Circulatory system

• Blood flows into the heart when in veins, and out into the body when in arteries
• The term used to describe the passage of blood twice through the heart during one complete circuit is double circulation
• When we observe blood under a microscope it is referred to as a blood smear and there are 4 main components which are

  1. Plasma
  2. Red blood cells
  3. White blood cells
  4. Platelets
• Plasma


  The liquid part of the blood is called plasma. Floating in plasma are red and white blood cells and small fragments of cells called platelets. Many substances are dissolved in the plasma including glucose, amino acids, hormones, antibodies etc.
• Plasma is the liquid part of blood: it is straw coloured. It is 90% water with many substances suspended or dissolved in it:

  Nutrients, including glucose, amino acids, digested fats, vitamins and mineral salts, e.g. sodium

  Waste products, produced by cells, especially carbon dioxide, which is taken to the lungs, and urea, which is taken to the kidneys

  Hormones, to regulate bodily processes e.g. growth

  Chemicals from white blood cells, needed for protection from diseases, e.g. caused by bacteria and viruses
• Red blood cell


  These are adapted to transport oxygen around the body. The oxygen easily combines with haemoglobin (rich in iron) in RBC's. Red blood cells are unique; the absence of a nucleus provides more room for oxygen to be carried around in each cell. They are biconcave discs - this shape provides a large surface area for diffusion and carrying oxygen
• White blood cells


  White blood cells protect the body from invasion by microorganisms

  There are two main types of white blood cells:

  • Phagocyte cells, which ingest any foreign cells they find (These cells have several nuclei)
  • Lymphocyte cells, which produce antibodies after exposure to a specific antigen, which then cause the destruction of any other cells with that antigen whenever they invade the body (These have one large nuclei)

  
• Platelets


  When you bleed, a self protecting mechanism operates to thicken the blood and form a clot. Platelets are small fragments of cells and are important in the process of clotting. They help convert fibrinogen ( a soluble plasma protein) to fibrin ( a meshwork of threads). Red blood cells are trapped there to form the clot, which hardens to form a scab
• Cell lysis



  There are several reasons why an animal cell is more susceptible to changes in water concentration

  • It has no cell wall to resist further water coming in
  • When the cell swells up, the membrane may burst because of the pressure (lysis). This is particularly true in red blood cells.
  • If the animal cell loses too much water by osmosis, it will shrivel up

  If a red blood cell is placed in pure water or a very dilute solution, then water will enter it by osmosis and it may lyse
• Arteries


  Thick wall containing elastic and muscle fibres to cope with the much higher pressure in these vessels

  Much smaller lumen compared to the thickness of the wall

  No valves

  Carry blood away from the heart

  Substances from the blood cannot pass through the artery walls
• Veins

  • Thinner wall containing less elastic and muscle fibres to cope
  • Much bigger lumen compared to the thickness of the wall
  • Have valves to prevent backflow of blood
  • Carry blood towards the heart
  • Substances cannot pass through the veins' walls
• Capillaries

  • Narrow, thin-walled vessels, just one cell thick
  • Microscopic (too small to see without a microscope)
  • Exchange of substances between cells and blood only takes place here
  • Connects arteries and veins
• Blood is oxygenated at arteries, deoxygenated at veins, and oxygenated at the artery end, but deoxygenated at the venous end of a capillary
• Capillaries are so good at their function because

  1. They have very thin walls
  2. They have a large surface area
  3. Body cells are never far way for a small diffusion distance
  4. Blood flows through them very slowly
• The pulmonary vein carries oxygenated blood from the lungs to the heart
• The aorta carries oxygenated blood from the heart around the whole body
• The vena cava carries deoxygenated blood from the body back to the heart
• The pulmonary artery carries deoxygenated blood from the heart to the lungs
• The hepatic artery carries oxygen and glucose to the liver
• The hepatic portal vein carries digested food from the small intestine (ileum) to the liver
• The renal artery carries blood rich in urea to the kidneys for excretion
• The renal vein carries purified blood ( low in urea) from the kidney to the vena cava; also CO2 back to the heart and lungs
• The heart has four chambers

  A) Left atrium

  B) Left ventricle

  C) Right ventricle

  D) Right atrium

  
• Heart dissection:

  1. Put the heart on the board
  2. Look at the blood vessels on the surface
  3. Feel the thinner right side and the thicker left side of the ventricle muscle
  4. Make sure that the thinner right side is to your left
  5. Cut around the heart horizontally
  6. If you lift up the two upper sides of the heart you will see the muscle in the middle of the heart that separates the two parts
• Order of blood starting from vena cava

  Vena cava -> right atrium -> opening (valve) between right atrium and ventricle -> right ventricle -> pulmonary artery-> pulmonary vein -> left atrium -> opening (valve) between left atrium and ventricle -> left ventricle -> aorta
• Regular exercise is hugely beneficial to the circulatory system. It burns up fat that may have otherwise blocked an artery or led to an increased risk of obesity
• The fitter you are the lower your resting heart rate. If you are fit, your cardiac muscle will be stronger and will be able to pump more blood per beast. Therefore, the heart has to pump less often to get the same amount of blood round the body in a given time
• 1. Unfit person has a higher resting heart rate
  2. Unfit person's heart rate goes up faster when exercise starts
  3. Fit person's heart rate has a lower maximum
  4. Unfit person takes longer to return to normal heart rate