chapter 7

• Type II pneumocyte will secrete pulmonary surfactant which is a anti-sticky chemical consists of phospholipid .This pulmonary surfactant will reduce the surface tension of inner alveolar wall and prevent the alveolar to collapse .
• The alveolar are clustered at the distal ends of alveolar ducts .The epithelial of alveolus consists of two type of cell which is Type I pneumocyte and Type II pneumocyte .Type I pneumocytes made about 95 percent of alveolus and it is a simple squamous cell to speed up gaseous exchange .Type II pneumocyte is a cuboidal cell to differentiate into new squamous cell and to secrete pulmonary surfactant which is a anti-sticky chemical consists of phospholipid .This pulmonary surfactant is to reduce the surface tension of inner alveolar wall and prevent collapse of alveolar .
• The adaptations of alveolar is that it provide large surface area for gaseos exchange, alveolar have one cell thick wall to maximise the oxygen and carbon dioxide diffusion, and alveolar have moist surface for gases to dissolve through , and alveolar is surrounded by numerous blood capillaries for oxygen and carbon dioxide diffusion .
• Haemoglobin is a conjugated protein which is made up by haem and globin .It is a quaternary structure .Each haemoglobin consists of four polypeptide chain which are two alpha and two beta chains .The hydrophobic group is point inward to maintain the 3D structure of the molecule while the hydrophilic group point inwards to make the molecule soluble .
• The functions of haemoglobin are to transport oxygen by binding to the iron atom of the haem group as oxyhaemoglobin,transport carbon dioxide by binding to the amino group of polypeptide side chains as carbaminohaemoglobin .Hb-NH2+CO2->Hb-NHCOO-H+.The other function of haemoglobin is to act as a pH buffer and bind to excess H+ to form haemoglobinic acid Hb+H+->HHb.
• Structure of erythrocyte is : biconcave dics shape ,no nucleus ,no organelles ,thickness is 2.0 um
• Adaptations of haemoglobin are haemoglobin can bind reversibly to oxygen molecule and haemoglobin have cooperative property.
• spectrin a network of fibrous protein to maintain the biconcave shape of erythrocyte
• Oxygen transport : Oxygen diffuse from the atmosphere to the air passage .The partial pressure of oxygen in alveolar is higher that partial pressure of oxygen in alveolar blood capillary .The oxygen will diffuse into the blood capillary .1.5 percent of oxygen will dissolve in the plasma of the blood while 98.5 percent of oxygen will bound to the haemoglobin in the erythrocyte .
• Oxygen transport : The first oxygen bind to one haem group will cause a slightly change of the shape of the haemoglobin and increase the affinity of haemoglobin towards oxygen molecule .The binding of the first oxygen facilitates the binding of second and third oxygen molecule to other haem group easily and rapidly. The binding of the fourth oxygen molecule to the haem group is slower due to distorted shape of haemoglobin .One haemoglobin will bind with four oxygen molecule reversibly to form unstable oxyhaemoglobin
• Pathways for carbon dioxide transport


  • First pathway (5% of CO2)
  • Second pathway (10% of CO2)
  • Third pathway (85% of CO2)
• First pathway


  1. CO2 directly dissolves into plasma cell

  2. CO2 reacts with water to form carbonic acid

  3. Carbonic acid dissociates into H+ and HCO3-
• Second pathway


  1. CO2 diffuses into red blood cell

  2. CO2 binds to amino group of polypeptide side chains of haemoglobin to form carbaminohaemoglobin
• Third pathway


  1. CO2 diffuses into red blood cell

  2. CO2 reacts with water to form carbonic acid with aid of carbonic anhydrase

  3. Carbonic acid dissociates into H+ and HCO3-

  4. HCO3- diffuses out to blood plasma due to the red blood cell membrane is highly permeable to HCO3-

  5. Cl- diffuses into red blood cell to maintain electrical neutrality (chloride shift)

  6. HCO3- carried to lungs as sodium hydrogencarbonate and transport to the pulmonary capillary

  7. H+ concentration will increase causing pH decrease .
• H+ concentration increases in red blood cell


  pH value decreases
• Decrease in pH


  Affinity of haemoglobin towards oxygen decreases
• Dissociation of oxyhaemoglobin


  Oxygen released to actively respiring tissue
• Free haemoglobin from dissociation of oxyhaemoglobin


  Binds with H+ to form haemoglobinic acid
• Third pathway (part 2 )

