Gaseous Diffusion and Transport Flashcards
Definition of oxygenation
NOT THE SAME AS OXIDATION, the addition of O2 to any system
Definition of anaemia
Defects in Hb production or RBC nos => anaemia
There is a reduced content of functional Hb in the blood and decreased O2 carrying capacity
Defintion of cyanosis
Deficient supply of O2 => tissues resulting in a bluish tinge, ceasing discoloration of the tissues
Definition of alveolar ventilation
Volume that reaches alveoli where gas exchange can occur that is physiologically useful
VA = minute ventilation - dead space
Definition of hyperventilation
Overventilation in proportion to metabolism
Results in decreased PaCO2
Definition of hypoventilation
Underventilation in proportion to metabolism
Results in increased PaCO2
O2 transport in the blood
- How
- Why
- Capacity
- O2 consumption at rest
How
-Via Hb, Fe2+ binds to O2
Why
-Low solubility, CO not large enough to sustain life
Capacoty
- 1g Hb = 1.34ml O2
- 200ml/L
O2 consumption at rest
-250ml/min at rest
Describe the O2 dissociation curve
- arterial O2 content and SaO2
- venous O2 content and SaO2
- at what kPa is O2 easily offloaded
Sigmoid
Arterial O2 = 200ml/L 100%
Venous O2 = 150ml/L 75%
8kPa, O2 easily off/onloaded
How does the
- Bohr effect
- Anaemia
- CO
- Foetal Hb affect O2 and Hb affinity
Bohr
-decreased pH, increased pCO2, temp, 2,3BPG => increased offloading
Anaemia
-Hb prod/RBC nos are low => O2 capacity, low nos of functional Hb => SaO2 lower but same amount offloaded
CO
-less O2 binds => decreased offloading
Hbf
-increased affinity for mother’s placental O2 => less offloading
Describe peripheral cyanosis
-what it is typically characterized by
Reduced flow to extremities => hypoxic tissue
Generally due to poor microcirculation
Describe central cyanosis
- what can it be caused by
- where would this be seen
Arterial hypoxemia /low SaO2
- PaO2 8kPa
- chronic resp
- R => L shunt
Seen in
- buccal mucosa
- lips
- ear lobes
Describe the 3 methods of transporting CO2
- HCO3 in plasma and RBC (60%)
- HbCO2 (30%)
- CO2 dissolved (10%)
HCO3 in plasma and RBC
- HCO3 buffer, bicarbonate released into plasma, exchanged with Cl
- fast reaction in RBC due to CA
- back reaction favored in lung => CO2 diffuses out
HbCO2
- NH2 + CO2 <=> NHCOOH
- lys, arg in deoxygenated Hb/protein => carbamino product
- Oxy Hb inhibits reaction, reversed in lung
CO2 dissolved
- Possible as CO2 more soluble than O2
- CO2 dissolved diffuses down PP∆ => lung
What is the Haldane effect?
CO2 carried is greater in partially deoxygenated blood than oxygen blood, irrespective of PCO2
Describe the CO2 binding curve
- arterial CO2 cont
- venous CO2 cont
Linear
Arterial CO2 cont
- 5.3kPa 480ml/L
- 6.1kPa 520ml/L
Describe the relationship between CO2, HCO3 and pH
- what is the pKa of H2CO3
- what is pH
- what is [HCO3]
- what is [CO2]
pH = pKa + log [HCO3]/[CO2]
7.4 = 6.1 + log [HCO3]/[CO2]
20 = [HCO3]/[CO2]
[HCO3] = 24mM [CO2] = 1.2mM
