Download Gas transport between lungs and tissues

Gas exchange
Quiz
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Surfactant is decreased in:
1. Term babies
2. Glucocorticoid therapy
3. Ventori mask short term oxygen
therapy.
• 4. Smokers
• 5. Abdominal surgery.
• 4
• Inspired air will be saturated with
water vapor in the lungs decreasing
PO2 in alveoli.
Insp. air
EXP. air
Po2
116
PCo2
32
PH2O
47
PN2
565
PO2
158
PCo2
0.3
PO2
100
PH2O
5.7
PCo2
40
PN2
596
PH2O
47
PN2
573
Gas transport between lungs
and tissues
PO2
PCO2
Inspired
PO2 158
PCO2 0.3
Vein
Alveolar
air
40
100
46
40
Expired
PO2 116
PCO2 32
Arterial
air
95
40
PH2o
47
47
47
PN2
573
573
573
Tissues
Co2
O2
O2 diffuses out of alveolar gas into
the blood stream and Co2 diffuses
into the alveoli from blood.
Diffusion across alveolo capillary
membrane made up of pulm.
epithelium, capillary endthelium and
their basement membrane.
Diffusion capacity of the lung
for a given gas is directly
proportionate to the alveolocapillary membrane area and
inversely proportion to its
thickness.
Gas transport
Prof. Omer Abdel Aziz
O2 transport
1.
2.
3.
4.
5.
O2 delivery to a tissue depends
on:
O2 entering lungs.
Adequacy of gas exchange.
Blood flow to tissues.
Capacity of blood to carry O2.
Factors affecting O2 diffusion
are: thickness, solubility, Po2.
Carriage of O2
1. Dissolved in plasma (2%):
amount dissolved is
proportionate to O2 tension at
Po2 100 0.3ml dissolved / 100ml
blood while at Po2 40 only
0.12ml / 100ml (venous).
Dissolved O2 reaches the
tissue, imp for cornea and
cartilages.
2. Combined with Hb in red cells 98%
Hb has 4 sub units attached to 4 haem
moieties each is formed from porphyrin
and ferrous iron,each of the 4 ferous
ions can bind with one O2 molecule.
Hb4 + O2
↔ Hb4 O2
Hb4O2 + O2
↔ Hb4O4
Hb4O4 + O2
↔ Hb4O6
Hb4O6 + O2
↔ Hb4O8
Each combination enhance the
next.
The amount of O2 combined with Hb is
tension dependent but the relation is
a sigmoid one and called O2
dissociation curve.
R. (relaxed state ) chain away from
each other
.
T ( tense state) globin chains close
to each other .
• With Hb of 15 g/dL , arterial
blood contains 19.8 ml/dL, in
venous blood (75% sat.) 15.2
ml/dL, so 4.6 ml O2 from each
deciliter
( 250 ml O2 delivered
to tissues per min).
• Amount of O2 depend on Hb
level.
Oxygen dissociation
curve
Prof. Omer Abdel Aziz
• Oxygen dissociation curve is
the relation of the % saturation
of Hb to the level of PO2 in mm
Hg.
• At PO2 100 sat. is 97.5%, at PO2
40 sat. is 75%.
Decreased affinity of Hb:
shift to the right
• Shift of O2 dissociation curve to the
right occur in:
• Arise in temp.
• A fall in pH ( PCo2)(Bohr effect).
• 2.3 diphosphoglycerate in red cells.
• Higher PO2 is required for Hb to bind
O2.
Increased affinity: Shift to
the left:
• 1. Low temp.
• 2. High pH.
• 3. Decreased
2,3,diphosphoglycerate.
• PO2 above 100 will not increase
saturation.
• At PO2 60 Hb is 89% saturated.
• A steep drop of saturation below
PO2 60.
O2 Dissociation curve
100 -
Temp
Saturation of Hb
Percentage O2
PH
Temp
PH
30
2.3.
DPG
-
10 20 30 40 50 60 70 80 90 100
Po2 mm Hg
Po2
%
Dis.
