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GI > Lecture 7 - Stomach > Flashcards

Lecture 7 - Stomach Flashcards

1
Q

Gastrin

A

Stimulated by:

  • Protein
  • Distention
  • Gastrin releasing peptide and acetylcholine (vagal stimulation) - PS triggers e.g. smell

Inhibited by:

  • Acid secretion (post -meal) - when food leaves stomach pH drops as acts as buffer
  • Somatostatin (stimulated by low pH)
  • Endochromaffin like cells - release histamine
  • reduced stomach distention and vagal activity

Site of secretion:
- G cells of antrum, duodenum and jejunum

Actions:

Stimulates gastric acid secretion and mucosal growth

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2
Q

Cholecystokinin

A

Stimulated by:

  • Protein
  • Fat
  • Acid - fatty acids and monoglycerides

Site of secretion:
- I cells of duodenum, jejunum and iluem

Action:
- Stimulates pancreatic enzyme and bicarbonate secretion

  • Gall bladder contraction tp expel bile
  • Growth of exocrine pancreas
  • Inhibits gastric emptying - more time fore digestion
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3
Q

Secretin

A

Stimulated by:

  • Acid (H+) - gastric juice
  • Fatty acids

Stimulated by:
- S cells of the duodenum, jejunum and ileum

Stimulates:

  • Pepsin secretion
  • Pancreatic and biliary HCO3- secretion - neutralise chyme
  • growth of exocrine pancreas
  • inhibits gastric acid secretion
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4
Q

Paracrine

A

Hormone which has effect only in the vicinity of the gland secreting it

Peptides released by endocrine cells acting in the local environment and diffuse short distances

e.g somatostatin by D cells in the antrum

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5
Q

Neurocrine

A

Peptides released by neurones due to action potential

e.g. gastrin releasing peptide released by the fibres of the postganglionic vagus nerve which stimulates gastrin release

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6
Q

Gastric inhibitory polypeptide (GIP)

A

Stimulated by:

  • Sugar - carbohydrates
  • Protein amino acids
  • fatty acids

Stimulated by:
- K cells of duodenum and jejunum

Action:

  • Insulin release
  • Inhibits gastric acid release
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7
Q

Functions of the stomach

A
  • Short term storage of food
  • Physical break down of food due to smooth muscle contractions
  • Chemical breakdown of food - proteases
  • Innate immunity - acidic
  • Activates enzymes
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8
Q

How is the stomach expandable

A

Temporary folds - rugae

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9
Q

Parts of stomach

A 
Fundus
Cardia - heart sits anterior 
Body 
Antrum 
Pylorus

Greater and lesser curvature

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10
Q

Where does the lesser omentum attach to

A

Stomach - first 1/3rd of duodenum near pylorus

Connect the liver and stomach

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11
Q

Layers of smooth muscle in stomach

A

Outer longitudinal layer
Middle circular layer
Inner oblique layer

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12
Q

Innervation of stomach

A

Autonomic NS

Enteric NS - Miessner’s and Auerbach’s plexus

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13
Q

Orad

A

Fundus
Proximal portion of body

Relaxes to relax the lower oesophageal sphincter to receive bolus via vagovagal reflex

  • Food enters without raising intra-gastric pressure too much
  • Prevents reflux
  • Distension of rugae
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14
Q

Relaxation neural reflex

A
  1. Mechanoreceptors detect distention of the stomach
  2. Impuslese are sent to the CNS via sensory neurones of vagus nerve
  3. Efferents sent via vagus nerve fibres to smooth muscle wall of orad
  4. Relaxation
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15
Q

Factors affecting gastric emptying

A
  • Fluids and isotonic solutions empty quicker
  • fat in duodenum - CCK decreases gastric emptying
  • H+ in duodenum - impulses to gastric SMC via interneurones of the myenteric plexus - increased force of contraction and AP frequency
    [Not affected by neural or hormonal inputs]
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16
Q

Caudad

A

Distal portion of body

Antrum

17
Q

Stomach lining

A

Stratified columnar
Rugae - folds
Gastric pits

18
Q

Epithelial cells

A

Cover surface and extend into pits

Parietal cells - HCL / IF
Chief cells - Pepsinogen
G cells - Gastrin 
Mucous cells 
D cells - somatostatin
Enterochromaffin like cells - histamine (paracrine)
19
Q

