Cardiovascular system

• Components of the cardiovascular system

  • The heart
  • Arteries
  • Veins
  • Capillaries
  • Blood
• Function of the cardiovascular system

  • Supplies your body's organs with oxygen and nutrients so your organs can do their jobs
  • Carries carbon dioxide and other waste away for disposal
• Components of the blood

  • Plasma
  • Platelets (Thrombocytes)
  • Red blood cells (Erythrocytes)
  • White blood cells (Leucocytes)
• Plasma

  • Straw-coloured fluid left after cells are removed
  • Contains proteins known as plasma proteins, hormones, glucose, amino acids and ions transported in the blood
• Platelets (Thrombocytes)

  • Small disc-shaped cell fragments without nuclei
  • Present in large quantities in the blood and important for blood clotting
• Red blood cells (Erythrocytes)


  • Differentiated without a nucleus
  • Filled with haemoglobin which is the protein that transports oxygen from the lungs to the tissues
• White blood cells (Leucocytes)

  Involved with protection against infection including immune response
• Types of blood vessels

  • Arteries
  • Capillaries
  • Veins
• Arteries

  • Carry blood away from the heart
  • Aorta is the largest artery which leads blood from the left ventricle of the heart to the body
  • The smallest arteries are called the arterioles
  • Arteries have an outer connective tissue layer for strength and support and thick layer of muscle and elastic tissue
  • The muscle allows constriction (narrowing) or dilatation (widening) of the arteries to regulate blood flow to different parts of the body
• Capillaries

  • The arterioles lead to the capillaries
  • These are the smallest vessels in the cardiovascular system and have a wall that is just a single cell thick
• Veins

  • Capillaries come together to form venules which merge into larger veins
  • The blood in the veins are at a much lower pressure in the veins because it has had to force its way through the narrow capillaries so the lumen is much larger than an artery
  • Veins have thinner walls as they do not need to absorb the pressure of the pumping of the heart
• Cardiac cycle

  1. Blood enters the right atrium from the vena cava

  2. Then flows via the tricuspid valve into the right ventricle

  3. From right ventricle it is pumped into the pulmonary artery to the lungs

  4. Returning from the lungs via the pulmonary veins, the blood enters the left atrium

  5. It then flows into the left ventricle from which the blood is pumped into the aorta and around the body
• Left ventricle contracts

  • Spike in pressure in the aorta
  • Spike in pressure can be felt as the pulse in arteries
  • Spike in pressure for each heart contraction can be used to measure the heart rate
• Cardiac muscle

  Specialised type of muscle that contracts in a regular pattern without any nerve input
• Sinoatrial (SA) node

  • Small patch of specialised cardiac muscle on the wall of the right atrium
  • Generates electrical signals that spreads over the surface of the right and left atria, causing to depolarise and contraction (atrial systole)
  • Also known as the pacemaker because it maintains the regular contraction of the heart
• Changes in acidity of the blood and blood pressure

  Detected by chemoreceptors and pressure receptors located in the aorta and carotid arteries
• Cardioregulatory centre in the medulla

  Responds to inputs from chemoreceptors and pressure receptors and sends nerve impulses to the SA node that either speed up or slow down the heart rate