Question

At puberty, the testes contain a finite number of cells and produce an enormous number of sperm cells during the life span of a male. Explain why testes do not run out of spermatogonial cells.

Short answer

Testes do not run out of spermatogonial cells because these cells are self-renewing. This occurs as type A spermatogonial cells can divide and make a copy of themselves through mitosis. One cell remains as a stem cell and the other cell moves on to become a sperm cell. In this way, the population of spermatogonial cells in the testes stays sustained over time, regardless of the number of sperm created.

Step-by-step solution

Understanding Spermatogonial Cells

Spermatogonial cells are the germ cells in males, which are located in the testes. They're responsible for the process of spermatogenesis or the production of sperm cells. They exist in several forms, namely the type A (dark, pale) and type B spermatogonia. Type A cells play a significant role in ensuring the continuity of this population of cells.

Explaining Spermatogenesis

Spermatogenesis is the biological process by which sperm cells are produced from spermatogonial stem cells in a sophisticated process of cell division and differentiation. The process begins with mitosis of the spermatogonium, DNA replication, and division of a cell into two identical spermatogonial stem cells. One of these remains as a stem cell and the other differentiates into a B type cell or primary spermatocyte, which is destined to become a sperm cell.

Why the Testes Don't Run Out of Spermatogonial Cells

Due to the process of spermatogenesis, one would assume that the testes would eventually exhaust the supply of spermatogonial cells. However, this doesn't occur because type A spermatogonial cells can undergo mitosis and divide into more spermatogonial cells, thereby replenishing the supply. They are essentially self-renewing. One of the two cells following mitosis remains a spermatogonial stem cell, ready to divide again, while the other cell progresses on to become a sperm cell.