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Understanding the basic anatomy and physiology of the human body

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:

This information is important so that you can gain an understanding of how the heart works and some of the conditions that may affect the functioning of the heart.

Click here to roll over a diagram to locate the major vessels and so that you can identify the location of the heart.

Activity 4

Click here to test your understanding of the location of the heart

Heart

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.

Heart chambers and valves

The chambers of the heart include the:

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:

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

Click here to see a diagram showing the heart chambers and valves. Roll your mouse over the diagram.

Blood vessels

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

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 and as it leaves the heart it branches into smaller arteries, eventually they become capillaries.

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 toward 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.

Venous and arterial circulation

Click on the buttons on the diagram to view the veins and arteries of the body.

Activity 5

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

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.

Drawing showing red and blue lines connecting to larger veins and arteries

Capillaries

Blood

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

Drawing of a tube with plasma in half of the tube, a small bit of white blood cells and platelets and the rest red blood cells

Components of blood

For more information on blood and blood products visit the Australian Red Cross Blood Service website at http://www.arcbs.redcross.org.au/ here is some great information in the general education section of this site.

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.

  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 colour. There are approximately 5 million RBC per cubic millimetre of blood and the average life span is 100 - 120 days.
Red blood cells

Red blood cells

  1. 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.
White blood cells

White blood cells

  1. 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.
Platelets

Platelets

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 conduction system that is made up of specialised neuromuscular tissue that sends out impulses. The impulses begin at the Sino-Atrial (SA) node in the right atrium and spread across the two atria. The atria then contract and the impulses from the S-A node reach the Atrio-Ventricular (AV) node in the right atrium. Messages from the A-V node then travel down the Bundle of His in the septum and continue through the Purkinje fibres to the walls of the ventricles.

An electrocardiogram, or ECG, is a diagnostic test that records the electrical impulses of the heart.

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:

Diagram of the flow of blood through arteries and veins

Diagram of the flow of blood through arteries and veins

Click here to see an animation of the blood flowing through the heart. Click on the box at the bottom of the following diagram and watch 'Bobby the red blood cell' make its way through the vessels, chambers and valves of the heart. Bobby changes colour from blue to red. Blue indicates that the blood cell is low in oxygen (deoxygenated). Bobby turns red (oxygenated) after he has picked up oxygen in the lungs.

Activity 6

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

Pulse

The pulse is the beat of the heart and the movement of blood through the arteries at various points in the body.

Graphic showing the outline of a body with arrows pointing at the head (temporal), neck (carotid), heart (apical) middle of the arm (brachial), wrist (radial), groin (femoral), knee (popliteal) and ankle (pedal)

Where the pulse can be found

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.

Drawing of a hand felling the neck of a person

The carotid pulse

Drawing of a hand feeling the wrist of a person

The radial pulse

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 are 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.

For further information, go to the Virtual Body at http://www.medtropolis.com/Vbody.asp