L12 AN2102 - Perineum

What is the perineum?

The region inferior to the pelvic diaphragm—the area you sit on.

What forms the anterior border of the perineum?

The pubic symphysis.

What forms the anterolateral borders of the perineum?

The ischiopubic rami.

What forms the lateral borders of the perineum?

The ischial tuberosities.

What forms the posterolateral borders of the perineum?

The sacrotuberous ligaments.

What forms the posterior border of the perineum?

The coccyx.

What line divides the perineum into two triangles?

A transverse line between the right and left ischial tuberosities divides The urogenital triangle (anterior) and the anal triangle (posterior).

What structures are found in the female urogenital triangle?

Labia majora, labia minora, vaginal orifice, external urethral meatus, and glans clitoris.

What erectile bodies make up the penis?

Two corpora cavernosa (dorsal) and one corpus spongiosum (ventral).

What structure contains the spongy urethra?

The corpus spongiosum.

What is the glans penis?

The distal expansion of the corpus spongiosum containing the external urethral orifice. the tip lol

What are the functions of the testes?

Exocrine: sperm production;

Endocrine: testosterone secretion.

What is the epididymis?

A structure that stores and matures sperm and continues as the ductus deferens.

What is the ductus (vas) deferens and where does it go?

A tube transporting sperm; ascends in spermatic cord → inguinal canal → pelvis.

What erectile tissue forms the clitoris?

Corpora cavernosa.

Does the clitoris contain a true corpus spongiosum?

No, it does not.

• The clitoris is composed of two corpora cavernosa (erectile bodies) but no single midline corpus spongiosum surrounding a urethra.

  • The female urethra is separate and does not pass through the clitioris

What structure in females is homologous to the corpus spongiosum?

The bulbs of the vestibule.

What are the labia majora?

Outer fatty skin folds of the female external genitalia.

What are the labia minora?

Inner folds that surround the vestibule of the vagina.

What is the superficial perineal pouch?

A potential space located between the deep perineal fascia and the perineal membrane, in the urogenital triangle.`

What structures form the boundaries of the superficial perineal pouch?

• Superior boundary: perineal membrane

• Inferior boundary: deep perineal fascia

  • Lateral boundaries: ischiopubic rami

Is the superficial perineal pouch above or below the perineal membrane?

Below the perineal membrane.

What forms the root of the penis in the superficial pouch?

• Bulb of the penis (midline; corpus spongiosum)

  • Crura of penis (paired corpora cavernosa along ischiopubic rami)

What muscles are found in the superficial pouch of the male?

• Bulbospongiosus (covers the bulb)

• Ischiocavernosus (covers crura)

• Superficial transverse perineal muscles

  • 
    

    

Which part of the urethra is found in the superficial pouch in males?

The proximal (bulbous) part of the spongy urethra.

What is the neurovascular supply in the male superficial pouch?

• Deep perineal branches of internal pudendal vessels

• Perineal branches of pudendal nerve

What parts of the vagina and urethra are in the superficial pouch?

• Perineal part of vagina

  • Distal perineal part of urethra

What erectile tissues are found in the superficial pouch in females?

• Bulbs of vestibule (paired; covered by bulbospongiosus)

• Crura of clitoris (with ischiocavernosus)

What gland is contained in the female superficial pouch?

Greater vestibular (Bartholin) glands, producing vaginal lubrication.

What is the female neurovascular supply?

Same as male:

• Deep perineal branches of internal pudendal vessels

• Perineal branches of pudendal nerve

Where is the deep perineal pouch located?

Between the perineal membrane (inferior) and the inferior fascia of the pelvic diaphragm (superior).

What forms the lateral boundary of the deep pouch?

Obturator fascia over obturator internus.

How does the deep pouch connect to the ischioanal fossa?

Anteriorly via ischioanal fat extensions.

What common structures appear in the deep perineal pouches of both sexes?

