Respiratory 4 Flashcards
What are the 2 ways oxygen is carried in the blood?
- Dissolved O2 = 2%
- Bound to hemoglobin = 98%
*O2 is poorly soluble in water/plasma
Describe dissolved O2.
-free in solution
-only form that produces partial pressure = drives O2 diffusion
-insufficient for tissue demands
Describe hemoglobin.
-O2 is reversibly bound to hemoglobin inside RBCs
-globular protein
-4 subunits = each contain:
>heme = iron binding porphyrin [Fe2+] (produced by mitochondria)
>polypeptide globin chain = alpha or beta (made by ribosomes)
Describe the type & sequence of amino acids that compose globin that define the diff types of mammalian hemoglobin.
- Adult hemoglobin (HgA) = 2 alpha 2 beta
- Fetal hemoglobin (HgE) = 2 alpha & 2 gamma
-high affinity for O2
-replaced by HgA in first yr of life
Describe the type & sequence of amino acids that compose globin.
-critical to O2 binding
-without globin = O2 irreversibly oxidize ferrous iron [Fe 2+] to ferric iron [Fe 3+]
doesnt unload O2
-amino acids in globin = cradle heme & limit access of O2 to ferrous iron = prevents oxidation & allows uptake & release of O2 in response to local PO2
-enzyme methemoglobin reductase = inside RBCs - keep iron in its reduced state
Describe how a molecule of hemoglobin can reversibly combine with 4 molecules of O2.
- Oxygenated hemoglobin = oxyhemoglobin
- Deoxygenated hemoglobin = deoxyhemoglobin
-for the subunits to bind to O2 - iron in heme must be ferrous Fe2+
Describe methemoglobin.
-abnormal variant of hemoglobin
-heme is in ferric state [Fe3+]
-methemoglobin DOESNT bind O2
>caused by drugs & congenital disease
>EX: actominophen (Tylenol) in cats; deficiency of methmemoglobin reductase
>blood is dark
>hypoxia when methemoglobin = 50%
Describe hemoglobin S.
-abnormal variant of hemoglobin
-sickle cell disease
-alpha subunits are normal - beta is NOT
-hemoglobin S (deoxygenated) = forms sickle shaped rods in RBCs
>deformation = occlusion of sm blood vessels
>O2 affinity decreased
Describe what the amount of O2 carried by the RBCs depends on.
- Hemoglobin content in blood
-decrease in Hb = anemia - Partial pressure of O2 in plasma
-oxyhemoglobin dissociation curve
Describe the binding of O2 to the heme group of Hb.
-4 step process
-oxygen affinity of heme influenced by oxygenation of the others
-when first heme is oxygenated = O2 affinity of second heme increases … etc
-heme-heme interactions = sigmoid shape of oxyhemoglobin dissociation curve
*percent saturation of heme doesnt increase linearly as PO2 increases
Describe what the amount of O2 combined with hemoglobin is determined by.
-PO2
-percent saturation increases as PO2 increases from 0-40mmHg & levels off between 50-100mmhg
>steepest = result of change in affinity of heme groups for O2 as each O2 binds
>”positive cooperativity”
What are the factors that affect the loading & unloading of O2 by the RBCs in the tissues?
DECREASE AFFINITY = unload O2
-increase in CO2 = high metabolism
-increase in H+ ions = high acidity
-increase in temp = high metabolism
What are the factors that affect the loading & unloading of O2 by the RBCs in the lungs?
INCREASE AFFINITY = load O2
-decrease in CO2
-decrease in H+ ions
-decrease in temp
Why does the oxyhemoglobin dissociation curve shift to the right or left?
-due to the affinity of hemoglobin for O2 varying w:
>blood temp
>pH
>CO2 tension
>intracellular conc of organic phosphates
changes in P50
Describe a shift to the right in the oxyhemoglobin dissociation curve.
-increase in P50 = 50% of saturation is met at a high value of PO2
-affinity is decrease = unload O2
When is it advantageous to unload O2 in the tissues?
- Increase in PCO2 & decrease in pH
- Increase in temp
- Increase in 2,3DPG
-byproduct of glycolysis in RBCs = increase during hypoxic conditions
-bind to beta chains & reduce affinity
Describe a shift to the left in the oxyhemoglobin dissociation curve.
-increased affinity
-decrease in P50 = 50% saturation met at low PO2
When is it advantageous to load O2 in the tissues?
- Decrease in PCO2 & increase in pH
- Decrease in temp
- Decrease in 2,3-DPG
- Hemoglobin F
What are the 3 forms CO2 is carried in the blood?
- Dissolved CO2 = free in solution (7%)
- Carbaminohemoglobin = bound to hemoglobin (23%)
- Bicarbonate (HCO3) = chemically modified form (70%)
How can CO2 be transported?
-in combination with hemoglobin & plasma proteins
-reacts w amine radicals of hemoglobin = form carbaminohemoglobin (CO2Hgb)
-reversible
-CO2 released in alveoli where PCO2 is lower than in pulmonary capillaries
-CO2 reacts the same w plasma proteins in tissue capillaries
Describe the hydration reaction.
-dissolved CO2 in plasma reacts w H2O = carbonic acid (H2CO3)
-happens SLOW in plasma & FAST in RBCs
-catalyzed by enzyme ‘carbonic anydrase’
Describe what happens when the carbonic acid is formed.
-dissociates into hydrogen & bicarbonate ions
-most of the H+ ions combine w hemoglobin bc the hemoglobin protein = acid base buffer
-bicarbonate diffuses from the RBCs into the plasma
-Cl- ions diffuse into RBCs = chloride shift
