Fluid Compartments

Question 1

List the main fluid compartment and sizes in a 70kg man

Answer 1

• Intracellular = 55% of body water

- Extracellular = 45% of body wate

Question 2

How can the extracellular fluid be subdivided?

Answer 2

Transcellular fluid - cerebrospinal, ocular, synovial = 2%

Blood plasma = 7%

Interstitial Fluid = 36%

Question 3

The Composition of the Main Fluid Compartments?

Answer 3

Extracellular - 
Na+ = 150
K+ = 5
Ca2+ = 2
Cl- = 110
Or. Phos = 5
Protein = 1
pH = 7.4

Intracellular - 
Na+ = 10
K+ = 150
Ca2+= 10^-4
Cl- = 5
Or. Phos = 130
Protein = 2
pH = 7.1

Question 4

Describe the Composition of the main fluid compartments?

Answer 4

CATIONS
Sodium - present in high concentrations outside cells
Potassium - present in high concentration inside cells
Calcium = important signalling ion, v. low concentrations inside cells, except in organelles which stores it (ER,SR)

ANIONS -
Chloride = high conc outside cells
Or. Phos. = high concentration inside the cells
Proteins = Anions present in low concentration and have a high charge

pH = slightly higher outside the cell than inside. lower H+ concentration ouside cell

Question 5

What is Osmolarity

Answer 5

Osmolarity - the concentration of a solution expressed as the total number of solute particles per litre.

Question 6

What is Tonicity?

Answer 6

a measure of the effective osmotic pressure gradient, as defined by the water potential of two solutions separated by a semipermeable membrane.

Question 7

What happens during Osmosis?

Answer 7

Osmosis moves water towards area of higher osmolarity and can change cell volume.

Question 8

Which one is more useful Osmolarity or Tonicity?

Answer 8

Tonicity - More useful, defines strength of a solution as it affects final cell volume. Depends on:

• Cell Membrane Permeability
• Solution Composition

Osmolarity does not depend on the cell permeability

Question 9

What is a Hypertonic Solution?

Answer 9

• Osmolarity of impermeant solutions: out>in
• Cell shrinks in solution
• Solution is hypertonic

Question 10

What is a Hypotonic Solution?

Answer 10

• Osmolarity of impermeant solutes: out

Question 11

What is an Isotonic Solution?

Answer 11

• Osmolarity of impermeant solutes: out=in
• Cell volume is unchanged
• Solution is isotonic

Question 12

Describe the Tonicity of real cells?

Answer 12

• Membranes are permeable to water
• Concentration of impermeable solutes is higher inside than outside the cell but they do not burst
• Due to Na/K pump that maintains a lower conc of Na+ inside the cell than outside.
• no net mvt of Na+ across the membrane
• cells have to actively maintain this state

Question 13

Summarise the methods of transport through the membrane

Answer 13

Passive - Down the EC gradient: -Through Lipid,Pores on Carriers

Active - against the EC gradient:
Primary - (Na/K pump)
Secondary - downhill mvt of one solute coupled to uphill mvt of another

Endo/Exocytosis:

• encapsulating in membrane as solute enters or before it leaves cell
• large molecules

Question 14

How does exchange across the capillary wall work?

Answer 14

• Small pores between endothelial cells.
• 8L of plasma leaks out everyday
• Colloid Osmotic Pressure (COP) - Osmotic pressure due to plasma protein
• COP draws water in
• Hydrostatic pressure - pressure in a circulatory system exerted by the volume of blood when it is confined in a blood vessel. This pushes water out.
• HP>COP = Plasma leaks out
• HP

Question 15

What is Oedema?

Answer 15

• Swelling of a tissue because of excess interstitial fluid.
• Imbalance of forces causing fluid to move between:
  Blood Plasma
  Interstitim
  Lymphatic Vessels
• Increased permeability of capillary walls to plasma proteins.
• Oedema - leakage of plasma into interstitium exceeds capacity of lymphatics to collect and return it to the circulation. Accumulates in the interstitial space.
• One of the cardinal signs of INFLAMMATION.