BIOL-2110 Lecture Notes - Lecture 2: Lipid Bilayer, Passive Transport, Facilitated Diffusion
Disposition
•How do compounds get into the body?
•Where do they go after being absorbed?
•Are there only chemical changes?
•How are the compounds excreted?
Disposition= ADME
- Absorption
- Distribution
- Metabolism
- Excretion
-Interactions b/w these processes determines concentration at
target site
Major organs:
GI tract (mouth, stomach, intestine)
lung
skin
First barrier: cell membranes
Passing through membrane is dependent on:
o size
o lipid solubility
o similarity to essential nutrients
o polarity/charge
Membrane Transport:
•Passive transport: passive diffusion, facilitated diffusion,
filtration
•Active transport: membrane pumps, endocytosis
Passive transport: driven by concentration gradient
•Rate= KA(C2-C1) (Fick’s Law)
o small hydrophilic molecules (<600 MW) through
aqueous pores, also called filtration (water, urea,
ethanol)
•Lipophilic molecules through phospholipid bilayer
o importance of physicochemical characteristics:
-Kow and pKa
Diffusion of weak acids/bases:
Henderson- Hasselbalch equation:
pKa= -log10(Ka)= -log10 ([H3O+][A-]/ [HA])
Or pKa for a weak acid or base is the…
Active Transport: transport against concentration gradient
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Document Summary
Excretion target site (cid:12167)(cid:1)gi tract (mouth, stomach, intestine) (cid:12167)(cid:1)lung (cid:12167)(cid:1)skin (cid:12167)(cid:1)first barrier: cell membranes. Passing through membrane is dependent on: size, lipid solubility, similarity to essential nutrients, polarity/charge. Membrane transport: passive transport: passive diffusion, facilitated diffusion, filtration, active transport: membrane pumps, endocytosis. Passive transport: driven by concentration gradient: rate= ka(c2-c1) (fick"s law, small hydrophilic molecules (<600 mw) through aqueous pores, also called filtration (water, urea, ethanol, lipophilic molecules through phospholipid bilayer, importance of physicochemical characteristics: (cid:8213)(cid:1)-kow and pka. Henderson- hasselbalch equation: pka= -log10(ka)= -log10 ([h3o+][a-]/ [ha]) Or pka for a weak acid or base is the . Active transport: transport against concentration gradient: requires energy, usually in form of atp, ex: sugars, proteins, through specialized membrane pumps, system can get saturated, compound specific (can have competitive inhibitors, energy dependent (sensitive to inhibition of energy supply) Toxicants- are absorbed through same processes as essential compounds: macronutrients (carbohydrates, lipids, amnioacids, micronutrients (vitamins, essential metals, oxygen.
