Semen in Human Reproduction

Semen is also called seminal fluid. Semen definition - it is the organic fluid ejaculated from the male reproductive tract which contains sperm cells. It also contains liquid to form a seminal plasma which helps to keep sperm viable. To define semen, it is clear that semen is made from the combination of different fluids having amino acids, citrate, enzymes, fructose, galactose, acid phosphate, mucus and spermatozoa. The total amount of semen after each ejaculation of human male averages between 2 and 5 ml. A normal human ejaculates about 200 to 300 million sperm. Semen contains degenerated cells moved from the network of tubules and ducts through which the semen has passed. The testicles constantly produce sperm from when they hit puberty throughout their entire life. And thus each millilitre of sperm on average contains between 40 and 60 million sperm cells, which means that each ejaculation can total 300 million sperm. In mature males, spermatozoa are produced by testes that contribute only ten percent of the total semen.

Appearance of Human Semen

A normal semen sample has a grey-opalescent appearance. If the semen is left open for some time, the semen initially clots or coagulates over the first hour and then it becomes liquefied.

• Volume: The semen volume per ejaculation is around 2 ml to 3 ml or more. The sperms constitute approximately 10% of semen volume.

• Smell: Semen normally smells like chlorine or a fishy odour.

• Taste: Semen normally tastes slightly sweet due to a high content of fructose and also the taste of semen keeps on changing slightly from person to person and may be affected by diet.

• pH of Semen: The pH level of semen should be 7.2 to 7.8, and is the normal pH of the body. If the pH range is lower than 7.2, it may mean that there is a low sperm count or malformations in the reproductive tract and it indicates a urinary tract infection, if the pH range is above 7.8.

• Sperm Concentration: The usual range of sperm in semen samples is 20 million/ml or more and a total count of 40 million or more than that.

After going through semen definition, let us have a look at the diagram, components, and storage of semen. 

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• Composition of Semen: The semen fluid is mainly generated from the secretions of male reproductive organs. Semen consists of potassium, enzymes, citric acid, phosphorylcholine, free amino acids, fructose, prostaglandin, and zinc. 46% to 80%of the fluid is given out by the seminal vesicles, 13% to 33% by the prostate gland, 5% from the testicles and epididymis, and 2% to 5% from Bulbourethral and urethral glands.

Components of Semen 

During ejaculation, the sperm passes through the ejaculatory duct and mixes with different fluids secreted by seminal vesicles, the prostate gland, and bulbourethral glands to form semen. Seminal vesicles secrete the yellow colour fluid which is viscous in nature and rich in fructose. Seminal vesicles make up to 70% of the total semen. The secretion of the prostatic gland is a whitish thin fluid containing proteolytic enzymes, citric acid, phosphatase, and lipids. The bulbourethral gland secretes the fluid which helps in the lubrication of the lumen in the urethra. 

Semen fluid containing seminal plasma provides protection and nutrition to the spermatozoa during their journey to the reproductive duct tract. The environment of the vagina is generally hostile in nature for spermatozoa, as it is very acidic, viscous and patrolled by immune cells. The components of the seminal plasma will reduce the hostile nature of the vagina. The smell and flavour of the semen are due to the basic amines like putrescine, spermine, spermidine, and cadaverine.

Healthy Semen 

Generally, healthy semen is a cloudy white or grey fluid with having jelly-like consistency. But sometimes it is yellow in colour and smells (bleach) due to the presence of alkaline substances. These substances are important to fight against the acidic nature of the female genital tract. Healthy male semen consists of approximately 200 -500 million sperm are released in each ejaculation.

Semen Volume 

The amount of semen ejaculated per ejaculation is known as semen volume. According to the international society for sexual medicine, the average semen volume ejaculated ranges from 1.25 to 5 millilitres. In simple words, the amount is equal to one quarter to one teaspoon of semen. Always keep in mind that the volume of semen varies from one time to another time.

Storage 

Highly fertile semen can be stored for seven days. Semen can be stored in diluent for example (IVT) Illini Variable Temperature diluent which is composed of sugar, salts, antibacterial agents, and gassed with carbon dioxide. There are also techniques for longer storage duration like semen cryopreservation. The longest semen preservation to date reported is for 21 years.

Did You Know?

How is semen produced? Semen is not produced by a single gland. Semen consists of a combination of different components like sperm and different fluids secreted by glands like seminal vesicles, the prostate gland and the bulbourethral glands.

When a person is about to ejaculate, semen travels through the tube called vas deferens. While travelling, it picks some sugary substance that acts as rocket fuel. Other fluids are also added to it while travelling to the urethra. The finished product will have only 10% of sperm and the rest consists of enzymes, Vitamin C, Calcium, Protein, Sodium, Zinc, Citric acid, and fructose sugar.