Lecture 5: Response of the Gut to a Meal

Question 1

Major function of the GI tract

Answer 1

extract water, nutrients, and electrolytes from food and to expel the undigested residue as feces

Question 2

what is motility?

Answer 2

Mechanism by which gut contents are moved from proximal to distal

Question 3

Describe the integrated response to a meal

Answer 3

Food is ingested–>digested–>absorbed–>eliminated. Motor and secretory behaviors aid in this process.

Question 4

4 major functions of the gut

Answer 4

1) secretion
2) digestion
3) absorption
4) motility

Question 5

Function of the Upper Esophageal Sphincter (UES)

Answer 5

closes off the pharynx and prevents air from entering into the esophagus during breathing, and prevents reflex of esophageal contents into the pharynx

Question 6

fx of the Lower Esophageal Sphincter (LES)*

Answer 6

protects esophagus from gastric reflux, allows entry of food into the stomach.

Question 7

fx of esophagus

Answer 7

transports bolus from pharynx to stomach, clears material refluxed from stomach.

Question 8

What does “basal tone” refer to?

Answer 8

The pressure that is always present in a normal state

Question 9

How does swallowing effect the intraluminal pressure of the esophagus, LES, and proximal stomach?

Answer 9

induces relaxation of LES and proximal stomach, and a series of contractions in the esophagus.

Question 10

Receptive relaxation in the proximal stomach in response to meal is dependent on which nerve?

Answer 10

vagus nerve, mediated by VIP and NO. vagus is very important for motility, etc. in all parts of the GI system

Question 11

luminal secretions from LES and cardia

Answer 11

mucus, bicarbonate

Question 12

luminal secretions from the fundus and body of the stomach

Answer 12

H+, mucus, pepsinogens, bicarb, lipase, intrinsic factor. First 3 are the most important

Question 13

In which part of the stomach does mixing/grinding/sieving/emptying occur?

Answer 13

Antrum

Question 14

luminal secretions from the antrum and pylorus

Answer 14

mucus, bicarb.

Question 15

main fx. of the fundus and body of the stomach

Answer 15

STORE food

Question 16

main fx of the pylorus

Answer 16

acts as a sphincter to prevent particles that are too large or in the wrong chemical composition from entering the Small Intestine

Question 17

What do parietal cells produce?

Answer 17

acid

Question 18

What do chief cells produce?

Answer 18

pepsinogen

Question 19

What do G cells produce?

Answer 19

gastrin

Question 20

What is gastrin?

Answer 20

An endocrine hormone that stimulates chief and parietal cells

Question 21

3 phases of gastric acid secretion in response to a meal

Answer 21

1) cephalic
2) gastric (largest)
3) intestinal

Question 22

Describe the cephalic phase of gastric secretion

Answer 22

Vagal afferents go from brain to GI tract and stimulate chief, parietal, ECL, and G cells to function. Ach is the NT to stimulate chief, parietal, and ECL cells, whereas GRP (gastrin releasing peptide) is the NT to stimulate G cells

Question 23

What converts pepsinogen to pepsin?

Answer 23

acid

Question 24

what does pepsin do?

Answer 24

breakdown protein

Question 25

what are oligopeptides?

Answer 25

protein breakdown products

Question 26

Explain why gastrin has endocrine properties

Answer 26

When it is produced by G cells, it feeds back on chief and parietal cells to upregulate their production of pepsinogen and acid

Question 27

3 mechs. of communication mediated responses in the GI tract

Answer 27

1) endocrine (hormone released from sensor cell, which enters into circulation and eventually activates target cell) 2) neurocrine (sensory neuron activates target cell) 3) paracrine (paracrine cells directly activate neighboring target cells via diffusion of paracrine mediators)

Question 28

ECL cells release:

Answer 28

histamines

Question 29

3 things that can stimulate a parietal cell

Answer 29

1) Ach 2) gastrin 3) histamine *parietal cell will still produce acid if 1-2 of the receptors for these molecules are blocked. There is no drug that blocks all 3 receptors*

Question 30

describe pathway of acid secretion from a parietal cell

Answer 30

acid flows from cell into the intestinal lumen via pathway created by canaliculi and mitochondria

Question 31

What is the function of mucus and bicarbonate secretions at the luminal surface of the stomach lining?

