Chapter 18, Problem 1P

Summary Introduction

To examine:  Whether the statement “In normal adult tissues, cell death usually balances cell division.” is true or false.

Concept introduction: Regulated cell death is a counterintuitive yet crucial process in eukaryotic metazoan organisms. Apoptosis in simple terms can be defined as programmed cell death. The cell is kept alive with the trophic factors which are produced under good nutritional conditions. In the absence of trophic factors, the cells activate a suicide program called as intrinsic pathway of apoptosis. Cells enter apoptosis when they don’t receive any signal or when apoptosis is initiated with signals from the adjacent cells (paracrine signaling) called death signals which bind to the death receptor called as extrinsic apoptotic pathway which occurs during development.

Answer to Problem 1P

Correct answer: The statement is true.

Explanation of Solution

The number of cells which perform the specified function in the target field that is, the area of growth is kept in check with the help of Growth Factors or trophic factors. When cells proliferate in a target field, the number of cells increases in that vicinity and if there is loss of cells in the target field the number of cells decrease in the target field. The selective survival of cells is based on the factor that if they receive the trophic factors or growth factors or not. Those that do not receive trophic factors or growth factors perish and the others alone survive. Cells which receive the trophic factors or growth factors perform their normal functions like cell growth and cell division. This selection process helps to keep the cell division and cell death in balance so abnormal growth or cell division or cell death does not takes place.

Conclusion

The target field or area of growth is where the number cells are kept in check by maintaining a balance between cell growth and cell division with the help of trophic factors or growth factors. Hence, the statement is true.