Colloids: solutions that contain larger molecular weight solutes (e.g., albumin and starch).Crystalloids: solutions that contain small molecular weight solutes (e.g., minerals, dextrose).MCEM Part A: MCQs – Ian Beardsell (of St. Textbook of Medical Physiology – Guyten, Hall Here is a fantastic explanation of osmosis and the fluid compartments from Dr. Effects of ingesting fluids of differing osmotic potential… There is a small net movement of water out of the plasma. This almost balances the hydostatic pressure created by the pump action of the heart that forces water out of the capillaries into the ISF. These impermeant proteins create an osmotic gradient that pulls water into the plasma. The crucial difference between plasma and ISF is that plasma contains more proteins. These proteins are the only constituents of plasma that do not cross into the ISF. Variations in intracellular large anion content mean that intracellular Cl – concentration varies considerably. Cl – will diffuse down this concentration gradient back into the cell.Īn asymmetric equilibrium is formed with the electrical and concentration gradients opposing each other – this is Donnan’s equilibrium.ĭonnan’s Equilibrium: ‘The presence of a charged impermeant ion (anionic protein) on one side of a semi-permeable membrane will result in an asymmetric distribution of permeant charged ions (Cl –)’. This creates a concentration gradient with higher concentration of Cl – outside of the cell.
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phosphate) force Cl – out of the cell down an electrical gradient. These, along with other large anions trapped in the cell (e.g. Intracellular proteins are negatively charged at physiological pH. Cl – and the Donnan EquilibriumĬl – ions are differentially distributed across the cell membrane due to their negative charge and because they can move freely across the cell membrane via protein channels. Intracellular Ca 2+is either actively transported out of the cell or into the endoplasmic reticulum/mitochondria – this leaves very low levels in the cell. The Na +-K + ATPase carrier protein has to be phosphorylated by one ATP molecule. It pumps 3 Na + ions out of the cell, and 2 K + into the cell. The Na +-K + ATPase pump acts to maintain the cellular environment by actively moving Na + and K + against their concentration gradient. This is prevented by the activity of the Na +-K + ATPase pump. Without intervention, this would eventually lead to equalisation of both ions on both sides of the membrane, which would be physiologically non-viable. K + and Na + follow their concentration gradients (K + out of the cell, Na + in).
![fluid compartments fluid compartments](https://www.78stepshealth.us/human-physiology-2/images/3205_16_3-fluid-compartments-cell.png)
These two compartments are separated by cell membranes, and are very different in their composition (i.e.
![fluid compartments fluid compartments](https://image3.slideserve.com/5708273/fluid-compartments-l.jpg)
Osmolality is the preferred expression of physiologists because it is independent of temperature and pressure. Osmolality – osmotic concentration per volume of solution (osmol/kg H 2O).Osmolarity – osmotic concentration per mass of solvent (osmol/L).It can be expressed as ‘osmolarity’ or ‘osmolality’: Osmotic potential is determined by the number of osmotically active particles per litre. Fluid at lower osmotic potential is hypotonic.Fluid at higher osmotic potential is hypertonic.Fluid at the same osmotic potential as plasma is hypotonic.The creation of osmotic gradients is the primary method for the movement of water in the body.
#Fluid compartments free
‘Osmosis is the movement of water across a semi-permeable membrane from regions of low solute concentration to those of higher concentration’.īiological membranes are semi-permeable – they allow the free movement of water but restrict the movement of solutes.