Exploring the human body - The cardiovascular system

The cardiovascular system

The cardiovascular system is one of the major body systems. It transports oxygen, carbon dioxide, waste products, nutrients and hormones to and from various parts of the body.

The cardiovascular system is made up of the heart, the blood vessels (arteries and veins and capillaries) and blood. The heart has major vessels that supply it with deoxygenated blood (travels back to the heart from the body), and major vessels that carry oxygenated blood away from the heart to all the parts of the body.

The major vessels that carry blood to and from the heart are:

inferior vena cava conveys deoxygenated blood (blood low in oxygen) from the lower extremities of the body to the heart
superior vena cava conveys deoxygenated blood from the upper extremities of the body to the heart
aorta conveys oxygenated blood (blood high in oxygen) away from the heart.

Activity - Heart

Click on the blue information icons on the torso to locate the major vessels so that you can identify the location of the heart.

The heart

Heart Chambers and valves

The heart is a hollow organ about the size of a fist and is composed of special muscle tissue (cardiac muscle). It lies under the breast bone in the centre of the cardiothoracic cavity. In the average lifetime the heart beats 250 million times and pumps 340 million litres of blood. The heart is a sophisticated pump that is controlled by an electrical current that is initiated in the brain.

The heart is divided into a left and right side by a muscular wall called the septum and has four chambers.

The chambers of the heart include the:

right atrium which receives deoxygenated blood (low in oxygen) from all over the body
right ventricle receives blood from the right atrium and sends it to the lungs via the pulmonary artery to become oxygenated and get rid of carbon dioxide

left atrium receives oxygenated blood from the lungs and sends it to the left ventricle
left ventricle receives blood from the left atrium and sends it out to the body via the aorta.

The heart wall consists of three layers - the endocardium is the inner lining, the myocardium is the muscle layer and the pericardium is the outer covering.

The chambers of the heart are separated by valves:

tricuspid valve is located between the right atrium and right ventricle
bicuspid (mitral) valve is located between the left atrium and left ventricle
pulmonary valve is between the right ventricle and the pulmonary artery
aortic valve is between the left ventricle and the aorta.

Activity - Heart chambers and valves

Answer these four questions about the heart chambers and valves. Use the blue arrow to scroll to the right and use the check button for feedback.

Activity

Click on the blue information icons on the heart diagram to see the heart chambers and valves.

Activity - Major vessels in the heart

In this activity you will revise the location and identity of the major vessels in the heart. Select the correct term and drag it to the correct space.

Blood vessels

The cardiovascular system consists of arteries, veins and capillaries. Arteries carry oxygenated blood to the cells of the body, veins carry deoxygenated blood away from the cells. Capillaries are tiny blood vessels connecting arteries to veins.

Arteries

Arteries are tubes that carry oxygenated blood (high in oxygen) away from the heart.

Arteries have thick, muscular, elastic walls. They branch-off forming arterioles with thinner walls that then become capillaries. Arteries carry blood rich in oxygen and nutrients.

Blood that comes from a wound to an artery is bright red and spurts. The aorta is the largest artery.

Veins

Veins are tubes that carry deoxygenated blood (low in oxygen) from the cells back to the heart where it is pumped to the lungs so that the blood can pick up more oxygen. The veins have one-way valves that help move the blood towards the heart.

Veins have thinner muscular walls. They carry blood back to the heart that is low in oxygen and high in carbon dioxide, a waste product.

Capillaries

Capillaries are very small vessels that surround the cells of the body and facilitate the movement of oxygen and nutrients into the cells and carbon dioxide and waste products away from the cells.

Venous and arterial circulation

View the images of the veins and arteries of the body below.

Body

Body with arteries (red)

Body with veins (blue)

Activity - Venous and arterial circulation

In this activity you will test your understanding of the veins and arteries in the body.

Blood

Blood is made up of a liquid (plasma) and cells. Blood is a connective tissue, a red body fluid made up of liquid (plasma) and cells. The human body contains 5 to 6 litres of blood. Fifty-five percent of the blood is plasma.

For more information on blood and blood products visit the Australian Red Cross Blood Service website at http://www.arcbs.redcross.org.au/.

Plasma

Plasma is a straw coloured watery fluid in which the blood cells are suspended.

