GF - Nutrients & Drug absorption Flashcards
carbohydrates
Diet contains disaccharides and complex polymers (starch and sucrose)
All carbs are broken down into monosaccharides & absorbed in the small intestine
What breaks down glucose polymers to disaccharides?
amylase
What breaks down disaccharides to monosaccharides?
maltase, surcrase, lactose
examples of glucose polymers
starch, glycogen
disaccharides examples
Glucose + Glucose: Maltose
Glucose + Fructose: Sucrose
Glucose + Galactose: Lactose
monosaccharides examples
Glucose, Fructose, Galactose
name transporters that transport fructose, glucose and galactose through the intestinal fluid to the capillary:
SGLT2
GLUT5
GLUT2
Decreased lactase activity is associated with a condition known as ______ __________
lactose intolerance
what stops disaccharides from converting into monosaccharides?
Lactase
What are proteins broken down into and where are they absorbed?
di/tri peptide & absorbed in small intestine
Proteins > smaller peptides (what enzyme?)
endopeptidase
smaller proteins > di/tri peptides. amino acids (what enzyme?)
exopeptidase
transporters of protein that transports them into the intentinal fluid (aminoacids) and capillary (di/tri peptides)
a.a - sodium co-transporter
di/tri - H+- PepT
Most lipids are __________ and must be emulsified to facilitate digestion in the aqueous environment of the intestine
hydrophobic
how are micelles formed?
bile salts coat lipids to make emulsions
describe micelles
small disks with bile salts,
phospholipids, fatty acids, cholesterol,
and mono- and diglycerides
nutrient digestion step by step
- micelles formed
- lipase and colipase digest triclycerides
Nucleic acid polymers (DNA & RNA) digest into ????? by pancreatic and intestinal enzymes and are absorbed via active transporters.
amino bases and monosaccharides
The fat-soluble vitamins
A, D, E, and K; are absorbed in the small intestine along with fats.
The water-soluble vitamins
C and most B vitamins; are absorbed by mediated transport.
B12 (seafood, milk, meat)
intestinal transporter for B12 is found only in the ileum and recognizes B12 only when the vitamin is complexed with a protein called intrinsic factor, secreted by the same gastric parietal cells that secrete acid)
Electrolytes
Sodium, potassium, chloride and water are absorbed through various pathways
paracellular diffusion
Drug absorption: 1. passive diffusion
FACTORS::
a) Rate of diffusion
-surface area
-thickness of the membrane
-molecular size & lipid solubility of the drug (diffusion constant)
what is rate of diffusion moving from GI tract to blood
b) Concentration of drug [D]/amount transfer
Transfer rate
Residence time at membrane
drug absorption: 2. active diffusion
REQUIRE carrier
Low lipid soluble (hydrophilic) drugs use transporters
Organic anion transporters (OATs)
Organic cation transporters (OCTs)
What will cross lipid bilayers by PASSIVE DIFFUSION?
un-ionised drugs (weak acids or weak bases)
Factors affecting ionisation
pH (i.e. concentration of H+ ions)
pKa of drug
(pH at which 50% of molecules are in each state)
what is the pH i
mouth
stomach
SI
7.4
1.5
5.3
factors influencing drug absorption
G.I. motility
G.I. secretions & enzymes
Drug-food/supplement interactions
Differences in luminal pH along the GI tract
Surface area per luminal volume
Blood perfusion
Presence of bile and mucus
The nature of epithelial membranes
Advantages of G. I absorption (physiological)
Large surface area for passive diffusion
Range of pH environments promotes the uptake of weak acids/bases
Richly vascularised (high blood supply)
Long tract and long dwell time
Some active transport (e.g. Levodopa taken up by phenylalanine transporter)
Small intestine is a major site for drug absorption
Kinetics of absorption (oral, intravenous, oral compromised)
How well us drug absorbed in body?
Bioavailability (F): measure of proportion of dose absorbed, compared to I. V. (same) dose
F= AUC of oral/AUC of I.V (for oral drug)
Time to peak (tmax): time required to reach maximum drug concentration in plasma (is a measure of rate of absorption)
tmax (oral)
