Composition of Human Semen

Semen is the grayish white bodily fluid which is emitted from the urethra during ejaculation. Semen contains sperms which can fertilize the female ova to produce new life. The average volume of semen in an ejaculation is about 2-5 ml. An ejaculation can contain 40-600 million sperms depending on the volume of the ejaculation and the length of time for which the ejaculation lasts.Semen is typically produced by the secretions from the male reproductive organs. During ejaculation, the sperms pass through ejaculatory ducts and mix with the fluids from reproductive organs such as testes, seminal vesicles, prostate gland, and the bulbourethral glands to form the semen.

The Contributions of the Different Reproductive Organs

The contributions of the different reproductive organs and their respective inputs towards forming the human semen are listed below:

• Testes: The secretions from the testes accounts for 2-5% of the semen. The testes produce about 200-500 million spermatozoa or sperms during an ejaculation.

• Seminal Vesicles: The seminal vesicles produce a viscous fluid which is yellowish in color and is rich in fructose. The seminal fluids contribute about 65-75% of the semen composition. Seminal fluid also contains citrate, amino acids, enzymes, and flavin. Seminal fluid provides the sugar required by the sperms for energy. Seminal fluids also contain prostaglandins which are important for suppressing the female immune system against the semen and thereby help in facilitating fertilization. Seminal fluids also contain vitamin C, proteins, and phosphorylcholine.

• Prostate Glands: The secretions from the prostate gland contribute 25-30% of the semen. The prostatic secretions contain citric acid, prostate-specific antigen, acid phosphatase, zinc, and proteolytic enzymes. The zinc content in the prostatic secretions are vital for stabilizing chromatin which contains the DNA in the sperms. Deficiency of zinc can lead to lower fertility as it can render the sperms fragile.

• Bulbourethral Glands: The bulbourethral gland secretions account for less than 1% of the semen content. These secretions provide the mucus which is important for the mobility of the sperm in the cervix and the vagina so that the sperms can swim. The mucus also provides a jelly like consistency to the semen.

The basic constituents of Semen

• Protein: Semen basically comprises of albumin protein structures and free amino acids. Around 50% by weight of semen content is composed of proteins.
• Fructose: The seminal fluid comprises about 2-5 mg of fructose and the amount of fructose is higher in men who are more fertile. Lower fructose levels in semen can lead to infertility.
• Catecholamines: The semen contains three main catecholamines, namely, adrenaline, noradrenaline, and dopamine. The levels of these three catecholamines determine vital semen parameters such as sperm count, sperm mobility, and overall fertility.

Other Physiological Characteristics of Semen

• Physical Appearance of Semen: Semen is grayish white in color and has an opalescent appearance. When left open in the air, semen tends to coagulate at first and then liquefies.
• Smell: Semen often smells like chlorine and at times can have a fishy odor.
• pH of Semen: The pH levels of semen can range between 7.2 to 7.8. A pH level lower than 7.2 might indicate a lower sperm count. A higher pH value often indicates a urinary tract infection.
• Volume: The normal semen volume per ejaculation is around 2-3 ml.

References:

• “A Review of the Physical and Chemical Properties of Human Semen and the Formulation of a Semen Simulant," by Derek H. Owen, et al. Published in January 2013, Volume 26, Issue 4 of the Journal of Andrology, accessed on 27 April 2015. Retrieved from: http://dx.doi.org/10.2164/jandrol.04104