The Heart

The Heart

The word cardiovascular comes from a Greek word cardiac meaning heart, and Latin word vasculum meaning vessel. The cardiovascular system comprises the heart and blood vessels - arteries, veins and capillaries.

The cardiovascular system carries and distributes oxygen, nutrients and chemicals in the blood to all cells of the body. It also helps remove waste products from the cells.

The heart is a hollow organ of muscle which pumps blood to every part of the body. It is located between the lungs in the centre of the chest, protected by the breastbone, ribs and the spine.

The heart is made of strong muscle, called myocardium, and sits in a sac of fibrous tissue - the pericardium. The heart's inner surface, which is in contact with the blood being pumped, is called the endocardium.

The heart has four chambers and is divided down the middle by a wall of muscular tissue, know as the septum, with an upper receiving chamber (the atrium), and a lower chamber (the ventricle) on each side.

The heart is in fact two pumps. The right side receives de-oxygenated blood from the body and pumps blood to the lungs to pick up oxygen. The much stronger left ventricle takes oxygenated blood coming back from the lungs and circulates it to the rest of the body.

Valves control the direction of blood from the atrium to the ventricle, and from the ventricles into the main arteries.

Each heartbeat has two phases. The phase when the muscle in both ventricles contract to pump blood is called systole. When the muscle relaxes, the chambers refill with blood ready for the next beat. This phase is called diastole.

Amazing heart facts

For its size, the heart has the capacity to pump large amounts of blood.

In the average adult, the heart:

• Beats 60 to 100 times a minute.
  
  
• Pumps between 70 and 100ml of blood with each beat.
  
  
• Completely recirculates the 5-6 litres of blood in the body every 1-1/2 minutes. In 24 hours the heart circulates up to 10,000 litres of blood.
  
  
• Could fill a petrol tanker in one day.
  
  
• Will beat over 2.5 billion times during an average lifetime of 70 years.
  
  
• Pumps blood to the lungs, back to the heart, out to the body and back to the heart again in about 23 seconds.

Blood

Blood is made up of cells and cell-like structures in a liquid known as plasma. Its simple appearance as a red liquid belies its very complex make-up and the very important role it plays in keeping us alive.

The body holds on average 70ml of blood for each kilogram of body weight. For example, this means that an average adult male body contains about 5-6 litres of blood.

Some examples of the functions of blood in the body.

Blood transports:

• oxygen from the lungs to cells through the body in the red blood cells
• carbon dioxide from the cells to the lungs
• nutrients from the digestive organs (for example the small intestine) to the cells
• waste products from the cells to the kidneys, lungs and sweat glands for elimination from the body
• hormones from endocrine glands to the cells
• enzymes to various cells.

Blood regulates:

• acid/base balance in the body
• body temperature
• water content of cells.

Blood protects against:

• blood loss (by clotting)
• harmful bacteria (via white cells and antibodies).

The circulatory system

The body has a network of vessels called arteries and veins to carry the blood pumped by the heart. The heart and blood vessels together are called the circulatory system because they circulate blood to and from the heart.

Arteries carry blood away from the heart; veins carry blood back to the heart from the rest of the body. Smaller branch arteries feed into even smaller blood vessels called capillaries which cannot be seen with the naked eye. Oxygen and nutrients pass into body tissues via the capillaries. The largest artery in the body is the aorta. It has branches which carry blood to the heart muscle, arms and legs, and internal organs.

The first branches of the aorta are the coronary arteries. These run back on to the surface of the heart itself to give the heart muscle its own blood supply.

In adults, the length of the network of vessels is about 95,000 kilometres long. This is equivalent to about two and a half times around the Earth's equator.

The Pulse

Every time the heart beats there is a pulse wave of blood through the arteries. The pulse can be felt by placing two fingers over the artery at the wrist or on either side of the neck. The pulse rate indicates how fast the heart is beating.

Measuring the pulse

The pulse can be felt on arteries close to the skin. It is named after the particular artery. For example, the radial pulse is named after the radial artery in the wrist.

The pulse is generally taken at the carotid artery or the radial artery.

When taking the pulse, the pads of the middle fingers are used. To determine the rate per minute, the number of pulses are counted over one of the following intervals:

• one whole minute
• 30 seconds then multiplied by two
• 15 seconds then multiplied by four.

When you exercise your pulse increases. Try taking your pulse at rest, and then jog on the spot for one minute. By how much did your pulse increase? Why does it increase?

Blood pressure

Blood pressure is the pressure of blood in the arteries as it is being pumped around the body by the heart.

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