Special Circulations Flashcards
Features of the pulmonary circulation in the lungs? How?
Low pressure and low resistance in order to accept the whole cardiac output.
Low resistance due to short, wide vessels and lots of capillaries connected in parallel
What are the two circulations of the lungs?
Pulmonary and bronchial
Normal pulmonary artery pressure?
12-15 mmHg
Normal pulmonary capillary pressure?
9/12 mmHg
Normal pulmonary vein pressure?
5mmHg
What adaptations does the pulmonary circulation have to promote efficient gas exchange?
High density of capillaries ➡️ large surface area
Short diffusion distance
How is the optimal ventilation-perfusion ratio maintained?
Diverting blood away from alveoli which are not well ventilated by hypoxic pulmonary constriction
Increased resistance means less flow to these alveoli.
What can chronic hypoxic vasoconstriction cause?
Right ventricular failure caused by a high afterload
What effect does being in the upright position have on pressure in the lungs?
Greater hydrostatic pressure on vessels in the lower part of the lung leading to fluid formation at the base of the lungs.
What is oncotic pressure?
Pressure exerted by large molecules such as plasma proteins which draws fluid into the capillary
What has the greatest effect in capillary hydrostatic pressure?
Venous pressure
If there is low pressure in the pulmonary system, how much fluid will leave the capillaries
A relatively small amount
What happens if pulmonary capillary pressure increases too far?
Pulmonary oedema can occur
What effect does pulmonary oedema have?
Impairs gas exchange
What percentage of the cardiac output does the brain receive?
15%
How does the cerebral circulation meet the high demand for oxygen?
High capillary density - large SA for gas exchange and reduced diffusion distance
High basal flow rate - (10x average of whole body)
High oxygen extraction - (35% above average)
How long does it take for irreversible damage to occur to neurones in ischaemia?
4 mins
What is a secure blood supply ensured by in the brain?
Structure - anastomoses between basilar and internal carotid arteries
Function - brain stem regulates other circulations; myogenic auto regulation; metabolic factors
What does myogenic autoregulation allow?
Maintains perfusion during hypotension by vasodilatation
What is hypercapnia? What does it lead to?
High pO2
Vasodilatation
What can panic hyperventilation cause?
Cerebral vasoconstriction leading to dizziness and fainting
What can and can’t pass through the blood-brain barrier?
Can: lipid soluble molecules such as O2 and CO2
Can’t: lipid insoluble solutes such as K+ and catecholamines
What is Cushing’s reflex?
An increase in intracranial pressure leads to impaired blood flow to vasomotor control regions. This increases sympathetic vasomotor activity which increases arterial blood pressure to help maintain cerebral bloodflow.
Where do the right and left coronary arteries arise from?
The right and left aortic sinuses
Why do the coronary arteries only fill during diastole?
In systole, contraction of the muscle makes the pressure in the arteries too high for filling
How is cardiac muscle adapted for high blood flow?
High capillary density to efficiently deliver oxygen
Continuous production of NO by coronary endothelium maintains a high basal flow
Why do you get angina on exercise if you have atheroma?
Coronary arteries fill mostly during diastole. Diastole is shortened during exercise and cannot meet high oxygen demand.
Other than exercise, what can also cause angina?
Stress and cold. Causes sympathetic coronary vasoconstriction.
What does the skeletal muscle circulation need to be adapted to do?
Increase oxygen nutrient delivery during exercise.
Remove metabolites during exercise.
Regulate arterial blood pressure.
How is blood flow increased during exercise to skeletal muscle?
Opening more capillaries under influence of vasodilators. Nervous activity and metabolites reduce vasoconstrictor tone.
About what percentage of capillaries in skeletal muscle are open at rest?
50%
What regulates AVAs?
Sympathetic nervous system
