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

ThermoregulationORGAN 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

OsmoregulationORGAN 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 CO2, release O2 and H2O through stomata

• Guard cells surround the stomata– Water abundant water

pressure in guard cells is HIGH, stomata OPEN, release water, CO2 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 MammalsORGAN 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

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