Structure of stomach

A

Large proximally to small distally

Upper stomach - sustained contractions for basal tone

Lower stomach - strong peristalsis - more muscular and narrow

Contractions every 20 seconds

20
Q

Chyme

A

Enters duodenum 3 times a minute

21
Q

Coeliac trunk branches

A
  • Splenic
  • Left gastric
  • Common hepatic

[SMA below coeliac trunk]

22
Q

Coeliac trunk

A

Splenic artery –> short gastric arteries and left gastroepiploic artery

Common hepatic –> gastroduodenal artery –> Superior pancreaticoduodenal artery

–> Right gastric comes off and anastamoses with the left gastric

–> Proper hepatic to right and left hepatic arteries

23
Q

Left gastroepiploic artery

A

Supplies the lesser curve of the stomach and anastamoses with the right gastroepiploic

24
Q

Left and right gastric artery

A

Supplies lesser curve of stomach

25
Q

Gastroduodenal artery

A

Common site for ulcer to perforate artery

  • peritonitis
  • vomit blood
26
Q

HCL

A

Acidic conditions activate pepsinogen to pepsin
Innate immunity

Parietal cells pump out H+ into stomach against the conc gradient via K+/H+ ATPase

Acid causes iron absorption in stomach

27
Q

Pernicious anaemia

A

Autoimmune destruction of parietal cells

Less intrinsic factor secreted so decreases absorption of Vit B12 in ileum - macrocytic anaemia

28
Q

Roles of stomach areas

A

Cardia - mucous secretion

Fundus and body- HCL / mucus and pepsinogen

Pylorus - gastrin / somatostatin

[lots of crossover]

29
Q

Cell distribution

A 
Parietal cells - Body
Chief cells - Body
G cells -  Antrum
Mucous cells  - Antrum
D cells - Antrum
30
Q

Phases of digestion

A

Cephalic
Gastric
Intestinal

31
Q

Cephalic phase

A

Parasympathetic stimuli e.g. smell and tasting

Vagus nerve stimulates gastric secretions before food is swallowed to parietal cells (HCL release) and G cells via GRP

Increases gut motility

30% of HCL secretion

32
Q

Gastric phase

A

60% of HCL secretion

Distention of stomach stimulates the vagus nerve to release GRP and Ach which stimulates gastrin release from G cells and parietal cells to release HCL

Proteins and amino acids stimulate gastrin secretion from G cells

Food acts as a buffer increasing pH somewhat, which removes G cell inhibition by stomatostatin

Myenteric plexus and gastrin causes strong smooth muscle contractions

Enterochromaffin like cells also release histamine that stimulates acid secretion by parietal cells

33
Q

Intestinal phase

A

10 % HCL production

Initially: Chyme stimulates gastrin release as partially digested proteins in the duodenum

Progress: Inhibition of G cells

  • Presence of lipids activates the enterogastric reflex which decreases vagal stimulation
  • Chyme stimulates CCK and secretin
34
Q

Stomach body glands

A

oxyntic glands

35
Q

Antrum glands

A

Pyloric glands - deeper pits

36
Q

Mucin

A

Secreted by foveolar cells

Mucin creates a viscous mucus layer that adheres to the epithelium and prevents chemical digestion of stomach by acid

HCO3- secreted into mucus layer - neutral pH

Rich vascular blood supply - remove acid that breaches mucous layer

High epithelial cell turnover to replace damaged cells

Prostoglandins promote processes

37
Q

Why does NSAIDs like aspirin and ibroprofen cause stomach ulcers?

A

Inhibits prostoglandins that promote HCO3- release into the mucous layer and mucous layer formation.

Therefore more likely for mucous layer to be breached and physical damage to occur to the epithelium of the stomach by gastric acid causing an ulcer.

38
Q

What breaches the stomach defense

A

Alcohol - dissolves mucous layer

Helicobacter pylori - chronic active gastritis

NSAIDs - inhibit prostoglandins

GI (18 decks)

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