The Circulatory System

The Circulatory System

characteristics of blood vessels (Summary)

Structure and Function of blood vessels

Circulatory Disease

Systemic and Pulmonarycirculation

Created by and used with the permission of Ray Morgan

How Blood Moves Through The Four Chambers Of The Heart

Cardiac output

The Cardiac CycleHeart Rateand Stroke volume

The coronary arteries

Blood vessels and Valves of the Heart

Structure of the Heart

The Heart

Location and function of the heart

Created by and used with the permission of Ray Morgan

Blood Pressure

What is blood pressure (BP)? Blood pressure is defined as 'the amount of pressure that is exerted on the artery walls as the blood moves through them'. This is vital for driving the circulating blood through the blood vessels to the various places in the body, forcing it through the tiny capillaries, and enabling it to move upwards against gravity.The pressure of blood flowing through the arteries varies due to the pumping action of the heart. When the heart contracts (ventricular contraction), blood is pumped out of the heart and into the arteries under the hlghest pressure (systolic BP). When the heart relaxes (ventricular relaxation) between pumps, the pressure in the arteries is at its lowest (diastolic BP). The pumping and relaxation phases of the heart are referred to as 'systolic" and "diastolic", respectively. Without this pressure, blood would gravitate, or pool, in the lowest parts of the body.Blood pressure is constantly changing to meet the body's needs. It is normal for it to increase during exercise and to decrease in periods of rest, such as when sleeping. Long-term, regular aerobic exercise can have a normalising effect on elevated blood pressure.

Cardiovascular responses to exercise

Implications of Hypertension and hypotension on exercise participation

Blood Pressure responses to exercise

The first number represents the highest level blood pressure reaches when the heart contracts (systolic) and pumps blood into the arteries. The second number represents the lowest level blood pressure reaches In the arterles when the heart relaxes (diastolic).Systolic pressure - The contraction phase of the myocardiumDiastolic pressure - The relaxation phase of the myocardium.Classifications of blood pressure measurementsHypotension This is low blood pressure and is a reading of <90 systolic over <60 diastolic. Hypotension is not generally considered a health risk but could be indicative of other health issues. It is most common in those who are young, female, of slight build, fit and strictly vegetarian.Normal - 90-120 systolic over 60-80 diastolic. Normal blood pressure indicates a healthy cardiovascular system, with sufficient pressure to supply all of the organs with blood, but not too high to cause damage.Pre-hypertension - 120-140 systolic over 80-90 diastolic. Pre-hypertension is not a contraindication to exercise but does sugsest that lifestyle changes should be advised to prevent the condition worseningHypertension - >140 systolic over >90 diastolic. Hypertension is very common. It is most likely in those who are older, male, overweight, unfit, stressed and have a poor diet. Chronlc hypertenslon results in a constant strain and battering of the smooth inner artery walls, which is associated with an increased risk of coronary heart disease, stroke, kidney dysfunction and some forms of dementia. High blood pressure often accompanies atherosclcrosis and arteriosclerosis. By managing blood pressure with a healthy lifestyle -and in some cases medication - the risk of associated disease can be decreased.

Created by and used with the permission of Ray Morgan

How Blood Moves Through The Four Chambers Of The Heart

As illustrated in the the diagram, the atria receive blood from the body or lungs and the ventricles pump blood to the body or lungs.The left atrium receives oxygenated blood from the lungs via the pulmonary veins and the right atrium receives blood from the vena cava. The left ventricle pumps oxygenated blood through the aorta to the rest of the body. Two large vein (finferior and superior vena cava) return de-oxygenated blood from the body to the right atrium. When the right ventricle contracts de-oxygenated blood is pumped to the lungs via the pulmonary arteries. Heart valves between the atria, ventricles, and aortic and pulmonary arteries determine the pathway of blood through the heart and stop the backward flow of the blood.

The vascular system has two major pathways of circulation. These are pulmonary (lungs) and systemic (body).Pulmonary circulationPulmonary circulation is the flow of blood from the right side of the heart to the lungs and then back to the left side of the heart.The right ventricle pumps de-oxygenated blood via the pulmonary arteries to the lungs. Pulmonary diffusion then takes place in the lungs. Carbon dioxide is exhaled, and oxygen is inhaled. This exchange takes place via the pulmonary capillaries. The capillaries unite to form venules and then veins and finally to form the two pulmonary veins from both lungs that return oxygenated blood to the left atrium.Systemic circulationSystemic circulation is the flow of blood from the left side of the heart to all parts of the body and then back to the right side of the heart. The left ventricle pumps blood via the aorta into the arteries, arterioles and capillary networks throughout the body. The capillaries merge to form venules and veins. The veins return blood to the right atrium.

Systemic and pulmonary circulation

Arteries

The arteries carry blood away from the heart at high pressure to the capillaries. Arteries become progressively smaller, becoming arterioles as they reach the tissues. Arteries are characterised by their thick walls, made up of smooth muscle and elastic connective tissue that allow them to expand and recoil. The internal diameter of arteries which allows the passage of blood is small which also acts to support this high-pressure environment. Following ventricular contraction, the expansion and recoil of the artery wall contributes to the maintenance of adequate blood pressure. The pressure in the large arteries is very high, but diminishes as the arteries become smaller and get further away from the heart. Without this pressure, blood would gravitate to the lowest parts of the body. Blood pressure enables the circulating blood to move upwards against gravity to supply blood to the brain, as well as forcing blood through the tiny capillaries.

