32 - Transport of O2 and CO2 in the Blood Flashcards
1) Know the different forms of respiratory gases in the blood
• Dissolved gases
o In solution, only dissolved gas molecule generate partial pressure (needed for diffusion).
o Oxygen = .3% of total O2 in blood (not main form of transport)
o When pt breaths 100% O2, then it is important transport mechanism
o Nitrogen = carried only in this form
• Conjugated gases
o O2, CO2, and CO are bound to proteins in blood. O2 and CO bind Hb. CO2 bind Hb and plasma proteins
• Chemically modified gases
o Majority of CO2 is carried in blood as HCO3-
• Adult Hb (HbA):
o 2 α and 2 β chains (each bound to heme group).
o Each heme group contains porphyrin ring with Fe2+.
o Each HbA can bind 4 O2.
• Fetal Hb (HbF):
o 2 α and 2 γ chains.
o Has ↑ affinity than HbA.
o This aids in movement of O2 from mother child.
• Methemoglobin:
o Iron in Fe3+ state and will not bind O2.
o Causes include oxidation by nitrites and sulfonamides or a deficiency in methemoglobin reductase.
• Hemoglobin S (HbS):
o β subunits are abnormal and has ↓ affinity for O2.
o This causes sickle cell disease and could possible occlude small blood vessels.
3) Describe the difference between O2 binding capacity and O2 content
O2 binding capacity:
o Maximum O2 volume that can combine with Hb.
o Determined by multiplying the blood [Hb] with the amount of O2 that can bind per gram of Hb.
1.34 (mL O2/gHb) x 15 (g Hb/dL) = 20.1 mL O2/dL blood
O2 content:
o Actual O2 amount per volume of blood.
o (O2 binding capacity x SaO2) + Dissolved O2 = O2 content
o SaO2 = % Hb saturation with O2
4) Know how O2 delivery to tissue is calculated
• O2 delivery = Cardiac Output x O2 content
5) Know the characteristics of the O2-Hb dissociation curve
• Is the relationship between arterial pressure of O2 and % O2 saturation
• Has sigmoidal curve:
o Flat upper part indicates SaO2 is kept relatively constant with variations in PO2. The steep lower part (b/t 15-40 mm HG) indicates a large amount of O2 can be unloaded with a small drop in PO2.
These above functions show the Hb is a buffer for O2
Hb sets an upper limit of tissue PO2 to 40 mm Hg
Exercise = small ↓ PO2 in tissues = large ↑ in O2 release and ↑ tissue blood flow
P50 indicates…
• P50 is the pressure of oxygen where 50% of Hb is saturated with oxygen. This is used as an indicator of change in affinity for hemoglobin.
o ↑P50 = shift right = weaker Hb-O2 binding = wants to release O2
o ↓P50 = shift left = stronger Hb-O2 binding = wants to hold onto O2
6) Know the factors that affect the O2-Hb dissociation curve and their clinical implications
Right shift
• Right Shifts: (decreased affinity for O2)
o ↑ temperature (Fever)
o ↑ CO2 (CO2 Bohr effect)
o ↑ 2,3-DPG (end product of RBC metabolism; chronic hypoxia, anemia, acclimation to high altitude)
o ↓ pH (acid Bohr effect)
6) Know the factors that affect the O2-Hb dissociation curve and their clinical implications
Left shift
• Left Shifts: (increased affinity for O2)
o ↓ temperature (hypothermia)
o ↓ CO2
o ↓ 2,3-DPG (stored blood)
o ↑ pH (alkalosis)
6) Know the factors that affect the O2-Hb dissociation curve and their clinical implications
2,3 - DPG
o Will reduce uptake at high pressures of O2 but will increase release at lower pressure of O2.
o Net effect is more unloading of O2 to tissues.
6) Know the factors that affect the O2-Hb dissociation curve and their clinical implications
CO poisoning
• Carbon Monoxide binds Hb at the same place O2 does, but 250x better.
• CO poisoning
o In CO poisoning, the pressure of O2 in the arterials stays roughly normal so there is no feedback mechanism to indicate the ↓O2 getting to tissues.
7) Know the forms of CO2 transport in the blood
- 7% is in dissolved form
- 23% is conjugated with Hb
- 70% is chemically modified to HCO3-
8) Describe the Bohr effects and the physiological significance
• Bohr effects:
o Tissues metabolize, producing CO2 and acid (↑CO2 and ↓pH).
o Both of these results shift the oxygen dissociation curve to the right, allowing for and increase in release of O2.
