respiratory 23 Flashcards
what are the 2 ways in which oxygen is transported in the blood?
-bound to haemoglobin( major way)
-dissolves in solution( plasma)
haemoglobin structure
Hemoglobin: polypeptide, alpha & beta chains. 4 binding sites within the hemoglobin molecule: haem moiety( Iron ions).
To each haem moiety 1 molecule of O2 can bind. .
Allosteric effect
The speed with which O2 molecules are loaded onto haemoglobin: 4th>3th>2nd>1st
Allosteric effect: when the 1st molecule of O2 binds it turns the haemoglobin molecule to expose the next haem moiety. Same happens with the next O2 molecules. The more molecules are taken up the faster it is. Co-operative binding property.
what is the difference in % of saturation of haemoglobin between systemic veins and systemic arteries.
25%
why is haemoglobin saturation decreased at lower PO2?
Haemoglobin loses affinity for O2 at lower PO2.
It releases O2 at lower PO2 in the tissues.
This change in affinity is key for delivering/releasing O2 to the tissues.
At tissues – more CO2, lower pH, so O2 is released
why is haemoglobin saturation higher in the lungs?
increased affinity for O2. encourages O2 uptake in the lung
At lungs – less CO2, higher pH, so O2 is taken up
what is the saturation of haemoglobin if the person has lost half of their blood?
still 100%. Haemoglobin molecule is not affected
what factors reduce the affinity of haemoglobin for oxygen?
increased CO2, [H+], temperature, DPG
What factors increase the affinity of haemoglobin for oxygen?
Decreased CO2, [H+], temperature, DPG
Increased CO
Bohr shift
the shift to the right of the oxygen equilibrium curve of both adult and fetal blood in response to an increase in PCO2 or a decrease in pH, or both.
For a given PO2 more oxygen is released
what is the importance of fetal haemoglobin having a higher affinity for O2 than adult haemoglobin?
otherwise would not be able to draw blood from mother’s circulation
Why does haemoglobin loose its affinity for O2 at lower PO2?
-decreased in pH
In an acidic environment, Hb has less affinity for O2.
At tissues- more CO2, lower pH, so O2 is released
At lungs- less CO2, higher pH, so O2 is taken up
The Haldane effect
physicochemical phenomenon which describes the increased capacity of blood to carry CO2 under conditions of decreased haemoglobin oxygen saturation
Greater affinity for CO2 in the tissues
Myoglobin function
stores O2 around skeletal muscle where it can be later released in conditions of low CO2
Has very high affinity for O2
why is the oxygen saturation curve sigmoidal?
due to cooperative binding
what is hemoglobin called when its a 100% saturated?
Oxyhaemoglobin
what is the rate-limiting step of the formation of HCO3-?
formation of H2CO3 from H2O and CO2
what is the main way of carrying CO2 in the body?
in the form of bicarbonate that was rapidly formed in RBC and diffused into the plasma 60%
+ 20% of rapidly formed bicarbonate stayed in RBC
how much of CO2 is carried in plasma?
70%
how much CO2 is carried in RBC?
30%
what are the ways in which CO2 can be transported in blood?
rwhat is the enzyme that catalyzes the formation of H2CO3 in RBC?
carbonic anhydrase
what dictates which way this process goes?
Law of Mass action
Law of Mass action
law of mass action, law stating that the rate of any chemical reaction is proportional to the product of the masses of the reacting substances
describe the chemical basis of CO2 release of O2 uptake in the alveoli
-CO2 dissociates from the carbamino compound-> diffuses out of the RBC into plasma and into alveoli
-Haemoglobin gains affinity for O2. O2 diffuses from the alveoli into plasma and into RBC-> binds with haemoglobin
-HCO3- diffuses back into RBC from plasma. Carbonic anhydride and H+ combine to form carbonic acid(H2CO3)
-Carbonic acid(H2CO3) dissociates back into CO2 and H2O.
H2O and CO2 diffuse out of RBC into plasma. CO2 diffuses out into alvoli.
-Chloride shift reversed
where are peripheral chemoreceptors located
near major blood vessels
In the Carotid body( located at the bifurcation of the common carotid artery in the neck. Between where the internal and external carotid arteries originate. (Close to baroreceptors in the wall of
Carotid sinus. ) Connected by the sinus nerve, which joins the glossopharyngeal
nerve( 9th cranial nerve) then to the medulla oblongata(brainstem)
where are central chemoreceptors located?
within medulla oblongata
what stimulates peripheral chemoreceptors?
what is the role of peripheral chemoreceptors?
Peripheral chemoreceptors monitor changes in arterial blood O2, and within seconds after the onset of hypoxia they trigger cardiorespiratory changes (i.e., increase in breathing and blood pressure), which are important for maintaining O2 homeostasis
what stimulates central chemoreceptors?
H+ ions in CSF predominantly stimulate Central chemoreceptors.
These come from the dissociation of H2CO3 into HCO3- and H+
Neural cells in the medulla become activated and stimulate breathing
Brain is intrinsically sensitive to H+ ions
DOES NOT RESPOND TO LOW O2(hypoxia) ONLY TO HIGH H+ from evelated CO2
why are central chemoreceptors slow to respond?
H+ cannot exit the blood
Vessels as they are charged, but CO2 can
Takes time for this process to occur
+ limted carbonic anhydrase in CSF
~30 sec
what is the ventilatory response to hypoxia?
As PaO2 decreases min. ventilation increases. After persistent hypoxia ventilation slows due to central depressant effect within the brainstem(important respiratory neurons in the brainstem are depressed by prolonged hypoxia)-> apnoea-> individual will gasp as the last attempt to auto-ressucitate
PERIPHERAL CHEMORECEPTORS ONLY!
what is referred to as the dog leg relationship?
ventilatory response to hypercapnia( high CO2)
Very sensitive to CO2
As PCO2 increases the ventilation rate increases sharply
central chemoreceptors ~80%
peripheral chemoreceptors ~20%
what is Ondine’s curse?
No central chemoreceptors and you can die in your sleep. Related to a missing transcription factor.
