Red blood cells, which carry oxygen to body tissues, live for only about 120 days. Replacement cells are produced by cell division in bone marrow.
How many cell divisions must occur each second in your bone marrow just to replace red blood cells? Here is some information to use in calculating your answer: There are about 5 million red blood cells per cubic millimeter (mm³) of blood. An average adult has about 5 L (5,000 cm³) of blood. (Hint: What is the total number of red blood cells in the body?
What fraction of them must be replaced each day if all are replaced in 120 days?

Verified step by step guidance

1. Calculate the total number of red blood cells in the body by multiplying the concentration of red blood cells (5 million cells per mm³) by the total blood volume in mm³. Convert the blood volume from liters (5 L) to mm³ using the conversion factors: 1 L = 1,000 cm³ and 1 cm³ = 1,000 mm³.
2. Determine the number of red blood cells that need to be replaced each day by dividing the total number of red blood cells by 120 (since red blood cells live for 120 days).
3. Calculate the number of red blood cells that must be replaced each second by dividing the daily replacement number by the number of seconds in a day (24 hours × 60 minutes × 60 seconds).
4. Recognize that each cell division produces two daughter cells. Therefore, determine the number of cell divisions required per second by dividing the number of red blood cells replaced per second by 2.
5. Summarize the process: The total number of red blood cells is calculated, the daily replacement rate is determined, the replacement rate per second is found, and the number of cell divisions per second is calculated by accounting for the fact that each division produces two cells.

Key Concepts

Red Blood Cell Lifespan

Red blood cells (RBCs) have a lifespan of approximately 120 days in the human body. After this period, they are removed from circulation and must be replaced. Understanding this lifespan is crucial for calculating the rate of RBC production needed to maintain adequate oxygen transport in the body.

Bone Marrow Function

Bone marrow is the primary site of hematopoiesis, the process of blood cell formation, including red blood cells. It produces new RBCs through cell division, ensuring that the body maintains a sufficient supply to replace those that are lost. This concept is essential for understanding how the body compensates for the continuous turnover of blood cells.

Cell Division Rate Calculation

To determine how many cell divisions occur each second in the bone marrow, one must calculate the total number of RBCs in the body and the daily replacement rate. Given that an average adult has about 5 liters of blood containing approximately 5 million RBCs per cubic millimeter, this calculation involves understanding volume, concentration, and time to find the necessary production rate.