Fluid compartments and solutes

Question 1

What are anions and examples?

Answer 1

• Organic phosphate main intracellular anion (key intracellular metabolite roles in ATP production and cell signalling)
• Phosphorylation of proteins for activation and inactivation
• Proteins are anions with mostly net negative charge (although low conc, highly -ve charge)
• inside cell more acidic than plasma - 2 fold difference in proton conc
• Blood and intracellular compartment osmolarity identical so no significant osmotic effect (except kidney)

Question 2

What are cations?

Answer 2

• Sodium in plasma
• Potassium in cell (neutralsied by anions e..g protein, nucleic acids and phosphorylated proteins)
• Extracellular chloride high conc in plasma than cell

Question 3

What is osmolarity?

Answer 3

Osmolarity is measure of conc of all solute particles in a solution - too simple concept and unreliable as not depends on cell permeability instead use tonicity

Question 4

What is tonicity?

Answer 4

Toncity: strength of solution as affects final cell volume - depends on cell membrane permeability and solution composition

Question 5

What is hypertonic solution?

Answer 5

-Osmolarity of impermeant solutes outside the cell are greater than inside cell - so cell shrinks in solution

Question 6

What is a hypotonic solution?

Answer 6

-Osmolarity of impermeant solutes outside the cell are less than inside cell - so cell swells in solution

Question 7

What is an isotonic solution?

Answer 7

-Osmolarity of impermeant solutes outside the cell are identical to in inside cell - so cell volume stays the same

Question 8

Why don’t cells burst?

Answer 8

Cells don’t burst as Na+k+ATPase maintains conc of Na+ ions much lower inside cell than outside
ATPase makes membrane “effectively impermeable” to Na+ because any Na+ that diffuses down Na+ gradient is pumped out again so no net movement of Na+ across membrane

Question 9

What is important to consider in transplantation?

Answer 9

• Need to be cold
• The composition of the perfusion solution can reduce the deterioration in hypothermia, prolonging the time available to transport and keeping the organ viable
• Notably the Na+K+ATPase stops functioning below 15°C which is compounded by the fact that without circulation there is little O2 and therefore little ATP to fuel the pump. Unless precautions are taken, Na+ will enter the cell (along with Cl-) and water will also enter as K+ exits. Cells are likely to swell and their membranes bleb, resulting in cell death.
• One precaution is to perfuse the organ with a solution known as University of Wisconsin solution (UW). This is formulated to reduce hypothermic cell swelling and enhance preservation.

Question 10

What are the three main factors to reduce cell swelling in UW-infused tissues?

Answer 10

Lack of Na+ or Cl- (therefore no influx possible).
Presence of extracellular impermeant solutes (lactobionate ions, raffinose).
Presence of a macromolecular colloid (starch).

Question 11

What is exchange across capillary wall like?

Answer 11

• All blood vessels (e.g. arteries, capillaries, veins, lymphatics) are lined by endothelial cells which have pores.
• Each day, 8L of plasma leaks out of blood vessels. Since the volume of blood plasma is around 3L, the entire plasma volume must pass into the interstitial space and back into the blood circulation every 9 hours
• In normally capillary higher conc of plasma proteins inside capillary than outside generated colloid osmotic pressure (COP)
• Flow of blood create hydrostatic pressure so “push” molecules through
• Solute and fluid moment across vessel wall determined by balance between these two
• In a normal capillary although the COP draws solute and fluid into the vessel, the slightly greater hydrostatic pressure results in net leakage from the capillary under normal conditions.

Question 12

What is an oedema?

Answer 12

• Oedema describes accumulation of fluids within tissues and results due to imbalance in normal cycle of fluid exchange in tissues causing fluid to accumulate in interstitial spaces
• Cause by increase permeability walls
• In leaky capillary, proteins lost through an increase in pore size so reduces COP and so fluids more readily pushed out from capillary

Question 13

What are lymphatic capillaries?

Answer 13

• To combat loss of plasma fluids into tissues, lymphatic capillaries collect interstitial fluid that is destined to return to the blood circulation
• Fluid constantly lost from blood vessels passing into interstitial to be drained by lymphatic vessels
• Lymph fluid returns to circulation via lymphatic ducts in subclavian region or via lymph nodes
• When leakage of plasma into the interstitial exceeds capacity of lymphatics to cleat and return in to circulation, oedema result as fluid accumulates in interstitial space

Question 14

What is an inflammatory oedema?

Answer 14

• Oedema sign of inflammation
• Infectious and inflammatory stimuli often results in oedema
• Inflammation around sites of insect bites as caused local blood vessels to become leaky
• Swelling occurs as rate of leakage from vessel greater than rate at which lymphatics can drain it

Question 15

What is a hydrostatic oedema?

Answer 15

• High BP (if overweight) so increased hydrostatic pressure in vessels and so pushes kore fluid out of vessels and can lead to accumulation of interstitial fluid
• Compromised function of the lymphatics (in elephantiasis and breast cancer survivor)
• Breast cancer: ancillary lymph nodes removed as part of treatment/diagnosis so can remove pathway of drainage from the upper limb on the affected side so accumulation of fluid
• Elephantiasis, parasitic worms block lymphatic vessels, preventing drainage of the lymph, lymphatics in right groin region blocked preventing drainage of interstitial fluid from right lower limb