What is the prostate gland?

Structure and Functions

The prostate is the largest of several glands that are referred to as the accessory glands of the male reproductive tract, the others being the seminal vesicles and the bulbourethral glands. Unlike the latter two, which evolved morphologically in smaller pairs, the prostate evolved as a single gland, approximately four centimeters in diameter in adults. It surrounds the urethra, the tubular tract that carries both semen and urine. During the early embryonic stage of life, both urinary organs and accessory sex glands are formed, through the cell-division process, out of the same original source of specialized cells in the intermediate mesoderm (called the nephrotome) and the cloaca.

In fact, up to a certain point in the growth of the human embryo, it is not possible to distinguish the pattern that will lead to formation of the male and female gonads. Following what is called the ambisexual stage, the undifferentiated gonad, or reproductive terminus, begins to evolve into a male or female reproductive organ, becoming either a testis or an ovary. Then, in the male, the three accessory sex glands begin to form. Their eventual key functions in the reproductive process will not begin, however, until the onset of puberty in the individual’s growth cycle. Male puberty, or sexual maturity, is initiated when secretions from the testis and pituitary gland activate secretions from other organs, including the prostate gland. It is at this stage that elevated levels of androgenic steroids in the body cause the prostate to attain its full size and begin to secrete the fluids that are essential in the male reproductive function.

The function of all necessary reproductive glands, and of the prostate gland in particular, is to secrete fluids that affect the fertilization potential of the spermatozoa in the seminal fluid as it passes from its source in the testicles through the vas deferens duct. The vas deferens joins the
urethra at a point just before the latter is encased by the prostate gland. Thereafter, the urethra serves as a channel for passage of seminal fluid through the penis.

When the adult prostate gland is functioning efficiently, the prostatic secretions that pass into the vas deferens should make up about 30 percent of the volume of the male seminal fluid. Although the process of prostate secretion after puberty is continuous, the composite elements of these secretions may vary. One notable variation in content occurs during moments of sexual excitement. A comparison of “resting” prostatic fluids with fluids obtained from ejaculation resulting from sexual stimulation suggests that the latter contains a higher level of certain enzymes, particularly acid phosphatase, than the former.

All “resting” prostatic fluid is only slightly basic, with an approximate pH of 7.2. The pH level may increase to 7.7 in men suffering from prostatitis. The main components of the fluid include diastase, an enzyme of the amylase group; proteolytic enzymes, especially fibrinolysin; citric acid; acid phosphatase, also an enzyme; cephalin, a chemical group containing amino acids that is found mainly in nervous-system tissues; cholesterol; magnesium; zinc; and calcium. In humans, but not necessarily in all mammals, calcium is more highly concentrated in prostatic fluid than in the blood plasma.

There are other differences between humans and other mammals with respect to the glandular origins of separate component elements of seminal fluid. Whereas citric acid originates in the human prostate gland, in other species it may come from the seminal vesicles, as is the case for boars, or it may flow in generally equal amounts from each of the accessory sex glands, such as in rabbits and guinea pigs. In all cases, citric acid is synthesized by chemical reactions within the originating glands.

There is general agreement that the fertilizing potential of spermatozoa is enhanced when combinations of these various prostatic fluid constituents join the flow of semen. No evidence has been found of an identifiable target effect by any one specific element, although tests of relative concentrations of citric acid in semen suggest an influence on the activity level of testicular hormones, especially androgen. Additionally, with regard to the fertilization potential of male spermatozoa carried in the seminal fluid, citric acid reacts chemically with other component elements in ways that may delay the coagulation of seminal plasma or contribute to its capacity to be absorbed at the appropriate time in the fertilization process.

Research has also tentatively established that the fertilization potential of spermatozoa may depend on levels of zinc contained in secretions from the prostate gland. One chemical effect of zinc is to slow the breakdown of genetically vital chromosomes in individual sperm cells. This function of zinc has not been tied directly to potential fertility levels, however, since surgical removal of the section of the prostate where zinc is in the highest concentration (the dorsolateral portion of the gland) has not changed reproductive capacities in laboratory rats. Because prostate surgery involving human patients is almost exclusively connected with attempts to arrest prostate cancer, no research data have been recorded that can be compared with experiments performed on animals.

