Lecture 8 - Special Circulations Flashcards
Why is the bronchial circulation needed?
- Bronchi too far away for efficient diffusion
- Meets the metabolic requirements of the lungs
Name the two circulations of the lungs?
- Bronchial circulation
- Pulmonary circulation
Is the pulmonary circulation in series or parallel with systemic?
-Series
What is the cardiac output at rest?
5L/min
What is the maximum cardiac output (non-athlete)?
20-25L/min
What is special about the pulmonary pressure and resistance?
-They are both low
How is the resistance low in the pulmonary circulation?
- Many capillaries in parallel with each other
- Short wide vessels
- Arterioloes have relatively little smooth muscle
Name the pressures in the chambers on the heart, aorta and pulmonary artery during systole and diastole?
- RA 0-8mmHg
- LA 1-10mmHg
- LV 100-140mmHg systole, 1-10mmHg diastole
- RV 15-30mmHg systole, 0-8mmHg diastole
- Aorta 100-140mmHg systole, 60-90mmHg diastole
- PA 15-30mmHg systole, 4-12mmHg diastole
Why is the diastolic pressure in the pulmonary artery higher than that in the right ventricle?
-When pulmonary valve closes, the recoil in the artery maintains the diastolic pressure
What is the mean arterial pressure in pulmonary circulation?
-12-15mmHg
What is the mean capillary pressure in the pulmonary circulation?
-9-12mmHg
What is the mean venous pressure in the pulmonary circulation?
-5mmHg
How is the pulmonary circulation adapted for efficient gas exchange?
Very high density of capillaries and short diffusion distance produces a high O2 and CO2 transport capacity
How does high capillary density help gas exchange in the lungs?
Provides a large surface area over which gas can be exchanged.
What constitutes the diffusion barrier between the air and the blood?
- Epithelium of alveoli (type1 pneumocytes/squamous), attached to their basement membrane
- Endothelium of capillary
What is required for efficient oxygenation?
Ventilation of the alveoli must be matched by perfusion of the alveoli
How is the ventilation perfusion ratio maintained?
By diverting blood away from those alveoli which are not well ventilated, thus those which are ventilated have adequate perfusion
What is the most important mechanism is regulating pulmonary vascular tone?
Hypoxia pulmonary vasoconstriction
What is hypoxia pulmonary vasoconstriction?
Alveolar hypoxia results in the vasoconstriction of pulmonary vessels ensuring that perfusion matches the ventilation, helping to optimise gas exchange
When can hypoxia pulmonary vasoconstriction become problematic?
At high altitude or chronic conditions where there is wide spread reduced ventilation
Why at high altitude/in chronic conditions does hypoxia pulmonary vasoconstriction to cause a problem?
Promotes wide-spread chronic vasoconstriction as oxygen is reduced to all alveoli. This increases the resistance in the lungs and increases the afterload on the right ventricle.
What effect does an increased afterload on the right ventricle have?
Can lead to right ventricle failure as the RV is poorly tolerant to increases in afterload
Describe how the pulmonary vessels in the base of the lungs are influenced by gravity
In upright position there is greater hydrostatic pressure in vessels at the lower part of the lung, this distended the vessels here
Describe how the vessels in the apex of the lungs are effected by gravity
Lower hydrostatic pressure when in upright position so they collapse during diastole