Lecture 16 - GI Physiology Flashcards
Differentiate between slow waves and spike potentials in the GI.
RL16 S83-84
Slow waves:
- local potentials propagated through gap junctions
- generated by cells of Cajal (pacemakers)
- increased frequency increases membrane potential
Spike potentials:
- action potentials that occur when slow wave membrane potentials exceed -40mV
- frequency determined by slow wave potential
What system is responsible for the reflexes of the GI system and what are the main reflexes within and outside the system?
RL16 S85
Enteric nervous system which is self contained in the gut wall.
Reflexes within GI tract:
- most secretion
- peristalsis
- mixing contractions
- local inhibition
What is the stimulus/inhibition for secretion, site of secretion, and actions of gastrin?
RL16 S86
Stimulus:
- peptides and AAs
- stomach distension
- vagal stimulation
Inhibition:
- excess gastric acid
- somatostatin
Secretion:
-G cells (intestine)
Actions:
- gastric acid secretion
- mucosal growth
What is the stimulus for secretion, site of secretion, and actions of cholecystokinin?
RL16 S87
Stimulus:
- small peptides and AAs
- fatty acids and monoglycerides
Secretion:
-I cells (intestine)
Action:
- FEEDBACK control of DUODENUM
- bicarbonate secretion
- gastric emptying
- inhibits hunger
- pancreatic and gallbladder secretion
What is the stimulus for secretion, site of secretion, and actions of secretin?
RL16 S88
Stimulus:
-acid and fat in duodenum
Secretion:
-S cell (intestine)
Action:
- pepsin secretion
- bicarbonate secretion
- inhibits gastric acid
- pancreatic secretion
What is the stimulus for secretion, site of secretion, and actions of GIP?
RL16 S89
Stimulus:
-protein, fat, and CARBOHYDRATE
Secretion:
-K cells (duodenum and jejunum)
Actions:
- insulin secretion
- inhibits gastric acid
What is the stimulus for secretion, site of secretion, and actions of motilin?
RL16 S90
Stimulus:
-fat and acid
Secretion:
-M cells (duodenum and jejunum)
Actions:
-intestinal motility
Secreted during fasting
What GI hormone controls feedback of the duodenum?
RL16 S87
CCK
What is the only GI hormone to respond to the presence of carbohydrates?
RL16 S89
GIP
What is the composition of saliva at different flow rates?
RL16 S91
Low flow:
- low sodium, chloride, and bicarbonate
- high potassium
- has time to reabsorb electrolytes
High flow:
-closer to plasma concentrations due to lack of time to reabsorb electrolytes
What nerves stimulate saliva production?
RL16 S92
Cranial nerves VII and IX (facial and glossopharyngeal)
What do chief cells and parietal cells release?
RL16 S95-96
Chief cells:
-pepsinogen
Parietal cells:
-HCl
What mechanisms result in gastric secretions?
RL16 S98-99
Parasympathetic (vagal nerve/CN X):
- direct through innervation of parietal cells
- indirected through innervation of G cells resulting in gastrin production
Gastrin stimulation:
- secondary messengers of IP3/Ca++
- from G cells
Histamine stimulation:
- secondary messenger of cAMP
- from enterochromaffin-like cells
What mechanisms result in inhibition of gastric secretions?
RL16 S100
Somatostatin:
- from delta pancreas cells
- inhibits GASTRIN, insulin, and glucagon
- directly binds receptors adenyl cyclase activity
- indirectly through inhibition of histamine and gastrin
Prostaglandins:
-activation of G protein that inhibit adenyl cyclase
