Respiratory System 3 - Gas Exchange and Transport

Question 1

Explain Daltons law

Answer 1

The pressure of a gas mixture is equal to the sum of the partial pressures of gases in that mixture

Question 2

Explain Ficks law

Answer 2

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)

Question 3

Explain Henrys law

Answer 3

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

Question 4

Explain Boyles law

Answer 4

At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas.

Question 5

Explain Charles law

Answer 5

At a constant pressure, the volume of a gas is proportional to the temperature of that gas

Question 6

How does respiratory gas transport change in high altitude?

Answer 6

• 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

Question 7

How does air change as it moves down the respiratory tree?

Answer 7

The air is:

• Warmed
• Humidified
• Slowed
• Mixed (with preexisting air)

Question 8

What is the total oxygen delivery at rest?

Answer 8

16mL/min

Question 9

Describe the structure of a haemoglobin molecule

Answer 9

• 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

Question 10

Describe the process of co-operative binding in haemoglobin

Answer 10

• 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)

Question 11

Compare methaemoglobin and oxyhaemoglobin

Answer 11

• 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

Question 12

Why is the pattern of the oxygen dissociation curve important?

Answer 12

• 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

Question 13

What would cuase the oxygen dissociation curve to shift left?

Answer 13

• Increased affinity due to decreased temperature
• Alkalosis (high bases)
• Hypocapnia (reduced CO2)
• Reduced 2,3-DPG

Question 14

What would cause the oxygen dissociation curve to shift right?

Answer 14

• Increased temperature
• Acidosis
• Hypercapnia
• Increased 2,3-DPG

Question 15

What causes an upwards shift of the oxygen dissociation curve?

Answer 15

Polycythaemia (increased haemoglobin concentration)

Question 16

What causes the oxygen dissociation curve to shift down?

Answer 16

Anaemia

Question 17

What causes a downwards and leftwards shift of the oxygen dissociation curve?

Answer 17

Increased haemoglobin bound to carbon monoxide

Question 18

Compare the oxygen dissociation curves of foetal and adult haemoglobin.

Answer 18

• Foetal haemoglobin has a greater affinity to extract blood from the mothers placenta
• There is a leftwards shift

Question 19

Compare the oxygen dissociation curves of adult HbA and myoglobin

Answer 19

• Myoglobin curve shifts left

- Myoglobin as a greater affinit, to extract oxygen from the blood and store it

Question 20

What is oxygen flux?

Answer 20

Diffusion of oxygen bound to haemoglobin from the tissues

Question 21

How can CO2 be transported in the blood?

Answer 21

• 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

Question 22

Compare venous and arteriole CO2 transport

Answer 22

• 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

Question 23

Define pulmonary transit time

Answer 23

The amount of time the blood is in contact with the respiratory exchange surface (0.75s)

Question 24

Describe ventilation perfusion matching in the lungs

Answer 24

• 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