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Gastrointestinal System > Physiology of the Stomach > Flashcards

Physiology of the Stomach Flashcards

1
Q

What are the functions of the stomach

A

Reservoir
Anti-microbial
Digestion & Absorption
Auto-digestion defence
Intrinsic factor Production

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2
Q

What is meant by reservoir function?

A

Regulation of food delivery to the small intestine

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3
Q

What is the anti-microbial function of the stomach?

A

Protects against pathogens via HCl

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4
Q

What are the digestion and absorption functions of the stomach?

A

Initiation of protein digestion with pepsin

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5
Q

What is the auto-digestion defence?

A

Protection of itself from acid and other factors with a mucosal layer

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6
Q

What is the importance of the intrinsic factor?

A

Essential for vitamin B12 absorption

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7
Q

What are the luminal secretion of the LES and cardia region?

A

Mucus
HCO3-

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8
Q

What is the motility of the LES and cardiac region like and why?

A

Prevention of reflux
Entry of food
Regulation of belching

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9
Q

What is the function of bicarbonate in the stomach?

A

Neutralize HCl

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10
Q

What are the luminal secretions of the fundus and the body of the stomach?

A

H+
Intrinsic factor
Mucus
HCO3-
Pepsinogens
Lipase

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11
Q

What is the motility of the fundus and body region like?

A

Reservoir
Tonic force during emptying

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12
Q

What are the luminal secretions of the antrum and pylorus?

A

Mucus
HCO3-
Gastrin

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13
Q

What is the motility of the antrum and pylorus region like?

A

Mixing
Grinding
Sieving
Regulation of emptying

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14
Q

Where are the majority of glands found?

A

In the upper part, the fundus. Gastrin thus needs to move to that part of the stomach.

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15
Q

What is the secretory product of the surface mucous cells?

A

Mucin in an alkaline fluid

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16
Q

What is the secretory product of the mucous neck cells?

A

Mucin in an acid fluid

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17
Q

What is the secretory product of parietal cells?

A

HCl & intrinsic factor

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18
Q

What is the secretary product of the chief cells?

A

Pepsinogen & lipase

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19
Q

What is the secretory product of G cells?

A

Gastrin

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20
Q

Where are goblet/mucous cells found?

A

Entire luminal surface and extend into the glands as mucous neck cells

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21
Q

What is the mucosal protection system?

A

Mucosa keeps hydrogen ions within the lumen of the gut and prevents their diffusion to epithelial lining.

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22
Q

What are the mechanisms of protection (4)?

A

Mucous secretion
Bicarbonate
Epithelial tight junctions
High blood to mucosa

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23
Q

What are the functions of HCl secretion from the parietal cells?

A

Crucial for activating pepsinogen
Killing bacteria

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24
Q

What is the importance of intrinsic factor secretion?

A

Essential for Vitamin B12 absorption

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25
Q

What is the clinical significance of the parietal cells?

A

Any damage to them due to chronic gastritis can lead to achlorhydria and pernicious anemia

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26
Q

What is the function of vitamin B12?

A

Erythropoiesis and neurologic function

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27
Q

What is achlorydhia?

A

Absence of stomach acid secretion

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28
Q

What is the H+/K+ ATPase?

A

Apical membrane of parietal cells that pumps H+ against concentration gradient

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28
Q

What is the key player for HCl secretion?
Where is it located?

A

H+/K+ ATPase, located in the walls of tubulovesicular structures

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29
Q

Where is ATPase found in parietal cells?

A

Tubulovesicles

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30
Q

What happens when the tubulovesicular structures get stimulated?

A

They move to the apical membrane of cell and fuse with it causing:
1. Insertion of more H+/K+ ATPase
2. Increasing the apical (luminal) surface area by 5 to 10 times

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31
Q

Where are the tubulovesicular structures during the resting phase?

A

Inside the cytosol

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32
Q

What is the process of HCl secretion?

A

CO2 and Cl- diffuse from the blood into the stomach cell
CO2 combines with H2O to form H2CO3
H2CO3 dissociates into bicarbonate and H+
H+ combines with Cl- in duct of gastric gland to form HCl-

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33
Q

Why does H+ combine with Cl- in the duct of gastric gland?

A

If they were to combine within the cells, due to its acidic environment, it would destroy the cells

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34
Q

Why is an ATP pump necessary in the HCl secretion process?

A

Necessary to pump the HCl- into the duct since the concentration of HCl- is a about a million times more concentrated in the duct than in the cytosol of the cell

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35
Q

What is the strongest factor of regulation for the gastric acid secretion?

A

Parasympathetic innervation via the vagus nerve is the strongest stimulant t of gastric H+ secretion

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36
Q

What are the positive stimulants of gastric acid secretion?

