Homeostasis

• Communication


  Essential for the survival of organisms as all living organisms must be able to detect and respond to changes in their internal and external environments
• Cell signalling


  Communication between cells, in the form of electrical signals carried by neurones or with the help of hormones
• Neuronal cell signalling


  Faster and short term
• Chemical cell signalling


  Slower and long term
• Types of cell signalling

  • Endocrine signalling
  • Paracrine signalling
  • Autocrine signalling
• Homeostasis


  Ensures a constant internal environment consisting of factors such as temperature, water potential, pH and blood glucose level is maintained, despite changes in the external environment
• Negative feedback


  • Counteracts any change in internal conditions
  • Reverses all changes to restore the optimum conditions
• Elements needed for negative feedback pathway

  • Sensory receptors
  • Effectors
• When a change is detected

  Receptors pass the message via the nervous or hormonal system to the effectors which bring about a response to restore the optimum conditions
• Positive feedback


  Increases the original change in the conditions
• Ectotherms


  Organisms which regulate their body temperature with the help of external source
• Ectotherms


  • Unable to increase their respiration rate to increase the internal production of heat
  • Control their body temperature by exchanging heat with their surroundings
• Endotherms


  Able to maintain a constant body temperature, independent of the external temperature
• Endotherms


  • Contain thermoreceptors which monitor core body temperature changes and communicate them to the hypothalamus
  • Hypothalamus coordinates appropriate responses to restore the optimum temperature through either physiological or behavioural responses
• Actions taken by endotherms to control body temperature

  • Shivering
  • Sweat glands
  • Hairs on skin
  • Arterioles
• Why do multicellular organisms need internal communication systems?

  • to respond to their internal and external environment changes
  • to coordinate organ function
• What is homeostasis?


  Homeostasis is the body's ability to maintain a stable internal environment despite external changes.
• What are receptors?


  Proteins or cells that detect and respond to specific signals or stimuli.
• Another behaviourso methods:


  • basking in the sun
  • pressing against warm surfaces
  • digging hurried
  • hibernation
  • Panting
• How do enforcers use the nervous system to regulate temperature?

  Thermoreceptors inin blood detect change in temp

  Hypothalamus sends impulses to defectors in skin:

  • Vasodilation/construction
  • Sweating
• Explain the role of the skin in thermoregulation

  • vasodialation/construction of arterioles
  • supplying skin capillaries controla heat loss to skin surface
  • hair detector muscles contract =follicles protrude to tap air for insulation
  • Evaporation of sweat cools skin
• Endocrine vs Nervous system:

  Endocrine:

  • Hormones travel in blood
  • Slower
  • Long lasting
  • Widespread

  Nervous system:

  • Nerve impulse across synapse via nerotransmitters
  • Faster
  • Brief effect
  • Localised
• Examples of things regulated in homeostasis:

  • Temperature
  • Blood on
  • Blood glucose
  • Blood water levels
• Examples of positive feedback:


  Childbirth - oxytocin levels increase resulting in contraction
• What is a hormone?

  A hormone is a chemical messenger.

  Hormones are produced by endocrine glands and carried in the bloodstream
• Optimum Temperature for Enzymes

  Temperature range where enzymes work best; potential denaturation at extreme temperatures