10
13.5
0.03
40
75
0.12
60
89
0.15
100
97.5
0.3
2,3 diphosphoglycerate
(2,3 DPG )
• A large amount in RBCs, formed
from 3- phosphoglyceraldehyde
a product of glycolysis.
• It is an anion which binds with
Hb and releases O2. Half life 6
h.
Factors affecting 2,3
DPG:
• 1. Low pH ( acidosis ) decreases 2,3
DPG.
• 2. Thyroid hormone, growth
hormone, androgen leads to
increased 2,3 DPG concentration.
• 3. Exercise increases 2,3 DPG after
60 min.
• 4. High altitude increases 2,3 DPG
releasing O2.
Cont.
• 5. Hb F ( alpha2 gama2) poor
binding to 2,3 DPG leading to
increased affinity to O2 and more
O2 moves from mother to fetus.
• 6. In blood banks 2,3 DPG
decreases, shifting the curve to
the left, increasing O2 affinity and
less oxygen released ?
• 7. Anemia can increase 2,3 DPG.
Quiz
• In inhabitants of high altitude the oxygen
dissociation curve can shift to the right
due to:
• 1. Increased temperature.
• 2. Increased 2,3 DPG.
• 3. Decreased pH.
• 4. Increased PCO2.
• 5. Increased Hb.
• 2
P50:
• It is the partial press. Of O2 at which Hb is
50 % saturated. It is increased by:
• 1. Thyroid hormones, growth H. &
androgens.
• 2. Exercise.
• 3. High altitude.
• 4. Increased temp.
• 5. Decreased pH.
• The higher the P50, the lower is the Hb
affinity for O2.
Myoglobin
• It is an iron containing pigment
in skeletal muscles.
• Binds one molecule of O2.
• Its curve to the left of Hb so it
takes O2 from Hb.
Quiz
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P50 is increased in:
1. Low temp.
2. Low PCO2
3. High pH.
4. Decreaed 2,3 DPG.
5. Thyrotxicosis.
Gas exchange at the
tissues:
•
By simple diffusion: PaO2 in
capillaries is higher than tissues,
so O2 diffuses to the tissues. PCO2
is higher in tissues, so CO2 diffuses
into capillaries.
Hypoxia:
• Decreased O2 supply to the
tissues produces hypoxia.
Types:
• 1. Hypoxic hypoxia: decreased
PaO2 as in pulmonary and
cardiac diseases, high altitude.
Hypoxia cont.
• 2. Anemic hypoxia: anemia, CO
decrease Hb available to carry O2.
• 3. Stagnant hypoxia: decreased
blood flow as in shock.
• 4. Histotoxic hypoxia: prevention of
oxygen utilisation at tissues level eg
cyanide.
• Oxygen therapy can help in hypoxic
hypoxia & slightly in anemic h.
Quiz
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Hypoxia in shock is :
1. stagnant
2. hypoxic
3. histotoxic
4. anemic
5. neurogenic.
CO2 Transport
From tissues to lungs by plasma & RBCs:
1. Dissolved 10%.
2. Carbonic acid Co2 + H2o ↔ H2Co3 ↔
H+ HCO3, 70%, slow in plasma due to
absence of carbonic anhydrase, more
in RBCs:
• Hco-3 diffuse and Cl- enters (Band3)
Chloride shift in RBC more fluid enters
increasing HCT.
• H+ Buffered by Hb.
3.Combined to protein: Carbamino
protein, carbamino- hemoglobin.
Co2
• Co2 carried by blood
independent on Pco2.
• Oxy Hb shift curve to the right
helps release of Co2 at alveoli
(Haldane
effect)
Co2
In
blood
Hb
Hb0
• Asphyxia: Decreased PaO2,
increased PCO2.
• Hypercapnia: increased PCO2.
• Hypocapnia: decreased PCO2.
Cyanosis
• Definition: it is diffused bluish
coloration of skin and mucus
membranes due to presence of large
amount of reduced Hb (5 g or more).
• Types:
• 1.Central: in heart failure, right to
left shunts; cyanosis is general(
tongue & extremities)
• 2. Peripheral: flow of blood is slowed
in capillaries as in cold, venous
obstruction & heart failure.
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