GI 2 Flashcards
where is digestion initiated
in the mouth
- chewing
- saliva
- swallow
when is bolus referred to as chyme
once enters the stomach
explain the anatomy breakdown of intestine
first 1/3: duodenum
middle 1/3: jejunum
final 1/3: ileum
trace pathway of food bolus from mouth to small intestine
mouth–>esophagus–>stomach–>SI
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)
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
what two cells are found in the lamina propria of GI tissue
stromal cells and fibroblasts
how is surface area increased in small intestine
finger like projections
microvilli “brush border”
what is present within each microvillus?
capillary bed
lacteal
what is a lacteal
lymphatic duct responsible for absorbing fats
5 basic categories of useable food
carbs proteins fat vitamins minerals
when we eat carbs what form do we usually get from our diet
polysaccharides
disaccharides
DO NOT get monosaccharides
what form does carb have to be in to be absorbed into the blood
monosaccharide
polysaccharides
starch
glycogen
cellulose
disaccharides
sucrose
lactose
maltose
monosaccharides
glucose
fructose
galactose
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
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
what effect do sweetners have in the absorption in the SI
increase expression of GLUT2 transporter
proteins are broken down into
amino acids
where are 2 locations proteins are broken down
stomach
small intestine
what proenzyme is produced in the stomach
pepsinogen
pepsinogen
proenzyme
converted to pepsin by HCl in stomach
what does HCl do to make proteins more susceptible to enzymes in the stomach
unravels the proteins
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
- Na/K pump maintains Na gradient
- Na goes into cell and H+ goes out
- creates gradient for H+
- H+ want to diffuse into cell and bring peptides in with it
- peptidases in cytoplasm can further breakdown peptides to AAs if need be
- 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
SI
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
