Lecture 20 - colon (freeman)

Question 1

microbial digestion - perfect environmental conditions

Answer 1

availability of substrate
prolonged rentention time
anaerobic conditions
continuous buffering
hydration of contents

Question 2

colon motility

Answer 2

prolonged retention time
propulsion and retropulsion
pacemaker in pelvic flexure

Question 3

neutralization of contents

Answer 3

high Cl and low bicarb concentration in pancreatic fluid and intestinal fluid

Question 4

how are contents neutralized in ileum and distal jejunum?

Answer 4

Cl/HCOe exchange

Cl may provide a source for exhange of bicarb for neutrailization later in the cecum

Question 5

large intestine function

Answer 5

absorb large volumes of water, Na and bicarb in response to a cyclic pattern of microbial digestion

95% of Na, bicarb and water in large intestine is reabsorbed daily

Question 6

cecum function

Answer 6

water conservation

Question 7

distal colon function

Answer 7

conserve sodium and water retained earlier for microbial ferementation

Question 8

a high fiber diet will need…

Answer 8

more water for microbial fermentation/buffering

Question 9

ion transport: Na absorption in proximal colon

Answer 9

electoneutral exchange with H

Question 10

ion transport: Na absorption in distal colon

Answer 10

aldosterone-controlled (Na/K exchange - Na out, K in)

Question 11

enterosystemic cycle

Answer 11

a process that conserves water lost in digestive secretions

important when:

1. feeding practices alter “normal grazing” patterns (like horses being fed twice a day)
2. animals with diarrhea

Question 12

horses and enterosystemic cycle

Answer 12

horses are continuous grazers and consume hi fiber diets - large ECF volumes are drawn into colon daily and need to be replaced.

horses fed in ways that deviate from normal grazing –> plasma volume can decrease by 15%! –> result: hypovolemia (shock)

decrease in ECF –> hypovolemia –> activates renin-angiotensin-aldosterone system –> Increase renin –> increase angiotensin –> increase aldosterone –> aldosertone secretion can increase colonic and kidney reabsorption of Na and water –> dehydrating components to point of impaction and colic!