Topic 33 - The characteristics of the lung circulation, the perfusion of the lungs, gas diffusion in the lungs

Question 1

Words to include

Answer 1

• Inner respiration
  
  • Blood → cell
• Outer respiration
  
  • Blood → outside world

The characteristics of the lung circulation

• Arteries
  
  • Dual blood supply
  • A. pulmonales
    
    • Right ventricle → alveolar capillaries
    • Oxygen deficient blood (99%)
    • Functional
  • Aa. bronchiales
    
    • Oxygen rich blood (1%)
    • Nutritive
• Veins
  
  • V. bronchalis (1%)
    
    • Vv. pulmonalis (99%)
      
      • Lungs → left atrium
      • Oxygenated
  • V. azygous
    
    • Lungs → Right atrium
    • Systemic circulation
  • Contamination:
    
    • Vv. bronchiales
    • Coronary veins
• Oxygen deficiency
  
  • Hypoxia
  • Vasoconstriction
• Cardiac cycle
  
  • ±800 msec
• O₂ & CO₂ diffusion
  
  • 250 msec

Ratio of ventilation and perfusion

• Alveolar air
• Afferent capillary
• Efferent capillary
• Normal condition
  
  • Blood gas balanced with alveolar air
  • Arterialized
• Alveolus is plugged
  
  • Blood flows away unchanged
• Blood flow stops (capillary plug)
  
  • No blood flow
  • Alveolar gas pressure = atmospheric

Influence of gravity on lung circulation

• Low pressure in lung circulation
• Gravitational forces
• Dorsal areas of lung
  
  • Gravitional forces are low
  • Perfusion is absent
  • During systole and diastole: P_alv > P_a > P_v
• Middle areas of lung
  
  • Perfusion is sporadic
  • Alveolar capillaries
    
    • Open during systole
    • Closed during diastole
  • During systole: P_a > P_v > P_alv
  • During diastole: P_^a > P^_alv > P_v
• Ventral areas of lung
  
  • Contiuous perfusion
  • Alveloar pressure can not compress capillaries in systole and diastole
  • During systole and diastole: P_a > P_v > P_alv

Regulation of perfusion

• Neural factors
  
  • Parasympathetic
    
    • N. vagus
      
      • Acetylcholine
    • Vasodilation
  • Sympathetic
    
    • Noradrenic fibers
      
      • α-receptor stimulation
      • Vasoconstriction
    • Adrenalin
      
      • β-receptors
      • Vasodilation
    • α-receptors mainly
  • Adrenalin
    
    • β-receptors
    • Alveolar dilation
    • Ventilation ↑
    • Anaphylactic shock
      
      • Adrenaline reduces reaction
• Hypoxia
  
  • Little oxygen
  • Diameter of blood vesses opposite of in systemic circulation
  • Local hypoxia → local stenosis (constriction)
• Blood pressure
  
  • Blood pressure ↑ → Vascular tone ↓
  • Minute volume

Diffusion of gasses in the lung

• Determined by:
  
  • Partial pressure relations of gases
  • Gas permability of membranes
  • Size of exchange surface
• Maintainance of gas exchange:
  
  • ​Continous and varying oxygen consumption
  • CO₂ production
• Partial gas pressure values of alveolar air
  
  • pO₂ = 100 mmHg
  • pCO₂ = 40 mmHg
• Total exchange
  
  • During first 200 msec

Question 2

Topics to include in the essay

Answer 2

1. Definition of inner respiration and outer respiration
2. The characteristics of the lung circulation
   
   • Arteries
   • Veins
3. The perfusion of the lungs
   
   • Ratio of ventilation and perfusion
     
     • Normal condition
     • Alveolus is plugged
     • Blood flow stops (capillary plug)
   • Influence of gracity on lung circulation
   • Regulation of perfusion
     
     • Neural factors
     • Hypoxia
     • Blood pressure
4. Gas diffusion in the lungs

Question 3

Give the imporance and division of respiration

Answer 3

• Inner respiration: Blood → cell
  
  • ​Energy generating
• Outer respiration: Blood → outside world
  
  • ​Gas exchange
• Respiration is an essntial physological process participating in:
  
  • Oxygen supply
  • CO₂ removal
  • Control of hydrogen ion concentration in blood

