cardiovascular system

• Heart components:

  • Heart is a pump
  • Blood enters via atria and passes into the ventricles
  • Heart contains valves (bicuspid, tricuspid and semi-lunar) which prevent back-flow
  • The ventricles have thick muscle wall and atria have relatively thin walls
• Arteries:

  • Carry blood away from the heart
  • Largest artery is the aorta which divides into smaller arteries supplying all the organs of the body
  • Arteries have thick layer of muscle and elastic tissue
  • These muscles allow constriction and dilation of arteries to regulate blood flow
• Veins:

  • Return blood to the heart, veins bring deoxygenated blood back to the heart for re-oxygenation
  • Low pressure: Veins handle blood with less pressure than arteries
  • Thin walls: Veins have thinner and less muscular walls due to lower pressure needs
  • Lumen: The inner space of a vein is wider than that of arteries
  • Valves: Most veins have one-way valves that prevent blood from flowing backward, aiding in circulation against gravity
• Capillaries:

  • Smallest blood vessels
  • Their walls are formed by a single layer of endothelial cells, allowing for efficient exchange of molecules between blood and surrounding tissues
  • Capillaries are critical for the exchange of gases, nutrients, waste products, and water between blood and tissues
  • Their vast network throughout the body ensures maximum surface area for efficient exchange
• Composition of blood:

  • Blood is made up of plasma, platelets, red blood cells, and white blood cells
  • Plasma is the straw-coloured fluid, making up about 55% of the total volume
  • Platelets are tiny blood cell fragments that stop bleeding by clumping together and forming clots at wound sites
  • Red blood cells are oxygen carriers packed with haemoglobin
  • White blood cells are the body's defenders, protecting from infections and foreign invaders
• Functions of the cardiovascular system:

  • Facilitates the circulation of blood to transport nutrients, oxygen, carbon dioxide, hormones, and blood cells
• Key terms:

  • Systole: "pumping" phase, where the heart muscles forcefully contract
  • Diastole: "resting" phase, where the heart muscles relax after contraction
• Regulation of heart rate:

  • Sinoatrial (SA) Node: pacemaker located in the right atrium, generating electrical impulses that initiate each heartbeat
  • Atrioventricular (AV) Node: acts as a gatekeeper, delaying the signal for a brief moment to ensure efficient pumping
  • Bundle of His: transmits the electrical signal throughout the ventricles, triggering their coordinated contraction and pumping blood out to the body and lungs
• Electrocardiography (ECG) to monitor heart activity:

  • P wave is caused by depolarisation of the atria initiated by SAN
  • QRS complex is caused by depolarisation of the ventricles initiated by the electrical signals generated by AVN and transmitted along the bundle of His
  • T wave is caused by repolarisation of the ventricles
  • The cause of the U wave is not certain
• Heart disease in ECG:

  • Atrial fibrillation: faster and more irregular heartbeat caused by disorganised electrical signals in the atria
  • Ventricular fibrillation: caused by disorganised electrical signals in the ventricles, causing them to twitch randomly rather than contracting in an organised way
• Other abnormalities:

  • Tachycardia: heart beats too rapidly
  • Bradycardia: heart beats too slowly
  • Ectopic heartbeat: heartbeats too early, followed by a pause