4.0 Digestive

Question 1

how are contents of stomach released to duodenum, what happens upon the release

Answer 1

• 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

Question 2

what triggers the release of CCK

Answer 2

pressence of lipids and carbs

Question 3

what triggers release of GIP

Answer 3

presence of lipids and carbs

Question 4

what triggers the release of secretin

Answer 4

dec pH

Question 5

what is the status of digestion of the chyme when it enters the SI

Answer 5

• 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

Question 6

digestion of alcohol

Answer 6

20% in stomach

80% in SI

Question 7

what is the most common type of motion in the SI?

what initiates it?

Answer 7

• segmentation = most common
• initated by intrinsic paceaker cells (Cajal cells)

*moves contents steadily twds ileocecal valve

Question 8

pacemaker activity in diff regsions of small intestine

Answer 8

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

Question 9

how is the intensity of segmentation controled

Answer 9

• 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

Question 10

when does peristalsis occur?

what happens during it?

Answer 10

• 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

Question 11

release of ____ regulates peristalsis

Answer 11

released ACh by ACHe releasing (cholinergic) sensory neuron in SI sends messages to diff interneutons in myenteric plexus

• regualtes peristalsis

Question 12

what are the two places ACh can be sent for peristalsis, what is the effect?

Answer 12

• 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

Question 13

release of ____ stimulates pancreatic secretion

Answer 13

• 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

Question 14

What controls the flow of digestive juices? what relaxes it?

Answer 14

Sphincter of Oddi (hepatopancreatic sphincter) controls flow of digestive juices (bile and pancreatic)

Cholecystokinin(CCK) relaxes it

Question 15

describe the composition of pancreatic juice

Answer 15

• 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

Question 16

Question 17

what physical featues in the small intestine help with the absorption of nutrients

Answer 17

• large circular folds
• filli and microvilli
• blood capillaries

*ahve a lacteal running thru middle of villi

Question 18

how are carbohydrates abrobed

Answer 18

*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

Question 19

how are sucrose, maltosea nd alctose broekn down

Answer 19

Sucrose —sucrase—> Glucose + fructose

Maltose — maltase—> glucose + glucose

Lactose —lactase—> glucose + galactose

Question 20

how are protiens digested

Answer 20

• Pepsin in stomch -> cleaves proteins -> polypeptides
• in SI: Pancreatic enzymes: trypsin, chymotrypsin and carboxypeptidase

brush border enzymes: aminopeptidaes, carboxypeptidass, dipeptidases

Question 21

how do proteins get absorbed

Answer 21

• AA by cotransport with Na+
• Dipeptides and tripeptides via secondary active transport with H+ gradient (then broekn down itno single aa)

Question 22

How are fats digested?

Answer 22

• 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

Question 23

how are fats absorbed

Answer 23

• 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

Question 24

describe the digestion of nucleic acids

Answer 24

• 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

Question 25

what electrolytes are absorbed/how?

Answer 25

- Na+ is coupled with absorption of glucose and AAs - Iron is transported into cells where it binds to ferritin - Anions passively follow the electrical potential established by Na+ - K+ diffuses across the intestinal mucosa in response to osmotic gradients - Ca2+ absorption is regulated by vitamin D and parathyroid hormone (PTH)

Question 26

what methods can ions be transported by?

Answer 26

- diffusion, co transport, active, or carrier mediated

Question 27

how is water absorbed

Answer 27

95% is absorbed in SI by osmosis - water moves bidirectionally across intestinal mucosa - Net osmosis occurs whenever a concentration gradient is established by active transport of solutes into mucosal cells

Question 28

what are the 3 unique features of the LI

Answer 28

- Teniae coli - three bands of longitudinal smooth muscle in its muscularis - Haustra - pocketlike sacs caused by the tone of the teniae coli - Epiploic appendages - fat-filled pouches of visceral peritoneum \* saclike cecum lies below the ileocecal valve and contains a wormlike vermiform appendix

Question 29

what types of cells are found in the large intestine? what strucutral features is it missing that other organs in the digestive system have?

Answer 29

- colon mucose = simple columnar epithelium except in anal canal - anal canal = stratefied squamous epithelium -\> merges w/ true skin surrounding the anus - Does NOT have circular folds, villa, or cells that secrete digestive enzymes

Question 30

what produces mucus in the LI

Answer 30

- goblet cells - eases the passage of feces and protects intestinal wall from irritating acids and gases

Question 31

describe the motility of the large intestine where does it priamrily occur

Answer 31

- movements = haustral contractions (slow segmentating movements lasting 1min, occur ever 30 sec - occurs ainly in transverse and descending colon -\> reflect local controls of smooth muscle within the walls of the individual haustra - as haustrum fills with food residue, the distension stimulates its muscle to contract, which propels the luminal contents into the next haustrum - LI has mass movements contractile waves -\> move over alrge areas of colon 3-4x/day, forces contents to rectum

Question 32

what reflexes are activates when food enters teh stomach

Answer 32

- Gastroileal reflex: in the SI - Gastrocolic reflex: in colon

Question 33

what does bulk (fiber) do to the stool

Answer 33

- softens the stool and can inc strength of colon contractions

Question 34

what is the function of large intestine

Answer 34

- Other than digestion of enteric bacteria, no further digestion takes place - reclaims vitamins, water and electorlytes \*major fucntion is propulsion of fecel material towards anus (storage) \*not essential for life (but convient bc want to be able t control your defication)

Question 35

describe the bacteria in the colon

Answer 35

- remaining bacteria from the SI colonize the colon - \> Metabolize some host-derived proteins (mucin, heparin, and hyaluronic acid) - \> Ferment some of the indigetibel carboydrates (cellulose, xylan and others) - release irritating acids and mix of gases (dimethyl sulfide, H2, N2, CH4, and CO2) - 500mL of gas (flatus)/day, more if consume carb heavy foods (beans) - synthesize B complex vitamind and most of vit K in liver requires to synthesize some of the clotting proteins

Question 36

describe the anus

Answer 36

- has a pectinate line to sep superior and inferior - \> Superior: mucoase innervated by visceral sensory fibers, INSENSITIve to pain - \> Inferior: very sensitive to pain bc of somatic sensroy fibers' - has 2 superficial venous plexuses: 1 in part of anal columns and 2 the anus \*If these (hemorrhoidal) veins are inflamed, itchy varicosities called hemorrhoids can form

Question 37

painful vs not painful hemorrhoids

Answer 37

- external are painful, if on internal vein will hang out ed of anus

Question 38

describe defication

Answer 38

- dsitension of rectal walls caused by feces - \> stimulates contraction of rectal walls - \> relaxes internal anal sphincter - Voluntary signals stimulate relaxation of the external anal sphincter and defecation occurs