LECTURE 7: PUMPS AND EPITHELIA Flashcards
Ionic Currents: 4
1 * Cells NOT at EQUILIBRIUM
2 * Cell are in a STEADY STATE WITH CONSTANT CURRENT
3 * CONSTANT FLOW REQUIRE ACTIVE TRANSPORT
4 * ACTIVE TRANSPORT MAINTINS ION GRADIENTS
Maintaining the Ion Gradients:
- V + 61mV,V + -88mV. eNa eK
- Vm -70 mV
- Neither ion at equilibrium
- Na+ flows in and K+ flows out.
What keeps internal K+ high and intracellular Na+ low?
1 * Sodium/potassium ATPase pumps K+ in and Na+ out
2 * Constant pump activity counters the leak of ion
across cell membrane.
3 * Required to keep normal electrolyte concentrations
Osmosis NaCl vs Urea
1 * Iosmotic NaCl is iostonic
2 * Iosmotic urea is hypotonic because urea enters.
Maintaining the Ion Gradients:
-70mV
15mM Na+
140 mM K+
1 * Sodium is excluded by ATPase pump
2 * Negative potential repels Cl-
3 * Pump failure leads to cell swelling in normal saline
Na+/K+ ATPase = 6
1 * Active ion pump required to keep constant ionic gradients.
2 * Constant ionic gradients maintain resting membrane potential.
3 * Prevents sodium entry makes isosmotic saline isotonic.
4 * Sodium and potassium far from equilibrium
5 * Chloride close to equilibrium in most cells
7 * Active transport of ions is a major metabolic energy cost at rest.
Thermodynamic Limits = 6
1 * Pumps move against concentration gradient because
U (ATP) > U(x)+u(e)
2 * That is energy from ATP use must be greater than the sum of the chemical and electrical potential energy.
3 * Pumps have a limit, cannot pump against very high gradient.
4 * Really high H+ gradient across mitochondrial inner membrane.
5 * Runs F(0) F(1) ATPase (a H+ pump) backwards.
6 * Makes ATP.
Epithelia and Endothelia EXPLAIN = 5
1 * Absorption and secretion by epithelia.
2 * PARACELLULAR goes between cells.
3 * TRANSCELLULAR goes through cells.
4 * TWO CELL membranes to cross.
5 * E.g.Intestine
SELECTIVE PASSAGE THROUGH CELLS = BLOOD VESSEL
NO PASSAGE BETWEEN CELLS = Lumen (contains undigested food and potent digestive enzymes) , luminal border, Lateral border, Tight junction (cell 1) (epithelial lining intestine) , Basolateral border (Cell2)
EXPLAIN TIGHT JUNCTIONS - Paracellular, Kiss? = 3
1 * PARACELLULAR MOVEMENT limited by tight junctions.
2 * TIGHT JUNCTION JOIN cell membrane of adjacent cells.
3 * JOIN AT KISS SIGHTS BY membrane proteins.
Epithelia and Endothelia == 8
1 * ENDOTHELIAL cells line blood vessels.
2 * ENDOTHELIUM mostly leaky.
3 * BLOOD BRAIN BARRIER formed by endothelial cells with TIGHT JUNCTIONS
4 * Blood Brain Barrier limits entry of circulating hormones and drugs to brain.
5 * EPITHELIA line lungs, gut, bladder, kidneys, glands etc.
6 * Epithelia control movement across the set issue layer.
7 * Absorption and secretion by epithelial transport
8 * Pumping epithelia move substances across tissue layers
Understanding Electrogenic Potentials = 5
1 * Na+/K+ATPase generates Na+ current.
2 * Basolateralsurface becomes positive.
3 * Voltage creates driving potential for Cl-
4 * When iCl=iNa voltage stops changing.
5 * Water follows by osmosis
Electrogenic potentials
slide 15
Understanding Anion movement. equation?
= 5
V = iR
1 * Accumulation of positive charge gives voltage
2 * Voltage causes movement of anions dependent on ohms law
3 * If iNa+ > i(Cl-) voltage will increase
4 * Once i(Cl) = i(Na+)
- Increased resistance to anion flow will increase voltage
Understanding Ion Flux? EQUATIONS?
= 5
V = iR
J = (i/ zFA)
- If you know the current, you can calculate the ion flow.
- Flow will be current divide by valance and Faraday’s constant.
- Flux is flow on area
- For toad skin only sodium and
chloride are moving
- For toad skin only sodium and
- Divide by F and area of skin to get flux in mmoles/sec/cm2
Understanding Absorption of Glucose? === 6
1 * Glucose up take by intestine
2 * Primary active transport keeps cell Na+ low
3 * Na+ linked to Glucose entry on apical side (gut lumen).
4 * Na+ gradient powers glucose uptake into cell
5 * High Glucose in cell powers facilitated diffusion
6 * Carrier on basolateral (blood) side move glucose out
Amino Acid Absorption = 2
1 * Uptake of amino acids in gut also powered by Na+.
2 * Active transport of many other molecules is secondary.
Understanding DRUG EXCRETION = 5
1 * Organic molecules moved this way too.
2 * Excretion of penicillin and aspirin through multi-specific OAT (organic anion transporter)
3.* ALPHA-ketogluterate (aKG) linked to drug
4 * Sodium linked to aKG
5 * Linked to Na/K ATPase
Lipid Absorption in Intestine = 3
1 * Exocytosis linked to secondary active transport
2 * Lipids (cholesterol, Free fatty acids (FFA), monoglyceride (MG), phospholipids) enter across lipid layer.
3 * Exocytosis of lipid particles (chylomicrons)
UNDERSTANDING OF ABSORPTION OF FOOD …8
1 * Epithelia lining of the intestine absorbs nutrients.
2 * Glucose and other sugars transported linked to sodium uptake.
3 * Amino acids transported linked to sodium uptake
4 * Lipid transported by diffusion across apical surface and exocytosis across basilateral surface.
5 * Case of sugar intake with no other food.
6 * No sodium in gut, no sugar uptake
7 * Sugar stays in gut, water enters gut by osmosis
8 * Diarrhoea and dehydration.
Summary = 6
1 * Constant ionic pumping maintains cellular ionic gradient
2 * Use of ATP to pump Na+ out of cells make isosmotic NaCl isotonic
3 * Active transport of ions can create charge separation and electrogenic potentials
4 * Movement of ions and organic molecules across epithelial membranes depends on the transporters and channels present
5 * Counter ion (e.g. Cl-) will follow the movement of a pumped ion when an electrogenic potential is developed
6 * Sweat, glandular secretions, renal secretion and reabsorption all depend on membrane transport at epithelia
