Rectum/Anal Canal Flashcards
The rectum is technically a part of what gastrointestinal structure?
Large intestine (between the sigmoid colon and the anal canal)
What is the rectosigmoid junction of the rectum and where is it located?
Upper limit of the rectum located at the middle of the sacrum
What is the anorectal junction and where is it located?
The lower limit of the rectum located at the upper border of the pelvic diaphragm
What muscles forms a sling around the rectum at the anorectal junction?
Puborectalis
What is the rectal ampulla and where is it located?
Dilated terminal portion of the rectum located immediately above the pelvic diaphragm
How many transverse rectal folds are there?
Three
Does the rectum have mesentery, omental appendices, or haustra?
No.
Does the rectum have taeniae coli?
Yes, but it’s spread out as a complete layer unlike the intestines
Peritoneum covers what parts of the upper third of the rectum?
Front and sides
Peritoneum covers what parts of the middle third of the rectum?
Front
Peritoneum covers what parts of the lower third of the rectum?
There is no peritoneal covering here
The anal canal is between what two structures?
Pelvic diaphragm and anus
About how many anal columns lie in the anal canal?
5-10
What vascular structures do each anal column contain?
Small branch of the superior rectal artery and a small tributary of the superior rectal vein
What are the longitudinal folds of mucosa which lie in the upper half of the anal canal?
Anal columns
What are the crescent-shaped folds which connect the lower ends of the anal columns?
Anal valves
What are the recesses located between the anal valves and the wall of the anal canal?
Anal sinuses
What marks the lower limit of the anal valves around the circumference of the anal canal?
Pectinate line
What is the bluish white zone located inferior to the pectinate line?
Anal pecten
What is the distal termination of the anal canal where it meets the skin?
Anocutaneous line
Which anal sphincter is under involuntary control?
Internal anal sphincter
Which anal sphincter is a continuation of the smooth muscle layer of the rectum below the pelvic diaphragm?
Internal anal sphincter
What are the three parts of the external anal sphincter?
Subcutaneous, superficial, and deep parts
What is the nerve supply of the external anal sphincter?
Nerve to external anal sphincter (S4)
What is the function of the external anal sphincter?
Closes anal orifice
Which anal sphincter is under voluntary control?
External anal sphincter
From where does the superior rectal artery arise?
Inferior mesenteric artery
From where does the middle rectal artery arise?
Internal iliac artery
From where does the inferior rectal artery arise?
Internal pudendal artery
From where does the median sacral artery arise?
Abdominal aorta
What arteries make up the blood supply of the rectum and anal canal?
Superior, middle, and inferior rectal arteries and the median sacral artery
What are internal hemorrhoids?
Varicosities of the superior rectal vein
Internal hemorrhoids cause bulging of what anal structures?
Anal columns
Are internal hemorrhoids painful?
No, painless
Where do internal hemorrhoids occur?
Above the pectinate line
What are external hemorrhoids?
Varicosities of the inferior rectal vein
Where do external hemorrhoids occur?
Below the pectinate line
Are external hemorrhoids painful?
Can be very painful
What are the causes of both types of hemorrhoids?
Pregnancy, heavy lifting, sitting, straining-chronic constipation, portal hypertension
Why can heavy lifting cause hemorrhoids?
Due to the increased intra-abdominal presure
What would be a possible morbid underlying cause of hemorrhoids?
Portal hypertension
What group of people are at a high risk for developing hemorrhoids?
Long distance trunk drivers
What is the epithelium like in the anal canal above the pectinate line?
Columnar or cuboidal
What is the epithelium like in the anal canal below the pectinate line?
Stratified squamous
What is the nerve supply of the anal canal above the pectinate line?
Autonomic fibers
What is the nerve supply of the anal canal below the pectinate line?
Pudendal nerve
What is the venous supply of the anal canal above the pectinate line?
Superior rectal
What is the venous supply of the anal canal below the pectinate line?
Middle, inferior rectal
Which lymph nodes are found in the anal canal above the pectinate line?
Internal iliac
Which lymph nodes are found in the anal canal below the pectinate line?
Superficial inguinal
The upper visceral 2/3 of the anal canal is from which embryologically derived structure?
Hindgut
The lower somatic 1/3 of the anal canal is from which embryologically derived structure?
Proctodeum
What part of the GI tract accumulates fecal matter?
Sigmoid colon
What is usually contained in the rectum?
Nothing; it is usually empty
How does the sigmoid colon empty its contents into the rectum?
Through mass peristaltic movement
During defecation, what muscles contract to increase pressure within the rectum?
The longitudinal muscle layer of the rectum and the anterior abdominal wall muscles
What muscle relaxes during defecation to decrease the angle of the perineal flexure?
Puborectalis
What is opened due to the increase in pressure within the rectum during defecation?
Internal anal sphincter
What is relaxed under voluntary control during defecation?
External anal sphincter
What are the steps of defecation?
- Sigmoid colon empties contents into rectum by mass peristalsis
- Muscles contract to increase rectal pressure
- Puborectalis relaxes
- Internal anal sphincter opens
- External anal sphincter relaxes
