Heart

Question 1

Describe the parts played by the sinoatrial node (SAN) and the atrioventricular node (AVN) in controlling the heartbeat.

Answer 1

1SAN initiates / sends heart beat;
2Myogenic / beats spontaneously / does not require nerve impulse;
3Rate of beating influenced by nerves:
4Wave of electrical activity / impulses / excitation passes over atrium;
5Triggers contraction of atrium;
6Electrical activity can only pass to ventricles / along bundle of His by way of AVN
7Fibrous tissue prevents passage elsewhere;
8 Delay at AVN;
9 Allows blood to empty into ventricles / atria to empty;

Or

1. SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction;
2. Non-conducting tissue prevents immediate contraction of ventricles/prevents impulses reaching the ventricles;
3. AVN delays (impulse) whilst blood leaves atria/ventricles fill;
4. (AVN) sends wave of electrical activity / impulses down Bundle of His;
5. Causing ventricles to contract from base up;

Question 2

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.

Answer 2

1. Atrium has higher pressure than ventricle (due to filling/contraction);
2. Atrioventricular valve opens;
3. Ventricle has higher pressure than atrium (due to filling/contraction);
4. Atrioventricular valve closes;
5. Ventricle has higher pressure than aorta;
6. Semilunar valve opens;
7. Higher pressure in aorta than ventricle (as heart relaxes);
8. Semilunar valve closes;
9. (Muscle/atrial/ventricular) contraction causes increase in pressure;

Question 3

Cardiac Output

Answer 3

Cardiac Output is the amount of blood flowing through the heart each minute. It is calculated as the product of the heart rate and the stroke volume:

Cardiac output = heart rate x stroke volume

• The heart rate can be calculated from the pressure graph by measuring the time taken for one cardiac cycle and using the formula:

Heart rate (beats per minute) =60 ÷cycle time (s)

• The stroke volume is the volume of blood pumped in each beat.

Both the heart rate and the stroke volume can be varied by the body. When the body exercises the cardiac output can increase dramatically so that

• Oxygen and glucose can get to the muscles faster
• Carbon dioxide and lactate can be carried away from the muscles faster
• Heat can be carried away from the muscles faster

Question 4

What is atheroma? (2)

Answer 4

Plaque/ fatty material/ cholesterol/ foam cells/ lipoprotein build up;

In artery/ blood vessel wall;

Question 5

Describe how atheroma can lead to an aneurysm. (2)

Answer 5

Weakens artery wall;

So that it swells/ bursts;

Question 6

Describe how atheroma may form and lead to a myocardial infarction.(6)

Answer 6

1 fatty substance / foam cells / cholesterol in artery wall / under endothelium;
2 formation of plaques / atherosclerosis / atheroma narrows lumen of artery;

3 atheroma creates turbulence / damage to lining of artery;
4 (turbulence) increases risk of blood clot / embolus;
5 blood clot / thrombus breaks off;
6 (blood clot) lodges in coronary artery;
7 reduced blood supply to heart muscle;
8 reduced oxygen supply;
9 leads to death of heart muscle;

Question 7

Cigarette smoking and a diet high in saturated fat increase the risk of myocardial infarction. Explain how.(6)

Answer 7

Carbon monoxide combines with haemoglobin/causes less
oxygen to be transported;
Decreases concentration of antioxidants in blood;
Increases the damage done to artery walls;
Blood clot may occur;*
Blood pressure increased*
Blocks flow of blood to heart/in carotid arteries;*

Saturated fat associated with cholesterol;
Cholesterol deposited in arteries;
Atheroma formation;
Blood clot may occur*;
Blood pressure increased*
Blocks flow of blood to heart/in carotid arteries*;

*Allow reference to these points only once.

Cholesterol / blood clot causes constriction of coronary arteries;
Less oxygen transported to heart muscle tissue;

Question 8

Explain how smoking and a high blood cholesterol concentration increase the risk of developing coronary heart disease. (6)

Answer 8

CHD = heart muscle receives inadequate amount of blood or oxygen / (coronary) blood supply reduced;

Smoking:

Raises concentration of fibrinogen (in blood) / increased risk of clotting;
Increases viscosity of blood;
(Nicotine) causes platelets to stick together / causes vasoconstriction;
Carbon monoxide associated with plaque formation;
Reduces ability of arteries to dilate / reduces elasticity;

Cholesterol:

Fatty streaks / deposits adhere to wall of arteries;

Atheroma / atherosclerosis / plaque;

Narrows lumen of artery;

Damages endothelium;

Can lead to formation of thrombus / blood clot;

Clots need to be in context

Question 9

Explain the effect of smoking on blood pressure; (2)

Answer 9

Because arteries cannot dilate / dilate less;
Heart must work harder to force blood through;
Increases blood pressure;

Question 10

Explain how smoking might lead to the formation of a blood clot. (3)

Answer 10

Higher blood pressure causes damage to blood vessel lining / endothelium/ collagen;
Platelets stick together / form a plug / adhere to collagen fibres;
Release of thromboplastin / thrombokinase;
Fibrinogen converted to insoluble fibrin;
Platelet plug trapped by fibrin mesh;