Homeostasis

1. Homeostasis: stability, balance, or equilibrium within a cell or body. 
• organism's ability to keep constant internal environment
• adjustments must be made continuously to stay near a set point
2. Feedback regulation loops
• endocrine system plays important role
• hormones regulate activity of body cells
• response to stimulus changes internal conditions
• self-adjusting mechanism is feedback regulation
• negative feedback: response to stimulus reduces original stimulus
• positive feedback: response to stimulus increases original stimulus
3. Negative feedback loop
• most common feedback loop
• acts to reverse the direction of change
• Examples: carbon dioxide increase signals lungs to increase activity and exhale more carbon dioxide (breathing rate increases) 
• Body temperatures rises, receptors sense temperature change and send signals to the brain
1. Skin makes sweat and blood vessels near skin surface dilate
• positive feedback is less common in biological systems
• speed up direction of change
• Ex. Lactation. Baby suckles = more milk production
• since positive feedback speeds up direction of change, it leads to increasing hormone concentration, which is a state further away from homeostasis
4. Examples of homeostasis in animals
• regulation of amounts of water and minerals in body (osmoregulation) happens in the kidneys
• removal of metabolic waste (excretion). Done by kidneys and lungs. 
• regulation of body temperature, done mostly by skin
• regulation of blood glucose level. Mostly done by liver and insulin and glucagon secreted by pancreas
5. Endocrine system
• includes glands that secrete hormones into bloodstream
• hormones: created by cells that change other cells; messengers
• regulates metabolism and development through feedback mechanisms
• endocrine system release hormones that affect skin and hair color, appetite, and secondary sexy characteristics in humans
6. Urinary system
• rids body of protein and nucleic acid buildup in the blood
• directly involved in maintaining blood volume
• kidneys maintain correct salt and water content in body
7. Reproductive system
• does little for homeostasis of organism
• sex hormones have affect on other body systems
• no estrogen (from ovaries) = impaired bone development
8. Disruption of Homeostasis
• may lead to state of disease
• caused by two ways
• deficiency: cells not getting what they need
• toxicity: cells being poisoned by things they don't need
• when interrupted, body can become better or worse depending on external influences
9. Internal influences
• genetics
• some genes can be turned on or off depending on external factors
• some cannot be stopped from developing diseases and disorders
• medicine can help body return to homeostasis
• Example: Type 1 diabetes
• insulin replacement therapy brings body's handling of glucose back into balance
10. External influences
• nutrition: if diet lacks certain vitamins or minerals the cells will function poorly, and increases risk of developing disease
• physical activity: essential for proper functioning of cells and bodies
• adequate rest and regular physical activity is important
11. Mental health
• mental and physical health are inseparable
• negative stress can negatively affect mental health
• physical activity increases mental and physical wellbeing