Composition and control of intracellular fluid
Intracellular fluid composition
Note
In normal physiology, the osmolality in all body compartments is the same (285mOsmol/kg)
Calcium is used in many secondary messenger pathways. If the intracellular concentration were high, these systems would be popping off constantly! Hence why its concentration is controlled at a nearly undetectable level.
| Compound | Concentration |
|---|---|
| Osmolality | 285mOsmol/kg |
| pH | 7.0 to 7.4 (slightly acidic compared to ECF) |
| Na+ | 10-15mmol/L |
| K+ | 150mmol/L |
| Cl- | 10mmol/L (varies substantially on cell type) |
| Mg2+ | 10-20mmol/L |
| Ca2+ | <1mmol/L |
| Lacate | 1mmol/L |
| Bicarbonate | 10-15mmol/L |
| Protein | 200g/L (albumin <1g/L) |
Describe how controlling intracellular fluid composition can maintain homeostasis and integrity
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A nebulous inclusion in the exam syllabus that appears to never have been examined.
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By correcting to intracellular hypotonicity / extracellular hypertonicity
- cells increase their permeability to Na+ and Cl- by inserting ion channels into the cell membrane
- e.g. NKCC channel, Na+/H+ exchanger, Cl-/HCO3- exchanger
- → influx of Na+ and Cl-
- → ↑osmolality
- cells also create new solutes which stay in the cell, raising its osmolality
- also known as 'idiogenic osmoles'
- e.g. amino acids and polyols
- cells increase their permeability to Na+ and Cl- by inserting ion channels into the cell membrane
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By correcting intracellular hypertonicity / extracellular hypotonicity
- K+ channels channels open causing efflux
- → ↓osmolality while maintaining electroneutrality
- cells can also secrete idiogenic osmoles into the ECF
- K+ channels channels open causing efflux
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By maintaining the resting membrane potential
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