Pelvic Cavity - LO 2

2. Understand the gross features and anatomical relationships of the pelvis and pelvic cavity.

The pelvis connects the lower back (i.e. lumbar vertebrae & sacrum) to the lower limbs (i.e. femurs). The pelvic cavity is the inferior portion of the abdominopelvic cavity below the level of the pelvic brim, which contains and transmits portions of reproductive, urinary, and digestive systems.

The bony pelvis is composed of a pair of coxal bones (which meet in an anterior symphysis), flanking the sacrum. 

The coxal bones are each a set of three fused bones (ilium, ischium, and pubis).

When discussing the pelvis, it is sometimes useful to delimit the true pelvis (the region inferior to the pelvic brim) from the false pelvis (the region superior to the pelvic brim). 

The pelvis contains viscera of the GI, urinary, and reproductive (and associated endocrine) systems.

The pelvis transmits the distal portions of the digestive system: the distal sigmoid colon, rectum, and anal canal. The rectum is found in the posterior aspect of the pelvic cavity. 

The pelvis contains the urinary bladder, and transmits the ureters to the the urinary bladder. The ureters enter the pelvic cavity adjacent to the bifurcation of the common iliac aa., and connect to the posterior aspect of the urinary bladder. The urinary bladder is found in the anterior aspect of the pelvic cavity, closely associated with the pubic symphysis. 

When present in the pelvis, reproductive structures are typically situated anterior to the rectum, and posterior, lateral, or superior to the urinary bladder. 

The pelvic viscera are variably covered by the peritoneum. Depending on their relationship to the peritoneum, these structures may be intra-, retro-, or subperitoneal. The rough boundary between retroperitoneal and subperitoneal is the nadir of the recto-uterine or rectovesical pouch. 

In the female pelvis, the peritoneum contacts the anterior abdominal wall, covers the posterior portion of the bladder, reflects superiorly to cover the anterior surface of the uterus, traverses over the fundus of the uterus, and covers the posterior surface of the uterus. At about the level of the internal os of the cervix, the peritoneum reflects onto the rectum and continues up the posterior wall. This leaves the vagina and the bottom third of the rectum devoid of any peritoneal covering.

Areas where the peritoneum reflects from one piece of viscera to another are named: vesico-uterine pouch/bladder reflection/anterior cul-de-sac and recto-uterine pouch/posterior cul-de-sac/pouch of Douglas.

As gravity may conduct fluid inferiorly, materials (blood, exudate, etc.) may accumulate in the recto-uterine pouch. This area may be accessed with a hypodermic needle via the posterior vaginal fornix in a procedure called culdocentesis.

In the male pelvis, the peritoneum contacts the anterior abdominal wall, covers the posterior portion of the bladder and reflects superiorly onto the rectum and continues up the posterior wall. This leaves the prostate, seminal vesicles, and the bottom third of the rectum devoid of any peritoneal covering.

The place where the peritoneum reflects from the bladder to the rectum is called the recto-vesical pouch

Inferior to the pelvic viscera is the muscular floor of the pelvic cavity, the pelvic diaphragm. The pelvic diaphragm separates the pelvic cavity from the perineum, which will be discussed in the following session.