Final answer:
Polycythemia results in increased blood viscosity, decreased blood flow, and increased blood resistance due to a higher red blood cell count. This condition can be caused by high altitude adaptation, dehydration, or diseases such as polycythemia vera, which significantly affect blood circulation.
Step-by-step explanation:
Polycythemia is a condition characterized by an increased number of red blood cells (RBCs) in the bloodstream, leading to an elevated hematocrit. The possible effects of an increased red blood cell count are increased blood viscosity, decreased blood flow, and increased blood resistance. High altitude living or conditions such as dehydration can instigate a transient rise in RBC count. However, polycythemia vera, a bone marrow disease, results in overproduction of immature erythrocytes, significantly compromising blood circulation and increasing the effort required by the heart to pump blood. Liver conditions affecting plasma protein levels can also alter blood viscosity and flow.
The viscosity of blood is crucial for maintaining proper blood flow and resistance. When viscosity increases due to elevated RBC level, the blood becomes thicker, akin to moving from sipping milk to a milkshake through the same straw. This increased viscosity hampers the ease with which blood can flow, thereby escalating the resistance within blood vessels and reducing the rate of blood flow. Additionally, erythropoietin (EPO), a hormone that stimulates RBC production, can also have a vasoconstrictive effect, further increasing resistance and amplifying the effects of polycythemia on blood flow.