GI Secretions I -Covasa Flashcards
What are the constituents of saliva and their functions?
- water: dissolution of nutrients, aid in swallowing/speech
- bicarb: neutralize gastric acid (reflux)
- Mucins (glycoproteins): lubrication, antimicrobial, protective
- Amylase, ribonuclease: digestion
- lysozyme, lactoferrin, IgA (immune protection)
- epidermal and nerve growth factor (repair and protection)
- Inorganic solutes (Ca and phosphate): tooth formation and maintenance
What are the concentrations of ions (Na+, Cl-, K+, HCO3-) in saliva compared to plasma ?
- salivary concentrations vary but it is hypotonic*
- salivary [Na] and [Cl] «_space;plasma
- salivary [K+] > plasma
- normally rich in [HCO3-]
What salivary enzyme is important in neonates?
lipase (because they develop less pancreatic lipase)
Is stomach digestion of food critical?
NO! can remove the stomach and it doesn’t impair nutrient availability
What is the stomach critical for?
the absorption of Vit B12 because parietal cells secrete intrinsic factor
What is the function of the Fundic Enterocromafin-like Cell (ECL)? How does it respond to ACh and gastrin stimulation?
control acid secretion
-histamine is secreted by the ECL cell in response to ACh and Gastrin (indirect pathway)
–>histamine stimulates H2 receptor on parietal cells–> inc cAMP–> stimulate acid secretion
How does smell or taste affect gastric acid secretion from the ECL cells?
-smell or taste initiates a cephalic vagal reflex –> release ACh from vagal nerve endings in gastric mucosa
–> ACh binds to Muscarinic receptors on ECL cells to stimulate histamine secretion
–> histamine stimulates acid secretion by H2 receptor activation (on parietal cells)
How does distention or stretch of the stomach stimulate acid secretion?
-distention triggers gastrin secretion by G cells into venous drainage
–> gastrin binds to receptor on ECL cell –> trigger Histamine
–> histamine binds H2 receptor on parietal cells and triggers acid secretion
How do most H2 Receptor Antagonists work?
Competitive inhibition of the H2 receptors on parietal cells
(which all of the stimulators (ACh, Gastrin and Histamine) work through to stimulate acid secretion)
What is the strongest agonist of H+ release in the stomach?
Histamine
Histamine, ACh and Gastrin all work together to cause H+ secretion
How does somatostatin affect acid secretion?
(released from D cells) –>inhibits acid secretion in the fundus in response to acid in the antrum?
-affects G-cells, ECL cells and parietal cells
What 3 secretory systems regulate gastric acid secretion?
- neurocrine (vagus)
- endocrine (gastrin)
- Paracrine (histamine)
-parietal cells have receptors for histamine (H2), ACh (M3) and gastrin (CCK-2) which allows for the neural and humoral mechanisms to work together to inc acid secretion
Most stomach secretion occurs during the ____ phase
gastric
How do proton pump inhibitors prevent acid secretion?
irreversibly inhibits the K+/H+ ATPase proton pump on the parietal cells (final path for acid secretion)
(normally, K+/H+ ATPase pumps K+ into cell in exchange for H+ secretion into the canaliculus)
Where does the most intestinal Na+ absorption take place? By what transporters?
-highest in the jejunum
–enhanced with glucose, glalactose and neutral amino acids
- Na+-nutrient symporter (SGLT I)
- Na+-H+ Antiporter
- Cl-HCO3- antiporter
- GLUT2 basolateral membrane facilitated diffusion into the blood
