Oxygen in the blood Flashcards
solubility factor for oxygen? is oxygen soluble?
Oxygen is not very soluble in water
– Solubility factor for O2 = 0.01 mmol.l-1.kPa-1
how can u calculate the amount of Oxygen dissolved in plasma?
O2 dissolved = solubility x pO2
At pO2 of 13.3 kPa only 0.13 mmol.l-1 is dissolved
so
0.01 mmol.l-1.kPa-1
how much is CO?
Maximum CO?
5l/min
Max CO= 25l/min
CO cannot meet the needs of the body by just dissolved oxygen alone.
so we need some kind of transport system to transport that oxygen
ok
Oxygen binding pigments?
which one has the highest affinity for oxygen?
• Haemoglobin – present in blood
– Tetramer – binds 4 oxygen molecules
• Myoglobin – present in muscle cells
– Monomer – binds 1 oxygen molecule
myoglobin!!
structure of hemoglobin!
Draw an oxygen-haemoglobin dissociation curve, label the axes correctly &
indicate the normal values of
(i) alveolar pO2
(ii) capillary pO2 in a typical tissue.
alveolar pO2= 13.3
Moods of Haemoglobin
When PO2 is low Hb is in the tense or relaxed state?
When pPO2 is low Hb is tense
which means its hard for the first molecule of hemaglobin to bind!
Hb saturated above ______
unsaturated below _______
Half saturated at ______
Hb saturated above 9-10kPa
Virtually unsaturated below 1kPa
Half saturated at 3.5 – 4 kPa
what is normal hemoglobin concentrations
how can u calculate the oxygen content of arterial blood
If Hb concentration is normal ≈ 2.2 mmol.l-1
Each Hb molecule binds 4 O2 molecules
Therefore oxygen content = 8.8 mmol.l-
if a patient is anaemic,
what will happen to pO2 ?
what about oxygen content ?
pO2 will be normal, but oxygen content will be lower
huh why? ask alaa ask
what is the pO2 in the tissues?
typically 5 kPa
cuz its given up all its oxygen!
The lower the tissue pO2, the more O2 will dissociate from Hb
ok?
How low can tissue pO2 get?
- Tissue pO2 must be high enough to drive diffusion of O2 to cells
- It cannot fall below 3 kPa in most tissues
what is capillary density?
which muscles have it high?
defined as the number of capillaries per unit cross-sectional area of muscle.
metabolically active tissues!
If u have a high capillary density (ex: in heart muscle) you can get the Po2 in that tissue to be low… why?
bc u dont need the oxygen to diffuse over a LARGE ditance!
Draw the effects on the haemoglobin oxygen dissociation curve of
(i) a fall in pH (ii) a rise in temperature. Iii) an increase in 2-3 DPG
↓pH promotes _____state of Hb
shift graph to the RIGHT causing higher chance for o2 to dissociate
T state
Explain the difference between oxygen saturations (‘Sats’) partial pressure of oxygen PaO2 and oxygen content of blood
Over the whole body about _____% of oxygen from arterial blood is given up
27
when does 2,3-Bisphosphoglycerate increase?
2,3-BPG levels increase with anaemia or at altitude
describe CO poisoning and graph
Hypoxemia vs hypoxia
- *• Hypoxemia** - low pO2 in arterial blood
- *• Hypoxia –** low oxygen levels in body or tissues
• If pO2 levels are low not all the Hb will be saturated
if Hb levels r low, not enough O2 will be present in the blood
what conditions can cause hypoxia?
shock> peripheral vasoconstriction
places where tissues r using oxygen faster than it is delivered!
- peripheral arterial disease
- raynaud’s disease
Define cyanosis and explain its significance
Bluish colouration due to unsaturated haemoglobin
Can be peripheral (hands or feet) due to poor local circulation
Raynaud’s phenomenon
where the blood supply to certain parts of the body, usually the fingers and toes, becomes temporarily reduced when exposed to cold temperatures
what type of cyanosis is this?
central (more serious)
(mouth, tongue, lips, mucous membranes) due to poorly saturated blood in systemic circulation
(maybe prob with lungs, cardiac,….)
which congenital disease can cause cyanosis
how does the pulse oximeter work?
O2 Saturation is estimated using a pulse oximeter.
Detects pulsatile arterial blood, and ignores the venous blood
saturated Hb is gunna absorbs less of the red spectrum
doesnt say how much is Hb concentration!
Arterial Blood Gas Analysis
This requires an arterial blood sample (as opposed to a venous blood sample obtained by venepuncture).
This is obtained by arterial puncture usually from the radial artery.
Hence it is an invasive technique.
Would pulse oximetery be useful in assessing a patient w/ suspected CO poisoing?
NO
they will look very rosy cheeked, cuz Carboxyhemoglobin is BRIGHT RED
