Digestion 4: Digestion & Absorption Flashcards
what are the nutrients we get from diet?
- carbs
- fat
- protein
- water, electrolytes, vitamins
what are the nutrients absorbed by the small intestines?
- monosaccharides
- fatty acids
- monoglycerides
- cholesterol
- AA
- water, vitamins, electrolytes
what type of transport is endocytosis or exocytosis?
transcytosis
function of sucrase
sucrose → glucose + fructose
function of maltase
maltose → glucose + glucose
function of lactase
lactose → glucose + galactose
function of amylase
starch, glycogen → disaccharides
2 ways in which shorter peptide chains can be formed
- endopeptidase → shorter peptide chains
2. exopeptidase (aminopeptidase & carboxypeptidase) → digest peptide chains from either end to release AA
what is needed when peptide chains are broken?
H2O (hydrolysis)
does body make more aminopeptidase or carboxypeptidase
carboxypeptidase
function of lipase
triglyceride → monoglyceride + FFA
what are the fats that we eat? What is the main one?
- triglycerides (90%)
- phospholipids
- cholesterol
how does monosaccharides get through epithelial cells in small intestines?
enter: facilitated diffusion & co-transport
exit: facilitated diffusion
how does fat get through epithelial cells in small intestines?
enter: diffusion
exit: exocytosis as chylomicrons
how does AA and short peptides get through epithelial cells in small intestines?
enter: facilitated diffusion & co-transport
exit: facilitated diffusion & co-transport
brush-border enzyme for AA?
dipeptidases
which macronutrient is not digested in the stomach?
lipids
carbs get some digestion from leftover salivary amylase
digestion of carbs at the small intestines
- pancreatic a-amylase
2. lactase, maltase, sucrase
digestion of proteins at the small intestines
- trypsin, chymotrypsin, elastase, carboxypeptidase
2. dipeptidase
digestion of fat at the small intestines
bile acids;
pancreatic lipase
function of salivary amylase
starch → MALTOSE + maltotriose + dextrin
__% of starch digestion occurs in mouth, __% occur in stomach
5;
35
about ___ min after swallowing, salivary amylase becomes inactivated by low stomach pH
30-40
function of pancreatic amylase
starch → MALTOSE + maltotriose + dextrin
even though pancreatic amylase == salivary amylase, it is more potent because…
- food is smaller at small intestines, so there is more SA for it to act on
- food stays in intestines longer
___ is important for pancreatic amylase activity because…
bicarb;
need to neutralize acidic chyme so pancreatic amylase is at the optimal pH
how to explain the symptoms of lactose intolerance?
diarrhea: lactose in large intestines draw water into lumen
gas: bacteria in large intestines use lactose as food → gas is byproduct of fermentation
cramps: build up of CO2 → distention → peristalsis
what is used to absorb monosaccharides?
GLUT-5 & SGLT (sodium glucose linked transporter)
brush-border enzymes used to digest saccharides
- maltase-glucoamylase
- dextrinase
- sucrase
- lactase
where are brushborder enzymes located?
embedded in walls of small intestines
which transporters are used to absorb glucose, galactose, and fructuse?
SGLT: glucose & galactose (exit by facillitated diffusion or GLUT2)
GLUT5: fructose (exits the cell using GLUT2)
there is competition for absorption of the different monosaccharides. What is the order?
absorbed first → last:
galactose > glucose > fructose
function of pepsin
protein → peptides + AA
- endopeptidase
- cleaves at aromatic AA (FYW)
pancreas secretes ____ for protein digestion
zymogens
- chymotrypsinogen
- procarboxypeptidase
- procolipase
- prophospholipase
function of enterokinase
activate trypsinogen → trypsin
how are zymogens activated?
- enterokinases activate trypsinogen → trypsin
2. trypsin activates rest of zymogens
activated pancreatic enzymes for protein digestion
- chymotrypsin
- carboxypeptidase
- colipase
- phospholipase
Pancreatitis
if trypsinogen is activated too early → digestion of the pancreas
how does the pancreas protect itself from being digested by protein-digesting enzymes?
- separate trypsinogen from lysozymes in cytoplasm
- trypsin can digest itself
- pancreas can make trypsin inhibitor (secreted if trypsin present in pancreas)
___ and ___ are endopeptidases, while ___ removes AA from C-term
trypsin & chymotrypsin;
carboxypeptidase
brushborder enzymes for proteins
- aminopeptidase (cleave from N-term)
- dipeptidase (dipeptide → AA)
where are aminopeptidase & dipeptidase located?
embedded in brushborder
which forms of protein can be absorbed?
