Pelvis and Perineum

The Pelvic girdle

The pelvic girdle is the collection of ring shaped bones that connect the vertebral column to the right and left femurs.  They function to bear the weight of the upper body, transfer weight from the axial to the appendicular skeleton, and attachment for the muscles of movement in the lower body.  The pelvic girdle consists of three bones:  right and left hip bones and the sacrum.  Five fused bones come together to form the sacrum.  In infancy and childhood the hip bones are three individual bones: the ilium, ishium, and the pubis.  After puberty these bones fuse to form one hip bone.  The hip bones are connected by what is known as the pubic symphysis.  There are two primary joints of the pelvic girdle. These joints are the sacroiliac joints and the pubic symphysis.

Pelvic Fractures

Pelvic fractures often occur in the weak spots in the pelvis.  They are often the result of direct trauma such as an automobile accident or direct force to the pelvis due to a fall.  The weak spots of the pelvis are the pubic rami, the acetabula, sacroiliac joints, and the alae of the ilium. Other side effects of a pubic fracture are injured soft tissue, nerves and organs.  When the pubo-obturator area is injured, the fracture then becomes complicated, because this area has a close relationship with the urinary bladder and urethra. Pelvic fractures can also cause the urinary bladder or the urethra to tear. 

Urinary Organs

Wastes from the kidneys must be excreted from the body by way of the urinary organs.  The ureters are the muscular tubes that move urine from the kidneys to the urinary bladder.  Ureters are about 25-30 cm in length and are thick muscular tubes.  They are considered retroperitoneal just like the kidneys.  The urinary bladder is the organ that stores urine for excretion. It is a hollow organ with strong muscular walls.  There are some subtle differences in the characteristics of the female urethra and the male urethra. The male urethra is 18-22 cm long, and it serves as an accessory organ to the reproductive system.  The male urethra is where the sperm exits the body.  There are four portions of the male urethra: preprostatic part, prostatic urethra, intermediate part, and the spongy urethra.  The female urethra is about 4 cm in length and is not apart of the reproductive system in females. 

Rupture and Hernia of the Urinary bladder
Oftentimes during childbirth women lose the support of the urinary bladder because of damage to the pelvic floor.  The perineal muscles could be lacerated, a lesion could be present on the nerves that innervate the bladder, or the fascia that supports the bladder could rupture.  Pelvic fractures can cause the bladder to rupture.  When the bladder ruptures, it is often followed by a torn peritoneum.  With a ruptured bladder urine is allowed to excape extraperitoneally and intraperitoneally.

Anal Canal
The anal canal is where the large intestine terminates and becomes the external opening for the release of wastes.  This canal ends at the anus.  The anal canal is surrounded by two sphincters that are between the anococcygeal ligaments and the perineal body.  These sphincters must relax before wastes can exit the body.  The internal anal sphincter is the involuntary sphincter of the two anal canal sphincters and surrounds the upper two-thirds of the anal canal.  It prevents leakage or flatulence, so it is contracted most of the time.  It relaxes in response to fecal material or gas.  The external anal sphincter is the voluntary sphrincter of the anal canal.  It forms the inferior one-third of the anal canal.  This sphincter blends with the puborectalis muscle. 

Hemorrhoids

Internal hemorroids are the entering of  rectal mucosa into the anal canal.  Because the anal sphincters are contracting, the blood flow to this mucosa is hindered.  This causes the ulceration and strangulation.  The arterial anastomoses in this area generate bright red bleeding. Internal hemorrhoids are typically not painful, because this area is innervated by visceral afferent pain fibers. Blood clots in the veins of the external rectal venous plexus is what causes the formation of external hemorrhoids.  Pregnancy, chronic constipation, and straining on the toilet seat are some of the predisposing factors for external hemorrhoids.  The area where external hemorrhoids form is innervated by somatic sensory fibers and often causes pain.