Lecture 9 - Special Circulations Flashcards
what are the two lung circulations?
pulmonary and bronchial
describe the bronchial circulation
part of systemic
meets metabolic requirements of lung
describe the pulmonary circulation
blood supply to alveoli required for gas exchange
how does pulmonary circulation work?
accepts entire co
low resistance due to short wide vessels, lots of capillaries in parallel and arterioles with little smooth muscle
what is the normal pressure in the pulmonary artery?
12-15mmHg
what is the normal pressure in the pulmonary capillaries?
9-12mmHg
what is the normal pressure in the pulmonary veins?
5mmHg
what is ventilation perfusion matching in the pulmonary circulation?
for efficient oxygenation, ventilation of the alveoli needs to be matched with perfusion
the optimal ventilation/perfusion ratio is 0.8
to maintain, must divert blood away from alveoli that arent well ventilated - hypoxic pulmonary vasoconstriction
what results from chronic hypoxic vasoconstriction?
right ventricular failure
chronic increase in vascular resistance puts high afterload on right ventricle
how is tissue fluid formed?
hydrostatic pressure of blood in capillary pushes fluid out
oncotic pressure exerted by large molecules like plasma proteins draws fluid back in
what is pulmonary oedema?
pulmonary system is low pressure so only a small amount of fluid leaves
if capillary pressure increases, pulmonary oedema can happen
fluid is mainly at bottom of lungs when standing but spread evenly when lying down
what is the relationship between mechanical work and oxygen demand of myocardium?
almost linear relationship until very high 02 demand where there is a small increase in o2 extracted
describe the features of the coronary circulation
right and left coronary arteries arise from right and left aortic sinuses and fill during diastole
in systole, pressure in coronary arteries is too high for filling
cardiac muscle has high capillary density to efficiently deliver o2
continuous production of NO by coronary endothelium maintains high basal flow
describe consequences of partial of total occlusion of coronary arteries
functional end arteries so prone to atheroma
narrowed leads to angina on exercise
sudden obstruction by thrombus causes mi
what factors influence blood flow through the brain?
receives about 15% of co
cerebral circulation meets high o2 demand with high capillary density, large sa, reduced diffusion distance, high basal flow rate and high o2 extraction
how is secure blood supply to the brain ensured structurally?
anastomoses between basilar and internal carotid arteries
how is secure blood supply to the brain ensured functionally?
brainstem regulates other circulations
myogenic autoregulation maintains perfusion during hypotension
metabolic factors control blood flow
how is secure blood supply to the brain ensured by myogenic autoregulation?
cerebral resistance vessels respond to changes in transmural pressure
increased = vasoconstriction
decreased = vasodilation
how is secure blood supply to the brain ensured by myogenic regulation?
cerebral vessels are sensitive to changes in arterial pCO2
increased = vasodilatation
decreased = vasoconstriction
how is secure blood supply to the brain ensured by regional activity?
areas with increased neuronal activity have increased blood flow
how is secure blood supply to the brain ensured by cushings reflex?
increased intracranial pressure impairs cerebral flow
impaired low to vasomotor control regions of brainstem increases sympathetic vasomotor activity, increasing arterial bp, leading to peripheral vasoconstriction and more flow to brain
describe the cutaneous circulation
role in temperature regulation
blood flow to skin is heavily regulated by sns
decreased core temperature leads to sympathetic innervation causing increased tone in arteriovenous anastomoses decreasing blood flow to apical skin
describe the skeletal muscle circulation
metabolic activity variesat rest most capillaries are shut off by contraction of pre capillary sphincters
