- Pelvis is a ring bone consisting of 4 bones. Two hip bones in front and sides, and sacrum and coccyx posteriorly. All pelvic viscera, i.e. terminal part of digestive and urinary systems, and components of genital system are located in pelvis.
- The pelvis is divided by the plane of the pelvic inlet (pelvic brim or superior aperture of the pelvis) into two pans:
- Upper part called false pelvis (or greater pelvis).
- Lower part called true pelvis (or lesser pelvis).
- Cavity of true pelvis is called pelvic cavity. It is continuous above with abdominal cavity at pelvic inlet (pelvic brim) and is limited below by the pelvic diaphragm which separates it from perineum.
The pelvic floor is formed by 'pelvic diaphragm' which consists of levator ani) and coccygeus. The pelvic diaphragm separates the perineum below from pelvis above. Pelvic diaphragm is traversed by urethra, anal canal anal in females: vagina.
Internal Iliac Artery
It is smaller terminal branch of common iliac artery (the large terminal branch is external iliac artery). It begins at the level of L5-S1 disc space in front of sacroiliac joint and ends near the upper margin of greater sciatic notch, by dividing into anterior division (anterior trunk) and posterior division (posterior trunk).
Branches of anterior division (anterior trunk)
|Superior vesical||Obturator||Middle rectal|
|Inferior vesical (only in males)||Vaginal artery (only in females)||Uterine artery|
|Inferior gluteal||Internalpudendal (only in females)|
Branches of posterior division (posterior trunk)
Two lateral sacral
Pelvic Autonomic Nervous System
- The sympathetic part of ANS comprises a pair of sympathetic trunks and hypogastric plexus of nerves (superior and inferior hypogastric).
- Each pelvic sympathetic trunk consists of four sacral ganglia on each side and the single ganglion impar in center (Ganglion impar:-Sympathetic chains of both side unites in front of coccyx to form ganglion impar).
- Superior hypogastric plexus (presacral nerve) lies in front of L5 below aortic bifurcation. It is formed by three sympathetic roots: One middle and two lateral. Middle root is derived from aortic plexus (through inferior mesenteric plexus) and each lateral root is formed by 3rd and 4th lumbar splanchnic nerves. Parasympathetic fliers from the pelvic splanchnic nerves reach it through inferior hypogastric plexus. Branches of superior hypogastric plexus are:-
- Right and left hypogastric nerves: - Join with pelvic splanchnic nerve of corresponding sides to form right and left inferior hypogastric plexus. This nerve carries fibers from T10 to L2 segments.
- Branches to ureteric, testicular or ovarian, and common iliac plexus.
- Inferior hypogastric plexuses (right and left) are composed of both sympathetic and parasympathetic fibers.
- Middle rectal plexus: - Supplies the rectum.
- Prostatic plexus: - Supplies prostate, seminal vesicles, and ejaculatory ducts.
- Vesical plexus: - Supplies urinary bladder, terminal part of ureter and seminal vesicles.
- Utero-vaginal plexus: - Supplies uterus, uterine tube, ovaries and erectile tissue of vestibule.
- Inferior hypogastric plexus lies on side of rectum, seminal vesicle (cervix in females), prostate (vaginal fornix in females), and posterior part of urinary bladder.
Pelvic splanchnic nerves (Nervi erigentes)
The nervi erigentes represent the sacral outflow of parasympathetic system and arise from ventral rami of S2, S3, and S4. They join the right and left hypogastric nerves to form the inferior hypogastric plexus and are distributed to pelvic organs. Thus distribution of pelvic splanchnic nerve is same as of inferior hypogastric plexus(described above).
- Preganglionic sympathetic fibers for pelvic organs reach in superior hypogastric plexus. Sensory sympathetic fibers (for pain) from body of uterus, urinary bladder and other pelvic organs also reach superior hypogastric plexus.
- From superior hypogastric plexus, postganglionic sympathetic fibers are carried by right and left hypogastric nerves.
- Pelvic splanchnic nerve (carrying preganglionic parasympathetic fibers and also parasympathetic sensory fibers for pain sensation from cervix and over distended bladder and distension of hollow pelvic viscera) joins right and left hypogastric nerves to form inferior hypogastric plexus of corresponding side.
- From inferior hypogastric plexus, autonomic fibers are distributed to various pelvic organs.
Pelvic fascia is formed of connective tissue and continuous above with fascia of abdominal wall and below with fascia of perineum. It is divided into parietal and visceral layers.
Parietal pelvic fascia
The parietal pelvic fascia lines the walls of the pelvic and is named according to the muscle it overlies, for example obturator fascia covering obturator internus and piriformis fascia covering piriformis. It also forms superior and inferior fasciae of pelvic diaphragm.
Visceral layer (endopelvic fascia)
This layer covers and supports all the pelvic viscera. It consists of loose or dense connective tissue depending upon the distensibility of the organ. It ensheathes the vagina, supravaginal cervix, uterus, urinary bladder, urethra and rectum. Hypogastric sheath is the condensation of endopelvic fascia which acts as barrier, separating two potential spaces (retropubic and presacral) and also coveys neurovascular structure.