• Central urethra

• External urethral sphincter (inferior part)

• Anterior ischioanal fat extensions

• compressor urethrae

• deep transverse perineal mussscles

  • 
    

    

What part of the urethra is found in the deep perineal pouch in males?

The intermediate (membranous) urethra, the narrowest urethral segment.

What glands are located in the deep perineal pouch in males?

Bulbourethral (Cowper’s) glands, which lubricate the spongy urethra.

What neurovascular structures enter in the deep perineal pouch in males?

Dorsal neurovascular bundle of the penis.

What urethral part is located in the deep perineal pouch in females?

The proximal perineal part of the urethra.

What vaginal portion is present in the deep perineal pouch?

The transition portion (pelvic → perineal vagina).

What neurovascular structure enters here?

Dorsal neurovasculature of the clitoris

What is the “urogenital diaphragm”?

Historical term describing:

• Perineal membrane

  • Deep perineal muscles (deep transverse + sphincter + compressor urethrae)

What does the urogenital diaphragm functionally do?

Supports urogenital organs and provides sphincter control.

What is the pelvic diaphragm?

Muscular floor of pelvis:

• Mainly levator ani

• Also coccygeus

What forms the superior boundary of the deep perineal pouch?

The inferior fascia of the pelvic diaphragm.

What does the anal triangle contain?

• Anal canal

• Ischioanal fossae

What are boundaries of the ischioanal fossa?

• Lateral: ischium + obturator internus fascia

• Medial: external anal sphincter

  • Superomedial: levator ani

What fills the ischioanal fossa?

Ischioanal fat pad for expansion during defecation.

What runs in the pudendal canal?

• Pudendal nerve

• Internal pudendal artery & vein

What crosses the fossa to anal canal?

Inferior rectal nerve, artery, vein

What are anal columns?

Vertical mucosal folds containing venous plexuses.

What happens when anal column veins swell?

Internal hemorrhoids.

What is an anal valve?

A fold of tissue joining adjacent anal columns.

What are anal sinuses?

Recesses behind anal valves that collect mucus/debris; lubricate defecation.

---

What embryological transition occurs at the pectinate line?

endoderm above the pectinate line, ectoderm below the pectinate line

What is innervation above the line?

Visceral, autonomic → dull, poorly localized pain.

What is innervation below the line?

Somatic (inferior rectal nerve) → sharp, well-localized pain.

What hemorrhoids occur above the line? Painful?

Internal hemorrhoids → painless.

What hemorrhoids occur below the line? Painful?

External hemorrhoids → painful.

Blood supply above vs below the line?

• Above: superior rectal artery (IMA)

• Below: inferior rectal artery (internal pudendal)

Lymph drainage above vs below pectinate line?

• Above: internal iliac nodes

• Below: superficial inguinal nodes

What pathway drains blood above the pectinate line?

Portal system → liver → possible first-pass metabolism.

What pathway drains below the pectinate line?

Systemic circulation → bypasses liver → stronger drug effect.

What spinal levels form the pudendal nerve?

S2–S4 (“keeps the penis off the floor”)

Explain the course of the pudendal nerve.

• Leaves pelvis → greater sciatic foramen

• Passes behind sacrospinous ligament

• Enters perineum → lesser sciatic foramen

• Travels in pudendal canal

• 
  

What are the 4 main branches of the pudendal nerve (S2-S4)

• Inferior rectal nerve

• Deep perineal nerves

• Superficial perineal nerves

• Dorsal nerve of penis/clitoris

What does the dorsal branch of pudendal nerve supply?

Sensory to glans and body of penis/clitoris.`

What happens if the pudendal nerve is injured?

• Perineal numbness

• Urinary/fecal incontinence

  • Erectile dysfunction possible

What are the major branches of the internal pudendal artery?

• Inferior rectal

• Perineal

• Deep artery of penis/clitoris

• Dorsal artery of penis/clitoris