One area of research that has established irrefutable evidence in connection with fertility levels deals with the effects of certain drugs on the functioning of the accessory sex glands, including the prostate. Tests on morphine and methadone users, for example, have shown a definite reduction in the volume of human seminal ejaculate. Methadone, and in some cases morphine, can actually cause a reduction of the weight and volume of the testes, seminal vesicles, and prostate glands of laboratory mice. Specific constituent elements of prostate secretions that appear to be reduced when drugs such as morphine sulfate are administered include prostatic fructose and different forms of glucose that contribute to metabolic activity in the prostate gland itself.

In addition to medical or self-administered drugs, chemicals that enter the body through the food chain, such as the pesticide DDT, can also affect the functioning of the prostate. In mice, the testosterone metabolic process, which is very much dependent on the prostate, has been shown to be significantly retarded when DDT is administered under close controls. Dieldrin is another pesticide that affects the ability of prostate tissue in mice to absorb testosterone.

Disorders and Diseases

In general terms, diseases of the prostate gland tend to fall into two main categories: nonproliferative and proliferative. The latter category is characterized by two forms of dangerous physical change in the tissues of the gland itself: lesions and neoplasms (or tumors).

Diseases of the nonproliferative type, although painful and potentially quite dangerous to the patient’s health, may be treated by modern medical means. One subgroup in this category is congenital anomalies. Some of these have slowly developing symptoms and may be discovered only when some other difficulty, such as urinary irregularities or infertility, is the initial cause for the doctor’s examination. The most common form of anomaly is the congenital cyst, which occurs as a result of obstructions in the normal flow of secretions through the prostate gland. Secretion blockage is sometimes caused by irregular development of the parenchyma, the functioning tissues of the gland itself. Subsequent development of a cyst in the prostate itself further impedes the normal flow of secretions within and from the gland.

Congenital cysts usually occur in the prostatic utricle, an oblong protrusion measuring about three millimeters that is palpable when a medical doctor performs a rectal examination. The abnormality is generally discovered in patients in their early twenties. In newborn infants, the fact of recent estrogenic stimulation in utero can have the temporary effect of making the utricle three times its eventual normal length. If the prostatic utricle does not shorten during childhood and early adulthood, examining doctors will be alerted to the existence of a cyst and the possible need for surgical intervention.

A second form of nonproliferative disease in the prostate involves the formation of tiny calculi, or stones, inside the gland. True prostatic calculi are generally rare, but they may occur when prostatic secretions are altered by one of several possible factors, including infection or some form of metabolic dysfunction. Altered secretions can lead to abnormal chemical deposits inside the organ. These deposits in turn attract mineral concentrations, particularly of calcium salts, the main component of calculi.

Although pathology texts list up to five forms of proliferative tumors that can attack the accessory reproductive glands, the prostate gland itself is mainly vulnerable to two out of the five: prostatic carcinoma and primary prostatic sarcoma. More common and less dangerous proliferative lesions (inflammations, not tumors) affecting the prostate involve many different forms of hyperplasia. Although the causes of such lesions can vary, their effect may be summarized as inflammation leading to either the obstruction of normal secretions originating in the prostate or the potentially harmful addition to prostate secretions of foreign by-products of the inflammatory process.

The most common proliferative lesion of the prostate, nodular prostatic hyperplasia (NPH), leads directly to urological disease, usually in middle-aged and elderly males. Its high incidence is reflected in the widespread need for some form of prostate surgery among men over fifty. The disease derives its name from the fact that it displays multinodular areas of inflammation, which makes it difficult for specialized surgeons to localize areas demanding attention. Doctors are still uncertain of the exact origins of NPH and the complexities of hormonal phenomena associated with the disease. It appears, however, that NPH is a combination of the more simply diagnosed prostatic hyperplasia (prostate enlargement) and a hypertrophy (tissue constriction) of the inner zones of the prostate gland itself.

Although these various forms of lesions affect a high percentage of the adult male population, the greatest pathological menace associated with the prostate gland involves malignant tumors. Prostatic cancers represent the second most common form of
cancer occurring among American males, with more than two hundred thousand cases diagnosed each year in the United States. Early diagnosis can usually result in treatment and cure. Because of the difficulties associated with diagnosis and the complexities of possible treatments, however, a large percentage of those suffering from prostate cancers die from the disease.

There is a problem of extended delay in the appearance of symptoms; approximately 70 percent of the total recorded cases remain locally latent for years. Yet even the prostatoglandular tumors that have clinical manifestations are often discovered too late for effective medical intervention.

