Gas Transport And Pulomonary Blood Flow

Question 1

How soluble is O2 in plasma

Answer 1

Poorly soluble
Need an alternative method of carriage to deliver required amount to the body

Question 2

What is Haemoglobin made up of

Answer 2

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

Question 3

How much oxygen can 1g of Hb carry

Answer 3

1.36ml

Question 4

What is the oxygen capacity of blood

Answer 4

Mammalian blood average (Hb) = 150g/l
1L blood leaving the lungs can carry about 200ml O2

Question 5

What does oxygen content depend on

Answer 5

The oxygen capacity and the PAO2 in normal animals

Question 6

What is cooperative binding

Answer 6

Binding of an O2 molecule to a Haem binding site increases the affinity of the other sites for O2
The converse is also true

Question 7

What percentage of carbon dioxide is - dissolved in plasma, as carbamino compounds and bicarbonate ions

Answer 7

Dissolved in plasma = 5%
As carbamino compounds = 30%
As bicarbonate ions = 65%

Question 8

What are carbamino compounds

Answer 8

CO2 combines with proteins
Vast majority with Hb in erythrocytes = carbaminohaemoglobin = HBCO2

Question 9

What facilitates loading of CO2 at tissues

Answer 9

Offloading of O2
CO2 binds more readily to deoxyHb

Question 10

Where are bicarbonate ions and what happens

Answer 10

Within erythrocytes
HCO3- diffuses out into plasma

Question 11

Where does Cl- move and what happens at the lungs

Answer 11

Cl- moves into cell to maintain electrochemical neutrality = chloride shift
Reaction reversed at the lungs

Question 12

What happens to H+

Answer 12

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

Question 13

What is oxygen binding to Hb facilitated by and what happens conversely

Answer 13

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

Question 14

What are the alveolar vessels and extra-alveolar vessels

Answer 14

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

Question 15

What is the diameter of the blood vessels affected by

Answer 15

The transmural pressure

Question 16

What does inflation of the lung cause

Answer 16

Dilation of the extra-alveolar vessels but compression of the alveolar vessels

Question 17

What is pulmonary vascular resistance

Answer 17

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

Question 18

How is vasculature controlled

Answer 18

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

Question 19

What is autonomic innervation by here

Answer 19

Pulmonary plexus and vagus
(Not the main influence on pulmonary blood flow)

Question 20

What is the sympathetic innervation

Answer 20

B receptors cause vasodilation
a receptors cause vasoconstriction
Net effect = overall vasoconstriction

Question 21

What is the parasympathetic innervation

Answer 21

Release of nitric oxide causes vasodilation
Direct smooth muscle action causes vasoconstriction
Net effect overall = vasodilation

Question 22

What does nitric oxide cause, where does it come from and what stimulates it’s release

Answer 22

Causes vasodilation
Released from endothelial cells in response to
Parasympathetic stimulation
Bradykinin
Increased speed of blood flow in vessel

Question 23

What does alveolar hypoxia cause, what does it aim to maintain and when is it problematic

Answer 23

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

Question 24

What gives the eventual effect on pulmonary blood flow

Answer 24

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

Question 25

How does this link to the heart

Answer 25

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