What are the interstitial cells of Cajal
electrical pacemakers in the GI system
form netwerk between smooth muscle cells
synapctic- like contacts with smooth muscle cells
likely responsible for slow-waves together with smooth muscle cells
Name neurotransmitters affecting the enteric nervous system
- acetylcholine (most common excitatory)
- norepinephrine/epinephrine (most common inhibitory)
- adenosine triphosphate
- serotonine
- dopamine
cholecystokinin - substance P
- vasoactive intestinal peptide
- somatostatin
- leuenkephalin/metenkephalin
- bombesin
Gastrin: stimuli for secretion, site of secretion, actions
Stimuli: protein, gastric distention, nerve products( gastrin-releasing peptide)
Site: G cells in stomach, duodenum and Jejunum
Actions: gastric acid secretion, mucosal growth
Cholecystokinin: stimuli for secretion, site of secretion, actions
Stimuli: protein, fat, acid (mostly in intestinal contents)
Site of secretion: I cells of duodenum, Jejunum and ileum
Actions: stimulates pancreatic enzyme secretion, pancreatic bicarbonate secretion, gallbladder contraction, growth of exocrine pancreas
Inhibits gastric emptying
Secretin: stimuli for secretion, site of secretion, action
Stimuli: mostly response to acid in duodenum, also fat
Site of secretion: S cells of duodenum, Jejunum and ileum
Actions: stimulates bicarbonate from pancreas, pancreatic enzyme secretion, gallbladder contraction, exocrine pancreas growth,
inhibitsgastric emptying
Gastric inhibitory peptide: stimuli for secretion, site of secretion, actions
Stimuli: proteins, fat, carbohydrates
Site of secretion: K cells of duodenum and Jejunum
Actions: insulin release, inhibits gastric acid secretion, decrease gastric motor activity
Motilin: stimuli for secretion, site of secretion, actions
Stimuli: fat, acid, nerve
During fasting
Site: M cells of duodenum and Jejunum
Actions: stimulates GI motility
Causes of increased blood flow during GI activity
Vasodilation:
- from Mucosa: cholecystokinin, vasoactive intestinal peptide, gastrin, secretion
- from GI glands: kallidin, bradykinin
- O2 decrease: causes vasodilation and adenosine increase (also causes vasodilation)
What is an important mixing mechanism in the stomach
Retropulsion:
peristaltic waves reaching pylorus that is not completely open or constricted = antral contents are squeezed through peristaltic ring toward body
What is the vasovagal reflex of the stomach
distension of the stomach causes reflex (stomach-brain-stomach), reduces muscular tone and bulges stomach progressively
Intestinal factors that cause inhibition of gastric emptying
- duodenal distention
- mucosal irritation
- increases acid content
- increased osmolality
- increased protein and fat break-down products
- cholecystokinin, gastric inhibitory peptide
Intrinsic factor: location of secretion, function
Location: parietal cells
Function: Vitamin B12 absorption in ileum
Why do pancreatic enzymes only get activated in the SI and how is activation inhibited in the pancreas?
- proteolytic enzymes would digest pancreas
- trypsin inhibitor (also secreted by pancreatic glandular cells) inhibits activation of trypsin
- trypsin activates other enzymes, therefore their activation is also inhibited by trypsin inhibitor
What cells secrete bicarbonate in the pancreas?
ductules and ducts of epithelial cells
Which factors regulate pancreatic secretion?
- Acetylcholine (digestive enzymes)
- Cholecystokinin (digestive enzymes)
- Secretin (water and sodium bicarbonate)
Which factor increase bile secretion?
- lower amount of bile in the enterohepatic circulation
- secretin
What is the typical life cycle of an intestinal epithelial cell?
5 days
How much water does a horse/cow consume/day?
Horse: 24-30 L/day
Cattle: 30 - 60 L/day
