Lecture 5: Cell Physiology of Ions 2

Question 1

what is hypocalcaemia

Answer 1

• insufficient free calcium in the blood
• overreactive tendons, reflexes and muscle contractions
• paraesthesias (pins and needles or loss of sensation)
• arrhythmia and seizures

Question 2

what is Chvostek’s sign

Answer 2

when angle of the jaw is tapped and facial muscles on that side twitch momentarily due to hypocalcaemia

Question 3

changes in ion concentrations during fertilisation

Answer 3

when the first sperm reaches the egg, Ca2+ concentration increases 5 to 10 fold, triggering the raising of fertilisation envelope (barrier from other sperms)

Question 4

what is an excitable cell

Answer 4

• a cell that can propagate an action potential

- eg neurons and myocytes

Question 5

what is a non-excitable cell

Answer 5

• a cell that can’t propagate an action potential

- anything but neurons and myocytes, eg liver and epithelial cells

Question 6

movement of Na+ and Cl-

Answer 6

Cl- follows the movement of Na+ and other permeable cations

water follows Cl-

Question 7

composition of plasma

Answer 7

• highest in Na+ conc.

- slightly more negative in electrical potential than extracellular fluid

Question 8

composition of intracellular fluid

Answer 8

• highest in total cations and therefore low water potential
• highest in protein and electrolyte concentration
• most negative voltage

Question 9

composition of extracellular space

Answer 9

• higest Cl- conc. as it lacks protein anions
• lowest electrolyte conc.
• very high water potential

Question 10

what are ionic concentrations measured in

Answer 10

milli Equivalents or mEq

Question 11

how is calcium found in cells

Answer 11

• free calcium in solution
• uncharged in bone
• bound to proteins like calbindin
• can be sequestered eg in sarcoplasmic reticulum

Question 12

where is free calcium found

Answer 12

• in cytosol, 100 nanoM

- in blood, 1.2 milliM so 10,000 times as much as in cytosol

Question 13

what happens in an action potential

Answer 13

• action potential triggers increase in cytosolic Ca2+ concentration
• this leads to muscle contraction or synaptic contraction

Question 14

what are the rules of ionic balance

Answer 14

• concentration of positive and negative ions must (nearly) balance
• any ion that leaves the cell must be replaced by another ion of that type coming into the cell
• energy maintains gradients and reestablishes them across membranes

Question 15

pH of cytosol and extracellular fluid

Answer 15

• cytosol: 7.40

- extracellular fluid: 7.20

Question 16

examples of use of carbonic anhydrase

Answer 16

• red blood cells: chloride shift for removing H+ from muscle
• lungs: eliminates CO2 source from blood
• pancreas: secreting bicarbonate
• gastric parietal cell: secreting acid into stomach

Question 17

what happens in the gastric parietal cell (with carbonic anhydrase reaction)

Answer 17

1) CO2 from blood and H2O enter the cell
2) H+ leaves from apical side of cell and HCO3- leaves from basolateral side and ends up in blood
3) H+/K+ proton pump aka ATPase pumps H+ out of the cell. inhibited by omeprazole
4) HCO3- leaves by chloride bicarbonate exchanger. inhibited by oxonol dyes

Question 18

what happens in the gastric parietal cell (with K+ and Cl-)

Answer 18

• K+ and Cl- build up in cell
• K+ and Cl- channels open, letting them out
• forms HCl in lumen of the stomach, making it acidic
• in case of K+ depletion, sodium potassium pump pushes K+ in and any leaked Na+ out
• inhibited by ouabain and digitalis

Question 19

what drug is prescribed for acid reflux

Answer 19

omeprazole

Question 20

draw a gastric parietal cell

Answer 20

check