At the end of this unit, you should know that :
- The components of the cardiovascular system are the heart and blood vessels.
- There are three types of blood vessel: arteries, capillaries and veins.
- Arteries carry blood away from the heart and must be able to withstand the pressure caused by the heartbeat. They have thick, elastic walls which can stretch and recoil in response to the heartbeat. Blood pressure decreases as blood moves along arteries away from the heart.
- Capillaries allow the exchange of materials to take place between the blood and body cells. Their walls are only one cell thick and have a tiny diameter just wide enough to enable red blood cells to pass through them. Blood pressure is less than in arteries.
- Veins carry blood back to the heart. Blood pressure is very low in veins so that they have much thinner, less elastic walls than arteries. They also contain valves which prevents blood flowing backwards. Blood is pushed towards the heart when the veins are squeezed as the muscles around them contract.
- Arteries have a smaller lumen than veins.
- The mammalian heart consists of two atria (upper chambers) and two ventricles (lower chambers).
- The left and right sides of the heart are completely separated from each other by the septum.
- The right atrium receives deoxygenated blood from the body via the venae cavae and passes it to the right ventricle through the tricuspid valve. The right ventricle pumps the blood out into the pulmonary artery which carries it to the lungs to be reoxygenated.
- Oxygenated blood from the lungs is carried back to the left atrium of the heart via the pulmonary vein. The left atrium passes the blood to the left ventricle through the bicuspid valve. The left ventricle then pumps the blood out into the aorta which carries it round the body.
- The bicuspid and tricuspid valves are known as atrio-ventricular (AV) valves. Semilunar valves are found at the entrance to the aorta and pulmonary artery. Their function is to prevent the backflow of blood.
- The atrio-ventricular valves are attached to the walls of the ventricles by tendons called chordae tendinae which prevent the valves inverting when the ventricles contract.
- The atria have thinner walls than the ventricles because they only need to generate enough pressure to push the blood down into the ventricles.
- The left ventricle is much thicker than the right because the left ventricle has to pump blood all around the body while the right ventricle has only to pump blood to the lungs, which are situated next to the heart.
- The mammalian circulatory system is a closed double circulation. It is said to be closed because blood is carried round the body enclosed in vessels. It is a double circulation because, in one complete circulation of the body, blood passes through the heart twice, once going to the lungs (pulmonary circulation) and once to the rest of the body systems (systemic circulation).
- The cardiac cycle refers to the pattern of contraction and relaxation of the heart muscle which occurs during one complete heartbeat. Contraction of the heart muscle is known as systole, while relaxation is called diastole.
- The pulse rate corresponds to the heart rate and can be measured by gently placing the fingers over the pulse and counting. The heart rate increases directly in proportion to the amount of work done.
- Normal resting heart rates are 60-100 bpm, but are lower in fitter people.
- The stroke volume is the volume of blood pumped out of the heart with each heartbeat.
- Cardiac output is the volume of blood pumped out of the heart every minute. It is usually measured in litres/minute.
- An individual’s cardiac output is be worked out by multiplying the heart rate by the stroke volume.
- Blood pressure describes the pressure in the aorta and is measured using a sphygmomanometer and stethoscope. Blood pressure in measured in mm Hg.
- Sytolic blood pressure is the pressure in the arteries when the heart contracts (systole).
- Diastolic blood pressure is the pressure in the arteries when the heart relaxes (diastole).
- Blood pressure is written as systolic/diastolic. Normal blood pressure for an adult is 120/180 mm Hg.
- People with blood pressures over 160/95 mm Hg have high blood pressure and are hypertensive. Hypertension is one of the main causes of cardiovascular disease (CVD).
- Atherosclerosis is another disease process which leads to CVD. It results from a build up of plaque on the inner lining of arteries, which reduces the flow of blood through the artery.
- Examples of CVD are: thrombosis, angina pectoris, myocardial infarction (heart attack), stroke.
- A thrombosis occurs when a blood clot forms in a artery, completing blocking the flow of blood. If this happens in one of the coronary arteries in the heart it causes a heart attack or myocardial infarction. If it occurs in an artery in the brain it causes a stroke.
- Angina pectoris occurs when the blood vessels in the heart are partially blocked due to atherosclerosis. During exercise blood flow cannot increase to meet the needs of the heart muscle and chest pain results. The pain disappears when the exercise stops.
- Coronary heart disease (CHD) is more common in countries with high fat diets, high smoking rates and sedentary lifestyles (such as the
UK). Developing countries tend to have lower incidences of CHD but numbers there are increasing. - Modifiable risk factors in CVD are those which can be decreased by lifestyle changes. They include: diet, smoking, activity and obesity.
- Non-modifiable risk factors cannot be decreased by lifestyle changes. They include: age, gender, heredity and race (ethnicity).
- Exercise increases heart rate and cardiac output.
- During exercise systolic blood pressure increases but diastolic blood pressure remains constant.
- Regular exercise improves recovery time.
- During exercise more blood is distributed to skeletal muscles and the skin, while less blood is distributed to abdominal organs. The distribution of blood to the brain remains constant both before and during exercise.
- Cardiac hypertrophy is a fundamental adaptation to increased workload imposed by exercise training. It involves the muscle fibres of the heart becoming larger as a result of increased protein synthesis. This increase in size of the cardiac muscles enables them to contract more forcibly.
- The stroke volume of the heart of an endurance athlete is much greater than that of an untrained individual as a result of cardiac hypertrophy.
- Protective effects of exercise include: improved myocardial circulation, enhanced contractile properties of myocardium, improved blood lipid profile, lowered heart rate and blood pressure, decreased body fat.
- Maximal testing involves measuring the maximum rate at which the body is able to take up and use oxygen (VO2max). The greater the VO2max the fitter is the individual.
- Sub-maximal testing
- involves measuring heart rate and oxygen consumption at lower intensity exercise levels than that used in maximal testing;
- assumes that there is a linear relationship between heart rate, oxygen consumption and level of exercise;
- is less accurate than maximal testing because heart rate can be affected by factors other than exercise.
- A stress test records an individual’s ECG traces before, during and after exercise
- The results of a stress test are used to establish exercise limits and to develop a fitness programme for the rehabilitation of cardiac patients.