Lecture 45 - Colon Flashcards
what are the 3 main colonic functions
- microbial fermentation
- reabsorption of water and electrolytes
- storage and evacuation
what are the primary cell types in the colon
- absorptive columnar
- goblet cells
- enteroendocrine cells
- Paneth cells
T/F: there are no distinct villi or nutrient transporters in the colon
TRUE
what are short-chain fatty acids
produced by microbes in the gut
also known as VFAs
what are the 3 main VFAs/SCFAs
- acetate
- butyrate
3 proprionate
what are haustra
saccules in the colon, giving it its segmented appearance for enlargement
T/F: carnivores rely on SCFAs for energy
FALSE - herbivores
____ undergoes pre-gastric fermentation and ____ undergo hindgut fermentation
bovine; equine
describe pre-gastric fermentation strategies
- bacteria ferment all dietary components to SCFAs and gas
- fiber retained until digested
- synthesize high quality protein and vitamins
- urea in saliva
T/F: SCFAs are absorbed directly across the epithelium of the rumen
TRUE
too much digestible carbohydrates in the rumen causes
metabolic acidosis
Describe colonic fermentation strategies
- poorly digested carbohydrates fermented to SCFAs
- any proteins/vitamins synthesized and unavailable due to lack of transporters
- high volume of voluntary food intake to compensate for low digestive efficiency
The average person secretes ____ of fluid into the GI tract each day
7L
in dogs and cats the greatest volume of fluid reabsorption is in the
small intestine
the most efficient absorption of water occurs in the
descending colon
what is the job of the ascending colon?
absorb remaining water and product for stool formation
what is the job of the descending colon?
store feces
describe absorption in the ascending colon
- surface epithelium absorbs Cl- and water
- crypt epithelium secretes NaCl and water
describe absorption in the descending colon
both surface and crypt cells absorb NaCl and water enhanced under the control of aldosterone
where is aldosterone made
zona glomerulosa of the adrenal
what locations will aldosterone act to reclaim sodium/water
- kidney
- salivary gland
- descending colon
what is RAAS
Renin-Angiotensin Aldosterone System
regulates blood volume, electrolyte balance, and systemic vascular resistance
why do horses not absorb water in the small intestine
large volumes of fluid are needed for bacterial fermentation in the large intestines
SCFA results in the local production of ______ for…
prostaglandins; inhibit absorption
Aldosterone enhances the reabsorption of _____ and secretion of _____
Na+; K+
where do contractions begin in the colon
transverse right flexure
what is mass movement
type of peristalsis which starts at ileocolic junction and evaluates entire contents (dog, cat, humans)
what is a common site for feed impacture in horses
pelvic felxure
describe colonic mobility in the horse in 7 steps
- ingesta reaches cecum 2hrs post
- cecum mixes every 3-4 minutes
- contractions at pelvic flexure
- anti-persistaltic contractions resist the flow of ingesta and result in retention for fermentation
- separation by particle size
- fecal balls appear in distal colon
- 24-96 hours post ingestion feces
what nerves are involved in defecation
1 pelvic splanchnic n. (parasymp)
2. pudenal n
