A small pool of stem cells replenishes the human body with about 200 billion new blood cells daily. But the elaborate circuitry that determines if a cell will develop into a T cell, red blood cell, or one of the nine or more other blood cell types remains largely unknown. A research team led by scientists from the Broad Institute and Brigham and Women’s Hospital has taken a systematic approach to help decipher this circuitry, compiling a comprehensive catalog of the factors that determine a blood cell’s fate. Their work appears in the January 21 issue of Cell.
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
The impedance of extremeeties such as fingers, arms and legs changes with the blood flow in and out, so this provides another method for plethysmography.
The arterial pulse wave has a very low amplitude and is superimposed on the venous blood volume changes. Pulse wave measurements are possible in many locations including the head (this measurement is called rheoencephalography). Pulse waves can also be measured in the fingers and toes with photoplethysmography.