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Undeleted > Lecture 5: Response of the Gut to a Meal > Flashcards

Lecture 5: Response of the Gut to a Meal Flashcards

1
Q

Major function of the GI tract

A

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

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2
Q

what is motility?

A

Mechanism by which gut contents are moved from proximal to distal

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3
Q

Describe the integrated response to a meal

A

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

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4
Q

4 major functions of the gut

A

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

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5
Q

Function of the Upper Esophageal Sphincter (UES)

A

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

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6
Q

fx of the Lower Esophageal Sphincter (LES)*

A

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

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7
Q

fx of esophagus

A

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

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8
Q

What does “basal tone” refer to?

A

The pressure that is always present in a normal state

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9
Q

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

A

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

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10
Q

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

A

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

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11
Q

luminal secretions from LES and cardia

A

mucus, bicarbonate

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12
Q

luminal secretions from the fundus and body of the stomach

A

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

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13
Q

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

A

Antrum

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14
Q

luminal secretions from the antrum and pylorus

A

mucus, bicarb.

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15
Q

main fx. of the fundus and body of the stomach

A

STORE food

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16
Q

main fx of the pylorus

A

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

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17
Q

What do parietal cells produce?

A

acid

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18
Q

What do chief cells produce?

A

pepsinogen

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19
Q

What do G cells produce?

A

gastrin

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20
Q

What is gastrin?

A

An endocrine hormone that stimulates chief and parietal cells

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21
Q

3 phases of gastric acid secretion in response to a meal

A

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

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22
Q

Describe the cephalic phase of gastric secretion

A

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

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23
Q

What converts pepsinogen to pepsin?

A

acid

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24
Q

what does pepsin do?

A

breakdown protein

25
Q

what are oligopeptides?

A

protein breakdown products

26
Q

Explain why gastrin has endocrine properties

A

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

27
Q

3 mechs. of communication mediated responses in the GI tract

A

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
Q

ECL cells release:

A

histamines

29
Q

3 things that can stimulate a parietal cell

A

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
Q

describe pathway of acid secretion from a parietal cell

A

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

31
Q

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

A

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
Q

Role of retropulsion in the stomach

A

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

33
Q

fun fact

A

composition of food itself influences how much gastrin is produced

34
Q

Neg. feedback mech. for gastrin release

A

Acid produced by parietal cells inhibits gastrin release from G cells

35
Q

acid in the antrum –> somatostatin and gastrin secretion

A

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

36
Q

What type of cells produce somatostatin?

A

D cells

37
Q

Under what conditions does the stomach empty?

A

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
Q

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

A

lipid (longest) > protein > pectin

39
Q

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? **

A

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
Q

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

A

isotonic

41
Q

Contents of stomach are usually hyper/hypo/isotonic?

A

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

42
Q

factors effecting pH in small intestine

A
  • 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
Q

Exocrine fxs of the pancreas

A

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

44
Q

Endocrine fxs of the pancreas

A

secrete hormones into the portal vein

45
Q

CCK stimulates pancreatic enzyme secretion by neural and hormonal pathways

A

:)

46
Q

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

A

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

47
Q

Where is bile stored?

A

gall bladder

48
Q

major solid component of bile

A

bile acids

49
Q

amylase

A

pancreatic enzyme that breaks down starch and glycogen into smaller sugars

50
Q

lipase

A

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

51
Q

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

A

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

52
Q

intraluminal products of starch and protein digestion in the small intestine

A

monosaccharides, peptides, and amino acids.

53
Q

consumption of meal –> intestinal blood flow

A

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

54
Q

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

A

:)

55
Q

fasting –> intestinal motility

A

decreases

56
Q

4 main functions of the colon and rectum

A

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
Q

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

A

bacteria will “go to town” on them and produce a lot of water, acid, and gas –> diarrhea

58
Q

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

A

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

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