Answer 31

Raises the pH to near 7 near the cell surface and protects the lining from the harsh low pH in the rest of the stomach

Question 32

Role of retropulsion in the stomach

Answer 32

pylorus closes and food is forced back into proximal stomach. Ensures breakdown of food particles

Question 33

fun fact

Answer 33

composition of food itself influences how much gastrin is produced

Question 34

Neg. feedback mech. for gastrin release

Answer 34

Acid produced by parietal cells inhibits gastrin release from G cells

Question 35

acid in the antrum --> somatostatin and gastrin secretion

Answer 35

stimulates somatostatin release from D cells, which inhibits gastrin secretion from nearby G cells. This is PARACRINE INHIBITION.

Question 36

What type of cells produce somatostatin?

Answer 36

D cells

Question 37

Under what conditions does the stomach empty?

Answer 37

only when intragastric pressure exceeds duodenal pressure and pyloric resistance. Influenced by the physical and chemical composition of a meal and by food type, pH, and osmolarity

Question 38

Order protein, pectin, and lipid by how long they stay in the stomach

Answer 38

lipid (longest) > protein > pectin

Question 39

What 2 things does the duodenum release in response to entrance of HCl, amino acids, and fatty acids entering the duodenum? What effect does this have? **

Answer 39

CCK (in response to fat/amino acids) and secretin (in response to acid). These inhibit secretion and emptying in the stomach. CCK also stimulates the vagus n. to stimulate pancreatic enzyme secretion

Question 40

Ingesta must be hyper/hypo/isotonic to enter small intestine?

Answer 40

isotonic

Question 41

Contents of stomach are usually hyper/hypo/isotonic?

Answer 41

Hypertonic. They transition to isotonic in the duodenum via secretions of pancreas, liver, and duodenum. (Can also sometimes start off at hypotonic)

Question 42

factors effecting pH in small intestine

Answer 42

- H+ input from gastric acid - HCO3 input from pancreatic duct cells/biliary duct cells/duodenal mucosa - buffers from dietary protein/peptides/fatty acids/bile acids - H+ absorption

Question 43

Exocrine fxs of the pancreas

Answer 43

Secrete digestive enzymes, cofactors, and HCO3 into the duodenum. CCK is a major player in the fx of the pancreas

Question 44

Endocrine fxs of the pancreas

Answer 44

secrete hormones into the portal vein

Question 45

CCK stimulates pancreatic enzyme secretion by neural and hormonal pathways

Answer 45

:)

Question 46

fx of trypsin. What is its inactive form? What is it activated by?

Answer 46

Activates zymogens to active enzymes and breaks down proteins. Trypsinogen = inactive form. Activated by enteropeptidase.

Question 47

Where is bile stored?

Answer 47

gall bladder

Question 48

major solid component of bile

Answer 48

bile acids

Question 49

amylase

Answer 49

pancreatic enzyme that breaks down starch and glycogen into smaller sugars

Question 50

lipase

Answer 50

pancreatic enzyme that digests long-chain triglycerides into monoglycerides and fatty acids

Question 51

Which cells accomplish most of the absorption and digestion in the small intestine?

Answer 51

cells on the tip of the villi. Proteins intercalated into the membrane lining of these cells are responsible for digestion

Question 52

intraluminal products of starch and protein digestion in the small intestine

Answer 52

monosaccharides, peptides, and amino acids.

Question 53

consumption of meal --> intestinal blood flow

Answer 53

increases. Whenever there is an increase in work, there has to be increased blood flow and motility in that tissue

Question 54

absorbed products of lipolysis are synthesized into triglycerides in enterocytes (intestinal absorptive cells) and exit as chylomicrons

Answer 54

:)

Question 55

fasting --> intestinal motility

Answer 55

decreases

Question 56

4 main functions of the colon and rectum

Answer 56

1) absorption of water/ions 2) bacterial fermentation of nonabsorbed nutrients 3) storage of waste and indigestible materials 4) elimination of waste and indigestible materials

Question 57

What happens if there is failure o breakdown of soluble components prior to the colon?

Answer 57

bacteria will "go to town" on them and produce a lot of water, acid, and gas --> diarrhea

Question 58

ingestion of a meal --> colonic motility. What initiates this?

Answer 58

increases. Initiated by hormonal signals from the stomach and intestine, and neural efferents from the CNS