5 Overview of the Respiratory System

Question 1

Chest wall

• Respiratory system consists of…
• Chest wall includes…

Answer 1

• Respiratory system consists of…
  
  • Lungs
  • Chest wall
• Chest wall includes…
  
  • Rib cage
  • Thoracic spine
  • All structures attached to the rib cage & thoracic spine
    
    • Respiratory muscles (including the diaphragm)
    • Other skeletal muscles
    • Fat

Question 2

Parenchyma:
Lungs

Answer 2

• Divided into lobes, segments, and lobules

Question 3

Airways

• Upper airways
• Lower airways
• Terminal bronchioles
• Respiratory bronchioles

Answer 3

• Upper airways
  
  • Above the vocal cords
  • Nose, mouth, pharynx, larynx
• Lower airways
  
  • Below the vocal cords
  • Conducting airways, respiratory airways
• Terminal bronchioles
  
  • Each terminal bronchiole provides gas to a separate pulmonary lobule
• Respiratory bronchioles
  
  • Each respiratory bronchiole provides gas to a lung acinus

Question 4

Respiratory system

• Function of the respiratory system
• This depends on…

Answer 4

• Function of the respiratory system: “gas exchange”
  
  • Maintain a normal partial pressure of oxygen (PaO2) & carbon dioxide (PaCO2) in the arterial blood
  • Remove CO2 from and add O2 to the mixed venous blood
• This depends on…
  
  • Ventilation: movement of air into and out of lungs
  • Perfusion: movement of blood into and out of lungs
  • Matching of ventilation & perfusion
  • Gas diffusion: movement of molecules along their pressure gradients

Question 5

Ventilation

• Definition
• Functions
• Regulated by…

Answer 5

• Definition
  
  • Repetitive movement of gas into and out of the lungs (i.e. breathing)
  • Ventilation = breathing
• Functions
  
  • Delivers oxygen to and removes carbon dioxide from the alveoli
  • Controls CO2 excretion by the lungs and therefore regulates the PaCO2
• Regulated by…
  
  • Neurons in the medulla, which receive input from the cerebral cortex and from peripheral receptors

Question 6

Ventilation

• Inspiration
• Expiration

Answer 6

• Inspiration
  
  • Occurs when the respiratory muscles increase the volume of the respiratory system
  • Active proces
• Expiration
  
  • Occurs when the elastic recoil of the respiratory system decreases its volume
  • Passive process

Question 7

Perfusion

Answer 7

• The flow of mixed venous blood from the right ventricle through the pulmonary arteries and the alveolar capillaries
• Delivers CO2 and removes O2 from the alveoli

Question 8

Ventilation-perfusion relationships

• Each alveolus receives…
• The relationship between ventilation and perfusion
• Ideally, all alveoli should receive…
• In reality…
• Ventilation-perfusion relationships are important because…

Answer 8

• Each alveolus receives…
  
  • A certain volume of gas (ventilation; V) and blood flow (perfusion; Q) each minute
• The relationship between ventilation and perfusion
  
  • The V/Q ratio
• Ideally, all alveoli should receive…
  
  • The same amount of ventilation and perfusion
  • I.e. V/Q should be 1.0
• In reality…
  
  • There is a range or distribution of V/Q ratios in the lungs
• Ventilation-perfusion relationships are important because…
  
  • The V/Q ratio of each alveolus determines the PO2 and PCO2 of the alveolar gas (PAO2, PACO2) in each alveolus
• Normal vs. lung disease
  
  • Normally, ventilation and perfusion are well-matched
  • Lung disease produces mismatching between ventilation and perfusion
    
    • This causes the PaO2 to fall and the PaCO2 to rise as the range or distribution of V/Q ratios increases

Question 9

Diffusion

• Definition
• Affected by…
• O2 & CO2
• O2
• CO2

Answer 9

• The movement of molecules from a region of high to low partial pressure
• Affected by…
  
  • Partial pressure gradients
  • Area of contact between alveolar gas and capillary blood
  • Distance for gas diffusion
• O2 and CO2 move between the alveoli and the pulmonary capillary blood along partial pressure gradients
• O2 dissolves in and diffuses through the alveolar epithelium, the capillary endothelium, the plasma (where some remains dissolved) and the erythrocyte, where it combines with hemoglobin
• CO2 diffuses in the opposite direction

Question 10

Diffusion

• The rate of gas diffusion varies directly with…
• The rate of gas diffusion varies inversely with…

Answer 10

• The rate of gas diffusion varies directly with…
  
  • The contact area between alveolar gas and capillary blood
  • The partial pressure gradient
• The rate of gas diffusion varies inversely with…
  
  • Diffusion distance

Question 11

Diffusion

• Normally,…
• Lung disease…

Answer 11

• Normally,…
  
  • Complete equilibration occurs, so that the alveolar gas and the capillary blood leaving the alveoli have the same PO2 and PCO2
• Lung disease…
  
  • Can cause incomplete equilibration, which causes the PaO2 to fall and the PaCO2 to increase

Question 12

Diffusion: O2

Answer 12

• Once O2 has been added to the arterial blood, it must be transported to the tissues and organs of the body
• Almost all O2 is carried combined with hemoglobin and a very small amount is dissolved in the plasma
• In the systemic capillaries, O2 enters cells by diffusing along its partial pressure gradient

Question 13

Diffusion: CO2

Answer 13

• CO2 is a byproduct of cellular metabolism
• It diffuses out of cells and into the systemic capillary blood and is then transported back to the lungs
• Most of the CO2 combines with hemoglobin or is converted to bicarbonate (HCO3), and a small amount dissolves in the plasma
• In the pulmonary capillaries, CO2 diffuses into the alveolar gas