export_gi 3 Flashcards
where does digestion occur?
upper part of SI
intraluminal phase
secrete enzymes
epithelial phase
- brush border hydrolases
- enterocytes
nutrients absorbed in proximal SI
calcium, fat, AAs, sugar
nutrients absorbed in middle SI
sugars, AAs
nutrients absorbed in distal SI
bile salts, vit B12
3 types of carbs
mono-, di-, polysaccharides
what types of carbs are absorbed?
- mono
- di/poly need to be digested
enzymes that break down carbs
salivary amylase (mouth), HCl (stomach), pancreatic amylase (SI)
brush border enzymes for carbs
maltase, isomaltase, sucrase, lactase
lactose intolerance
- no lactase
- inc luminal osmolarity–>
- net water gain in lumen–>
- luminal distension–> peristalsis
- diarrhea
how is glucose absorbed into epithelial cells?
- secondary active: Na-glucose cotransporter (SGLT) - apical
- facilitated: glucose transporter (GLUT) - basolateral
transport from interstitial fluid to blood
capillary pores
protein digestion products
AAs, dipeptides, tripeptides
what enzymes digest protein?
- pepsin, HCl (stomach)
- trypsin, chymotrypsin, carboxypeptidase (pancreatic)
-enterokinase, aminopeptidase (brush border)
what activates pepsinogen
HCl –> pepsin
what cells secrete pepsinogen?
chief cells
what cells sectere HCl?
parietal cells
cascade of enzyme activation of enterokinase…
trypsinogen –> trypsin –> activates other zymogens
endopeptidase vs exopeptidase
endo- cleaves anywhere in protein
exo- only cleaves terminal amino acid
how do AAs cross apical membrane?
- secondary active, coupled to Na+
- multiple types for diff AAs
how do AAs cross basolater membrane?
facilitated diffusion
how are small peptides transported?
secondary active coupled to H+ into cytosol
-broken down to AAs inside
where is all protein digestion done?
upper SI
how are full proteins absorbed?
transcytosis- e ndo then exocytosis
what enzyme digests lipids?
lipases
emulsification
break down of fat into droplets
-mechanical disturuption
-bile salts and phospholipids
what are triglycerides broken into?
monoglyceride + 2 FAs
bile salt fxns
emulsify fat
where and what are bile salts made (from)?
liver, cholesterol
colipase
- amphipathic
- binds water-soluble lipase to fat droplets
what happens once triglys are broken down?
- some absorbed
- micelles
micelles
contain small amounts of fat-soluble vitamins and cholesterol
how are monoglys and FAs absorbed?
simple diffusion
chylomicrons
- tryglys, phospholipids, cholesterol, fat-sol vitamins
- secreted by exocytosis into interstitial fluid
-enter lymph system and empty in veins in thoracic duct
what happens to FAs and monoglys in epithelial cells?
enter smooth ER and form triglys –> packaged to chylomicrons in golgi
olestra and orlistat
can’t be digested by lipases, lipase inhibitor
fat-soluble vitamins
- A,D,E,K
- absorbed with lipids
-dissolved in droplets, micelles, chylomicrons
water-soluble vits
require diffusion or special transport proteins
-exception: vit B12
vit B12
- absorbed when bound to intrinsic factor
- complex binds to receptors on lumin surface or ilium
what secretes intrinsic factor?
parietal cells in stomach
why do we need vit B12?
-RBC production
causes of low B12?
diet, loss of parietal cells, ileum injury
where is most water absorbed?
80% SI
what drives fluid absorption?
osmotic gradient?
where/how is sodium transported?
active in jejumum, ileum, and colon
-generates osmolarity gradient
how are Cl- and HCO3- absorbed?
passively following Na+
how is iron controlled?
- cellular storage and carrier proteins
- control absorption not excretion
active transport into intestine epithelial cells
intracellular storage molecule for iron
ferritin (get into cell via DMT1)
what happens to free iron?
in bloodstream in transferrin complex (transport protein linked to ferritin in cells)
what happens to iron-ferritin in epithelial cells?
released back to lumen, excreted
during normal iron stores…
- inc ferritin synth
- dec absorption
during low iron stored
- dec ferritin synth
- inc absorption
hemochromatosis
too much iron absorption –> toxic effects
causes of pancreatitis
- alcohol, drugs, gallstones, genetic mutations
- blocked duct
- acinar cell injury
- defective intracellular transport
symptoms of pancreatitis?
abdominal pain, nausea, vomiting
effects of chronic pancreatitis
- acinar cell loss
- pancreatic fibrosis
causes of liver disease
drugs, toxins, viral, alcohol, metabolic
hepatic failure
- 80-90% liver function lost
- hepatic destruction
symptoms of liver failure
- jaundice
- hypoalbuminemia (dec synth of liver cells)
-hyperammonemia (inability to clear toxin ammonia products)
acute liver failure
- hepatic necrosis
- induced by dugs/toxins
cirrhosis
- liver cell necrosis, inflammation
- hypatocyte dysfunction
-due to alcohol, hepatits
