Salivary And Gastric Acid Secretions Flashcards
T/F Mastication is not essential for digestion of food
T
Functions of salivary components
. Lubricating food (mucins) for ease of swallowing
. Dissolving components in food for the sensation of taste
. Maintaining the health of oral tissues
. Allaying thirst
. Facilitating speech
. Promoting absorption of vit. B12
. Initiating digestion of carbs
. Neutralizing H in the distal esophagus
. Promoting health of esophageal epithelium
Secretion by acinar cells
. Primary electrolyte secretion isotonic to plasma
. Secretes the enzyme amylase (active form)
. Secretes mucins
. Tight junctions are permeable to water
Modification by ductal cells
. Actively reabsorbs Na
. HCO3 is exchanged for luminal Cl
. Actively secretes HCO3
. Tight junctions are impermeable to water
. Aldosterone inc. the absorption of Na by ductal cells but not the rate of salivary secretion
Regulation of salivary secretion
. Parasympathetic and sympathetic (not enteric) nn. Control the rate and volume of salivary secretion
. Rate and volume of salivary secretion is not under direct hormonal control
Salivary reflex
. Initiated by smell, taste, and/or tactile stimuli in mouth
. Reflex integrated in brainstem
. Parasympathetic and sympathetic efferent n. Activities are inc. and salivary secretion is inc.
. Parasympathetic nervous system is most important, resulting in sustained, high volume secretion of watery saliva
. SNS input to salivary glands inc. secretion of proteins and maintains high blood flow to gland by releasing no adrenergic vasodilators
Rate of salivary secretion is inc. by ___
. Inc. by nausea and vomiting
. Inc. parasympathetic n. Activity
Rate of salivary secretion is dec. by ___
. Fatigue, sleep, fear, dehydration
. Inhibition of parasympathetic nervous system
The final salivary secretion is ___ at all flow rates
Hypotonic
. HCO3 secretion is high
What occurs at slowest salivary flow rate
. Ductal cells reabsorb most Na
. HCO3 is exchanged for Cl
. Lowest conc. Of Na and highest conc. Of K in final salivary secretion
What occurs at fastest salivary flow rate?
. Ductal cells reabsorb little Na
. Highest conc. Of Na and lowest conc. Of K in final salivary secretion
. Active secretion of HCO3
Aldosterone effect on salivary secretion
. Modify the electrolyte conc. Of final secretion by inc. ductal cell Na reabsorption
. Do NOT regulate rate of salivary flow
. Inc. synthesis and insertion of ENaC into apical membrane of salivary ductal cells
Substances that aid in food digestion
. HCl from parietal cells
. Pepsinogen from chief cells
. intrinsic factor from parietal cells
. Gastric lipase from chief cells
Endocrine and paracrine substances that modulate HCl secretion
. Gastrin from G cells
. Histamine from enterochromaffin -like cells
. Somatostatin from D cells
Substances that protect the stomach lining
. Mucins from surface mucous cells and mucous neck cells
. HCO3 from surface mucous cells ad mucous neck cells
Function of HCl
. Denature protein
. Kill most ingested bacteria
. Dissolve CT in food
. Maintain low gastric luminal pH for pepsinogen activation and optimal pepsin activity
Secretory mechanism of HCl
. Apical membrane of parietal cell contains H-K ATPase that transports K into the cell and H out of cell against electrochemical gradients (primary active transport)
. H ion comes from action of the enzyme CA
. On basolat. Membrane, Cl is exchanged for excess bicarbonate ion
. HCO3 enters venous circulation and inc. pH of gastric venous blood
. Cl leaves the cell on apical membrane by facilitated diffusion
. HCl secretion followed by passive diffusion of H2O
. Rate-limiting step in HCl secretion is availability of ATP for proton pump
Agonists of HCl secretion
. They are synergistic
. W/o them secretion is significantly limited
. ACh inc. Ca
. Gastrin inc. Ca
