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GI > Functions of the stomach > Flashcards

Functions of the stomach Flashcards

1
Q

How do hormones work?

A

Hormones are secreted into the bloodstream;
Peptides are released from endocrine cells into portal circulation and pass through the liver before entering systemic circulation

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2
Q

What does the portal vein drain and to where?

A

Stomach, spill,. pancreas, SI and colon into the liver

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3
Q

What drains the liver?

A

Hepatic veins into the IVC

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4
Q

What is paracrine signalling?

A

a hormone what has effect only in the vicinity of the gland secreting it so the peptides release by endocrine cells act in their local environment and diffuse short distance

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5
Q

What is neurocrine signalling?

A

Peptides released by neurones in the GI tract - these are released after their action potential

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6
Q

What is an example of a neurocrine hormone?

A

GRP (Gastrin releasing peptide)

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7
Q

How does GRP work?

A

It is released from the post-ganglionic fibres of the vagus nerve

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8
Q

What does GRP cause?

A

an increased release of gastrin from G cells

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9
Q

What are the 2 families of GI hormones?

A

Gastrin and Secretin

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10
Q

What hormones are in the Gastrin family?

A

Gastrin and CCK (cholecystokinin)

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11
Q

What hormones are in the Secretin family?

A

Secretin and Gastric Inhibitory Polypeptide

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12
Q

What does gastrin do?

A

Increases gastric acid secretion from G cells in the antrum of the stomach

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13
Q

What does CCK do?

A

The I cells in the DUODENUM release CCK which increases pancreatic and gallbladder secretions

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14
Q

What does CCK stimulate?

A

The contraction of the gall bladder and the pancreas stimulated

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15
Q

What does secretin do?

A
  • secreted from S cells in the duodenum
  • stimulates the pancreas and gall bladder to release HCO3 rich secretions which neutralises chyme
  • decreases gastric acid secretion
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16
Q

What does GIP do?

A
  • secreted by cells in the duodenum and jejunum

- increases insulin release and decreases gastric acid secretion

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17
Q

What are the basic functions of the stomach?

A
  • receive food (short term storage facility)
  • disrupt food (vigorous contractions of the smooth muscle
  • digestion (mainly proteins)
  • disinfect
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18
Q

What are the sphincters in the stomach?

A 
lower oesophageal (entry point)
pyloric (exit point)
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19
Q

What are the regions of the stomach?

A
  • cardia
  • fundus
  • antrum
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20
Q

What would you typically find in the antrum upon X-ray?

A

gas - black area

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21
Q

What is the epithelium lining the LOS?

A

stratified squamous

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22
Q

What is the epithelium of the stomach?

A

simple columnar (secretory)

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23
Q

What are the muscle layers of the stomach?

A
  • circular
  • oblique
  • longitudinal

ALL aid in mechanical digestion

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24
Q

what is the anatomical position of the stomach?

A
  • on the left hand side

- sits behind the liver next to the spleen

25
Q

What is the difference in the walls of the upper and lower stomach?

A

the upper stomach has slightly thinner walls to allow for expansion of the stomach to accommodate more food
the lower stomach has slightly thicker walls to aid in mechanical digestion
-the mucosa layer is folded to form rugae

26
Q

Why is the stomach larger at the top and smaller at the bottom?

A

to allow for food to accelerate down to the pyloric sphincter

27
Q

What are the different epithelial cells in the stomach?

A

-muscous cells
-pareital cells
-chief cells
-g cells
-Enterochromaffin like cell
-D cells
(My parents cuddle gently every day)

28
Q

What do mucus cells do?

A

secrete mucus

29
Q

What do parietal cells secrete ?

A

HCL and intrinsic factor

30
Q

What is special about parietal cells?

A

they have lots of mitochondria as they are very active

31
Q

Why are parietal cells so active?

A

they secrete H+ ions through the proton pump against a large concentration gradient (as there is a large HCL conc already in the stomach

32
Q

What is the alkaline tide?

A

because the production of the acid bicarbonate is also produced, it moves into the blood causing a rise in the pH of the blood
-so the alkaline tide is an increase in pH during digestion

33
Q

What are parietal cells stimulated by?

A
  • gastrin
  • histamine
  • ACh
34
Q

Where is ACh released from?

A

released by the vagus nerve when the parasympathetic nervous system is activated

35
Q

What does the intrinsic factor do?

A

important for vitamin B 12 absorption

36
Q

What do chief cells secrete?

A

pepsinogen

37
Q

What is the function of pepsinogen?

A

it is the precursor to pepsin which it is converted to in the presence of acid
-pepsin is a proteolytic enzyme that acts on proteins and polypeptides (hydrolyses them)

38
Q

What do G cells do?

A

secrete gastrin

39
Q

What does gastrin do?

