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ESA 3 - Gastrointestinal System > Stomach > Flashcards

Flashcards in Stomach Deck (102):
1

What are the functions of the stomach? 

  • Stores food
  • Disinfects food
  • Breaks food down in chyme

2

How does the stomach break food down into chyme? 

  • Chemical disruption
    • Acid
    • Enzymes
  • Physical disruption 
    • Motility

3

Where do stomach secretions come from? 

Gastric pits

4

What are gastric pits? 

Indentations in the stomach mucosa that are openings to gastric glands 

5

What do gastric pits contain? 

Neck cells 

6

What do gastric glands contain? 

Parietal, Chief, and G-cells, along with smooth muscle cells

7

Label this diagram

  • A - Gastric pit (opening to gastric gland)
  • B - Mucous epithelium
  • C - Lymphatic vessel 
  • D - Lamina propria
  • E - Muscularis mucosae
  • F - Submucosa 
  • G - Oblique muscle 
  • H - Circular muscle 
  • I - Longitudinal muscle 
  • J - Serosa
  • K - Artery and vein 
  • L - Myenteric plexus
  • M - Gastric pit 
  • N - Gastric gland 
  • O - Mucous cells 
  • P - Neck 
  • Q - Parietal cells 
  • R - Chief cells 
  • S - Smooth muscle cells
  • T - G cell 

8

What substances are secreted by the stomach? 

  • Hydrochloric acid
  • Proteolytic enzymes 
  • Mucus
  • HCO3-
  • Gastrin

9

What proteolytic enzyme is secreted by the stomach? 

Pepsin

10

What is the cellular origin of hydrochloric acid in the stomach? 

Parietal (oxyntic) cells 

11

What is the purpose of HCl secreted by the stomach? 

Acid keeps luminal pH < 2 

12

What is the cellular origin of proteolytic enzymes in the stomach? 

Chief cells 

13

What is the function of proteolytic enzymes in the stomach? 

Non-specifically breaks down proteins to peptides 

14

What is the cellular origin of mucus in the stomach? 

Neck cells (surface cells) 

15

What are the characteristics of stomach mucus? 

  • Sticky
  • Basic

16

Why is stomach mucus sticky? 

So it is not removed easily from the stomach lining

17

Why is stomach mucus basic? 

Due to amine groups on proteins 

18

What is the cellular origin of HCO3- in the stomach? 

Neck cells (surface cells)

19

What is the purpose of HCO3- in the stomach? 

Provides a buffer for Hions

20

Where is HCO3- secreted by neck cells into? 

The mucus

21

What is the cellular origin of gastrin? 

G-Cells

22

What is the function of gastrin in the stomach? 

Binds to surface receptor on parietal cell, stimulating acid and intrinsic factor 

23

Are body fluids acid or alkaline? 

Most are slightly alkaline 

24

What must be true for a slightly alkaline body fluid to secrete H+ ions? 

It must be created in large quantities 

25

Where does the production of a large amount of body fluid with the intent of secreting H+ occur? 

In the mitochondria of parietal cells 

26

How is H+ produced in parietal cells? 

By splitting water into Hand OHions 

27

What happens to OH- ions produced from the splitting of water in parietal cells? 

They combine with CO2 from metabolsim to from HCO3-, which is exported to the blood

28

How much HCO3- enters the blood for every mole of H+ secreted into the stomach? 

1 mole 

29

What allows parietal cells to produce H+ at a high rate? 

They have lots of mitochondria 

30

Can the ions produced in the mitochondria of parietal cells accumulate in the cell? 

No 

31

How is the problem of the ions produced by parietal cells being unable to accumulate overcome? 

Parietal cells have invaginations in their cell walls called canaliculi 

32

What do canaliculi possess that are required for their function? 

Proton pumps 

33

What do the proton pumps in canaliculi do? 

Expel H+ from parietal cells up a high concentration gradient 

34

What is the result of the concentration gradient canaliculi are pumping against being very high? 

