Important Landmarks of the Urogenital System Fig. 1
A. Urinary Bladder
- An extra peritoneal organ that lies behind the pubic symphisis and superior pubic rami. It is made up of smooth muscle and its mucosal lining consist of transitional epithelium.
- Arterial Supply – supplied by superior, middle and inferior vesical arteries.
- Venous Drainage – veins coming from the prostate drains form the postatic venous plexus
- Innervation – innervated by the pelvic splanchnic nerves (nervi erigentes) and the hypogastric nerve.
- Function – its main function is for storage of urine.
B. Male Urethra
- Divided into 3 segments
- Prostatic Urethra – the most proximal portion that begins at the vesical neck at the apex of the trigone of the urinary bladder and extends through the prostate gland ending at the superior facia of the urogenital diaphragm.
- Membranous Urethra – begins at the superior facia of the urogenital of the diaphragm, extends at the deep transverse perineal muscle ending at the inferior facia of the urogenital diaphragm.
- Penile (Cavernous) Urethra – begins at the inferior facia of the urogenital diaphragm and extends into the bulb of the penis and terminates at the external urethral meatus of the glans penis.
C. Seminal Vesicle
- Each seminal vesicle (about 3 cm. long) is dilated convulatory tube over 9 cm. long. They join the vas deferens where the ampulla becomes the ejaculatory duct. Both seminal vesicles are located at the posterior base of the urinary bladder.
- Function – contribute seminal fluid.
D. Urogenital Diaphragm
- Lies inferior to the urogenital hiatus of the levator anti muscle and supports this potentially weak region of the pelvic floor.
E. Vas Deferens
- Represents the mesonephric (Wolfian) duct. It has a muscular wall, which accounts for the cordlike composition. It has 4 portions such as the external, internal, ampulla and the ejaculatory duct. In the ampulla where the sperm is briefly stored during emission and before ejaculation.
- Blood Supply – artery of the vas deferens
- Parasympathetic – produces emission. Slow peristaltic waves along the vas deferens move spermatozoa from the epididymis to the ampulla, where the sperm is stored before ejaculation.
- Sympathetic – produces strong contraction of the smooth muscle of the vas deferens producing ejaculation.
- Sensory Afferents – travels through the pelvic plexus and along the pelvic splanchnic nerves to sacral levels S2-S4. As a result, pain of deferentitis or from prolonged engorgement of the ampulla is referred to the perineum.
F. Testes – where the production of sperm (spermatogenesis) takes place.
- What is the prostate?
- The prostate is a semi circular organ measuring 3 cm (height) x 3 cm (width), x 5 cm (length) with an estimated volume of 20 grams. Considered as part of the male genitourinary and reproductive tract (Figure 1), it is located under the urinary bladder, in front of the seminal vesicles, behind the symphysis pubis of the pelvic bone, on top of the base of the penile shaft, and surrounding the back part of the urethra.
- The prostate comprises of a network of glands, ducts (exocrine glands), and smooth muscles enclosed in a capsule (Figure 2). The seminal vesicle has a tube called the ejaculatory duct that passes behind the prostate, passing inside the prostate, and exits into the back part of the urethra. A nerve responsible for erectioncalled splanchnic nerve also passes through the prostate (Figure 3).
A. Lowsley’s Classification (Figure 2) – on the basis of endoscopic appearance
A.1 Median Lobes – surrounds the prostatic urethra – Predisposed to Benign Prostatic hyperplasia (BPH)
A.2 Right and Left Lateral Lobe – formerly termed as anterior lobes.
A.3 Right and Left Posterior Lobes – most perdisposed region to malignant transformation which may explain metastasis of prostatic cancer to the vertical column and brain.
B. McNeal’s Classification (Figure 3) – Histological Landmarks
B.1 Peripheral Zone (Figure 4)
- Ducts horizontal in orientation
- Prone to Prostatitis and Cancer
- 75% Total Glandular Volume
B.2 Central Zone (Figure 4)
- Ducts more oblique in orientation
- 25% Total Glandular Volume
B.3 Transitional Zone
- Preprostatic zone
- Prone to BPH
Gland of the Prostate (Figure 5)
Secretory glands made up of ducts (approximately 20 in number) with grape shaped saccule ends or acini.
Secretory Cells lining the ducts are stimulated by hormones to expel prostatic fluid. During sexual activity, smooth muscle contracts to expel the fluid. The basal cell also found lining the ducts of the prostate might be responsible for most types of prostatic hyperplasia as a result of uncontrolled prostatic tissue growth.
|Vascular, Lymphatic and Nerve Supply|
Neurophysiology of Continence and Micturition:
The parasympathetic and sympathetic maintains an important role in urinary continence. During bladder filling, sensory nerve endings detect progressive stretching of the bladder wall and convey information via the parasympathetic to the spinal cord and brain which produces reflex contractions in the bladder neck and prostatic urethra as well as in the external urethral sphincter thereby maintaining continence.
As volume of urine increases, starting from 300-500 ml., awareness of the need to void develops. Voluntary voiding is accomplished by stimulation of the parasympathetic nerve fibers causing coordinated contraction of the detrusor muscle and the bladder body. Nerve impulses passing down the sympathetic and pudental motor fibers cease momentarily, allowing relaxation of normally tonically contracted bladder neck, prostatic urethra and external thus allowing urine to flow.
Erectile function is supervised by parasympathetic fibers, which pass in the so-called neurovascular bundles of Walsh lying underneath the prostate. These fibers are responsible for producing vasodilation within corpora cavernosa.
Physiology of the Prostate:
Prostate came from the ancient Greek word prostátēs meaning “one who stands before, protector, and guardian”. True to its definition, the prostate’s function is to protect and aid the sperm during the process of fertilization. The prostate gland serves as a filter against microorganism that may harm the spermatozoa stored in the vas deferens. Most of the constituents of the prostatic fluid contains antibacterial factor (Table 2).
The prostate fluid also contains elements to liquefy the semen so that sperm can be released within the gelatinous consistency of semen. Prostatic fluid mixes with seminal vesicle secretion and spermatozoa forming the ejaculate.