Necessary Life Functions

Necessary Life Functions in Humans

Terms and Nomenclature

Maintaining Boundaries:  Humans must maintain boundaries so that the internal environment remains distinct from the external environment surrounding them. In single celled organisms, the external boundary is a limiting membrane that encloses its contents and lets in needed substances while restricting entry of potentially damaging or unnecessary substances. 

                Integumentary System  maintains boundaries in humans by adding protective

                layer of membrane (skin) around internal organs that fends out bacteria and 

                keeps damaging effects of heat, sunlight, and chemicals in the external 

                environment.

Movement: Activities promoted by the muscular system and allows humans to manipulate the external environment. Occurs in cardiovascular, digestive, and urinary systems.
                Contractility: On the cellular level, this is the muscle's ability to move by
                                     shortening.
Responsiveness or Excitability: ability to sense changes (which serve as stimuli) in the environment and then respond to them. Occurs most notably in the nervous system.
Digestion: Breaking down of ingested foodstuffs to simple molecules that can be absorbed into the blood. The nutrient-rich blood is then distributed to all body cells by the cardiovascular system. In Humans, this occurs primarily in the Digestion system.
Metabolism: Broad term that includes all chemical reactions that occur within body cells. It includes breaking down substances into their simpler building blocks, synthesizing more complex cellular structures from simpler substances, and using nutrients and oxygen to produce ATP. Occurs in Digestive and Respiratory Systems and is regulated by the Endocrine System Glands.
                catabolism: Breaking down of substances into simpler building blocks.
                anaboloism: Synthesizing more complex cellular structures from simpler
                                   substances.
                cellular respiration: Using nutrients and oxygen to produce ATP.
Excretion: Process of removing wastes from the body produced during digestion and metabolism. Common wastes removed from the body include indigestible food residues in feces, nitrogen-containing metabolic wastes in urine, and carbon-dioxide (by-product of cellular respiration).
Reproduction: Occurs at the cellular and the organismal levels. In cellular reproduction, the original cell divides, producing two identical daughter cells that may then be used for body growth or repair. Reproduction of the human organism, or making of a whole new person, is the major task of the reproductive system.
Growth: Increase in size of a body part or the organism as a whole. It is usually accomplished by increasing the number of cells. However, individual cells also increase in size when not dividing. For true growth to occur, constructive activities must occur at a faster rate than destructive ones.