ANIMALS

Question 1

The circulatory system is

Answer 1

a system of blood vessels with a pump (the heart) and valves to make sure the blood flows one way.

Question 2

Single circulation

Answer 2

fish have a heart consisting of one blood-collecting chamber (the atrium) and one blood ejection chamber (the ventricle). It sends blood to the gills, where it is oxygenated. The blood then flows to all parts of the body before returning to the heart. This is known as single circulation because the blood goes through the heart once for each complete circulation of the body.

Question 3

Double circulation

Answer 3

Blood passes through the heart twice for each complete circulation of the body. The right side of the heart collects deoxygenated blood from the body and pumps it to the lungs. The left side collects oxygenated blood from the lungs and pumps it to the body. The double circulatory system helps to maintain blood pressure, making circulation efficient. Figure 9.1 shows the double circulatory system.

Question 4

double circulatory system

Answer 4

Question 5

The heart is a pump made of muscle that

Answer 5

moves blood around the body. The muscle is constantly active, so it needs its own blood supply, through the coronary artery, to provide it with oxygen and glucose.

Question 6

The heart has two sides. The right side receives deoxygenated blood from the body and then pumps blood to the lungs for oxygenation. The septum separates the left side from the right side. The left side receives oxygenated blood from the lungs and pumps it to the body.

Question 7

There are four chambers. The right and left

Answer 7

atria receive blood from veins and squeeze it into the ventricles. The right and left ventricles receive blood from the atria and squeeze it into arteries. Figure 9.2 shows the main parts of the heart. A surface view of the heart would also show the presence of coronary arteries on the surface of the ventricle muscle walls. For the Core paper, the valves in the heart do not need to be named. You only need to be able to identify where the valves are and understand that they allow the flow of blood only one way.

Question 8

part of heart

Answer 8

Question 9

Structure of the heart

Answer 9

The wall of the left ventricle is much thicker than the wall of the right ventricle because it needs to build up enough pressure to move the blood to all of the main organs. The walls of the atria are much thinner than those of the ventricles. This is because the contraction of the atria needs to be powerful enough only to move blood down into the ventricles, while the ventricles are moving blood around the body and through all of the organs. The septum divides the left side of the heart from the right side. This prevents the mixing of oxygenated and deoxygenated blood.

Question 10

Function of the heart

Answer 10

Heart muscles in the atria contract to build up sufficient pressure to move blood through the tricuspid (right side) and bicuspid valves (left side) into the ventricles. These valves then shut to prevent the backflow of blood. As the muscles in the ventricles contract, blood pressure builds up and the blood is forced through the semilunar valves into the pulmonary artery (right side) and aorta (left side). Once the pressure wave has passed, the semilunar valves close to prevent blood from the arteries being sucked back into the ventricles.

Question 11

Monitoring the activity of the heart

Answer 11

There are a number of ways by which the activity of the heart can be monitored:

• Pulse rate: the ripple of pressure that passes down an artery as a result of the heartbeat can be felt as a ‘pulse’ when the artery is near the surface of the body. • Heart sounds can be heard using a stethoscope. This instrument amplifies the sounds of the heart valves opening and closing.
• An ECG is an electrocardiogram. To obtain an ECG, electrodes, attached to an ECG recording machine, are stuck onto the surface of the skin on the arms, legs and chest. Electrical activity associated with heartbeat is then monitored and viewed on a computer screen or printed out.

Question 12

Effect of physical activity on pulse rate

Answer 12

A heartbeat is a contraction, each of which squeezes blood to the lungs and body. The heart beats about 70 times a minute, more if you are younger, and the rate becomes lower the fitter you are. This beat can be felt as a pulse in the wrist (radial artery) or neck (carotid artery). During exercise, pulse rate increases from the resting rate and stays high until physical activity slows down or stops. After exercise, the pulse gradually returns to normal.

Question 13

Effect of physical activity on heart rate

Answer 13

During exercise, heart rate increases to supply the muscles with more oxygen and glucose. These are needed to allow the muscles to respire aerobically, so they have sufficient energy to contract.

Question 14

Coronary heart disease (a heart attack)

Answer 14

is caused by blockage of the coronary arteries. These supply the heart muscle with oxygen and glucose. Without these, the muscle cells stop contracting and die.

Question 15

risk factor heart attack

Answer 15

Question 16

Prevention of coronary heart disease

Answer 16

Maintaining a healthy, balanced diet will lower the chance of a person becoming obese. The low intake of saturated fats that is part of a balanced diet reduces the chances of atheroma and thrombus formation. An obese person is less likely to take regular exercise. Regular, vigorous exercise can also reduce the chances of a heart attack. This may be because it increases muscle tone – not only of skeletal muscle, but also of cardiac muscle. Good heart muscle tone leads to an improved coronary blood flow and the heart requires less effort to keep pumping.

