Bulbourethral Gland
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On dissection, the bulbourethral glands can be found in the deep perineal pouch of the male. They are situated posterolaterally to the membranous urethra and superiorly to the bulb of the penis.
Embryologically the bulbourethral glands are derived from the urogenital sinus, along with the bladder, prostate and urethra. Their development is greatly influenced by DHT (dihydrotestosterone).
The bulbourethral glands are found inferior to the prostate and they sit posterolaterally to the membranous urethra (the smallest section of the urethra, which lies inferior to the prostatic urethra). In other terms, the glands sit at the base of the penis, within the deep part of the perineal pouch. They lie within the urogenital diaphragm between the two layers of fascia that form it. They can also be described as sitting at the apex (bottom) of the prostate, superior to the bulb of the penis. The glands themselves are enclosed by the muscular fibers of the urethral sphincter. Their anatomical name comes from their proximity to the bulb and urethra of the penis.
The two primary bulbourethral glands are located within the muscle of the urogenital diaphragm. It is also common to find accessory bulbourethral glands that sit within the bulbospongiosus tissue. The main bulbourethral glands are able to empty into the bulbous urethra by piercing the bulbospongiosum of the proximal penis.
The bulbourethral glands have their own unique blood supply. They are supplied by the bulbourethral arteries that arise from the common penile artery. The venous drainage is equivalent to the arterial supply. The lymphatic drainage is via the internal and external iliac group of lymph nodes.
A bulbourethral gland is typically made of tubules and acini, which is why we can characterize it as a tubulo-alveolar gland (exocrine). Each gland is formed of a number of lobules that are enclosed within a fibrous capsule. Histologically, they are lined by pseudostratified epithelium.
Within these lobules, we find acini lined by columnar cells. A thin layer of myoepithelial cells surrounds each separate acini. Microscopic analysis of these cells shows a large amount of intracytoplasmic mucin. Each of these acini open into a duct, which joins other adjacent ducts and all eventually form the central excretory duct of the gland; cuboidal cells line each duct.
The bulbourethral glands function to lubricate the spongy urethra for the passage of the ejaculate. Due to the alkaline pH of the excreted fluid, they also act to neutralize residual acidic urine that remains in the spongy urethra. The gland is also responsible for the production of prostate specific antigen; this component is important for a common test used to screen and assess the progression of prostate cancer. The combined fluid output of these glands is 5% of the total ejaculate volume.
Upon sexual excitement, the bulbourethral glands typically secrete clear glycoproteins into the bulbous urethra (proximal part of the spongy urethra). The function of the glands and other supportive male sexual structures depend on normal testicular development and function. In addition to the glycoproteins, they also secrete other substances during sexual stimulation such as an alkaline fluid that helps in neutralizing the acidity of urine and of the vagina, and provides lubrication to for the passage of ejaculate. This fluid is known as pre-ejaculate. In a minority of men, sperm can be present in the pre-ejaculate.
The bulbourethral glands develop during the 10th- 12th week of gestational life and arise from the urogenital sinus. They develop from the pelvic urethra; the shortest section of urethra known as the membranous urethra. An essential component to their development is dihydrotestosterone, which is the form of testosterone developed when the 5-alpha reductase enzyme that modifies testosterone. The same form of testosterone is responsible for the growth of facial hair in males.
Stones may form in the bulbourethral glands