mammalian heart: structure and function

• circulatory system: systems which transport fluids containing materials needed by the organism, as well as waste materials that need to be removed
• closed circulatory system: blood is pumped around the body and is always contained within a network of blood vessels
• open circulatory system: the blood, or blood equivalent is inside the body cavity and bathes the organs
• • double circulatory systems have two loops; one to the lungs and one to the body
  • single circulatory systems have one loop that includes the lungs and the body
• humans have a closed, double circulatory system; in one complete circuit of the body blood passes through the heart twice
• • the right side of the heart pumps deoxygenated blood to the lungs for gas exchange; pulmonary circulatory system
  • blood then returns to the left side of the heart, so that oxygenated blood can be pumped at high pressure around the body; systemic circulatory system
• the heart is protected in the chest cavity by the pericardium, a tough and fibrous sac
• • the septum is a wall of muscular tissue that separates the left and right sides of the heart
  • it is important to ensure blood doesn't mix between the left and right sides of the heart
• valves are important for keeping blood flowing forward in the right direction and for maintaining the correct pressure in the chambers of the heart
• valves in the heart

  • open when the pressure of blood behind them is greater than the pressure in front of them
  • close when the pressure of blood in front of them is greater than the pressure behind them
• the valves are attached to the heart walls by valve tendons, or cords; these prevent the valves from flipping inside out under high pressure
• left ventricle: thicker muscle than right ventricle for strong contraction to pump blood all the way around the body; the right ventricle in comparison only has to pump blood to the nearby lungs
• ventricles: thicker walls than atria to pump blood out of the heart; the atria in comparison only pump blood into the ventricles
• AV valves: prevent backflow of blood from ventricles into atria

  SL valves: prevent backflow of blood from aorta or pulmonary artery into ventricles
• two blood vessels bring blood into the heart

  • vena cava brings blood from the body
  • pulmonary vein brings blood from the lungs
• two blood vessels take blood away from the heart

  • pulmonary artery takes blood to the lungs
  • aorta takes blood to the body
• muscle of the heart itself is supplied with blood by a series of blood vessels known as the coronary arteries

  they can be seen running across the surface of the heart