GI Secretory Functions, Digestion, Absorption Flashcards Preview

Physiology II Exam 2 > GI Secretory Functions, Digestion, Absorption > Flashcards

Flashcards in GI Secretory Functions, Digestion, Absorption Deck (53)
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What stimulates gland secretion?

-food contact and local epithelial stimulation

-autonomic stimulation (parasympathetic)

-higher brain centers

-hormonal stimulation


What are the functions of mucus?

-adheres to food and other particles

-spreads thin films over surfaces

-coats wall of gut, preventing actual contact with food

-causes fecal particles to adhere to one another

-resistance to digestion by GI enzymes

-has atmospheric properties making it useful for buffering small amounts of acids and bases


What are the functions of saliva?

-initial starch digestion and initial triglyceride digestion

-lubrication of food and protection of mouth and esophagus


What is the composition of saliva?

-high K and bicarbonate conc

-low Na and Cl


-presence of alpha-amylase, lingual lipase, and kallikrein


What is the difference between low and high saliva flow rates?

-lowest osmolarity
-lowest Na, Cl, and CO3-
-highest K

-composition closest to plasma


What are the salivary gland secretions?

-parotid gland secretions are almost entirely serous

-submandibular and sublingual secretions are mixed


What occurs during the first stage of salivary secretion?

-occurs in acini

-secretion contains ptyalin (alpha-amylase)

-composition is isotonic with ionic conc similar to plasma


What happens during stage two of salivary secretion?

-occurs in salivary ducts

-active reabsoption of Na

-active secretion of K

-active/passive secretion of bicarbonate ions

-passive reabsoption of Cl due to -70mv in ducts


What controls salivary gland secretion?

-cranial nerves VII and IX

-production if controlled mostly by parasympathetic system, but also by sympathetic system, both can result in saliva production


Describe how parasympathetic stimulation of salivary gland secretion functions.

-muscarinic cholinergic receptors on both acinis and ducts

-second messenger is inositol 1,4,5-triphosphate (IP3) and increased Ca+2


Describe how sympathetic stimulation of salivary gland secretion functions.

-B-adrenergic receptors

-second messenger is cAMP


What are some factors the increase saliva production?

-food in mouth (para)


-conditioned reflexes



What are some factors that decrease saliva production?

-inhibition of parasympathetic system:
+anticholinergic drugs


What are the secretory cells in gastric glands?

-mucus neck cells

-chief/peptic cells

-parietal/oxyntic cells


What are the different gland types?

-unicellular mucous

-crypts of Lieberkuhn

-tubular glands

-complex glands -> salivary glands, pancreas, liver


What do chief cells do?

-secrete pepsinogen (pH range of activity: 1.8-3.5)

-secrete intrinsic factor


What stimulates the release of pepsinogen?

-ACh from vagus nerves or gastric enteric nervous plexus

-response to acid in stomach


What do parietal cells secrete?

-secrete HCl


What is the mechanism of secretion for HCl?

-dissociation of water inside the cell into H+ and OH-

-OH- + CO2 -> HCO3 +H+

-HCO3 is exchanged for Cl- ions
+HCO3 increases blood pH and will even tail be secreted by pancreas to neutralize H+ in duodenum

-Cl- ions are secreted through chloride channels into the canaliculi

-H+ are pumped out of the cell in exchange for K+

-K+ leaks outside the cell but is transported back in via H-K ATPase pump

-Na+ is reabsorbed into the cell due to Na-K basolateral pump


What are the two pathways that parasympathetic stimulation increases H+ secretion?

-CN X innervates parietal cells
-stimulates H+ secretion directly
-utilizes ACh and muscarinic receptor

-CN X innervates G cells
-stimulates gastrin secretion
-gastrin stimulates secretion of H+
-neurotransmitter is GRP (gastrin releasing peptide)


How is gastrin secreted?

-secreted by gastrin G) cells in pyloric glands

-two forms: G-34 and G-17 (more abundant)

-released in response to presence of protein in pylorus

-causes enterochromaffin-like cells to release histamine -> stimulates H+ secretion

-second messenger on parietal cells is IP3/Ca+2


How is histamine stimulated?

-stimulates secretion of H+ by activating H2 receptors on parietal cell membrane

-H2 receptor is coupled to adenyl cyclase via Gs protein

-second messenger is cAMP


What are the two pathways that somatostatin inhibits gastric H2 secretions?

-somatostatin binds to receptors on the parietal cell that are coupled to adenyl cyclase via a GI protein
-antagonistic to stimulatory action of histamine

-inhibits the release of histamine and gastrin


What do prostaglandins do?

-inhibits gastric H2 secretions by activating G1 protein, inhibiting adenyl cyclase


What are the three phases of gastric secretions?

-cephalic phase (via vagus, parasympathetic so excite pepsin and acid production)

-gastric phase (1. Local nervous secretory reflexes 2. Vagal reflexes 3> gastrin-histamine stimulation)

-intestinal phase (1. Nervous mechanisms 2. Hormonal mechanisms)


What are the digestive enzymes for proteins?

-trypsin, chymotrypsin, and carboxypolypeptidase

-trypsin inhibitor
+secreted by the glandular cells
+necessary to prevent the action of trypsin on the pancreatic tissues themselves


What is the digestive enzyme for carbs?

-pancreatic amylase


What are the digestive enzymes for fat?

-pancreatic lipase, cholesterol esterase, phospholipase


What are some characteristics of pancreatic secretions?

-high volume


-same Na and K ion concs as plasma

-higher bicarbonate conc than plasma

-Lowe Cl- conc than plasma

-low flow rates: isotonic fluid composed mostly of Na and Cl

-high flow rates: isotonic fluid composed mostly of Na and bicarbonate


How do the acinar cells help form pancreatic secretions?

-produce small volume of pancreatic secretion composed mainly of Na and Cl