Lecture 5: Cell Physiology of Ions 2 Flashcards
what is hypocalcaemia
- insufficient free calcium in the blood
- overreactive tendons, reflexes and muscle contractions
- paraesthesias (pins and needles or loss of sensation)
- arrhythmia and seizures
what is Chvostek’s sign
when angle of the jaw is tapped and facial muscles on that side twitch momentarily due to hypocalcaemia
changes in ion concentrations during fertilisation
when the first sperm reaches the egg, Ca2+ concentration increases 5 to 10 fold, triggering the raising of fertilisation envelope (barrier from other sperms)
what is an excitable cell
- a cell that can propagate an action potential
- eg neurons and myocytes
what is a non-excitable cell
- a cell that can’t propagate an action potential
- anything but neurons and myocytes, eg liver and epithelial cells
movement of Na+ and Cl-
Cl- follows the movement of Na+ and other permeable cations
water follows Cl-
composition of plasma
- highest in Na+ conc.
- slightly more negative in electrical potential than extracellular fluid
composition of intracellular fluid
- highest in total cations and therefore low water potential
- highest in protein and electrolyte concentration
- most negative voltage
composition of extracellular space
- higest Cl- conc. as it lacks protein anions
- lowest electrolyte conc.
- very high water potential
what are ionic concentrations measured in
milli Equivalents or mEq
how is calcium found in cells
- free calcium in solution
- uncharged in bone
- bound to proteins like calbindin
- can be sequestered eg in sarcoplasmic reticulum
where is free calcium found
- in cytosol, 100 nanoM
- in blood, 1.2 milliM so 10,000 times as much as in cytosol
what happens in an action potential
- action potential triggers increase in cytosolic Ca2+ concentration
- this leads to muscle contraction or synaptic contraction
what are the rules of ionic balance
- 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
pH of cytosol and extracellular fluid
- cytosol: 7.40
- extracellular fluid: 7.20
examples of use of carbonic anhydrase
- 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
what happens in the gastric parietal cell (with carbonic anhydrase reaction)
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
what happens in the gastric parietal cell (with K+ and Cl-)
- 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
what drug is prescribed for acid reflux
omeprazole
draw a gastric parietal cell
check
