Biology

• Circulatory system


  An example of an organ system whose role is to transport oxygen and nutrients to the body's tissues
• Components of the circulatory system

  • Blood
  • Blood vessels
  • Heart
• Blood


  • Carries oxygen and nutrients
• Blood vessels


  • Hold the blood
• Heart


  • Pumps the blood to keep it moving through the vessels
• Double circulatory system


  Two distinct loops - one carries deoxygenated blood from the heart to the lungs where it gains oxygen and then flows back to the heart, the other carries oxygenated blood to the rest of the body where it gives up its oxygen to the tissues becoming deoxygenated and then flows back to the heart
• Heart


  • Consists of 4 chambers with thick muscular walls, with veins and arteries coming in and out
• Atria


  Top chambers of the heart
• Ventricles


  Bottom chambers of the heart
• Valves


  • Prevent the blood from flowing backwards, ensuring it always flows in the right direction
• Path of blood through the heart

  1. Flows into the heart via the vena cava and pulmonary vein

  2. Flows into the right and left atria

  3. Atria contract and push blood into the ventricles

  4. Ventricles contract and push blood out into the pulmonary artery and aorta

  5. Atria refill with new blood and the cycle repeats
• Pacemaker cells


  • Produce small electrical impulses that spread through the muscular walls of the heart causing them to contract
• Artificial pacemaker


  A small device implanted under the skin above the heart that carries electrical current down to the heart telling it to contract regularly
• Artery


  Any vessel that carries blood away from the heart
• Vein


  Any vessel that carries blood to the heart
• Arteries don't always carry oxygenated blood and veins don't always carry deoxygenated blood
• Coronary arteries


  • Small arteries that branch off the aorta to supply the heart muscle with oxygenated blood
• The heart acts as the pump for the circulatory system
• Arteries


  • Carry blood away from the heart
  • Blood inside them is at high pressures
  • Have a thick layer of muscle tissue to keep them strong
  • Have a thick layer of elastic tissue so they can stretch and recoil
• Capillaries


  • Exchange nutrients and oxygen with the tissues
  • Have walls that are only a single cell thick
  • Are permeable so substances can easily diffuse through them
  • Have a tiny lumen but a huge total cross-sectional area
  • Blood flows more slowly through them
• Veins


  • Carry blood back to the heart
  • Have relatively large lumens
  • Have relatively thin walls with only small layers of elastic fibers and smooth muscle
  • Have valves to prevent blood from flowing backwards
• Calculating rate of blood flow

  1. Divide the volume of blood by the time it took to flow

  2. Example: 2500 ml of blood passes through the aorta in 8 minutes, so the rate of blood flow is 2500 ml / 8 minutes = 320 ml/min
• Cardiovascular disease


  A general term that refers to diseases of the cardiovascular system, which is basically the heart and blood vessels
• Coronary heart disease


  When the coronary arteries which supply blood to the heart muscle start to get blocked by the buildup of layers of fatty material, causing the lumen of the arteries to become narrower so that less blood can flow through, which means that less oxygen reaches the heart muscle
• Treatments for coronary heart disease

  1. Stents

  2. Statins
• Stent


  An expandable tube that can be placed inside the arteries to hold them open, ensuring that the blood can keep flowing
• Stents


  • The surgery is relatively quick and they're effective for a long time
  • There are risks such as inducing a heart attack, leading to an infection, and a small risk of the patient later developing a blood clot near the stent
• Statins


  Medications that alter the balance of cholesterol in the bloodstream, decreasing the amount of bad (LDL) cholesterol and increasing the good (HDL) cholesterol, lowering the overall risk of coronary heart disease, strokes, and heart attacks
• Statins


  • They have to be taken regularly for years and can cause side effects such as headaches and kidney failure
• Faulty heart valves


  The valves can get damaged or weakened either naturally over time or due to other things like heart attacks and infections, leading to either not enough blood being able to pass through or the valve not closing properly, causing blood to leak backwards
• Treatments for faulty heart valves

  1. Valve replacement with biological valves from another human or a pig, or mechanical valves

  2. Requires surgery and there is an ongoing risk of blood clots
• Heart failure


  When the heart isn't able to pump blood around the body properly anymore
• Treatments for heart failure

  1. Medications can help, but the only proper treatment is a new heart

  2. Can replace with a biological heart from a donor or an artificial heart, but artificial hearts are generally only a temporary fix until a donor heart can be found

  3. Heart transplants have the risk of the body's immune system rejecting the new heart
• Sometimes people require a heart and lung transplant if the lungs are also diseased, but this is very complicated surgery and difficult to find suitable donors