Lecture 9: The Colonic Phase Flashcards Preview

Gastrointestinal > Lecture 9: The Colonic Phase > Flashcards

Flashcards in Lecture 9: The Colonic Phase Deck (27):
1

Sections of the Large Intestine

1) Cecum
2) Colon
3) Rectum
4) Anus

2

Function of the large intestine?

digestion and absorption that was not done in small intestine

absorbs water

stores waste

3

What is the important sphincter between the small intestine and large? Is it normally closed or open?

ileocecal sphincter

closed

4

What opens the ileocecal sphincter?

peristalsis but the electrical activity of the small intestine does NOT propagate thru the ileocecal valve

5

What regulates colonic function?

Neural pathways

6

What two reflexes influence colonic function?

1) Local (activated by passage of bolus of fecal matter - stimulate short bursts of Cl- and fluid secretion)
2) Long reflex arcs

7

What are the 2 long reflex arcs?

1) Gastrocolic reflex (distention of stomach, increases colonic motility)
2) Orthocolic reflex (rising from bed)

8

What hormone does the colon (and terminal ileum) secrete?

Peptide YY (in response to lipid in lumen)

9

What effects does Peptide YY have on the GI tract?

1) decreases gastric emptying and overall intestinal motility
2) reduces Cl- and fluid secretion (to reduce propulsion of chyme)

10

What are haustrations and how are they formed?

segments of large intestine; formed by short duration contractions

11

Why are haustrations important?

optimize water absorption and mixing

12

What is responsible for producing long duration contractions in the colon?

taeniae coli

13

Where is propulsion of bolus the most vigorous?

small intestine

14

high amplitude propagating contractions occur in healthy individuals _____ times a day from cecum to rectum to clear colon

10

15

Which autonomic branch enhances motility in the large intestine?

parasymp --> vagus controls haustrations in cecum and colon

16

The major role of the colonic epithelium is to absorb and secrete ____________ and ______ (not nutrients)

electrolytes and water

17

What special nutrient can the colon alone absorb?

Short chain fatty acids (SCFA) which are produced by colonic bacteria

18

How are SCFAs absorbed in the colon?

in a Na dependent fashion by symporters (Sodium Monocarboxylate Transporters SMCTS)

19

What key Na concentration feature is key to absorb SCFAs?

low intracellular Na (established by Na/K-ATPase)

20

Where is Na absorbed in the colon and how?

distal colon via ENaC (epithelial Na channel)

21

What opens ENaC?

neurotransmitters or hormones (Na enters the cytosol and is transported across basolateral membrane by Na/K ATPase)

22

How is ENaC implicated in patients with IBS?

these patients have reduced ENaC so water is not absorbed with Na (since Na is not absorbed) leading to diarrheal symptoms

23

True or false: The rectum contains circular muscle?

FALSE

24

What type of muscle makes up the anal canal?

smooth and skeletal

25

What type of muscle makes up the internal anal sphincter?

circular

26

What type of muscle makes up the external anal sphincter?

striated

27

What relaxes the internal anal sphincter?

filling of the recturm