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Gastrointestinal > The Stomach > Flashcards

The Stomach Flashcards

1
Q

Functions of the stomach

A
  • temporary storage
  • start digestion of protein
  • small amount of carb digestions
  • disinfect (acidic environment)
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2
Q

What controls the release of chyme into the duodenum from the stomach?

A

Pyloric sphincter

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3
Q

What type of epithelium lines the stomach?

A

Simple columnar epithelium

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4
Q

Outline the lower oesophageal sphincter

A
  • at the junction of the oesophagus + stomach
  • decreases reflux into oesophagus
  • intrinsic smooth muscle of stomach
  • right crus of diaphragm loops around +acts to close when intra abdominal pressure increases
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5
Q

Adaptations to prevent reflux

A
  • lower oesophageal spinchter
  • acute angle of food entering stomach from oesophagus
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6
Q

What is receptive relaxation?

A
  • peristalsis alert stomach that food is on its way
  • reflex relaxation of proximal stomach due to rugae
  • receptive relaxation
  • fundus distended
  • stomach can fill without significant rise in pressure
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7
Q

Describe the muscles of the stomach

A

Oblique
Circular
Longitudinal

Thinner proximal
Thicker distally

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8
Q

Describe the epithelial surface of the stomach including the cells and their functions

A
  • epithelial surface lined with surface mucous cells: produce mucus which acts as a protective layer
  • parietal cells: produce HCl + intrinsic factor
  • chief cells: secrete pepsinogen > pepsin (facilitated by acidic condition of stomach)
  • G cells: produce gastrin
  • gastric pits > gastric glands | contain parietal, chief + enerteroendocrine cells
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9
Q

What cells are in gastric pits??

A

Parietal cells
Chief cells
Enteroendocrine cells

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10
Q

Parietal cells
Location
Function
Stimulated by

A
  • body + fundus of stomach
  • Produce HCl > makes the stomach acidic
  • produce intrinsic factor > aids B12 absorption in terminal Ileus
  • stimulated by gastrin from G cells
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11
Q

Chief cells
Location
Function

A
  • in body + fundus of stomach
  • Secrete pepsinogen
  • Converted to pepsin (protease)
  • Facilitated by the acidic condition of the stomach
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12
Q

G cells
Location
Function
Stimulated by

A
  • pyloric antrum of stomach
  • secrete gastrin > increases gastric acid secretion
  • stimulated by GRP, ACh + amino acids
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13
Q

Mucous cells
Location
Function

A
  • cardia, body + fundus of stomach
  • secrete mucus + HCO3- ions > forms thick alkaline mucus layer adhered to epithelium > protects from acidic damage
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14
Q

Protective mechanisms of the stomach

A
  • surface mucous cells: secretes mucous + alkaline HCO3 > alkaline mucous layer
  • cells of stomach replaced regularly
  • release prostaglandins
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15
Q

Outline the role of prostaglandins as a protective mechanism of the stomach

A
  • increase mucosal blood flow
  • support mucus layer
  • generally protective
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16
Q

What stimulates stomach acid production?

A
  • sensory triggers: sight, smell, taste
  • gastric triggers: stretch, present of amino acids + peptides, food acts as buffer (pH increases)
  • intestinal triggers: chyme in duodenum > presence of partially digested proteins
17
Q

What decreases stomach acid production?

A
  • reduction in stomach distension
  • low pH detected
18
Q

How do parietal cells produce acid?

A

Proton pump
H+ and K+ exchange

19
Q

Outline the resting and active state of parietal cells

A

Resting phase
- proton pumps are in tubulovesciles
- tubulovesciles lack K+ permeability + not in contact with apical membrane

Active phase
- tubulovesicles attach to apical membrane (contains K+ channels)
- apical membrane has microvilli + canaliculi to increase SA

20
Q

What are the phases of digestion?
What is their % of HCl production in stomach?

A

Cephalic 30% HCl
Gastric 60% HCl
Intestinal 10% HCl

21
Q

What stimulates parietal cells?

A

Gastrin receptors
Histamine receptors
Muscarinic receptors

22
Q

Outline gastrin stimulation

A
  • G cells stimulated by peptides + amino acids
  • gastrin released into blood stream
  • binds to choleocystokinine receptor
    .
  • GRP due to stretch
  • ACh (muscarinic receptor) due to sensory triggers
23
Q

Outline histamine stimulation of parietal cells

A
  • entero-chromaffin cells stimulated by ACh (muscarinic receptor) + gastrin (CCK receptor)
  • entero-chromaffin like cells produce histamine
  • bind to H2 receptor on parietal cell > HCl produced
24
Q

How is acid secretion inhibited?

A
  • drop in pH detected by D cells
  • produce somatostatin
  • bind to G cell via somatostatin receptor + prevent gastrin release
25
Q

How is HCl produced in the parietal cell?

A
  • within the parietal cells: H2O + CO2 > H+ + HCO3-
  • Cl- ions actively transported into cell from blood by Cl-/HCO3- exchanger (HCO3- out into blood > alkaline tide)
  • Cl- passively diffuse into stomach lumen through Cl- channels
  • H+ enter stomach lumen by H+/K+ ATPase
  • secretion of HCl into stomach
26
Q

How many parts does the stomach have?
Name them

A

5 parts
Cardia
Fundus
Body
Antrum
Pylorus

27
Q

What vertebral level does the pyloric sphincter lie at?

A

L1
On the transpyloric plane

28
Q

What anatomical structures lie on the trans pyloric plane?

A

Pyloric sphincter
Neck of pancreas
SMA origin
Portal vein forms
Spinal cord ends
Hilum of kidneys (ish)

29
Q

How do the pyloric sphincter and lower oesophageal sphincter differ?

A
  • pyloric sphincter is a strong + bulky muscular sphincter
  • lower oesophageal sphincter has smaller muscle + relies of acute angle with stomach + right crus of diaphragm
30
Q

What causes the alkaline tide following a meal?

A
  • movement of HCO3- across the basolateral membrane of pariteal cells into blood in exchange for Cl- via Cl-/HCO3- exchanger
  • pH of blood transiently rises after a meal
31
Q

What is the alkaline tide?

A

The transient increased of blood pH after a meal due to movement of HCO3- from parietal cells into blood in exchange for Cl-

32
Q

Fuction of stomach acid

A
  • sterilising luminal contents
  • denaturing enzymes
  • activation of protease enzymes (pepsinogen > pepsin via acidic environment)
  • does NOT break fats down

Gastrointestinal (28 decks)

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