  8. decrease the affinity of haemoglobin towards oxygen

  9. Oxyghaemoglobin dissociation release oxygen and haemoglobin .Oxygen is release to actively respiring tissue .

  10. The free haemoglobin will react with hydrogen ion to form haemoglobinic acid .
• Unloaded of carbon dioxide : The bicarbonate ion form blood plasma will react with the H+ to form carbonic acid .The carbonic acid will converted back to H20 and CO2 .The CO2 is also unloaded from carbaminohaemoglobin and diffuse into the plasma from erythrocyte .The CO2 diffuse back into the alveolar space in lungs .CO2 will be exhaled during expiration .
• Oxygen dissociation curve is the percentage of saturation of oxygen molecule in a pigment at various partial pressure of oxygen
• There are three types of pigment in the oxygen dissociation curve which is the myoglobin, adult haemoglobin HbA, fetal haemoglobin HbF.
• Important feature of oxygen dissociation curve is that the haemoglobin have high affinity towards oxygen even at low partial pressure of oxygen .The loading tension of haemoglobin is until 95 percent of Hb is saturated .The unloading tension of haemoglobin is at 50 percent of Hb is saturated .

  The oxygen dissociation curve has a S-shape sigmoid curve due to haemoglobin have cooperative property .
• Bohr shift is the decrease of affinity of haemoglobin towards oxygen so that oxyhaemoglobin will dissociate and release oxygen to the actively respiring tissue .
• Myoglobin is a red pigment found in muscle cell
• Myoglobin is a red pigment found in muscle cell .Each myoglobin molecule has one polypeptide and one haem group .As this it only bind with one oxygen molecule .The myoglobin have higher affinity for oxygen than haemoglobin .As this it binds strongly with oxygen molecule to form oxymyoglobin which is more stable than oxyhaemoglobin .The oxymyoglobin acts as oxygen store in muscle cell to delay the onset of anaerobic respiration during vigorous exercise .The curve is hyperbolic in shape because myoglobin does not have cooperative property .
• The foetal haemoglobin is made up of two alpha and two gamma polypeptide chain .It is different form the maternal haemoglobin as maternal haemoglobin is made up of alpha and beta polypeptide chain .The foetal haemoglobin has higher affinity towards oxygen than maternal haemoglobin.As this ,foetal haemoglobin can obtain oxygen from maternal haemoglobin even at low partial pressure of oxygen to ensure that sufficient oxygen supply to the foetus .
• Double Bohr Effect :

  The maternal haemoglobin is able to dissociate oxygen from maternal blood to foetal blood .The carbon dioxide released by foetal blood diffuse into the maternal blood will increase the partial pressure of carbon dioxide in maternal blood and shifts the oxygen dissociation curve to right .The lowering of partial pressure of carbon dioxide in foetal blood will shift its own oxygen dissociation curve to the left . This is known as Double Bohr Effect .
• Factors that increase the oxygen supply for foetus :
• Double Bohr effect makes the oxygen transfer from maternal blood to foetal blood more efficiently .
• The factor that cause oxygen supply to the foetus increase :

  increase the blood flow of the maternal blood

  increase the blood flow of the foetal blood

  have high concentration of foetal haemoglobin

  The foetal haemoglobin has high affinity towards oxygen than maternal haemoglobin

  Double Bohr Effect
• Factors that cause the dissociation of oxyhaemoglobin

  -high partial pressure of carbon dioxide

  -low pH value

  -high temperature
• Describe Bohr effect :

  The partial pressure of carbon dioxide is high and will shift the oxygen dissociation curve to the right .The affinity of haemoglobin towards oxygen decrease causing the oxyhaemoglobin dissociate to release oxygen to actively respiring tissue

  Physiological advantages of Bohr effect is to ensure that the actively repairing tissue can get greatest amount of oxygen .
• To compare the oxygen dissociation graph we must considerate :

  -Partial pressure of oxygen

  -metabolism rate

  -The total surface area per volume ratio (greater animal with have smaller TSA/V)
• Inspiratory reserve volume is the maximum addition volume of air that can be inhaled after a normal tidal inspiration
• Expiratory reserve volume is the maximum addition volume of air that exhaled during exhalation after a normal tidal expiration .
• Tidal volume is the volume of air that can be inhaled in and exhaled out with each breath during normal breathing .
• Residual volume is air that remain in lungs all time and cannot be expelled even forced expiration to prevent collapsing of alveolus .
• vital capacity is the maximum air that can be exchanged after a forced inspiration followed by a forced expiration .
• The total lung capacity is the total volume of air that the lungs can hold .