Reproductive System, Male

The normal male reproductive system is composed of numerous anatomical structures, including the testis, the excretory ducts, the auxiliary glands, the penis, and the various hormones that control reproductive functions.

The testis is responsible for the production and maturation of sperm in a process called spermatogenesis. It is also the site of synthesis and secretion of androgens (male sex hormones). The testes (plural) develop in the abdomen and descend into the scrotum in the normal male. The scrotum is a muscular sac in which the testes hang from the spermatic cord.

The testis is subdivided into the tubular compartment and the interstitial compartment. The tubular compartment is composed of up to 900 seminiferous tubules, which are populated by three main types of cells: germ cells, peritubular cells, and Sertoli cells. Germ cells become mature sperm in the spermatogenic process. Peritubular cells produce various factors that aid in the transportation of mature sperm to the epididymis. Sertoli cells secrete various factors that determine the sperm production and testis size of an adult male.

Androgens are produced in the interstitial compartment of the testis. Leydig cells are responsible for the production and secretion of testosterone. Immune cells such as macrophages and lymphocytes are also found in the interstitial compartment and aid in the proliferation and hormone production of Leydig cells.

Sperm cells are composed of a head (containing the nucleus and acrosome), the body (containing the mitochondria, or energy-producing organelles), and the tail. The nucleus contains the cell's genetic material (chromatin) while the acrosome contains enzymes that are capable of penetrating the protective layers around the egg. The mitochondria provide energy for tail motility; this is essential for movement of the sperm through the female reproductive tract.

The auxiliary glands include two bulbourethral glands, one prostate, and two seminal vesicles. These glands contribute the secretions that compose semen. The bulbourethral glands (also called the glands of Cowper) secrete a fluid that lubricates the urethra prior to ejaculation. The prostate secretes a fluid rich in zinc, citric acid, choline, and various proteins. The secretions of the seminal vesicle are high in fructose (an energy source for sperm) and prostaglandins (fatty-acid derivatives).

The penis is the male organ of sexual reproduction and consists of three elongated bodies that cause erection, the two corpora cavernosa and the corpus spongiosum. These tissues become engorged with blood when stimulated by the nervous system during arousal. Blood is supplied by the superficial and deep arterial systems (which carry blood to the penile skin and erectile tissue, respectively). The urethra runs through the corpus spongiosum to the glans penis (distal end of the penis). The organ is covered with loose skin that forms the prepuce (foreskin) over the glans penis.

Normal reproductive function is dependent on complex interactions between various hormones. A portion of the brain called the hypothalamus secretes releasing hormones that travel to the pituitary gland, located at the base of the brain. The secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus triggers the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. LH stimulates testosterone production by Leydig cells in the testis, and FSH promotes spermatogenesis.

The male sexual act can be divided into three main steps: erection, emission, and ejaculation. Erection is the result of increased blood flow to the erectile tissues of the penis; stimulation of the nervous system during arousal causes a release of acetylcholine (a neurotransmitter) that in turn causes vasodilation (increase in the diameter of blood vessels). Emission is the passage of sperm and secretions into the urethra mediated by release of the hormone adrenaline. Ejaculation occurs when the sperm are forced from the urethra by contraction of the bulbocavernous muscles. A release of noradrenaline causes the blood vessels in the penis to contract, decreasing blood flow and resulting in detumescence (loss of erection).

In order to fertilize the ovum, ejaculated sperm must move into the vaginal tract, pass through the cervix, survive in the uterus, and enter the fallopian tubes. Usually only healthy, motile sperm will reach the ovum and have the opportunity to fertilize it. Numerous protective layers (including the oolemma, the zona pellucida, and the zona radiata) surround the ovum, and sperm cells must penetrate each of these layers for fertilization to occur. Binding of a sperm cell to the zona pellucida induces the acrosome reaction, which permits the sperm to penetrate the zona pellucida and reach the egg membrane. The sperm and egg membranes fuse to form a zygote, and subsequent reactions prevent the binding of additional sperm cells to the egg membrane.

Diseases of the male reproductive system are classified based on the localization (e.g., testis, pituitary gland, etc.) and cause (e.g., congenital malformation, cancerous tumor, etc.) of the disorder.

Some common examples of andrological disorders include:

Regular exercise is important for the physical, mental, and emotional health of men. Exercise promotes:

Men most often stick with an exercise program when they enjoy the activity, whether as an individual, with a partner, or with a group or team. Exercise can take place at home, outdoors, at a health club or fitness center, or as part of an after-work group activity. Working out with a friend, utilizing a personal trainer, competing, or setting personal goals can help maintain motivation.

The most efficient cardiovascular exercises for improving physical fitness include:

Many men enjoy exercise benefits while engaging in a sports activity. These activities may include:

Making time to participate in a fitness routine is important for a variety of reasons. Exercise helps to:

The American Heart Association recommends 30 minutes of exercise five times a week in conjunction with a heart-healthy diet regimen. A regular exercise routine and nutritious diet will also help in weight management.

Men should be sure to include not only weight training, but aerobic, strength, and flexibility training as well. Incorporating a variety of different types of training helps boost muscle mass, tone, metabolism, endurance, and overall well-being. Loss of muscle mass generally occurs around age 40 and strength training in particular will help generate and maintain muscle function and physique for men in this age group or older.

Many men enjoy circuit training as an exercise program. Circuit training combines cardiovascular exercise, endurance, and strength training exercise, as individuals move between various machines at set intervals.

Men should pay attention to their nutritional needs before, during, and after exercising. Many foods enhance a good exercise regimen and help muscles recover well after a good workout, so paying particular attention to vitamin, mineral, and fluid replenishment is important. Balanced nutrition should include lean protein, unsaturated fats, complex carbohydrates, and plenty of water.

Vitamin B6 in particular, as well as eating garlic, onions, scallions, leeks, and chives (allium vegetables), may help reduce the risk of benign prostatic hypertrophy (BPH) and prevent the loss of testosterone. Eating fish high in omega-3 fatty acids can also help protect from prostate disease and infection. A blood test measuring prostate-specific antigen (PSA) can be performed by your physician to help determine prostate health. The American Cancer Society recommends yearly testing for all men aged 50 or older, and earlier testing for men with known cancer risks.

A good exercise program should start off slowly and progress moderately and at a safe degree of intensity, keeping in mind how your fitness level will change over time. Pay attention to your level of energy before, during, and after exercising, to help you decide when and how to progress to the next level of intensity, duration, and type of exercise. A professional trainer may be of help when putting together a fitness schedule and routine.

Remember to read food labels to examine not only calorie, fat, carbohydrate, and protein content, but also to determine serving size in relation to these numbers. Dieticians may be of assistance in understanding these food labels. A well-balanced fitness and nutrition regimen can improve not only the way you look and feel, but also have a positive impact on the health and quality of your life.

Stéphanie Islane Dionne
Revised by Laura Jean Cataldo, RN, Ed.D.