Gas exchange

What is gas exchange

Exchange of CO₂ and O₂ at cells and tissues through diffusion

List 5 adaptations of gas exchange surfaces

• Large surface area

• Thin tissue layer (1 cell thick)

• Permeable membranes

  Dense network of capillaries with constant blood flow surrounding to maintain concentration gradient for diffusing gases

• Covered in layer of moisture: allows gas to dissolve and diffuse rapidly

Respiration

Release of ATP energy from organic compounds in cells.

What is partial pressure? What factors affect it

Pressure exerted by single gas when its found in mixture of gasses

• Total pressure exerted by all gas in the mixture

• Concentration of target gas

Low partial pressure of O₂

Low haemoglobin affinity to O₂

High partial pressure of O₂

High haemoglobin affinity to O₂

O₂ dissociation curve (x and y axis, Shape description)

Shows affinity of haemoglobin for oxygen

• X axis = partial pressure

• Y axis = O₂ saturation of haemoglobin

Sigmoid shape

• Start at low PP low saturation.

• PP increase, saturation increase

• High PP, curve flattens out because most haemoglobin are fully saturated

What is the max amount of O₂ that can bind with 1 Haemoglobin

4

What happens to affinity for O₂ when more O₂ binds to 1 haemaglobin

Conformational change in shape of haemoglobin occurs

Increases affinity o

What is co-operative binding

When binding of one molecule to another facilitates the binding of another to the same molecule

O₂ Partial pressure in the lungs

HIgh partial pressure. Haemoglobin becomes fully saturated

O₂ Partial pressure in respiring tissue

Respiring tissue uses O₂, low concentration of O₂, and low Partial pressure of O₂

Haemoglobin release O₂, diffuse into respiring tissue to provide more O_2.

CO₂ modes of transport (3)

1. Some CO₂ is bounded in haemaglobin

2. Small amount of CO₂ dissolved in blood plasma

3. Most CO₂ is reversibly converted to HCO₂ ⁺ ion in blood cells

Difference between Foetal and Adult Haemoglobin

Foetal: 2 alpha 2 gamma haemoglobin parts

Adult: 2 alpha 2 beta

Which has higher affinity to O₂, Adult or foetal haemoglobin

Foetal

What is Bohr shift

When affinity for O₂ decreases due to increase in CO₂ partial pressure or decrease in pH.

Steps of gas exchange at tissues in terms of haemoglobin

1. Tissue use O₂ and produce CO₂ during aerobic respiration

2. Very low partial pressure and affinity for O₂ and high partial pressure and affinity for CO₂

3. High partial pressure of CO₂ causes Bohr shift, further decreasing affinity for O₂

4. Haemoglobin in blood release O₂ and take up CO₂ due to partial pressures

Steps of gas exchange at lungs in terms of haemoglobin

1. O₂ diffuse from alveoli to blood and CO₂ diffuse from blood to alveoli

2. High partial pressure and affinity for O₂ and low partial pressure and affinity for CO₂

3. High O₂ and low CO₂ partial pressure, haemoglobin picks up O₂

What is formed by CO₂ after it diffuse into red blood cells

Carbonic acid

(CO₃ + H₂O → H₂CO₃)

What happens to the carbonic acid in red blood cells

1. H₂CO₃ dissociates to form hydrogen carbonate ions (H₂CO₃ → HCO₃^- + H⁺)

2. HCO₃^- leaves cell and Cl^- enters cell (Chloride shift)

3. H⁺ binds to haemoglobin and causes conformational change

4. O₂ affinity decrease

5. CO₂ is released when partial pressure of CO₂ in blood plasma is low.