Doctors looking for symptoms of prostate cancer, beyond those that might appear in physical examination via the rectum, pay particular attention to several likely warning signs. These include possible malignant repercussions stemming from prostatic lesions, especially NPH; sacral, lower back, or upper pubic pain; excessive urinary retention; and uneven or interrupted urinary flow. In recent years, screening for prostate cancer has involved measuring the prostate-specific antigen (PSA) level in a blood sample. PSA levels in males with a normal prostate generally measure around two nanograms or less. Elevated levels may indicate the presence of a tumor. The test remains inexact, however, since even a benign prostatic hypertrophy (BPH), or prostate enlargement, may result in an increase in PSA values.

If a physician suspects the presence of cancer in the prostate region, three forms of
biopsy may be used. The most accurate method involves actual surgical opening and removal of sections for laboratory biopsy. This method is the most expensive, however, and is recommended mainly when physicians are convinced that a radical prostatectomy should probably follow initial surgical intervention, for reasons that may not be limited to concerns about cancer. Of the other two methods of diagnosis, core needle biopsy and needle
aspiration biopsy, the former has a slightly higher level of accuracy, while the latter is safer and generally has fewer complications.

A complicating factor that makes prostate cancers among the most difficult to treat is similar to what has been observed with NPH. In NPH, which is a proliferative lesion, multinodular development complicates localization of the diseased area for treatment. In the case of prostatoglandular carcinoma, approximately 30 percent of diagnosed patients have diffused, as opposed to focal, growth development patterns. In such cases, radical prostatectomy, despite the fact that it usually leaves the patient impotent, is generally believed to be the best course of action.

A second, less common category of prostate cancer is referred to as primary prostatic sarcoma. Although this disease represents only 2 percent of all prostate cancers, it differs from the more common prostatic carcinoma in that it may occur in male patients of any age and has been diagnosed in infants as young as four months. Another serious factor is that if this form of cancer appears in the prostate, it frequently extends directly to other adjacent organs or structures, primarily the bladder, seminal vesicles, or rectum.

Perspective and Prospects

Although statistics show that as of 2009, prostate cancer was the most common cause of cancer among men and the second most common cause of cancer death among men, the medical world remained divided over questions of prognosis. Doctors called upon by the National Cancer Institute hesitated to reach a consensus about the central question of relative success rates of radiation treatment versus surgical intervention. Part of the problem, the institute learned, was that because patients are most often diagnosed at an advanced age—according to the American Cancer Society, as of 2012, the average age at diagnosis was sixty-seven—data gathered on their physical condition do not provide sufficiently random samplings for comparison with the population as a whole. A main reason for apparent dissatisfaction with too-focused data is that, because of the typically late discovery of prostate cancer, one central consideration in choosing between surgery or radiation treatment is rendered less vital; past a certain stage in advanced adulthood, diminished sexual reproductive capacity also diminishes patient sensitivity to the possibility that surgical removal of cancerous growth in the prostate will almost certainly bring about impotence.

Significant research has addressed the possible causes of prostate cancer. In a significant number of cases, researchers have observed a specific form of deoxyribonucleic acid (DNA) translocation in cells making up the tumor, lending support to the belief many forms of such cancers result from certain mutations. In the future, observation of such specific mutations from biopsy material may allow for improved methods of screening.

Bibliography

American Cancer Society. http://www.cancer.org

Blute, Michael. Mayo Clinic on Prostate Health: What to Do about Prostate Enlargement, Inflammation and Cancer. 2d ed. Rochester, Minn.: Mayo Clinic, 2003.

Fox, Arnold, and Barry Fox. The Healthy Prostate: A Doctor’s Comprehensive Program for Preventing and Treating Common Problems. New York: John Wiley & Sons, 1996.

McClure, Mark W. Smart Medicine for a Healthy Prostate: Natural and Conventional Therapies for Common Prostate Disorders. New York: Avery, 2001.

Marieb, Elaine N. Essentials of Human Anatomy and Physiology. 10th ed. San Francisco: Pearson/Benjamin Cummings, 2011.

Marx, Jean. “Fused Genes May Help Explain the Origins of Prostate Cancer.” Science 310 (October 28, 2005): 603.

"Prostate Diseases." MedlinePlus, May 20, 2013.

Westheimer, Ruth, and Pierre Lehu. Sex for Dummies. 3d ed. Hoboken, N.J.: John Wiley & Sons, 2006.

Yeo, Lehana, et al. "The Development of the Modern Prostate Biopsy." InTechOpen, December 2, 2011.

Zangwill, Monica, and Igor Puzanov. "Conditions InDepth: Prostate Cancer." Health Library, October 11, 2012.