L4 - the heart

• The circulatory system is made up of the heart, the blood vessels and the blood. Its function is to transport oxygen and nutrients to cells and remove waste like carbon dioxide
• Double circulatory system:

  -right side pumps the deoxygenated blood to the lungs to be oxygenated

  -left side pumps oxygenated blood to the rest of the body

  -on both sides, the heart squeezes the blood, putting it under pressure. this forces the blood through the circulatory system
• Deoxygenated blood pathway:

  -body

  -vena cava

  -right atrium

  -right ventricle

  -pulmonary artery

  -lungs
• Oxygenated blood pathway:

  -lungs

  -pulmonary vein

  -left atrium

  -left ventricle

  -aorta

  -body
• Heart position and structure:

  -in humans, lies just off center towards the left of the chest cavity

  -main part consists of firm, dark red muscle called cardiac muscle

  -cardiac muscle is myogenic, meaning it initiates contraction without external nervous stimulation, and involuntary, as it functions without conscious control

  -muscle cells work together to produce the heartbeat (cardiac cycle)
• External anatomy:

  -heart is a muscle and so requires its own blood supply for aerobic respiration

  -heart receives blood through arteries on its surface, called coronary arteries

  -it’s important that these arteries remain clear of plaques as this could lead to angina or a heart attack (myocardial infarction)
• Chambers of the heart:

  -heart made up of four chambers; left and right atria, and left and right ventricles

  -atria are the top chambers in the heart that collect blood from blood vessels (veins)

  -ventricles are the bottom chambers in the heart that pump blood into blood vessels (arteries)
• Heart chambers:

  -ventricles have thicker walls than the atria because they need to pump blood further and at higher pressures

  -left ventricle has a thicker wall than the right because it pumps blood to the entire body, while the right ventricle on pumps blood to the lungs, requiring less force
• Blood vessels of the heart:

  -pulmonary vein

  -aorta

  -vena cava

  -pulmonary artery
• Pulmonary vein moves oxygenated blood into the left atrium from the lungs
• Aorta moves oxygenated blood from the left ventricle to the body
• Vena cava moves deoxygenated blood into the right atrium from the body
• Pulmonary artery moves deoxygenated blood from the right ventricle to the lungs
• Septum:

  -wall of muscle that separates the ventricles from each other

  -this ensures that the oxygenated blood in the left side and the deoxygenated blood in the right side are kept separate
• Valves of the heart:

  -they only open one way

  -only open when there is higher pressure behind the valve, this ensures that blood only flows in one direction (is unidirectional) preventing back flow
• Atrioventricular valves:

  -connect the atria to the ventricles

  -stop blood flowing back into the atria when the ventricles contract

  -also known as tricuspid and bicuspid valves
• Tricuspid valve is on the right side
• Bicuspid valve is on the left side
• Semilunar valves:

  -connect the ventricles to the arteries (pulmonary and aorta)

  -prevent flow of blood back into the heart
• Tendinous cords:

  -attached to the valves

  -sometimes called heart strings

  -prevent the valves from turning inside out when the ventricle walls contracts (can happen due to pressure inside)
• Systole is cardiac muscle contraction
• Diastole is cardiac muscle relaxation
• Cardiac cycle is the sequence of contraction and relaxation of the cardiac muscle in the walls of the heart. It has 3 main stages: atrial systole, ventricular systole, and diastole

  
• Diastole:

  -ventricles and atria relax

  -semi lunar valves close

  -blood flows passively into the atria
• Atrial systole:

  -ventricles relax, and atria contract

  -increases atrial pressure

  -atrioventricular valves open

  -blood flows into the ventricles
• Ventricular systole:

  -ventricles contract, and atria relax

  -ventricular pressure increases

  -semi lunar valves open

  -atrioventricular valves close

  -blood flows into the arteries