Homeostasis

What is homeostasis? (same) (state) Regulation and internal maintenance of the body The body works best when internal conditions are within an acceptable range; homeostasis helps to do this

Feedback Loops Homeostasis controls internal conditions with feedback loops NEGATIVE feedback loop – the product inhibits the process that creates them –Ex: control of body temperature, thermostat –Common homeostatic mechanism POSITIVE feedback loop – the product amplifies the process that creates them –Ex: labor, global warming

Feedback Loop NEGATIVE POSITIVE

Homeostasis Examples Thermoregulation (temperature) Osmoregulation (water) Gas Exchange Blood Glucose Other examples: –pH –Blood pressure –Hormone levels –Metabolism

Thermoregulation ORGAN IN CHARGE  BRAIN Hypothalamus scans temperature of blood as it passes through –Too high  blood vessels dilate, sweating occurs –Too low  blood vessels constrict, shivering

Osmoregulation Regulation of the balance of water and solutes (salt, ions) in the body Aquatic Organisms: –(Freshwater) Protists – don’t forget about the contractile vacuole! –Freshwater fish – environment is hypotonic to the fish; fish take in lots of water Solution  fish excrete LOTS of very dilute urine to conserve solutes –Saltwater fish – environment is hypertonic to the fish; fish loses water to osmosis Solution  fish have specialized gills to excrete excess ions FRESHWATER SALTWATER

Osmoregulation ORGAN IN CHARGE  BRAIN/KIDNEYS Terrestrial Animals –Water is constantly being lost through evaporation, perspiration, urination Water lost through these avenues needs to be replaced by drinking and eating –Concentration of urine allows solutes to be excreted while conserving water (kidneys)

Osmoregulation – Land Animals

OSMOREGULATION (Plants) ORGAN IN CHARGE  LEAF Leaves take in CO 2, release O 2 and H 2 O through stomata Guard cells surround the stomata –Water abundant  water pressure in guard cells is HIGH, stomata OPEN, release water, CO 2 enters –Water scarce  water pressure in guard cells is LOW, stomata CLOSED, loss of water limited Generally  –Stomata open during the day (photosynthesis) –Stomata closed during the night (decreased photosynthesis, prevent water loss) –Exceptions  HOT DRY conditions may result in closed stomata during the day

Gas Exchange in Mammals ORGAN IN CHARGE  LUNGS Oxygen-rich air (poor in CO 2 ) is taken in during inhalation; moves to alveoli Oxygen-poor blood (rich in CO 2 ) vessels surround the alveoli Passive transport moves the oxygen from alveoli into the blood, CO 2 from blood into the alveoli Oxygen delivered to cells through the blood vessels; CO 2 expelled during exhalation

Regulation of Blood Glucose ORGAN IN CHARGE  PANCREAS Blood sugar too high: –Pancreas releases insulin; body cells take in glucose and moves it to long term storage in liver (glycogen) Blood sugar too low: –Pancreas releases glucagon; stimulates liver to break down stored glycogen (into glucose) and release into bloodstream