SA:V

• Hemoglobin


  Oxygen-carrying protein in red blood cells
• Erythrocytes (red blood cells)


  • Biconcave structure for large surface area to volume ratio
  • Each contains around 300 million hemoglobin molecules
  • Lose nucleus before entering circulation, allowing more space for hemoglobin
• Heme


  Prosthetic group in hemoglobin containing iron ion (Fe2+)
• Conjugated protein


  Protein with a prosthetic group (heme)
• Oxygen binding to hemoglobin

  1. Hemoglobin binds oxygen

  2. Becomes oxyhemoglobin

  3. Reaction is reversible, oxyhemoglobin can release oxygen
• Oxygen dissociation curve


  Graph showing percentage saturation of hemoglobin with oxygen against partial pressure of oxygen
• Oxygen dissociation curve has an S-shaped (sigmoid) curve
• At low oxygen partial pressures


  Hemoglobin has low affinity for oxygen
• When one oxygen molecule binds

  Affinity of hemoglobin for oxygen increases (positive cooperativity)
• As oxygen partial pressure decreases in tissues


  Hemoglobin unloads oxygen, decreasing its oxygen affinity
• In alveoli, hemoglobin is around 97% saturated with oxygen
• In very active tissues like muscle during intense exercise, the last oxygen molecule may unload from hemoglobin
• Haemoglobin carries oxygen from the lungs to the rest of the body's tissues and organs.
• Bohr effect


  The effect of carbon dioxide on the oxygen affinity of hemoglobin
• Bohr effect

  1. Increased carbon dioxide

  2. Decreased oxygen affinity of hemoglobin
• Double circulatory system


  Oxygenated blood is pumped from the heart to the lungs, then returns to the heart and is pumped around the whole body
• Blood flow through the human heart


  1. Oxygenated blood enters right atrium through vena cava

  2. Deoxygenated blood pumped from right atrium to right ventricle

  3. Right ventricle pumps deoxygenated blood to lungs through pulmonary artery

  4. Oxygenated blood returns from lungs to left atrium through pulmonary vein

  5. Blood passes from left atrium to left ventricle

  6. Left ventricle pumps oxygenated blood to body through aorta
• Heart structure


  • Heart is formed from cardiac muscle
  • Heart has two completely separate sides
  • Top two chambers are atria with thin muscular walls
  • Bottom two chambers are ventricles with thicker muscular walls
  • Atria and ventricles separated by atrioventricular (AV) valves
  • Right and left sides of heart separated by septum
• Myogenic


  The heart muscle triggers its own beat, the heart does not need an external signal to beat
• Atrioventricular (AV) valves


  Valves that open in the right direction, attached to tendons
• Initiation of heartbeat


  1. Cells in sinoatrial node (pacemaker) depolarize

  2. Wave of electrical excitation spreads across atria

  3. Atria contract (atrial systole)

  4. Electrical excitation reaches atrioventricular node

  5. Atrioventricular node transmits electrical excitation down Purkinje fibers

  6. Ventricles contract from apex upwards
• Vena cava


  Blood vessel that brings deoxygenated blood to right atrium, has superior and inferior branches
• Atrioventricular node


  • Detects electrical excitation passing over atria
  • Transmits electrical excitation down Purkinje fibers after a short delay
• Pulmonary artery


  Blood vessel that carries deoxygenated blood from right ventricle to lungs
• The delay between atrial and ventricular contraction ensures ventricles contract after atria
• Cardiac cycle


  Blood moves through the heart
• Ventricles contracting from apex upwards ensures maximum volume of blood is pumped out
• Pulmonary vein


  Blood vessel that brings oxygenated blood from lungs to left atrium
• At the end of the previous cardiac cycle, both the atria and ventricles are in diastole (relaxed)
• The events taking place in the heart during the heartbeat are called the cardiac cycle
• Blood flow during diastole


  1. Blood flows into the atria through the vena cava and pulmonary vein

  2. Pressure in the atria rises

  3. Atrioventricular valves open

  4. Blood flows down from the atria into the ventricles
• Aorta


  Large blood vessel that carries oxygenated blood from left ventricle to body
• Pressure and volume changes in the heart during the cardiac cycle


  Shown in a graph with two parts: top graph shows pressure changes, bottom graph shows volume changes in the left ventricle
• Coronary artery


  Blood vessel that branches directly from aorta to supply heart muscle with oxygen and nutrients
• Atrial systole


  1. Atria contract

  2. Remaining blood pushed from the atria down to the ventricles
• Pressure graph


  • Green line: pressure in left atrium

  Red line: pressure in left ventricle

  Orange line: pressure in aorta
• Right and left sides of heart contract at the same time
• Cardiac output


  The volume of blood pumped into the circulatory system in one minute
• Cardiac cycle pressure changes


  Left atrium contracts, pressure increases, blood flows into left ventricle

  Left ventricle contracts, pressure massively increases, atrioventricular valve closes, semilunar valve opens, blood flows out to aorta

  Left ventricle relaxes, pressure falls below left atrium, atrioventricular valve opens, blood flows in from left atrium
• Ventricular systole


  1. Ventricles contract

  2. Ventricular pressure rises rapidly

  3. Atrioventricular valves close

  4. Semilunar valves in the pulmonary artery and aorta open

  5. Blood pumped from the ventricles out of the heart