HAEMOGLOBIN Lesson Objectives: Describe the role of haemoglobin in carrying oxygen and carbon dioxide 2. Explain the significance of the different affinities of foetal haemoglobin and adult haemoglobin for oxygen.

Recap Circulation Starter: Review KS3/4 knowledge of red blood cells: Draw a red blood cell from the front and from the side 2. Suggest how the cell is adapted to its function. (think about its shape, size and its organelles)

Erythrocytes (RBCs) Adaptations: Biconcave shape maximises surface area for gas exchange Small and flexible to pass through narrow capillaries No nucleus – more room to carry respiratory gases Packed with haemoglobin (Hb)

Haemoglobin Haemoglobin is made up of: 1. 4 globular proteins (amino groups) 2. 1 iron ion (prosthetic group) Haemoglobin is the molecule that allows erythrocytes to carry respiratory gases (especially oxygen) It has an affinity for oxygen (can carry 4 O2 molecules) When haemoglobin becomes oxygenated, it is known as oxyhaemoglobin

In the lungs, oxygen diffuses into blood plasma In the lungs, oxygen diffuses into blood plasma. It then passes down a concentration gradient and into erythrocytes. Oxygen binds to Haemoglobin to maintain this concentration gradient Oxygen binds to the ‘haem’ Fe2+ group of haemoglobin.

In respiring tissue, oxygen dissociates (releases) from oxyhaemoglobin Oxygen can then diffuse out of the erythrocytes and to the respiring cells Oxygen binds to Haemoglobin to maintain this concentration gradient Oxygen binds to the 4 globular groups of haemoglobin.

Oxygen Transport The amount of oxygen in the tissue is referred to as its partial pressure for oxygen (pO2) or its oxygen tension. It is measured in kPa. Ventilation allows lung tissue to have a high pO2 Where the pO2 is high, more oxygen is able to associate with haemoglobin molecules to be transported The percentage of haemoglobin saturation is highest here

Oxygen Transport In respiring tissue, the pO2 is low At low pO2, oxygen dissociates from oxyhaemoglobin and can diffuse to the respiring cells.

Oxygen Dissociation Graph As pO2 increases, the saturation of haemoglobin increases. Predict what an oxygen dissociation graph would therefore look like.

Oxygen Dissociation Curve S-Shaped curve ‘% Hb Saturation with oxygen’ is not directly proportionate to ‘pO2’ It is very difficult to achieve 100% saturation of haemoglobin The conformation of the haemoglobin molecule changes as oxygen molecules become associated with it. This changes haemoglobin’s ability to associate with further oxygen molecules.

Oxygen Dissociation Curve After the first oxygen molecule associates, the conformation of the haemoglobin changes Conformational change makes it easier for the 2nd and 3rd oxygen molecules to associate It is difficult to associate a 4th oxygen molecule. This is because the haemoglobin molecule becomes ‘full’ This is why the curve plateaus below 100%

Oxygen Dissociation Curve B Explain the changes ‘A’ and ‘B’ A

Foetal Haemoglobin In pregnancy, foetal and maternal blood is kept separate To get oxygen from maternal to foetal blood, foetal haemoglobin needs a stronger affinity for oxygen than maternal haemoglobin Comparatively, foetal haemoglobin oxygen dissociation curves are to the left of adult curves – their stronger O2 affinity means they can become saturated at lower pO2

HAEMOGLOBIN Lesson Objectives: Describe the role of haemoglobin in carrying oxygen and carbon dioxide 2. Explain the significance of the different affinities of foetal haemoglobin and adult haemoglobin for oxygen.

HAEMOGLOBIN (2) Lesson Objectives: Describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the Bohr effect). 2. Explain the significance of the different affinities of foetal haemoglobin and adult haemoglobin for oxygen.

Carbon Dioxide Transport Carbon dioxide is transported through the circulatory system in 3 ways: Dissolved in plasma (5%) 2. Associated with Hb to form carbaminohaemoglobin (10%)

CO2 Transport – 3rd Way 85% of CO2 is transported as hydrogen carbonate ions. CO2 dissolves in water to form carbonic acid (carbonic anhydrase catalyst) CO2 + H2O  H2CO3 Carbonic acid releases H+ protons (acid dissociation – chemistry) H2CO3  HCO3- + H+ HCO3- ions diffuse out of the erythrocyte. Cl- diffuse into the cell to balance the charge  CHLORIDE SHIFT

CO2 Transport – 3rd Way Question 1: What will happen to the environment within the erythrocyte? H+ ions will bind with the Hb to form haemoglobinic acid Question 2: If Hb is absorbing H+ ions, what can we say Hb is acting as?

CO2 effect on O2 Dissociation We know that oxygen dissociates from oxyhaemoglobin where the pO2 is low (i.e. in respiring tissue). If H+ ions can bind with Hb, they must compete with oxygen In respiring tissue: More CO2 produced More Carbonic acid formed More H+ dissociated More competition for Hb More oxygen dissociation

CO2 effect on O2 Dissociation Conclusion: In a CO2-rich environment (i.e. at respiring tissue), more oxygen dissociates from oxyhaemoglobin Oxygen dissociation curve shifts to the right (requires higher pO2 to saturate Hb due to H+ competition) This is known as the Bohr effect

HAEMOGLOBIN Lesson Objectives: Describe the role of haemoglobin in carrying oxygen and carbon dioxide 2. Explain the significance of the different affinities of foetal haemoglobin and adult haemoglobin for oxygen.