Cell Membranes IV

Question 1

Two layers of the lumen?

Answer 1

1. Apical (free) surface
   - faces external environment (lumen)
   - not connected to anything
2. Basolateral
   - associated with underlying connective tissue
   -basal lamina -> reticular lamina (these 2 basement membrane)

Question 2

Absorption?

Answer 2

From lumen of organ to ECF

Question 3

Secretion?

Answer 3

From ECF to lumen of organ

Question 4

What are tight junctions of lumen surface?

Answer 4

• found closer to apical membrane on lateral surface
• connect epithelial cells together
• strands of transmembrane proteins link together to form tight junctions that prevent substances from readily moving between epithelial cells

Question 5

What is transcellular transport?

Answer 5

Across epithelial cell
- moves from apical membrane and basolateral membrane to move from lumen to ECF
- transporter on both membranes

Question 6

What is paracellular transport?

Answer 6

Between tight junctions of epithelial cells
- limited to a couple ions or water

Question 7

What is transcytosis?

Answer 7

Combination of receptor mediated endocytosis followed by vesicular transport and contents released by exocytosis
- least likely of 3

Question 8

Why are transporting epithelia polarized?

Answer 8

Polarized distribution of membrane transporters ensures one-way movement
- one side active (low to high), one passive (high to low)

Question 9

Why is body as a whole electrically neutral but cells are in electrical disequilibrium?

Answer 9

ECF has slight excess of cations
ICF has slight excess of anions

Question 10

What is the membrane potential?

Answer 10

The electrical disequilibrium between the ECF and the ICF

Question 11

What is the electrochemical gradient?

Answer 11

Combination of electrical and concentration gradients

Question 12

What is the equilibrium potential?

Answer 12

For any given concentration gradient of a single ion, the membrane potential that exactly opposes the concentration gradient
Ex) when concentration gradient for K+ is 150mM ICF and 5mM ECF
Ek= -90mV

Question 13

What does the Nernst equation calculate?

Answer 13

Equilibrium potential (membrane potential that would result if the membrane were completely permeable to only one ion)

Question 14

What is the resting membrane potential?

Answer 14

Membrane potential of a cell when it is not active
-mostly determined by K+

Question 15

What is resting membrane potential of excitable cells (muscles, neurons)?

Answer 15

Ranges fro -40 to -90 mV

Question 16

Can we measure the absolute electrical charge of a cell?

Answer 16

No, can only describe electrical gradients on a relative scale comparing ICF to ECF

Question 17

Why is resting membrane potential due to potassium?

Answer 17

Cell membrane is about 40 times more permeable to K+ (way more K+ leak channels than Na+)
Ena= +60
Ek= -90
Membrane potential= -70

Question 18

What maintains membrane potential?

Answer 18

Na-K ATPase
- 3 Na OUT/ 2 K in
- creates negative ICF

Question 19

What two factors influence a cell’s membrane potential?

Answer 19

1. The concentration gradients of different ions across the membrane (na, K, Cl, Ca2+)
2. The permeability of the membrane to those ions (opening gated channels)

Question 20

Repolarization?

Answer 20

Return to resting membrane potential from depolarized state

Question 21

Hyperpolarization?

Answer 21

Membrane potential becomes more negative

Question 22

Depolarization?

Answer 22

Membrane potential becomes more positive