Lecture 20: Oxygen Carriage in Blood
High Altitude
Oxygen Uptake in the Lungs is Increased About 70X by Hemoglobin in the Red
Cells
•In the lungs oxygen must enter the blood
• A small amount of oxygen dissolves directly in the serum, but 98.5% of the
oxygen is carried by hemoglobin
• All of the hemoglobin is found within the red blood cells (RBCs or erythrocytes)
• The hemoglobin content of the blood is about 15 gm/deciliter (deciliter = 100
mL)
• Red cell count is about 5 million per microliter
Each Hemoglobin Can Bind Four O2 Molecules (100% Saturation)
• Hemoglobin is a protein molecule with 4 protein sub-units (2 alphas and 2 betas)
• Each of the 4 sub-units contains a heme group which gives the protein a
red color
• Each heme has an iron atom in the center which can bind an oxygen
molecule (O2)
• The 4 hemes in a hemoglobin can carry a maximum of 4 oxygen
molecules
• When hemoglobin is saturated with oxygen it has a bright red color; as it loses
oxygen it becomes bluish (cyanosis)
The Normal Blood Hematocrit is Just Below 50%
• Blood consists of cells suspended in serum
• More than 99% of the cells in the blood are red blood cells designed to carry
oxygen
• 25% of all the cells in the body are RBCs
• The volume percentage of cells in the blood is called the hematocrit
• Normal hematocrits are about 40% for women and 45% for men
At Sea Level the Partial Pressure of O2 is High Enough to Give Nearly 100%
Saturation of Hemoglobin
• As the partial pressure of oxygen in the alveoli increases the hemoglobin in the
red cells passing through the lungs rises until the hemoglobin is 100% saturated
with oxygen
• At 100% saturation each hemoglobin carries 4 O2 molecules
•This is equal to 1.33 mL O2 per gram of hemoglobin
• A person with 15 gm Hb/deciliter can carry:
• Max O2 carriage = 1.33 mL O2/gm X 15 gm/deciliter = 20 mL O2/
deciliter
