5.15 Male Internal Genitals

Prostate (357-9)

A partly glandular, partly fibromuscular organ, under bladder but above urogenital diaphragm.

4x3x2cm; base lies superiorly; fused with bladder base. 

Gland enclosed by true capsule; outside this is a condensation of pelvic fascia called false capsule; prostatic plexus of veins lies between these layers. 

Base

Upper surface; fused with neck of bladder, whole length of gland is traversed by urethra.

Apex

Blunt; lowest part where urethra emerges ® membranous urethra (surrounded by sphincter urethrae)

Anterior aspect

Behind retropubic space (Retzius), connected to pubis by puboprostatic ligaments. 

Inferolateral surfaces

Clasped by levator prostatae parts of levator ani

Posterior surface

In front of lower rectum, separated by rectovesical fascia.

 

Structure

Prostate ® 30% of seminal fluid vol. Female equivalent = paraurethral glands (Skene’s)

Acini within characteristic stroma of smooth muscle & connective tissue.

Anterior to urethra is mainly fibromuscular.

 

Prostatic urethra (3-4cm)

Runs closer to anterior than posterior surface.

Ejaculatory ducts pierce posterior surface & pass through to open into prostatic urethra 1/2-way down

-           (where prostate’s own ducts also open).

Prostatic urethra characterised by midline ridge, = urethral crest with depressions on each side called prostatic sinuses.

-           at midlength of ridge is seminal colliculus or verumontanum a midline rounded eminence

-           central depression formed by prostatic utricle which is remnant of paramesonephric ducts; homologue of female uterus.  Ejaculatory ducts open alongside it; multiple prostatic ducts open on crest of verumontanum and adjacent to it.

-           This forms lower limit of extent of TURP (external urethral sphincter lies below).

 

Old ‘lobes’: obsolete; anterior used to be pre-urethral, middle b/n ejaculatory ducts and prox urethra; and posterior & lateral back and sides.

-           now considered as central and peripheral zones:

Central: wedge-shaped base of gland, apex a verumontanum, surrounds ejaculatory ducts

-           ducts open on verumontanum around orifices of ejaculatory ducts

Peripheral: surrounds central zone behind and below; does not reach base & extends as gland’s apex.

-           ducts open into prostatic sinuses

Outer zones tend to be involved with malignancy cf inner zones involved with hypertrophy.

 

Blood supply

Prostatic branch of inferior vesical artery, + small branches from MRA and internal pudendal.

Veins form plexus which receives deep dorsal vein of penis and drains into internal iliacs. 

Lymphatics

Across pelvic floor ® internal iliac & sacral nodes; may ® external iliacs.

Innervation

PNS (cholinergic) ® acini (via pelvic splanchnics)

SNS ® muscles (inf hypogastric plexus); contract in ejaculation to expel prostatic fluid.

Development

Pelvic part of urogenital sinus ® lateral epithelial buds ® outer prostatic acini;

Dorsal buds from above entry of mesonephric ducts ® acini of inner zone.

Different derivation accounts for different pathologies in inner (® BPH) & outer (® cancer) parts. 

Ductus deferens (358)

Continuation of epididymis.

Passes from deep ring along side wall of pelvis ® back of bladder.

No other structure between it & the peritoneum. (340)

-           hooks around interfoveolar ligament and inferior epigastric artery at deep inguinal ring.

Crosses: EI vessels, obliterated umbilical artery, obturator nerve, artery & vein, ureter. (358) 

Dilates as ampulla where sperm are stored, parallel to SV.  Ampulla and SV join to form ejaculatory ducts which pass through the prostate to drain into prostatic urethra (open on verumontanum)

-           ductus itself makes only a small contribution to the seminal fluid volume

Artery to vas (from inferior or superior vesical) runs with duct to lower pole of epididymis. 

Seminal vesicle (358)

Blind-ended, infolded tube. At bladder base behind rectovesical fascia; top just covered by peritoneum.

-           lateral to ampulla of DD, covered by fascia of Denonvilliers.  Produces 60% of seminal fluid.

-           secretes fluid of fructose, fibrinogen, vitamin C and prostaglandins.

Blood Flow:

Superior vesical ® ductus deferens (sometimes inferior)

-           accompanies ductus to lower pole of epididymis, may anastomose there with the testicular

Inferior vesicle & middle rectal ® seminal vesicles

Lymph

Accompany blood vessels to nearest iliac nodes

Nerve

Sm muscle ® from inferior hypogastric plexus (mainly L1; motor; reqd for fertility).

Structure

Ductus def has very thick wall compared to lumen; inner and outer longitudinal and inner circ coats

-           stereocilia (elongated microvilli) line the mucous membrane.

Seminal vesicle wall is thinner than ductus wall. Single tube is much convoluted.  Columnar.

Development

Ductus: main derivative of mesonephric duct

SV: forms from duct diverticulum at back of prostate.