Cell physiology of ions Flashcards
Name the different fluid compartments in the body. (4)
Plasma:
Na+ based.
Intercellular fluid, between cells (interstitial): Contains mainly the components of the plasma without blood proteins.
Intracellular fluid, within cells:
K+ based with many anions.
Transcellular:
Within the lumen of tubes and organs. such as the bladder or stomach.
How can ions cause cardiac arrhythmias?
Incorrect regular of ions cause electric irregularities in myocytes.
What can cause an imbalance of ions? (7)
Trauma/ haemorrhage:
Cause loss of ions from the blood.
Diabetes:
Diuretics produced which causes the loss of ions.
Kidney dysfunction:
Irregular control of ion concentration.
Hormonal imbalances:
Irregular control of the concentration of ions, such as from the pituitary glands
Dehydration:
Greater concentration of ions and irregular water potential
Diarrhea and vomiting:
Causes dehydration and loss of ions
Vitmain imbalance:
Disrupts Ca2+ concentrations.
Different ways in which ions are stored in the body. (6)
Free in solution
Tightly bound to another molecule or ion.
Sequestered: trapped behind membranes in organelles such as Ca2+ in the sarcoplasmic reticulum.
Chelated: Bound to a specific ion/ molecule which prevents it from further reacting with any other molecule/ion.
Buffered: Bound to a molecule/ ion but not specifically bound.
Inside teeth/ bones
Different methods of ions travelling across the membrane (5)
Protein channels:
Moving down its concentration gradient via passive diffusion.
The channels are ion specific
Protein pumps:
Membrane proteins uses ATP to pump specific ions across the membrane against their concentration gradient.
Exchangers:
Membrane proteins that bring in one specific ion in exchange for releasing another specific ion.
Co-transporters:
Membrane proteins that couple transport ions are the same time across the membrane, down their concentration gradient.
Leak:
Ions diffusion across the membrane without the use of a membrane protein.
Ions as a secondary messenger
Transmits information from outside across the plasma membrane by receiving a signal from a primary messenger like a hormone.
e.g the activation of protein kinase C by Ca2+
Voltage
Difference in potential energy between two separate points.
This is the force that pushes the current, in this case the charged particles (ions)
Resistance
How easy it is for current to flow.
Increase width and length of a space allow less resistance, more flow of current.
Resistance (R) = Voltage (V) / Current (I)
Conductance
How well a system conducts electricity, reciprocal of resistance:
Conductance (g) = Current (I) / Voltage (V)
The ionic differences inside and outside the cells are resting potential/
Inside: High K+, low Na+
Outside: High Na+, low K+
Movement of ions across the membrane leads to an ionic current.
The chemical force on ions
Difference in concentrations of ions across the membrane.
K+ usually has a higher concentration inside the cell compared to that outside. This pushes the chemical force of K+ outside the cell.
The electrical force on ions
This is based on changes in membrane potential over time.
Occurs when there is an unbalance of positive and negatively charged ions.
Equilibrium potential
Based on the net force acting on ions:
Net force: chemical force + electrical force
At equilibrium, the potential= 0
Chemical force = -1 x electrical force
The electrical force is equal and opposite to the chemical force
Hypocalcaemia
Occurs when the levels of Ca2+ in the blood are too low: below 2.1 mmol/L or 4.3 mEq/ L
Causes paraesthesia: pins and needles sensation due to peripheral nerve damage.
Test:
Chvostek’s sign- tapping of facial nerve sees twitching in facial muscle.
Trousseau’s sign- tetany in the hand when stimulated with bp pressure pump.
Milliequivalent (mEq)
The amount of substances need to react with an arbitrary amount of another substance in a reaction:
The substance reacts with 1 mol of H+ in an acid/base reaction.
Reacts with 1 mol of electrons in a redox reaction.
Ionic rules of a cell
- Charges must always be balanced.
- Ions must always be replaced.
- Energy always maintains ionic gradients.
Maintain pH
pH always maintained within narrow ranges:
In extracellular fluid: 7.40 +/- 0.05
In the cytosol: 7.2
Excitable vs non-excitable cells
Excitable cells:
Cells that are able to be stimulated by/ generate electricity.
Includes: neurones, myocytes, beta pancreatic cells
Non-excitable:
Not responsive to electricity. Which is every other cells:
Especially epithelial cells.
Relationship between Na+, Cl- and water
Na+ is usually pumped across ion channels.
Cl- usually follows Na+.
Water always follows the movement of Cl-, as seen in the kidneys.
Main ionic component of plasma.
Na+ concentration is highest here to balance negatively charged proteins, anions.
This makes it slightly more negative than extracellular fluid.
Main compenents of intracellular fluid
Cations are highest.
Proteins are highest.
Electrolyte concentration is the highest.
The most negative voltage of all bodily fluids.
Ionic components of extracellular fluid.
Highest Cl- composition since there is a lack of protein anions.
Lowest electrolyte concentration.
How is Ca2+ stored in the body
Free in solution.
Inside bone: very unreactive with enzymes. Unless an osteoblast is involved.
Bound to proteins: Also makes it less reactive.
Very low in the cytosol. An increase in its concentration is due enzyme/ protein action.
Ca2+ in muscle contraction.
High cytosolic concentration is needed to make myosin attach to actin during muscular contraction.
This moves myosin from cocked position to attachment.
Functions of carbonic anhydrase
Creates acid or base which is secreted:
Acid in stomach
Bicarbonate in the pancreas
Indirectly helps the transportation of H+ and CO2 across the membrane.
Chloride shift in red blood cells to balance charge.
The production of acid from the gastric parietal cells.
- Water and carbon dioxide reacts to form bicarbonate and acid (H+) , using carbonic anhydrase.
- Acid is secreted out the apical membrane in the lumen of the stomach.
H+ is exchanged with K+ using an exchanger protein, H+/K+- ATPase.
This requires ATP - Bicarbonate is released via the basolateral membrane into the blood.
HCO3- is exchange with Cl-
This process is passive. - A build up of Cl- and K+ causes both of them to leave via their specific ion channels, down a concentration gradient.
- The Secretion of Cl- and H+ forms HCl, the acid.
- Na/ K ATPase is used to restore normal Na and K concentrations.
Drug that inhibits H+/K+- ATPase
Omeprazole; a proton pump inhibitor (PPI)
Molecule that inhibits the Cl-/ HCO3- exchanger
Oxonol dyes
Molecules that inhibits Na+/ K+- ATPase
Ouabain
Digitalis
