Body fluids

• Intraosseously - into the bone
• Intravenously - into the vein
• Subcutaneously - under the skin
• Orally - drinking

It is the fluid that surrounds tissues but is not contained within vessels (it is a type of extracellular fluid).

• Diffusion
• Active transport
• Bulk flow

Diffusion is when substances move down an electrochemical gradient (from a high concentration to a low concentration).

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.

Active transport is the movement of substances against their concentration gradient using energy in the form of ATP.

• 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.

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

• Separation of two solutions by a semi-permeable membrane
• Difference in the concentration of impermeable solutes

The measure of solute concentration - number of solute particles per litre of solution

Comparison of the concentration of impermeable particles between two solutions

• Hypertonic - high tonicity
• Hypotonic - low tonicity

• a) 2/3
• b) 1/3

• 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

• 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)

• Biggest change is a decrease in the CHP
• Net absorption occurs (more water moves into the capillary)