CVS 8 Special Circulations Flashcards
2 circulations of the lungs
Bronchial circulation - meets the metabolic requirements of the lungs
Pulmonary circulation - required for gas exchange
Cardiac output at rest
5L/min
Maximum cardiac output
20-25L/min
Pressure in right atria
0-8mmHg
Pressure in left atria
1-10mmHg
Pressure in right ventricle
15-30mmHg - systole
0-8mmHg- diastole - same as RA
Pressure in left ventricle
100-140mmHg - systole
1-10mmHg - diastole - same as LV
Compare and contrast the features of pulmonary and systemic circulation
pulmonary circulation:
- lower pressure + resistance
- short, wide vessels
- many capillaries
- arterioles have little smooth muscle
systemic circulation
- higher pressure + resistance
- larger, narrower vessels
- variable blood flow to capillaries
- arterioles have thick walls
Adaptations to promote efficient gas exchange
High density of capillaries - large surface area
Short diffusion distance
What is hypoxic pulmonary vasoconstriction?
Occurs when alveoli are not well ventilated
Vasoconstriction of pulmonary vessels
Ensures perfusion matches ventilation
Helps optimise gas exchange
Consequence of chronic hypoxic vasoconstriction
Increases resistance > hypertension
Outline when the vessels of the lungs are open/closed
- apical vessels - collapse during diastole
- vessels at the level of the heart - constantly open
- vessels at base of lungs - increased hydrostatic pressure > vessels distended
Effect of exercise on pulmonary blood flow in lungs
- apical vessels - open due to increase pressure
- vessel at level of heart - constantly open
- vessels at base of lungs - increased hydrostatic pressure > vessels distended
Outline the formation of tissue fluid
- hydrostatic pressure pushes fluid out of capillary
- oncotic pressure draws fluid into capillary
How does the cerebral circulation meet the high demand for oxygen?
High capillary density > large surface area
High basal flow rate
Reduced diffusion distance
High O2 extraction
How is secure cerebral blood supply ensured?
structurally:
- circle of Willis
.
functionally:
- myogenic autoregulation maintains perfusion in hypotension
- metabolites control blood flow
- brain stem regulates other circulation
What is hyper and hypocapnia?
High + low CO2 partial pressure
What happens to cerebral vessels in hypercapina and hypocapina?
hypercapina - vasodilation
hypocapina - vasoconstriction
How does myogenic auto regulation control blood supply?
Vasoconstriction if BP increases
Vasodilation if BP decreases
Fails below 50mHg
What act as vasodilators?
Increased [K+]
Increased osmolarity
Inorganic phosphates
Adenosine
Decreased pH
Outline atereovenous anastomoses?
In apical skin
Under neural control
Decrease core temperature closes AVAs
Increased core temperature opens AVAs > dilate > blood nearer to suface
What is the ventilation-perfusion ratio?
V:Q
Ratio between the volume of air coming in and out of lungs and the volume of blood flowing past the lungs in pulmonary circulation
What is the optimal V:Q ratio?
0.8
