Fluid Compartments And Solutes Flashcards
What is the most abundant cation in the plasma?
Most abundant cation inside cells?
Are chlorides found at a higher conc intracellularly or in the plasma?
Most abundant cation in the plasma = Na+
Most abundant cation within cells = K+ high intracellular conc of K+ is neutralised by anions e.g proteins, nucleic acids
Cl- is higher in conc in the plasma than inside cells.
What is the main intracellular anion and what are its roles?
Why are proteins anions?
What is the pH of the cell inside compared to the plasma?
Are there differences in the osmolarity of cells intracellularly and in the plasma?
Organic phosphate is the main intracellular anion. Has roles in ATP production, cell signalling, phosphorylates proteins for their activation and inactivation.
Proteins are anions as they have net negative charge.
Inside of the cell is slightly more acidic than plasma.
Osmolarity between blood and intracellular compartment is identical so there’s not normally a significant osmotic effect. Except in regions of the kidney where fluids are concentrated.
Define the term diffusion
Define the term osmosis
What is an osmole?
Diffusion = the spontaneous movement of a solute down a conc grad until the solute molecules reach an equilibrium.
Osmosis = the movement of water down its concentration gradient (through a semi permeable membrane). Osmosis moves water toward an area of higher osmolarity, hence can change cell volume, which has consequences for cell function and survival.
Osmole = the number of moles of solute that contribute to the osmotic pressure of a solution.
Why can there be no net change in the volume of a cell even if the osmolarity inside the cell is greater than the osmolarity outside the cell?
If the membrane is permeable to both water and solute then there will be no net change to the volume of the cell as water and solute are able to diffuse in and out.
What is tonicity?
Tonicity = strength of a solution, it affects the final cell volume. Tonicity depends on cell membrane permeability and solution composition.
Define the following terms:
Hypertonic solution
Hypotonic solution
Isotonic solution
Hypertonic solution: osmolarity of the impermeant solutes outside the cell are greater than inside the cell. Hence, cell shrinks in solution as water moves out by diffusion.
Hypotonic solution = osmolarity of impermeant solutes outside the cell are less than those inside cell. Cell therefore swells in solution.
Isotonic solution = osmolarity of impermeant solutes outside the cell is identical to those inside the cell. The cell volume removes the same (net diffusion = 0).
The concentration of impermeant solutes (proteins) is much higher inside the cell than in the interstitial fluid or plasma, so why don’t cells burst?
Cells don’t burst because the N+K+ATPase pump maintains the concentration of Na+ ions to be much lower inside the cell than outside.
The sodium potassium pump makes the membrane effectively impermeable to Na+, any sodium ions that diffuse in down their concs grad are actively pumped back out. Hence, the intracellular osmolarity of impermeant solutes balances the extracellular osmolarity of impermeant solutes.
When transporting donated organs and tissues why do ischaemic changes occur?
How can these ischaemic changes be slowed down?
What is a problem that accompanies the method used to slow down ischaemic changes and allow more time for transportation?
When any tissue loses its blood supply, ischaemic changes occur.
This can be significantly slowed down by rapid cooling of the tissue/organ to 4oC. Tissues are perfumed w cold solutions via the arterial supply. Even when cooled, tissues/organs deteriorate.
The sodium potassium pump stops functioning below 15oC and without circulation there little O2 and hence little ATP to fuel the pump. Na+ will enter the cell (along w Cl-) and water will also enter as K+ exits. Cells are likely to swell & membranes bleb —> cell death.
What precautions can be taken to prevent cell swelling and death during the transportation of donor organs?
What 3 main factors reduce cell swelling?
What protects organs from damage from reactive oxygen species?
Perfusion organs with the university of Wisconsin solution (UW). Formulated to reduce hypothermic cell swelling and enhance preservation.
3 main factors serve to reduce cell swelling in UW infused tissues:
- lack of Na+ or Cl- (so no influx possible)
- presence pressure extracellular impermeant solutes (lactobionate ions, raffinose)
- presence of macromolecular colloid (starch)
Allopurinol and glutathione act as antioxidants and protect organs from damage from ROS.
How many litres of plasma leaks out of blood vessels each day?
8L of plasma leaks out of blood vessels. Vol of blood plasma is ~3L, so the entire plasma volume passes into interstitial space and back into the blood circulation every 9 hours.
How do the following molecules traverse the porous endothelial cells that line blood vessels?:
Lipid soluble subs
Small water soluble subs
Plasma proteins
Exchangeable proteins
Lipid soluble subs: pass THROUGH the endothelial cells
Small water soluble substances: pass through the PORES between cells
Plasma proteins: generally can’t cross the endothelial cell membranes and can’t get through the pores between cells
Exchangeable proteins: moved across by vesicular transport
What is the colloid osmotic pressure (COP)?
Why is there a tendency to push molecules through the capillary pores?
Colloid osmotic pressure = osmotic pressure generated in the capillaries as there is a higher conc of plasma proteins inside the capillary than outside.
There is a tendency to push molecules through the capillary pores due to the flow of blood through the vessel which generates a hydrostatic pressure inside the vessel which is greater than that in the tissues which it’s passing through.
COP draws solute and fluid into the vessel, but the slightly higher hydrostatic pressure results in net leakage from the capillary under normal conditions.
Define the term oedema
What causes oedema?
Oedema = accumulation of fluid in the interstitial spaces caused by an imbalance in the normal cycle of laid exchange in tissues.
Common cause of oedema: increase in the permeability of capillary walls. Leaky capillary has increased pore size which reduces COP and so fluids are more readily pushed out from the capillaries.
- High BP increases hydrostatic pressure —> more fluid pushed out of vessels -> can lead to accumulation in IF
- axillary lymph nodes being removed -> removes pathway of drainage from upper limbs on the affected side -> accumulation of fluid
- elphantiasis - parasitic worms can block lymphatic vessels.
The lymphatic system returns interstitial fluid/plasma j to the blood circulation, where does lymph fluid enter the lymphatic system?
What happens when the leakage of plasma into the interstitium exceeds the capacity of the lymphatics?
Lymph fluid enters the lymphatic system via the lymphatic ducts in the subclavian region or via lymph nodes.
Oedema results.
What is oedema a cardinal sign of?
Oedema is a cardinal sign of inflammation. Infectious and inflammatory stimuli often result in oedema.