This is a very energy intensive process 

35

What are the proton pumps in canaliculi a key target for? 

Drug action 

36

Why are the proton pumps in canaliculi a key target for drug action? 

Because if inhibited, they will reduce the amount of acid in the stomach 

37

Draw a diagram illustrating the mechanism of secretion of stomach acid 

 

 

38

What controls gastric acid secretion? 

A complex of neural and endocrine systems 

39

What stimulates parietal cells? 

  • Acetylcholine
  • Gastrin 
  • Histamine

40

How do acetylcholine, gastrin, and histamine act to control parietal cells? 

They act via seperate receptors to promote acid secretion 

41

What is Ach released from? 

Postganglionic parasympathetic neurones 

42

What stimulates the release of Ach from postganglionic parasympathetic neurones in the stomach? 

Gastric distention as food arrives 

43

What receptors does Ach act on in parietal cells? 

Muscarinic 

44

What releases gastrin? 

Endocrine cells in the stomach, G-cells 

45

What kind of molecule is gastrin? 

A 17-aa polypeptide 

46

What does gastrin bind to? 

Surface receptors in parietal cells 

47

What stimulates gastrin secretion?

The presence of peptides and Ach from intrinsic neurones 

48

What inhibits gastrin secretion? 

Low pH in the stomach 

49

What does the inhibition of gastrin by low pH in the stomach act as? 

Feedback control 

50

What releases histamine? 

Mast cells 

51

What happens to histamine once released? 

It diffuses locally to bind to H2 receptors on parietal cells 

52

How does histamine stimulate acid secretion? 

Via c-AMP

53

What does histamine work as? 

An amplifier 

54

Why does histamine work as an amplifier? 

Gastrin and Ach stimulate mast cells 

55

What are the phases of gastric secretion? 

  1. Cephalic phase 
  2. Gastric phase 
  3. Intestinal phase 

56

What is the cephalic phase led by? 

The brain 

57

What happens in the cephalic phase? 

The sight and smell of food, and the act of swallowing, activates the parasympathetic nervous system, which stimulates the release of Ach 

58

What is the effect of the release of Ach in the cephalic phase? 

It stimulates parietal cells directly and via histamine, increasing stomach acid 

59

What happens in the gastric phase? 

  • Once food reaches the stomach, it causes distension, further stimulating Ach release, and subsequently parietal cells, increasing acid
  • The arrival of food will also buffer the small amount of stomach acid in the stomach in between meals, causing luminal pH to rise. This disinhibits gastrin, increasing acid 
  • Acid and enzymes will then act on proteins to produce peptides, further stimulating gastrin release as the pH falls and the initial disinhibition is removed, increasing acid 

60

What happens in the intestinal phase?

  • Once chyme leaves the stomach in significant quantities, it stimulates the release of the hormones cholecystokinin and gastric inhibitory polypeptide from the intestines that antagonise gastrin, decreasing acid
  • Coupled with this, the small amount of acid left in the stomach is no longer being buffered by food, and the low pH inhibits gastrin, decreasing acid

61

What is the clinical relevance of the low pH of the stomach between meals? 

It can aggravate ulcers 

62

What is the result of the low pH of the stomach between meals aggrevating ulcers? 

Pain from ulcers is particuarly bad at night 

63

What drugs may inhibit acid secretion? 

  • H2 receptor inhibitors 
  • Proton Pump Inhibitors (PPIs)

64

Give an example of a H2 receptor inhibitor

Cimetidine 

65

How does a H2 receptor inhibitor exert its effects? 

Removes the amplification of gastrin / Ach signal

66

Give an example of a proton pump inhibitor? 

Omeprazole

67

How does a proton pump exert its effects? 

Prevents H+ ions being pumped into parietal cell canaliculi

68

Why do neck cells secrete mucus? 

To protect the mucosa 

69

Why does the stomach mucosa need protection? 

