HOW DO CELLS FUNCTION?

Cells are the basic building blocks of the bodily structures. Cells attach to and interact with each other to form, say, the liver, the lungs, or the bones. Each cell, in turn, functions as its own mini factory, contributing to general function of the organ ot os a part of (for example, enabling the stomach to digest food) and ensuring its own self-preservation. A single organ contains billions of cells. The cells comprised by an organ, however, differ from each other and may contribute to different types of tissues within that organ. For example, certain cells within the lungs form the major lung tissue, called lung parenchyma that gives lungs their substance. Other cells within the lungs form the tough, fibrous structures that surround the lungs and give them their shape. Still other cells contribute to the blood vessels that supply the lung tissue with blood, while entirely different cells make up the nerves associated with the lungs. Any one of these cells could potentially develop into a cancerous cell; this explains why so many different types of cancers might arise in the same organ.

The blueprints for a cell’s function, development, reproduction, and eventual death are contained in structures called DNA (short for deoxyribonucleic acid). The DNA, in turn, is combined to form chromosomes, and chromosomes are housed in a central cell structure called the nucleus. The machinery that carries out the cell’s functions is found in the area surrounding the nucleus, called the cytoplasm.Cells reproduce by dividing into identical halves. These halves then mature, carry out the same functions as their parent, and in turn divide to form four identical cells, and so on. As an individual grows from embryo into a fetus and then into infancy, childhood, and finally adulthood, the number of these dividing cells exceeds the cells that are being replaced (older, dying cells), and organs and tissues grow. Once an individual reaches adulthood, though, cell division slows to keep pace with cell loss, and organs and tissues maintain their size.

Most cells live for a given amount of time (this can very from minutes to years) and then udergo programmed cell death, a process called apoptosis. It is as if each cell came with its own, predetermined expiration date, brought about by its own DNA. As cells age, they lose some or all of their ability to function. They then can no longer contribute as much to the organ or body part to which they belong, and that organ or body part will therefore not function as well. For example, an aging platelet (a cell in the bloodstream whose job is to facilitate blood clotting) will not stem bleeding as well as a young platelet that has freshly entered the bloodstream from the bone marrow. Apoptosis is the body’s built-in mechanism for removing these dysfunctional cells so as to keep its organs operating as efficiently as possible.