Maintaining “balanced” body function Homeostasis

HOMEOSTASIS Def: Def: body’s ability to maintain balance; body’s ability to maintain balance; relative constancy/stability of its internal environ. relative constancy/stability of its internal environ. If disturbed, a variety of negative-feedback loops/mechanisms usually return body to normal If disturbed, a variety of negative-feedback loops/mechanisms usually return body to normal “Negative” because it opposes the change “Negative” because it opposes the change Positive feedback  stimulate/amplify a response Positive feedback  stimulate/amplify a response Uterine contractions, blood clotting… Uterine contractions, blood clotting…

Homeostasis: See Fig. 5-2, p. 114 When disturbance goes beyond the “normal” fluctuation  disease; When disturbance goes beyond the “normal” fluctuation  disease; Too far from normal  death. Too far from normal  death.

Homeostasis: Maintained by Negative Feedback Loops Negative Feedback Loops (NFL): Negative Feedback Loops (NFL): body condition goes beyond acceptable limits NFL will work to bring condition back (-) within normal parameters. body condition goes beyond acceptable limits NFL will work to bring condition back (-) within normal parameters. Temp high… lower temp  normal Temp high… lower temp  normal [O 2 ] low… increase [O 2 ]  normal [O 2 ] low… increase [O 2 ]  normal Requires help from body (teamwork) Requires help from body (teamwork)

Negative Feedback

NFL Teamwork: Real-Life Example Controlled Condition: Room Temperature Controlled Condition: Room Temperature Disturbance: Cold wind from window open Disturbance: Cold wind from window open NFL: Temp. from warm  cool, bring back (-) to warmer condition NFL: Temp. from warm  cool, bring back (-) to warmer condition Sensor: Thermometer, senses change in heat Sensor: Thermometer, senses change in heat Control Center: Thermostat, compares w/ norm. room temperature Control Center: Thermostat, compares w/ norm. room temperature Effector: Furnace, heats, to adjust temp Effector: Furnace, heats, to adjust temp Effect: ? Effect: ?

CONTROLLED CONDITION Must be maintained at a homeostatic level/ within normal limits CONTROLLED CONDITION Must be maintained at a homeostatic level/ within normal limits Causes condition to go Disturbance: Causes condition to go outside of normal limits SENSOR Senses the change SENSOR Senses the change CONTROL CENTER Compares the change to what is normal so that the proper adjustment can be made CONTROL CENTER Compares the change to what is normal so that the proper adjustment can be made EFFECTOR Causes a change in the opposite direction of the disturbance (NFL) EFFECTOR Causes a change in the opposite direction of the disturbance (NFL) Specific Effect  Homeostasis NEGATIVE FEEDBACK LOOP

CONTROLLED CONDITION Body Temperature CONTROLLED CONDITION Body Temperature Cold Weather Disturbance: Cold Weather SENSOR Cold Receptors (free nerve endings) SENSOR Cold Receptors (free nerve endings) CONTROL CENTERBrain Brain Effect: Shivering NEGATIVE FEEDBACK LOOP EFFECTOR Skeletal Muscles EFFECTOR Skeletal Muscles

CONTROLLED CONDITION Blood Glucose Level CONTROLLED CONDITION Blood Glucose Level Disturbance: Ingesting candy/soda SENSOR “Glucose Receptors” SENSOR “Glucose Receptors” CONTROL CENTER Pancreas (Beta cells in the islets of Langerhans-also act as the receptors) CONTROL CENTER Pancreas (Beta cells in the islets of Langerhans-also act as the receptors) Effect: Cells absorb glucose from the bloodstream NEGATIVE FEEDBACK LOOP EFFECTOR Body Cells (glucose  ATP); Liver/skeletal muscle (glucose  glycogen) EFFECTOR Body Cells (glucose  ATP); Liver/skeletal muscle (glucose  glycogen) via hormone: insulin

CONTROLLED CONDITION Blood Volume CONTROLLED CONDITION Blood Volume Disturbance: Dehydration SENSOR Baroreceptors in hypothalamus & thorax SENSOR Baroreceptors in hypothalamus & thorax CONTROL CENTER Posterior Pituitary Gland (Brain) CONTROL CENTER Posterior Pituitary Gland (Brain) Effect: Decreases excretion of water as urine NEGATIVE FEEDBACK LOOP EFFECTORKidney Kidney via hormone: ADH: Anti-diuretic hormone (Decrease BP)

CONTROLLED CONDITION Arterial PCO 2 CONTROLLED CONDITION Arterial PCO 2 Disturbance: Exercise SENSOR Chemoreceptors Chemoreceptors SENSOR Chemoreceptors Chemoreceptors CONTROL CENTER Medullary Respiratory Centers (Brain) CONTROL CENTER Medullary Respiratory Centers (Brain) Effect: Increased ventilation (more CO 2 exhaled) NEGATIVE FEEDBACK LOOP EFFECTOR Respiratory Muscles EFFECTOR Respiratory Muscles