Pulmonary Blood Flow, Gas Exchange and Transport Flashcards
What is the function of the pulmonary circulation?
To deliver carbon dioxide to the lungs and pick up oxygen to take back to the start
What type of blood does the pulmonary artery carry?
Deoxygenated blood
What type of blood does the pulmonary vein carry?
Oxygenated blood
Is the bronchial circulation part of the pulmonary or systemic circulation?
Systemic circulation
How is the flow and the pressure of the pulmonary circulation described?
High flow, low pressure
What is the partial pressure of oxygen in the alveoli and arterial blood?
100mmHg (13.3 kPa)
What is the partial pressure of oxygen in venous blood and tissue?
40mmHg (5.3 kPa)
What is the partial pressure of carbon dioxide in the alveoli and arterial blood?
40mmHg (5.3 kPa)
What is the partial pressure of carbon dioxide in venous blood and tissue?
46mmHg (6.2 kPa)
If carbon dioxide has a smaller partial pressure gradient then why does it diffuse at close to the same rate as oxygen?
Carbon dioxide is much more soluble in water than oxygen is so diffuses at a fast rate
What directly effects the rate of diffusion across the membrane?
The partial pressure gradient, gas solubility and available surface area
How does the thickness of the membrane effect the rate of diffusion across the membrane?
The thicker the membrane the slower the diffusion
How do the alveolar cells increase the rate of diffusion?
They have a large surface area and a thin membrane
Where are the capillaries situated in relation to the alveoli and why?
Directly behind the type 1 pneumocytes - this gives the shortest distance and speeds up diffusion
How does emphysema affect gas exchange?
It destroys the alveoli and so reduces the surface area for gas exchange
How does a fibrotic lung disease affect gas exchange?
It thickens the alveolar membrane which slows gas exchange
How does a pulmonary oedema affect gas exchange
Fluid in the interstitial space increases diffusion distance and slows the gas exchange (carbon dioxide diffusion may be normal due to the increased solubility)
How does asthma affect gas exchange?
It increases airway resistance which decreases ventilation lowering the partial pressure gradient
Why is the blood flow higher at the base of the lungs than at the apex of the lungs?
At the base the arterial pressure exceeds the alveolar pressure which lowers the vascular resistance - the opposite is true at the apex of the lung
What is shunt?
When ventilation decreases in an area of the lung and oxygenated blood from other areas is mixed with the deoxygenated from this area
What happens to the arterioles when the alveoli are under ventilated?
The arterioles are constricted diverting blood to better ventilated alveoli
What happens when ventilation is greater than blood flow?
An increase in alveolar oxygen - pulmonary vasodilation
A decrease in alveolar carbon dioxide - bronchial constriction
What is physiological dead space?
Alveolar Dead Space + Anatomical Dead Space
What is the capacity of haemoglobin for oxygen?
200ml/L of blood
How is most of the carbon dioxide in the blood transported?
In solution in the plasma
How many molecules of oxygen can one haemoglobin bind?
4
What is the most abundant form of haemoglobin?
HbA
What is HbF?
Fetal haemoglobin - binds with a higher affinity than adult haemoglobin
How is glycosylated haemoglobin useful in measuring how controlled diabetes is?
Glucose binds permanently to the Hb for the lifetime of the RBC - high levels suggest poorly controlled diabetes
What is the main determinant of haemoglobin oxygen saturation
The partial pressure of oxygen in arterial blood
Does myoglobin have a higher or lower affinity for oxygen than haemoglobin
Higher
What is anaemia?
Any condition where the oxygen carrying capacity of the blood is compromised
What would happen to the partial pressure of oxygen in arterial blood in anaemia?
It would be normal
What would increasing the pH do to the oxygen-haemoglobin dissociation curve?
The curve would shift to the left
What would increasing the partial pressure of carbon dioxide do to the oxygen-haemoglobin dissociation curve?
The curve would shift to the right
What would decreasing the temperature do to the oxygen-haemoglobin dissociation curve?
The curve would shift to the left and 100% saturation would be reached at very low partial pressures of oxygen
What is 2,3-DPG?
A product of the metabolism of red blood cells which increases when there is inadequate oxygen supply e.g. in people with lung disease, heart disease and those living at high altitudes
What does increasing the levels of 2,3-DPG do to the oxygen-haemoglobin dissociation curve
The curve would shift to the right
Why is carbon monoxide so dangerous?
Haemoglobin has a very high affinity for CO and it dissociates very slowly
What are the symptoms of carbon monoxide poisoning?
Hypoxia, anaemia, nausea, headaches, cherry red skin and mucous membranes
What happens to the respiratory rate during carbon monoxide poisoning?
It is unaffected due to the normal arterial partial pressure of carbon dioxide
What is hypoxaemic hypoxia?
Hypoxia caused by a reduction in oxygen diffusion at lungs either due to reduced atmospheric oxygen or tissue pathology e.g. emphysema and fibrosis
What is anaemic hypoxia?
Hypoxia caused by a reduction in the oxygen carrying capacity of blood due to anaemia e.g. RBC loss or iron deficiency
What is stagnant hypoxia?
When heart disease causes inefficient pumping to lungs/around the body
What is histotoxic hypoxia?
When poisoning prevents cells utilising oxygen delivered to them e.g. carbon monoxide/cyanide
What is metabolic hypoxia?
Hypoxia caused by the oxygen delivery to the tissues does not meet the metabolic demand
How does hypoventilation affect hydrogen ion concentration?
Hypoventilation causes carbon dioxide retention which leads to increased hydrogen ion concentration causing respiratory acidosis
How does hyperventilation affect hydrogen ion concentration?
Hyperventilation blows off carbon dioxide which decreases the hydrogen ion concentration causing respiratory alkalosis
