Fluid Compartments and Solutes

Question 1

What is an osmole

Answer 1

The number of moles of solute that contributes to the osmotic pressure of a solution
Increased osmolarity = increased number of solute particles

Question 2

Is the inside of the cell more acidic than outside

Answer 2

Yes

Question 3

Tonicity

Answer 3

The strength of a solution which contributes the final cell volume. Tonicity depends on both cell membrane permeability and the solution composition

Question 4

Hypertonic solution

Answer 4

I​n a hypertonic solution, the osmolarity of the impermeant solutes outside the cell are greater than those inside the cell. The cell therefore shrinks in the solution.

Question 5

Hypotonic solution

Answer 5

n a hypotonic solution, the osmolarity of the impermeant solutes outside the cell are less than those inside the cell. The cell therefore swells in the solution.

Question 6

Isotonic solutions

Answer 6

​n an isotonic solution, the osmolarity of the impermeant solutes outside the cell is identical to those inside the cell. The cell volume therefore remains the same.

Question 7

Why don’t cells normally burst

Answer 7

Cell membrane (dashed line) is permeable to H2O molecules ( blue circles). The concentration of impermeant solutes (proteins, orange squares) is higher inside the cell than in the interstitial fluid.
The cells don’t burst because the Na+K+-ATPase maintains the concentration of Na+ ions (cyan squares) much lower inside the cell than outside. 
The ATPase makes the membrane “effectively impermeable” to Na+ because any Na+ that diffuses in down the Na+ concentration gradient is actively pumped out again. Thus there is no net movement of Na+ across the membrane.
The intracellular osmolarity of impermeant solutes (mainly proteins at high concentration and low concentration Na+) balances the extracellular osmolarity of impermeant solutes (mainly high concentration Na+).

Question 8

When does the NaKATPase stop working, at what temperature

Answer 8

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 - this is formulated to reduce hypothermic cell swelling and enhance preservation

Question 9

Three main factors to reduce cell swelling in UW infused tissues

Answer 9

Three main factors serve to reduce cell swelling in UW-infused tissues:
• Lack of Na+ or Cl- (therefore no influx possible).
• Presence of extracellular impermeant solutes (lactobionate ions, raffinose).
• Presence of a macromolecular colloid (starch)
Allopurinol and glutathione acts as an antioxidants, helping to protect the organs from damage from reactive oxygen species (ROS).

Question 10

Colloid pressure

Answer 10

​n a normal capillary, higher concentrations of plasma proteins inside the capillary than outside, generates an osmotic pressure known as the colloid osmotic pressure (COP). The flow of blood through the vessel also generates a hydrostatic pressure inside the vessel which is greater than that in the tissues though which it is passing. Thus, there is a tendency to “push” molecules though the capillary pores.

Question 11

Oedema

Answer 11

Oedema results due to an imbalance in the normal cycle of fluid exchange in tissues causing fluid to accumulate in the interstitial spaces. A common cause of oedema is an increase in the permeability of capillary walls. I​n a leaky capillary, proteins are lost through an increase in pore size which reduces the COP and so fluids are more readily pushed out from the capillary.

Question 12

How does the lymph fluid return to the circulation

Answer 12

Via the lymphatic duct in the subclavian region or via lymph nodes

Question 13

How does in a oedema form

Answer 13

When the leakage of plasma into the interstitium exceeds the capacity of the lymphatics to collect and return it to the circulation, oedema will result as fluid accumulates in the interstitial space.


Question 14

Why can breast cancer survivors have oedema

Answer 14

The breast cancer survivor is likely to have had axillary (armpit) lymph nodes removed as part of her diagnosis or treatment. This can remove the pathway of drainage from the upper limb on the affected side, resulting in the accumulation of fluid.

Question 15

Elephant iris

Answer 15

n elephantiasis, parasitic worms can block lymphatic vessels, thereby preventing drainage of the lymph

Question 16

High blood pressure and oedema

Answer 16

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.


Question 17

Inflammatory oedema

Answer 17

Oedema is one of the cardinal signs of inflammation. - infectious and inflammatory stimuli often results in oedema