Gas Exchange Flashcards
What is the total combined area for gas exchange?
40-100m^2
How many alveoli are in each lung?
300 million
How many capillaries are in each alveolus?
1000
Which directions do oxygen and CO2 diffuse in?
O2 diffuses from the alveoli into the capillaries
CO2 diffuses from the capillaries into the alveoli
Name the 7 layers in which O2 must diffuse through (applies to CO2 as well)
- Alveolar epithelium
- Tissue interstitium
- Capillary endothelium
- Plasma layer
- Red cell membrane
- Red cell cytoplasm
- Haemoglobin
Which term is given to describe the idea of there being wrong proportions of alveolar airflow and capillary blood flow?
Ventilation-perfusion inequality
What is ventilation?
Alveolar airflow
What is perfusion?
Capillary blood flow
What is the main effect of ventilation-perfusion inequality?
The partial pressure of oxygen is decreased in systemic arterial blood
What is the main cause of natural ventilation-perfusion inequality?
Gravity.
Describe the two main consequences of ventilation-perfusion inequalities, caused by disease.
- There may be ventilated alveoli but no blood supply i.e. a blood clot
- There may be blood supply but no ventilation due to a collapsed alveoli i.e. shunt
Name two homeostatic responses which correct ventilation-perfusion inequalities.
Hypoxic pulmonary constriction
Local bronchoconstriction
Describe the effect of hypoxic pulmonary constriction.
- A decrease in ventilation in alveoli will lead to a decrease in alveolar PO2 and the blood vessels surrounding it
- The decrease in PO2 leads to vasoconstriction - diverting blood away from the poorly ventilated area
This effect is unique to the pulmonary arterial vessels. It ensures blood flow is directed away from disease areas of the lung.
Describe the effect of local bronchoconstriction.
- If there is decreased blood flow to a region in the lung, there is a lower PCO2
- Bronchoconstriction occurs to divert airflow away to areas with better perfusion
This process improves the efficiency of pulmonary gas exchange.
What effect on gas exchange is there with an ageing lung?
Impaired gas exchange due to:
- stiffer costal cartilage - harder to breathe
- respiratory muscle decreases in mass
- reduction in type IIA muscle fibres so you get more tired when you breathe
- loss of elastic recoil in lungs
- reduction in alveolar surface area
- ventilation-perfusion mismatch increases
