Perineum

Inferior part of pelvic outlet between thighs, separated from pelvic cavity superiorly by pelvic floor

Boundaries:

  • Anterior – Pubic symphysis, mons pubis/base of penis
  • Posterior – Tip of coccyx, intergluteal cleft
  • Lateral – Medial thigh, inferior ischiopubic rami, sacrotuberous ligament
  • Roof – Pelvic floor
  • Base – skin and fascia

Image result for perineum boundaries

 

Blood supply: Internal and external pudendal

Nerves: Pudendal, ilioinguinal, posterior cutaneous nerve of thigh

Lymphatics:

  • Glans penis/clitoris – Deep inguinal nodes
  • Testis/ovaries – Lumbar
  • Rest of perineum – Superficial inguinal

 

Perineal body:

Fibromuscular mask at junction of urogenital and anal triangle. Has skeletal muscles, smooth muscles, collagen and elastic fibers

Muscles that attach to it:

  • Levator ani
  • Bulbospongiosum
  • Superficial and deep transverse perineal muscles
  • External anal sphincter
  • External urethral sphincter

 

Clinicals:

  • Damage during childbirth – Stretching or tearing, therefore possible prolapse of pelvic viscera. Can be avoided by episiotomy (surgical cut in the muscular area between the vagina and the anus)
  • Pudendal and ilioinguinal nerve block – during labour or episiotomy

 

Anal triangle

Contents:

  • Anal aperture
  • External anal sphincter muscle
  • Two ischioanal fossae – spaces lateral to anus

Ischioanal/ischiorectal fossae:

Boundaries:

  • Anterior – Pelvic diaphragm, perineal body
  • Posterior – Sacrotuberous ligament, gluteus maximus
  • Superior – Levator ani
  • Inferior – Perineal skin
  • Medial – Anal canal, external sphincter
  • Lateral – Ischial tuberosity, obturator internus

 

Image result for ischioanal fossa

 

Content: 

  • Fat
  • Internal pudendal vessels
  • Pudendal nerve
  • Inferior rectal vessels and nerve

 

Clinicals:

  • Ischianal abscess – infection due to wound
  • Anal fissure – anal valve tears

 

Urogenital triangle

Coronal section:

Image result for urogenital triangle coronal section

 

Superficial perineal pouch:

Boundaries:

  • Anterior – continuous with Scarpa’s fascia
  • Roof – Perineal membrane
  • Floor – Perineal fascia
  • Lateral – Ischiopubic ramus

Contents:

  • Root of penis
  • Superficial perineal muscles
  • Ischiocavernosus and bulbospongiosum muscles
  • Vestibular glands (♀)
  • Superficial transverse perineal nerve
  • Clitoris (♀)
  • Bulb of vestibule (♀)

 

Deep perineal pouch:

Boundaries:

  • Superior – Pelvic diaphragm
  • Inferior – Perineal membrane
  • Lateral – Obturator fascia

Contents:

  • Deep transverse perineal muscles
  • External urethral sphincter
  • Membranous urethra
  • Bulbourethral glands
  • Internal pudendal vessels
  • Artery of bulb of penis

 

Clinicals:

  • Extravasation of urine – interruption of urethra, collection of urine in scrotum or penis
  • Bartholin’s gland cyst

Pelvic diaphragm

Separates pelvic cavity (true pelvis) and perineum (genitalia and anus)

Pelvic viscera (bladder, rectum, genital organs) reside in pelvic cavity

Pierced by: Rectal hiatus, urogenital hiatus (urethra, vagina)

Functions:

  • Support viscera
  • Resistance to increase in intrapelvic pressure while coughing etc
  • Sphincter action on urethra and rectum
  • Support fetal head

 

Clinicals:

  • Injury during childbirth – prolapse of pelvic viscera, urinary/rectal incontinence

 

Urinary bladder

 

Image result for urinary bladder parts

 

Position: Anterior in pelvic cavity, posterior to pubic symphysis, infront of uterus, cervix and vagina

2 sphincters:

1. Internal urethral sphincter:

  • Males: Circular smooth fibers, autonomic control, prevent seminal regurgitation during ejaculation
  • Females: No muscle

2. External urethral sphincter: Skeletal muscle under voluntary control

Relations:

