The Prostate Gland

Having a kiwifruit size (or slightly larger than a walnut) and weighs approximately 20 grams, the prostate gland is a part of the male reproductive system, located below the bladder, in front of the rectum and surrounded by the pelvic muscles. The prostate also surrounds the urethra, a muscular tube that connects the urinary bladder to the external sex organs to carry semen as well as urine out of the body.

The prostate gland consists of about 4 zones (also called lobes): Anterior fibro-muscular zone (or stroma), peripheral zone, central zone, and transition zone. Each zone has its main role physiologically, pathologically and diagnostically. The anterior fibro-muscular zone is made up mostly of muscle and fibrous tissue, and represents about 5% of the prostate gland. The peripheral zone is the main target during rectal exam because the physician can feel it by inserting a finger in the rectum; it represents up to 70% of the prostate size and the original site of more than 70% of prostatic cancerss. The transition zone is the main site where enlarged prostate (benign prostatic hyperplasia or simply BPH) develops; nearly 20% of prostatic malignant tumors originate in this zone. And the central zone is made of approximately 25% of the prostate gland, and accounts for about 2.5% of prostate cancers. The central zone has fewer incidences of malignant tumors, but its cancerous conditions tend to be more aggressive.  

All of those zones of the prostate consist of different types of cell which has different function each. For instance, the epithelial cells form the glandular portion of the prostate and they are the type of cells that recovers the prostatic wall (the internal part of the prostate gland). Most prostatic cancers tend to develop from the epithelial cells. The stromal cells, in the other hand, form the surrounding muscle and connective tissues. It is believed that complex stromal-epithelial cellular interactions can lead to BPH (enlarged prostate). It is also believed that miscommunication betweenepithelial cells and stromal cells is often the cause of many prostatic diseases.  

Prostate Functions  

Although all the prostate's functions are not clearly known, the prostate gland plays various roles; its primary function, however, is to produce and store the seminal fluid, a slightly alkaline and thick white liquid containing spermatozoa that is ejaculated by the male genital tract. Duringsexual climax, the prostate gland contacts its smooth muscles to propel the seminal fluid into the urethra. The prostatic fluid is expelled in the first ejaculate fractions, together with most of the spermatozoa. Being alkaline, the semen helps neutralize the acidity of the vaginal tract, thus prolong the lifespan of sperm. 

To work properly, the prostate gland also needs secretion of the male hormone called androgens. Also called androgenic hormone or testoid, the androgens from a group of hormones that help to stimulate and control the development and maintenance of male sex characteristics. Among of the androgens, there is testosterone. Produced by the testes, the testosterone participates in the formation and development of the testis and prostate. In addition, it also believed that the testosterone play a major role in the formation of secondary sexual characteristics: increased muscle, bone mass and the growth of body-hair. 

Prostate Diseases

In spite of its important functions, the prostate is subject to many medical conditions, mainly: prostate cancer, prostatitis (Prostate infection), enlarged prostate (BPH). See each condition separately for more details.

References:

http://library.med.utah.edu/WebPath/TUTORIAL/PROSTATE/PROSTATE.html

http://www.unboundmedicine.com/5minute/ub/view/5-Minute-Clinical-Consult/116490/all/Prostatic+Hyperplasia,+Benign+%28BPH%29  

http://www.mastersmensclinic.com/prostate.htm

http://en.wikipedia.org/wiki/Prostate#Zones

http://en.wikipedia.org/wiki/Testosterone