the heart

• How is the left ventricle adapted for it's function?

  Has thicker, muscular walls than the right ventricle - allows it to contract more powerfully and pump blood all around the body
• How is the right ventricle adapted for it's function?

  Less muscular walls so its contractions are only powerful enough to pump blood to the nearby lungs
• How are the ventricles adapted for their function?

  They have thicker walls than the atria so they can pump blood out of the heart
• How are the atrioventricular valves adapted for their function

  They link the atria to the ventricles and stop the backflow of blood when the ventricles contract
• How are the semi-lunar valves adapted for their function?

  They link the ventricles to the pulmonary arteries and aorta, stopping the backflow of blood to the heart after ventricles contract
• How are the cords in the heart adapted to their function?

  They attach the atrioventricular valves to the ventricles to stop them from being forced up into the atria when the ventricles contract
• How do heart valves work?

  They are only open one way, and they open and close depending on the relative pressure of the heart chambers. If the pressure is higher behind the valve, it's forced open, but if the pressure is higher infront of the valve, it's forced shut. The flow of blood is unidirectional
• Heart Dissection Practical

  1. Wear gloves and lab coat
  2. Place heart given on dissection tray
  3. Look at the outside of the heart, and try to identify the four main vessels attached
  4. Identify the right and left atria, the right and left ventricles and the coronary arteries
  5. Using a clean scalpel, carefully cut along next to the left ventricle, so you can see inside it
  6. Measure and record the thickness of the ventricle walls and note any differences between them
  7. Next, cut open the atria and look inside them too - note whether the atria walls are thicker or thinner than the ventricle walls
  8. Find the atrioventricular valves, followed by the semi-lunar valves - look at the structure and see if you can see how they only open one way
  9. Wash your hands and disinfect all work surfaces once you've completed the dissection
• What is the cardiac cycle?

  Ongoing sequence of contraction and relaxation of the atria and ventricles that keep blood continuously circulating around the body
• What is the first stage of the cardiac cycle?

  1. Ventricles relax, atria contracts

  The ventricles are relaxed, the atria contracts and decreases the volume of the chambers and increasing the pressure inside the chambers - this pushes the blood into the ventricles

  There's a slight increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria
• What is the second stage in the cardiac cycle?

  2. Ventricles contract and the atria relax

  The atria relax, and then the ventricles contract (decreasing the volume and increasing the pressure inside the chamber).

  The pressure becomes higher in the ventricle than in the atria, which forces the atrioventricular valves to shut, preventing back flow. The pressure in the ventricles is also higher that in the aorta and the pulmonary artery, forcing the semi-lunar valves to open and blood is forced out and into the arteries.
• What is the third stage of the cardiac cycle?

  3. The ventricles relax and the atria relax.

  The ventricle and the atria both relax, and the higher pressure in the pulmonary arteries and aorta close the semi-lunar valves to prevent any backflow into the ventricles.

  Blood returns back to the heart and the atria fills again due to the higher pressure in the vena cava and pulmonary vein. This then increases the pressure in the atria, and as the ventricles continue to relax the pressure falls below the pressure of the atria, so the atrioventricular valves open - this allows blood to flow passively and into the ventricles from the atria.
• What is the equation to calculating the cardiac output?

  cardiac output = stroke volume x heart rate