Homeostasis

Homeostasis  

  • State of internal balance  

  • Body is constantly working to maintain this balance even though environment is changing  

  • Narrow range  

  • Feedback systems are activated to return back to homeostasis  

  • e.g. body temperature, blood pressure, blood sugar levels 

 

3 main components  

  1. Receptors – sensors that detect the stimulus occurring to the body  

  2. Control center (Hypothalamus) - analyses the information sent from the receptors, compares to the set point and determines a response  

  3. Effectors – cell or organ that produces a response under the instruction by the control center  

 

Feedback pathways  

  • Negative feedback – responds to reduce or stop the undesirable initial stimulus  

  • Most homeostatic control systems are negative feedback systems  

  • Body temp, blood pressure, blood sugar levels – narrow range, if leave the negative feedback reacts  

  • Positive feedback – responds to enhance or continue the initial stimulus  

  • Less common  

  • Childbirth, breastfeeding, blood clotting  

 

Body temperature regulation  

  • Hypothalamus –0 control center for body temp 

  • Optimal temp is 37 degrees Celsius (35.8 - 38.2 degrees) 

  • Enzyme reactions within the body vital for survival  

  • Elevated body temp destroys enzymes  

 

Increased body temperate  

  • Receptors - thermoreceptors in skin detect increase skin temp  

  • Control center – hypothalamus  

  • Effectors –  

    blood vessels in skin – vasodilate   

    Sweat glands in skin  - sweat  

  • Blood vessel in the skin vasodilate increasing blood vessel diameter. Blood flow closer to skin surface. Heat is transferred onto skin surface. Heat is lost from the skin surface by heat exchange mechanisms (conduction, convention, radiation).  

  • Sweat glands in skin – produce sweat onto skin surfave. Heat transferred into the sweat. Heat is removed as the sweat evaporates  

 

Decreased body temp  

  • Receptors – thermoreceptors in skin detect decrease in skin temp  

  • Control centre – hypothalamus --> convey message through neurons  

  • Effectors  

    Skeletal muscles – shiver  

    Blood vessels in skin – vasoconstrict  

Blood vessles in skin  

  • Vasoconstrict – decrease blood vessel diameter  

  • Decreased blood flow near skin surface – pale skin  

  • Heat is conserved to warm the body and not lost onto skin surface  

Skeletal muscles  

  • Muscles rapiudly contract (shivering) 

  • Producing heat warming the body  

 

Postive feedback 

Child birth 

  • Head of fetus presses on cervix 

  • Receptors inn cervix detcts stretch  

  • Message sent to brain  

  • Release of oxytocuin from pituitary gland  

  • Oxytocun causes uterus to contract  

 

SUMMARY  

Stimulus --> recptiors --> control centre -->effectors --> response 

 

Negative feed back – reduce the stimual  

Postive feedback – enhance the stimulus