The heart and blood vessels (2.2.2)

• The heart is an organ in the circulatory system. The system carried oxygen and nutrients to every cell in the body and removes the waste products
• The heart pumps the blood around the body in a double circulatory system.
• This means there are two circuits

  1. Deoxygenated blood flows into the right atrium and then into the right ventricle which pumps it to the lungs to undergo gaseous exchange
  2. Oxygenation blood flows into the left atrium and then into the left ventricle which pumps oxygenated blood around the body
• Structure of the heart

  • Muscular walls to provide a strong heartbeat
  • The muscular wall of the left ventricle is thicker because blood needs to be pumped around the whole body
  • 4 chambers that separate the oxygenated blood from the deoxygenated blood
  • Valves to make sure blood does not flow backwards
  • Coronary arteries cover the heart to provide its own oxygenated blood supply
• Process: 1. Blood flows into the right atrium through the vena cava, and left atrium through the pulmonary vein.

  2. The atria contract forcing the blood into the ventricles.

  3. The ventricles then contract, pushing the blood in the right ventricle into the

  pulmonary artery to be taken to the lungs, and blood in the left ventricle to the

  aorta to be taken around the body.

  4. As this happens, valves close to make sure the blood does not flow backwards.
• The natural resting heart rate (around 70 beats per minute) is controlled by a group of cells found in the right atrium that act as a pacemaker- they provide stimulation through small electrical impulses which pass as a wave across the heart muscle, causing it to contract. Without this, the heart would not pump fast enough to deliver the required amount of oxygen to the whole body.
• An artificial pacemaker can be used if the individual has an irregular heartbeat. It is an electrical device that produces a signal causing the heart to beat at a normal speed.
• Arteries

  • Carry blood AWAY from the heart
  • Layers of muscle in the walls make them strong
  • Elastic fibres allow them to stretch
  • This helps the vessels withstand the high pressure created by the pumping of the heart
• Veins

  • Carry blood TOWARDS the heart
  • The lumen (the actual tube in which blood flows through) is wide to allow the low pressure blood to flow through
  • They have valves to ensure the blood flows in the right direction
• Capillaries

  • Allow the blood to flow very close to cells to enable substances to move between them
  • One cell thick walls create a short diffusion pathway
  • Permeable walls so substances can move across them
• Types of blood vessels in the body

  • Arteries
  • Veins
  • Capillaries
• The lungs are found in the thorax (top part of your body) and are protected by your ribcage. They supply oxygen to your blood and remove carbon dioxide.
• The gas exchange system is made up of the:
• Trachea ( the windpipe , air moves through here)
• Intercostal muscles (which contract and relax to ventilate the lungs)
• Bronchi (air from the trachea move into these, lead to each lung)
• Alveoli (bronchioles lead to the alveoli, air sacs where gaseous exchange occurs)
• Diaphragm (separates the lungs from the digestive organs, moves down causing inhalation)
• Ventilation: 1. The ribcage moves up and out and the diaphragm moves down causing the volume of the chest to increase. 2. Increased volume results in lower pressure. 3. Air is drawn into the chest as air moves from areas high pressure (the environment) to low pressure (the lungs). 4. The opposite happens when exhaling.
• Gas exchange: 1. Upon inhalation, the alveoli fill with oxygen. 2. The blood in the capillaries surrounding the alveoli is deoxygenated (ithas come from the pulmonary vein). It has lots of carbon dioxide as this is a product of respiration. 3. Oxygen diffuses down its concentration gradient into the capillary bloodstream, which has a low concentration of oxygen. 4. Carbon dioxide diffuses down its concentration gradient from the blood to the alveoli
• Alveoli are adapted for this to take place in a number of ways:

  ● They are very small and arranged in clusters, creating a large surface area for diffusion to take place over ● The capillaries provide a large blood supply, maintaining the concentration gradient ● The walls of the alveoli are very thin, meaning there is a short diffusion pathwa