28 2 Mechanisms of Homeostasis KEY CONCEPT Homeostasis

28. 2 Mechanisms of Homeostasis KEY CONCEPT Homeostasis is the regulation and maintenance of the internal environment.

28. 2 Mechanisms of Homeostasis Conditions within the body must remain within a narrow range. • Homeostasis involves keeping the internal environment within set ranges.

28. 2 Mechanisms of Homeostasis • Control systems help maintain homeostasis. – sensors gather data pore – control center receives sweat data, sends messages glands – communication system delivers messages to target hair organs, tissues follicle – targets respond to change muscle goose bump

28. 2 Mechanisms of Homeostasis Negative feedback loops are necessary for homeostasis. • Feedback compares current conditions to set ranges. • Negative feedback counteracts change. Negative Feedback Loop Holding breath, CO 2 levels rise, O 2 / CO 2 level returns to normal Control system forces exhale, inhale

28. 2 Mechanisms of Homeostasis • Positive feedback increases change. – Torn vessel stimulates release of clotting factors platelets blood vessel fibrin clot white blood cell red blood cell – growth hormones stimulate cell division

28. 2 Mechanisms of Homeostasis KEY CONCEPT Systems interact to maintain homeostasis.

28. 2 Mechanisms of Homeostasis Each organ system affects other organ systems. • An organ system must do a specific job. • Organ systems must also work together to keep the organism healthy.

28. 2 Mechanisms of Homeostasis • Organ systems must also work together to keep the organism healthy. – Organ systems work together to produce Vitamin D. – Thermoregulation maintains a steady body temperature. UV light 1 Skin absorbs UV light 2 Liver produces inactive vitamin D 3 Kidneys produce active vitamin D 4 Active vitamin D used in bones

28. 2 Mechanisms of Homeostasis A disruption of homeostasis can be harmful. • Homeostasis can be disrupted for several reasons. – sensors fail – targets do not receive messages – injury – illness

28. 2 Mechanisms of Homeostasis • Short-term disruption usually causes little or no harm. • Long-term disruptions can cause more damage. • Diabetes is a serious long-term disruption of homeostasis. pancreas 1 Pancreas cells attacked; insulin declines 2 Blood glucose levels rise, 3 fats kidneys Body burns fat; blood more acidic, 4 Cells impaired; all organs damaged.