Prostate gland histology

Definitions & Key takeaways

The prostate gland is a large and dense exocrine gland found in the male reproductive system, measuring approximately 3 x 3 x 5 cm. It surrounds the urethra and is responsible for producing a fluid that makes up a portion of semen. The prostate gland has four zones. There is the central zone surrounding the ejaculatory ducts; the peripheral zone surrounding the lateral and posterior sides of the central zone; the transitional zone which is the one to undergo hyperplasia benign prostatic hyperplasia; and the periurethral zone, a small zone surrounding the urethra.

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The prostate gland is a large and dense exocrine gland that’s responsible for secreting a white alkaline fluid that makes up about 30 to 50 percent of the seminal fluid volume.
It’s the largest accessory sex gland in the male reproductive system, measuring approximately 3 cm in length and width, and a height of 5 cm.
The average weight of a normal prostate gland is about 11 grams. Due to its similar size and shape, it’s sometimes compared to a walnut.
The gland surrounds the most proximal portion of the urethra or prostatic urethra, just below the bladder and consists of 30 to 50 branched tubuloalveolar glands, such as the ones seen in this low power image of the prostate.
The glands all drain into converging ducts that eventually empty into the prostatic urethra. The alkaline fluid that’s secreted by the prostate gland also includes various small molecules, fibrinolysin, citric acid, and the clinically important prostatic acid phosphatase or PAP, and prostate-specific antigen or PSA.
Normally, only a small amount of PSA will leak into the prostate’s vasculature and circulate in an individual’s blood. But a high level of circulating or serum PSA is a sign of abnormal prostatic tissue, which could be caused by prostate cancer, inflammation, or benign prostatic hyperplasia.
Because of this association, a PSA serum level is often used as a tumor marker for prostate cancer. And even after a patient has had their prostate cancer removed, PSA is used to monitor for a possible recurrence of the prostate cancer.
PSA and PAP immunostains can also be used on tissue samples to assist with the diagnosis of prostate cancer, such as this section from a lymph node, where a PSA stain is highlighting a metastatic prostate adenocarcinoma in brown.
Similar to this image at 40x magnification, the prostate will have glandular structures called acini that are surrounded by supporting fibromuscular stroma.
Each acinus has two layers of cells: an epithelial layer and a basal layer. The glandular epithelial cells can become hyperplastic and consist mostly of simple columnar and cuboidal cells, with some regions having pseudostratified columnar epithelium.
The basal layer consists of smaller stem cells that rest on the basement membrane. The basal layer will not be seen in prostatic carcinoma.
There are also neuroendocrine cells present, but they aren’t easily identified with an H&E stain. With age, the acini have a higher probability of accumulating thick secretions that form hyaline spherical masses or concretions, called corpora amylacea, which can be seen in these three alveoli.
They can vary in size, but typically have layered or lamellated bodies that can be seen under the microscope. Over time, they may become partially calcified as well.
The corpora amylacea are normal findings in the prostate and can be seen in normal lung tissue as well. The prostate gland is also divided into four main zones: the periurethral, transitional, central, and peripheral zones.
Also, the anterior surface of the prostate consists of a dense fibromuscular stroma made of irregular connective tissue and smooth muscle that contracts during ejaculation, however, the prostate doesn’t have a true distinct capsule itself.
The central zone is the area that surrounds the ejaculatory ducts and comprises about 25 percent of the prostate’s glandular tissue.
The peripheral zone makes up 70 percent of the glandular tissue and surrounds the lateral and posterior sides of the central zone.
This is the zone that’s palpable during digital rectal exams and is also the zone that’s most susceptible to prostatic carcinomas as well as inflammation.
The transitional zone comprises about 5 percent of the glandular tissue and contains the mucosal glands. This is the zone that undergoes hyperplasia in older individuals with benign prostatic hyperplasia or BPH.
When compared to a normal prostate’s glandular epithelium, we can see that a prostate with BPH has a significantly increased number of columnar epithelial cells that protrude further into the lumen; particularly in the upper right of this image.
Hyperplasia of the supporting tissue or stroma can also be seen with BPH. Even though BPH leads to an increased amount of prostate tissue, it does not lead to prostatic carcinoma.
The hyperplastic tissue compresses the prostatic urethra, causing difficulties with urination. And finally, the periurethral zone is a small zone surrounding the urethra, which contains mucosal and submucosal glands.
As BPH progresses, this zone’s stromal components may also increase in size and contribute to urethral compression. Although the different zones are not clearly separated histologically or anatomically, they are important clinically due to their associations with different pathological processes.
Alright, as a quick recap. The prostate gland is a large, dense exocrine gland responsible for secreting a white alkaline seminal fluid that contains various molecules, fibrinolysin, citric acid, PAP, and PSA.
The gland consists of branched tubuloalveolar glands and is divided into four zones: the central, peripheral, transitional, and periurethral zones.
Prostate cancer is most closely associated with the peripheral zone, and BPH is typically associated with the transitional zone.
Each zone has glandular epithelium that consists mostly of simple columnar or cuboidal cells, and a basal layer of stem cells that rest on the basement membrane.
Older individuals have an increased number of corpora amylacea, which are hyaline spherical masses within some alveoli that may partially calcify over time.