Unit1-Ch1: Lecture #2 Homeostasis and Feedback http://www2.d125.org/science/secure/anatomy/som/homeo.mp4 (view) http://www2.d125.org/science/secure/anatomy/som/homeo.pdf (guide)

Definitions: Homeostasis is derived from “Homeo” = same “Stasis” = stand still Therefore, By Definition, Homeostasis refers to the body’s ability to maintain a stable internal environment

Control System: Three Parts Receptor: Also known as the sensor, responds to stimuli (sensors in skin) Control center (set point): brain & spinal cord (analyzes information and decides on a response) Effector: Supplies the means for the control center’s response, influences stimuli (muscle or gland)

Reflex: the simplest response possible Sensor – responds to stimulus Sensory (Afferent) Neuron – brings message into Control Center Interneuron – a relay between afferent and efferent neurons Motor (Efferent) Neuron – brings response out of CNS and delivers That response to the effector Effector – the item that influences the stimuli

S = A = M = E =

Homeostatic Mechanism: An example using body temperature.

Types of Feedback: Negative Feedback: Function: to maintain homeostasis Inhibitory: Produces an action opposite of the stimulus or initial conditions Stabilizing: returns conditions to the normal homeostatic balance Most Common: the majority of feedback mechanisms in the human body EXAMPLES: heart rate, temperature, breathing, glucose Positive Feedback: Not Homeostatic Amplifies the change that is occurring Destabilizing: disrupts homeostasis Stimulatory EXAMPLES: childbirth • Stimulus: pressure on cervix • Causes a release of oxytocin which causes smooth muscle contraction • Contractions create more pressure on cervix and cycle intensifies until baby is delivered • No more stimulus In positive feedback systems, the output enhances or exaggerates the original stimulus Example: Regulation of blood clotting