Gas Transport And Pulomonary Blood Flow Flashcards
How soluble is O2 in plasma
Poorly soluble
Need an alternative method of carriage to deliver required amount to the body
What is Haemoglobin made up of
4 x Haem units with associated globin chain
Haem = pigment molecule containing Fe2+
Each ferrous iron molecule can bind to one O2
One Hb can bind 4 x O2 molecules
How much oxygen can 1g of Hb carry
1.36ml
What is the oxygen capacity of blood
Mammalian blood average (Hb) = 150g/l
1L blood leaving the lungs can carry about 200ml O2
What does oxygen content depend on
The oxygen capacity and the PAO2 in normal animals
What is cooperative binding
Binding of an O2 molecule to a Haem binding site increases the affinity of the other sites for O2
The converse is also true
What percentage of carbon dioxide is - dissolved in plasma, as carbamino compounds and bicarbonate ions
Dissolved in plasma = 5%
As carbamino compounds = 30%
As bicarbonate ions = 65%
What are carbamino compounds
CO2 combines with proteins
Vast majority with Hb in erythrocytes = carbaminohaemoglobin = HBCO2
What facilitates loading of CO2 at tissues
Offloading of O2
CO2 binds more readily to deoxyHb
Where are bicarbonate ions and what happens
Within erythrocytes
HCO3- diffuses out into plasma
Where does Cl- move and what happens at the lungs
Cl- moves into cell to maintain electrochemical neutrality = chloride shift
Reaction reversed at the lungs
What happens to H+
Can’t diffuse easily out of the erythrocyte
Buffered (in part) by haemoglobin
Binds more easily to deoxyHb
Keeps reaction moving to the right - facilitates further uptake of CO2
What is oxygen binding to Hb facilitated by and what happens conversely
Relatively low CO2 and high pH
As CO2 is released at the lungs O2 binds more easily
(Not exchanging with one another)
Conversely CO2 binds more readily to deoxyHb as does H+
As O2 is released at the tissues CO2 binds more easily
(Some binds to Hb some converts to bicarbonate and H+ which also binds to Hb)
The necessary interactions within the erythrocyte facilitate one another
What are the alveolar vessels and extra-alveolar vessels
Alveolar vessels = capillaries running in alveolar septa which participate in gas exchange
Extra-alveolar vessels = vessels which move blood to and from the lungs
In quadrupeds the dorsocaudal lung fields are preferentially perfused
What is the diameter of the blood vessels affected by
The transmural pressure
What does inflation of the lung cause
Dilation of the extra-alveolar vessels but compression of the alveolar vessels
What is pulmonary vascular resistance
Pulmonary vascular resistance is low compared to systemic
PVR = P(pulmonary artery) - P(left atrium) / cardiac output
Capillaries contribute significantly to this resistance
Differential to systemic circulation
Capillary flow in lungs is pulsatile
How is vasculature controlled
Pulmonary arteries and arterioles contain smooth muscle in the walls which can contract or relax
(Varies between species dogs and sheep have little, cattle and pigs have lots)
Relaxation = dilation of arteries = decreased PVR
Contraction = constriction of arteries = increased PVR
Various neural and humoral controls
What is autonomic innervation by here
Pulmonary plexus and vagus
(Not the main influence on pulmonary blood flow)
What is the sympathetic innervation
B receptors cause vasodilation
a receptors cause vasoconstriction
Net effect = overall vasoconstriction
What is the parasympathetic innervation
Release of nitric oxide causes vasodilation
Direct smooth muscle action causes vasoconstriction
Net effect overall = vasodilation
What does nitric oxide cause, where does it come from and what stimulates it’s release
Causes vasodilation
Released from endothelial cells in response to
Parasympathetic stimulation
Bradykinin
Increased speed of blood flow in vessel
What does alveolar hypoxia cause, what does it aim to maintain and when is it problematic
Causes vasoconstriction
(Opposite effect to hypoxia elsewhere is tissues)
Aims to maintain V:Q by diverting blood to well ventilated alveoli
Problematic if generalised (e.g. altitude)
Degree of response dependent on amount of vascular smooth muscle
What gives the eventual effect on pulmonary blood flow
The balance of the two previous factors
The autonomic nervous system plays a relatively small part and can be over ridden by local factors in the respiratory system
How does this link to the heart
Pulmonary circulation arises from the right ventricle and returns to the left atrium
Increased PVR (pulmonary hypertension)
Increases after load on the right heart which can lead to heart failure
