Large Intestine Flashcards
What are the 6 main parts of the large intestine called?
Cecum Ascending Colon Transverse Colon Descending Colon Sigmoid Colon Rectum
What kind of enema is used as contrast in imaging of the large intesting
Barium enema
What are haustra?
The haustra (singular haustrum) of the colon are the small pouches caused by sacculation, which give the colon its segmented appearance.
What kind of valve is the ileoceacal valve?
flutter valve - one way
During ileal distension is the ileoceacal valve open or closed?
open
During caecal distension is the ileocaecal valve open or closed?
closed
What is haustration?
Slow contractions of the circular muscle squeeze contents to and fro, as in segmentation
What is a mass movement?
Occasionally (a few times a day), become organised into a peristaltic wave. Haustra briefly disappear as the mass movement sweeps by, then reform.
What is the coordination of motility in the large intestine controlled by?
Most control is intrinsic, via the enteric nervous system.
Some parasympathetic control.
Motility also affected by enteroendocrine and neurocrine influences, from cells releasing what?
5-HT and Peptide YY
What reflexes can trigger mass movements?
Gastrocolic and orthocolic reflexes.
What is an ileal brake?
The presence of undigested lipid in distal ileum and proximal colon releases peptide YY, slowing gastric emptying and small bowel peristalsis
What is responsible for digestion in the colon?
Bacteria, not enzymes!
When bacteria digest fibre, what is produced?
short chain fatty acids such as butyric acid, hydrogen, and methane.
When bacteria digest urea and amino acids, what is produced?
ammonia
When bacteria digest bilirubin, what is produced?
urobilinogen and stercobilins
When bacteria digest cysetine and methionine, what is produced?
hydrogen sulphide
How are short chain fatty acids absorbed by colonocytes?
Na+ linked transporter. important source of energy for colonocytes
What are ENaC channels?
allow transcellular sodium transport
What hormone is salt absorption in the colon stimulated by?
aldosterone
Which 2 toxins increase cAMP?
cholera and E.coli
What secretagogue does C.Dificile increase?
Ca2+
What type of diarrhoea do cholera, E.coli and C.Dificile lead to?
secretory diarrhoea
What is the balance of potassium in the colon determined by?
plasma [K+], adosterone and cAMP
What type of muscle does the internal anal sphincter have?
smooth muscle
What type of muscle does the external anal sphincter have?
skeletal muscle
What is the dentate (pectinate) line?
Where the epithelium becomes stratified squamous
As faeces enter the rectum, the pressure rises. What does this trigger?
reflex relaxation of the internal anal sphincter, and the urge to defaecate.
What is the purpose of sitting or squatting to defecate?
Sitting or squatting increases the rectosigmoid angle, facilitating the passage of faeces.
What provides the motive force of defecation?
Rectal peristalsis, sometimes triggering
a colonic mass movement, plus raised intraabdominal pressure (Valsalva manoeuvre)
