Final answer:
Polycythemia is the term used to describe an increase in the numbers of circulating erythrocytes. It can be caused by factors such as dehydration or living at high altitudes, and it can also be associated with a bone marrow disease called polycythemia vera.
Step-by-step explanation:
An increase in the numbers of circulating erythrocytes is termed polycythemia. Polycythemia is the condition characterized by an elevated red blood cell count. It can be caused by factors such as dehydration or living at high altitudes, and it can also be associated with a bone marrow disease called polycythemia vera. The increased number of erythrocytes in polycythemia can lead to increased blood viscosity, higher blood pressure, and difficulty in blood circulation.