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MP221 > Physiology of the stomach > Flashcards

Physiology of the stomach Flashcards

1
Q

What are the functions of the stomach?

A
  • Temporary storage of food
  • Mechanical digestion by stomach movements
  • regulation of passage of chyme (partially digested food) into the small intestine
  • Secretion of intrinsic factor - essential for absorption of vitamin B12
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2
Q

what does the antrum secrete?

A

mucus, pepsinogen and gastrin

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3
Q

what does the body of the stomach secrete?

A

secretes mucus, pepsinogen and HCL

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4
Q

Why is the antrum thicker than the body

A

To produce more powerful contractions for mechanical digestion

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5
Q

what is the pyloric sphincter important for?

A

regulating transport into the duodenum

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6
Q

What is the HCL produced in the body important for?

A

targeted effects

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7
Q

How is food mechanically digested in the stomach?

A
  • Muscularis enables food to be churned - particularly in the antrum where the muscle wall is thicker (more powerful contractions)
  • Food is mixed with gastric juices to produce chyme (make sure optimal coverage from secretion particularly enzymes)
  • chyme passes thought pyloric sphincter to duodenum
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8
Q

what are the 3 key types of cells that produce gastric juices?

A

Zymogenic (cheif cells)
Parietal cells (oxyntic cells)
Goblet (neck) cells

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9
Q

What does zymogenic cells do?

A
  • A zymogen is an inactive form of an enzyme
    Secretes pepsinogen (zymogen) which is converted into the enzyme pepsin (active) which requires an acid environment
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10
Q

What does parietal cells do?

A

Secretes HCL and intrinsic factor (absorption of B12) - required for protein digestion

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11
Q

What do goblet (neck) cells do?

A

Secrete mucous (lubrication)

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12
Q

What do G cells do?

A

Secrete gastrin

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13
Q

What do enterochromaffin (mast like cells) do?

A

secretes histamine

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14
Q

What do D cells secrete?

A

Somatostatin

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15
Q

Where are more parietal cells located and why?

A

More in the body - there is an absence in the antrum (chyme is more interested to move through the pyloric sphincter)

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16
Q

What happens during chemical digestion in the stomach?

A

Proteins are broken down by pepsin
Gastric lipase breaks down fat at higher pH (5-6) - this is limited but important for lipid digestion in infants from breast milk

17
Q

What is transferred in and out the lumen from parietal cells and what does it regulate?

A

Protons are transferred out by a proton pump and chloride ions also leave
Potassium enter the parietal cell (Build up of HCL in stomach lumen)

This regulated how much HCL is produced for conversion of pepsinogen to pepsin for protein digestion

18
Q

What are features of the mucosal wall that prevents the stomach from digesting itself?

A
  • Tight junction between mucosal epithelial cells prevent leakage of gastric juice onto the underlying tissue
  • Mucous secreted by epithelial/goblet cells have higher pH, providing localised neutralisation and physical barrier to acid
    -Prostaglandins increase mucosal thickness and stimulate bicarbonate production
19
Q

What are the three phases of gastric secretion?

A

Cephalic, gastric and intestinal phase

20
Q

What are the three phases of gastric secretion?

A

Cephalic, gastric and intestinal phase

21
Q

what happens in the cephalic phase?

A

There is increased secretion and increased HCL - stimulated by senses, thought of food or decreased bp

Nerve impulses to the medulla oblongata causes parasympathetic neurones via vagus nerves to increase HCL and pepsin in the stomach
Gastrin secretion is also promoted in the antrum which stimulates further HCL and pepsin secretion

22
Q

what happens in the gastric phase ?

A

Stimulated by stomach distension due to the presence of food

Stomach distension trigger parasympathetic reflex (increases gut activity) leading to further HCL, pepsin and gastrin secretions

23
Q

What happens during intestinal phase?

A

Decreased secretion

Stimulated by digested proteins/fats in duodenum
Presence of fat of low pH in duodenum inhibits gastric secretion

Chyme which enters duodenum containing fat or enough HCL to lower pH below 2 will trigger gastric secretions

24
Q

What are the three main routes of gastric secretions being released in the duodenum?

A

(i) neuronal impulses are sent to the medulla to decrease parasympathetic stimulation of gastric glands
(ii) local reflexes in the gut will lead to decreased secretion
(iii) Release of three hormones (secretin, gastric inhibitory peptide and cholecystokinin) travel via bloodstream to gastric glands and inhibit secretion

25
Q

How does neuronal inhibition of HCL secretions occur?

A

-Partially digested protein and presence of fat in duodenum, combined with lower pH from gastric acid inhibits secretion by ‘enterogastric reflex’
- Reflex mediated by medulla oblongata
- Leads to decreased parasympathetic stimulation

26
Q

how does hormonal inhibition of hcl secretion work?

A
  • secretin and cholecystokinin released from duodenum
    -other inhibitors include GIP, gastrone and VIP
  • Somatostatin (paracrine agent) released in response to increased HCL
27
Q

what paracrine substance is secreted by enterochromaffin-like cells?

A

Histamine

28
Q

What enzyme begins digestion of polysaccharides

A

Amylase

29
Q

what can peptic ulcers be treated with ?

A

Proton pump inhibitors

30
Q

what factors can contribute to gastroesophageal reflux?

A

Smoking and caffeine

31
Q

Why does an increase in intracellular calcium ions cause smooth muscle to contract,

A

contractile proteins within smooth muscle cells are sensitive to changes in intracellular calcium

32
Q

What increases antral contraction?

A

Distensions of the stomach
Increased gastrin

33
Q

What does stomach emptying include?

A
  • constriction of the lower oesophageal sphincter
  • contraction of gastric muscularis
  • Relaxation of pyloric sphincter
34
Q

what is an ulcer?

A

erosion of the mucosal layer, leading to inflammation and damage to underlying tissue

35
Q

what are the main causes of gastric ulcers?

A

H.pylori infections
NSAID use
Factors like smoking, caffeine, alcohol, stress may contribute

MP221 (14 decks)

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