Lecture 45 - Colon

Question 1

what are the 3 main colonic functions

Answer 1

1. microbial fermentation
2. reabsorption of water and electrolytes
3. storage and evacuation

Question 2

what are the primary cell types in the colon

Answer 2

1. absorptive columnar
2. goblet cells
3. enteroendocrine cells
4. Paneth cells

Question 3

T/F: there are no distinct villi or nutrient transporters in the colon

Answer 3

TRUE

Question 4

what are short-chain fatty acids

Answer 4

produced by microbes in the gut
also known as VFAs

Question 5

what are the 3 main VFAs/SCFAs

Answer 5

1. acetate
2. butyrate
   3 proprionate

Question 6

what are haustra

Answer 6

saccules in the colon, giving it its segmented appearance for enlargement

Question 7

T/F: carnivores rely on SCFAs for energy

Answer 7

FALSE - herbivores

Question 8

____ undergoes pre-gastric fermentation and ____ undergo hindgut fermentation

Answer 8

bovine; equine

Question 9

describe pre-gastric fermentation strategies

Answer 9

• bacteria ferment all dietary components to SCFAs and gas
• fiber retained until digested
• synthesize high quality protein and vitamins
• urea in saliva

Question 10

T/F: SCFAs are absorbed directly across the epithelium of the rumen

Answer 10

TRUE

Question 11

too much digestible carbohydrates in the rumen causes

Answer 11

metabolic acidosis

Question 12

Describe colonic fermentation strategies

Answer 12

• 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

Question 13

The average person secretes ____ of fluid into the GI tract each day

Answer 13

7L

Question 14

in dogs and cats the greatest volume of fluid reabsorption is in the

Answer 14

small intestine

Question 15

the most efficient absorption of water occurs in the

Answer 15

descending colon

Question 16

what is the job of the ascending colon?

Answer 16

absorb remaining water and product for stool formation

Question 17

what is the job of the descending colon?

Answer 17

store feces

Question 18

describe absorption in the ascending colon

Answer 18

1. surface epithelium absorbs Cl- and water
2. crypt epithelium secretes NaCl and water

Question 19

describe absorption in the descending colon

Answer 19

both surface and crypt cells absorb NaCl and water enhanced under the control of aldosterone

Question 20

where is aldosterone made

Answer 20

zona glomerulosa of the adrenal

Question 21

what locations will aldosterone act to reclaim sodium/water

Answer 21

1. kidney
2. salivary gland
3. descending colon

Question 22

what is RAAS

Answer 22

Renin-Angiotensin Aldosterone System

regulates blood volume, electrolyte balance, and systemic vascular resistance

Question 23

why do horses not absorb water in the small intestine

Answer 23

large volumes of fluid are needed for bacterial fermentation in the large intestines

Question 24

SCFA results in the local production of ______ for…

Answer 24

prostaglandins; inhibit absorption

Question 25

Aldosterone enhances the reabsorption of _____ and secretion of _____

Answer 25

Na+; K+

Question 26

where do contractions begin in the colon

Answer 26

transverse right flexure

Question 27

what is mass movement

Answer 27

type of peristalsis which starts at ileocolic junction and evaluates entire contents (dog, cat, humans)

Question 28

what is a common site for feed impacture in horses

Answer 28

pelvic felxure

Question 29

describe colonic mobility in the horse in 7 steps

Answer 29

1. ingesta reaches cecum 2hrs post 2. cecum mixes every 3-4 minutes 3. contractions at pelvic flexure 4. anti-persistaltic contractions resist the flow of ingesta and result in retention for fermentation 5. separation by particle size 6. fecal balls appear in distal colon 7. 24-96 hours post ingestion feces

Question 30

what nerves are involved in defecation

Answer 30

1 pelvic splanchnic n. (parasymp) 2. pudenal n