Cardiovascular Circulations Flashcards
What are the two circulations to the lungs and what are their uses
Bronchial circulation - meets metabolic requirements of the lungs
Pulmonary circulation - required for gas exchange
What are the pressures in the ventricles, atria, pulmonary artery and aorta
RA - 0-8
RV - 15-30/0-8
Pulmonary artery - 15-30/4-12
LA - 1-10
LV - 100-140/1-10
Aorta - 100-140/60-90
What are the two features of the pulmonary circulation
Low pressure
Low resistance - short, wide vessels. Many capillaries.
What are the adaptations that promote efficient gas exchange in the lungs
High capillary density in alveolar wall
Short diffusion distance - thin layer of tissue
What is the V/Q ratio and what is it needed for
The vetilation - perfusion ratio
Needed to maintain efficient oxygenation
What does the lung do to maintain a high V/Q ratio and what is this called
Diverts blood from alveoli that are not well ventilated to other areas
Use the hypoxic pulmonary vasoconstriction
What is hypoxic pulmonary vasoconstriction
Where alveolar hypoxia results in vasoconstriction of pulmonary vessels so that poorly ventilated alveoli are less well perfused to optimise gas exchange
What effect can chronic hypoxic vasoconstriction cause and why
Can cause RV failure
Chronic hypoxia causes a chronic increase in vascular resistance
This increases the afterload on the RV as it is having to pump against a higher resistance
This causes RV hypertrophy which can then lead to RV heart failure
How does gravity affect pressure in the lungs while in the postural position
Causes there to be a greater hydrostatic pressure on the vessels in the lower part of the lungs
This means the vessels near the top (above the heart) collapse during diastole while those near the bottom become distended due to the increased hydrostatic pressure
What is the effect of exercise on pulmonary flow
Increased cardiac output - reduces capillary transit time
Increase in pulmonary arterial pressure
Opening of apical capillaries
What causes a pulmonary oedema and give some examples of how it can be caused
An increased capillary pressure
Arterial and venous pressure increases cause an increased hydrostatic pressure which results in more fluid leaving forming an oedema
Can be because of an increase in left atrial pressure due to mitral valve stenosis or LV failure
How do you treat a pulmonary oedema
Use diuretics to relieve symptoms
Treat underlying cause
Why does a large proportion of the cardiac output go to the cerebral circulation and how is it specialised to meet this requirement
Due to the high oxygen consumption by the grey matter
Cerebral circulation has:
High capillary density
High basal flow rate
High oxygen extraction
How is a secure cerebral blood flow ensured
Anastomoses between basilar and internal carotoid arteries
Myogenic autoregulation
Metabolic facotrs control blood flow
Brainstem regulates other circulations
What does myogenic autoregulation ensure and how
Ensures that the cerebral blood flow is maintain when the BP changes
Increased BP causes vasoconstriction while decreased BP causes vasodilation
Is a response to changes in transmural pressure
How does metabolic regulation maintian a secure cerebral blood flow
Vessels are very sensitive to changes in arterial PCO2
Hypercapnia causes vasodilation to perfuse the area more
Hypocapnia causes vasoconstriction to perfuse the area less
What metabolites cause vasodilation of cerebral arterioles
Increased PCO2
Increased [K+]
Increased Adenosine
Decreased PO2
Which reflex is activated when there is an increased intracranial pressure impairing cerebral blood flow, what does it do and what can causes the increased pressure
Cushing’s reflex
Impaired blood flow to vasomotor control regions increases sympathetic vasomotor activity causing an increased BP and helps maintian cerebral blood flow
Cerebral tumour or haemorrhage can cause increased pressure
Where do the left and right coronary arteries arise
Right and left aortic sinuses
When does the majority of blood flow occur in the left coronary artery and why
Occurs mainly during diastole due to increased pressure during systole by the force of muscle contraction making it harder for blood to flow through coronary artery
Describe the coronary artery circulation and what local metabolites cause vasodilation
High capillary density with the capillaries being continuously perfused
Continous NO production by coronary endothelium maintians high basal flow
Vasodilators - adenosine, increased [K+], decreased pH
What type of arteries are coronary arteries and why is this an issue
They are functional end arteries meaning there are few arterio-arterial anastomoses
Means they are prone to atheromas and obstruction by thrombuses
Describe the featues of the skeletal muscle circulation
Capillary density depends on muscle type - postural muscles have higher density
High vascular tone
Only half of capillaries are perfused at rest - allows for increased recruitment
Opening of precapillary sphincters allows more capillaries to be perfused
What agents act as vasodilators during metabolic hyperaemia
Increased K
Increased osmolarity
Inorganic phosphates
Adenosine
Increased H
Adrenaline on B2 receptors
