GI Flashcards
What cells in the stomach produce HCl (gastric acid)?
Parietal cells
What else do parietal cells produce?
Intrinsic factor
What is the function of intrinsic factor?
Absorption of vitamin B12
What cells in the stomach produce pepsinogen?
Chief cells
What is the active form of pesinogen?
Pepsin
What is the role of pepsin?
The breakdown of proteins - specifically collagen, thus helps the breakdown of meat
What protects the stomach from acid?
Mucus
What produces the mucus?
Mucus secreting neck cells
Which parts of the stomach have full gastric glands - contain all the cells
Body and fundus - the cardiac and pyloric regions are devoid of parietal and chief cells
What is the epithelial lining of the stomach?
Simple columnar epithelium
What are the deep invaginations of the surface epithelium called?
Gastric pits
How many layers of muscle are present in the stomach?
3
Is the muscle in the stomach smooth or skeletal?
Smooth
What does the muscularis mucosa have in addition to two layers of smooth muscle?
Elastic tissue - this helps cause the stomach to collapse on emptying
Whereabouts in the gastric glands are the parietal cells located?
Predominently in the upper part, near the gastric pits
What shape are the parietal cells?
Globular
What enzyme are the parietal cells rich in?
Carbonic anhydrase
What is the average pH for the stomach?
2
What shape are chief cells?
Pyramidal
Whereabouts in the gastric glands are the chief cells located?
In the deeper part of the gland
What else, in addition to pepsinogen, do the chief cells produce?
Lipases
What is the difference between the gastric glands in the cardiac and pyloric regions compared to the body and fundus?
Those in the cardiac and fundus regions are:
1) Shorter
2) Coiled (rather than straight)
3) Composed mainly of mucous neck cells (similar to those in the glands of the body and fundus)
What cells are also found in the stomach in addition to the parietal, chief and mucous cells?
Enteroendocrine cells
What are the two phases that turn on gastric secretion?
1) Cephalic
2) Gastric
What are the two phases that turn off gastric acid secretion?
1) Gastric
2) Intestinal
What happens in the cephalic phase to turn on gastric acid secretion?
1) PNS activated by sight, smell, taste and chewing
2) PNS releases acetylcholine
3) Acetylcholine increases gastrin secretion and histamine secretion
4) These increase gastric acid secretion from the parietal cells
What happens in the gastric phase to turn on gastric acid secretion?
1) Gastric distention occurs and peptides and amino acids arrive in stomach
2) This increases gastrin secretion
3) gastrin secretion acts directly on parietal cells and increases histamine secretion
4) Overall increase in gastric acid secretion occurs
What happens in the gastric phase to turn off gastric acid secretion?
1) Luminal pH falls
2) Gastric acid secretion is inhibited
3) Histamine secretion is therefore inhibited
4) Somatostatin secretion is stimulated
5) Parietal cells activity is inhibited and gastric acid secretions are reduced
What factors are involved in the intestinal phase?
1) Duodenal distention
2) Low luminal pH
3) Hypertonic luminal contents
4) Presence of amino and fatty acids
What is released in the intestinal phase in response to the factors in the duodenum?
Entergasterones
What are the two enterogaterones?
1) Secretin
2) Cholecystokinin (CCK)
What is the role of secretin?
It inhibits gastrin release and promotes somatostatin release
What is the role of CCK?
It is the major hormone responsible for gallbladder contraction and pancreatic enzyme secretion
Proteins are involved in the gastric turning on phase, how does the mechanism work?
The proteins act directly on gastrin release but also act as buffers removing the H+ ions and thus increasing pH. The increase in pH therefore decreases somatostatin release which thus leads to lack of inhibition of the parietal cells
What are the three types of solution that can occur inside the body in terms of solute concentration?
1) Isotonic
2) Hypotonic
3) Hypertonic
What is meant by isotonic?
Where the concentration of the solute is the same both inside and outside the cell
What is meant by hypotonic?
Where the concentration of the solute is greater inside the cell
What is meant by hypertonic?
Where the concentration of the solute is greater outside the cell
What is the parasympathetic neurotransmitter involved in gastric acid regulation? Does it increase or decrease production?
Acetylcholine - it increases production
What is the hormone involved in gastric acid regulation? Does it increase
Gastrin - it increases it
Whta are the two paracrine factors involved in gastric acid regulation? Do they increase or decrease the production?
1) Histamine - increase
2) Somatostatin - decrease
What are the three defence mechanisms in the mucosa of the stomach?
1) Alkaline mucus
2) Tight junctions between epithelial cells
3) Replacement of damaged mucosa cells
What are the three main causes of peptic ulcers?
1) Helicobacter pyori
2) NSAIDs
3) Chemical irritants
How does helicobacter pylori cause peptic ulcers?
1) Releases urease
2) Urease splits into CO2 and ammonia
3) Ammonia combines with H+ to form ammonium which damages the gastric epithelium
How do NSAIDs cause peptic ulcers?
NSAIDs inhibit cyclo-oxygenase 1 which is needed for prostaglandin secretion. Prostaglandins are needed to stimulate mucus secretion thus there is decreased mucus
What is a gastrinoma?
A tumour of the pancreas or duodenum that secretes excess gastrin
What major structures pass through the diaphragm?
1) Inferior vena cava
2) Oesophagus
3) Aorta
At what level does the Inferior vena cava pass through the thoracic diaphragm?
T8
At what level does the oesophagus pass though the thoracic diaphragm?
T10
At what level does the aorta pass through the thoracic diaphragm?
T12
