Pelvis

Female Pelvis

Describe the anatomy of the uterus (30 Marks)

DESCRIPTION OF UTERUS

• Thick walled, pear shaped hollow muscular organ
• Normally anteverted (relative to the vagina) and anteflexed (relative to the cervix)
• Secondary sex organ where fertilised ovum implants and fetal development occurs

PARTS OF UTERUS

• Fundus of the uterus – rounded part superior to the orifices of the uterine tubes
• Body of the uterus – superior 2/3 of the organ, includes fundus of the uterus, lies within the layers of the broad ligament and is freely moveable. Has two surfaces: anterior (vesical) and posterior (intestinal surface)
• Isthmus of the uterus – between the body of the uterus and cervix of the uterus, 1cm long
• Cervix of the uterus – cylindrical, narrow 1/3 of the uterus, 2.5cm long in adult, non pregnant women.
  • Supravaginal part of cervix – above the vagina
    • Separated from bladder anteriorly by loose connective tissue
    • Separated from the rectum posteriorly by rectouterine pouch
  • Vaginal part of cervix – protrudes into the vagina and
    • contains the external os of the uterus
    • Surrounded by vaginal fornix

INTERNAL PARTS OF UTERUS

• Uterine horns – superolateral corners of the uterine cavity where the uterine tubes enter
• Internal os
• Cervical canal
• External os

3 LAYERS OF THE UTERINE WALL

• Perimetrium – serosa or outer serous coat, consists of peritoneum supported by a thin layer of connective tissue
• Myometrium – middle coat of smooth muscle. Main branches of the blood vessels and nerves of the uterus are located in this coat.
• Endometrium – inner mucous coat – firmly adherent to the myometrium.

CERVIX

• Mostly fibrous tissue made up of collagen, small amount of smooth muscles and elastin

LIGAMENTS 

Gubernaculum ligaments:

• Ligament of the ovary attaches the uterus posteroinferior to the uterotubal junction
• Round ligament of the uterus attaches anteroinferiorly to this junction
  • ^^^These two ligaments are from ovarian gubernaculum

Broad ligament:

• Broad ligament of the uterus –
  • double layer of peritoneum (mesentery) that extends from the sides of the uterus to the lateral walls and floor of the pelvis.
  • Laterally, the broad ligament is prolonged over the vessels as the suspensory ligament of the ovary
  • Uterine tube lies in the antero-superior free border of the broad ligament, within a small mesentery called mesosalpinx
  • Ovary lies within a small mesentery called the mesovarium on the posterior aspect of the broad ligament, inferior to the mesosalpinx and mesovarium
  • Mesometrium – largest part of the broad ligament, inferior part

3 ligaments from cervix:

• Transverse cervical ligaments (cardinal) extend from the cervix + lateral parts of the fornix of the vagina to à lateral walls of the pelvis
• Uterosacral ligaments – from sides of the cervix à pass superior and posterior à to the middle of the sacrum.
• Pubocervical ligament

Ovarian ligament:

• Suspensory ligament of the ovary – lateral part of the broad ligament that covers the ovarian vessels

RELATIONS

• Peritoneum covers the uterus anterior and superiorly except for the cervix. Peritoneum is reflected anteriorly from the uterus onto the bladder and posteriorly over the posterior part of the fornix of the vagina to the rectum
• Inferior: pelvic diaphragm, bladder, cervix
• Anterior: vesicouterine pouch, superior surface of bladder, pubic symphysis
  • Supravaginal part of the cervix is separated from the bladder by only fibrous connective tissue
• Superior: peritoneal cavity
• Posterior: rectovesical pouch with loops of bowel, anterior surface of the rectum
• Laterally: broad ligament, transverse cervical ligaments, uterine artery crosses the ureter superiorly near the lateral fornix (2cm lateral to the supravaginal part of the cervix),

ARTERY

• Uterine artery arising from the anterior division of the internal iliac artery
  • Travels laterally to medially, travelling above the ureters 2cm lateral to the lateral fornix of the bladder
  • Then divides into the ascending and descending branches
  • Ascending branches supply the body of the uterus, fundus and fallopian tubes
  • Anastomoses with the vaginal artery inferiorly and the ovarian artery superiorly
• Vaginal artery from the anterior division of the internal iliac artery sends some ascending branches which anastomose with the uterine artery
• Ovarian artery from the abdominal aorta via suspensory ligament of the ovary supplies the ovary and sends some tubal branches to anastomose with the uterine artery

VEIN

• Uterine venous plexus formed on each side of the cervix and body of uterus
• Merges with the vaginal veins draining the vaginal venous plexus
• Drains via uterine veins (venae communicates around uterine artery)
• -> drain into the internal iliac veins
• Also drain via the ovarian veins from the ovary
• Lower vagina also drained by internal pudendal vein

LYMPH (travel along vessels and ligaments)

• Fundus and superior uterine body -> ovarian vessels -> lumbar (caval/aortic) lymph nodes
• Fundus near entry of the uterine tubes and attachment of round ligament -> run along round ligament -> superficial inguinal lymph nodes
• Uterine body and cervix -> broad ligament -> external iliac lymph nodes
• Cervix -> transverse cervical ligaments -> internal iliac lymph nodes
• Cervix -> uterosacral ligaments -> sacral lymph nodes

NERVE supply of the uterus + superior 4/5 of the vagina – visceral innervation only

• PNS from S2-4 pelvic splanchnic nerve
• SNS from lumbar splanchnic nerves and intermesenteric hypogastric plexus
• Both SNS and PNS go to inferior hypogastric plexuses -> uterovaginal nerve plexus -> travels with uterine arteries

• Uterovaginal nerve plexus (part of pelvic plexus) supplies vagina and uterus! – travels with the uterine artery at the junction of the base of the peritoneal broad ligament and superior part of the fascial transverse cervical ligament.
• Uterovaginal nerve plexus extends to the pelvic viscera from the inferior hypogastric plexus. SNS, PNS + visceral afferent fibres pass through this plexus
• PNS causes vasodilation of the clitoris and bulb of the vestibule

PAIN visceral afferent innervations

• Intraperitoneal, fundus, body (superior to pelvic pain line) -> follows SNS retrograde to reach the inferior thoracic-superior lumbar spinal ganglia T12-L2
• Sub peritoneal, cervical (inferior to pelvic pain line) -> follows PNS to S2-4

NON-PAIN Visceral afferent innervation -> follow PNS (S2-4)

VARIANTS

• Double / bicornate uterus – incomplete fusion of the embryonic paramesonephric ducts
• Retroverted uterus – during increased abdominal pressure, the uterus is pushed into or through the vagina – more likely for uterus to prolapse
• Unicornuate
• Didelphys/Septate/Arcuate uterus