Circulation in mammals and Heart Disease

Question 1

Describe the passage of blood through the heart.

Answer 1

1. Deoxygenated blood comes into the heart atria via the vena cava.
2. The blood is then taken to the lungs via the pulmonary artery.
3. The oxygenated blood comes back to the heart via the pulmonary vein.
4. The blood is pumped around the body via the aorta.

Question 2

What is the role of the arteries?

Answer 2

They carry blood from the heart to the rest of the body.

Question 3

What adaptations do the arteries have?

Answer 3

1. The walls are thick and muscular to maintain high blood pressure.
2. The walls have elastic tissue to recoil as the heart beats which also maintains the high pressure.
3. They have a small lumen
4. A folded endothelium which allows the arteries to stretch and maintains high blood pressure.

Question 4

What is the role of the veins?

Answer 4

They carry blood from the body to the heart.

Question 5

What adaptations do the veins have?

Answer 5

1. Wider lumen
2. Very little elastic and muscle tissue.
3. They contain valves which help stop the backflow of blood.

Question 6

What is the role of the capillaries?

Answer 6

Where the exchange of substances between the blood and cells happens.

Question 7

What adaptations do the capillaries have?

Answer 7

1. They have walls that are one cell thick to decrease the diffusion distance.
2. There are a large number of capillaries to increase the surface area for exchange.

Question 8

What is tissue fluid?

Answer 8

The fluid that surrounds cells in tissues.

Question 9

What is tissue fluid made out of?

Answer 9

Small molecules like oxygen, water and nutrient that leave the blood plasma.

Question 10

Why does tissue fluid not contain red blood cells and big proteins?

Answer 10

They are too big to move through the capillary walls.

Question 11

What is the process in which tissue fluid is made?

Answer 11

pressure filtration.

Question 12

What happens in pressure filtration?

Answer 12

At the arteriole ends of the capillaries, the hydrostatic pressure is higher in the capillaries compared to the tissue fluid. This forces fluid into the spaces around the cells creating more tissue fluid. At the venule end of the capillaries, the hydrostatic pressure is lower as some water has left the capillaries. Due to the loss of fluid and an increase in the concentration of big proteins at the venule end the water potential inside the capillaries is lower compared to the tissue fluid. This causes water to move back into the capillaries via osmosis. The excess tissue fluid is then drained by the lymphatic system.

Question 13

How do heart valves work?

Answer 13

If there is pressure in front of the valve it is forced shut and if there is pressure behind it the valves are forced open.

Question 14

What are the different parts of the cardiac cycle?

Answer 14

1. Atrial systole
2. Ventricular systole
3. Diastole

Question 15

What happens during atrial systole?

Answer 15

The atria contract, this decreases the volume of the chambers and increases the pressure. The blood is then pushed into the ventricles. There is a slight increase in the pressure and volume of the ventricles as it receives the blood.

Question 16

What happens during ventricular systole?

Answer 16

The atria relax. The ventricles contract and this decreases the chamber volume and increases the pressure. The pressure inside the ventricles is higher compared to the atria which causes the AV valves to close. The pressure inside the ventricles is higher compared to the arteries so the semi-lunar valves open. This forces blood out of the heart and into the arteries.

Question 17

What happens during diastole?

Answer 17

The ventricles and atria relax. The pressure in the arteries is higher compared to the ventricles so the semi-lunar valves are forced closed. The atria start to fill again and because the pressure inside the ventricles keeps decreasing blood is pushed passively into the ventricles through the AV valves. The atria contract and the process restarts.

Question 18

How do you measure the cardiac output?

Answer 18

stroke volume x heart rate

Question 19

What is the heart rate?

Answer 19

The number of beats per minute.

Question 20

What is the stroke volume?

Answer 20

The volume of blood pumped during each heartbeat. cm cubed

Question 21

What is cardiovascular disease?

Answer 21

Diseases associated with the heart and blood vessels.

Question 22

What do most cardiovascular diseases start with?

Answer 22

The formation of an atheroma.

Question 23

Hoe does an atheroma form?

Answer 23

1. Damage occurs to the endothelium of arteries and fatty deposits build up under the lining.
2. The build-up hardens to form a fibrous plaque called an atheroma.

Question 24

What does an atheroma do?

Answer 24

It blocks the lumen of an artery and restricts blood flow. This causes the blood pressure to increase.

Question 25

What is an aneurysm?

Answer 25

The formation of atheromas weakens the arteries. When blood travels through the weakened arteries at high pressure they can push the inner layers of the arteries through the elastic layer and cause a ballon-like swelling called an aneurysm. If this burst it can cause a haemorrhage.

Question 26

What is thrombosis?

Answer 26

When the atheromas rupture and damage the arteries platelets and fibrin accumulate at the site of damage. This can completely block arteries and stop blood flow.

Question 27

What are the risk factors for cardiovascular disease?

Answer 27

1. High blood pressure.
2. High cholesterol levels
3. Cigarette smoking ( which contains carbon monoxide.)

Question 27

What is myocardial infection?

Answer 27

A heart attack. It is caused by the coronary arteries being blocked and no longer supplying the heart muscle with oxygen which it needs for respiration and the release of energy so the heart can beat.