Lecture 9 - Special Circulations

Question 1

what are the two lung circulations?

Answer 1

pulmonary and bronchial

Question 2

describe the bronchial circulation

Answer 2

part of systemic

meets metabolic requirements of lung

Question 3

describe the pulmonary circulation

Answer 3

blood supply to alveoli required for gas exchange

Question 4

how does pulmonary circulation work?

Answer 4

accepts entire co

low resistance due to short wide vessels, lots of capillaries in parallel and arterioles with little smooth muscle

Question 5

what is the normal pressure in the pulmonary artery?

Answer 5

12-15mmHg

Question 6

what is the normal pressure in the pulmonary capillaries?

Answer 6

9-12mmHg

Question 7

what is the normal pressure in the pulmonary veins?

Answer 7

5mmHg

Question 8

what is ventilation perfusion matching in the pulmonary circulation?

Answer 8

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

Question 9

what results from chronic hypoxic vasoconstriction?

Answer 9

right ventricular failure

chronic increase in vascular resistance puts high afterload on right ventricle

Question 10

how is tissue fluid formed?

Answer 10

hydrostatic pressure of blood in capillary pushes fluid out

oncotic pressure exerted by large molecules like plasma proteins draws fluid back in

Question 11

what is pulmonary oedema?

Answer 11

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

Question 12

what is the relationship between mechanical work and oxygen demand of myocardium?

Answer 12

almost linear relationship until very high 02 demand where there is a small increase in o2 extracted

Question 13

describe the features of the coronary circulation

Answer 13

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

Question 14

describe consequences of partial of total occlusion of coronary arteries

Answer 14

functional end arteries so prone to atheroma
narrowed leads to angina on exercise
sudden obstruction by thrombus causes mi

Question 15

what factors influence blood flow through the brain?

Answer 15

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

Question 16

how is secure blood supply to the brain ensured structurally?

Answer 16

anastomoses between basilar and internal carotid arteries

Question 17

how is secure blood supply to the brain ensured functionally?

Answer 17

brainstem regulates other circulations
myogenic autoregulation maintains perfusion during hypotension
metabolic factors control blood flow

Question 18

how is secure blood supply to the brain ensured by myogenic autoregulation?

Answer 18

cerebral resistance vessels respond to changes in transmural pressure
increased = vasoconstriction
decreased = vasodilation

Question 19

how is secure blood supply to the brain ensured by myogenic regulation?

Answer 19

cerebral vessels are sensitive to changes in arterial pCO2
increased = vasodilatation
decreased = vasoconstriction

Question 20

how is secure blood supply to the brain ensured by regional activity?

Answer 20

areas with increased neuronal activity have increased blood flow

Question 21

how is secure blood supply to the brain ensured by cushings reflex?

Answer 21

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

Question 22

describe the cutaneous circulation

Answer 22

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

Question 23

describe the skeletal muscle circulation

Answer 23

metabolic activity variesat rest most capillaries are shut off by contraction of pre capillary sphincters