Marrow
The spaces inside bones hold marrow. Red marrow makes the blood cells, more than two million red cells every second, along with the white cells and platelets. At birth all marrow is red. Through childhood the marrow in the shafts of the long bones turns into yellow marrow, which is mostly fat.
Red bone marrow, magnified: fat cells among the blood-forming cells, Gray's Anatomy, 1918, figure 72Wikimedia Commons, Henry Vandyke Carter, Public domain (Gray72.png)
In an adult, red marrow remains in the skull, the vertebrae, the ribs, the sternum and the hip bones, and in the upper ends of the femur and humerus. To test it, doctors draw a sample with a needle, most often from the back of the hip bone.
After heavy blood loss, yellow marrow can turn red again and make blood.
Sources
- Arthur Guyton and John Hall, Textbook of Medical Physiology, 13th ed. (2016), ch. 33.
- Susan Standring (ed.), Gray's Anatomy, 42nd ed. (2020), chapter on bone and cartilage.
Prev: Cells that build and remove boneNext: Cranium and face