Homeostasis and Integration

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Homeostasis and Integration

• The parameters of homeostasis
• Integration through feed back loops
• Nervous, endocrine and neuroedocrine reflexes
• Midterm test
• Monday Oct. 7 830 920
• multiple choice questions
• Location A- P in the Education Gym
• Q-Z in Erie Hall (lecture hall)

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What does all this have to do with homeostasis?

• Maintain a stable internal environment
• Parameters that are under homeostatic control
• Factors affecting cells osmolarity, pH,
  temperature
• Materials that cells need nutrients, water,
  sodium, calcium, oxygen, signaling molecules

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Properties of homeostasis

• The nervous system co-ordinates many functions
• Many functions have tone. These are not merely
  on or off. E.g. blood vessels, hearing
• Some functions occur by antagonistic control
  (glucagon/insulin)
• The effect of a ligand depends on the receptor

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The effect of a ligand depends on the receptor
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Antagonistic control of heart rate -parasympathet
ic stimulation
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Antagonistic control of heart rate -sympathetic
stimulation
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Homeostatic mechanisms are local or over long
distances

• E.g. of local control, paracines.
• Long distance, reflex controls usually include
  nervous or endocrine components

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A response loop for a reflex pathway

• An input signal
• Integration of the signal
• Output signal
• Stimulus ? receptor ? afferent pathway
• integrating center ? efferent pathway
• effector ? response

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Sensory receptor systems

• Stimulation can be external or internal
• External special senses
• Internal pH, osmolarity, baroreceptors
• All sensory receptors have a threshold stimulus
  for evoking a response

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Afferent Pathway

• From the sensory receptor to the integrating
  center

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Integrating center

• Receives information
• Response is initiated
• Sometimes two conflicting inputs arrive to the
  integrating center

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Efferent pathway

• If nervous reflex, the pathway of the nerve
• If endocrine, the target cell with appropriate
  receptors

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The response loop
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Name different response loops

• Automatic pet watering system

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Negative feedback loops

• preserve homeostasis (osmolarity, oxygen tension)
• Stabilize the physiological variable
• Can restore normal state
• What if the disturbance is beyond the normal
  range? (catastrophic)

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Positive feedback loops

• Foster change
• Reinforce the stimulus
• E.g childbirth, development,

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Feed forward

• A stimulus warns a regulatory system
• E.g. the odor of food is a feed forward stimulus.
  ? salivation and secretion of digestive enzymes

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Some reflexes are cyclic

• Circadian rhythm, on a 24 hour cycle