List the main fluid compartment and sizes in a 70kg man
- Intracellular = 55% of body water
- Extracellular = 45% of body wate
How can the extracellular fluid be subdivided?
Transcellular fluid - cerebrospinal, ocular, synovial = 2%
Blood plasma = 7%
Interstitial Fluid = 36%
The Composition of the Main Fluid Compartments?
Extracellular - Na+ = 150 K+ = 5 Ca2+ = 2 Cl- = 110 Or. Phos = 5 Protein = 1 pH = 7.4
Intracellular - Na+ = 10 K+ = 150 Ca2+= 10^-4 Cl- = 5 Or. Phos = 130 Protein = 2 pH = 7.1
Describe the Composition of the main fluid compartments?
CATIONS
Sodium - present in high concentrations outside cells
Potassium - present in high concentration inside cells
Calcium = important signalling ion, v. low concentrations inside cells, except in organelles which stores it (ER,SR)
ANIONS -
Chloride = high conc outside cells
Or. Phos. = high concentration inside the cells
Proteins = Anions present in low concentration and have a high charge
pH = slightly higher outside the cell than inside. lower H+ concentration ouside cell
What is Osmolarity
Osmolarity - the concentration of a solution expressed as the total number of solute particles per litre.
What is Tonicity?
a measure of the effective osmotic pressure gradient, as defined by the water potential of two solutions separated by a semipermeable membrane.
What happens during Osmosis?
Osmosis moves water towards area of higher osmolarity and can change cell volume.
Which one is more useful Osmolarity or Tonicity?
Tonicity - More useful, defines strength of a solution as it affects final cell volume. Depends on:
- Cell Membrane Permeability
- Solution Composition
Osmolarity does not depend on the cell permeability
What is a Hypertonic Solution?
- Osmolarity of impermeant solutions: out>in
- Cell shrinks in solution
- Solution is hypertonic
What is a Hypotonic Solution?
- Osmolarity of impermeant solutes: out
What is an Isotonic Solution?
- Osmolarity of impermeant solutes: out=in
- Cell volume is unchanged
- Solution is isotonic
Describe the Tonicity of real cells?
- Membranes are permeable to water
- Concentration of impermeable solutes is higher inside than outside the cell but they do not burst
- Due to Na/K pump that maintains a lower conc of Na+ inside the cell than outside.
- no net mvt of Na+ across the membrane
- cells have to actively maintain this state
Summarise the methods of transport through the membrane
Passive - Down the EC gradient: -Through Lipid,Pores on Carriers
Active - against the EC gradient:
Primary - (Na/K pump)
Secondary - downhill mvt of one solute coupled to uphill mvt of another
Endo/Exocytosis:
- encapsulating in membrane as solute enters or before it leaves cell
- large molecules
How does exchange across the capillary wall work?
- Small pores between endothelial cells.
- 8L of plasma leaks out everyday
- Colloid Osmotic Pressure (COP) - Osmotic pressure due to plasma protein
- COP draws water in
- Hydrostatic pressure - pressure in a circulatory system exerted by the volume of blood when it is confined in a blood vessel. This pushes water out.
- HP>COP = Plasma leaks out
- HP
What is Oedema?
- Swelling of a tissue because of excess interstitial fluid.
- Imbalance of forces causing fluid to move between:
Blood Plasma
Interstitim
Lymphatic Vessels - Increased permeability of capillary walls to plasma proteins.
- Oedema - leakage of plasma into interstitium exceeds capacity of lymphatics to collect and return it to the circulation. Accumulates in the interstitial space.
- One of the cardinal signs of INFLAMMATION.