Question 17

Treatment of coronary heart disease

Answer 17

The simplest treatment for a patient who suffers from coronary heart disease is to be given a regular dose of aspirin. This prevents the formation of blood clots in the arteries, which can lead to a heart attack.

Methods of removing or treating atheroma and thrombus formations include the use of angioplasty, a stent and, in the most severe cases, bypass surgery. Angioplasty involves the insertion of a long thin tube called a catheter into the blocked or narrowed blood vessel.

A wire attached to a deflated balloon is then fed through the catheter to the damaged artery. Once in place, the balloon is inflated to widen the artery wall, effectively freeing the blockage. In some cases, a stent is also applied. This is a wire-mesh tube that can be expanded and left in place. It then acts as scaffolding, keeping the blood vessel open and maintaining the free flow of blood. Some stents can give a slow release of chemicals to prevent further blockage of the artery. In bypass surgery, a section of blood vessel from a different part of the body, such as the leg, is removed. This is then attached around the blocked region of artery to bypass it, allowing blood to pass freely. This is a major, invasive operation because it involves open-heart surgery.

Question 18

Arteries carry blood,

Answer 18

at high pressure, away from the heart to organs of the body. Veins return blood, at low pressure, from organs towards the heart. Capillaries link arteries to veins. They carry blood through organs and tissues, allowing materials to be exchanged.

Question 19

artery

Answer 19

Question 20

vein

Answer 20

Question 21

capillary

Answer 21

Question 22

Functions of arterioles, venules and shunt vessels

Answer 22

The arterioles, linking arteries to capillaries, have proportionately more muscle fibres than arteries. When the muscle fibres of the arterioles contract, they make the vessels narrower and restrict the blood flow (a process called vasoconstriction; see Chapter 14). In this way, the distribution of blood to different parts of the body can be regulated. Shunt vessels, linking the arterioles with venules, can dilate to allow the blood to bypass the capillaries in the skin. This helps to reduce heat loss. Venules return blood to veins.

Question 23

The lymphatic system

Answer 23

The lymphatic system is a collection of lymph vessels and lymph nodes. It has three main roles:

• The return of tissue fluid to the blood in the form of lymph fluid. This prevents fluid build-up in the tissues. • The production of lymphocytes. These are made in lymph glands such as the tonsils, adenoids and spleen. The glands become more active during an infection because they are producing and releasing large numbers of lymphocytes.
• The absorption of fatty acids and glycerol from the small intestine. Each villus contains a lacteal – a blind-ending lymph vessel.

Question 24

Plasma is a

Answer 24

liquid that transports substances to cells and carries wastes away from cells. It acts as a pool for amino acids (these cannot be stored in the body) and contains blood proteins that are important in blood clotting.

Question 25

substance carried in plasma

Answer 25

Question 26

types of cells

Answer 26

Question 27

Transport of oxygen

Answer 27

Oxygen is not included in the table above, as it is transported in red blood cells. Oxygen combines with haemoglobin to form oxyhaemoglobin. The oxygen is released from the red blood cells in capillaries where surrounding oxygen levels are low.

Question 28

lymphocytes phacocyte

Answer 28

Lymphocytes are involved in the production of antibodies, which are needed to fight disease (see Chapter 10). They can attach themselves to antigens (foreign proteins) and clump them together. Phagocytes have the ability to change their shape and move to engulf harmful bacteria by a process called phagocytosis.

Question 29

platelets

Answer 29

Platelets clump together when tissues are damaged and block the smaller capillaries. The platelets and damaged cells at the wound produce a substance that acts on a soluble plasma protein called fibrinogen. As a result, it is changed into insoluble fibrin, which forms a network of fibres across the wound. Red blood cells become trapped in this network and so form a blood clot. The clot not only stops further loss of blood, but also prevents the entry of pathogens (disease-causing organisms) into the wound.

Question 30

Transfer of materials between capillaries

Answer 30

and tissue fluid As blood enters capillaries from arterioles (small arteries), it slows down. This allows substances in the plasma, as well as oxygen from red blood cells, to diffuse through the capillary wall into the surrounding tissues (the capillary wall is thin and permeable). Liquid in the plasma also passes out. This forms tissue fluid, bathing the cells. Waste products from the cells, e.g. carbon dioxide, diffuse back through the capillary walls into the plasma. Some of the tissue fluid also passes back.