Summary of Benign prostatic hyperplasia
Transcript for Benign prostatic hyperplasia
Content Reviewers:Rishi Desai, MD, MPH, Yifan Xiao, MD, Evan Debevec-McKenney, Sam Gillespie, Ahmed A. Abu Ajeene
Benign prostatic hyperplasia
In benign prostatic hyperplasia, or BPH, prostatic refers to the prostate gland, hyperplasia means an increase in the number of cells, and benign means that these cells aren’t malignant, so they don’t invade neighboring tissues.
So, benign prostatic hyperplasia is the non-cancerous growth of the prostate gland.
This condition is common in men over 50, and is often considered a normal part of aging.
The prostate is a small gland, about the size and shape of a walnut, that sits under the bladder and in front of the rectum.
The urethra which is the tube through which urine leaves the bladder, goes through the prostate before reaching the penis.
And that part of the urethra is called the prostatic urethra.
The prostate is covered by a capsule of tough connective tissue and smooth muscle.
Beneath this layer, the prostate can be divided into a few zones.
The peripheral zone, which is the outermost posterior section, is the largest of the zone and contain about 70% of the prostate’s glandular tissue.
Moving inward, the next section is the central zone which contains about 25% of the glandular tissue as well as the ejaculatory ducts that join with the prostatic urethra.
Last, is the transitional zone, which contains around 5% of the glandular tissue as well as a portion of the prostatic urethra.
The transitional zone gets its name because it contains transitional cells which are also found in the bladder.
At the microscopic level, each of the tiny glands that make up the prostate is surrounded by a basement membrane made largely of collagen.
Sitting within that basement membrane, is a ring of cube-shaped basal cells as well as a few neuroendocrine cells interspersed throughout.
Finally, there’s an inner ring of luminal columnar cells, which are within the lumen or center of the gland. Luminal cells secrete substances into the prostatic fluid, that make it slightly alkaline that give it nutrients which nourish the sperm and help it survive in the acidic environment of the vagina.
During an ejaculation, sperm leave the testes, travel through the vas deferens, into the ejaculatory ducts, and travel through the prostatic urethra.
Smooth muscles in the prostate contract and push the prostatic fluid into the urethra where it joins the sperm as well as the semen which is the fluid that comes from the seminal vesicles.
The luminal cells also produce prostate specific antigen, or PSA, which helps to liquefy the gel-like semen after ejaculation, thereby freeing the sperm to swim.
The basal cells and luminal cells of the prostate rely on stimulation from androgens, or male sex hormones, for survival.
The androgens include testosterone, which is produced by the testicles, and dihydrotestosterone, which is produced in the prostate itself.
This androgen is produced by the prostatic enzyme 5α-reductase which converts testosterone into the more potent dihydrotestosterone.
Since androgens are steroids, so they can cross the cell membrane and bind to the androgen receptors within the cell’s nucleus.
This inhibits the apoptosis of or programmed cell death, allowing luminal and basal cells in the prostate to keep growing and multiplying.
Dihydrotestosterone is ten times more potent than testosterone because it can bind to androgen receptors much longer.
Now, after the age of 30, men produce about 1% less testosterone per year.
But for unclear reasons, 5α-reductase activity increases with age, so even with less testosterone, there could be an increase in dihydrotestosterone.