LECTURE 7: PUMPS AND EPITHELIA

Question 1

Ionic Currents: 4

Answer 1

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

Question 2

Maintaining the Ion Gradients:

Answer 2

1. V + 61mV,V + -88mV. eNa eK
2. Vm -70 mV
3. Neither ion at equilibrium
4. Na+ flows in and K+ flows out.

Question 3

What keeps internal K+ high and intracellular Na+ low?

Answer 3

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

Question 4

Osmosis NaCl vs Urea

Answer 4

1 * Iosmotic NaCl is iostonic

2 * Iosmotic urea is hypotonic because urea enters.

Question 5

Maintaining the Ion Gradients:
-70mV
15mM Na+
140 mM K+

Answer 5

1 * Sodium is excluded by ATPase pump

2 * Negative potential repels Cl-

3 * Pump failure leads to cell swelling in normal saline

Question 6

Na+/K+ ATPase = 6

Answer 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.

Question 7

Thermodynamic Limits = 6

Answer 7

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.

Question 8

Epithelia and Endothelia EXPLAIN = 5

Answer 8

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

Answer 9

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)

Question 10

EXPLAIN TIGHT JUNCTIONS - Paracellular, Kiss? = 3

Answer 10

1 * PARACELLULAR MOVEMENT limited by tight junctions.

2 * TIGHT JUNCTION JOIN cell membrane of adjacent cells.

3 * JOIN AT KISS SIGHTS BY membrane proteins.

Question 11

Epithelia and Endothelia == 8

Answer 11

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

Question 12

Understanding Electrogenic Potentials = 5

Answer 12

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

Question 13

Electrogenic potentials

Answer 13

slide 15

Question 14

Understanding Anion movement. equation?

= 5

Answer 14

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+)

5. Increased resistance to anion flow will increase voltage

Question 15

Understanding Ion Flux? EQUATIONS?

= 5

Answer 15

V = iR

J = (i/ zFA)

1. If you know the current, you can calculate the ion flow.
2. • Flow will be current divide by valance and Faraday’s constant.
3. • Flux is flow on area
4. • For toad skin only sodium and
     chloride are moving
5. • Divide by F and area of skin to get flux in mmoles/sec/cm2

Question 16

Understanding Absorption of Glucose? === 6

Answer 16

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

Question 17

Amino Acid Absorption = 2

Answer 17

1 * Uptake of amino acids in gut also powered by Na+.

2 * Active transport of many other molecules is secondary.

Question 18

Understanding DRUG EXCRETION = 5

Answer 18

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

Question 19

Lipid Absorption in Intestine = 3

Answer 19

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)

Question 20

UNDERSTANDING OF ABSORPTION OF FOOD …8

Answer 20

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.

Question 21

Summary = 6

Answer 21

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