4.0 Digestive Flashcards
how are contents of stomach released to duodenum, what happens upon the release
- when stomach ready to release pyloric sphincter opens, stomach contracts to release contrents
- only small amount of chyme goes into SI
- duodenum detects contects have entered it -> secrets secretin (bc of dec pH), GIP and CCK (bc senses lipids and carbs)
- those hormones enter circulation and inhibit peristalsis, inhibit chief cells from releasing pepsinogen, and parietal cells from releasing acid and intrinsic factpr
what triggers the release of CCK
pressence of lipids and carbs
what triggers release of GIP
presence of lipids and carbs
what triggers the release of secretin
dec pH
what is the status of digestion of the chyme when it enters the SI
- Chyme is slowly released into duodenum ( v acidic could damage if too much at a time)
- no fat digestion!
- carbs and proteins are only partially digestioned
- chyme is hypertonic and has low pH -> requres constant mixing for proper digestions
- virtually all ntrient abs takes place in SI
digestion of alcohol
20% in stomach
80% in SI
what is the most common type of motion in the SI?
what initiates it?
- segmentation = most common
- initated by intrinsic paceaker cells (Cajal cells)
*moves contents steadily twds ileocecal valve
pacemaker activity in diff regsions of small intestine
cajal cell pacemaker activity differs in different regions of the GI tract:
-3 per minute in the stomach
12-14 per minute in the duodenum lots
8-9 per minute in the ileum
3 per minute in the colon
how is the intensity of segmentation controled
- by short and long reflexs
Long reflex: PSN activity enhances, SNS activity decreases
- more intense the contractions = greater mixing
* basic contractile rhythems of varioues intestinal regions remain unchances
when does peristalsis occur?
what happens during it?
- peristalsis occurs after most nutrients have been absorbed
- segmentations movements wane and duodenal mucosa begins to release motilin
- peristaltic waves initiate at the duodenum and sweep slwoly along the intestine, mving 5-70cm before dying out
- each wave is initiated a bit more distally (migrating motility complex MMC)
- process sweeps the alst remnants of meal, bacteria and other debris into LI
release of ____ regulates peristalsis
released ACh by ACHe releasing (cholinergic) sensory neuron in SI sends messages to diff interneutons in myenteric plexus
- regualtes peristalsis
what are the two places ACh can be sent for peristalsis, what is the effect?
- impulses sent proximally: causes contraction and shortening of circular muscle layer
- impulses sent distally cause shortening of logitudional layer and distension of intestine
* overall: proximal area constricts and foces chyme along tract - lumen of distal part of intestine enlage to receive it
release of ____ stimulates pancreatic secretion
- secretin and cholecystokinin (CCK)
- > Acidic chyme enterine duodenium signals releast of Sectretin
*causes secretion of bicarbonate rich pancreatic juice
-> fatty protein in chyme entering duodenum incudces CCK releas
*causes secretion of enzyme rich pancreatic juices
What controls the flow of digestive juices? what relaxes it?
Sphincter of Oddi (hepatopancreatic sphincter) controls flow of digestive juices (bile and pancreatic)
Cholecystokinin(CCK) relaxes it
describe the composition of pancreatic juice
- has enzymes and electrolytes (primarily HCO3-_ that neutralize acid chyme
- from exnymes are released as inactive zymogen and hten activatied
Zymogens in pancreatic juice: trypsin, chrmotrypsin, elastase, carboxypeptidase, phospholipase
Active enzymes: lapase, amylase, cholesterolesterase, ribonucleaes, deoxtribonuclease
what physical featues in the small intestine help with the absorption of nutrients
- large circular folds
- filli and microvilli
- blood capillaries
*ahve a lacteal running thru middle of villi
how are carbohydrates abrobed
*primarily in SI
- begins in mouth with salivary amylase -> starts starch digestion
- pancreatic amylase -> digests startch to oligosaccharides
- Oligosaccharides hydrolyed by brush border enzymes (disaccharides -> monosaccharides)
*Beta 1,4 bonds in cellulose not hydrolyzed
how are sucrose, maltosea nd alctose broekn down
Sucrose —sucrase—> Glucose + fructose
Maltose — maltase—> glucose + glucose
Lactose —lactase—> glucose + galactose
how are protiens digested
- Pepsin in stomch -> cleaves proteins -> polypeptides
- in SI: Pancreatic enzymes: trypsin, chymotrypsin and carboxypeptidase
brush border enzymes: aminopeptidaes, carboxypeptidass, dipeptidases
how do proteins get absorbed
- AA by cotransport with Na+
- Dipeptides and tripeptides via secondary active transport with H+ gradient (then broekn down itno single aa)
How are fats digested?
- bile salts are produced and released by SI, stored in gall bladder -> to duodenum
- hydrophobic side ass w/ lipid and hydrophillic w/ water -> forms a bile-acid coated lipid droplet
*enzymes can only attach the surface so need to icnrease the SA by breaking down fat globule into smaller parts
- once emulsified -> digestion by lipases -> longchain FA and monoglycerides
how are fats absorbed
- short chian fatty acids -> simple iffusion across SI into blood capillary
- > long chain fA and monoglycerides -> simple diffusion but processed i epithelium as chylomicrons -> then go to lacteal of a villus
describe the digestion of nucleic acids
- digested by Pancratic ribconucleases and doxyribonuclease in SI
- absorbed by active transport via membrane carriers
> absorbed in villi & transported to liver via hepatic portal vein
