Properties of special circulations Flashcards
Where is the arterial supply for the coronary arteries
Emerges out of the base of the aorta, after it exits the left ventricle. Blood collects in veins, drains into coronary sinus, delivering blood to the right atrium
Describe the special requirements of coronary circulation
Needs a high basal supply of O2, 20x resting skeletal muscle
Increase O2 supply in proportion to oincreased demand/cardiac work
Describe special structural features of coronary circulation
High capillary density, large SA for O2 transfer, reduces diffusion distance, diffusion time proportional to d^2, so O2 transport is fast
How does cardiac muscle have shorter diffusion distance
High number of fibres and capillaries. Fibres are smaller than in skeletal muscle.
Describe special functional features of blood circulation during normal activity
High blood flow - 10x the flow per weight of rest of body,
Relatively sparse sympathetic innervation
High nitric oxide released leading to vasodilation
High O2, extraction (75%), average in body is 25%
Describe special functional features of circulations during increased demand
Coronary blood flow increases in proportion to demands
Production of vasodilation, adenosine K+, acidosis, outcompete relatively low sympathetic vasoconstriction
Circulating adrenaline dilates coronary vessels due to abundance of B2-adrenoceptors
What causes a Bohr shift in haemoglobin saturation/amount of O2 in plasma during normal activity
Coronary sinus blood returning to right atrium from myocardial tissue has a higher CO2 content due to high capillary density, SA and small diffusion difference.
High CO2 and low pH shifts curve to the right, haemoglobin less affinity for oxygen, more oxygen unloaded. 75% unloaded
What does increased oxygen requirement produce in terms of blood flow
Increase in blood flow. Myocardium metabolism generates metabolites to produce vasodilation, increasing blood flow (metabolic hyperaemia)
e.g. Adenosine, produced by ATP metabolism, and is released from cardiac myocytes, also increases in pCO2, H+, K+ levels.
What are functional end arteries
Arteries that occur where only a single artery supplies blood to a particular area of tissue, whereas collateral arteries provide an alternate path for blood to get to a particular area of tissue, so it receives blood from more than one artery.
What is angina caused by (and possible myocardial infarction)
Slow narrowing of an artery e.g. buildup of an atheroma
What is necrosis
When tissue no longer contracts or conducts a depolarisation signal (cell death)
What is thrombosis
Total occlusion of left anterior descending coronary artery - Ischemic tissue, acidosis, pain, impaired contractility, sympathetic activation, arrhythmias, cell death
What is stable angina
Pain in the chest/breathlessness during exercise caused by metabolic hyperaemia
How is systole different in a failing heart
No complete expulsion of the blood, so ESV exerts a pressure in the ventricle during diastole. This opposes cardiac circulation.
How is diastole a window for cardiac blood flow
Aortic pressure remains high because of stretchiness of aorta, ventricular pressure decreases, allowing blood flow around arteries
