Properties Of Special Circulations

Question 1

What are the special requirements of coronary circulation?

Answer 1

Needs a high basal supply of oxygen - 20x resting skeletal muscle.
Increased oxygen supply in proportion to increased demand/ cardiac work

Question 2

What are the special structural features of coronary circulation?

Answer 2

High capillary density

Large Surface area for O2 transfer

Together these reduce diffusion distance to myocytes

Question 3

What are the special functional features of coronary circulation during normal activity?

Answer 3

• 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

Question 4

What are the special functional features of coronary circulation during increased demand?

Answer 4

• 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

Question 5

What does myocardium metabolism generate?

Answer 5

Metabolites to produce vasodilation and increase blood flow

Question 6

What do functional end arteries have?

Answer 6

Low number of branches between the arteries

Question 7

What are the two causes of ischaemic heart disease?

Answer 7

Sudden or slow obstruction

Question 8

What are sudden obstructions in the heart and what do they produce?

Answer 8

Acute thrombosis, which produces a myocardial infarction

Question 9

What are slow obstructions of the heart?

Answer 9

Atheroma causing narrowing of the lumen

Question 10

What is a thrombosis?

Answer 10

Occlusion leading to obstruction of blood flow to interior left ventricle

Question 11

What happens to the heart muscle in thrombosis?

Answer 11

• ischemic tissue, acidosis, pain
• impaired contractility
• sympathetic activation
• arrhythmias
• cell death (necrosis)

Question 12

What mechanical factors can reduce coronary flow?

Answer 12

• short diastole (high heart rate)
• increased ventricular end diastolic pressure
• reduced diastolic arterial pressure

Question 13

What are the special properties of cutaneous circulation?

Answer 13

• Defence against the environment
• Lewis triple response to trauma
• temperature regulation

Question 14

What does skin temperature depend on?

Answer 14

Skin blood flow and ambient temperature

Question 15

What are the special structural features of cutaneous circulation?

Answer 15

• arterio-venous anastamoses
• sympathetic vasoconstrictor fibres
• sudomotor vasodilator fibres

Question 16

What are arterio-venous anastomoses?

Answer 16

Direct connections of arterioles and venules that expose blood to regions of high surface area.
Involved in connection, conduction, radiation and evaporation

Question 17

What do sympathetic vasoconstrictor fibres release?

Answer 17

Noradrenaline acting on alpha 1 receptors

Question 18

What are sudomotor vasodilator fibres driven by?

Answer 18

Temperature regulation in the hypothalamus

Question 19

What are the special functional features of cutaneous circulation?

Answer 19

• Response to ambient and core temperatures
• paradoxical cold vasodilation
• core temperature receptors in the hypothalamus control sympathetic activity to skin

Question 20

What is the paradoxical cold vasodilation?

Answer 20

If you get so cold your veins go hypoxic, they relax so blood rushes in and saves the skin.

Question 21

What is paradoxical cold vasodilation caused by?

Answer 21

Paralysis of sympathetic transmission

Question 22

What is the purpose of paradoxical cold vasodilation?

Answer 22

Protects against skin damage

Question 23

How do sympathetic nerves react to local cold?

Answer 23

Releasing noradrenaline which binds to alpha 2 receptors on vascular smooth muscle in skin

Question 24

What is the relationship between cutaneous perfusion and core temperature?

Answer 24

Increased cutaneous perfusion with increased core temp

Question 25

What does increased core temp stimulate?

Answer 25

Temperature receptors in the anterior hypothalamus

Question 26

What does stimulation of temp receptors in the hypothalamus cause?

Answer 26

Sweating and vasodilation

Question 27

What are some other functional specialisations of the cutaneous circulation?

Answer 27

Baroreflex, RAAS, ADG stimulated vasoconstriction of blood vessels, emotional connection and response to skin injury

Question 28

What happens when blood pressure drops?

Answer 28

It is directed to more important organs

Question 29

What can prolonged obstruction of blood flow by compression cause?

Answer 29

Severe tissue necrosis

Question 30

How is prolonged obstruction of blood flow by compression avoided?

Answer 30

Shifting position/ turning to ease reactive hyperaemia or high skin tolerance to ischaemia

Question 31

What happens in postural hypotension/oedema due to gravity?

Answer 31

Standing for long periods of time in hot weather will decrease central venous pressure and increased capillary permeability