The "Blood Apple Tree". A simple and straightforward metaphor for teaching blood and bone marrow physiology.

Haematology is a rapidly growing field of medicine. The advent of new molecular biology methods has enhanced our knowledge of blood disorders, but further complicated the study of this important branch of medicine. Although, modern day students tend to have better information technology skills than their predecessors and seem to be very interested in molecular biology methods, the comprehension of some key points in Haematology remains problematic. In our experience, students often experience difficulty understanding how the generation of blood occurs. We present the "Blood Apple Tree", a simple metaphor between the bone marrow and an apple tree, which has proven to be a helpful teaching tool for medical students approaching the basics of Haematology. We all know that blood production occurs within the bone marrow, however just for the moment use your fantasy and imagine that the bone marrow is like an orchard of apple trees. Each apple tree has just three branches. Let's imagine these branches are red, yellow and white (Figure 1). The red branch produces red apples (erythrocytes), the yellow branch produces yellow