Physiology of the heart 3

Question 1

What is the coronary supply and why is it unusual?

Answer 1

Supply goes from the outside in rather than other way round. Heart when it contracts obstructs its own blood supply&raquo_space; blood pushed back into arteries

Question 2

CORONARY BLOOD FLOW EQUATION

Answer 2

coronary blood flow = perfusion pressure / resistance

Question 3

What factors influence resistance to flow?

Answer 3

Flow down the tube, length of tube, blood viscousity, diameter of tube (MOST IMPORTANT - R TO POWER 4 RELATIONSHIP)

Question 4

What is meant by the perfusion pressure? When does coronary blood flow occur?

Answer 4

Pressure gradient that drives the coronary blood pressure –> coronary blood flow occurs during diastole. Once the aortic valve snaps shut during relaxation, perfusion of blood to the coronary arteries occurs

Question 5

How is perfusion pressure measured (corresponding values)

Answer 5

Top end of perfusion gradient can be measured by the aorta (diastolic aortic pressure)
Bottom end of ventricular pressure can be measured by the left ventricular diastolic end pressure (this is due to capillaries diffusing through the myocardium to the inner ventricle wall)
DIFFERENCE BETWEEN THESE 2

Question 6

Cardiac O2 consumption for arrested, resting and heavy exercise ?

Answer 6

Arrested (alive but not contracting) - 2ml/min/100g
Resting - 8ml/min/100g
Heavy exercise - 70ml/min/100g

Question 7

O2 consumption from brain, kidney, skin and muscles?

Answer 7

Brain - 3ml/min/100g
Kidney - 5ml/min/100g
Skin - 0.2ml/min/100g
Resting muscle - 1ml etc
Contracting - 50ml etc... high demand in contracting muscles!

Question 8

What does arterial O2 concentration depend on?

Equation for O2 delivery??

Answer 8

How much O2 bound to haemoglobin (1 molecule = 4 molecules O2)
o2 delivery = arterial o2 conc x coronary blood flow

Question 9

What is anaemia characterised by?

Answer 9

Reduced O2 delivery (low iron)

Question 10

What impacts aortic pressure?

Answer 10

Local and mechanical factors

Question 11

How can perfusion pressure be measured? Approx values?

Answer 11

Aortic pressure = around 120mmHg !! aorta can support high pressure due to the presence of valve
LVDEP = around 8-10mmHg –> once the heart contracts, contract goes up and then straight back down as the heart relaxes (no vlave present to support)

Question 12

Factors influencing coronary blood flow?

Answer 12

INCREASED HEART RATE = decreased time between systoles, causes a decrease in perfusion time
RAISED LVDEP or DECREASED DP = decreased perfusion pressure (decrease at either end of equation as the gradient for perfusion is decreased)

Question 13

What is meant by autoregulation of the coronary circulation?

Answer 13

Ability of an organ to maintain blood flow despite changes in perfusion pressure.

Question 14

What is the impact of perfusion pressure and resistance on coronary blood flow?

Answer 14

Decreased perfusion pressure = decreased coronary blood flow
Decreased resistance AND perfusion pressure = coronary blood flow srays the same

Question 15

What is the impact of hypoxia on vascular control of the coronary arteries

Answer 15

Causes vasodilation via a circulating molecule called adenosine
ALso causes build up of lactic acid, co2 and K+/H+ ions

Question 16

What hormones are released by the heart and where do they act?

Answer 16

ANP - atrial natriuretic peptide - released by heart due to the stretching of atria and ventricular smooth muscle cells

BNP - brain natriuretic peptide

Question 17

What is the impact of ANP and BNP?

Answer 17

KIDNEY - increase renal excretion of Na+ and H20
S.MUSCLE.CELLS - relaxation (apart from renal arterioles)
Blood vessels - increase vascular permeability

Also inhibit the release of angiotensin II, endothelin and aldesterone

Question 18

ANP / BNP mechanism of action?

Answer 18

Peptides attach to receptors and are then metabolised.

The enzyme involved is NEUTRAL ENDOPEPTIDASE. This is inhibited by VALSARTAN (heart failure therapy)

Question 19

What receptors do hormones act on in the large and small arteries and why is this important?

Answer 19

IMPORTANT PHYSIOLOGICALLY as they impact small arteries that cover a large surface area. Large arteries are more important pathologically
Large coronal arteries = A receptors –> cause vasoconstriction
Small vessels =B2 adrenergic receptors, stimulation causes vasodilation