Iii

T lymphocyte B lymphocyte

Agranular leukocytes

Macrophage m

T lymphocyte B lymphocyte

Agranular leukocytes

Macrophage

Plasma cell

Figure

(a) Origin and development of blood cells from a hemocytoblast (stem cell) in bone marrow. (b) Light micrograph of a hemocytoblast (arrow) in red bone marrow (500x).

infection. Hospitalization for blood transfusions may be necessary if the person experiences painful sickling "crises" of blocked circulation.

A bone marrow transplant can completely cure sickle cell disease, but has a 15% risk of causing death. A new treatment is an old drug, used to treat cancer, called hydroxyurea. It activates dormant genes that produce a slightly different form of hemoglobin in the fetus. Because of the presence of the functional fetal hemoglobin, the sickle hemoglobin cannot crystallize as quickly as it otherwise would. Sickling becomes delayed, which enables red blood cells carrying sickled hemoglobin to reach the lungs faster—where fresh oxygen restores the cells' normal shapes.

Top view

7.5 micrometers

2.0 micrometers

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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