Lecture 39 11/16/23 Flashcards
What are the characteristics of gastrointestinal hormones?
-produced by enteroendocrine cells
-released by physiologic stimuli
-circulate in blood
-bind to receptors at distant sites
-evoke biological response
What are the phases of gastrointestinal secretions?
-cephalic
-gastric
-intestinal
What triggers the cephalic secretory phase?
sight, smell, or thought of food
What triggers the gastric secretory phase?
presence of food in stomach
What triggers the intestinal secretory phase?
presence of food in intestines
What secretions are produced during the cephalic secretory phase?
-majority of salivary secretion
-20-30% of gastric and pancreatic secretions
What secretions are produced during the gastric secretory phase?
-60% of gastric acid secretion
-5-10% of pancreatic secretions
What secretions are produced during the intestinal secretory phase?
-70% of pancreatic secretions
-10% of gastric acid secretion
Which organs/glands receive parasympathetic vagus nerve input during the cephalic phase?
-salivary glands
-gastric glands
-pancreas
Which nerves provide parasympathetic innervation to just the salivary glands?
-glossopharyngeal nerve
-facial nerve
What are the functions of saliva?
-lubricate food
-begin digestion process
-antibacterial activity
-evaporative cooling
-pH regulation
How does saliva play a role in pH regulation?
bicarbonate in saliva neutralizes acids produced by bacteria
What type of saliva is produced by animals with simple stomachs?
neutral saliva
What type of saliva is produced by ruminants?
basic saliva with high concentrations of phosphate ions (in large quantities)
What are the two functional areas of the stomach?
-oxyntic glands
-pyloric glands
Which cells are found within the oxyntic glands?
-parietal cells
-enterochromaffin-like cells
-D-cells
-chief cells
Which cells are found within the pyloric glands?
-D-cells
-G-cells
What are the stimuli for gastrin release?
-stretch
-peptides
-amino acids
-acetylcholine
What are the effects of gastrin?
-activation of parietal cells
-activation of enterochromaffin-like cells
-promotion of epithelial growth in stomach/duodenum
-activation of pancreatic acinar cells
What is the stimulus for histamine release?
gastrin
What is the effect of histamine?
activation of parietal cells
What are the characteristics of parietal cells?
-secrete HCl
-activated by 3 secretagogues: acetylcholine, gastrin, and histamine
What happens once a parietal cell is activated?
-conformational change in which luminal membranes become enfolded; increases surface area for gastric acid secretion
-insertion of H+/K+/ATPases in the membrane, which become proton pumps
Which type of receptor does histamine interact with on parietal cells?
H2
Which secretagogue is the most potent for parietal cells?
histamine
What are the characteristics of parietal cell proton pumps?
-secrete acid solution with 0.8 pH
-carbonic anhydrases catalyze combination of CO2 and OH- to produce bicarbonate
-bicarbonate is secreted into interstitial fluid while Cl- ions enter cell
Which cells produce pepsinogen?
chief cells
What are the stimuli for pepsinogen production?
-acetylcholine
-HCl
What is pepsinogen?
enzyme precursor of pepsin
When does pepsinogen get activated into pepsin?
in the presence of acid
What are the characteristics of pepsin?
-begins protein digestion
-mostly digests collagen
-only provides 10-20% of total protein digestion
What is the stimulus for somatostatin secretion?
rapid drop in gastric pH
What are the actions of somatostatin?
-inhibit gastrin secretion
-inhibit parietal cell acid secretion
-inhibit gastric motility
