Homeostasis

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Circadian rhythm

• Body’s day and night cycle
• Repeats over 24 hours
• Tells us to go to sleep
• Is governed by natural light

Homeostasis

• Maintenance of a constant internal environment
• Some of the major internal conditions that need to be maintained at optimal levels include:
  • Blood glucose levels
  • Blood water levels
  • Body temperature
  • Blood oxygen levels
• Body tries to stay at constant temperature (37.5˚ C)
  • Optimal temperature for chemical reactions in cells
• To keep temperature the same it must balance the heat loss and heat gain
• Our bodies use behavioural and physiological methods to control temperature
  • Behavioural: Change clothes, cold drink, seek cool place, reducing activity
  • Physiological: Sweating, goose bumps, shivering, increasing activity

Negative Feedback Loop

• Components
  • Stimulus
    • Change in internal environment
  • Receptor
    • Detects change
  • Modulator (coordinator)
    • Control centre that processes information from receptor and sends information to effector
  • Message
    • Message that is sent from modulator/coordinator to effector
  • Effector
    • Part of body that carries out response
  • Response
    • Process that occurs in effector
  • Feedback
    • Change in internal conditions
• Most homeostatic control mechanisms display negative feedback
• Negative feedback is when the response is opposite to the stimulus and returns the body to its set point

Temperature

• Homeothermic - 37˚ C
  • Need for a constant body temperature
  • Chemical reactions
  • Enzymes (denaturation)
  • Nerve malfunction
  • Death
  • 30-32-37-42-44
• Variation in body temperature due to
  • External influences
  • Rate of activity
  • Biorhythms - 24 hr ($\downarrow$ morning, $\uparrow$afternoon)
  • Menstrual cycle ($\uparrow$ 2nd half due to hormones)

Heat Production

• Heat is produced in the body by:
  • Normal cellular metabolism/respiration
  • Action of muscles during movement and exercise
  • Shivering (involuntary muscle contractions)
  • Hormonally increasing metabolic rate (up to 40 x)
• Heat can also be gained from the environment by exposing yourself to the sun or another heat source

Heat Loss

• Heat is lost through the skin and mucous membranes by
  • CCR
• Conduction
• Convection
• Radiation
  • Evaporation of sweat
  • Heat can also be lost from the body by exposing yourself to cold mediums

Receptors

• The receptors for temperature are called thermoreceptors
• 2 types
  • Cold
  • Heat
• Thermoreceptors send nerve impulses to brain (hypothalamus)

Modulator and Message

• Modulator or control centre for temperature is in the brain (hypothalamus)
• Sends nervous impulses(electrical messages to effectors)

Effectors, Response and Feedback

• Effector
  • Part of the body that carries out a response to counteract the effect of the stimulus
• Response
  • The process that occurs in the effector
• Feedback
  • The change in internal conditions as a result of the action of the effectors

Effectors and Response: Skin

• Blood vessels carry heat to the skin from the body core
• Diameter of blood vessels to the skin is controlled by nerves that cause vasoconstriction and vasodilation
• Vasodilation occurs to increase heat loss through CCR
• Vasoconstriction occurs to decrease heat loss through CCR
• Evaporation of water from the skin and lungs, accounts for a considerable proportion of heat loss
• Piloerection (goosebumps)
  • Hair follicles raise hair from surface to trap a warm layer of air (little effect)

Effectors and Response: Brain

• Cold conditions
  • Brain $\to$ Changed behaviour, e.g. $\downarrow$ SA(surface area) huddling in a ball, extra clothes = $\downarrow$Heat Loss
  • Brain $\to$ Changed behaviour, e.g. voluntary activity = $\uparrow$ ­Heat production
  • Brain $\to$ Changed behaviour, e.g. heat-seeking behaviour = $\uparrow$ ­Heat production
• Hot conditions
  • Brain $\to$ Changed behaviour, e.g. ­$\uparrow$ SA by changing shape = $\uparrow$ ­Heat loss
  • Brain $\to$ Changed behaviour, e.g. $\downarrow$ Voluntary actions = $\downarrow$ Heat production
  • Brain $\to$ Changed behaviour, e.g. cool-seeking/heat-avoiding behaviour = $\downarrow$ Heat gain, $\uparrow$ ­heat loss

Effectors and Response: Muscles

• Skeletal muscles $\to$ Shivering = rapid muscle contraction = $\uparrow$ ­Heat production