Flashcards in CVS - special circulations Deck (47)
When is it the most difficult for blood to flow through the coronary circulation?
Especially in the isovolumetric contraction stage and also systole, due to the contraction of cardiomyocytes putting pressure on and constricting the coronary arteries.
How is cardiac muscle adapted to increase its blood flow relative to skeletal muscle?
1. Smaller fibre diameter, therefore smaller diffusion distance
2. Higher capillary density
3. Constant perfusion of all capillaries
4. Continuous production of NO (vasodilator) by coronary endothelium which maintains a high basal blood flow
How is the coronary blood flow increased to meet extra demand?
Vasodilation due to metabolic hyperaemia (adenosine, increase in K+, CO2 and decrease in O2.
What factors, other than exercise, can trigger angina?
Stress, cold, infection etc... anything that causes sympathetic coronary vasoconstriction.
What is a systemic functional role dof skeletal muscle blood flow?
Important role in regulating arterial blood pressure
How does the baroreceptor reflex maintain blood pressure?
The baroreceptors detect a drop in blood pressure and lead to an increase in sympathetic outflow. This increases the sympathetic vasomotor tone (NA binding to alpha-1 receptors causes vasoconstriction), increasing peripheral resistance and causing an increase in arterial blood pressure.
How is skeletal muscle able to alter its blood flow so dramatically?
1. High vasomotor tone - permits lots of dilation
2. Half its capillaries are perfused at any one time, at rest - can increase its recruitment significantly
What controls vasodilation in skeletal muscle?
1. Metabolic vasodilators - K+, increased osmolarity, inorganic phosphates, adenosine, H+
2. Adrenaline - acting through B2 receptors
What are some of the systemic roles of the cutaneous circulation?
1. Temperature control (main function) - main heat dissipating surface
2. Maintaining blood pressure - e.g. vasoconstriction in shock
Give some examples of apical skin:
Areas with a high surface area to volume ratio e.g. ears, nose, toes
What is the main regulator of cutaneous circulation blood flow?
The sympathetic nervous system.
Most blood flow through the skin goes through which type of blood vessels?
Arterio-venous anastamoses, rather than capillaries, therefore it is not nutritive.
Non-apical skin loses heat by dilation of vasodilation of capillary beds and increased sweating. How does apical skin lose heat?
By shunting blood through arterio-venous anastamoses (low resistance shunt), as veins lie closer to the surface of the skin.
The main regulator of cutaneous blood flow is the sympathetic nervous system. What else mediates it?
It is not affected much by local metabolites, but is affected by mediators released from sweat glands (bradykinin?), causes vasodilation. Circulating vasodilators from other sources sometimes also increase skin blood flow.
Aterio-venous anastomoses are under what control?
Neural control - by sympathetic vasoconstrictor fibres. They are not regulated by local metabolites.
What is the cutaneous circulatory response to an decrease in core body temperature?
Sympathetic vasocontrictor drive to the AVAs is increased which results in decreased blood flow through the apical skin and less heat dissipation.