Tissues 5- Fluid Compartments of the Body

Question 1

What are the main fluid compartments in the body, with values relating to a 70kg man

Answer 1

Intracellular fluids- 23L and 55%
Extracellular fluids - 19L and 45%

Interstitial fluid between cells- 15L and 36%
Blood plasma 3L 7%
Transcellular fluid 1L 2%

Question 2

Describe the composition of fluids in the body

Answer 2

Cations

• Na+ is the main cation in the EC
• K+ is the main IC cation
• Free Ca2+ low IC concentration- small changes in number of ions makes a big difference in concentration – signals therefore easily produced

Anions

• Cl- main EC anion
• Organic phosphates main IC anion
• Proteins—low concentrations in EC and IC – high charge and high molecular weights

pH
- IC more acidic than EC.

Question 3

What is osmolarity

Answer 3

A measure of the concentration of solute particles in a solution

Question 4

What is tonicity

Describe the terms hypertonic, hypotonic and isotonic

Answer 4

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

• if cell shrinks in the solution, the solutionis hypertonic. (osmolarity of impermeant solutes out > inside
  the cell- water moves out)
• if cell swells in the solution, the solution is hypotonic. (osmolarity of impermeant solutes out < inside of
  the cell- water moves in)
• If cell volume is unchanged, the solution is isotonic. (osmolarity of impermeant solutes out = inside of
  cell)

Question 5

Describe Passive transport

Answer 5

 Passive: down an electrochemical (charge and concentration) gradient

• Through lipid bilayer: e.g. lipids, oxygen, carbon dioxide, steroid hormones
• Through pores/channels: e.g. water, ions, urea. some are gated by chemical ligands/voltage, therefore can
  exist as open/closed.
• On carriers: e.g. facilitated diffused of lactic acid out of muscle cells after exercise. Characteristic binding of
  carrier to solute followed by a conformational change, therefore specific.

Question 6

Describe active transport

Answer 6

 Active: can transport up an electrochemical (charge and concentration) gradient, often on carriers

• Primary: uses ATP hydrolysis energy, e.g. Na/K pump
• Secondary: uses “down-hill” movement of one solute COUPLED to “up-hill” movement of a different solute,
  e.g. Na moving into cell coupled with H+
  , Ca, glucose

Question 7

Describe Endocytosis/exocytosis and examples of both

Answer 7

 Endocytosis/Exocytosis: encapsulation in membrane as solute enters or before it leaves the cell. Generally
large molecules.

• Endocytosis of nerve growth factors
• Exocytosis of peptide hormones from endocrine glands

Question 8

What is Colloid Osmotic Pressure?

How does that affect the fluid movement in capillaries?

Answer 8

Colloid Osmotic Pressure (COP) - Osmotic Pressure due to plasma protein

COP draws water in

Hydrostatic pressure pushes water out

Solute and fluid movement across a vessel wall is determined by the balance between the opposing pressures.

Hydrostatic Pressure > COP = Plasma Leaks Out

Hydrostatic Pressure < COP = Flow Into Vessel

Question 9

What is oedema

Answer 9

Oedema - swelling of a tissue because of excess interstitial fluid

Causes: 
Imbalance of forces causing fluid to move between the: 
Blood Plasma 
Interstitium 
Lymphatic Vessels 

This causes an increased permeability of capillary walls to plasma proteins.

when the leakage of plasma into the interstitium exceeds the capacity of the lymphatics to collect and return it to the circulation - fluid accumulates in the interstitial space resulting in swelling.

Question 10

Where does lymph fluid return to

Answer 10

Lymph fluid returns to the circulation in nodes (50%) or in the lymphatic ducts in the subclavian region (50%).