Session 9 Flashcards
What is the function of the Bronchial lung circulation.
Part of the systemic circulation and meets the metabolic needs of the lungs
What are the 2 circulations in the lungs?
Bronchial
Pulmonary
What is the function of the pulmonary lung circulation?
Blood supply to the alveoli and is needed for gas exchange.
What is the pressure in the right atrium?
0-8mmHg
What is the pressure in the right ventricle?
15-30mmHg systolic
0-8mmHg diastolic
What is the pressure in the pulmonary artery?
15-30mmHg systolic
0-8mmHg diastolic
What is the pressure in the left atrium?
1-10 mmHg
What is the pressure in the left ventricle?
100-140mmHg systolic
1-10mmHg diastolic
What is the pressure in the aorta?
100-140mmHg systolic
60-90mmHg diastolic
What is the mean arterial, capillary and venous pressure in the pulmonary circulation?
Arterial - 12-15 mmHg
Capillary - 9-12 mmHg
Venous - 5 mmHg
How does the pulmonary circulation ensure low resistance?
Has short and wide vessels
Has many capillaries in parallel
Has very little smooth muscle
How does the pulmonary circulation ensure efficient gas exchange?
Has a large surface area due to high density of capillaries in th alveolar wall
Thin layer of tissue to create a short diffusion pathway
What does the alveoli need for efficient oxygenation?
Must match the ventilation with perfusion
An optimal Q : V ratio is 0.8 for one alveoli.
How can the pulmonary circulation ensure there is an optimal Q : V ratio?
Hypoxia pulmonary vasoconstriction - diverting blood away from the alveoli that are not well ventilated. Possibly due to disease.
What can chronic hypoxia vasoconstriction cause?
Right ventricular hypertrophy because increase in vault resistance –> pulmonary hypertension –> right ventricle having to work harder.
When can chronic hypoxia vasoconstriction occur?
At high altitudes
Consequence of lung disease
What is capillary transit time?
How long it takes for red blood cells to move along a vessel. (Flow)
When can capillary transit time decrease?
Extra point - How?
During exercise. There is NO compromise to gas exchange.
Extra point - an increase in cardiac output –> increase in pulmonary arterial pressure –> opening of apical capillaries –> increase O2 uptake of lungs –> increased blood flow –> decreased capillary transit time.
What determines fluid formation?
Starlings forces
What influences capillary hydrostatic pressure more, arterial or venous pressure in the systemic circulation?
Venous pressure in systemic circulation.
What pressure causes fluid to leave pulmonary capillaries?
Hydrostatic pressure
What pressure causes fluid to enter pulmonary capillaries?
Colloid oncotic pressure.
What happens if the hydrostatic pressure is too high and too much lymph is formed in the lung?
It will impair gas exchange
What is the typical movement (in/out) of fluid along a pulmonary capillary?
More fluid moves out at the arterial end
More fluid moves in at the venous end
At what atrial pressure will you get oedema?
20-25
When could you have high pressure in theft atrium?
Mitral valve stenosis.
Left ventricular failure.
What can relieve the symptoms of pulmonary oedema?
Diuretics as they reduce the blood volume which reduces hydrostatic pressure.
How does posture effect pulmonary oedemas?
The fluid is at the base of the lung when standing and spread out over the lung when lying down
How does the effect of hydrostatic pressure on pulmonary vessels vary with gravity?
Top vessels collapse during diastole
Vessels in line with the heart continuously open
Vessels at the bottom distend
How does the structure of the cerebral circulation secure O2 supply?
Anastomoses between the basilar and internal carotid arteries
Circle of willis
How can the function of the cerebral circulation ensure secure O2 supply?
The brain stem can regulate other circulations
The metabolic factors
Myogenic autoregulation
How is the cerebral circulation adapted to meet the high demand for O2?
Has a high capillary density so there is a large surface area and slow diffusion rate.
Has a high basal flow rate.
Has high O2 extraction.
How does myogenic auto regulation work?
An increase in blood pressure causes vasoconstriction.
A decrease in blood pressure causes vasodilation.
Only works above 50mmHg
Maintains blood flow with changing pressures.
What is Hypercapnia?
An increase in CO2 causes vasodilation
What is Hypocapnia?
Extra point - What can cause it?
A decrease in CO2 causes vasoconstriction.
Extra point - By hyperventilation
How can regional activity in the cerebral circulation alter blood flow?
Increases the concentrations of metabolites eg K+ which cause vasodilation and therefore an increase in blood flow.
What is the Cushings reflex?
It is a response to increase in inter cranial pressure (cold be de to a haemorrhage or tumour)
There is an increase in sympathetic output so contraction of arteries occur and increases the arterial blood pressure - maintained cerebral blood flow.
When does blood flow in the left coronary artery?
Mainly Diastole.
How does the coronary circulation ensure adequate blood flow and O2 supply?
High capillary density
Short diffusion pathway - smaller diameter than skeletal capillaries
Continuous production of NO by the endothelium which is a vasodilator.
What is the relationship between coronary blood flow and myocardial O2 demand?
Almost linear.
How can blood flow be increased more in coronary circulation?
Metabolic hyperaemia due to vasodilators such as adenosine, K+, H+
What are functional end arteries prone to?
Extra point - What can this cause?
Atheromas
Extra point - Stable Angina as blood flow is most during exercise, but diastole is reduced so coronary vessels fill less.
What can cause unstable angina?
Stress and cold due to sympathetic vasoconstriction of the coronary vessels.
What are vessels in the skeletal circulation rich in?
Innervation by sympathetic vasoconstrictor fibres.
How can the skeletal circulation increase O2 and nutrient delivery/removal of metabolites during exercise?
Only half of the vessels are perfused at rest so in exercise there is increased recruitment which allows increased flow and a decreased distance of diffusion.
What are the important vasodilation molecules?
K+ H+ Inorganic phosphates Osmolality Adenosine
What causes vasodilation?
Adrenaline acting on beta 2 adrenoreceptors
What causes vasoconstriction?
Noradrenaline acting on alpha 1 adrenoreceptors.
What is the metabolic requirement of the cutaneous circulation?
Low
What is the cutaneous circulation responsible for?
Temperature regulation
Blood pressure maintenance
How does the cutaneous circulation control blood pressure?
Vasoconstriction can cause an increase in total peripheral resistance which leads to an increase in arterial pressure.
What is Apical skin?
An area that has a high surface area to volume ratio.
What structure is in apical skin?
Artereovenous anastomoses. (Glomus body in Spring like shape)
How can artereovenous anastomoses regulate heat loss?
They can increase the surface area to volume ratio so more heat is lost.
What controls artereovenous anastomoses?
NOT controlled by metabolites
Sympathetic vasoconstriction.
Decrease in core temperature increases the sympathetic tone.
Increase in core temperature decreases the sympathetic tone so relaxation and shunt to Venus plexus.
How does non apical skin regulate heat loss?
Has the vasodilator Bradykinin which comes from the ACh sympathetic innervation of sweat glands.
