10/4/21, 2:40 AMRequirements for Human Life: Metabolism, Growth & Reproduction | Study.com1/4Requirements for Human Life: Metabolism, Growth & ReproductionThis lesson discusses the basics of life, from cells to functions of the human organisms. Also included is howwe handle food intake, power our movements, respond to sources of food and water, aversion to dangers,and how we develop and reproduce.Organization of the Human OrganismThe basic building block of life is thecell, and humans are comprised of trillions of cells. Fromthe cellular level, it progresses to:Tissues - composed of similar cellsOrgans - composed of various cell and tissue typesSystems - collectively work together to promote a certain function for the organism, such as thecardiovascular system delivers oxygenated blood throughout the body and returns deoxygenatedblood to the heart, where it can be circulated and reoxygenated in the lungs. The largest system is theintegumentary system that consists of skin, hair, nails, and other associated structures. It providesshape to the organism and acts as a physical barrier to prevent diseases and other harmful factorsfrom penetrating the internal organs.The human body can also be thought of as being arranged in di±erent compartments, such asthe external one that includes skin and outward organs, like the nose, oral cavity, eyes, ears,etc., vs internal compartments.Internal compartments include:The skull that contains the brainThe neck that contains structures, such as the trachea, esophagus, larynx, thyroid/parathyroidglands, and blood vesselsThe thorax region that contains the thymus (in young animals), heart, and lungsThe abdominal region that contains many of the gastrointestinal organs, spleen, reproductive tractin females, and urinary bladderThe retroperitoneal region that contains the kidneysThe testes that descend into the scrotumOther structures include the arms, legs, and the urogenital system, i.e., the penis in males.Cells lining such structures as the intestines, respiratory system, and bodily surfaces preventpathogens from entering into the bloodstream and circulating to other organs. It is worthnoting, however, that many body systems, such as the gut, contain resident bacteria that tend to
10/4/21, 2:40 AMRequirements for Human Life: Metabolism, Growth & Reproduction | Study.com2/4be commensal and even bene²cial by producing factors, such as vitamin K and vitamin B12, thatwe cannot synthesize on our own.