Special circulation

Question 1

What are some special adaptations of the coronary circulation?

Answer 1

High capillary density
High basal blood flow
High oxygen extraction (75% compared to 25% whole body average)

Question 2

What are the 2 ways in which coronary blood flow is controlled?

Answer 2

Intrinsic mechanism
Extrinsic mechanism

Question 3

What are the intrinsic mechanisms of coronary blood flow control?

Answer 3

Decreased pO2 causes vasodilation of the coronary arteries
Metabolic hyperaemia matches flow to demand
Adenosine is released from ATP during increased respiration, which acts as a potent vasodilator

Question 4

What are the extrinsic mechanisms of coronary blood flow control?

Answer 4

Coronary arterioles are supplied by sympathetic vasoconstriction nerves, but this is over-ridden by metabolic hyperaemia due to increased HR and SV
This means sympathetic stimulation results in coronary vasodilation
Adrenaline is also released by the adrenal glands due to sympathetic stimulationn, which activates ß2 receptors, and causes further vasodilation
ß2 receptors are more abundant in coronary arteries and arterioles

Question 5

How do varicose veins occur?

Answer 5

Blood can pool in the lower limb veins, when venous valves become incompetent

Question 6

Why do varicose veins not decrease Cardiac Output?

Answer 6

There are chronic compensatory systems that increase blood volume

Question 7

What is meant by the skeletal muscle pump?

Answer 7

Large veins in the limbs lie between skeletal muscles
Contraction of these muscles thus aids venous return

Question 8

How do pulmonary arterioles protect against hypoxia?

Answer 8

Hypoxia causes vasoconstriction of the pulmonary arterioles, which helps divert the blood supply away from the poorly ventilated alveoli, to the well ventilated alveoli