mucus glands, particularly the bulbourethral glands.

Sperms

• The total count of sperm is about 100-150 million/mL of semen. Sterility occurs when the sperm count falls below 20 million/mL.
• Though the sperm can be stored in the male genital tract for longer periods, after ejaculation the survival time is only about 24-48 hours at a temperature equivalent to body temperature.
• The rate of motility of sperm in the female genital tract is about 3 mm/minute. The sperm reach the fallopian tube in about 30-60 minutes after sexual intercourse. The uterine contractions during the sexual act facilitate the movement of sperm.

Structure of Spermatozoon

Spermatozoon (pleural = spermatozoa) is the male reproductive cell, developed in the testis. It is also called the sperm. The matured spermatozoon is 60 p Song.

Each spermatozoon consists of four parts:

1. Head
2. Neck
3. Body
4. Tail.

Head

• The head of the sperm is oval in shape (in front view), with a length of 3-5 p and a width of up to 3 p. The anterior portion of the head is thin.
• The head is formed by a condensed nucleus, a thin cytoplasm, and a thin cell membrane. The anterior two-thirds of the head is like a thick cap and it is called an acrosome (Galea capitis).
• Acrosome develops from the Golgi apparatus and it is made up of mucopolysaccharide and acid phosphatase. It also contains hyaluronidase and proteolytic enzymes which are essential for the sperm to fertilize the ovum.

Neck

• The head is connected to the body by a short neck. Its anterior end is formed by a thick disc-shaped anterior end knob, which is also called a proximal centriole.
• The posterior end is formed by another similar structure known as the posterior end knob. It gives rise to the axial filament of the body. Often, the neck and body of sperm are together called midpieces.

Body

• It is cylindrical with a length of 5-9 p and a thickness of 1 |j. The body of the sperm consists of a central core called an axial filament covered by a thin cytoplasmic capsule.
• The axial filament starts from the posterior end knob of the neck. It passes through the body and a perforated disc called the end disc or end ring centriole. Finally, the axial filament reaches the tail as an axial thread.
• In the body, the axial filament is surrounded by a closely wound spiral filament consisting of mitochondria.

Tail

The tail of the sperm consists of two segments:

1. The chief or main piece of tail: It is enclosed by a cytoplasmic capsule and has an axial thread. It is 40-50  long
2. The terminal or end piece of the tail: It has only the axial filament.

Products From Seminal Vesicles

The products of seminal vesicles are given.

Products From Prostate Gland

The products of the prostate gland are given.

Semen Analysis

Analysis of semen evaluates the qualities of semen which is useful to investigate infertility.

The parameters that are measured during semen analysis are:

1. Volume
2. Reaction and pH
3. Liquefaction
4. Sperm count
5. Morphology of sperm
6. Motility of sperms
7. Pus cells and RBCs
8. Fructose level.

Qualities Of Semen Required For Fertility

The minimum required qualities of semen for fertility are:

1. The volume of semen per ejaculation must be at least 2 mL
2. Sperm count must be at least 20 million/mL
3. The number of sperms in each ejaculation must be at least 40 million
4. 75% of sperms per ejaculation must be alive
5. 50% of sperm must be motile
6. 30% of sperms must have a normal shape and structure
7. Sperms with head defects must be less than 35%
8. Sperms with midpiece defects must be less than 20%
9. Sperms with tail defects must be less than 20%.

Applied Physiology

Azoospermia

Azoospermia is a condition characterized by a lack of sperm in semen. It is a congenital disease. It is also caused by excess use of corticosteroids and androgens.

Oligozoospermia

It is a low sperm count with less than 20 million of sperms /mL of semen. Oligozoospermia causes infertility.

Teratozoospermia

Teratozoospermia is a condition characterized by the presence of sperms with abnormal morphology. It is also called teratospermia. It occurs in Crohn’s disease, Hodgkin’s, disease, and celiac disease. The abnormal morphology of sperm results in infertility.

Aspermia

It is the lack of semen. It occurs due to retrograde ejaculation. Retrograde ejaculation is the entrance of semen into the urinary bladder instead of entering the urethra. It is due to dysfunction of the sphincter of the bladder which is caused by prostatic surgery or excess use of drugs. Aspermia leads to infertility.

Oligospermia

Oligospermia is a genetic disorder characterized by low volume of semen.

Hematospermia

Hematospermia is the appearance of blood in sperm. It occurs due to an infection of the urethra or prostate. It is also common in congenital bleeding disorders.