. Histamine inc. cAMP (paracrine released from ECL cells in gastric mucosa)
Antagonists of HCl secretion
. Somatostatin (paracrine from D cells in gastric mucosa) dec. cAMP
. Prostaglandins (generated from arachidonic acid) dec. cAMP
Gastrin function
. Hormone
. Inc. HCl, intrinsic factor, histamine, and pepsinogen secretion
. Inc. rate of gastric emptying
. Stimulates growth of gastric mucosa (trophic hormone)
. Promotes mass movements in colon (gastrocolonic reflex)
Regulation of gastrin secretion
. G cells express receptors in their basolateral membrane that directly inc. or dec. gastrin secretion
. Protein digestion products in gastric lumen activate GRP-releasing IPANS to inc. gastrin secretion (short neural reflex)
Substances that inc. gastrin secretion from G cell
. Gastrin-releasing peptide (GRP) released from enteric neurons
. ACh
. Protein digestion products in gastric lumen (GRP)
. Secretin
. Gastric distension: long and short neural reflexes
Substances hat dec. gastrin secretion from G cells
. Express receptors in their basolat. Membrane that when activated directly dec. gastrin release
. Somatostatin: paracrine released from D cells of gastric mucosa when pH of gastric lineal contents is under 3
Histamine function
. Stimulates secretion of HCl and intrinsic factor
. Inhibits secretion of somatostatin
. Paracrine
Histamine regulation of secretion
. ECL cells express receptors in their membrane for gastrin to inc. histamine secretion and for somatostatin to dec. histamine secretion
Somatostatin function
. Inhibits secretion of HCl, intrinsic factor, pepsinogen, histamine, and gastrin
. Inhibits secretion of peptides from endocrine cells
. Constricts blood vessels and dec. local blood flow
Somatostatin regulation of secretion
. Cytoplasmic processes of D cells allow for control of G, ECL, and parietal cells
. D cells express receptors in their basolateral membrane for ACh and histamine that dec. SS secretion and secretin and CCK that inc. SS secretion
.pH of gastric contents alters SS secretion w/ pH under 3 inc. and pH over 3 dec. SS secretion
Interregulation of HCl secretion
. G, ECL, and D cells along w/ enteric neurons and vagus n. Interact to modulate HCl secretion from parietal cells
Activation of vagus pathway to HCl secretion
. Enteric neurons release ACh that activates muscarinic receptors to inc. HCl by parietal cells
. ACh and GRP directly inc. gastrin from G cells
. ACh inhibits somatostatin from D cells
. Gastrin travels into blood to directly inc. release of histamine from ECL cells and HCl from parietal cells
. Histamine activates H2 receptors ti inc. HCl
. Histamine activates H3 receptors to dec. release of somatostatin inc. acid secretion
.pH under 3 in gastric lumen inc. release of somatostatin from D cells
Effect of food in stomach on HCl
. When food enters, smooth m. Distended, dietary protein digestion begins, and pH of stomach inc. due to buffering by food
. Normal interregulation is still occurring
. Distension activates IPANS and vagal afferent nn.
. Short and long neural reflexes inc. HCl secretion
. Protein digestion products in gastric lumen inc. GRP release from enteric neurons to inc. gastrin release from G cells (short reflex)
.pH under 3 in gastric lumen results in dec. release of somatostatin from D cells
. Lower local levels of somatostatin inc. release of gastrin from G cells, histamine from ECL cells, and HCl from parietal cells
Result of presence of food in duodenum
. The acidic pH, fat content, high osmolarity, and distension of duodenal smooth m. Inhibit HCl secretion
. Acidic chyme stimulates secretin release from S cells
. Fat stimulates release of CCK from I cells
. Secretin and CCK inhibit HCl secretion by inc. SS secretion from D cells
. Hyperosmotic chyme and smooth m. Distension inhibit HCl secretion through short and long neural reflexes
