1. Homeostasis

2. 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

3. 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

4. Feedback Loop
NEGATIVE
POSITIVE

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

6. 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

7. Osmoregulation
FRESHWATER
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
SALTWATER

8. 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)

9. Osmoregulation – Land Animals

10. Guard Cells (Plants) ORGAN IN CHARGE  LEAF
Leaves take in CO2, release O2 and H2O through stomata
Guard cells surround the stomata
Water abundant  water pressure HIGH, stomata OPEN, release water, CO2 enters
Water scarce  water pressure 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

11. Gas Exchange in Mammals ORGAN IN CHARGE  LUNGS
Oxygen-rich air (poor in CO2) is taken in during inhalation; moves to alveoli
Oxygen-poor blood (rich in CO2) vessels surround the alveoli
Passive transport moves the oxygen from alveoli into the blood, CO2 from blood into the alveoli
Oxygen delivered to cells through the blood vessels; CO2 expelled during exhalation

12. 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