Cellular Physiology

Question 1

What is the Nernst Equation?

Answer 1

this calculated the potential difference generated by freely permeable ion across a membrane when it is in electrochemical equilibrium.

Question 2

What is the Goldman-Hodgkin-Katz equation?

Answer 2

this calculates the membrane potential when the permeability of different ions is taken into account.

Question 3

What is osmolality?

Answer 3

Osmolality is the number of osmoles of solute/kg of solvent. The normal plasma osmolaltiy is 285-290mmol/kg

Question 4

What is osmolarity?

Answer 4

It is the number of osmoles of solute/litre of solvent and is therefore affected by temperature.

Question 5

What is tonicity?

Answer 5

Tonicity is a measure of the effective osmolarity of a solution.

Question 6

What is osmotic pressure?

Answer 6

Osmotic pressure is the theoretical pressure that would have to be applied to prevent a litre from moving from a solution of pure water to a solution containing dissolved particles.

Question 7

What is oncotic pressure?

Answer 7

the colloid osmotic pressure - or the component of total osmolality which is due to colloids.
the typical value is 25-28mmHg

Question 8

What is the normal value for Na+ in blood plasma?

Answer 8

140mmol/l

It is the main extracellular cation.

Question 9

Where is K+ found within the body?

Answer 9

It is the main intracellular cation.
Intracellular: 90% ~
Extracellular fluid: 2%
Bone: 8%

Question 10

What are the functions of K+?

Answer 10

1. Maintain membrane potential
2. component of intracellular tonicity
3. involved in Na+/K+ pump
4. neuromuscular activity

Question 11

What are the features seen on an ECG of hyperkalaemia?

Answer 11

ECG changes are occur about a K+ level >5.5mmol/l

1. tall tented T waves.
2. shortening of Q-T interval.
3. PR prolongation.
4. flattening of p waves.
5. widening of QRS complex.
6. sine wave appearance, VF, asystole.

Question 12

Features of an ECG of hypokalaemia?

Answer 12

Occur at levels <3mmols/l
1. peaked P waves
2/ flattening of T waves
3. prolonged QT
4/. shortened PR interval
5/ Torsades de point/VT

Question 13

What is the normal range of plasma Magnesium?

Answer 13

0.7-1.0mmol/l

Question 14

What are the functions of Magnesium?

Answer 14

Magnesium is essential for many processes of homoeostasis.
It is a co-factor for metabolism, nerve/muscle actions as well as being important in the production of DNA/RNA and protein synthesis.

Intracellelar catalyst - acitvates 300 enxzumes.
required for sodium pump, oxidative phosphorylation and all reactions involving ATP.

Nerve/muscle effects:
1/ reduces membrane excitability
2. physiological antagonist of calcium.
3. transmitter release and excitation contraction coupling are inhibited by Mg++
4. potentiation of syccinylcholine _ NDNMB.
5 smooth muscle relaxation - vasodilation

physiological blocker of NMDA receptor.