Special Circulations Flashcards
What are the 2 lung circulations?
Bronchial circulation
- part of systemic circulation
- for metabolic requirements of the lungs
Pulmonary circulation
- blood supply to alveoli
- required for gas exchange
What are features of the pulmonary circulation?
Low pressure
- lower than systemic
Low resistance
- short wide vessels
- lots of capillaries
What are the adaptations of the vessels for gas exchange?
High density of capillaries - large SA
Short diffusion distance
Large surface area
What is the optimal V/Q ratio?
0.8
How is the V/Q ratio maintained?
Blood is diverted away from poorly ventilated alveoli
What is hypoxic pulmonary vasoconstriction?
Mechanism - regulating pulmonary vascular tone
Alveolar hypoxia results in vasoconstriction of pulmonary vessels
Poorly ventilated alveoli are less well perfused
What is the effect of chronic hypoxic vasoconstriction?
Right ventricular failure
Why does chronic hypoxic vasoconstriction cause right ventricular failure?
Chronic increase in vascular resistance
Chronic pulmonary hypertension
High afterload on RV
What can cause chronic hypoxic vasoconstriction?
Altitude
Lung disease
What is the effect of exercise on pulmonary blood flow?
Increased CO
Small increase in pulmonary arterial pressure
Opens apical capillaries
Increased O2 uptake
How is tissue fluid formed?
Hydrostatic pressure of blood in capillary
- pushes fluid out of capillary
Oncotic pressure - exerted by large molecules
- draws fluid into capillary
What is the effect of low capillary pressure in the lungs?
Low tissue fluid / lymph at lungs
What can cause pulmonary oedema?
Lung capillary pressure increases
Mitral stenosis
- increase LA pressure
- increase pulmonary vein pressure
LV failure
- more blood in LV
- increase pulmonary vein pressure
What is the effect of pulmonary oedema?
Impairs gas exchange
- affected by posture
What are features of cerebral circulation?
High capillary density
- large SA
High basal flow rate
High O2 extraction
Why is good blood supply to brain vital?
Neurones are very sensitive to hypoxia
Few seconds = loss of consciousness
4 minutes = irrerversible damage
How is blood supply secured?
Structurally
- anastomoses between basilar and internal carotid arteries
Functionally
- myogenic autoregulation maintains perfucion during hypotension
- metabolic factors control blood flow
- brainstem regulates other circulation
What is myogenic autoregulation?
Repsonse to changes in BP
Increase BP = vasoconstriction
Decrease BP = vasodilation
What is metabolic regulation?
Cerebral vessels are sensitive to changes in Pco2
Hypercapnia = vasodilation Hypocapnia = vasoconstriction
What is the effect of changes in regional activity?
Increases neuronal activity = increased blood flow
What is Cushing’s reflex?
Response to raised ICP
Raised ICP impairs cerebral blood flow
Impaired blood flwo to vasomotor control regions
Increases sympathetic vasomotor activity
- increases arterial BP
- helps maintain cerebral blood flow
What are features of coronary circulation?
Deliver O2 at a high basal rate
High capillary density
Short diffusion distance
Continuous production of NO
When does left coronary artery flow mainly occur?
Diastole
During systole - increased LV pressure
What happens to blood flow with increased O2 demand?
Blood flow increases
