GI 6-7

imissyou419's version from 2017-04-06 22:05

Section 1

Question Answer
Cephalic phase Triggerthought of food, sight, smell or taste of food
Cephalic phase Initiation of Response and Responsesmedulla oblongata regions activated (i.e. nucleus tract solitarii) by cerebral cortex and/or feeding centre in hypothalamus,
facial & glossopharyngeal nerves stimulated (stimulate salivary glands),
vagus nerve activated (affect stomach);

salivary glands secrete more saliva, stomach secretions and motility increased
Gastric phase Triggerpresence of food in stomach
Gastric phase Initiation of Response and Responsesstretch receptor - distention
chemoreceptors - pH increase (peptides buffer acid in stomach)
G cells release gastrin

Increased gastric juice secretions including HCl from parietal cells
Increased gastric motility
Enhanced gastric emptying - relaxation of pyloric sphincter (gastrin)
Intestinal phase TriggerPresence of chyme in duodenum
Intestinal phase Initiation of Response and ResponsesStretch receptors - distension
Chemoreceptors - partially digested nutrients (CCK released - proteins > fat) and acids (secretin released)

Stretch causes enterogastric reflex - PNS inhibited and SNS activated to stomach -> Inhibition of gastric secretions and motility (SNS)
Pancreatic acinar cell secretions increased, gallbladder contraction (CCK)
Closure of pyloric sphincter (CCK) - inhibit gastric emptying, opening of sphincter of Oddi
Pancreatic ductal cell secretions increased (secretin) -> more bicarbonate
Stimulate hepatocytes to make more bile salts (bicarb and water to increase volume of bile)
What increases gastric emptying and how?Distention of stomach (stretch receptors, activate PNS, release gastrin to help with motility), partially digested proteins (cause gastrin release, increase in pH triggers chemoreceptors -> gastrin release), alcohol (stimulate G cells to release gastrin -> cause pyloric sphincter to open faster than usual without fatty meal)

Stimulate gastrin or PSYN -> Increase pylorus opening
What decreases gastric emptying and how?Digested proteins and fat causing distention of duodenum causes secretion of CCK which decreases pylorus opening (since enterogastric reflex initiated - information going to medulla oblongata, turn off PNS and turn on SNS)

Section 2

Question Answer
Carbohydrate digestionStarts in the mouth with salivary amylase (it is inactivated in stomach)
Pancreatic amylase from acinar cells digest carbs in small intestine
Brush border enzymes in small intestine (alpha dextrinase, lactase, maltase, sucrase) digest it to monosaccharides to be absorbed
Amylasedigest complex carbs (starch, glycogen) to disaccharides
Maltasedigest maltose to 2 glucose
Sucrasedigest sucrose to 1 glucose + 1 fructose (fructose sound sweet and sucrose is sweet)
Lactasedigest lactose into 1 glucose + 1 galactose
Alpha-dextrinasedigest amylopectin to alpha-limit dextrins
How is glucose or galactose absorbed?through Na+/glucose or galactose symporter on luminal side using Na+ concentration gradient (have basolateral Na+/K+ ATPase maintaining gradient)
GLUT2 uniporter on basolateral membrane transport glucose, galactose, or fructose to liver
How is fructose absorbed ?GLUT5 (fructose uniporter) on luminal side, use GLUT5 on basolateral membrane to move fructose to liver
Protein digestionstarts with pepsinogen -> pepsin in presence of HCl (chief cells) in stomach
pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase, elastase) from pancreatic acinar cells, activated through enterokinase
Brush border enzymes (aminopeptidases, dipeptidases)
Exopeptidasesdigest terminal peptide bonds to release a.a.
e.g. aminopeptidases (small intestine) and carboxypeptidases (pancreas)
EndopeptidasesDigest internal peptide bonds
Protein absorptionNa+/a.a. symporter on luminal side, Na+/a.a. antiporter on basolateral move a.a. into blood and Na+ into cell, concentration gradient maintained by basolateral Na+/K+ ATPase
H+/Di- and tri-peptides symporter on luminal side, H+/a.a. antiporter on basolateral side moving H+ into cell
H+ concentration maintained low inside cell by Na+/H+ antiporter
Peptidases inside enterocytes can convert di and tri peptides into monopeptides

As a baby, small peptides carried by transcytosis (able to absorb antibodies from breast milk)
Lipid digestionstart in stomach with lingual lipase working (it is made in salivary glands),
Gastric lipase in stomach
Mechanical digestion helps lingual and gastric lipase work better
Liver/gallbladder release bile, emulsify fat by detergent action of bile in small intestine
Pancreatic lipase (works best b/c get help from bile salts and colipase)
Mechanism of Bile functionBile acids are detergent (not enzyme), helps increase SA of fat droplets, action site is within small intestine
part hydrophobic (associated with lipid), part hydrophilic (associate with aqueous environment)
Bile salts originate from cholesterol, modified
Micellesbile salt coated lipid droplet
Mixed micelles can have phospholipids be component
Most partially digested lipids, cholesterol on inside of micelles
Colipasesecretion from pancreas, cofactor that helps with even better function of pancreatic lipase by moving bile acids to allow pancreatic lipase to come into contact to surface of triglycerides (it does not digest the fat though)
Fat absorptionmicelles move closer to mucosa membrane of small intestine, monoglycerides and fatty acids cross luminal membrane with help of protein transporters (flippase and floppases), absorbed fats directed to smooth ER by fatty acid binding proteins, resynthesized into triglycerides, cholesterol leaves micelle and protein transporter moves it into cell, directed to smooth ER, production of apolipoproteins in rough ER coat absorbed lipids - chylomicrons, go to lacteals (lipoprotein lipases remove some fat) eventually draining into vena cava, chylomicron remnant taken by liver
Fat soluble vitaminsADEK, absorbed as fatty acids and monoglycerides (CCK will be triggered, bile released, micelles formed, solubilize fat soluble vitamins)
Water soluble vitaminsBC, absorbed via transporters (can be saturated)

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