L 27 Genital System & Perineum – Key Vocabulary

Learning Objectives

• Identify anal and urogenital (UG) triangles and list their contents.
• Describe boundaries of the perineum and its subdivision into superficial & deep spaces.
• Locate the perineal membrane, its attachments, and structures piercing it.
• Define the perineal body, its muscular attachments, and clinical significance.
• Inventory deep-perineal-space structures.
• Name male and female external genital parts, erectile tissues, superficial muscles, and glands.
• Compare erectile bodies in ♀ vs ♂.
• Locate male & female gonads, genital ducts, accessory glands.
• List major uterine supports and their pelvic positions.
• Trace sperm from seminiferous tubules to external urethral orifice.
• Contrast vasculature to pelvic organs, gonads, and external genitalia.
• Map pudendal-nerve distribution and fiber types.
• Summarize autonomic innervation: what is visceral vs. somatic.
• Explain clinical correlations in lecture (hernia, vasectomy, hysterectomy supports, Bartholin cyst, prostate hyperplasia, pelvic pain line, etc.).

Genital System Overview

• Components = external genitalia (penis, scrotum, vulva); gonads (testes, ovaries); genital ducts (ductus deferens, uterine tubes, uterus, vagina).
• Topography
– Pelvic cavity: ♂ genital ducts & glands lie sub-peritoneally; ♀ ducts & gonads (uterus, tubes, ovaries) are intraperitoneal.
– External genitalia of both sexes occupy the perineum.
• Sex-based description is by typical morphology at birth; natural variation & gender diversity acknowledged.

Perineum Overview

• Definition: Space inferior to pelvic diaphragm/floor containing external genitalia, termini of urinary/GI/genital tracts, erectile bodies, perineal muscles, glands, neurovasculature.
• Boundaries
– Superior: pelvic diaphragm.
– Peripheral (ant/lat/post): bony & ligamentous pelvic outlet.
• A line between ischial tuberosities divides perineum →
– Posterior anal triangle.
– Anterior urogenital (UG) triangle.

Anal Triangle

• Contains anus & anal canal (terminal GI segment).
• External anal sphincter
– Skeletal muscle encircling canal; attaches to perineal body, coccyx, puborectalis.
– Innervation: inferior rectal nn. (pudendal, $S2-S4$).
• Ischioanal fossae (R & L)
– Pyramid-shaped fat-filled spaces lateral to canal; allow diaphragm motion & anal expansion.
– Fossae continuous posterior to canal (R↔L) and continuous anteriorly with deep perineal space → infection pathway.

Urogenital Triangle

Perineal Membrane

• Dense CT sheet spanning UG triangle.
• Lateral attachment: ischiopubic rami.
• Openings: urethra (♂ & ♀) and vagina (♀).
• Creates two spaces:
– Deep perineal space (superior to membrane / inferior to pelvic diaphragm).
– Superficial perineal space (inferior to membrane).

Perineal Body

• Midline musculo-fibrous mass fused to posterior border of perineal membrane.
• Convergence site: external anal sphincter, puborectalis slips, superficial & deep transverse perineal, bulbospongiosus, plus fibers from levator ani.
• Integrity crucial for pelvic-floor support & fecal continence; vulnerable in childbirth & surgery.

Deep Perineal Space (Pouch)

• Continuous posteriorly with ischioanal fossae (infection route).
• Contents:
– Deep transverse perineal mm.
– External urethral sphincter (plus surrounds prostate in ♂ / vagina in ♀).
– Bulbourethral glands (♂ only).
– Portions of urethra (both sexes) & vagina (♀).
– Neurovasculature (branches of pudendal/internal pudendal).
• Muscle innervation: perineal branches of pudendal n. $S2-S4$.

Superficial Perineal Space (Pouch)

• Membranous boundary: Colles fascia (continuous with Scarpa fascia & dartos fascia).
– Colles attaches to ischiopubic rami laterally and posterior border of perineal membrane → pouch closed on three sides; limits fluid spread.
• Contents:
– Root of penis / clitoris (erectile bodies).
– Superficial perineal muscles.
– Neurovasculature.
– Segments of urethra (both), vagina (♀), greater vestibular glands (♀).

External Genitalia

Male

• Penis (erect in anatomic position)
– Surfaces: dorsal (toward abdomen) & ventral (toward scrotum).
– Shaft composed of three erectile bodies bound by deep fascia:
· 1 corpus spongiosum (ventral, carries spongy urethra).
· 2 corpora cavernosa (paired dorsal).
– Glans = distal expansion of corpus spongiosum; features corona & external urethral orifice.
– Prepuce (foreskin) = skin/fascia hood over glans.
• Scrotum
– Cutaneous sac derived from anterior abdominal wall layers.
– Dartos muscle (smooth) in wall; wrinkles skin to conserve heat.

