Semen
Semen is a fluid released from the male reproductive system during ejaculation, consisting of spermatozoa (sperm) and secretions from various glands. It typically measures 2 to 5 milliliters and has an alkaline pH ranging from 7.2 to 7.8. Sperm only makes up about 5% of semen, with concentrations generally between 20 to 150 million sperm per milliliter. The seminal fluid, which constitutes about 60% of the volume, provides nutrients like fructose to support sperm energy and contains prostaglandins that facilitate muscle contractions, aiding sperm movement. Other components include enzymes from the prostate that activate sperm motility and antibiotic agents that help protect against infections.
Disorders related to semen can lead to infertility, affecting approximately 15% of males, often linked to low sperm counts or motility. Additionally, conditions such as prostate hypertrophy and prostate cancer are notable concerns, particularly in older men. Prostate health issues can lead to urinary complications and may require various treatments. Understanding these aspects of semen is essential for comprehending male reproductive health and addressing associated medical conditions.
Subject Terms
Semen
Biology
Also known as: Ejaculate
Anatomy or system affected: Genitals, glands, reproductive system
Definition: The fluid ejaculated by the male at orgasm, consisting of sperm and secretions from accessory glands.
Structure and Functions
Semen is released from the male reproductive system during ejaculation. It is a milky white, sticky fluid of 2 to 5 milliliters with an alkaline pH (7.2–7.8). It consists of spermatozoa (sperm) produced in the testes plus secretions of accessory glands: paired seminal vesicles that lie on the posterior surface of the bladder, the singular prostate gland that surrounds the urethra, and paired bulbourethral glands that lie just inferior to the prostate.
Sperm comprises only 5 percent of the semen, with 20 to 150 million sperm per milliliter. Seminal fluid contributes about 60 percent of the volume and contains high levels of fructose used by the sperm as an energy source. Seminal fluid also contains prostaglandins that stimulate smooth muscle contraction. This helps propel the semen through the urethra for release and aids in movement of sperm upward in the female reproductive tract. Two proteins, semenogelin I and II, inhibit sperm motility and protect the semen in the male urethra. The semenogelins cause the semen to form a temporary coagulate when deposited in the vagina. After fifteen to thirty minutes, the coagulum dissolves.
The prostate contributes about 30 percent of semen volume as a milky, slightly acidic fluid. It is high in citrate, used as a nutrient by the sperm, plus several enzymes, including a protease called prostate-specific antigen (PSA). PSA hydrolyzes the semenogelins and helps to activate the motility of sperm. Prostatic fluid also contains seminal plasmin, an antibiotic active against Escherichia coli (E. coli), and several other bacteria that can cause urinary tract infections. The bulbourethral glands produce a thick, alkaline mucus that contributes only about 5 percent of semen volume. It is secreted in advance of ejaculation in order to neutralize any residual acidity from urine in the urethra. It also acts as a lubricant on the head of the penis to aid in vaginal penetration.
Disorders and Diseases
Disorders relating to semen involve pathologies of the individual glands. Infertility occurs in approximately 15 percent of males when there is a sperm count less than 20 million per milliliter, low sperm motility, or high levels of abnormal sperm. Decreased counts may be a result of testicular tumors, trauma, radiation, or infection with mumps virus. Infertility can also occur with autoimmunity when antibodies that bind to sperm are produced. Testicular cancer usually requires surgical removal of the testis. Semen can also transmit sexually transmitted infections, including human immunodeficiency virus (HIV).
Prostate hypertrophy, noncancerous enlargement of the prostate, occurs frequently in men over the age of fifty. It causes partial urethral obstruction, resulting in urinary hesitation, frequent urination, and possible painful urination. It may be treated with medication or corrected surgically. Prostate cancer occurs in one of every six men in their lifetime. Treatments include surgery, radiation, or hormonal therapy. Serum PSA increases in prostate cancer, and monitoring of PSA levels is important.
Bibliography
Basu, S. C. Male Reproductive Dysfunction. 2nd ed., Jaypee Brothers Medical Publishers, 2011.
Lilja, Hans, David Ulmert, and Andrew J. Vickers. “Prostate-Specific Antigen and Prostate Cancer: Prediction, Detection, and Monitoring.” Nature Reviews Cancer, vol. 8, no. 4, Apr. 2008, pp. 268–278.
Marieb, Elaine N., and Katja Hoehn. Human Anatomy and Physiology. 9th ed., Pearson, 2013.
Poiani, Aldo. “Complexity of Seminal Fluid: A Review.” Behavioral Ecology and Sociobiology, vol. 60, no. 3, July 2006, pp. 289–310.
"Prostate Enlargement: Benign Prostatic Hyperplasia." National Institute of Diabetes and Digestive and Kidney Disease, 2014, www.niddk.nih.gov/health-information/urologic-diseases/prostate-problems/prostate-enlargement-benign-prostatic-hyperplasia. Accessed 15 July 2023.
"Semen Analysis." Lab Tests Online, 20 Nov. 2018, labtestsonline.org.uk/tests/semen-analysis. Accessed 15 July 2023.
"Spermatoceles." Urology Care Foundation, www.urologyhealth.org/urology-a-z/s/spermatoceles. Accessed 15 July 2023.