A

Acetylcholine
Gastrin
Histamin

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37
Q

What is the function of Gastrin in the acid secretion process?

A

Can stimulate histamine cells to produce histamine which then stimulates parietal cells

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38
Q

What are the receptors for each stimulus of gastric acid secretion?

A

Acetylcholine: M3 muscarinic receptors
Gastrin: CCK2
Histamin: H2
Somatostatin: Somatostatin receptors

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39
Q

What is the negative stimulus of gastric acid secretion?

A

Somatostatin

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40
Q

What is the pathway that Gastrin follows to increase gastric acid secretion?

A

Release of gastrin –> Release of IP3/DAG which causes Ca2+ secretion or PKC –> CamK - II secretion

41
Q

What happens if PKC, PKA or CamK - II is released?

A

Cytoskeletal arrangements (PKA and PKC)
Membrane trafficking
Activation of K+ and Cl- channels
HCO3-/Cl- exchanger
Insertion of K+/H+ ATPase
Release of HCl

42
Q

What is the pathway that histamine follows to increase gastric acid secretion?

A

Release of cAMP –> PKA

43
Q

What do chief cells produce?

A

Pepsinogen

44
Q

What is pepsinogen?

A

The inactive form of pepsin which is released instead in order to not cause damage to the epithelial cells.

45
Q

When is pepsisnogen activated?

A

When the pH < 3

46
Q

What is the function of pepsins?

A

May digest as much as 20% of the protein in a typical meal

47
Q

Where is the rest of the 80% of proteins digested?

A

By nucleases in the large intestine

48
Q

Why is rennin secreted?

A

Liquids move very fast from the stomach to the small intestine, babies for instance, they cannot digest milk because of how fast it moves, rennin helps coagulate it.

49
Q

Where is rennin secreted from?

A

Chief cells

50
Q

What is the purpose of rennin?

A

Helps coagulate milk allowing it to be retained more than briefly in the stomach

51
Q

Where is acetylcholine secreted from?

A

Enteric neurons

52
Q

Where is gastrin secreted from?

A

G cells in the gastric antrum

53
Q

Where is histamine secreted from?

A

ECL cells in the gastric corpus

54
Q

Where is cholecystokinin (CCK) secreted from?

A

I cells in the duodenum

55
Q

Where is secretin secreted from?

A

S cells in the duodenum

56
Q

What is the result of parasympathetic innervation on submucosal plexus?

A

Can activate the submucosal plexus and stimulate the production of acetylcholine

57
Q

Why is the blood an important component when it comes to Gastrin?

A

Blood acts as the transporter for gastrin since it needs to move from the antrum to the body of the stomach

58
Q

What are different kinds of innervation?

A

There is the local innervation and the efferent one, long stretched.

59
Q

What re the different gastric secretion phases?

A

Cephalic via vagus nerve
Gastric phase
Intestinal phase

60
Q

What is the cephalic phase triggered by?

A

Smelling, chewing and even the thought of food

61
Q

What is the cephalic phase mediated by?

A

The vagus nerve

62
Q

What percentage of acid secretion does the cephalic phase account for?

A

10 to 30%

63
Q

What is the function of the cephalic phase?

A

Stimulates chief cells to secrete pepsinogen
Directly stimulates G cells to secrete gastrin
Directly stimulates ECL cells to secrete histamine

64
Q

During the first 30 minutes of the meal which phase of gastric secretion continues through?

A

The cephalic phase

65
Q

What is the process of the cephalic phase?

A

Taste or small or even thoughts of food stimulate the medulla oblongata

The vagus nerve carries parasympathetic action potentials to stomach

Preganglionic parasympathetic vagus nerve fibers stimulate postganglionic neurons in the enteric plexus

Postganglionic neurons stimulae secretion by pariental and chief cells and stimulate gastric secretion by G cells

66
Q

Where is gastrin carried to during the cephalic phase?

A

Through the circulation back to the stomach, where it stimulates secretion by parietal and chief cells

67
Q

What is the gastric phase triggered by?

A

The presence of food

68
Q

What % of acid secretion does gastric phase account for?

A

60 to 70%

69
Q

How does gastric distention occur?

A

Vagovagal reflex + local enteric reflexes

70
Q

What is the process of the gastric phase?

A

The presence of food in the stomach is detected and activates the vago-vagal reflexes to stimulate secretions

71
Q

How does the chemical nature of chyme help stimulate the gastric secretion?

A

Chyme is acidic so…
Stimulates G cells to secrete gastrin
Stimulates chief cells to secrete pepsinogen
Stimulates ECL cells to secrete histamine
Histamine then stimulates secretion of HCl

72
Q

How does the gastric phase occur?