Female (Vulva)

• Mons pubis: fat pad over pubic symphysis.
• Labia majora: paired fatty folds lateral to labia minora.
• Labia minora: paired thin folds medial; unite anteriorly forming clitoral prepuce.
• Clitoris: body + glans made of two fused corpora cavernosa.
• Vestibule: space between labia minora—houses external urethral orifice, vaginal orifice, greater vestibular-gland ducts.

Erectile Tissues – Roots

Male Root of Penis

• 2 Crura (proximal corpora cavernosa) diverge alongside pubic symphysis; attach to ischiopubic rami & inferior perineal-membrane surface.
• 1 Bulb (proximal corpus spongiosum) midline; anchored to inferior perineal membrane; pierced by urethra → forms spongy urethra.

Female Root of Clitoris

• 2 Crura analogous to ♂; attach as above.
• 2 Bulbs of vestibule (paired, pear-shaped) lie lateral to vestibule/vaginal opening; attach to inferior perineal membrane; swell during arousal to constrict vaginal/external-urethral orifices.
• Greater vestibular glands (Bartholin) sit posterior to bulbs; secrete mucus for lubrication. Obstructed ducts → Bartholin cyst.

Superficial Perineal Muscles (all pudendal n. $S2-S4$; supplied by perineal branches of internal/external pudendal aa.)

• Bulbospongiosus
– Origin: perineal body (♂) or perineal body + each vestibular bulb (♀).
– Insertion: ☿ fascia of corpora spongiosum & cavernosa; ♀ pubic arch & fascia of clitoris.
– ♂: compress bulb & urethra → expel semen/urine; aid erection.
– ♀: compress vestibular bulbs/glands, constrict vaginal orifice; aid clitoral engorgement.
• Ischiocavernosus
– Origin: ischiopubic rami.
– Insert: perineal membrane & crura.
– Function: compress crura → maintain erection/engorgement.
• Superficial transverse perineal
– Origin: ischiopubic rami & ischial tuberosities.
– Insert: perineal body.
– Function: stabilize pelvic floor & perineal body.

Male Genital Ducts, Glands & Gonads

Testis

• Site of spermatogenesis & testosterone production.
• Internal seminiferous tubules produce sperm.
• Blood supply: testicular aa. off abdominal aorta.
• Venous: pampiniform plexus → testicular vv.; right → $IVC$, left → left renal v.

Epididymis

• Tubular structure on posterior testis; sperm storage & maturation; continuous with ductus deferens.

Ductus (Vas) Deferens

• Thick-walled smooth-muscle tube transporting sperm to ejaculatory duct.
• Vasectomy = surgical ligation for permanent contraception.

Descent & Spermatic Cord

• Fetal descent: testes migrate retroperitoneally through inguinal canal into scrotum, dragging vessels, nn., & ductus.
• Spermatic cord components: testicular a., pampiniform plexus, lymphatics, autonomic nn., ductus deferens; enclosed in abdominal-wall fascial layers.
• Inguinal canal weakness → inguinal hernia (bowel loop enters canal adjacent to cord).

Accessory Glands

• Seminal vesicles (paired) on posterior bladder – secrete fructose-rich alkaline semen component; ducts join ductus deferens → ejaculatory ducts.
• Ejaculatory ducts pass through prostate & open into prostatic urethra.
• Prostate gland – encircles prostatic urethra; secretes enzyme-rich alkaline fluid; ducts open directly into urethra. Enlargement (BPH or carcinoma) compresses urethra; palpable per rectum.
• Bulbourethral (Cowper) glands – in deep perineal space; secrete alkaline pre-ejaculate to neutralize urine.

Female Genital Ducts, Glands & Gonads

Ovaries

• Site of oogenesis & estrogen/progesterone production.
• Suspensory ligament of ovary = peritoneal fold containing ovarian a./v. & nerves.

Uterine (Fallopian) Tubes

• Muscular conduits for oocytes → uterine cavity.
• Abdominal ostium = distal opening.
• Fimbriae sweep oocyte inward.
• Tubal ligation = permanent sterilization.

Uterus

• Hollow smooth-muscle organ between bladder & rectum; typically anteverted (vs vagina) & anteflexed (vs cervix).
• Parts
– Body (upper $\tfrac{2}{3}$): fundus (palpated to estimate gestational age), uterine horns (connect tubes), central uterine cavity.
– Cervix (lower $\tfrac{1}{3}$): cervical canal between internal os (superior) & external os (inferior into vagina).
• Wall layers
– Perimetrium (serosa).
– Myometrium (smooth muscle; contracts menses & labor).
– Endometrium (mucosa; partially shed menstruation; implantation site).
• Supports
– Ovarian ligament (ovary→uterus).
– Round ligament of uterus (uterus→labia majora via inguinal canal).
– Broad ligament (double peritoneal fold over uterus/tubes/ovaries).
– Passive: bladder support & pelvic diaphragm.
• Pelvic-floor injury → prolapse / stress incontinence.
• Pap smear: collect epithelial cells around external os to screen for cervical cancer.

