Fluid Compartments and Solutes

Question 1

What cations are found in molecules?

Answer 1

Sodium is most plentiful cation in plasma

Potassium is most plentiful cation in cells

Question 2

What anions are found in molecules?

Answer 2

Organic phosphate is the main intracellular anion and is a key metabolite with roles in ATP production and cell signalling

Question 3

How does the pH inside a cell compare to plasma?

Answer 3

Inside a cell is slightly more acidic than plasma

Question 4

How does osmolarity compare between in a cell to plasma?

Answer 4

Osmolarity between blood and intracellular compartment is identical- there’s not really an osmotic effect
One exception is regions of the kidney where fluids are concentrated

Question 5

What is osmosis?

Answer 5

Movement of water towards an area of high osmolarity

Question 6

Define osmole

Answer 6

The number of moles of solute that contribute to the osmotic pressure of a solution

Question 7

What is tonicity?

Answer 7

Defines the strength of a solution as it affects the final cell volume
It depends on both cell membrane permeability and solution composition

Question 8

What is a hypertonic solution?

Answer 8

In a hypertonic solution, osmolarity of impermeant solutes outside cell are greater than those inside cell
Therefor cell shrinks in solution

Question 9

What is a hypotonic solution?

Answer 9

Osmolarity of impermeant solutes outside cell are less than those in the cell
Cell swells in solution

Question 10

What is an isotonic solution?

Answer 10

Same osmolarity inside and outside cell

Question 11

Why don’t cells bursts?

Answer 11

Cells don’t burst because of the Na+/K+/ATPase pump - maintains a low conc. of Na+ in cells

Na+ is actively pumped out so there’s no net movement of Na across cell

Question 12

What methods are used by solutes to cross membranes?

Answer 12

Active transport: uses ATP hydrolyse

Passive transport: transporter-mediated, channel-mediated,

Question 13

How are tissues/ organs preserved?

Answer 13

In transport of tissues and organs they are perfused with cold solutions via arterial supply to rapidly cool the tissue/ organ to 4 deg. C- sows ischaemia

Na+/K+/ATPase stops functioning below 15 deg. C- little ATP to fuel pump
This means reactions need to be taken to stop Na and water entering cells and K+ exiting- could cause cells to burst

Question 14

What precautions are taken to prevent cell death in organs being transported or transplantation?

Answer 14

Perfuse organs with University of Wisconsin solution (UW)- formulated to reduce hypothermic cells shrinking and enhance preservation
UW infused tissue has:
-lack of Na+ or Cl-
-presence of extracellular impermeant solutes
-presence of macromolecular colloid

Question 15

What is the importance of exchange between blood and tissue?

Answer 15

Each day 8L of plasma leaks out of blood vessels
Since volume of blood plasma is 3L entire plasma volume must pass into interstitial space and back into circulation blood every 9 hours

Question 16

How do molecules leave plasma?

Answer 16

Plasma proteins are too big to pass through endothelium
Lipid-soluble substances pass through endothelial cells
Exchange proteins are moved across by vesicular transport
Small water-soluble substances pass though pores between cells

Question 17

Why are molecules pushed through capillary pores?

Answer 17

In a normal capillary there’s a higher conc. of plasma proteins inside capillary than outside, this generates an osmotic press known as colloid osmotic pressure
Flow of blood through the vessel also generates a hydrostatic pressure inside the vessel which is greater that in the tissue its passing
Thus there’s a tendency to push molecules through capillary pores

Question 18

How does a normal capillary differ from a leaky one?

Answer 18

Solute and fluid movement across a vessel wall is determined by the balance between these opposing pressures (Colloid osmotic pressure and hydrostatic pressure)

In a normal capillary, although COP draws solute and fluid into the vessel, slightly greater hydrostatic pressure results in net leakage from the capillary under normal circumstances

Question 19

What is oedema?

Answer 19

Accumulation of fluid within tissues

Its due to an imbalance in normal cycle of fluid exchange in tissues causing fluid to accumulate in interstitial space

Question 20

What is a common cause of oedema?

Answer 20

Increased permeability of capillary walls

Question 21

What happens in a leaky capillary?

Answer 21

Proteins are lost through an increase in pore size which reduces COP so fluids are more readily pushed out of capillary

Question 22

What is the role of lymphatic capillaries?

Answer 22

To combat loss of plasma fluids of tissues, lymphatic capillaries collect interstitial fluid thats destined for return to the blood circulation

Fluids are constantly being lost from blood vessels and passed into interstitum bro be drained by lymphatic vessels

Question 23

How does lymph fluid return to circulation?

Answer 23

Via lymphatic ducts in subclavian regions or via lymph nodes

Question 24

When does oedema occur in relation to lymphatics?

Answer 24

When leakage of plasma in interstitum exceeds capacity of lymphatics to collect and return it to circulation

Question 25

What is inflammatory oedema?

Answer 25

Oedema is one of the first signs of inflammation

Question 26

What is hydrostatic oedema?

Answer 26

High blood pressure can lead to increased hydrostatic pressure in vessels
This pushes more fluid out of vessels and can lead to accumulation of interstitial fluid

Question 27

What is elephantiasis?

Answer 27

Parasitic worms can block lymphatic vessels therefor preventing drainage of the lymph

Question 28

How do you calculate osmolarity?

Answer 28

Multiply the concentrations (mmol/l) of each molecule by the number of ions in it

e.g. in NaCl there are 2 ions (1x Na and 1x Cl)

Glucose counts as 1 molecule

Question 29

What is the units of osmolarity?

Answer 29

Mosmol/l