the cardiac cycle

• Right atrium

  • Deoxygenated blood flows into the right atrium from the body.
  • The vein that pumps deoxygenated blood into the right atrium is called the vena cava.
  • The right atrium is the first chamber that deoxygenated blood flows through
• Right ventricle

  • When the walls of the right atrium contracts, deoxygenated blood flows into the right ventricle.
  • The atrioventricular valves prevent blood from flowing back into the atria from the ventricles.
  • Then the walls of the right ventricle contracts, blood is pumped out of the pulmonary artery to the lungs.
  • The semi-lunar valves prevent blood from flowing back into the right ventricle from the pulmonary artery.
• Left atrium

  • Oxygenated blood flows into the left atrium from the lungs.
  • The vein that pumps oxygenated blood into the left atrium is called the pulmonary vein.
• Left ventricle

  • When the walls of the left atrium contracts, oxygenated blood flows into the left ventricle.
  • The atrioventricular valves prevent blood from flowing back into the atria from the ventricles.
  • The walls of the left ventricle are considerably thicker than the right ventricle.
  • The left ventricle has to transport blood all the way around the body but the right ventricle only has to transport blood to the lungs.
• Aorta

  • When the left ventricle contracts, blood is pumped out of the heart to the rest of the body.
  • Oxygenated blood leaves the heart through the aorta.
  • The semi-lunar valves prevent blood from flowing back into the left ventricle from the aorta.
• 1. Atrial contraction

  • Blood from the lungs flows into the left atrium and blood from the body flows into the right atrium simultaneously.
  • The atria contract, increasing the pressure in the atria.
  • The blood in the atria is forced into the ventricles.
  • The ventricles are relaxed and fill with blood.
• 2) Ventricular contraction

  • The atria relax and the ventricles start to contract.
  • Contraction of the ventricles causes the pressure inside the ventricles to increase.
  • The pressure shuts the atrioventricular valves so that blood does not flow back into the atria.
  • The blood in the ventricles is forced out of the ventricles and out of the heart through the pulmonary artery or the aorta.
• 3) Relaxation

  • The blood in the pulmonary artery and the aorta is at high pressure. -The pressure shuts the semi-lunar valves so that blood does not flow back into the ventricles.
  • Both the ventricles and the atria relax and the atrioventricular valves reopen.
  • Blood flows into the ventricles and the atria from the pulmonary vein and vena cava.
• 4) Repeat

  • The cycle continues.
• what are the stage sof the cardiac cycle?

  atrial contraction

  ventricular contraction

  relaxation

  repeat
• The cardiac cycle describes the flow of blood from the atria to the ventricles and out of the heart in a single heartbeat. The average person has 60 − 100 heartbeats per minute while at rest.
• Pressure in the atria

  • When the atria contract, the pressure in the atria increases.
  • When the atria relax and the ventricles contract, the pressure in the atria decreases.
  • When both the atria and the ventricles relax, there is a slight increase as the atria fill with blood again.
• Pressure in the ventricles

  • When the atria contract, the pressure in the ventricles is relatively low. There is a slight increase in pressure as the ventricles fill with blood.
  • When the ventricles contract, the pressure increases dramatically. The pressure increases considerably more than when the atria contract.
  • When both the atria and the ventricles relax, there is a slight increase as the ventricles fill with blood again.
• Volume in the atria

  • When the atria contract, the volume in the atria decreases.
  • When the atria relax and the ventricles contract, the volume in the atria increases again.
  • When both the atria and the ventricles relax, there is a slight decrease when blood flows into the ventricles from the atria.
• Volume in the ventricles

  • When the atria contract, the volume in the ventricles increases slightly as they fill with blood.
  • When the ventricles contract, the volume decreases dramatically. The volume decreases considerably more than when the atria contract.
  • When both the atria and the ventricles relax, the volume increases as the ventricles expand again.
• what percentage of blood is made up of cells?

  45%

  • erythrocytes (RBC)
  • leukocytes (WBC)
  • thrombocytes (platelets)
• what percentage of blood is made up of plasma?

  55%

  • water (92%)
  • proteins
  • ions
  • nutrients
  • waste products
  • hormones
• erythrocytes:

  • large amounts of haemoglobin for oxygen transport
  • flattened, biconcave disc shape ensures large surface area to volume ratio for efficient gas exchange
  • the diameter is larger than diameter of capillary diameter this slows blood flow to enable diffusion of oxygen
  • they have no nucleus and no organelles this maximises space for haemoglobin
• Atrial systole

  • The walls of the atria contract
  • Atrial volume decreases
  • Atrial pressure increases 
  • The pressure in the atria rises, forcing the atrioventricular (AV) valves open
  • Blood is forced into the ventricles
  • There is a slight increase in ventricular pressure and chamber volume as the ventricles receive the blood from the atria
  • The ventricles are relaxed at this point; ventricular diastole coincides with atrial systole
• Ventricular systole

  • The walls of the ventricles contractVentricular volume decreases
  • Ventricular pressure increases
  • The pressure in the ventricles rises
  • This forces the AV valves to close, preventing back flow of blood
  • The pressure in the ventricles rises above that in the aorta and pulmonary artery
  • This forces the semilunar (SL) valves open so blood is forced into the arteries and out of the heart
  • During this period, the atria are relaxing; atrial diastole coincides with ventricular systole
  • The blood flow to the heart continues, so the relaxed atria begin to fill with blood