Basis of respiration

Question 1

Movement of gases

Answer 1

Gases move down a pressure gradient- diffusion.

The equilibrate between a membrane that is permeable

Question 2

Ideal gas equation

Answer 2

PV= nRT, P= V/ n(R)T

Therefore the pressure of a gas in a container is equivalent to volume/ the number of molecules and temperature.

Question 3

PIO2
FIO2
Patm

Answer 3

PIO2= pressure of inspired oxygen
FIO2= fraction of inspired oxygen
Patm= atmospheric pressure 

PIO2= FIO2 x Patm
0.21 x 760 mm Hg = 160 mm Hg

Question 4

The average p(O2) of inspired, dry air

Answer 4

160 mm Hg

Question 5

The average p(O2) of inspired air, saturated with water vapour

Answer 5

150 mm Hg

Question 6

The average p(O2) in alveolar gas

Answer 6

100 mm Hg

Question 7

The average p(O2) in arterial blood

Answer 7

95 mm Hg

Question 8

The average p(O2) in tissue

Answer 8

40 mm Hg

Question 9

The average p(O2) in mitochondria

Answer 9

4-10 mm Hg

Question 10

Alveolar gas equation

Answer 10

PAO2- p(O2) in the alveolus

PAO2= [(Patm - PH20) x FIO2] - (PaCO2 / RQ)
On average this is 100 mm Hg

PH20= p(water) in alveolus, 47 mm Hg.

PaCO2= p(CO2) in arteries, equivalent to how much oxygen has left alveolus. 40 mm Hg.

RQ= respiratory quotient, CO2 consumed/ O2 consumed, 0.8

Question 11

Respiratory quotient (RQ) of fats and carbohydrates

Answer 11

Fats- 0.7 averagely
Carbs- 1.0

Most people’s diet is a balance of the two, so the average RQ is 0.8.

Question 12

VO2

Answer 12

Oxygen consumption at rest

This is 250 ml/min

Question 13

Henry’s law, explaining O2 content in blood

Answer 13

The amount of dissolved gas is proportional to its partial pressure in the gas phase.

Since O2 is poorly soluble in blood, only 0.003 ml/ mm Hg/ dL is dissolved in blood plasma

Question 14

Haemoglobin states

Answer 14

Taut state (T)- O2 is unable to bind as units are tight.

Relaxed state (R)- O2 is able to unbind as polypeptide chains are loosened.

H+, 2,3- DPG and CO2 stabilise the T state, which promotes the release of O2.

Question 15

CaO2

Answer 15

Oxygen content in arteries- this is the relationship between the amount of O2 dissolved in the plasma and carried by Hb.

CaO2= [ PaO2 x 0.003 ml/dL] + [ 1.34 x Hg(g/ dL) x SaO2].

SaO2- saturation of O2 in Hb. Assuming it is 100%
1.34= 1g Hb carries 1.34 mL of O2
PaO2= 95
Hg= 15, there are 15 g of Hb per dL of blood.

Therefore:
CaO2 (ml/ dL)= 23
CaO2 (ml/ L)= 230, over 1000mL circulating in blood per min

Question 16

Delivery of oxygen

Answer 16

DO2= CaO2 x CO

CaO2= Content of O2 in the blood
CO= cardiac output

On average this is roughly 1000mL per min.

Question 17

Allosteric effectors in Hb

Answer 17

Ligands that bind on Hb and initiates a conformational change in Hb configuration.

Homotropic- Same ligand binds, O2. This triggers co-operative binding, triggering other units to bind to O2.

Heterotropic- Different ligands bind; H+, CO2, 2,3- DPG.
The binding of these ligands causes O2 to unbind and promotes the T state of Hb.

Question 18

Oxygen dissociation curve

Answer 18

This curve shows the relationship between the PaO2 and the SO2 in Hb.

When the curve plateaus, PaO2 and SO2 are at its highest. Hb is in R state and so all units are occupied by O2. O2 is carried in lungs.

At the steepest portion, around 40 PaO2, Hb is unloading O2. The T state is triggered so O2 is released in tissue.

Question 19

Temperature effect on SO2.

Answer 19

Higher temperature causes O2 dissociation curve to shift to the right, has a non-allosteric effect on Hb.

Higher temperature stabilises T state.

Question 20

P50

Answer 20

PaO2 at 50%- the p(O2) in the arteries that allow half of Hb to be saturated with O2.

The higher P50 is, the lower Hb has affinity for O2.
In HbF and myoglobin, P50 is lower than in HbA, in the same conditions.

Higher H+, CO2, 2,3-DPG and temperature increase P50.

Question 21

Fetal Hb, HbF

Answer 21

HbF is unable to bind to 2,3- DPG. This makes the T state less stabilise and R state favoured, allowing more O2 to bind.

HbF has a left shift in the O2 dissociation curve: Hb has a greater affinity to O2, P50 is lower.

This allows the fetus to obtain adequate amounts of O2 from mother’s blood, via placenta, which already has depleted amounts of O2.

Question 22

CO and Hb.

Answer 22

CO has an affinity to Hb over 200x stronger than O2.

Co binds to Hb to form carboxyhaemoglobin.

This prevents Hb from binding to O2 and also unloading as R state is always favoured. Despite high PaO2, CaO2 will be low.

Symptoms of CO poisoning:
Nausea/ vomitting
Headches
Dizziness
Confusion
Lead to death/ coma

Question 23

Met-Hg

Answer 23

Methemoglobin- Hb where Fe2+ in haem has been oxidised to Fe3+.

The binding of O2 to Met-Hg causes co-operartivity and increases O2 affinity to other units in ferrous states, prevents unloading of O2.

In the O2 dissociation curve, there is a LEFT shift.

Met-Hg makes blood a dark/blueish colour.

Question 24

Cyanosis

Answer 24

Blue-ish skin discolouration due to hypoxemia.

Occurs when 5.0 g/dL or more of deoxyhemoglobin is present or when O2 saturation is <80 %- Hb is not being saturated with O2.

Question 25

Transport of CO2 in the blood

Answer 25

90%- Bicarbonate. Made through carbonic anhydrase reaction.

5%- Dissolved in plasma

5%- Bound to Hb to form carbaminohaemoglobin.

When H+ is high, due to increase CO2, this causes release of O2. Deoxyhaemoglobin is a better proton acceptor than O2.

Question 26

PvCO2 and PACO2

Answer 26

PvCO2= p(CO2) in the veins. 45 mm Hg on average.

PACO2= p(CO2) in alveoli. 40 mm Hg on average

Question 27

Respiratory acidosis

Answer 27

Occurs when CO2 levels are too high in the arteries.

PaCO2> 40 mm Hg, cells with pH< 7.35= respiratory acidosis