Physical Education

The circulatory system

Also known as the cardiovascular system, your heart, blood vessels and blood itself are three essential components the body needs to survive. The circulatory system consists of two circuits that blood travels through; pulmonary and systemic. Exercise affects these systems, causing the heart to pump blood faster around the body, which in turn allows you to exercise for longer!

Components of the circulatory/cardiovascular system

The three components are:

  • The heart
  • Blood vessels
  • Blood

It is a double circulatory system. It comprises two separate circuits and blood passes through the heart twice.

The pulmonary circuit carries blood to the lungs to be oxygenated and then back to the heart. In the lungs, carbon dioxide is removed from the blood, and oxygen taken up by the haemoglobin in the red blood cells.

The systemic circuit carries blood around the body to deliver the oxygen and returns de-oxygenated blood to the heart. Blood also carries nutrients and waste.

The heart

NB The heart is seen from the front in the diagram. So the right side of the heart is shown on the left of the diagram. The left side is on the right side of the diagram.

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 [Heart rate: The number of heart beats per minute. ] x stroke volume [Stroke volume: The volume of blood pumped from heart with each beat. ] = cardiac output [Cardiac output: The amount of blood pumped by heart in one minute. Heart Rate x Stroke Volume = Cardiac Output. ]

These increase when exercising. See the 'Exercise and Training' revision bite for effects of exercise on the circulatory system.

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 vessels

There are three types of blood vessel:


  • 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


  • 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 lumenlumen: The central cavity of a hollow structure in an organism or cell.
  • Contain blood under low pressure
  • Have valves to prevent blood flowing backwards


  • 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 function of blood in exercise

blood is made up of plasma, red and white blood cells and platelets

Blood has four key components:


  • 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


  • 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 [Blood pressure: The force of blood against the artery walls. ] increases when you exercise, but is lower at rest when you are fit. It is also affected by age, smoking, stress, diet and weight.

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