Ch.21 Homeostasis

homeostasis

ability of an organism to maintain a constant internal environment

external change

a change in the surroundings in which an organism lives

internal change

a change in the surroundings of the cells in a multicellular organism

eg of external change

weather change, freshwater or seawater for fish

eg of internal change

tissue fluid in humans

blood and tissue pH at 7.4

kidneys control blood pH

blood glucose concentration

insulin lowers blood sugar concentration

toxic chemicals in the body

liver breaks them down, kidneys excrete them

oxygen and carbon dioxide levels..

lungs take in oxygen and excrete carbon dioxide

body temp at 37…

temp is controlled by the skin and blood vessels

3 processes involved in homeostasis

diffusion

osmosis

active transport

diffusion

spreading out of molecules from a region of high concentration to low concentration

osmosis

movement of water molecules across a selectively permeable membrane from a region of high water concentration to a region of low water concentration

active transport

movement of molecules across biological membranes against a concentration gradient (from low-high con)

organs involved in homeostasis

liver

lungs

kidneys (nephrons)

skin

parts of a homeostatic system

receptor (cell/organ) = sends message

control centre (brain) = receives message

effector (response) = responds to message

negative feedback

means that the correct level of one factor inhibits a previous step in the cycle

benefits of homeostasis

• controls environment surrounding our cells

• allows for optimal conditions

• allows organisms to function regardless of external environment

example of negative feedback involving a nervous pathway

temp is controlled by negative feedback

• normal temp = no sweat = retain heat

• high temp = sweat = cool down

thyroxine levels are..

controlled by negative feedback

thyroxine levels

• low concentration of thyroxine = TSH = thyroxine made

• correct concentration of thyroxine = no TSH = no more thyroxine made

what happens wehn thyroxine levels are low?

the pituitary gland secretes TSH, stimulating the thyroid to produce thyroxine

hormonal and nervous systems…

coordinate to maintain a constant internal environment in the body

hormonal and nervous system coordinating

• nervous sytem = fast-acting and has short-lived responses (localised)

• hormonal system = slow-acting with longer-lasting responses (widespread)