BIOL1412 Lecture #1 - Homeostasis PDF

Lecture #1 Homeostasis Textbook Chapter 1  Physiology and Homeostasis Physiology: the study of how the body functions and maintains homeostasis Homeostasis: maintenance of a relatively constant internal environment Cells have certain optimal conditions that must be carefully ma...

Lecture #1 Homeostasis Textbook Chapter 1  Physiology and Homeostasis Physiology: the study of how the body functions and maintains homeostasis Homeostasis: maintenance of a relatively constant internal environment Cells have certain optimal conditions that must be carefully maintained These conditions can only deviate from the optimal value so much before death occurs Conditions that must be carefully maintained include: Temperature pH CO2 O2 Blood pressure Concentration of ions (Na+, Cl- etc.) and volume of fluid both inside and outside of the cell Waste levels All of the body systems work together in order to maintain homeostasis When homeostasis is not maintained disease results  Homeostasis The nervous and endocrine systems function together to control all of the other body systems These two systems either: 1. Maintain homeostasis 2. Permit departures from homeostasis in a controlled fashion Example: pregnancy, blood clotting, growth, response to danger  Homeostasis Responses may occur in anticipation of a change Either subconscious or conscious Subconscious example: changes to heart rate or respiratory rate at the start of a sprint Proactive change that anticipates changes in blood gas levels that occur during exercise Conscious example: learned behavior that occurs in response to change Example: putting on a hat before heading outsideà anticipates heat loss and change in body temperature  Homeostasis Feedback mechanisms respond to changes in the system: The set point of a variable is the range of values that will not bring about any sort of response from the body Variables are monitored by receptorsà detect changes and feed them to the central nervous system for processing/interpretation so that a response can be produced Can also be fed to endocrine glands resulting in secretion Stimulusà receptorà control centerà effectorà response (sensory info) (input) (nervous and endocrine) (output) (systems)  Negative Feedback Negative feedback: most common mechanism of homeostatic control Output functions to reduce the input, moving the variable back to set-point The opposite direction from that which triggered the response Example: body temperature Set-point: 36-37.5oC High temperature: 40oC Detected by cells of the hypothalamus Sweat glandsà effectors that produce the CNS generated output (sweat)à the ‘doers’ Smooth muscle of blood vessels relaxà increased blood flow to the body’s surfaceà heat escapes to the atmosphere Result: increased heat loss leading to a drop in body temperature back to set-point values  Positive Feedback Positive feedback is less common than negative feedback but sometimes necessary Not a homeostatic mechanismà output acts to intensify the stimulus rather than to turn it down Example: uterine contractions during childbirth Input: increased contractions Posterior pituitary( nervous system) Oxytocin release Contractions increase further