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GI > Stomach > Flashcards

Stomach Flashcards

1
Q

What are the 4 functions of the stomach?

A

Storage

Start digestion of protein

Small amount of carbo and fat digestion (salivary amylase and lingual lipase start this in mouth)

Disinfect using innate immune system

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2
Q

What is chyme?

A

End product of digestion from the stomach

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3
Q

What is the sphincter between the stomach and oesophagus called?

A

Lower oesophageal sphincter

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4
Q

What is the region of the stomach just below this called?

A

The cardia

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5
Q

What are the 3 parts of the stomach?

A

Fundus - top
Body
Antrum - base

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6
Q

What is the transition of epithelia from oesophagus to stomach?

A

Stratified squamous in oesophagus to simple columnar in stomach

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7
Q

What is the sphincter between the stomach and the duodenum called?

A

Pyloric sphincter

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8
Q

What are the two parts of the lower oesophageal sphincter?

A

Intrinsic smooth muscle part (within stomach/oesophagus)

Right crus of diaphragm - crural part of muscle encased around oesophagus as it exits

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9
Q

2 parts of diaphragm

A

Costal
Crural - makes lower oesphageal sphincter

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10
Q

What is receptive relaxation?

A

A reflex triggered by peristalsis ensuring food does not get pushed back up to oesophagus by ensuring pressure does not get too high in stomach

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11
Q

Describe receptive relaxation

A

Peristalsis causes reflex relaxation of proximal stomach
= receptive relaxation

Fundus distends

Stomach can fill without significant rise in pressure

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12
Q

What allows the stomach to expand?

A

Rugae

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13
Q

What else prevents acidic reflux of stomach contents back to oesophagus?

A

Acute angle which oesophagus enters stomach

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14
Q

3 layers of muscle in stomach

A

Oblique (extra one)
Circular
Longitudinal

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15
Q

What are the 3 layers of stomach required for?

A

Mechanical breakdown of food using forceful contraction

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16
Q

Structure of superior and inferior stomach change

A

Fundus - dilated, thinner walled

Antrum - narrows, more muscular

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17
Q

What does the change in muscularity towards the antrum allow?

A

Food moves faster as it travels distally when stomach contracts

Small particles are accelerated towards pyloric sphincter, larger ones are left near fundus for more breakdown

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18
Q

What is present on the surface of the stomach?

A

Gastric pits - invaginations of epithelia
With gastric glands below (at base of pit)

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19
Q

What is the epithelia of stomach lined with?

A

Surface mucous cells -

These secrete mucous and bicarbonate to create neutral mucus lining of protection

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20
Q

Cells in gastric gland

A

Parietal

Chief

Enteroendocrine

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21
Q

Where are G cells mostly prevalant?

A

In antrum of stomach

22
Q

How does the stomach environment help pepsin production?

A

Hydrochloric acid - acidic environment facilitates change of inactive pepsinogen to pepsin

23
Q

What do chief cells secrete?

A

Pepsinogen - inactive pepsin (protease)

24
Q

What are the protective mechanisms of the stomach? It contains strong acid and proteases (could digest itself)

A

Cells are replaced regularly

Surface mucous cells - produce mucous and bicarbonate to create neutral pH protective layer

Mucosa has rich blood supply - remove acid to blood stream

25
Q

What else do the surface mucous cells secrete?

A

Prostaglandins

26
Q

Role of prostaglandins in stomach mucosa

A

Increase mucosal blood flow

Support mucus layer

Generally protective

27
Q

What transporter allows acid to be formed in the stomach?

A

H+K+ATPase - proton pump

Pumps H+ ions from parietal cell into stomach lumen in exchange for K+ ions (pumps these into parietal cell)

28
Q

Two states of parietal cell

A

Resting - no acid production

Active - pumping H+ and making acid

29
Q

What does the apical membrane of parietal cell contain?

A

K+ channels

30
Q

what is present within the parietal cell?

A

Tubulovesicles - these contain proton pumps

BUT are impermeable to K+

31
Q

What structures are formed by apical membrane of parietal cell?

A

Canaliculi - apical membrane invaginates down into cell

32
Q

What happens when the parietal cell is stimulated to become active?

A

Tubulovesicles and canaliculi of apical membrane come together to allow acid production by proton pump

(need to as tubulovesicles are impermeable to K+)

33
Q

3 Phases of digestion

A

Cephalic
Gastric
Intestinal

34
Q

What stimulates acid production in cephalic phase?

A

Sensory triggers:
Smell
Sight
Taste

35
Q

What stimulates acid production in gastric phase?

A

Gastric triggers:
Stretch of stomach

Presence of AA or small
peptides

Food acts as buffer and increases pH

36
Q

What stimulates acid production in the intestinal phase?

A

Intestinal triggers:
Chyme in duodenum - this goes on to inhibit

Presence of partially digested proteins

37
Q

How much acid does each phase produce?

A

Cephalic - 30%

Gastric - 60%

Intestinal - 10%

38
Q

What 3 are ‘on buttons’ which stimulate a parietal cell?

A

Gastrin receptors

Histamine receptors

Muscarinic receptors (Ach)

39
Q

How does gastrin stimulate parietal cell?

A

Peptides in stomach stimulate gastrin release from G cells

Goes through bloodstream (its a hormone)

Binds with CCK receptor on parietal cell
(cholecystokinin is same family as gastrin)

40
Q

How else are G cells stimulated to release gastrin and therefore activate parietal cell?

A

Via GRP binding - gastric releasing peptide when stretch is sensed
or
Ach binds to muscarinic receptor on G cell = release of gastrin

41
Q

What is the vagal stimulation on parietal cell?

A

Ach can bind to muscarinic receptor on parietal cell

Or can bind to muscarinic receptor on G cell and stimulate gastrin release which binds to CCK on parietal and activates

42
Q

what cell releases histamine?

A

Entero-chromaffin like cell - ECL

43
Q

How does histamine stimulate parietal cells?

A

Histamine binds to H2 receptor on parietal cell and stimulates`

44
Q

How is histamine release from entero-chromaffin like cells stimulated?

A

Vagal stimulation: Ach binds to muscarinic receptor on ECL cell
or
Gastrin binds to CCK receptor and stimulates

= histamine release

45
Q

How is acid secretion inhibited?

A

D cells detect decrease in pH from HCl

Release somatostatin, this binds to somatostatin receptor on G cells

= inhibits G cells producing gastrin

46
Q

What pump is involved in acid production in parietal cell?

A

H+/K+ ATPase
K+ channel
Cl- channel
(apical - stomach)

Cl- HCO3 (bicarbonate) exchanger
(basolateral - blood)

47
Q

What first must happen to water and CO2 within the parietal cell?

A

H2O and CO2 combine to form carbonic acid via CARBONIC ANHYDRASE in parietal cell

48
Q

What happens to the carbonic acid within the parietal cell?

A

This then disassociates into H+ and HCO3 (bicarbonate)

49
Q

What happens to the H+ next?

A

H+ gets pumped into stomach lumen via H+K+ATPase

(K+ is recycled using K+ channel on apical membrane)

50
Q

What happens to the bicarbonate in the parietal cell?

A

This moves into blood via Cl- bicarbonate (HCO3) exchanger on basolateral membrane

Cl- moves into cell, bicarbonate goes into VENOUS blood

51
Q

What is created by the flow of bicarbonate into venous blood from Cl-HCO3 exchanger?

A

Alkaline tide - pH of venous blood increases

52
Q

What happens to the Cl- ions once inside the parietal cell?

A

Flow into stomach lumen via Cl- channel on apical membrane

Form HCl by combining with H+

GI (32 decks)

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