Prostate Gland: Anatomy, Histology and Function
References: (Benninghoff, 1993).
Accessory Sex Glands
Any gland, which empties into the genital tract, is assigned to the accessory sex glands. The male accessory sex glands are the prostate, the paired seminal vesicles, and the paired bulbourethral (Cowper) glands.
Gross Anatomy of the Seminal Vesicles
The paired seminal vesicles are located behind the bladder and are each about 5 × 1 × 1 cm in size. Dorsal of the seminal vesicles is the rectum, lateral the ureter. The duct of the seminal vesicle opens into the ampulla of the ductus deferens Ampulla and forms the ejaculatory duct. See also anatomy of the epididymis and ductus deferens.
Gross Anatomy of the Prostate Gland
fig. prostate zones (McNeal, 1988): Drawing modified from (Benninghoff, 1993): prostate zones in different planes: frontal plane (top), sagittal plane (middle) and horizontal plane (bottom). The transition zone (hatched area) surrounds the urethra between colliculus and bladder neck. The central zone (without shading) forms a funnel (sagittal plane) or ring-like zone (horizontal plane). The central zone is located between transition zone and peripheral zone. The ejaculatory ducts run through the central zone. The peripheral zone includes the peripheral sections of the prostate gland (dotted area).
Surface Anatomy of the Prostate
The prostate gland is a pyramid-shaped organ with apex (contact to the urethra and directed downward) and basis (contact to the bladder and directed upward). The prostate lies below the urinary bladder and is located in front of the rectum. The prostate weighs about 20 g (3 cm long, 4 cm wide, 2 cm thick). There are considerable prostate size variations. The seminal vesicles are located at the base of the prostate.
Inner Gross Anatomy of the Prostate
The prostatic urethra runs through the prostate gland, dividing the prostate into a left and right lateral lobe. The paired ejaculatory duct perforates the prostate and opens into the middle of the prostatic urethra at the seminal colliculus (verumontanum). The prostatic utricle is a small indention at the seminal colliculus, it is a remain of the Müllerian duct. Usually the prostatic utricle is only 6 mm in size, but may be the reason for diverticula or cysts.
The prostate consists of about 30 glands with single ducts, which empty into the prostatic urethra.
Connective Tissue Layers of the Prostate
The prostate is surrounded by a dense organ capsule. The prostatic capsule is not present at the apex (transition to the external sphincter) and at the basis (transition to the detrusor muscle of the bladder). Two puboprostatic ligaments fix the prostate to the pubic bone. The endopelvic fascia covers ventrally the prostate (visceral sheet). The endopelvic fascia (Fascia diaphragmatis pelvis superior) extends to both sides and covers the levator ani muscle (parietal sheet). The fold between visceral and parietal endopelvic fascia is called Arcus tendineus fascia pelvis. The cavernous nerves run in the parietal layer of the endopelvic fascia latero-dorsal to the prostate. The Denovilliers' fascia separates dorsal the prostate from the rectum.
The rectourethral muscle is a smooth muscle that lies posterior to the apex of the prostate. It rises from the rectum and inserts on the perineal body fat, thereby separating the urethra from the rectum (Brooks et al, 2001).
Zonal Anatomy of the Prostate
Due to embryological and pathological aspects the prostate can be divided into different zones [fig. prostate zones] (McNeal, 1988):
surrounds the urethra between bladder neck and colliculus, about 5-10% of the prostate volume. Benign prostatic hyperplasia is a reason for a dramatic increase of the transition zone volume and leads to lower urinary tract symptoms (LUTS).
25% of the prostate volume. The central zone originates probably from the Wolffian duct. The central zone forms a funnel (sagittal section) or ring-like (horizontal) zone, which contains the ejaculatory ducts.
70% of the prostate volume, peripheral sections of the prostate gland.
Anterior fibromuscular stroma:
The anterior fibromuscular stroma, 5% of the prostate volume, is located anterior to the urethra and extends into the transition zone.
