6A: regulation of homeostasis

homeostasis

regulation of a constant internal environment despite changes in the external environment.

systems that control homeostasis

nervous and endocrine system

stimulus-response model

homeostatic regulation involving monitoring a variable and detecting changes outside normal range

stimulus

• change has occurred in the external or internal environment

• change in variable / change from normal level

  • e.g. change in temperature / glucose concentration

receptor

• stimulus detected by the receptor

• transfers into chemical / electrical signal

• cell receptors = embedded in membrane / cytosol

modulator

• processing / control center

• info from receptors is sent to the modulator

  • compares incoming info with an ideal condition

  • if not ideal, release molecules to alter effector

effector

• responds to signal from modulator, produces a response

• molecule / cell / organ

  • e.g. sweat glands, smooth muscle in blood cells

response

• effector initiates response to stimulus

• any change in function of a target cell, organ, organism

  • e.g. sweat cools body temperature back to 37C

stimulus-response diagram

negative feedback loop

• occurs when response counters (negates / reduces) the stimulus

• attempts to revert system back to the normal state

  • homeostasis usually involves

• normal level = set point

positive feedback loop

• occurs when response increases / amplifies the initial stimulus

• do not form part of homeostasis

  • e.g. contractions of childbirth

  • hormone oxytocin released

  • stimulates more contractions