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How can fluids be delivered into the body?
- Intraosseously - into the bone
- Intravenously - into the vein
- Subcutaneously - under the skin
- Orally - drinking
What is interstitial fluid?
It is the fluid that surrounds tissues but is not contained within vessels (it is a type of extracellular fluid).
How do solutes move between fluid compartments (between the ICF/ECF)?
- Active transport
- Bulk flow
Diffusion is when substances move down an electrochemical gradient (from a high concentration to a low concentration).
What is facilitated diffusion?
This is when proteins in the cell membrane are used to transfer a solute from one side of the membrane to another. When the solute binds to the protein this causes a conformational change in the shape of the protein causing it to flip and carry the solute across the membrane. The solute then dissociates from the protein and it has moved from a high concentration to a low concentration. Glucose and amino acids rely on facilitated diffusion. Facilitated diffusion does not require energy.
Define active transport
Active transport is the movement of substances against their concentration gradient using energy in the form of ATP.
What is the difference between primary and secondary active transport?
- In primary active transport the solute binds to a protein in the cell membrane and the presence of ATP releases energy which causes a conformational change in the protein. An example of this system is the Na+ / K+ pump.
- In secondary active transport the cell membrane protein does not use ATP - it is not the energy dependent protein. The concentration gradient of a second transport system is used to cause a conformational change in the protein; the stored chemical energy of the second system is used.
What is the Donnan effect?
The presence of a non permeable solute affects the distribution of permeable solutes
Osmosis is the net movement of water down a concentration gradient through a semi-permeable membrane
What does osmosis require?
- Separation of two solutions by a semi-permeable membrane
- Difference in the concentration of impermeable solutes
What is osmolarity?
The measure of solute concentration - number of solute particles per litre of solution
What is tonicity?
Comparison of the concentration of impermeable particles between two solutions
What kind of tonicity will a hypertonic and hypotonic solution have?
- Hypertonic - high tonicity
- Hypotonic - low tonicity
How much of total body water is
a) intracellular fluid
b) extracellular fluid
What are the four starlings forces?
- Capillary hydrostatic pressure - the pressure generated by the heart working to force blood through the circulatory system. This causes an increase in pressure inside the capillaries which moves water out into the interstitial space.
- Interstitial fluid hydrostatic pressure - there is a limited space that water can move into, so an increase in water to the interstitial fluid causes an increase in interstitial pressure. IFHP opposes CHP.
- Oncotic pressure - specifically relates to the osmotic pressure generated by proteins present in the plasma. These proteins are impermeable molecules so they draw water into the capillaries by osmotic action.
- Osmotic pressure due to interstitial fluid proteins - draw fluid out of the capillaries
What happens at the arteriole end of a capillary?
- The lymphatic system drains the interstitial space to get a negative IFHP (to pull more water out of the capillaries)
- Net filtration occurs (more water moves out of the capillary)
What happens at the venous end of the capillary?
- Biggest change is a decrease in the CHP
- Net absorption occurs (more water moves into the capillary)
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