- di- & tripeptides
- AA
- small peptides
absorption of di- & tripeptides
transporter: PepT1
- cotransport with H+ on both apical side
- exchange with H+ on basolateral side
- can be cleaved inside cell by peptidases → AA
- functionally linked to NHE to keep [H] inside the cell low
absorption of AA
- cotransport with Na+ on apical side
- exchange with Na+ on basolateral side
- Na/K-ATPase used to keep concentration of Na low inside cell
absorption of small peptides
transcytosis
gastric lipase is secreted by…
chief cells
digestion of fat in stomach
- gastric lipase
- agitation forms smaller fat droplets
what is 1 instance in which gastric lipase > pancreatic lipase?
ZE syndrome:
very acidic chyme means gastric lipase is in optimal environment, but pancreatic isn’t
why is 1 symptom of ZE syndrome malnutrition?
super acidic chyme makes all pancreatic enzymes (majority of digestion for all nutrients) less effective
what emulsify fats?
- bile salt (from liver)
- phospholipid lecithin (from liver)
purpose of emulsion?
increase SA for further digestion by pancreatic lipase
colipase
- pancreatic lipase can’t attach on emulsified fat due to bile salts
- colipase attaches bile salt on 1 end and lipase on other end → allows digestion to happen
micelles
- very small emulsified fat particles
- hydrophilic shell
- hydrophobic core (FFA, cholesterol, etc.)
- small enough to be soluble
absorption of fat
- FFA & monoglycerides diffuse into cell
- go to smooth ER → re-esterify back to triglycerides
- cholesterol enters cell via NPC1L1 (energy dependent transporter) → sER
- everything comes together at sER → packaged at Golgi → chylomicron
- leaves cell via exocytosis → lymphatic system → thoracic duct → subclavian vein
ezetimibe
drug that lowers cholesterol levels by preventing absorption
- block NPC1L1 transporter
function of lipoprotein lipase (LPL)
TG in chylomicrons → FFA + glycerol
chylomicrons is made up of…
- TG (most)
- Cholesterol
- PL
- apoproteins
LPL can be found most abundantly in…
- capillaries associated with muscles
- adipose tissues
- capillaries associated w/ lactating boobs
vit B12 sources
- made by bacteria
- seafood
- meat
- milk
Pernicious anemia causes
- lack of intrinsic factors being secreted by parietal cells
- not enough dietary B12
- too much bac’t in gut (eat up B12 before reaching ileum)
B12 is required for…
maturation of RBC
Pernicious anemia
condition where patients don’t have mature RBC because Vitamin B12 is required for the maturation of RBC
calcium can be absorbed 2 ways…
1) paracellular
2) hormone dependent absorption
hormone-dependent Ca absorption
- Ca enters cell through Ca-channel
- Ca bind to calbindin in cell (free Ca is very bad for cell
- when needed, Ca is released from calbindin and exits through Ca-ATPase
calbindin is increased by…
vit D (calcitriol)
how does 1,25(OH)2 vitD3 enhance Ca absorption?
1) increase Ca channels on apical membrane
2) increase amount of calbindin
iron is absorbed in which forms?
1) heme (easily absorbed)
2) ferrous (Fe++)
absorption of heme iron
transporter: HCP1 (heme carrier protein)
after getting into cell, dissociates → porphyrin + ferrous form
absorption of ferrous iron
transporter: DMT-1 (divalent metal transporter)
- Fe and H cotransporter
- ferrous form + apoferritin → ferritin
- ferritin can be used to store lots of iron inside cell until needed
what happens when we want to use iron bound in ferritin?
- ferrous iron transported outside by ferroportin
- ferroportin levels regulated by hepcidin
ferroportin regulation
- hepcidin causes internalization of ferroportin
- YES hepcidin = no ferroportin = no Fe leaving cells
- NO hepcidin = yes ferroportin = yes Fe leaving cells
hepcidin
hormone released by liver to regulate levels of ferroportin
Na+ absorption
apical membrane transporters for Na+:
- Na channel
- Na/Cl-cotransporter
- Na/H-exchanger
- Na/organic solute cotransporter
basolateral membrane transporters for Na+:
Na/K-ATPase
Cl- absorption
apical membrane transporters for Cl-:
- Na/Cl-cotransporter
- bicarb/Cl-exchanger
basolateral membrane transporter for Cl-:
- Cl channel
how does water get absorbed?
- paracellular pathway, following solute
- active transport with SGLT transporter
how does K+ get absorbed?
paracellular pathway, along with water
SGLT is only present on __ membrane
apical
how is water transported with SGLT?
- Na binds, then glucose/galactose
- follows glucose/galactose when it binds
- about 250 molecules moved every time
