L1 - Homeostasis

Question 1

Why are cells bathed in extracellular fluid?

Answer 1

Creates a constant environment that is stable and protects the cell from change of the outside environment

Question 2

What fraction of the bodies water id the ECF? and what fractions of this are the blood plasma and interstitial fluid?

Answer 2

ECF = 1/3 of body water

Interstitial fluid = 4/5
Blood plasma = 1/5

Question 3

What is are the levels of K+, Na+, Ca2+ and Cl- inside compared to outside an average cell?

Answer 3

Inside:
High K+ (139)
V. low Ca2+ (<0.0002)
Low Na+ (12)
Low Cl- (4)

Outside:
Low K+ (4)
High Na+ (145)
High Chloride (116)
Relatively high Ca2+ (1.8) - intracellular stores

Question 4

What is the resting membrane potential?

Answer 4

-70mV

Question 5

How can resting potential be measured?

Answer 5

Intracellular microelectrode - a probe inside and a probe outside the axon, amplified and displayed

Question 6

How is the resting potential established?

Answer 6

1) unequal distribution of K+ between inside and outside

2) Selective permeability of the resting cell membrane to K+

Question 7

What 2 gradients are in equilibrium at rest?

Answer 7

At rest there is an equilibrium between ELECTRICAL gradient and CONCENTRATION gradient

Question 8

Describe the function of the Na+/K+ ATPase

Answer 8

Pumps 3Na+ out of the cell at the same time as pumping 2K+ into the cell

Creates a high intracellular K+ concentration

Question 9

How is the value of the K+ equilibrium calculated?

Answer 9

The Nernst equation

Experiments by Hodgkin and Horowitz in 199 proved the equations

Varying K+ concentration outside the cell alters the membrane potential in NE