Question 4

The characteristics of the lung circulation

Answer 4

• In the functional areas of the lung, the walls of the blood-vesses are thinner than that of the corresponding systemic vessels
  
  • Therefor, lung vessels can take up a larger quantities of blood at lower pressure values than systemic circulation

Arteries

• The lungs has a dual blood supply:
  
  • A. pulmonalis:
    
    • ​Transfers the used blood for gas exchange from right ventricle → alveolar capillaries
    • 99% of the blood supply of oxygen deficeinet blood
    • Functional circulation
  • Aa. bronchales
    
    • ​Aorta → lung tissues
    • 1% of the blood supply to the lungs have oxygen rich blood from aa. bronchales
    • Nutritive circulation

Veins

• Two venous systems lead away blood from the lungs
• V. bronchails
  
  • ​1% of the blood leaves the lungs via v. broncahils
    
    • Part of the blood goes to vv. pulmonalis, thus mixing the local fresh blood with venous blood
• V. azygous
  
  • ​Systemic circulation → right atrium
  • Systemic circulation
• Vv. pulmonales
  
  • ​Lungs → left atrium
  • 99% of the blood coming out of the lungs is oxygenated
• Venous blood contaminates the refreshed blood through two sources:
  
  • V. bronchiales
  • Coronares

Question 5

The perfusion of the lungs

Ratio of ventilation and perfusion

Answer 5

1. Normal condition
   
   • ​Blood gaswill be balanced withalveolar air
     
     • ​Blood flows away arterialized
2. Alveolus is plugged
   
   • ​The arriving blood flows away unchanged (not refreshed)
3. Blood flow stops (capillary plug)
   
   • ​Infinite, no blood flow
   • Alveolar gas pressure = atmospheric

Question 6

The perfusion of the lungs

Influence of gravity on lung circulation

Answer 6

• Because of the very low pressure in the lung circulation, the importance of the gravitational forces affecting the blood is much greater here than in the systemic circulation
• Dorsal areas of the lung:
  
  • ​Ø perfusion
  • The gravitational forces are lower
  • The pressure in the alveoli compresses the blood vessels
  • During systole and diastole: P_alv > P_a > P_v
• Middle areas of the lung:
  
  • ​Perfusion is sporadic
  • The alveolar capillaries are:
    
    • Open during systole
    • Closed during diastole
  • During systole: P_a > P_v > P_alv
  • During diastole: P_a > P_alv > P_v
• Ventral areas of the lung:
  
  • ​Constant perfusion
  • Gravitation increases the blood pressure
    
    • The alveolar pressure can not compress capillaries either during systole or diastole
  • During systole and diastole: P_a > P_v > P_alv

Question 7

The perfusion of the lungs

Regulation of perfusion

Answer 7

Neural factors

• Parasympathetic
  
  • ​Acetylcholine relase from n. vagus → vasodilation
• Sympathetic
  
  • ​Noradrenic fibers gives vasoconstriction
    
    • ​α-receptor stimulation
  • Adrenalin gives vasodilation (relaxation of blood vessels)
    
    • β-receptors
  • Mostly α-receptors in these vessels
• Adrenalin (through β-receptors) creates alveolar dilation → increasing ventilation
  
  • ​Crucial in anaphylatic shock, adreanlin reduces the reaction

Hypoxia

• Little oxygen
• Affects the diameter of the blood vessels opposite of that in the systemic circulation
• Local hypoxia cause local stenosis (constriction), blood redistribution

Blood pressure

• Blood pressure ↑ → vascular tone ↓
• The lungs ability to achive an high minute volume in the case of increased physical activity without any change in the pressure conditions

Question 8

Gas diffusion in the lungs

Answer 8

• Determined by:
  
  • Partial pressure relations of the gases
  • Gas permeability of the membranes
  • Size of the exchange surface
• Maintenance of the gas exchange:
  
  • Continuous and varying oxygen consumption
  • CO₂ production
• Partial gas pressure values of the alveolar air are constant:
  
  • pO₂ = 100 mmHg
  • pCO₂ = 40 mmHg
• The result of gas exchange taking place in the alveoli differs from the result of the gas exchange of the total lung
• During the first 200 msec for both gases, a total exchange takes place, despite that pCO₂ is smaller than pO₂
  
  • Reason: flow of gases is determined by:
    
    • Pressure differences
    • Permeability