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)

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

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

Antagonistic control of heart rate: -parasympathetic stimulation

Antagonistic control of heart rate: -sympathetic stimulation

Homeostatic mechanisms are local or over long distances E.g. of local control, paracines. Long distance, reflex controls usually include nervous or endocrine components

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

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

Afferent Pathway From the sensory receptor to the integrating center

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

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

The response loop

Name different response loops Automatic pet watering system

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)

Positive feedback loops Foster change Reinforce the stimulus E.g childbirth, development,

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

Some reflexes are cyclic Circadian rhythm, on a 24 hour cycle