A

Distention of the stomach activates a parasympathetic reflex, AP are carried by the vagus nerves to the medulla oblongata

The medulla oblongata stimulates stomach secretions

Distension of the stomach also activates local reflexes that increase stomach secretions.

73
Q

How does the intestinal phase occur?

A

Chyme in the duodenum with pH less than 2 or containing fat digestion products inhibits gastric secretions by three mechanisms.

74
Q

What are the three mechanisms with which the gastric secretions are inhibited by?

A

Sensory vagal action potentials to the medulla oblongata, inhibit motor AP from medulla oblongata

Local reflexes inhibit gastric secretions and motility

Secretin and CCK produced by the duodenum inhibit gastric secretions

75
Q

How is gastric secretion regulated?

A

Through positive feedback effect
& Negative feedback effect

76
Q

What is the positive feedback effect that regulates gastric secretion?

A

As more HCl ad pepsinogen are secreted, more polypeptides and amino acids are released.

77
Q

What is the negative feedback effect that regulates the gastric secretion?

A

HCl secretion decreases if pH < 2.5
At a pH of 1.0, gastric secretion ceases

78
Q

What are the factors affecting gastric emptying?

A

Volume
Osmolarity
pH
Nutrient Content
Emotional States
Disease States
Exercise

79
Q

What is the effect of increased volume on gastric emptying?

A

Increased volume –> faster gastric emptying due to greater distension and stimulation of mechanoreceptors

80
Q

What osmolarity is optimal for gastric emptying rate?

A

Isotonic solutions

81
Q

What is the effect of hypertonic solutions on the gastric emptying?

A

Hypertonic solutions –> slower gastric emptying due to osmotic pressure effect

82
Q

What is the effect of pH on gastric emptying?

A

Low pH –> slower gastric emptying to allow for neutralisation

83
Q

What is the effect of carbohydrates on gastric emptying?

A

Rapid gastric emptying because carbohydrates cannot be digested in the stomach

84
Q

What is the effect of proteins on gastric emptying?

A

Moderate gastric emptying

85
Q

What is the effect of fats on gastric emptying?

A

Slowest gastric emptying due to hormonal regulation (CCK release)

86
Q

What is the effect of emotional states on gastric emptying?

A

Stress –> increased gastric motility and faster emptying
Depression –> decreased gastric motility and slower emptying

87
Q

What is the effect of different diseases on gastric emptying?

A

Diabetes: slower gastric emptying due to autonomic neuropathy

Hypothyroidism: reduced motility, leading to slower gastric emptying

88
Q

What is the effect of exercise on the gastric emptying?

A

Moderate exercise: may reduce gastric emptying rate

Intense exercise: significantly reduces the gastric emptying due to diversion of the blood flow

89
Q

What are the factors that inhibit gastric secretions?

A

Low pH
Presence of Fatty Acids & Lipids in Duodenum
Hyperosmolarity of chyme
Presence of secretin
Vagal inhibition
Emotional factors
Somatostatin release

90
Q

How does low pH inhibit gastric secretions?

A

When gastric contents become highly acidic, pH < 2, it inhibits further secretion of excess HCl

Negative feedback mechanism involving somatostatin

91
Q

How does the presence of fatty acid and lipids in the duodenum inhibit the gastric secretions?

A

Stimulates the release of GIP and CCK, which reduce gastric secretion

92
Q

How does hyperosmolarity of chyme inhibit the gastric secretion?

A

Highly concentrated chyme entering the small intestine leads to a reduction in gastric secretion to slow the gastric emptying rate

93
Q

How does the presence of secretin inhibit gastric secretions?

A

Released in response to acidic chyme in the small intestine, secretin inhibits gastric acid secretion

94
Q

How does vagal inhibition inhibit gastric secretions?

A

Reduced vagal stimulation can decrease the secretions of gastric juice

95
Q

How do emotional factors inhibit gastric secretions?

A

Stress, amity or depression cab inhibit gastric secretions through CNS mechanisms

96
Q

How does the somatostatin release inhibit gastric secretions?

A

Secreted by D cells in the stomach, somatostatin directly inhibits the secretion of gastrin, histamine and HCl

97
Q

What are enetrogastrones?

A

Any hormone secreted by the mucosa of the duodenum in response to protein, acidity etc.

Inhibitory function

98
Q

Where is CCK produced and what is its function?

A

Produced in the small intestine and can detect whether efficient digestion has occurred or not (depending on the presence of high-fat, and high-protein derivatives)

Inn that case the CCK will be decreased so that motility can be decreased and full digestion occurs

99
Q

What are local neural circuits?

A

Osmoreceptors, chemoreceptors
Mechanical distension in duodenum

100
Q
A

Gastrointestinal System (28 decks)

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