It contains antibodies (gamma globulin) and antitoxins, plasma proteins, mineral salts, nutrients, waste products such as urea and creatinine, gases such as oxygen and carbon dioxide, hormones and enzymes.

The blood cells float in the plasma. They are produced in the bone marrow and lymphatic tissues of the body. The bone marrow, liver and spleen destroy worn-out blood cells.

Blood cells

There are 3 types of blood cells.

Red blood cells

1. Erythrocytes or red blood cells (RBC) - carry most of the oxygen and small amounts of carbon dioxide. Haemoglobin carries the oxygen molecule and gives blood its red colour. There are approximately 5 million RBC per cubic millimetre of blood and the average life span is 100 - 120 days.

White blood cells

2. Leucocytes or white blood cells (WBC) - help fight infection as they can attack microorganisms. There are 7,000 - 8,000 WBC per cubic millimetre of blood.

Platelets

3. Thrombocytes (platelets) - are parts of cells which plug small leaks in the walls of blood vessels and initiate blood clotting. There are 200,000 to 400,000 per cubic millimetre of blood.

The flow of blood through the heart

The correct term for contraction of the heart is systole. This is followed by relaxation of the heart called diastole. One systole and diastole form the cardiac cycle. A cardiac cycle takes only 0.8 seconds and during this time the following events occur.

First, the upper chambers, or atria, of the heart relax and fill with blood as the lower ventricles contract, forcing out blood through the aorta and pulmonary arteries. Next the ventricles relax, allowing blood to flow into them from the contracting upper chambers. Then the cycle is repeated; this happens approximately 70 to 80 times per minute.

The rate and rhythm of the heart is regulated by the

nervous system that is made up of specialised nerves that sends out impulses.

An electrocardiogram, or ECG, is a diagnostic test that records the electrical impulses of the heart. It provides information about your heart rate and rhythm, and shows if there is enlargement of the heart due to high blood pressure or evidence of a previous heart attack.

The blood flows around the body continuously due to the regular beat of the heart. Beginning at cells, the passage of blood is as follows:

The diagram below shows the flow of blood through arteries and veins.

The blood cell leaves the heart through the pulmonary valve into the pulmonary artery where it travels to the lungs to be oxygenated.

The oxygenated blood cell returns to the heart through the pulmonary vein into the left atrium. It then moves into the left ventricle through the mitral valve.

The blood cell then moves from the heart into the body through the aorta passing through the aortic valve.

Activity - Blood flow through the heart

In this activity you will test your understanding of the flow of blood through the heart.

Pulse

The pulse is the beat of the heart and the movement of blood through the arteries at various points in the body. The pulse can be found at these major arteries:

Temporal
Carotid
Apical (apex)
Brachial
Radial
Femoral
Popliteal
Pedal (dorsalis pedis).

Counting a pulse

A pulse is defined as a wave of distension of an artery allowing the contraction of the left ventricle of the heart. When counting a pulse it is important to be aware of the rate, the rhythm and the volume.

The normal pulse rate for an adult is 60-100 beats per minute (BPM).

Terminology

Rate: The number of beats per minute.
Rhythm: The regularity of the beats.
Volume: The strength of the beat.
Bradycardia: Decrease in pulse below 60 b.p.m.
Tachycardia: Increase in beats above 100 b.p.m.
The carotid pulse.
The radial pulse.

Feeling the carotid pulse in the neck.

Feeling the radial pulse in the wrist.

Activity - Check for understanding

What are the names of the pulse positions below? Drag the labels to their correct position.

Taking a person’s blood pressure

Blood pressure is the amount of force exerted against the walls of an artery by the blood. The heart muscle contracts and relaxes. The period of contraction is called systole and the period of relaxation is called diastole.

Both systolic and diastolic pressure can be measured. Blood pressure is measured in millimetres (mm) of mercury (Hg). The systolic pressure is recorded over the diastolic pressure. The average adult has a systolic of 120mm Hg and a diastolic of 80 mm Hg. This is written as 120/80 mm Hg.

The normal blood pressure range for an adult is 100/60 to 135/80.

A person is described as having hypertension when they have a reading above 140/90. A reading of below 90/60 is described as hypotension.

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