GI 2 Flashcards by Randi Polster

where is digestion initiated

in the mouth

chewing
saliva
swallow

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when is bolus referred to as chyme

once enters the stomach

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explain the anatomy breakdown of intestine

first 1/3: duodenum
middle 1/3: jejunum
final 1/3: ileum

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trace pathway of food bolus from mouth to small intestine

mouth–>esophagus–>stomach–>SI

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how much fluid is absorbed compared to how much is excreted from the body and where is it mostly absorbed

massive amount of fluid is absorbed in the SI

much more than is excreted from the body (minimal amount is excreted in urine and feces)

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layers of GI tissues from lumen to just lining abdominal cavity

mucosa
- single layer of epithelial cells
- lamina propria
- muscularis mucosa
submucosa
- major blood vessels
- submucosal nerve plexus
muscularis externa
- circular muscle
- myenteric nerve plexus
- longitudinal muscle
serosa

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what two cells are found in the lamina propria of GI tissue

stromal cells and fibroblasts

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how is surface area increased in small intestine

finger like projections

microvilli “brush border”

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what is present within each microvillus?

capillary bed

lacteal

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what is a lacteal

lymphatic duct responsible for absorbing fats

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5 basic categories of useable food

carbs
proteins
fat
vitamins
minerals

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when we eat carbs what form do we usually get from our diet

polysaccharides
disaccharides
DO NOT get monosaccharides

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what form does carb have to be in to be absorbed into the blood

monosaccharide

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polysaccharides

starch
glycogen
cellulose

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disaccharides

sucrose
lactose
maltose

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monosaccharides

glucose
fructose
galactose

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where are ectoenzymes and what do they do

ectoenzymes are bound to the membrane of the brush border in the intestine

break down disaccharides to monosaccharides

ex: lactase

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how are monosaccharides absorbed through the intestinal tissue

Na/K pump creates Na gradient
- Na high outside cell, low inside cell, will want to move into cell
Na and glucose symporter pumps into cell (SGLT1)
Fructose will follow concentration gradient and diffuse into cell (GLUT5)
GLUT2 transporter will move glucose, fructose, galactose into blood

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what effect do sweetners have in the absorption in the SI

increase expression of GLUT2 transporter

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proteins are broken down into

amino acids

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where are 2 locations proteins are broken down

stomach

small intestine

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what proenzyme is produced in the stomach

pepsinogen

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pepsinogen

proenzyme

converted to pepsin by HCl in stomach

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what does HCl do to make proteins more susceptible to enzymes in the stomach

unravels the proteins

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what enzyme releases proenzymes into the small intestine for digesting proteins

pancrease

what are the proenzymes of the small intestine

trypsinogen chymotrypsin procarboxypeptidase A and B proelastase

why is trypsinogen so important

cleaved to trypsin by enteropeptidase trypsin essential for peptide breakdown because activates all the other proenzymes of the intestine

enteropeptidase

brush border enzyme cleaves trypsinogen to trypsin

oligosaccharides are broken down into disaccharides by

dipeptidylaminopeptidase

disaccharides to AA by

amino peptidase

two transporters for amino acids

Na dependent: brush border | Na independent: basolateral membrane

how does Na dependent transport work

1. Na/K pump maintains Na gradient 2. Na goes into cell and H+ goes out 3. creates gradient for H+ 4. H+ want to diffuse into cell and bring peptides in with it 5. peptidases in cytoplasm can further breakdown peptides to AAs if need be 6. diffuse into blood (passive)

what is the Na independent transporter

AA to the blood across basolateral membrane passive diffusion

protein degraded by

HCl and proteases

how are all proteases released

proenzymes

need enzymes for breakdown of peptides in two different parts of intestine to be sufficient

luminal peptidases | brush border enzymes

transporters can move proteins across apical membrane in what form(s)

peptides (di, tri) | AAs

fat breakdown is triggered by

lipase

three types of lipase

lingual gastric pancreatic

first place lipase is secreted

lingal lipase | von ebner's glands

which lipase is most important

pancreatic lipase

where does fat breakdown start

stomach

why does chyme stay in stomach for longer period of time

chemoreceptors sense FAs

why does the stomach mix chyme

so that SA increases that lipases can interact with

fat has two layers

fatty layer | aqueous layer

structure of bile salt

polar region and non polar region so interacts with both layers of emulsion droplet

how does lipase interact with the fat

colipase integrates into fat droplet | has polar and non polar region so now lipase can interact with triglyceride

how do micelles enhance absorption of FAs

micelles are in equilibrium with free FAs micelles are constantly breaking down and reforming

what form of fats are found in systemic circulation

triglycerides

how are fatty acids absorbed into the cell

monoglycerides

what happens when monoglycerides enter the endoplasmic reticulum of the cell

reform triglycerides

what form must triglyceride have to travel accross epithelial cell and be absorbed by lacteal

form chylomicron

fat soluble vitamins

A, D, E, K

how are fat soluble vitamins released into the body

with chylomicrons

the rest of vitamins besides A, D, E, K are water soluble vitamins except

vitamin B12

how does B12 get into the cell

binds to intrinsic factor (IF) and IF will bind to its receptor and taken into cell by receptor mediated endocytosis

where does most water absorption occur

where is Na absorbed in GI tract

throughout the entire GI tract

what ions do Na help to be absorbed

K, Cl, HCO3-

where is Na concentration the highest

where glucose, galactose, or AA are being transported

why do Ca not create salts in the stomach

low pH keeps Ca soluble

why is there a problem when Ca2+ enters the cell how do we fix the probelm

not acidic environment so Ca2+ will want to produce salts rapidly calbindin binds to Ca2+ and takes it to basolateral membrane where it can be release into the blood

what causes rickets

vitamin D deficiency cant absorb Ca2+

what does vitamin D do for Ca2+ absorption

increase Ca2+ transporters and binding proteins (calbindin)

what state is iron absorbed and what state is iron most present in the body

iron absorbed in ferrous state (Fe++) most iron in body is ferric iron (Fe+++)

how do you convert ferric iron to ferrous iron

iron reductase

what happens first to ferrous iron once it gets into the cell

converted back to ferric iron by feroxidase

what are the two pathways in the cell that iron can take

RELEASED: bind to carrier protein and moved to basolateral membrane to diffuse into blood STORE: bind to ferritin; inhibits release

GI 2 Flashcards

(68 cards)