Multiple Choice
Testosterone is categorized as which of the following types of hormones?
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16. The Endocrine System
Introduction to the Endocrine System
2:50 minutesProblem 26
Textbook Question
A reticulocyte count indicated that 5% of Tyler's red blood cells were reticulocytes. His blood test also indicated he had polycythemia and a hematocrit of 65%. Explain the connection between these three facts.
Verified step by step guidance1
Step 1: Understand the terms involved. A reticulocyte is an immature red blood cell (RBC) recently released from the bone marrow. The reticulocyte count indicates the percentage of these young RBCs in the bloodstream, reflecting bone marrow activity.
Step 2: Recognize that a normal reticulocyte count typically ranges from about 0.5% to 2.5%. A count of 5% suggests an increased production of RBCs by the bone marrow, often in response to a need for more oxygen-carrying cells.
Step 3: Polycythemia is a condition characterized by an abnormally high concentration of red blood cells in the blood. This is consistent with the hematocrit value, which measures the percentage of blood volume occupied by RBCs. A hematocrit of 65% is significantly elevated (normal is roughly 40-50%), confirming polycythemia.
Step 4: Connect the facts: The elevated reticulocyte count indicates that Tyler's bone marrow is producing and releasing more RBCs, which leads to an increased number of circulating RBCs, causing polycythemia and a high hematocrit.
Step 5: Summarize the physiological relationship: Tyler's body is likely responding to a stimulus (such as hypoxia or another cause) by increasing erythropoiesis, resulting in more reticulocytes entering the bloodstream, which raises the total RBC count and hematocrit, manifesting as polycythemia.
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2mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reticulocyte Count
Reticulocytes are immature red blood cells recently released from the bone marrow. The reticulocyte count measures the percentage of these cells in the blood, indicating the rate of red blood cell production. A higher count suggests increased bone marrow activity, often in response to anemia or blood loss.
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Polycythemia
Polycythemia is a condition characterized by an abnormally high concentration of red blood cells in the blood. This increases blood viscosity and hematocrit levels, which can lead to complications like clotting. It can be primary (due to bone marrow disorders) or secondary (due to increased erythropoietin from hypoxia).
Hematocrit
Hematocrit is the percentage of blood volume occupied by red blood cells. A normal range is about 40-50%, so a hematocrit of 65% indicates a high red blood cell concentration, consistent with polycythemia. It reflects the oxygen-carrying capacity and blood viscosity.
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