A

-activates parietal cells to produce HCL - gives greater control of HCL production due to the numerous ways it can be controlled

40
Q

What is gastrin release stimulated by?

A
  • strecthing of the stomach (detected by stretch receptos activating GRP which is released from the post-ganglionic fibre of the vagus nerve)
  • AA
  • ACH released from the vagus nerve too
41
Q

What inhibits G cells?

A

somatostatin as it reduces vagal activity

42
Q

What do enterochromaffin like cells?

A

secrete histamine

43
Q

What do D cells produce?

A

somatostatin

44
Q

What is the role of somatostatin?

A

inhibits HCl produced by inhibiting G cells
-also inhibits enterochroamaffin cells so less histamine is produced so less parietal cells are activated giving less HCl

45
Q

How does somatostatin work?

A

when food leaves the stomach, the pH falls (because food is acting as a buffer to the stomach acid) - this low pH is detected by D cells which release somatostatin which inhibits G cells so vagal activity reduces and also stomach distention is reduced

46
Q

Whats the difference between gastric pits and gastric glands?

A

the gastric pits are little holes in the stomach wall which give way to 5/6 tubular glands (which are deeper in the stomach walls)

47
Q

What is the distribution of cells in the stomach?

A

cardia - mainly mucus secretion
funds/body - mainly mucus, HCL and pepsinogen
Pylorus - mainly gastrin and somatostatin (and mucus)

48
Q

What is the function of mucus?

A

protects the epithelium of the stomach from acid secretion

49
Q

What type of contractions are in each region of the stomach?

A

upper - sustained contractions to create the basal tone

lower - strong peristalsis contractions with coordinated movements that occur every 20 seconds

50
Q

Why does the stomach get more muscular and narrow from proximal end to distal end?

A

the stomach can’t deposit lips of food into the duodenum and can only give it chyme therefore needs to have stogner contractions towards the end to aid in mechanical digestion

51
Q

The function of the stomach is to receive food - how does it do this?

A
  • the stomach needs to be able to store food
  • relaxation of the LOS allows food to move into the stomach
  • the stomach walls also relax which is mediated by a vagal reflex inhibiting the muscle tone without increasing intra-gastric pressure too much (also prevents reflux of stomach contents during swallowing
  • the stomach also has rugae (mucosal folds) which allow for distention
52
Q

What is the point in having acidic conditions in the stomach?

A
  • helps to unravel proteins
  • activates proteases to digest them (pepsinogen to pepsin
  • disinfects the stomach contents e.g. if any bacteria is in the food, the acid may kill it
53
Q

How is HCL production controlled?

A

-stimulare by gastrin, histamine and ACh

note that gastrin is very similar to CCK so the CCK receptors stimulates the HCL production when gastrin binds to it

54
Q

What are the phases of digestion?

A
  • cephalic
  • gastric
  • intestinal
55
Q

What occurs in the cephalic phase of digestion?

A

this is where the smell of food, sight of food and chewing stimulates parietal and G cells through the vagus nerve (parasympathetics)
-the vagus nerve releases GRP to activate G cells
30% of the HCL is produced
NOTE - anticipating food also increases gastric motility

56
Q

What occurs in the gastric phase of digestion?

A

this is where food filling the stomach causes it to distend which stimulates the vagus nerve to activate parietal and G cells
the presence of AA also activates G cells
-food will buffer the acid to prevent somatostatin production from D cells
-60% of the HCL is produced
-the enteric NS and gastrin cause strong mouth muscle contraction

57
Q

What occurs in the intestinal phase of digestion?

A

-this is a short phase where the food enters the duodenum and becomes chyme
-chyme initially stimulate gastrin secretion but the G cells then become inhibited
-inhibition due to the presence of acid in the duodenum which causes
1)somatostatin released from D cells to inhibit acid secretion from parietal cells
2)Acid causes release of secretin into the blood stream which inhibits release of gastrin by g cells
3) FA in the duodenum, cause release of GIP and CCK acting to inhibit secretion of acid by parietal cells
(GIP also suppresses gastrin release)
-final 10% of HCL produced here

58
Q

Why don’t the stomach digest itself?

A
  • muscus secreted from foveolar cells forming a viscous layer that adheres to the epithelium to prevent physical damage. HCO3- is also secreted into mucus layer to provide a pH neutral barrier against the stomach acid
  • rich blood supply to gastric mucosa can remove and buffer acid that has breached the mucus layer
  • prostaglandins are released that promote blood flow to the stomach bringing nutrients to the epithelia
  • high turnover of epithelial cells
59
Q

What can the stomach be weakened by?

A
  • alcohol (dissolves mucus layer)
  • helicobacter pylori (causes chronic active gastritis)
  • NSAIDs (inhibit prostaglandins)

GI (10 decks)

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