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.
What is the situation with normal cells in the body
Their membranes are permeable to H2O , and the concentration of impermeant solutes (proteins) is higher inside the cell than in the interstitial fluid, so why don’t cells burst?
Why don’t body cells burst
The cells don’t burst because the Na+pumps maintain the concentration of Na+ lower inside the cell than outside.
The cells don’t burst because the Na+pumps maintain the concentration of Na+ lower inside the cell than outside.
The pump makes the membrane “effectively impermeable” to Na+
because any Na+ that diffuses in down the Na + concentration gradient is pumped out again. Thus there is no net movement of Na+ across the membrane.
The intracellular osmolarity of impermeant solutes (mainly high conc proteins and low conc Na+) balances the extracellular osmolarlity of impermeant solutes (mainly high conc Na+).
Cells have to actively maintain this state.
What is transcytosis
Substance transported from one side of the cell to the other, often happens in endothelial cells
Simply, describe endocytosis and exocytosis
Endocytosis and exocytosis - encapsulation
in membrane as solute enters or before it leaves
the cell.
What happens when tissues lose their blood supply
When any tissue loses its blood supply, ischaemic changes occur, but these can be significantly slowed by rapid cooling of the tissue/organ to 0 - +4°C.
Tissues are perfused with cold solutions via the arterial supply.
Even when cooled, tissues/organs deteriorate.
The composition of the perfusion solution can reduce the deterioration in hypothermia, prolonging the time available to transport and keep viable.
What may happen to the water and electrolytes in cells after cooling
Sodium pumps stop working below 15°C. (also no O2 or ATP to fuel the pump)
What will happen to electolytes?
Na+ will enter the cell (with Cl-) and water will also enter, K+ exits.
Cells will swell and bleb which can cause cell death.
Blood can clot when blood is supplied again.
What is the University of Wisconsin solution
formulated to reduce hypothermic cell swelling and enhance preservation.
no Na+ or Cl- (no influx possible)
extracellular impermeant solutes (lactobionate ions, raffinose (a sugar))
macromolecular colloid (starch)
Together, these factors reduce cell swelling in cooled tissues.
UW mimics interstitial fluid- but no Na+ or Cl-
How much blood plasma leaks out of the blood every day
Each day, 8L of plasma leaks out of blood vessels. Since the volume of blood plasma is ~3L, the entire plasma volume must pass into the interstitial space and back into the blood circulation every 9 hours!
What substances can normally be exchanged through the capillary wall
Plasma proteins generally cannot cross the endothelial cell membranes & cannot get through the pores between cells
lipid-soluble substances pass through the endothelial cells
Exchangeable proteins are moved across by vesicular transport
Small water-soluble substances pass through the pores between cells
What are the opposing pressures in a capillary
Osmotic pressure due to plasma proteins (colloid osmotic pressure (COP)): more protein inside than outside the vessel
Hydrostatic pressure due to blood pressure
Solute and fluid movement across a vessel wall is determined by the balance between the opposing pressures.
What happens in a leaky capillary
Excess fluid loss from capillary to intersitital space: oedema
Increased pore size
Hydrostatic pressure»osmotic pressures
What is oedema
oedema (edema): swelling of a tissue because of excess interstitial fluid
When does oedema occur
Causes: imbalance in the normal cycle of fluid exchange in tissues causing fluid to accumulate in the interstitial spaces.
Fluid is constantly being lost from blood vessels, passing into the interstitium to be drained by lymphatic vessels.
When this is disrupted, oedema occurs
When the leakage of plasma into the interstitium exceeds the capacity of the lymphatics to collect and return it to the circulation, fluid accumulates in the interstitial space resulting in swelling:
What is the role of lymphatic capillaries
Lymphatic capillaries collect interstitial fluid that is destined for return to the blood circulation.
Capillaries- Interstitial fluid- lymph capillaries- lymph veins- lymph ducts- large circ. vein
Pressure decreases form left to right.
What is the role of the lymphatic system
The Lymphatic System returns interstitial fluid to the blood circulation
Lymph fluid returns to the circulation in nodes (50%) or via the lymphatic ducts in the subclavian region (50%).
What is oedema a sign of
Oedema is one of the cardinal signs of inflammation. Infectious and inflammatory stimuli usually result in oedema.
Inflammatory cells make capillary walls more leaky to let plasma proteins that will resolve inflammation enter the tissue.
What is hydrostatic oedema
This individual is likely to have high blood pressure, which means increased hydrostatic pressure in vessels. This pushes more fluid out of the vessels, and can lead to accumulation of interstitial fluid.
Describe the other causes of oedema
Both of these cases involve compromised function of the lymphatics.
The breast cancer survivor is likely to have had axillary (armpit) lymph nodes removed as part of her diagnosis/treatment. This can remove the pathway of drainage from the upper limb on the affected side, resulting in the accumulation of fluid.
In elephantiasis, parasitic worms can block lymph vessels, thereby preventing lymphatic drainage. In this case, the lymphatics in the right groin region will have been blocked, preventing the drainage of interstitial fluid from the right lower limb