Because the luminal pH of the stomach is usually below 2, and without any protection, this would dissolve mucosa

70

What does the mucus form in the stomach? 

An 'unstirred layer' that ions cannot move through easily 

71

What happens to H+ ions in the unstirred layer? 

They slowly diffuse in and react with the basic groups on mucus, and with HCO3- that is secreted by surface epithelial cells 

72

What is the result of the unstirred layer on HCO3-?

It means it stays close to the surface cells 

73

What is the result of HCO3- staying close to the surface cells? 

The pH at the surface cells is well above 6

74

What stimulates mucus and HCO3- secretion? 

Prostagladins 

75

What are prostaglandins promoted by? 

Most factors that stimulate acid secretion 

76

What agents can breach the stomachs defences? 

  • Alcohol
  • H. Pylori
  • NSAIDS

77

How does alcohol breach the stomachs defences? 

It dissolves the mucus, allowing the acid to attack the stomach

78

How does H. Pylori breach the stomachs defences? 

Surface cells become infected, inhibiting mucus/HCO3- production

79

How do NSAIDS breach the stomach defences? 

They inhibit prostaglandins, therefore reducing defences 

80

Why are some NSAIDS not harmful to the stomachs defences? 

Some are convereted to a non-ionised form by stomach acid, allowing them to pass through the mucus layer into cells before they re-ionise

81

Give an example of an NSAID that is converted to a non-ionised form by stomach acid? 

Aspirin 

82

What does a breach in the stomachs defences result in? 

Peptic ulcers 

83

What does the treatment of peptic ulcers involve? 

  • Reducing acid secretion
  • If present, eliminating H. Pylori with antibiotics 

84

What happens in receptive relaxation? 

As food travels down the oesophagus, a neural reflex carried out by the vagus nerve triggers the relaxation of the muscle in the stomach's wall 

85

What is the purpose of receptive relaxation? 

Prevents the pressure from increasing, so pressure in the stomach doesn't increase as it fills

86

Why is it important that the pressure in the stomach doesn't increase as it fills? 

  • Limits reflex
  • Allows us to consume large meals 

87

When can receptive relaxation not occur? 

If there is damage to the vagus nerve 

88

What kind of muscle does the stomach have? 

Longitudinal and circular

89

What drives the muscle in the stomach? 

A pacemaker 

90

Where is the pacemaker that drives the stomach located? 

In the cardiac region 

91

How often does the stomach pacemaker fire? 

~3 times a minute 

92

What does the firing of the stomachs pacemaker cause? 

Regular, accelerating peristalic contractions from the cardia to the pylorus 

93

What is the action of the stomachs pacemaker combined with to exert its effects? 

The stomach's funnel shape 

94

What is the result of the stomachs funnel shape and the firing of its pacemaker? 

It mixes the contents of the stomach and moves liquid chyme into the pyloric region 

95

When does the movement of liquid chyme into the pyloric region occur? 

As the accelerating peristaltic wave overtakes larger lumps

96

What happens to larger lumps when the accelerating peristaltic wave overtakes them? 

They are driven back into the fundus

97

What happens to chyme as the peristaltic wave overtakes large lumps? 

It is decanted into the pyloric region 

98

What is the oveall effect of the accelerating, rhymtic, peristaltic contraction of the stomach? 

It moves solid lumps backwards into the fundus of the stomach, whilst letting liquid chyme move forwards

99

What happens as chyme enters the pyloric region? 

A small squirt is ejected before the peristaltic wave reaches the pylorus and shuts it, so the rest of the chyme returns to the stomach 

100

How many squirts of chyme are ejected a minute? 

3, the same as the number of peristaltic waves 

101

What is the volume of chyme squirted out affected by? 

  • The rate of acceleration of peristaltic wave
  • Hormones from the intestine 

102

What slows gastric emptying? 

  • Fat 
  • Low pH 
  • Hypertonicity in the duodenum