The heart

• Humans have a double circulatory system. Like this ...

  
• The benefit of the double circulatory system is that the blood passes through the heart twice. It can travel rapidly to the body cells delivering the oxygen that the cells need.
• The heart is an organ consisting mainly of muscle tissue. The heart pumps blood around the body.
• The structures of the heart (part 1):

  1. The heart has four chambers. At the top we have the left atrium and the right atrium. At the bottom, we have the left ventricle and the right ventricle. Like this...

  
• The structures of the heart (part 2):

  1. The atria are separated from the ventricles by valves. Like this...

  
• The structures of the heart (part 3):

  1. The vena cava brings in deoxygenated blood from the body.
  2. The blood passes from the heart to the lungs in the pulmonary artery. In the lungs the blood collects oxygen.
  3. Oxygenated blood passes from the lungs to the heart in the pulmonary vein.
  4. Oxygenated blood is pumped from the heart to the body in the aorta. Like this...

  
• The pattern of blood flow through the heart:

  1. Blood enters the left atrium and the right atrium.
  2. The atria now contract and the blood is forced into the ventricles.
  3. The ventricles now contract and force blood out of the heart.
  4. The valves stop the blood from flowing backwards into the atria when the ventricles contract. Like this...

  
• The left side of the heart has a thicker muscular wall than the right side. Because the left ventricle pumps blood around the entire body, so it needs to provide a greater force. The right ventricle only pumps blood to the lungs.
• An important type of blood vessel are the coronary arteries. The coronary arteries branch out of the aorta and spread out into the heart muscle. The purpose of the coronary arteries is to provide oxygen to the muscle cells of the heart. The oxygen is used in respiration to provide the energy for contraction. Like this...

  
• The natural, resting heart rate is controlled by a group of cells found in the right atrium, its called the pacemaker. Sometimes the pacemaker stops working correctly. I this case, doctors can implant an artificial pacemaker. An artificial pacemaker is a small electrical device and it corrects irregularities in the heart rate. Like this...

  
• The circulatory system consists of a network of blood vessels connected to the heart and lungs.

  • The heart pumps deoxygenated blood to the lungs where gas exchange surfaces take up oxygen.
  • Oxygen diffuses into the blood from the alveoli.
  • Alveoli are specialised structures that have a large surface area to volume ratio and thin walls to maximise gas exchange.
• Carbon dioxide (waste gas) diffuses from the blood into the lungs (to be exhaled) via the alveoli.

  • Oxygenated blood then returns to the heart which pumps it out in arteries around the body towards organs.
  • Arteries narrow to capillaries as they pass through the organ.
  • A network of small capillaries allows for gas exchange with organ tissues .
  • Capillaries widen to veins as they move away from the organ to carry deoxygenated blood back towards the heart.
• The alveolus is the gas exchange surface in humans (part 1):

  
• The alveolus is the gas exchange surface in humans (part 2):

  
• A network of small capillaries allows for efficient gas exchange in organ tissues:

  
• The double circulatory system (part 1):

  • The human heart is part of a double circulatory system.
  • This means there are two circuits joined together.
  • The circulatory system is a system of blood vessels with a pump (the heart) and valves that maintain a one-way flow of blood around the body.
  • The right side of the heart pumps blood to the lungs for gas exchange (this is the pulmonary circuit).
  • The left side of the heart pumps blood under high pressure to the body (this is systemic circulation).
• The double circulatory system (part 2):

  • Mammals (and birds) have a double circulatory system
  • Not all animals do though - fish don't.
  • There are benefits of a double circulatory system:
  • Blood travelling through the small capillaries in the lungs loses a lot of pressure which reduces the speed at which it can flow.
  • By returning oxygenated blood to the heart from the lungs, the pressure can be raised before sending it to the body, meaning cells can be supplied with oxygenated blood more quickly.
  • This is important for mammals as they require a lot of oxygen to maintain their body temperature.
• The structure of the heart (part 2.1):

  • The heart is labelled as if it was in the chest so what is your left on a diagram is actually the right-hand side (and vice versa).
  • The heart is a pumping organ that ensures blood continuously flows around the body.
  • The heart has two distinct halves and acts as a double pump .
  • The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs where oxygen diffuses in from the alveoli and carbon dioxide diffuses out.
  • The left side of the heart receives oxygenated blood from the lungs and pumps it to the body.
• The structure of the heart (part 2.2):

  • Blood is pumped towards the heart in veins and away from the heart in arteries.
  • The chambers at the top of the heart are the atria, the chambers at the bottom the ventricles.
  • Valves are present to prevent blood flowing backwards.
  • The heart is made of a special type of muscle called cardiac muscle which never gets tired.
  • Cardiac muscle cells contain far more mitochondria than skeletal muscle to provide lots of ATP for energy.
• The structure of the heart (part 2.3):

  • The heart beats continuously so needs a constant supply of oxygen (and glucose) for aerobic respiration.
  • Cardiac muscle has its own blood supply via the coronary arteries which branch off from the aorta.
• The heart is labelled as if you are looking at it directly in someone’s body – so the left-hand side of an image of the heart is actually the right-hand side of the heart:

  
• Pathway of blood through the heart (part 1):

  • Deoxygenated blood (from the body) enters the heart via the vena cava, emptying into the right atrium.
  • Oxygenated blood (from the lungs) returns to the heart via the pulmonary vein, emptying into the left atrium.
  • The atria contract pushing the blood into the ventricles.
• Pathway of blood through the heart (part 2):

  • The right ventricle contracts forcing blood through the pulmonary artery to the nearby lungs where gas exchange occurs (and the blood becomes oxygenated).
  • At the same time the left ventricle contracts forcing the oxygenated blood through the aorta, out of the heart.
  • The oxygenated blood flows through arteries around the body delivering oxygen to organs and tissues.
  • Once the oxygen has been used up, deoxygenated blood returns to the heart through veins.