Tissues 5- Fluid Compartments Flashcards
What are the fluid compartments of the body
Intracellular (IC) (inside cells) = 23 L = 55% of body water Extracellular (EC) (outside cells) = 19 L = 45% of body water Interstitial fluid (IF) (between cells). = 15 L =36% of body water Blood plasma = 3 L = 7% of body water Transcellular fluid includes Cerebrospinal (CSF), ocular (eye), synovial fluid = 1 L = 2% of body water
Describe the barriers to fluids which creates the compartments
In most tissues, the extracellular environment is compartmentalised, these different compartments having different compositions and functions.
Extracellular fluids are compartmentalised by barriers.
A barrier you know well is the plasma membrane, which separates the intracellular and extracellular fluids.
The extracellular fluids are separated by layers of cells that form junctions with each other:
Epithelial cells layers separate various interstitial spaces.
Endothelial cells line blood vessels, and are the main barrier separating the fluid of the blood (the plasma) and the interstitial fluids.
What are the extracellular fluid compartments
Fluids in the apical (luminal) extracellular space
Fluids in the basal extracellular space: the interstitial fluids
Fluids of the blood: plasma
(blood is ~ 55-60% plasma)
What is the difference in composition between interstitial fluid and blood plasma
The blood plasma has more protein.
Describe the differences in composition between the plasma and intracellular fluid
Plasma has a higher Na+ conc IC has a greater K+ conc Plasma has a much higher Ca2+ conc Cl- has a higher plasma conc IC has a higher Organic Phosphate ion conc More protein in muscle than in plasma Plasma has a higher pH- lower H+ conc. Osmolarity is the same
Why is the osmolarity of the IF and plasma the same
Most cells and tissues are permeable to water, except for some regions of the Kidney- which have large osmolarities
Why do we use the plasma instead of interstitial cell fluid
Plasma has more consistent readings.
Why is it important that there is an extremely low con of Ca2+ in intracellular fluids
Ca2+ is an important intracellular signalling ion, hence low conc means adding or removing a small number of ions makes a big change in conc.
What is the role of endothelial cells
To separate blood from the rest of the body.
What causes cells to change volume
Solutes and water move across cell membranes & can change cell volume
What is diffusion
Diffusion: spontaneous movement of solute
Down conc gradient until equilibrium is reached.
What is osmosis
Osmosis: movement of water down its own
concentration gradient.
Osmosis moves water toward the area
of higher osmolarity & can change cell volume
What is meant by osmolarity
Osmolarity is a measure of the concentration
of all solute particles in a solution.
What is meant by permeability
How easily a solute crosses a membrane.
In which direction does the water move in osmosis
Osmosis moves water toward the area
of higher osmolarity & can change cell volume
Describe what would happen if a cell is placed in a solution with a lower osmolarity, and the membrane of the cell is permeable to solutes and water
H2O and solute both diffuse down their concentration gradients.
b) H2O will diffuse in both directions (inwards down its conc gradient, and out as solvent gradually increases in conc outside)
Final State
Osmi = Osmo H2O conc equal Solute conc equal No further net diffusion, or osmosis. After equilibration, no net volume change. However, in short term, osmotic shock can damage the cell, even though equilibrium would have been reached.
What would happen if a cell is placed in a solution with a lower osmolarity, and the membrane is impermeable to one solute but permeable to water
) H2O and solute both diffuse down their concentration gradients. Solute can’t diffuse out, therefore the H2O entering to reduce the conc of is retained. Final State Osmi = Osmo H2O conc equal Solute conc equal No further net diffusion, or osmosis. After equilibration, cell is swollen
What would happen if a cell is placed in a solution with a lower osmolarity, but the membrane is impermeable to all solutes, but permeable to water
H2O diffuses down its concentration gradient.
Solute can’t diffuse out, therefore the H2O entering to reduce the conc of is retained.
Final State Osmi may not be able to equilibrate with Osmo.
After equilibration, cell is swollen and may rupture.
Why is osmolarity not a reliable guide for cell systems
because it does not depend on cell permeability.
What is the importance of the Na+ pump
Virtually makes the cell impermeable to Na+, offsets the effects of high concs of protein in cells.
Define tonicity and why is it a more useful concept than osmolarity
Tonicity defines the “strength” of a solution as it affects final cell volume.
Tonicity depends on BOTH cell membrane permeability & solution composition - hence depends on cell type
Describe a hypertonic solution
Osm of impermeant solutes out > in, so cell shrinks in the solution. Solution is hypertonic.
Describe a hypotonic solution
Osm of impermeant solutes out < in, so cell swells in the solution.
Solution is hypotonic.
Describe an isotonic solution
Osm of impermeant solutes out = in,
so cell volume is unchanged.
The solution is isotonic.
