Circulatory system

• Circulatory system


  Network of organs and vessels which enables the flow of blood and transport of oxygen, carbon dioxide, nutrients and other molecules around the body
• Components of blood


  • Red blood cells
  • White blood cells
  • Plasma
  • Platelets
• Red blood cells


  • Biconcave disk shape gives large surface-area-to-volume ratio, increasing diffusion rate
  • Small and flexible to squeeze through capillaries
  • No nucleus, more space for haemoglobin, increasing oxygen-carrying capacity
• Phagocytes (white blood cells)


  • Can change shape to engulf foreign material
  • Flexible membrane to squeeze through pores in capillary walls and enter tissue fluid
  • Contain enzymes that digest pathogens
• Double circulatory system


  Blood flows through the heart in two circuits: pulmonary circuit and systemic circuit
• Pulmonary circuit


  1. Deoxygenated blood transported to lungs

  2. Gaseous exchange occurs between alveoli and capillaries

  3. Oxygenated blood returns to left side of heart
• Systemic circuit


  1. Oxygenated blood pumped to tissues and organs around body

  2. Exchange of materials occurs at tissues

  3. Deoxygenated blood returns to right side of heart
• Heart


  Muscular pump that pushes blood around the body, consisting of four chambers and associated blood vessels
• The wall of the left ventricle is thicker than that of the right ventricle, as it must pump blood a further distance at a higher pressure</b>
• Heart valves

  • Atrioventricular bicuspid (between left atrium and left ventricle)
  • Atrioventricular tricuspid (between right atrium and right ventricle)
  • Semilunar (between ventricles and arteries)
• Function of heart valves

  • Stop blood flowing backwards from the ventricles into the atria
  • Ensure that after leaving the heart, blood is not drawn back into the ventricles
• Types of blood vessels

  • Arteries
  • Veins
  • Capillaries
• Arteries


  Carry blood away from the heart under high pressure
• Veins


  Carry blood towards the heart under low pressure
• Capillaries

  Enable the exchange of materials at tissues
• Normally, deoxygenated blood travels in veins towards the heart and oxygenated blood travels in arteries away from the heart. The only exceptions are the pulmonary artery and pulmonary vein.
• Artery

  • Narrow lumen maintains high pressure
  • Thick wall to withstand high pressure
  • Thick layer of smooth muscle provides strength
  • Thick layer of elastic fibres allow stretch and recoil
  • Smooth inner lining to reduce friction
  • No valves
• Vein


  • Large lumen eases blood flow
  • Thin wall allows muscles to easily compress the vein aiding blood flow
  • Thin layer of smooth muscle and elastic fibres
  • Valves prevent backflow of blood
• Capillary


  • Form large network, greater surface area for diffusion
  • Walls one cell thick, giving a short diffusion distance
  • Walls permeable, allowing the exchange of substances
  • Narrow lumen decreases diffusion distance
• Cardiovascular disease (CVD)


  Group of diseases affecting the heart or blood vessels
• Cause of CVD


  1. Build up of fatty deposits on the walls of the arteries forms atheromas which reduce blood flow to muscle tissue

  2. Blood clots may form, blocking the arteries and stopping blood flow completely, leading to a heart attack or stroke
• Risk factors for CVD

  • High blood pressure
  • High blood cholesterol
  • Smoking
  • Obesity
  • Lack of exercise
  • Family history of heart disease
  • Poor diet
• Treatments for CVD


  • Improving diet and lifestyle
  • Medication (statins)
  • Angioplasty
• Improving diet and lifestyle

  Diet and lifestyle changes to reduce the risk of CVD or enhance the efficiency of other treatment methods
• Statins


  A group of drugs that lower blood cholesterol levels
• Angioplasty


  A small balloon is used to inflate an artery and a hollow tube (stent) is inserted into the lumen. The stent expands, holding the artery open.
• Pulmonary circuit

  The part of the circulatory system that carries deoxygenated blood from the right side of the heart to the lungs for gaseous exchange
• Arterial blood

  Blood that is currently being transported through the arteries, which are blood vessels that carry oxygenated blood away from the heart to the rest of the body