Male reproductive system anatomy and physiology
Anatomy of the male reproductive system
The male reproductive system is responsible for producing, transporting, and sustaining sperm cells. The sperm cells are called sex cells or gametes. A sperm cell contributes half of the genes of the new offspring. The gametes are produced in organs called gonads. Gonads are considered primary or essential sex organs. They are also responsible for producing hormones. The other organs in the reproductive system are secondary or accessory organs.
Testis
The primary reproductive organs in the male are the testes. Each testis is oval and measures about 1.6 inches (4 cm) long and 1 inch (2.5 cm) wide. The testes are surrounded by a white, fibrous capsule and are suspended together in a sac outside the body called the scrotum. Testes produce the gametes called spermatozoa. Spermatozoa are made up of three parts:
- Head: Contains the chromosomes in the nucleus; the acrosome covers the head of the sperm and contains enzymes to help penetrate the ovum.
- Midpiece: Contains mitochondria, which produce energy for movement.
- Tail or flagellum: Used for movement.
Spermatogenesis
The formation of sperm is called spermatogenesis. The spermatozoa are formed in a series of tightly coiled tiny tubes in each testis called the seminiferous tubules. From the seminiferous tubules, the formed spermatozoa travel to the epididymis, where they mature and are stored. The epididymis is a coiled tube almost 20 feet (6 meters) long and rests on top of and behind each testis.
From the epididymis, the spermatozoa move into the vas deferens or ductus deferens. Each vas deferens is a muscular tunnel about 18 inches (45 cm) long that connects to the base of the epididymis and passes along the side of the testis. The vas deferens travels into the pelvic cavity to just behind the bladder. Spermatozoa can stay in the vasa deferentia for several months in an inactive state.
The prostate gland is the size of a walnut and is found below the bladder in males. It surrounds part of the urethra. The prostate is considered a reproductive organ but it also affects the urinary system. When the prostate increases in size (as with benign prostatic hyperplasia [BPH]), it can obstruct the urethra, blocking the urine flow.
The prostate gland, seminal vesicles, and Cowper glands (or bulbourethral glands) provide fluid either to nourish or aid in motility and lubrication. The sperm and the fluid together make up a substance called semen. The ejaculatory duct begins where the seminal vesicles join the vas deferens, and this “tube” joins the urethra.
Urethra and penis
The urethra is found within the penis and transports the semen to the outside of the body. The urethra also transports urine to the outside of the body.
The body is the shaft of the penis. The penis is composed of three columns of highly vascular erectile tissue. There are two columns of corpora cavernosa and one of corpus spongiosum that fill with blood through the dorsal veins during sexual arousal. During ejaculation, the sperm exit through the glans penis, the tip of the penis. At birth, the glans penis is surrounded by a fold of skin called the prepuce or foreskin, which can be removed by circumcision.
Physiology of the male reproductive system
Several hormones are involved in the male reproductive system, including testosterone, follicle-stimulating, and luteinizing hormones.
Testosterone
At puberty , the interstitial cells in the testicles begin to produce testosterone . Testosterone is responsible for maintaining reproductive structures and for the development of sperm cells. Testosterone also helps with the development of secondary sex characteristics, which include a deep voice, broad shoulders, narrow hips, and additional body hair.
Follicle-stimulating and luteinizing hormones
In addition to testosterone, follicle-stimulating hormone (FSH), secreted by the pituitary gland, promotes the formation of spermatozoa. The pituitary gland also produces luteinizing hormone (LH), which stimulates the interstitial cells to produce testosterone. Under the influence of these hormones, sperm cells develop and move into the epididymis to mature.
Life span changes of the male reproductive system
The male reproductive system changes with age. The following sections discuss the changes to the male reproductive system over the life span.
Changes with puberty
The testicle develops in the abdomen and starts its descent into the scrotum in utero around the seventh month. At puberty, usually between ages 9 to 15, the pituitary gland secretes luteinizing hormone, which stimulates the testicles to start producing testosterone. Testosterone is responsible for the development of sperm and the secondary sex characteristics. The male secondary sex characteristics include a deep voice, broad shoulders, narrow hips, and additional body hair.
Changes in older adults
As a male gets older, gradual aging changes begin. Changes occur in the testicular tissue, sperm production, and erectile function. The testicular tissue mass decreases. Testosterone levels gradually decrease and may cause issues with erections. The testes continue to create sperm but at a slower rate. Benign prostatic hyperplasia can occur, leading to issues with urine retention, ejaculation, and a slowed urine stream.