gas exchange and breathing

Question 1

Dalton’s law

Answer 1

law of partial pressure

pressure of gas mixture = sum of pressures of gases in the mixture

Question 2

fick’s law

Answer 2

law of diffusion
molecules defuse down conc gradient, proportional to the conc gradient, SA, and diffusion capacity (numerator)
inversely proportional to thickness of exchange surface (denominator)
Vgas = [AD(P1-P2)]/T

Question 3

henry’s law

Answer 3

law of solubility

conc of gas that dissolves in fluid is proportional to pp gas and solubity of gas

Question 4

Boyle’s law

Answer 4

law of pressure

vol of gas inversely proportional to the pressure at constant temp

Question 5

Charles’ law

Answer 5

volume gas proportional to temperature of the gas

Question 6

why do you need to know composition of air people have been breathing

Answer 6

might explain clinical symptoms

Question 7

different compositions of air

Answer 7

oxygen therapy >21% O2
smoking - make O2 and CO2
high altitude - same proportion of O2 but a lower volume, because of low biometric pressure

Question 8

what happens to air as it goes down the respiratory tube

Answer 8

it is warmed
humidified
slowed and mixed

Question 9

air in the conducting pathways

Answer 9

100% saturation with H2O - know because you breathe out saturated air
less oxygen because of air mixing

Question 10

air in the respiratory airways

Answer 10

supersaturated - fascilitates GE
greater mixing of air so more dilution - gas particles move by diffusion, alveoli don’t change size
high CO2 conc so moves down gradient until it reaches airflow

Question 11

problem with oxygen solubility

Answer 11

CdO2 = 16ml/min but the vol of O2 consumption = 250ml/min

so cant rely on oxygen solubility alone

Question 12

describe haemoglobin

Answer 12

different genes = different globin monomers - all have 2a and then either 2 B, d, gamma
has Fe2+ at centre of tetrapyrrole porpyrin connected to globin covalently joined at histamine residue
90% = HbA
2% = HbA2
HbF - foetal
proportions change through development

Question 13

describe O2 transport

Answer 13

Hb low affinity to O2
coincidently bump into each other and bind
conformational change
higher affinity to other oxygen - exponential increase up to 300x, however there are fewer binding sites left
this is cooperative binding
also generate binding site for 2,3-DGB - push Hb into a more tense state - forcing oxygen out - allosteric action

Question 14

relationship between affinity and ‘tense’

Answer 14

lower affinity = more tense state

Question 15

describe methaemoglobin

Answer 15

.5-1% of Hb
Fe3+ - doesn’t bind to O2
involved in redox reaction in terms of ETC and managing electron donors and receivers, in equilibrium - constant flux from Hb
use methyl blue to increase Hb if methaemoglobin is too high

Question 16

why can methaemoglobin change our colour

Answer 16

Hb is a pigment

Question 17

why would linear oxygen dissociation curve be bad

Answer 17

too big range in lung and too small in tissue
in pul circulation - pp varies so have large range of binding
in systemic circulation - only small range that you could get O2

Question 18

describe oxygen dissociation curve

Answer 18

curve looks different at different parts of the body
steepness gives greater scope for removing oxygen from the blood
even if low PP in lungs - still get high percentage of saturation

Question 19

what causes a rightward shift in the oxygen dissociation curves

Answer 19

increase in temp from exothermic metabolic reactions
acidosis - from accumulation of protons and high CO2
hypercapnia - increased CO2
increased 2,3-DPG

Question 20

what causes a leftward shift in the oxygen dissociation curve

Answer 20

low temp
alkalosis
hypocapnia
low 2,3- DPG

Question 21

effect of shifts on O dissociation curves

Answer 21

L - more O2 bound at given pO2

R less O2 bound at pO2

Question 22

what causes an upward shift in O dissociation curve

Answer 22

polycythaemia - increased O carrying capability
tumour that increases erythropoiesis
greater conc of Hb in blood

Question 23

what causes a downward shift in O dissociation curve

Answer 23

anaemia - impaired O carrying capacity - lost 1/4 blood

saturation 100% but not enough vol

Question 24

what causes a downward and L shift

Answer 24

CO2 binding (carboxyhaemoglobin) - takes binding sites
reduces capacity
however increases affinity - less willing to get rid of O2

Question 25

foetal Hb

Answer 25

greater affinity than adult Hb

to extract blood from mother in placenta

Question 26

myoglobin

Answer 26

steeper than even foetal
provide O2 for early stage of exercise
high energy for a short time
higher affinity to get O2 for early stage exercise

Question 27

describe O transport

Answer 27

diffuse into plasma until pp = alveolar pp
o enter RBC and bind to Hb
blood returning to lungs - large drop in pO but only small drop in Hb conc

Question 28

why does blood arriving at the tissues have less O than in the lungs

Answer 28

lung tissue has brinchial circulation and a little bid drains into pulmonary circulation = haemodilution

Question 29

how do you calculate flux

Answer 29

net change in arterial oxygen/CO2 content

multiple by 50 - because CO 5L per minute

Question 30

describe co2 transport

Answer 30

co2 move into RBC react h2o in RBC with carbonic anhydrase enzyme - H2CO3 dissociate - bicarbonate moves out and cl- enters
or binds to amine end of Hb chain
protons mopped up by binding to -ve aa in Hb eg histidine
or co2 in blood react with h2o = bicarbonate and H+
change in dissolved vol of co2 is significant - no sigmoidal shape

Question 31

the co2 dissociation curve

Answer 31

means the Hbco2 is more in deox blood
Haldane effect
when Hb saturated with o2 - Hb not bind to co2

Question 32

what is transit time

Answer 32

time it takes for o2 to do GE - ie equilibrate in plasma and alveoli
CO2 more soluble so even faster than o2 (.75s)
during exercise blood goes faster so transit time = .25s

Question 33

describe ventilation perfusion matching

Answer 33

lung tissue and circulation are under the effect of gravity - gravity squashes the pleural space at the bottom and expands it at the top
at top - higher transmural pressure because pulled down - so less scope for them to be stretched more - take more pressure to inflate more
at bottom alveoli compliant and so airway ventilate more
also at top lower jintravascular pressure - less recruitment, more resistance so lower flow rate - more perfusion at the bottom
greater impact of perfusion in the zones than ventilation - because blood flow is denser
divide one by other = ventilation perfusion ratio
at top - wasted ventilation - because v little perfusion
at bottom wasted perfusion