GI physiology: stomach, small/large intestine

Question 1

What are the 3 layers and function of stomach smooth muscle?

Answer 1

longitudinal=>outer, for peristalsis
circular=> for mixing
oblique=> inner

Question 2

What structures can the stomach be divided into?

Answer 2

fundus, body, antrum

Question 3

how and where does receptive relaxation occur?

Answer 3

mediated by VIP occurs in fundus

Question 4

how is the receptive relaxation work as the stomach fills?

Answer 4

a vagovagal-mediated receptive relaxation occurs allowing storage

Question 5

Before reaching the small intestine, what happens to the bolus of swallowed food?

Answer 5

it is macerated and mixed w/ HCl, mucus, and pepsin => chyme => discharged at controlled rate

Question 6

How much chemical digestion occurs in the stomach?

Answer 6

very small amount

Question 7

How and where does the pacemaker of the stomach work?

Answer 7

w/in greater curvature produces basal electric rhythm (BER) of 3-5 waves/min

Question 8

What controls the magnitude of the gastric contractions?

Answer 8

increased by PANS;

decreased by SANS

Question 9

define migrating motor complexes (MMC)

Answer 9

propulsive contractions initiated during fasting that begin in stomach and move undigested material from stomach and small intestine into colon

Question 10

what mediates the migrating motor complexes?

Answer 10

motilin => repeat every 90-120min

Question 11

why are migrating motor complexes important for general health?

Answer 11

this is a housekeeping function that lowers the bacterial count in the gut

Question 12

what is the pylorus

Answer 12

continuous w/ circular muscle layer;

acts as “valve” to control gastric emptying

Question 13

What limits the movement of chyme into duodenum and promotes retropulsion?

Answer 13

pyloric sphincter contraction at time of antral contraction

Question 14

define retropulsion WRT gastric emptying

Answer 14

mixing by forceful regurgitation of antral contents back into fundus

Question 15

What delays gastric emptying?

Answer 15

• fat/protein in duodenum stimulating CCK release=> increases gastric distensibility
• H+ in duodenum via neural reflexes
• stomach contents that are hypertonic or hypotonic

Question 16

what is the primary role of the small intestine?

Answer 16

digestion and absorption of nutrients via specialized villi on epithelial surface

Question 17

What is the order of structures of the duodenum?

Answer 17

duodenum=> proximal pyloric end
jejunum
ileum

Question 18

Mucus production occurs throughout the GI tract. What produces it in the small intestine?

Answer 18

Brunner glands=> duodenum
Goblet cells => throughout intestine

Question 19

What are the functions of mucus?

Answer 19

lubrication of GI tract;
binding bacteria;
trapping Ig

Question 20

What may INCREASE rate of mucus secretion?

Answer 20

choinergic stimulation;
chemical irritation;
physical irritation

Question 21

How are gastritis, duodenitis and some peptic ulcer diseases related to small intestine?

Answer 21

any compromise of mucous protection can lead to damage and irritation

Question 22

regarding intestinal motility, how do small bowel slow waves move?

Answer 22

move caudally in circular smooth muscle => slows more distally

Question 23

what are the importance of segmentation contractions?

Answer 23

ring-like contractions that MIX INTESTINAL CONTENTS => occur at nodes along intestine

Question 24

define peristalsis

Answer 24

reflex response initiated by stretching of lumen of gut => propel contents caudally

Question 25

what modulates peristalsis?

Answer 25

autonomic input; | can occur in isolated loops of small bowel w/ no extrinsic innervation

Question 26

give the steps to peristalsis occurring

Answer 26

intrinsic control system senses stretch w/ CGRP; contractile wave initiated by ACh and substance P; relaxation caudal to stimulus initiated by NO & VIP

Question 27

what controls the contractions of the small intestine?

Answer 27

PANS increases; | SANS decreases

Question 28

How is small intestinal contents delivered to large intestine?

Answer 28

gastroileal reflex caused by food in stomach => stimulates peristalsis in ileum => relaxes ileocecal valve

Question 29

Why are small intestinal secretions alkaline?

Answer 29

neutralize acid nature of chyme from pylorus

Question 30

Since PANS activates peristalsis, what can be given for a dysfxn of PANS leading to constipation?

Answer 30

dopaminergic and cholinergic agents

Question 31

What muscles constitute the outer layer of the colon?

Answer 31

3 longitudinal bands of muscle => teniae coli

Question 32

How are haustra created?

Answer 32

colon is longer than teniae coli so haustra are created for them to fit

Question 33

How is mucus secreted in large intestine?

Answer 33

short, inward-projecting colonic glands => NO VILLI

Question 34

What are important immunological areas of the colon?

Answer 34

abundant lymphoid follicles => cecum and appendix

Question 35

Major fxns of colon

Answer 35

reabsorption of fluid and electrolytes; | temporary storage of feces

Question 36

What promotes movement of chyme in the colon?

Answer 36

peristaltic waves => increase speed distally

Question 37

What type of contractions are found only in the colon?

Answer 37

mass movement contractions

Question 38

What is the defecation reflex?

Answer 38

distention of rectum w/ feces

Question 39

What are important electrolytes that the large colon is responsible for absorbing?

Answer 39

Na+ actively transported w/ water following it; | K+ and HCO3 secreted into colon

Question 40

in normal feces, what % may be bacterial?

Answer 40

30%

Question 41

Why are bacteria a large portion of feces?

Answer 41

synthesize VITAMIN K, B-complex vitamins, folic acid; split urea to NH3; produce small organic acids from unabsorbed fat and carbohydrate

Question 42

How does PANS causes defecation feeling?

Answer 42

rectal distention w/ feces activates intrinsic and cord reflexes causing relaxation of internal anal sphincter

Question 43

What will lead to defecation actually occurring?

Answer 43

``` pudendal nerve causes external anal sphincter to relax; Valsalva maneuver (increased intra-abdominal pressure) leads to defecation ```

Question 44

What controls the gastrocolic reflex and what is its relation to defecation?

Answer 44

PANS=> distention of stomach by food INCREASES FREQUENCY OF MASS MOVEMENTS and produces urge to defecate