Final answer:
Abnormally low levels of erythrocytes are referred to as anemia, specifically hemorrhagic anemia in the context of the given options. The correct answer is 'c. hemorrhagic anemia'.
Step-by-step explanation:
Abnormally low levels of erythrocytes, also known as red blood cells (RBCs), are referred to as anemia. There are various types of anemia, each with different causes and characteristics. The options provided in the question refer to specific forms of anemia or conditions related to red blood cells:
- Sickle-cell anemia: A genetic disorder characterized by the production of an abnormal type of hemoglobin called hemoglobin S, causing erythrocytes to become sickle-shaped, particularly under low oxygen concentrations, which can lead to various health issues.
- Polycythemia: The opposite of anemia, this is a condition where there is an overproduction of red blood cells, leading to an increased blood viscosity and difficulty in circulation.
- Hemorrhagic anemia: A form of anemia caused by excessive blood loss, leading to a decrease in the number of red blood cells.
- Thalassemia: A genetic blood disorder causing improper formation and maturation of hemoglobin, leading to inefficient oxygen transport and destruction of red blood cells.