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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: 8:30 – 9:20– 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:-parasympathetic 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 pathwayintegrating 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