Pulmonary circulation and gas transport (physio) Flashcards
Route of pulmonary circulation after birth
Deoxy blood from tissues flow in right atrium (RA) -> right ventricle (RV) -> main pulmonary artery -> branches successively into small pulmonary arteries -> arterioles -> capillary bed around alveoli -> gas exchange -> oxygenated blood flow into small pulmonary veins (PV) -> 4 large PV -> left atrium (LA) -> left ventricle (LV) -> systemic circulation
Does pulmonary or systemic circulation have higher pressures?
Systemic
Features of pulmonary circulation
Low pressure
High flow -> lungs receive whole of CO at all times
Distribution of blood flow in lungs is not uniform
Other fns of pulmonary circulation
Metabolism of hormones
- angiotensin converting enzyme (ACE) converts angiotensin 1 -> angiotensin 2
What influences distribution of blood flow in lungs?
Gravity -> posture
- upright -> more blood flow at bottom
Muscular tone of pulmonary arterioles -> change diameter of arteriole
- distension
- pulmonary artery and arterioles have less muscular walls (compared to systemic) -> distend more easily w/ increased blood flow
- vasoconstriction
- decreased blood flow through capillaries
Describe pulmonary circulation in fetus
Lungs collapsed -> non-functional -> little blood floe thru lungs
Oxygenated blood from placenta enter via umbilical vein -> right heart -> left heart via foramen ovale (opening btw RA and LA) -> pulmonary artery -> aorta via ductus arteriosus -> systemic circulation
Special properties of pulmonary circulation in foetus
High pressure, low flow sys
Lungs are collapsed -> not useful for gas exchange
Special properties of pulmonary circulation after birth
Low pressure, high flow sys
Gravity-dependent
Blood flow through capillaries regulated by arteriolar tone
Factors affecting O2 transport
Respi sys
- lung fn
CVS
- CO, vascular constriction/dilation affecting blood flow in capillaries
Blood
- capacity to carry O2
Sources of O2 in blood
Hb in RBC
Dissolved free O2 molecules
- exerts pO2 in blood
Sources of CO2 in blood
Converted to HCO3-
Bound to proteins including Hb -> carbamino cmpds
Dissolved free CO2 molecules
- exerts pCO2 in blood
What do dissolved gases in fluid do?
Create gas pressure within fluid
What happens when there is increased dissolved gas in fluid?
Increase gas pressure in fluid
High vs low solubility gas
High solubility -> more free gas molecules dissolve to create a particular gas pressure in fluid
Low solubility -> fewer free gas molecules dissolve to create similar gas pressure in fluid
At equilibration, is the amt of gas dissolved in liquid in both compartments the same?
No, amt of gas dissolved depends on the solubility of the gas
If A more soluble than B in fluid, more A molecules will be dissolved in fluid when equilibrium reached
Does O2 have good solubility in blood?
No -> dissolved O2 is insufficient for physiological needs
Eqn for Hb fusion w/ O2
Hb + O2 <-> HbO2
Type of Hb for normal adult and foetus
Adult -> HbA
Fetal -> HbF
Does normal adult or foetus Hb have a higher affinity for O2?
HbF > HbA
- HbF have higher affinity -> Hb binds w/ higher efficiency than adult Hb -> extract O2 from mother
How many O2 molecules can 1 molecule of Hb bind to?
4 O2 molecules
- 1 Hb have 4 Fe -> bind to 4 O2
- each Fe atom bind reversibly to 1 O2 -> oxygenate tissue
Factors affecting amt of O2 carried by Hb
pO2 in blood
- higher pO2 -> more O2 binds to Hb up till saturation capacity
Conc of Hb in blood
- more Hb -> more O2 can bind
Affinity of Hb for O2
- higher affinity -> more O2 can bind
Factors affecting affinity of Hb for O2
pH
- low pH -> lower affinity
Temp
- higher temp -> lower affintiy
2,3-diphosphoglycerate
- increased levels -> lower affinity
Shape of HbO2 dissociation curve
Sigmoid shape (S-shaped curve)
What is the HbO2 dissociation curve?
Relate HbO2 and pO2 of blood
What happens when blood pO2 drops?
pO2 drop <100 - 60mmHg -> minimal drop in %HbO2 (based on curve)
- sufficient O2 supply in blood for tissues
pO2 drop to <60mmHg -> severe drop in %HbO2 -> decreased O2 supply in blood for tissues
How does affinity for O2 shift the HbO2 dissociation curve?
Higher affinity -> increased O2 binding to Hb -> increased %HbO2 -> shift left
Lower affinity -> decreased O2 binding to Hb -> decreased %HbO2 -> shift right
Purpose of Cl- in gas CO2 transport
Cl- shift maintains electrical neutrality -> move from plasma into RBC as HCO3- moves into plasma
- because RBC loses negatively charged ion
What happens when CO2 is excreted?
Removes H+
CO2 vs O2 dissociation curve
CO2 curve is much steeper and more linear
- as long as blood pCO2 decrease -> CO2 content in blood decrease