  • Anterior – pubic bone, median umbilical ligament
  • Posterior – Rectum, vas deferens, seminal vesicle, vagina, uterus
  • Superior – Peritoneum, sigmoid colon, coils of small intestine, fundus of uterus
  • Inferior – Pelvic diaphragm, prostate
  • Lateral – Obturator internus, levator ani muscles

Support: Median umbilical ligament, pelvic diaphragm, urogenital diaphragm, puboprostatic ligament (males) and pubovesical ligament (females)

Blood supply: Superior and inferior vesical, obturator, inferior gluteal, vaginal and uterine (for females)

Nerves: 

  • Sympathetic – Hypogastric nerve (T12-L2) – relax detrusor muscle, urine retention
  • Parasympathetic – Pelvic splanchnic (S2-S4) – contract detrusor muscle, stimulate micturition
  • Somatic – Pudendal nerve (S2-S4) – innervate external urethral sphincter, constrict (storage), relax (micturition)

Lymphatics: Internal and external iliac

Bladder stretch reflex:

Image result for Bladder stretch reflex:

Clinicals:

  • Spinal cord injury:
  1. Above T12 – No awareness of bladder filling, no control over external sphincter, constantly relaxed bladder
  2. Below T12 – Flaccid bladder, detrusor muscle paralysed, bladder fills uncontrollably
  • Rupture of bladder – fracture/injury, urine escapes to extraperitoneal or intraperitoneal
  • Cystocele – prolapsed bladder into anterior vagina wall
  • Cystostomy – opening of bladder to drain urine
  • Cystoscopy camera inserted into bladder via urethra

 

Urethra

Extent:

  • Males: Internal urethral orifice (bladder) – external urethral orifice (tip of glans)
  • Females: Neck of bladder – urethral orifice in vetibule

Blood supply: Inferior vesical, middle rectal, dorsal artery of penis, artery of bulb, internal pudendal, vaginal

Venous: Prostatic venous plexus, internal pudendal

Nerves: Inferior hypogastric plexus (sympathetic and parasympathetic), pudendal (somatic)

Lymphatics: Internal iliac, deep inguinal

NB: Male urethra divided into 4 parts:

  1. Preprostatic: Internal urethral orifice – prostrate
  2. Prostatic: Through prostate gland, ejaculatory duct and prostatic ducts drain into urethra here
  3. Membranous: Surrounded by external urethral sphincter – voluntary control
  4. Spongy: Through bulb and corpus spongiosum, bulbourethral glands empty here

 

Image result for male urethra divisions

 

Clinicals:

  • Urinary tract infection
  • Male catheterisation – insert tube through urethra into bladder when patient cannot pass urine

 

Rectum

Position: True pelvis, posterior end

Flexures: 2 anteroposterior and 3 lateral

Image result for rectum flexure

Final segment of rectum is called ampulla – relaxes to store faeces

Relations:

Image result for rectum relations

 

Blood supply: 

  • Superior rectal (from IMA)
  • Middle rectal (from internal iliac)
  • Inferior rectal (from internal pudendal)

Nerves: Hypogastric plexus

Lymphatics: Pararectal and internal iliac

Clinicals:

  • Hemorrhoids – thrombosis of external rectal plexus
  • Proctoscope – examine anal canal, rectum and sigmoid colon
  • Rectocele
  • Digital rectal examination

 

Difference between male and female pelvis

Image result for difference between male and female pelvis


 

Anal canal

Position: In anal triangle between ischioanal fossae, from rectum to anus

Relations: 

  • Lateral: Ischioanal fossae
  • Posterior: Coccyx and sacrum
  • Anterior: Perineal body, urogenital diaphragm, urethra, bulb of penis, vagina

Sphincters: 

  • Internal – upper 2/3, involuntary
  • External – Lower 1/3, voluntary

NB: Pectinate line – divides anal canal into upper (embryonic hindgut) and lower (ectoderm of proctodeum) parts

Blood supply: Superior rectal (above pectinate line), Inferior rectal (below)

Nerves: Autonomic – Inferior hypogastric plexus (above pectinate line), Somatic – pudendal nerve (below)

Lymphatics: Internal iliac (above pectinate line), superficial inguinal (below)

Clinicals:

  • Anal fissure – anal valve tears
  • Hemorrhoids – constipation
  • Perianal abscess
  • Anal fistula
  • Anorectal incontinence – pudendal nerve damage

 

These are summarized notes from various sources, mainly TeachMeAnatomy and Wikipedia

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