Lecture: Physiology 1: Cell physiology of ions

Question 1

What is a solvent?

Answer 1

A substance in which a molecule is dissolved to form a solution. In all biological systems, the solvent is water.

Question 2

What is a solute?

Answer 2

A substance than can be dissolved in another substance.

Question 3

What is an ionic gradient?

Answer 3

The difference in concentration of ions across a membrane.

Question 4

What is diffusion?

Answer 4

The process of solute molecules passively moving down their concentration gradient from an area of high concentration to an area of low concentration. Passive process that does not require energy; however, movement against a conc. gradient requires energy.

Question 5

What is osmosis?

Answer 5

The process of water (solvent) molecules passively moving down their concentration gradient. Process can happen across barriers and cell membranes that do not allow for movement of charged particles and does not require energy.

Question 6

What are cations?

Answer 6

Positively-charged ions; eg. Na+, K+, Ca2+, H+, Mg2+

Question 7

What are anions?

Answer 7

Negatively-charged ions; eg. OH-, Cl-, HCO3-, [SO4]2-, [PO4]3-, charged proteins

Question 8

Where are ions found?

Answer 8

Ions can be free in solution, buffered and non-specifically bound, chelated, tightly bound to molecules, sequestered behind membranes in organelles, or found in teeth/bone.

Question 9

How can ions be moved across membranes?

Answer 9

Ions can cross membranes via passive channels, passive co-transporters, passive exchanger, passive leaks or active pumps (use ATP).

Question 10

What are the causes of ionic imbalance in patients?

Answer 10

Trauma and haemorrhage, diabetes and diuretics, kidney dysfunction, hormonal imbalances, extensive diarrhoea and vomiting, dehydration, vitamin D imbalances, and poisons.

Question 11

What is voltage?

Answer 11

Voltage is the difference in potential energy between 2 points in an electrical field which provides the driving force for charged particles (ions) to move.

Question 12

What is current?

Answer 12

Current is the rate at which charged particles (ions) to move.

Question 13

What is resistance?

Answer 13

Resistance is the degree to which conductance and flow affects the flow of charge particles (ions).

Question 14

How does membrane potential change during action potentials?

Answer 14

When the cell is at rest, Vm (the membrane potential) = the resting membrane potential (Vrest). During the action potential Vm changes dramatically, yet the concentration gradients of the ions will remain virtually unchanged.

Question 15

What is the equation for the net force across a cell membrane?

Answer 15

Net force = chemical + electrical force

Question 16

How is the chemical charge and electrical charge of an ion formed?

Answer 16

Each charged particle (ion) produces a chemical force (diffusional force) which is based upon the difference in concentrations ACROSS the membrane, and an electrical force (membrane potential) which is based on a few positive charges being UNPAIRED with negative charges ON THE SAME SIDE OF THE MEMBRANE.

Question 17

What is homeostasis?

Answer 17

The maintence of a constant internal environment through the process of positive and negative feedback.

Question 18

What are excitable cells?

Answer 18

Cells hat can propagate an action potential (can produce or respond to electrical signals), which is a specific kind of amplified voltage response; eg. neurons and muscle cells (myocytes).

Question 19

What are non-excitable cells?

Answer 19

Cells that cannot propagate an action potential; eg. skin, liver, epithelial cells (e.g. gastric parietal cells).

Question 20

What are Milli-equivalent (mEq)?

Answer 20

A unit of amount of substance used that is formally defined as the amount of a substance which will enter solution.

Question 21

What are the rules of ionic balance?

Answer 21

• The concentration of positive and negative ions must “nearly” balance.
• Any ion that leaves the cell must be replaced soon by another ion of that type coming into the cell.
• Energy is always being used to re-establish the ionic gradients across membranes (eg. Na+/K+ ATPase pump).

Question 22

How are changes in blood pH corrected?

Answer 22

Corrected by the actions of the kidneys and the lungs. Carbonic anhydrase is a catalyst and is used to maintain and balance blood pH:
Co2 + H2o = H+ + HCo3-

Question 23

What inhibits carbonate/chloride ion channels?

Answer 23

Oxonol dyes

Question 24

What inhibits proton pumps?

Answer 24

Omeprazole

Question 25

What inhibits sodium/potassium ATPase pumps?

Answer 25

Ouabain and digitalis