Circulatory System

• Functions of Blood


  • Transporting oxygen and nutrients
  • Transporting CO2 and other wastes
  • Transporting chemical messengers (hormones)
  • Maintain pH
  • Distributing heat/maintain body temp
  • Maintaining water content and ion concentration of the body fluids
  • Protecting against disease-causing micro-organisms
  • Clotting when vessels are damaged
• Blood


  Composed of plasma (liquid part) and formed elements (non-liquid)
• Plasma


  Liquid part (55% of blood), mixture of water with dissolved substances
• Formed elements


  Non-liquid part (45% of blood), includes erythrocytes, leucocytes, thrombocytes
• Red Blood Cells


  • Transport oxygen from the lungs to all the cells in the body
  • Most abundant cell in the blood
  • Biconcave shape
  • No nucleus
  • Limits lifespan to ~120 days
• White Blood Cells


  • Play a role in protecting the body from infection
  • Larger than RBCs but make up only 1% of blood
  • Variety of structures and functions: neutrophils, monocytes, lymphocytes, basophils, eosinophils
• Blood is made of liquid part, plasma, and cells/cell fragments, the formed elements
• Plasma makes up 55% of blood, 91% of plasma is water, the rest is dissolved substances - nutrients, ions, gases, hormones, plasma proteins and wastes
• Formed elements make up 45% of blood volume and include red blood cells, white blood cells and platelets
• White Blood Cells


  • Can remove dead/injured cells and foreign microorganisms
  • Can live from minutes (infection present) to years (no infection)
• Red Blood Cells


  • Biconcave discs with no nucleus which allows more room for haemoglobin
  • Haemoglobin can combine with oxygen, giving RBCs their colour
  • Live for ~120 days - made in bone marrow, destroyed by liver and spleen
• Platelets


  • Very small cell fragments (no nucleus)
  • Approx. one third the size of RBCs
  • Formed in bone marrow and live approx. 7 days
  • Important in normal blood clotting
• Blood Clotting


  1. Vasoconstriction

  2. Platelet plug

  3. Coagulation

  4. Clot retraction

  5. Scab formation
• Red Blood Cells


  • Contain haemoglobin - able to combine with oxygen
  • Have no nucleus - more room for haemoglobin molecules
  • Shaped biconcave discs - increases surface area for oxygen exchange while thick edges give large volume to carry haemoglobin
• Oxygen is not very soluble in water - only ~3% carried in plasma, 97% carried in combination with haemoglobin as oxyhaemoglobin
• Oxygen transport


  1. Oxyhaemoglobin forms in high oxygen concentrations (capillaries in lungs)

  2. Oxyhaemoglobin breaks down in low oxygen concentrations (tissue fluid around cells)
• Oxyhaemoglobin


  Compound formed when oxygen binds to haemoglobin at the heme group
• Carbon dioxide transport


  1. 7-8% dissolved in plasma

  2. 22% combines with globin part of haemoglobin to form carbaminohaemoglobin

  3. 70% reacts with water forming carbonic acid then ionizes into bicarbonate ions
• Oxygen: 3% dissolved plasma, 97% oxyhaemoglobin. Carbon dioxide: 8% dissolved in plasma, 22% as carbaminohaemoglobin, 70% as bicarbonate ions
• Remaining nutrients and wastes dissolved and transported in blood plasma
• Nutrients transported in blood plasma

  • Ions: sodium, calcium, potassium, chloride and iodide
  • Organic nutrients: glucose, vitamins, amino acids, fatty acids and glycerol
• Wastes transported in blood plasma


  • Urea
  • Creatinine
  • Uric Acid
• Blood vessels


  Carry blood around the body in circulation, include arteries, veins and capillaries
• Arteries


  • Carry blood away from the heart
  • Walls contain smooth muscle with elastic fibres - able to contract and stretch to control blood flow
  • Large arteries (e.g. Aorta) divide into small arteries (arterioles) which supply blood to capillaries
  • Smooth muscle allows control of blood flow to capillaries, important during exercise
• Veins


  • Carry blood towards the heart
  • Capillaries join to make small veins, venules, which join to form larger veins
• Blood vessels


  Blood is carried around the body in these
• Circulation


  The movement of blood continuously flowing through the heart
• Types of blood vessels


  • Arteries
  • Veins
  • Capillaries
• Arteries


  • Carry blood away from the heart
  • Walls contain smooth muscle with elastic fibres - able to contract to push blood and stretch to accommodate extra blood and then recoil when relaxed
  • Do not contract and relax to pump blood along, but to control blood flood to various organs (vasoconstriction & vasodilation)
  • Large arteries (e.g. Aorta) that pump blood from heart divide into small arteries (arterioles) which then supply blood to capillaries
  • Also has smooth muscle - control of blood flow to capillaries very important
  • During exercise, wastes act as vasodilators to ensure adequate oxygen supply
• Veins


  • Carry blood towards the heart
  • Capillaries join to make small veins, venules, which join to make large veins (e.g. inferior/superior vena cava and pulmonary veins)
  • Do not have muscular walls - cannot change diameter
  • Relatively low blood pressure
  • Most pressure lost as blood flows through capillaries
  • As pressure constant, elastic walls not required
  • Have valves to prevent blood flowing backwards (due to low pressure)
• Capillaries


  • Link between arteries and veins
  • Very small
  • Form a network carrying blood close to nearly every cell in the body - allows cells to get requirements and pass wastes into blood
  • Walls of capillaries only one cell thick - allows substances to easily pass through between blood and surrounding cells
• The Heart


  • A pump that pushes blood around the body
  • Conical shaped and approx. 12cm long, 9cm at widest point and 6cm thick
  • Completely enclosed by pericardium, a membrane that holds it in place while still allowing it to move as it beats and preventing overstretching
  • Left and right sides are separated by the septum
• When looking at an image, you are viewing it as if it was in a human body. Therefore, the left and right sides of the heart will appear flipped.
• Circulation - Right side of the heart

  1. Receives deoxygenated blood from the body and pumps it to the lungs

  2. Vena Cava -> Right Atrium -> Right Ventricle -> Pulmonary Arteries -> Lungs
• Circulation - Left side of the heart

  1. Receives oxygenated blood from the lungs and pumps it around the body

  2. Pulmonary Veins -> Left Atrium -> Left Ventricle -> Aorta -> Body
• Parts of the heart

  • Pulmonary Trunk (branches into pulmonary arteries)
  • Superior Vena Cava
  • Right atrium
  • Inferior vena cava
  • Semilunar valves
  • Right ventricles
  • Aorta
  • Pulmonary vein
  • Left atrium
  • Atrioventricular valves
  • Left ventricle
  • Septum
• Circulation through the body

  1. Oxygenated blood flows through capillaries and oxygen and nutrients diffuse into cells

  2. Carbon dioxide and wastes diffuse from cells into the blood
• Circulation through the lungs

  1. Deoxygenated blood flows through capillaries of the lungs and oxygen diffuses into the blood

  2. Carbon dioxide diffuses out of the blood and into lungs
• Types of circulation


  • Pulmonary circulation
  • Systemic circulation
• Cardiac Cycle


  1. Atrial Systole: Atria contract filling the ventricles with blood

  2. Ventricular Systole: AV valves forced closed and contracting ventricles force SL valves open and blood moves into pulmonary artery and aorta

  3. Diastole: Atria and ventricles are relaxed, blood enter atria (and also ventricles due to open AV valves)