Properties Of Special Circulations Flashcards
What are the special requirements of coronary circulation?
Needs a high basal supply of oxygen - 20x resting skeletal muscle.
Increased oxygen supply in proportion to increased demand/ cardiac work
What are the special structural features of coronary circulation?
High capillary density
Large Surface area for O2 transfer
Together these reduce diffusion distance to myocytes
What are the special functional features of coronary circulation during normal activity?
- High blood flow - 10x the flow per weight of the rest of the body
- sparse sympathetic innervation
- high NO released leading to vasodilation
- high O2 extraction
What are the special functional features of coronary circulation during increased demand?
- coronary blood flow increases in proportion to demands
- production of vasodilators out compete the relatively sympathetic vasoconstriction
- circulating adrenaline dilates coronary vessels due to an abundance of beta 2 adrenoreceptors
What does myocardium metabolism generate?
Metabolites to produce vasodilation and increase blood flow
What do functional end arteries have?
Low number of branches between the arteries
What are the two causes of ischaemic heart disease?
Sudden or slow obstruction
What are sudden obstructions in the heart and what do they produce?
Acute thrombosis, which produces a myocardial infarction
What are slow obstructions of the heart?
Atheroma causing narrowing of the lumen
What is a thrombosis?
Occlusion leading to obstruction of blood flow to interior left ventricle
What happens to the heart muscle in thrombosis?
- ischemic tissue, acidosis, pain
- impaired contractility
- sympathetic activation
- arrhythmias
- cell death (necrosis)
What mechanical factors can reduce coronary flow?
- short diastole (high heart rate)
- increased ventricular end diastolic pressure
- reduced diastolic arterial pressure
What are the special properties of cutaneous circulation?
- Defence against the environment
- Lewis triple response to trauma
- temperature regulation
What does skin temperature depend on?
Skin blood flow and ambient temperature
What are the special structural features of cutaneous circulation?
- arterio-venous anastamoses
- sympathetic vasoconstrictor fibres
- sudomotor vasodilator fibres
What are arterio-venous anastomoses?
Direct connections of arterioles and venules that expose blood to regions of high surface area.
Involved in connection, conduction, radiation and evaporation
What do sympathetic vasoconstrictor fibres release?
Noradrenaline acting on alpha 1 receptors
What are sudomotor vasodilator fibres driven by?
Temperature regulation in the hypothalamus
What are the special functional features of cutaneous circulation?
- Response to ambient and core temperatures
- paradoxical cold vasodilation
- core temperature receptors in the hypothalamus control sympathetic activity to skin
What is the paradoxical cold vasodilation?
If you get so cold your veins go hypoxic, they relax so blood rushes in and saves the skin.
What is paradoxical cold vasodilation caused by?
Paralysis of sympathetic transmission
What is the purpose of paradoxical cold vasodilation?
Protects against skin damage
How do sympathetic nerves react to local cold?
Releasing noradrenaline which binds to alpha 2 receptors on vascular smooth muscle in skin
What is the relationship between cutaneous perfusion and core temperature?
Increased cutaneous perfusion with increased core temp
What does increased core temp stimulate?
Temperature receptors in the anterior hypothalamus
What does stimulation of temp receptors in the hypothalamus cause?
Sweating and vasodilation
What are some other functional specialisations of the cutaneous circulation?
Baroreflex, RAAS, ADG stimulated vasoconstriction of blood vessels, emotional connection and response to skin injury
What happens when blood pressure drops?
It is directed to more important organs
What can prolonged obstruction of blood flow by compression cause?
Severe tissue necrosis
How is prolonged obstruction of blood flow by compression avoided?
Shifting position/ turning to ease reactive hyperaemia or high skin tolerance to ischaemia
What happens in postural hypotension/oedema due to gravity?
Standing for long periods of time in hot weather will decrease central venous pressure and increased capillary permeability