Structure And Function Of Blood Vessels

The vascular, or circulatory system consists of the arteries and veins through which the heart pumps blood throughout the body. The prime purpose of the vascular system is the transport and exchange of materials (oxygen, carbon dioxide, nutrients, hormones, heat, metabolic waste products and protective white cells) between the blood and tissues, which takes place in the capillaries. With increasing age (and the presence of medical conditions/disease processes), blood vessels become less elastic and therefore less efficient carriers of blood. One example of this is when vessels become susceptible to atherosclerosis. This is when the inner walls of arteries become coated in places with atheromatic plaques: cholesterol-containing material that occludes (closes up) the vessels, preventing efficient blood circulation. Since the functioning of all tissues is dependent on good blood circulation, these factors have widespread effects on this system.

Characteristics Of Blood Vessels(Summary)

Structure of the Heart

The heart consists of four chambers: two upper atria and two lower ventricles. The walls of the four chambers are made of cardiac muscle, called the myocardium. The coronary arteries deliver a constant supply of oxygen-rich blood to the myocardium, which is necessary for the muscular contraction of the heart.The atria are smaller than the ventricles and have thinner muscle walls. The left ventricle has a thicker muscle wall than the right ventricle because the left ventricle must forcefully contract to pump blood all around the body via the aorta (the largest artery in the body), whereas the right ventricle only must pump blood to the lungs.

Location and function of the heart The heart is located posterior to the sternum, just left of the centre in the chest. It is about the size of an adult clenched fist and is a muscular pump responsible for circulating blood around the body. The circulating blood carries oxygen and nutrients around the body whilst also removing carbon dioxide and waste products to be expelled from the body

Veins

Veins carry blood back to the heart under low pressure. Smaller veins are called venules. The walls of veins are thin, made up of significantly less smooth muscle and elastic connective tissue than arteries; they therefore do not have the same capacity for elastic expansion and recoil as arteries and require the assistance of skeletal muscle to help venous return. Venous return is the amount of blood that is returned to the heart by the veins. The heart can only pump the blood that it receives. If venous return decreases, the heart contracts less forcefully, causing a decrease in blood pressure. The vena cava has two branches (inferior and superior) and returns blood from the body back to the right atrium. The pulmonary veins return blood back to the left atrium. Veins have one-way (non-return) valves at regular intervals to prevent the backflow of blood and larger diameters than arteries enabling them to hold approximately two-thirds of all circulating blood.Remember this: The pulmonary vein transports oxygenated blood from the lungs to the heart; all other veins carry de-oxygenated blood.

Cardiac Output

Cardiac output is the amount of blood pumped out by the ventricles in one minute. During exercise, cardiac output must increase to meet the body's demand for oxygen. A simple formula enables cardiac output to be determined:

• Cardiac output = stroke volume x heart rate

If an average stroke volume is 71 ml, and an average resting heart rate is 70 bpm, then:

• Cardiac output= 71 ml x 70 bpm = 4,970 ml per minute, or nearly 5 litres of blood

As indicated, a key adaptation to a regular endurance exercise programme is that the resting heart rate decreases and stroke volume increases. For example, a well-trained individual whose stroke volume is 100 ml and heart rate is 50 bpm has a cardiac output of:

• 100 ml x 50 bpm =5,000 ml

Cardiac output can be maintained with fewer beats in such individuals.

The Cardiac Cycle

The cardiac cycle is the sequence of events in one beat of the heart (the alternate contraction and relaxation of the heart). The contraction phase is called systole, which causes a volume of blood to be pumped to the arteries. When the heart relaxes, this is called the diastole and blood flows into the heart from the veins. This cycle of events helps to keep the blood moving from the veins through the heart and to the arteries.

Heart Rate

A healthy adult has a resting heart rate of between 60-80 beats per minute (bpm), whereas a well-conditioned individual tends to have a resting heart rate of around 35-50 bpm. The heart is a muscle and, just as skeletal muscles get stronger when exercised, so does the heart. The muscular walls of the left ventricle can sometimes increase in size, this is called cardiac hypertrophy.

Stroke Volume

Stroke volume is the amount of blood pumped out of the heart by the left ventricle in one beat. A normal stroke volume at rest is between 70-80 ml per beat. In well-trained individuals, stroke volume at rest is 100-110 ml per beat. During exercise, stroke volume increases, and in well-trained individuals, values as high as 200 ml per beat have been recorded.

Capillaries

Capillaries are the smallest of the blood vessels and carry blood from arterioles to venules. The capillary walls are only one cell thick. The diameter is just wide enough for the passage of a red blood cell, therefore flow is very slow. It is in the capillaries that the exchange of materials between the blood and tissues takes place; the process by which this exchange occurs is called diffusion.