L37 The Pelvis and Perineum Flashcards
What is the difference between the pelvis and perineum?
The Pelvis is basin-shaped found at the caudal end of the body cavity. It is continuous with the abdomen, there is no separation; it is surrounded by a bony pelvis, limited below by the pelvic floor/diaphragm. This is why peritoneal pouches are formed. It is important as the abdominal contents helps to protect the pelvic viscera.
The perineum is the area inferior to the pelvic floor. It is bounded by pelvic outlet, limited inferiorly by the skin. This is a point of attachment for rectile tissue and external genitalia.
What is the sacrospinous ligament?
From the sacrum to the ischial spine is the sacrospinous ligament.
What is the sacrotuberous ligament?
From the sacrum also to the ischial tuberosity is the Sacro-tuberous ligament.
What muscles make up the levator ani?
Running from the pubic symphysis wrapping around the rectum is the puborectalis. The puborectalis slings around the rectum. The rectum changes angle between the rectum and the anus. The puborectalis causes this angle change. This is important for the defecate to be held - during defecation, the puborectalis relaxes, the rectum straightens and enabling defecation.
Attaching from the pubis to the coccyx is the pubococcygeus. This attaches to the obturator arch (the tendinous arch).
From the ileum to the coccyx is iliococcygeus.
What muscles make up the lateral pelvic floor?
- Covering the internal aspect of the obturator foremen is the obturator internus . This muscle leaves the pelvis through the lesser sciatic foremen to attach onto the thigh bone. There is a slight defect in the membrane and muscle which will go onto form the obturator canal. This acts as a passage for some structures.
- Attaching the sacrum passing out of the greater sciatic foreman attaching to the femur is the Piriformis muscle. It is a pear shaped muscle. Found more posteriorly.
- The obturator fascia overlies the obturator internus. There is a larger where it is thickened called the obturator arch. The levator ani hangs from this.
- The posterior wall is formed by the sacrum.
Posteriorly there is the opening for the rectum and anteriorly for the urethra - there is also an opening for the vagina in females. Below the pelvic floor is pelvic cavity, above it is abdominal cavity. - From the ischial spine to the coccyx is the coccygeus. This sits on the interior aspect of the Sacro-spinal ligament.
What is the function of the bony pelvis?
Functions of the bony pelvis
- Surface for muscle attachment: muscles of trunk and lower limb - Transfers weight of trunk to (a) lower limbs (standing) or (b) ischial tuberosity (sitting) - Protect pelvic organs and developing embryo/foetus
As we stand, the pelvis is slightly tilted anteriorly. When we sit down, the pelvis is tilted. This means when gravity is pushing down the vertebral column, the force of gravity is transmitted to the ischium.
What are the fibrous attachments of the pelvis?
There are instead fibrous attachment points:
1. Perineal bony - essential for the integrity of the pelvic floor especially in female. Rupture during pregnancy can predispose to prolapse. It is found between the urethral opening and the rectum in male and between the vagina and rectum in the female. It is a fibromuscular mass. It is also a point of attachment for pelvic floor muscle to interdigitate and an attachment for external sphincters.
Anococcygeal body Between the anus and the coccyx. Found between the anus and the coccyx.
What are the branches of the internal lilac artery?
The common iliac artery branches into an external and iliac branch. The external branch goes under the inguinal ligament - it is then known as the femoral artery. Before it goes under the inguinal ligament, it gives rise to the inferior epigastric artery. This supplies some of the inferior aspect of the anterior wall. It gest covered with a part for peritoneum and forms a fold - the lateral umbilical fold. It is an elevation of peritoneum on the anterior abdominal wall.
The first branch of the internal lilac artery courses towards the anterior wall - umbilical artery. It courses towards the umbilicus, in the foetal circulation this is how blood from the mother to the foetus. In the adult, it becomes obliterated before it gets to the anterior abdominal wall. It becomes covered with peritoneum on the anterior abdominal wall - medial umbilical fold. Before it becomes obliterated, it gives rise to the superior vesical arteries - supplying the superior surface of the bladder. The next vessel in the internal iliac goes towards the defect in the foremen - obturator artery. The next branch is the uterine artery in the female, in the male it is the inferior vesical. In the female it goes onto supply the uterus and vagina, in the male it goes onto supply the seminal vesicle and the prostate. Further posteriorly, is the middle rectal artery (not everyone has this). Just coming off this is an artery that loops around the sacral spinal ligament and enters the perineum bypassing the pelvic floor - internal pudendal artery. This supplies the viscera of the perineum. Looping around this is the pudendal nerve. Slightly posteriorly is an inferior gluteal and a superior gluteal arteries leaving the pelvic cavity out of the greater sciatic foremen.
Where do the three bones of the bony pelvis articulate?
One pelvic bone is comprised of three bones that join together an ileum, and ischium and a pubis. These merge and fuse together in embryological development to form one pelvis. They articulate at the acetabulum, where the femur sits,
What is an episiotomy?
During child birth, the stretched levator ani can tear. Sometimes during childbirth a clinical; makes an incision through the perineal body to make child birth easier. It is called an episiotomy. It can be a midline episiotomy. A problem with this however is it can cause problems with continence in the future. The perineal body is relatively a vascular and so it does not heal as well. If cut through the muscle, there is more blood loss but it will recover better.
