Blood Supply, Gas Exchange, Ventilation and Perfusion Flashcards
What are the partial pressures of deoxygenated blood?
PO2: 40mmHg
PCO2: 46mmHg
Rate of diffusion is directly proportional to what?
Partial pressure gradient
Gas solubility
Surface area
Rate of diffusion is inversely proportional to what?
Membrane thickness
Why is the rate of CO2 diffusion so high despite the low pressure gdt?
CO2 much more soluble in water than O2
How does pulmonary oedema decrease the rate of diffusion?
Increased diffusion distance due to fluid in the interstitial space
What is ventilation?
Air getting to alveoli
What is perfusion?
Local blood flow
Where is the lung is blood flow best? Why?
The base
Because arterial pressure exceeds alveolar pressure
Roughly where in the lung does blood flow equal perfusion?
Rib 3
What are the local control measures to avoid shunt?
Bronchoconstriction to poorly perfused alveoli
Vasoconstriction to poorly ventilated alveoli
What is alveolar dead space?
Alveoli that are ventilated but not perfused
What is shunt?
Passage of blood through areas of the the lung that are poorly ventilated
What is Physiological Dead Space?
Alveolar and Anatomical dead space
Where is CO2 carried in the blood?
Solution in plasma
PaO2 is not the same as what?
Arterial O2 concentration
How much arterial O2 is extracted by peripheral tissues at rest?
25%
How much O2 in the blood is bound to Hb?
98%
How long is blood in contact with the alveoli?
0.75s
Why do fetal Hb (HbF) and myoglobin have a higher affinity for O2 than HbA?
To extract O2 from maternal blood?
What is anaemia?
Condition where the O2 carrying capacity of blood is compromised
What affect does decreasing blood pH have on affinity?
(acidosis)
Reduced affinity
What effect does increased temperature have on affinity?
Reduced affinity
What effect does increased PCO2 have on affinity?
Reduced affinity
What effect does having no 2, 3DPG have on affinity?
Huge increase in affinity
What effect does added 2, 3-DPG have on affinity?
Decreased affinity
In which situations does 2, 3-DPG increase?
Inadequate Oxygen supply
What pressure of CO causes progressive carboxyhaemoglobin formation?
0.4mmHg
What are the symptoms of CO poisoning?
Hypoxia
Anaemia
Nausea/headaches
Cherry red skin/mucous membranes
What are the effects of CO poisoning?
Potential brain damage
Death
What is Hypoxaemic Hypoxia?
Reduction in O2 diffusion at the lungs
What is Anaemia Hypoxia?
Reduction in O2 carrying capacity of blood due to anaemia
What is stagnant Hypoxia?
Heart disease resulting in inefficient pumping of blood to lungs/around body
What is Histotoxic Hypoxia?
Poisoning preventing cells using Oxygen delivered to them
What is metabolic hypoxia?
Oxygen delivery to tissues is inadequate compared to demand by cells
What does Hypoventilation cause?
CO2 retention
Respiratory acidosis
What does Hyperventilation cause?
CO2 reduction
Respiratory Alkalosis
What happens to CO2 when combined in erythrocytes with deoxyhaemoglobin?
Carbamino compounds are formed
What happens to the majority of CO2 (70%) when it binds with water?
Combines to form carbonic acid
Carbonic acid dissociated into bicarbonate and H+ ions
What happens to the bicarbonate?
Moves out the erythrocyte into the plasma in exchange for Cl- ions (chloride shift)
What happens to the excess H+ in carbonic acid dissociation?
Binds to deoxyhaemoglobin