BASIC LIFE PROCESSES

Certain processes distinguish organisms, or living things, from nonliving things. Following are the six most important life processes of the human body:

1.     Metabolism is the sum of all the chemical processes that occur in the body. One phase of metabolism is catabolism, the breakdown of complex chemical substances into simpler components. The other phase of metabolism is anabolism, the building up of complex chemical substances from smaller, simpler components. For example, digestive processes catabolize (split) proteins in food into amino acids. These amino acids are then used to anabolize (build) new proteins that make up body structures such as muscles and bones.

2.      Responsiveness is the body’s ability to detect and respond to changes. For example, an increase in body temperature during a fever represents a change in the internal environment (within the body), and turning your head toward the sound of squealing brakes is a response to a change in the external environment (outside the body) to prepare the body for a potential threat. Different cells in the body respond to environmental changes in characteristic ways. Nerve cells respond by generating electrical signals known as nerve impulses (action potentials). Muscle cells respond by contracting, which generates force to move body parts.

3.     Movement includes motion of the whole body, individual organs, single cells, and even tiny structures inside cells. For example, the coordinated action of leg muscles moves your whole body from one place to another when you walk or run. After you eat a meal that contains fats, your gallbladder contracts and releases bile into the gastrointestinal tract to help digest them. When a body tissue is damaged or infected, certain white blood cells move from the bloodstream into the affected tissue to help clean up and repair the area. Inside the cell, various parts, such as secretory vesicles, move from one position to another to carry out their functions.

4.     Growth is an increase in body size that results from an increase in the size of existing cells, an increase in the number of cells, or both. In addition, a tissue sometimes increases in size because the amount of material between cells increases. In a growing bone, for example, mineral deposits accumulate between bone cells, causing the bone to grow in length and width.

Differentiation is the development of a cell from an unspecialized to a specialized state. Such precursor  cells, which can divide and give rise to cells that undergo differentiation, are known as stem cells. Each type of cell in the body has a specialized structure and function that differs from that of its precursor (ancestor) cells. For example, red blood cells and several types of white blood cells all arise from the same unspecialized precursor cells in red bone marrow. Also through differentiation, a single fertilized human egg (ovum) develops into an embryo, and then into a fetus, an infant, a child, and finally an adult.

2.     Reproduction refers either to (1) the formation of new cells for tissue growth, repair, or replacement, or (2) the production of a new individual. In humans, the former process occurs continuously throughout life, which continues from one generation to the next through the latter process, the fertilization of an ovum by a sperm cell.