Respiratory System 3 - Gas Exchange and Transport Flashcards
Explain Daltons law
The pressure of a gas mixture is equal to the sum of the partial pressures of gases in that mixture
Explain Ficks law
Molecules diffuse from regions of high concentration to low concentration at a rate proportional to:
- The concentration gradient (P1-P2)
- The exchange surface area (A)
- The diffusion capacity (D) of the gas
And inversely proportional to the thickness of the exchange surface (T)
Explain Henrys law
At a constant temperature, the amount of a gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas above the fluid.
= solubility x partial pressure
Explain Boyles law
At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas.
Explain Charles law
At a constant pressure, the volume of a gas is proportional to the temperature of that gas
How does respiratory gas transport change in high altitude?
- There is the same proportion of each gas in the atmosphere
- However, the total partial pressure is lower
- This is similar to the difference in size between 1/5 of a cake and 1/5 of a muffin
How does air change as it moves down the respiratory tree?
The air is:
- Warmed
- Humidified
- Slowed
- Mixed (with preexisting air)
What is the total oxygen delivery at rest?
16mL/min
Describe the structure of a haemoglobin molecule
- Ferrous iron ion in the centre of each monomer
- 2 alpha subunits and 2 either beta, delta or gamma subunits (HbA, HbA2 or HbF)
- Subgroups are covalently bonded at the proximal histamine residue
Describe the process of co-operative binding in haemoglobin
- Initially haemoglobin has a low affinity for oxygen, it is hard for oxygen to bind
- As each oxygen molecule binds, the conformation changes to make the binding of the next oxygen molecule easier
- A binding site forms for 2,3-DPG once 4 oxygen molecules are bound, which basically makes haemoglobin more restricted, and oxygen is ejected out (allosteric behavior)
Compare methaemoglobin and oxyhaemoglobin
- Methhaemoglobin causes a blue colour on the skin, while oxyhaemoglobin causes a red colour
- Met Hb doesnt bind oxygen
- MetHb has an Fe3+ rather than Fe2+ group
Why is the pattern of the oxygen dissociation curve important?
- There is a small range in the pulmonary system, so the oxygen loading is large (95%-100%)
- Systemic has a large range, so that the amount of oxygen dissociation can be altered depending upon oxygen demand
What would cuase the oxygen dissociation curve to shift left?
- Increased affinity due to decreased temperature
- Alkalosis (high bases)
- Hypocapnia (reduced CO2)
- Reduced 2,3-DPG
What would cause the oxygen dissociation curve to shift right?
- Increased temperature
- Acidosis
- Hypercapnia
- Increased 2,3-DPG
What causes an upwards shift of the oxygen dissociation curve?
Polycythaemia (increased haemoglobin concentration)
What causes the oxygen dissociation curve to shift down?
Anaemia
What causes a downwards and leftwards shift of the oxygen dissociation curve?
Increased haemoglobin bound to carbon monoxide
Compare the oxygen dissociation curves of foetal and adult haemoglobin.
- Foetal haemoglobin has a greater affinity to extract blood from the mothers placenta
- There is a leftwards shift
Compare the oxygen dissociation curves of adult HbA and myoglobin
- Myoglobin curve shifts left
- Myoglobin as a greater affinit, to extract oxygen from the blood and store it
What is oxygen flux?
Diffusion of oxygen bound to haemoglobin from the tissues
How can CO2 be transported in the blood?
- Reacts with water to make bicarbonate (enzyme, carbonic anhydrase, present in the erythrocyte for this)
- In the erythrocyte, H+ binds to negative charges on amino acids, balancing out charge. Chloride shift occurs - HCO3- out and chloride moves in using AE1 transporter
- CO2 may also bind to haemoglobin or dissolve in plasma
Compare venous and arteriole CO2 transport
- Venous transport uses more carbaminohaemoglobin and more dissolved in plasma
- This is due to the dissociation graph. There is higher affinity of Hb to CO2 at higher concentrations
Define pulmonary transit time
The amount of time the blood is in contact with the respiratory exchange surface (0.75s)
Describe ventilation perfusion matching in the lungs
- Gravity means that the alveoli at the bottom of the lung are more squished than the ones at the top, so they have a greater capacity to expand in ventillation. Alveoli at the top have greater transmural pressure gradient and are less compliant
- Therefore, there is a higher flow rate and intravascular pressure in the capillaries, so there is increased perfusion at the bottom of the lung
- Perfusion changes more throughout the lung than ventillation, as the vessels are more compliant
