Chapter 94: Rectum, Anus and Perineum Flashcards
What is unique about the resting membrane potential in GI smooth muscle cells?
The resting membrane potential is not constant. It oscillates in slow waves over time, generated by pacemaker cells called the interstitial cells of Cajal
How many bacteria are there per gram of feces?
10^9 bacteria per gram of feces
- Up to 90% anaerobes
Where is the most common location for a perineal hernia in dogs?
Between external anal sphincter and levator ani
What anatomical difference is there regarding the perineum in dogs and cats?
Cats do not have a sacrotuberous ligament
Where is the colorectal junction? The rectoanal junction?
Colorectal is arbitrary but the entry of the cranial rectal artery can be used as a point.
Rectoanal is ventral to 2nd or 3rd caudal vertebrae (also where the mesorectum ends).
Intraperitoneal rectum has what four layers?
Mucosa
Submucosa
Muscularis (has inner circular and outer longitudinal layers)
Serosa
What is different about retroperitoneal rectum vs intraperitoneal?
It LACKS serosa
What is the main blood supply to the rectum?
Cranial rectal artery
The intrapelvic has poorer supply in dogs, but in cats the middle and caudal rectal aa. step up)
How long is the anal canal?
1-2 cm, beneath the 4th caudal vertebra
What muscles surround the anal canal?
Smooth internal and striated external anal sphincter.
What is the anorectal line?
Where columnar rectal epithelium changes to stratified squamous (cutaneous) zone
Where do the anal sac ducts open through?
The cutaneous zone.
Blood supply to the anus?
Right and left caudal rectal aa. and branches of the internal pudendal.
**Cranial rectal artery too **
Where does venous drainage from the anus end up?
CVC and Portal systems
Where does the lymph drainage of the anus go?
Sacral, medial and internal iliac nodes.
How long and how wide are the ducts of the anal sacs?
5mm long, 2mm wide
What are the anal sacs?
2 paranal sinuses between the inner smooth and outer striated sphincters lined with stratified squamous epithelium.
What is the perineal fascia?
Convergence of the fascia of the tail, pelvis and thighs at the anus.
What are the components of the pelvic diaphragm?
Pelvic fascia, coccygeus, levator ani
What are the ischiorectal fossae?
Bilateral, deep, pyramidal depressions lateral to the tail and anus.
These are filled with hernia contents in perineal hernias.
What is the blood supply to the pelvic diaphragm?
internal pudendal and caudal gluteal arteries
IMPORTANT
What are the circumanal glands?
Hepatoid glands that regress in adult females/ are testosterone influenced.
Circumanal gland tumor, also referred to as perianal tumor/adenoma or hepatoid gland tumor is a common perineal neoplasm. Usually benign.
What glands produce the anal sac yuck?
Paranal sinus glands. In the wall and duct of the sac, large, coiled apocrine tubules.
Which extends further caudal, external or internal anal sphincter?
Internal.
What is responsible for voluntary anal continence?
External anal sphincter, a circular band of striated muscle.
What are the three components of the pelvic plexus?
Parasympathetic pelvic nn.
1-3 sacral nerves
Sympathetic fibers from hypogastric n.
What nerve provides voluntary motor to the external anal sphincter?
Sensation?
Motor: Caudal rectal branch of pudendal nerve
Sensory: Perineal branch of pudendal nerve
What are cells of Cajal?
Pacemaker cells that allow slow waves of peristalsis to reach both layers of rectal mm.
