Lecture 33 - Gas transport and exchange

Question 1

Describe the diffusion of gases

Answer 1

o The process by which gas molecues move from areas of higher concentration to areas of lower concentration due to their random motion.
o Essential for exchange of oxygen and carbon dioxide in the body

Question 2

Describe and explain the factors in Fick’s law

Answer 2

o Fick’s law measures the flow (V) of gas across a membrane
o The factors affecting Fick’s law include area, diffusion constant, pressure and thickness

Question 3

Describe the limitation of gas transfer / diffusion

Answer 3

o Only dissolved gas contributes to the partial pressure
o Oxygen bound to Hb does not contribute to PO2
o Exercise will reduce time capillary blood spends in contact with alveolar exchange surface

Question 4

Describe ventilation-perfusion matching and its functional benefits.

Answer 4

o Refers to the matching of ventilation (airflow) and perfusion (blood flow) in the lungs to optimize gas exchange.
o Functional benefits include optimal gas exchange, waste removal, minimized shunting, effective gas transport, conservation of energy.

Question 5

Describe the properties and characteristics of pulmonary circulation

Answer 5

o Pulmonary blood pressure low (25/8 mm Hg)
o 10% of blood volume at any given time
o Shorter length of blood vessels
o Two circuits in parallel – is the right side of circulation
o Facilitates the exchange of gases
o Low resistance in pulmonary vessels
o Closely linked to expandability of the lungs
o Blood volume is matched to lung’s capacity
o Can rapidly adjust to changes in oxygen demands

Question 6

Describe the control of local blood flow (autoregulation) in the pulmonary vasculature

Answer 6

o Local control mechanisms try to keep ventilation and perfusion matched
o The ability of the blood vessels in lungs to regulate their own diameter and blood flow in response in changes in local conditions.

Question 7

Example of local vascular control

Answer 7

o Decrease ventilation
o Ventilation < perfusion
o Va/Q < 1
o Blood diverted from poorly ventilated regions to better ventilated alveoli
o Increase gas exchange
o Maintain PaO2

Question 8

What is PaO2

Answer 8

Partial pressure of oxygen in alveolar air

Question 9

Describe the transport of oxygen by haemoglobin

Answer 9

Haemoglobin is a protein found in RBCs and has a high affinity for oxygen, helps to carry oxygen from lungs to tissue and organs for cellular respiration and thus energy production.

Question 10

Describe the parts of the oxygen dissociation curve

Answer 10

o Oxygen bound to heme increases Po2
o Does not contribute to Po2 of blood
o When increasing large amounts of O2 are being delivered in tissue with little change to capillary PO2
o When plateau being reached large tolerance to PO2 within alveolar gas (PaO2) helps maintain large PO2 difference in alveolar. Assists with O2 loading.

Question 11

what is oxygen capacity

Answer 11

o Maximum amount of O2 that can combine with Hb
o All Hb binding sites are occupied only measured by exposing to very high PO2

Question 12

Describe and identify the factors that contribute to shift in Hb-binding curve

Answer 12

o What causes a right shift?
 Increased temperature
 Increases PCO2
 Increases H+
 Increases DPG
o Effect of pH
 Decreasing pH shifts curve to right
o Effect of PCO2
 Increase PCO2 blood shifts curve to right
o Effect of temperature on PO2
 Increasing temperature shifts curve to right

Question 13

What is oxygen saturation

Answer 13

Percentage of Hb percentage available binding site with O2 attached

Question 14

Describe and explain the relationship between PO2, O2 concentration, O2 saturation

Answer 14

o Haemoglobins affinity for oxygen changes in response to PO2 levels, the lower the PO2 level the lower the affinity for oxygen, represented by lower O2 saturation on the curve.
o Sigmoidal shape, which reflects the cooperative binding of oxygen by haemoglobin. As more oxygen binds to one of the four binding sites on haemoglobin, it becomes easier for additional oxygen molecules to bind
o Plateau phase = at high PO2 levels (i.e. in lungs) curve reaches a plateau where haemoglobin is nearly fully saturated with oxygen, thus small changes in PO2 have minimal impact on O2 saturation
o In tissue where PO2 is lower curve has steeper slope, thus small changes in PO2 result in significant changes in O2 saturation.

Question 15

Describe the forms that carbon dioxide can be carried through the blood

Answer 15

o Dissolved CO2
 Around 10%
 CO2 high solubility
o Carbamino compounds
 Around 30%
o Bicarbonate
 Around 60%

Question 16

Describe the methods of carbon dioxide transport in the blood

Answer 16

Through dissolved CO2, carbaminohaemoglobin and primarily as bicarbonate ion in a bicarbonate buffer system.