Week 0

Question 1

What factors affect blood flow?

Answer 1

1. Velocity-the distance blood travels in a unit of time.
2. Viscosity-thick, sticky consistency, it depends on red cell content. The more red cells, the more viscous the blood.
3. Laminar flow-‘straight ahead’ flow.
4. Turbulent flow-when flow is obstructed, vessels turn or blood flows over rough surfaces.
5. Vascular compliance-the increase in volume a vessel is able to accommodate for a given increase in pressure.

Question 2

What affects the regulation of blood pressure?

Answer 2

1. Arterial pressure- cardiac output x peripheral resistance.
2. Cardiac output-can he changed by heart rate, stroke volume or both.
3. Total resistance in the systemic circulation (SVR)- a function of the diameter of the arterioles (baroreceptors, arterial chemoreceptors, hormones and other mediators ie. Nitric oxide)
4. Venous pressure-the volume of blood within the veins and compliance of vessel walls.

Question 3

How does auto regulation maintain coronary circulation?

Answer 3

It enables organs to regulate blood flow by altering the resistance (diameter) in their arterioles. It helps ensure constant coronary blood flow despite shifts in the perfusion pressure within the stated range.

Question 4

What are the 5 factors that affect cardiac output?

Answer 4

1. Frank-starling law of the heart
2. Laplace’s law
3. Afterload
4. Myocardial contractility
5. Heart rate

Question 5

How does frank-starling law of the heart affect cardiac output?

Answer 5

The law states that the stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch causing a more forceful systolic contraction.

Question 6

What is Laplace’s law and how does it affect cardiac output?

Answer 6

The law states that the wall tension is related directly to the product of intraventricular pressure and internal radius and inversely related to the wall thickness.
It is useful in understanding aneurysm formation, distensibility in blood vessels, and the effects of ventricular dilation on myocardial contraction.

Question 7

How does afterload affect cardiac output?

Answer 7

It is the resistance to ejection of blood from the ventricle.
Decreased afterload enables the heart to contract more rapidly, increased afterload slows contraction and causes higher workloads against which the heart must function to eject blood.

Question 8

How does myocardial contractility affect cardiac output?

Answer 8

Stroke volume depends on the force of contraction (myocardial contractility). It can be affected by:

1. Changes in the stretching of the ventricular myocardium caused by changes in the preload.
2. Alterations in the inotropic stimuli of the ventricles.
3. Adequacy of myocardial oxygen supply.

Question 9

What 5 structures that direct circulation through the heart?

Answer 9

1. Heart wall-epicardium, myocardium and endocardium
2. Chambers of the heart-right and left atrium, right and left ventricle
3. Fibrous skeleton
4. Valves of the heart-mitral and tricuspid (control blood flow from the atria to the ventricles), and the aortic and pulmonary valve (controls blood flow out of the ventricles)
5. Great vessels-superior and inferior vena cava, pulmonary artery, pulmonary vein and the aorta.