pulmonary circulation Flashcards
what are the 2 circulations in the lung?
pulmonary and bronchial
what circulation is the bronchial circulation part of?
systemic circulation
what does the bronchial circulation supply?
capillary beds in the trachea and bronchi smooth muscle
where do bronchial arteries branch off from?
early parts of the descending aorta
where does the bronchial venous drainage drain into?
bronchial veins in the right atrium
pulmonary veins going into the left atrium
where are the bronchial arteries found?
travelling along the main bronchi
how long does it take for blood to pass through the lungs?
5 seconds
what is the surface area of the lungs?
50-100m2
what are the special anatomical features of the pulmonary circulation?
thin walled pulmonary arteries
large diameter
highly distensible
what letter represents blood flow?
Q
give an equation to calculate blood flow
pressure gradient/resistance
which has lower pressure; the pulmonary or systemic circulation?
pulmonary
how does the blood flow equation show that pulmonary resistance is low?
pulmonary circulation has the same blood flow as the systemic circulation
pulmonary circ has a lower pressure than the systemic circulation
to make blood flow the same, the pulmonary circulation needs to have a lower resistance
what happens if pulmonary arterial resistance rises?
pulmonary arterial hypertension
right heart enlarges and eventually fails
which nerve supply carries pain and touch sensation from the lungs and to what spinal level does it go?
somatic nerve supply
to T2-T6
where does the sympathetic nerve supply of the lungs originate from?
T2 to T4-6
which part of the lungs do the sympathetic nerves innervate?
smooth muscle in the bronchial walls and small pulmonary vessels
what action do the sympathetic nerves innervating the lungs bring about?
bronchodilation and vasodilation
what receptors and neurotransmitter cause bronchial smooth muscle to relax and dilate?
adrenergic beta receptors
noradrenaline
what nerve delivers parasympathetic innervation to the lungs?
the vagus
what action do the efferent parasympathetic fibres innervating the lungs cause?
bronchoconstriction
stimulates secretion of mucus in the bronchi
where does gas exchange in the lungs occur?
alveolar ducts and alveoli
and to the respiratory bronchioles to a small extent
when upright, which part of the lungs has the lowest pressure?
the base
why is the base of the lung well perfused when upright?
gravity helps blood circulate because pulmonary blood pressure is low
describe the blood flow in zone 1 of the lungs and explain it
intermittent flow - Pa > PA > Pv
pressure varies during inspiration and expiration
flow ceases during expiration when lung pressure is at its maximum
alveoli squash the capillaries flat and blocks them bc they’re at a higher pressure
when is total cessation of flow in the apices seen?
when a person is ventilated with positive pressure or haemorrhage
where is zone 2 of the lungs?
3cm above the heart
describe the flow of blood in zone 2 of the lungs and explain it?
pulsatile flow; Pa > PA > Pv
flow fluctuates during inspiration and expiration bc of changes in alveolar pressure
flow greater in systole than diastole
what part of the lungs is zone 3?
the base
describe and explain the flow of blood in zone 3 of the lungs
continuous blood flow because the arterial and venous pressure always exceed alveolar pressure
Pa > Pv > PA
what is radioactive xenon used for and how?
measuring the distribution of blood flow in the upright lung
xenon injected into the venous blood
enters into the alveolar gas from pulmonary capillaries
radiation counters measure amount of xenon passing through each lung
what letter represents lung compliance?
C
what is lung compliance?
measure of stretchability of the lungs
how is lung compliance measured?
the change in volume per unit pressure change
C = dV/dP
when is the work of breathing lowest?
when a given change in pressure gives the largest change of volume
which part of the lungs has the highest compliance?
the base
at the base of the lungs, which is larger; Q or V?
Q
at the apex of the lungs, which is larger; Q or V?
V
describe the gas content of blood in the apex and the base?
apex - high PO2 and low PCO2 bc good gas exchange but little blood flow
base - low PO2 and high PaCO2 bc little ventilation
what is the V/Q ratio in conditions of airway obstruction
lower than normal
what is the V/Q ratio in conditions of blood flow obstruction?
higher than normal
give an example of a blood flow obstruction
embolism
what does pulmonary hypoxia cause and how does this help?
local vasoconstriction
directs blood away from poorly ventilated, hypoxic regions of the lungs
what does systemic hypoxia cause?
vasodilation
what changes occur to the pulmonary circulation during exercise?
pulmonary arterial pressure doesn’t change
pulmonary arterial resistance decreases
what is the mechanism for reducing vascular resistance in the lungs?
pulmonary arteries and arterioles are thin walled
distend when exercise starts
stretching generates reflex relaxation of arterial smooth muscle
vessels relax and enlarge, reducing vascular resistance
what happens to the alveoli when there’s increase PO2?
arterioles dilate
why is pulmonary vascular resistance high in the foetus?
hypoxic vasoconstriction in the foetal lungs
what is the foramen ovale?
the hole in the foetal atrial wall which shunts blood between the left and right atria
when does the foramen ovale close?
shortly after birth
what is the ductus arteriosus?
short tube joining the aorta and pulmonary artery
what is the purpose of the ductus arteriosus?
allows some of the blood from the right ventricle to bypass the lungs and enter the aorta directly
when does the ductus arteriosus close?
immediately after a baby takes their first breath
