Lecture 5: Response of the Gut to a Meal Flashcards Preview

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Flashcards in Lecture 5: Response of the Gut to a Meal Deck (58):
1

Major function of the GI tract

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

2

what is motility?

Mechanism by which gut contents are moved from proximal to distal

3

Describe the integrated response to a meal

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

4

4 major functions of the gut

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

5

Function of the Upper Esophageal Sphincter (UES)

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

6

fx of the Lower Esophageal Sphincter (LES)*

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

7

fx of esophagus

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

8

What does "basal tone" refer to?

The pressure that is always present in a normal state

9

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

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

10

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

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

11

luminal secretions from LES and cardia

mucus, bicarbonate

12

luminal secretions from the fundus and body of the stomach

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

13

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

Antrum

14

luminal secretions from the antrum and pylorus

mucus, bicarb.

15

main fx. of the fundus and body of the stomach

STORE food

16

main fx of the pylorus

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

17

What do parietal cells produce?

acid

18

What do chief cells produce?

pepsinogen

19

What do G cells produce?

gastrin

20

What is gastrin?

An endocrine hormone that stimulates chief and parietal cells

21

3 phases of gastric acid secretion in response to a meal

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

22

Describe the cephalic phase of gastric secretion

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

23

What converts pepsinogen to pepsin?

acid

24

what does pepsin do?

breakdown protein

25

what are oligopeptides?

protein breakdown products

26

Explain why gastrin has endocrine properties

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

27

3 mechs. of communication mediated responses in the GI tract

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)

28

ECL cells release:

histamines

29

3 things that can stimulate a parietal cell

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*

30

describe pathway of acid secretion from a parietal cell

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

31

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

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

32

Role of retropulsion in the stomach

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

33

fun fact

composition of food itself influences how much gastrin is produced

34

Neg. feedback mech. for gastrin release

Acid produced by parietal cells inhibits gastrin release from G cells

35

acid in the antrum --> somatostatin and gastrin secretion

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

36

What type of cells produce somatostatin?

D cells

37

Under what conditions does the stomach empty?

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

38

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

lipid (longest) > protein > pectin

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? **

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

40

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

isotonic

41

Contents of stomach are usually hyper/hypo/isotonic?

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

42

factors effecting pH in small intestine

-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

43

Exocrine fxs of the pancreas

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

44

Endocrine fxs of the pancreas

secrete hormones into the portal vein

45

CCK stimulates pancreatic enzyme secretion by neural and hormonal pathways

:)

46

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

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

47

Where is bile stored?

gall bladder

48

major solid component of bile

bile acids

49

amylase

pancreatic enzyme that breaks down starch and glycogen into smaller sugars

50

lipase

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

51

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

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

52

intraluminal products of starch and protein digestion in the small intestine

monosaccharides, peptides, and amino acids.

53

consumption of meal --> intestinal blood flow

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

54

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

:)

55

fasting --> intestinal motility

decreases

56

4 main functions of the colon and rectum

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

57

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

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

58

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

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

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