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Oxygen Transport in Blood - Coggle Diagram
Oxygen Transport in Blood
Discuss the significance of cyanosis
D: abnormal bluish discolouration of skin & mucous membranes
due to high levels of deoxygenated Hb
classification
PERIPHERAL
decreased blood flow
increased oxygen extraction
extremities are blue
CENTRAL
low Hb saturation/abnormal Hb
lips
mucous membranes
tongue are
blue
Explain the carriage of oxygen in simple physical solution in blood
Dalton's Law
D:
total pressure
exerted by mixture of inert gas
=
sum of partial pressures
of
individual gases
in a volume of air
total pressure of mixture of gases =
760mmHg
pressure of...
nitrogen
(77%)
77/100
x760
=
585mmHg
oxygen
(21%)
21/100
x760
=
160mmHg
water
(1%) +
other
(1%)
2/100
x760
=
15mmHg
1Atm = 760 mmHg / 101.3 kPa
PARTIAL PRESSURE of a GAS in SOLUTION
D: partial pressure gas would need in gaseous phase to equilibrate with that solution
concentration of gas
in solution is
NOT THE SAME
as its
partial pressure
solubility of gas affects its concentration
Henry's Law
D: the no. of molecules dissolving in liquid directly proportional to the partial pressure of the gas
factors dictating PaO2
alveolar ventilation
matching ventilation to perfusion
concentration of O2 in
inspired air (FiO2)
journey of oxygen & partial pressure
inspired air - 159 mmHg
alveolar air - 104 mmHg - 13.8kPa
oxygenated blood - 95 mmHg - 12.7kPa
tissue fluid (in respiring tissue) - 40 mmHg - 5.4kPa
deoxygenated blood - 40 mmHg
Explain the carriage of oxygen as oxyhaemoglobin in the blood
adult Hb
4 peptide chains
(2 alpha & 2 beta)
each chain
haem group
each containing iron atom
(where O2 binds)
fetal Hb
4 peptide chain
(2 alpha & 2
gamma
)
means that fetal Hb can bind to
oxygen
MORE TIGHTLY
than adult Hb
so
HIGH AFFINITY Hb
OXYGEN SATURATION (SO2)
D: amount of O2 bound to Hb relative to maximal amount of O2 that can bind to Hb
Hb + O2 <-----> HbO2
(oxyhaemoglobin)
reversible reaction
at lungs = Hb + O2 ----> HbO2
at tissues = HbO2 ----> Hb + O2
1g Hb combines with 1.34 mL O2
therefore
150g/L of Hb in blood
so
200mL/L O2 bound to Hb
equation to calculate SO2
volume of O2 bound to Hb (mL/L)
oxygen capacity (mL/L)
oxygen capacity =
amount of O2 bound to Hb
AND
amount of O2 dissolved in plasma
X 100
SaO2
O2 saturation in arterial blood
measured using probe (pulse oximeter) applied to finger/earlobe
should be
>98%
total oxygen content in blood = 204 mL/L
3 mL/L (plasma) + 201 mL/L (Hb)
Describe the oxygen dissociation curve for arterial blood, venous blood, fetal blood and anaemic blood
ODC
illustrates relationship between PO2 in blood & no. of O2 molecules bound to Hb
description of graph
Plateau
(>60mmHg)
increase in PO2 over wide range 60-100
minimal effect on Hb saturation (90-100%)
Steep increase
(<60mmHg)
large amount O2 binds with Hb
even though only small increase in PO2
facilitates release&diffusion of O2 into tissues
S-shaped
Hb has specific affinity for O2
as PO2 increases - Hb saturation increases
clinical significance
NORMAL
PaO2 = >80
SaO2 = >95
SERIOUS HYPOXEMIA
PaO2 = <60
SaO2 = <90
VERY SERIOUS HYPOXEMIA
PaO2 = <40
SaO2 = <75
P50
D: the point on curve where 50% of Hb saturated with O2
in normal healthy adult = 27mmHg
when ODC shifts to
RIGHT
increases O2 dissociation
P50 INCREASES
why?
increased CO2
- increases H+ ions & decreases pH
aids release of O2 from Hb - Bohr effect
increased body temp
- allows more O2 released into tissue
increased 2,3-DPG
(formed in RBC during glycolysis)
hypoxia, decreased Hb & increased pH = increases 2,3-DPG
when ODC shifts to
LEFT
O2 dissociation inhibited
P50 DECREASES
why?
exhaled CO2 (decreased)
= increases pH
decreased body temp
- higher Hb affinity (O2 not lost from Hb)
means in cold temps why extremities blue
O2 not reaching peripheries
decreased 2,3-DPG
FETAL Hb
give LEFT SHIFT
P50 lower
higher affinity for O2 than adult Hb
(holds on to O2 tighter)
due to gamma subunits
benefits
can extract more O2 from mother
fetal blood less O2 because shares with mother
ANAEMIC Hb
anaemia compared to normal
1.@ venous
normal = 150mL/L
anaemic = 50mL/L
2.@ arterial
normal =200mL/L
anaemic = 100mL/L
differences between V and A are the SAME
both 50mL/L difference
50mL/L of oxygen used by tissues in both
at V and A - anaemic MUCH LOWER
about half the value of normal
Hb saturation
SAME for both normal and anaemic
why?
saturation given as a percentage
anaemic
despite less Hb
as long as Hb normal
then 98% Hb should still have O2 bound
Discuss the causes of hypoxia
HYPOXIC hypoxia
low O2 uptake in lungs
causes
high altitude
lung failure
ANAEMIC hypoxia
low Hb
causes
iron deficiency
CO poisoning
ISCHAEMIC/STAGNANT hypoxia
low circulation
causes
shock
heart failure
embolism
HISTOTOXIC hypoxia
causes
cyanide poisoning
(inhibits mitochondria)
low tissue O2 utilisation
Explain the Fick principle which relates the oxygen extraction from blood and blood flow to oxygen consumption
equation used:
oxygen consumption (mL/min) =
arterio-venous O2 content difference
x
cardiac output
cardiac output
D: volume of blood pumped out by heart each minute
5L/min
total oxygen to tissues per min
200L x 5 = 1000mL/min
CaO2 = arterial O2 content
CvO2 = venous O2 content
oxygen consumption
=
(200-150) x 5 = 250mL/min