Jack Hunt (the heart)

There are three types of blood vessel:

Arteries

• Carry blood away from the heart (always oxygenated apart from the pulmonary artery which goes to the lungs)
• Have thick muscular walls
• Have small passageways for blood (internal lumen)
• Contain blood under high pressure

Veins

• Carry blood to the heart (always de-oxygenated apart from the pulmonary vein which goes from the lungs to the heart)
• Have thin walls
• Have larger internal lumen
• Contain blood under low pressure
• Have valves to prevent blood flowing backwards

Capillaries

• Found in the muscles and lungs
• Microscopic – one cell thick
• Very low blood pressure
• Where gas exchange takes place. Oxygen passes through the capillary wall and into the tissues, carbon dioxide passes from the tissues into the blood

The heart is a muscular pump. When it beats it pumps blood to the lungs and around the body. The amount of blood pumped can be calculated:

heart rate x stroke volume = cardiac output

These increase when exercising.

The heart has four chambers. The two atria collect the blood. The two ventricles pump the blood out of the heart.

Valves prevent the blood from flowing backwards.

The septum separates the two sides of the heart.

The right side of the heart pumps de-oxygenated blood (blood not containing oxygen) to the lungs to pick up oxygen. The left side of the heart pumps the oxygenated blood from the lungs around the rest of the body.

Blood has four key components:

Plasma

• Fluid part of blood
• Carries carbon dioxide, hormones and waste

Red blood cells

• Contain haemoglobin which carries oxygen
• Made in the bone marrow. The more you train the more red blood cells are made.

White blood cells

• An important part of the immune system, they produce antibodies and destroy harmful microorganisms
• Made in the bone marrow

Platelets

• Clump together to form clots
• Protect the body by stopping bleeding

When exercising blood does the following things:

• Transports nutrients and waste
• Delivers oxygen to the working muscles
• Removes heat (temperature regulation)
• Dilutes/carries away lactic acid (acidic balance)

Blood pressure increases when you exercise, but is lower at rest when you are fit. It is also affected by age, smoking, stress, diet and weight.