Vagina

• Fibromuscular tube cervix → vestibule; normally collapsed but distensible.
• Functions: copulation organ, menses outlet, inferior birth canal segment.

Vasculature & Lymphatics

Gonads

• Ovarian & testicular aa. originate directly from abdominal aorta.
• Venous drainage: right ovarian/testicular vv. → $IVC$; left vv. → left renal v. → $IVC$.
• Ovarian vessels in suspensory ligament; testicular vessels in spermatic cord (with pampiniform plexus for heat exchange).

Pelvic Viscera

• Branches of internal iliac a.
– Uterine & vaginal aa.
– Superior & inferior vesical aa. (bladder) with branches to ducts/glands & cervix.
• Venous plexuses (vaginal, prostatic, etc.) drain → internal iliac vv.

External Genitalia / Perineum

• Primarily internal pudendal a. (off internal iliac):
– Inferior rectal aa. → anal canal, sphincter.
– Perineal aa. → muscles, erectile tissue, vaginal orifice.
• Scrotum & labia majora also supplied by external pudendal aa. (from femoral a.).
• Venous drainage parallels arteries (internal & external pudendal vv. → internal iliac vv. / femoral vv.).

Lymph Flow

• Nodes follow vessels → internal/external iliac nodes → common iliac → lumbar trunks → cisterna chyli → thoracic duct.

Innervation

Somatic (Pudendal N.)

• Origin $S2-S4$ ventral rami; exits pelvis via greater sciatic foramen → wraps sacrospinous ligament → re-enters via lesser sciatic foramen → perineum.
• Branches (accompany internal pudendal vessels):
– Inferior anal/rectal nn.
– Perineal nn. (superficial sensory & deep motor).
– Dorsal n. of penis/clitoris (sensory).
• Supplies motor to superficial/deep perineal mm. & external anal sphincter; sensory to perineum & genitalia.
• Injury affects sexual sensation & urinary/fecal continence.

Autonomic (Visceral Motor)

• Mixed pelvic plexuses carry sympathetic + parasympathetic fibers.
• Sympathetic: spinal levels $T11-L2/3$ via lumbar & sacral splanchnic nn.
– Vasoconstriction.
– Internal urethral sphincter contraction (prevent micturition/backflow).
– Smooth-muscle peristalsis of genital tract; gland secretion during emission/ejaculation.
• Parasympathetic: $S2-S4$ via pelvic splanchnic nn.
– Vasodilation of erectile-tissue arteries → erection/engorgement.
– Detrusor (bladder) contraction for micturition.

Visceral Sensory & Pelvic Pain Line

• Visceral afferents carry pain, distension, etc.
• Pelvic pain line = peritoneal contact border.
– Above line (peritoneal contact): afferents run with sympathetics → $T12-L2/3$ DRG (e.g., ovaries) → refer to abdomen/low back.
– Below line (no peritoneal contact): afferents run with parasympathetics → $S2-S4$ DRG (e.g., cervix, bladder base) → refer to groin/perineum.
• Autonomic nerve injury during pelvic surgery → urinary, anorectal, sexual dysfunction.

Clinical Correlations (Sampling)

• Bartholin (greater vestibular) cyst: duct obstruction → painless swelling; may need drainage.
• Vasectomy: ductus deferens ligation; permanent male contraception.
• Inguinal hernia: bowel loop protrudes via inguinal canal near spermatic cord.
• Benign prostatic hyperplasia (BPH) / carcinoma: prostate enlargement compresses prostatic urethra; palpable on digital rectal exam.
• Pelvic-floor trauma (childbirth) → perineal body damage → prolapse & incontinence.
• Pudendal nerve block used for perineal analgesia during childbirth.

Self-Study Prompts

• Inspect pelvic models: position of pelvic diaphragm vs urethra, vagina, anal canal.
• Compare penile vs clitoral erectile-body configuration.
• Trace male vs female urethra & locate external urethral orifice.
• List muscles inserting on perineal body.
• Name superficial-perineal muscles/fascia attaching to ischiopubic rami.
• Draw oocyte route: ovary → fimbriae → abdominal ostium → uterine tube → uterine cavity.
• Describe blood supply: gonadal aa. vs internal-iliac branches vs pudendal aa.
• Identify primary somatic nerve of perineum (pudendal n.).

Practice Exam Samples

1. Blood from left gonad drains directly into?
   – Correct: Left renal vein.

2. Which structure connects uterine cavity & cervical canal?
   – Correct: Internal os.

Numerical / Root Values Recap
• Pudendal n. roots: $S2-S4$.
• External anal & perineal mm. innervation: $S2-S4$.
• Sympathetic genital pathway: $T11-L2/3$.
• Parasympathetic (pelvic splanchnic): $S2-S4$.