Topic 5 - Interstitia fluid (ISF): transport through the capillary wall; measurement and composition of ISF

Question 1

Words to include in interstitial fluid (ISF): transport through the capillary wall

Answer 1

Formation of ISF

• Intravascular space
• Interstitial space
• Transport through capillary wall
  
  • Small molecular weight
    
    • Water
    • Electrolytes
    • Anelectrolytes
  • Permeate
  • Protein movement restricted
    
    • Sinusoids in liver (ø)
  • Pinocytosis
  • Exocytosis
  • Capillary wall
    
    • Collid barrier
    • Endothel
    • Basement membrane
  • Fenestration
  • Interendothelial ways
  • Transcellular way
  • Cytosis
    
    • Endocytosis
    • Exocytosis
    • Pynocytosis
• Forces determining transport
  
  • Diffusion
    
    • No restriction
  • Osmotic conditions
  • Electric forces
  • Hydrostatic forces
  • Theorem
    
    • Dialyzing
      
      • Capillary
      • Interstitium
  • Electroneutrality
    
    • Anions
    • Cations
  • Thermodynamic rule
• Gibbs-Donnan balance
  
  • Electroneutrality prevails
  • E_anion + E_cation = 0
  • Distribution quotient
  • Protein anions
  • Diffusible ion concentrations
    
    • Intravasal compartments
    • Interstitium

Capillary / ISF balance

• Hydrostatic pressure
  
  • Water out of plasma
• Osmotic pressure
  
  • Water into plasma
• Filtration
  
  • Arterial end of capillary
  • Hydrostatic pressure ↑
  • Oncotic pressure ↓
• Resorption
  
  • Venous end of capillary
  • Oncotic pressure ↑
  • Hydrostatic pressure ↓
• Oedema
  
  • ISF overproduction
  • Isoosmotic hypervolemia
    
    • Local
    • General

Question 2

Words to include in measurement and composition of ISF

Answer 2

Measurement of ISF

• ISF = EC - intravasal volume

Composition of ISF

• Cations
  
  • Na⁺
  • K⁺
  • Mg²⁺
  • Ca²⁺
• Anions
  
  • Cl^-
  • HCO₃^-
  • Protein filtrated
• Lymph
  
  • Lymph capillaries
  • Valves
  • Lymph nodes
  • Ductus thoracicus
  • Intersitial drainage
  • Protein resorption
  • Content of lymph:
    
    • Fat
    • Protein
    • Lymphocyte
• IC fluid
  
  • Protozoa
    
    • Excrete water actively
    • Water pump
  • Plant cell
    
    • Osmotic pressure
    • Thick cell wall
  • Mammalian cell
    
    • Active ion transport
    • Water pump

Question 3

Which factors determine the formation of ISF?

Answer 3

1. Transport through the capillary wall
2. Forces determining transport

Question 4

ISF: transport through the capillary wall

Transport of various molecules

Answer 4

• Water, electrolytes and anelectrolytes with small molecular weight can permate the capillary wall without restriction
  
  • ​Protein movement is restricted (only a small amount can get to the ISF)
    
    • Mainly by:
      
      • Pinocytosis
      • Exocytosis
  • Protein concentration of the ISF is high due to proteins being large enough that they cannot return to the capillary
  • Sinusoids in the liver are permable for proteins
  • Capillary wall is a barrier for colloids
    
    • They are transported with specific carrier system

Question 5

ISF: transport through the capillary wall

Give the different types of pathways

Answer 5

1. Through fenestration
2. Through interendothelial ways
3. In a transcellular way
4. By cytosis
   
   • ​​Endocytosis
   • Exocytosis
   • Pynocytosis

Question 6

ISF: transport through the capillary wall

Forces determining transport

Answer 6

• Composition of the ISF is determined by:
  
  • Diffusion
    
    • ​Most important force to ensure transport of substances
    • The greatest part of substances crossing the capillary membrane is transported in this way
    • Particles moving without restriction continuously as a result of diffusion
  • Osmotic conditions
  • Electric forces
  • Hydrostatic forces
• Theorem:
  
  • If the movement of some component is restricted between two compartments the concentration of the diffusible ions will be different in the two compartment after the balance develops
• Principles:
  
  • Electroneutrality
    
    • Total amount of anions and cations have to be equal in certain compartments
  • Thermodynamic rule
    
    • Product of the concentrations of diffusible ions must be equal to both sides of the membrane

Question 7

Electroneutrality

Answer 7

• Balance of distribution caused by proteinate anion
  
  • ​Gibbs-Donnan balance
• Electronetrality prevails
  
  • E_anion + E_cation = 0
• According to the rules of Gibbs Donnan balance the diffusible ion concentrations in the intravasal compartment and the interstitium may hardly differ
• There is a much smaller difference between the protein concentration in the plasma and the ISF than between the protein concentration of the IC compartment and that of the ISF
• Permeability of the cell membrane for electrolytes is regulated

Question 8

Capillary / ISF balance

Answer 8

• Osmotic pressure moves water into plasma
• Hydrostatic pressure moves water out of plasma
• Filtration on the arterial end of capillary:
  
  • Hydrostatic pressure is higher than osmotic pressure
• Resorption on the venous end of the capillary:
  
  • Oncotic pressure is higher than hydrostatic pressure

Question 9

Cause of oedema

Answer 9

• ISF overproduction
  
  • ​Isoosmotic hypervolemia, local or general
• Diagnostic sing:
  
  • After pressing the edematous area with the hand the area keeps the impression of the hand
  • As the fluid having been pressed out of the can reenter only slowly to its original place

Question 10

Meaurement of ISF

How to calculate ISF?

Answer 10

ISF = EC - intravasal volume

Question 11

Composition of ISF

Answer 11

• Cations
  
  • ​Na⁺
  • K⁺
  • Mg²⁺
  • Ca²⁺
• Anions
  
  • ​Cl^-
  • HCO₃^-

Question 12

Lymph

1. Role
2. Composition

Answer 12

1. Role:
   
   • Interstitial drainage
   • Protein resorption
2. Content:
   
   • Fat
   • Protein
   • Lymphocyte