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.

WHAT IS THE NORMAL STRUCTURE AND FUNCTION OF AN ORGAN IN THE BODY?

Every organ in the body performs specific duties. Each organ functions as a member of a community of organs, all contributing to the good of the body as a whole. The brain, the "high commander," dictates the functions of most organs. The heart pumps blood (at varying rates and pressures, depending on the brain's signals) to other tissues and organs, the lungs breathe air (providing necessary oxygen to tissues and organs via the bloodstream), and the stomach digests food (providing nutrients to itself and other organs and tissues in the body). The pancreas and gallbladder assist with that digestion, while the liver and kidneys help to process and excrete toxins from the body. The reproductive organs (ovaries in a woman and testes in a man) ensure that the elements that define the individuality of a person (the genes) get passed on to the next generation. Every organ is composed of tissues; tissues are, in turn, composed of cells.

The human body has evolved with a complicated set of organs, each of which performs specific functions and each of which relies on and communicates with other organs for the good of the whole individual. The brain, for example, controls higher-order functioning (memory, thought, sensory input and output) and basic bodily functions (breathing, the beating of the heart, the drive to eat and sleep). It transmits electrical signals to the heart to beat faster or slower, to the movement. It also sends out hormonal signals through the release of chemicals from the pituitary gland. These signals affect other organs, including the heart, lungs, kidneys, reproductive organs, and thyroid gland. The organs affected by the brain then vary their function, in turn sending out signals (either electrical, chemical, or both) to still other organs, then back to the brain to provide "feedback" about how the organ is responding to the brain's initial stimulus.

A scenario may clarify these interactions. You are walking in the forest one day when a tiger jumps out from the bushes. Your brain thinks, "Oh my God, it's a tiger! I'm in trouble!" - a process known as "higher-order functioning." It then transmits electrical signals to the heart to beat faster, to the lungs to breathe harder (basic bodily functions), and to the muscles to tense up, preparing you to flee from or to fight the tiger (your choice!). At the same time, the brain triggers to the pituitary gland (also located in the skull) to release hormones, including one that stimulates the adrenal glands to produce adrenaline (epinephrine). Adrenaline also in turn, send signals back to the brain to tell it "Okay - we're really moving now! You can stop signaling us to work harder. We're already doing it!" (feedback). These organs work together to ensure survival.

Organs, then, perform specific functions, but they also respond to both electrical and chemical stimuli from other organs, all for the good of the individual.