Vascular and Nerve Supply of the Prostate
The male accessory sex glands are supplied by branches of the internal iliac vessels.
Arteries of the prostate:
the inferior vesical artery approaches the prostate from laterodorsal and divides into urethral and capsular branches. The urethral branches perforate the basal prostate and bladder neck at 4 and 8 clock (view from lithotomy position) and supply the transition zone. Bleeding due to TURP or Adenomectomy are therefore expected at the bladder neck at the 4 and 8 clock position.
Capsular branches join the cavernous nerves posterolateral of the prostate and run to the pelvic floor. Small arteries branch off at right angle and perforate through the organ capsule.
Additional arterial supply: branches from the middle rectal artery, internal pudendal artery or obturator artery.
Veins of the prostate:
the blood from the accessory sex glands drains via the vesicoprostatic plexus to the internal iliac veins. The vesicoprostatic plexus is particularly strong under the puboprostatic ligaments and pubic bone (Santonini's plexus), where the blood from the deep penile vein joins the plexus.
Nerval supply of the prostate:
the autonomic innervation reaches the prostate via the cavernous nerves and perforates together with the arterial branches the capsule of the prostate. The cavernous nerves run between the capsule of the prostate and the fascia of the levator ani muscle latero-posterior to the prostate.
Parasympathetic signals stimulate glandular activity; the sympathetic innervation of α1-receptors mediates smooth muscle contraction (see below).
Bulbourethral Glands (Cowper's glands)
The paired Cowper's glands lie laterally to the membranous portion of the urethra and open via a 2–5 cm long duct into the spongy urethra.
Microscopic Anatomy of the Prostate and Accessory Sex Glands
Histology of the Seminal Vesicle
The seminal vesicle consists of a duct-like glandular tissue, about 15 cm long, with strong muscle-containing wall. The seminal vesicle ducts are lined with pseudostratified columnar epithelium.
Histology of the Prostate
The tubuloalveolar glands have pseudostratified columnar epithelium of varying height. The columnar cells contain apical secretory granules. Basal cells are found between the columnar cells for regeneration of the epithelium. Each gland is surrounded by connective tissue and smooth muscle (fibromuscular stroma). The stroma accounts for about 70% of the prostate mass. The prostate glands open on both sides of the Colliculus in the prostatic urethra. During ejaculation, the smooth muscle contracts and leads to the expulsion of the glandular content.
Histology of the Bulbourethral Glands (Cowper's Glands)
Cowper's glands are made of tubular glands, which are surrounded by smooth muscle cells.
Function (Physiology) of the Accessory Sex Glands
Physiology of the Prostate
The prostatic fluid is thin, slightly acidic (pH 6.4) and forms about 20% of semen volume. It contains spermine (for the motility of sperms), spermidine, prostataglandins (for uterus stimulation), zinc (affects testosterone metabolism of the prostate), citric acid (buffer), immunoglobulins, phosphatases and proteases (see liquefaction of the semen).
Control of Urine or Semen Flow
The prostate acts as a kind of valve, preventing urine flow during the ejaculation and or permitting urine flow in between. Micturition is made possible under parasympathetic activity and low sympathetic activity, this leads to the relaxation of the bladder neck.
Ejaculation is controlled by the sympathetic nervous system. The activation of prostatic alpha-receptors leads to the contraction of the smooth muscle stroma of the bladder neck; this causes the expulsion of the prostate gland content and closes the bladder neck for an antegrade ejaculation. Injury of the sympathetic nerves (e.g. due to retroperitoneal lymphadenectomy) leads to retrograde ejaculation.
Physiology of the Seminal Vesicles
The seminal vesicles produce an alkaline (pH 7.4) secret of gelatinous consistency, which contains fructose and forms half of the semen volume.
Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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Benninghoff 1993 BENNINGHOFF, A.:
- Makroskopische Anatomie, Embryologie und Histologie des
München; Wien; Baltimore : Urban und Schwarzenberg, 1993