Unit 10.3

• The cardiac cycle

  1. The two atria contract

  2. The two ventricles contract

  3. The heart relaxes
• Heart sounds

  Generated during a cardiac cycle
• How heart sounds are generated

  1. When the atria contract, the ventricles are relaxed and filling with blood

  2. When the ventricles contract, the atrioventricular valves close and vibrate, preventing blood from flowing back into the atria and producing the longer, low-pitched "lub" sound of the heartbeat

  3. After the ventricles contract, the shorter and sharper "dub " sound of the heartbeat results from the closing of the semilunar valves to when the back pressure prevents arterial blood from flowing back into the ventricles
• Systole


  Contraction of the heart muscle (ventricle)
• Diastole

  Relaxation of the heart muscle (ventricle)
• Nodal tissue


  • A type of cardiac muscle with both muscle and nerve characteristics
  • Enables the heart to contract and relax rhythmically
• Impulses in the SA node and the AV node

  1. The SA node (the pacemaker located in the upper dorsal wall of the atrium) initiates the heartbeat, sending out a stimulus (an excitation electrical impulse, every 0.85s), which causes the atria to contract and also stimulates the AV node

  2. The SA stimulus reaches the AV node in the base of the right atrium near the septum, and the AV node signals the ventricles to contract

  3. Impulses pass down the two branches of the atrioventricular bundle to the Purkinje fibres, and thereafter the ventricles
• detected by an ECG: Atrial Fibrillation multiple, chaotic impulses are generated from the AV node, causing an irregular, fast heartbeat Ventricular Fibrillation uncoordinated contraction of the ventricles; This is more serious as blood is not being pumped out of heart effectively. It can occur after a heart attack, injury, or drug overdose
• The pulmonary circuit

  Circulates blood to and through the lungs (so that carbon dioxide is removed from the blood and oxygen can enter the blood)
• Systemic circuit

  Circulate the blood to deliver oxygenated blood to the body tissues and remove carbon dioxide from the blood
• Blood flows in arteries

  The contractions from the left ventricle send the blood through the aorta and arteries to the arterioles and then the capillary beds
• Circulatory path of legs

  left ventricle -> aorta ->common iliac artery ( femoral artery ( leg capillaries ( femoral vein ( common iliac vein ( inferior vena cava ( right atrium
• Blood pressure can be measured with a device called a sphygmomanometer,
• Blood pressure decreases as blood flows from the aorta into the arteries, arterioles, and capillaries. Blood is under minimal pressure in capillaries since capillaries have a high total cross-sectional area. Velocity also decreases (gets slower) as it flows from aorta into the arteries, arterioles, and capillaries. There is a slight increase in the velocity as it gets pushed through the venules, then veins.