Bulbourethral glands or Cowper’s glands are a component of the male reproductive system. They are not as well known as the testes or the vas deferens; however, their contribution is very important.
Their basic function is to contribute fluid to the ejaculate, which we will explore further. In this article we will cover the anatomy and physiology as well as the embryology of the Cowper’s glands. We will also discuss their clinical relevance, with regards to cancer and recurrent infection.
The Cowper’s glands are named after the English surgeon William Cowper who discovered the glands in the seventeenth century. Anatomically, they are also named bulbourethral glands because of their location. They are a pair of small, pea sized (1 cm), exocrine glands that are found in the male reproductive system. The structure is also present in a vast array of male mammals. These glands are homologous to the Bartholin’s gland found in the female reproductive system.
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.
Vasculature & Lymphatics
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 secondary to stasis of secretions, infection with proteus or other urea-splitting bacteria, or even due to diabetes mellitus, which increases infection risk throughout the body.
This is inflammation of the bulbourethral glands and presents with fever, malaise, and in some cases severe perineal pain. The inflammation is usually caused by infections from the same organisms that cause urinary tract infections, for example; E. coli, and Klebsiella. If the patient presents with a chronic bacterial infection, there is a chance that they are suffering from a congenital anatomical defect, such as a syringocele, which becomes a focus of bacterial infection. High dose antibiotics are the treatment, as well as correction or removal of the underlying defect.
Neoplasms of the glands can result in a stricture of the urethra, resulting in urinary retention and other complications. As the bulbourethral glands are composed of glandular tissue, the cancer type is adenocarcinoma.
The glands also release prostate specific antigen, and neoplasm of the gland will result in a raised level. Due to this, they may be confused with neoplasms of the prostate, which also results in a raised prostate specific antigens and lower urinary tract symptoms such as frequency, urgency, and retention. Surgery as well as radiotherapy is the preferred method of treatment.