Pulmonary blood flow gas exchange and transport Flashcards
What change occurs to alveolar ventilation with height from base to apex?
It declines
What change occurs to compliance with height from base to apex?
It declines
Where does exchange I occur?
Between atmosphere and lungs
Where does exchange II occur?
Between lung and blood
Where does exchange III occur?
Between blood and cells
How is Bronchial circulation (nutritive) supplied?
It is supplied via the bronchial arteries arsing from systemic circulation to supply oxygenated blood to airway smooth muscle, nerves and lung tissue.
How is pulmonary circulation (gas exchange) supplied?
It consists of L & R pulmonary arteries originating from the right ventricle.
How does air move across membranes?
Air diffuses across membranes down partial pressure gradient.
What are alveoli composed of?
- Type I cells for gas exchange
- Type II cells that synthesise surfactant
Alveolar macrophages ingest foreign material that reaches the alveoli.
Effect of Emphysema
Destruction of alveoli reduces surface area for gas exchange.
-Emphysema usually caused by smoking
Effect of Fibrotic lung disease
Thickened alveolar membrane slows gas exchange. Loss of lung compliance may decrease alveolar ventilation.
Effect of Pulmonary edema
Fluid in interstitial space increases diffusion distance. Arterial PCO2 may be normal due to higher CO2 solubility in water.
Effect of Asthma
Increased airway resistance decreases airway ventilation.
How do ventilation and perfusion affect each other?
Ventilation and perfusion ideally match (compliment) each other.
Ventilation in alveoli is matched to perfusion through pulmonary capillaries.
Why is blood flow higher than ventilation at the base of the lungs?
Arterial pressure exceeds alveolar pressure. This compresses the alveoli.
What is Shunt?
Term used to describe the passage of blood through areas of the lung that are poorly ventilated.
-Shunt is the opposite of alveolar dead space.
Pulmonary vasodilation
Increase in alveolar PO2
Mild bronchial constriction
Decrease in alveolar PCO2
Alveolar dead space
Refers to alveoli that are ventilated but not perfused.
Anatomical dead space
Refers to air in the conducting zone of the respiratory tract unable to participate in gas exchange as walls of airways in this region are too thick.
Physiologic dead space
PDS = Alveolar DS + Anatomical DS
How much does Haemoglobin in red blood cells increase O2 carrying capacity?
It increases the O2 carrying capacity to 200ml/L.
Is arterial partial pressure of O2 (paO2) the same as arterial O2 concentration/content?
NO
-PaO2 refers purely to O2 in solution and is determined by O2 solubility and the partial pressure of O2 in the gaseous phase that is driving O2 into solution.
Why do gases not travel in the gaseous phase in plasma?
If they did = bubbles in blood = fatal air embolism
What is the major determinant of the degree to which haemoglobin is saturated with oxygen?
Partial pressure of oxygen in arterial blood
How long does it take saturation to complete after contact with alveoli?
After 0.25s contact with alveoli (0.75s total contact time)
What is the most efficient PO2 to maximise haemoglobin oxygen load?
100 mm Hg
What is Anaemia?
Any condition where the oxygen carrying capacity of the blood is compromised (e.g. iron deficiency, haemorrhage, vit B12 deficiency).
What chemical factors affect the affinity of haemoglobin for O2?
- pH
- PCO2
- Temperature
- DPG conc (diphosphoglycerate)
What increase in chemical factors decrease the affinity of haemoglobin for O2?
-PCO2 and temperature
Decrease in pH decreases affinity for O2.
What is formed when Carbon Monoxide binds to haemoglobin?
Carboxyhaemoglobin
-This has an affinity 250 times greater than O2.
What are the 5 main types of hypoxia?
- Hypoxaemic Hypoxia (most common)
- Anaemic Hypoxia
- Stagnant Hypoxia
- Histotoxic Hypoxia
- Metabolic Hypoxia
Hypoxaemic Hypoxia
Reduction in O2 diffusion at lungs either due to decreased PO2atmos or tissue pathology.
Anaemic Hypoxia
Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/iron deficiency)
Stagnant Hypoxia
Heart disease results in inefficient pumping of blood to lungs/around the body.
Histotoxic Hypoxia
Poisoning prevents cells utilising oxygen delivered to them e.g. CO/cyanide.
Metabolic Hypoxia
Oxygen delivery to the tissues does not meet increased oxygen demand by cells.
What is a erythrocyte?
A red blood cell, which (in humans) is typically a biconcave disc without a nucleus
-Erythrocytes contain haemoglobin
Normally, why is pH stable in ECF?
Because all CO2 produced is eliminated in expired air.
-However hypo/hyperventilation will affect this.
What does hypoventilation cause?
Causes CO2 retention, leading to increased (H+) bringing about respiratory acidosis!!
What does Hyperventilation cause?
Causes more CO2 loss, leading to decreased (H+) bringing about respiratory alkalosis.
