1. Homeostasis: maintaining an internal balance
SBI 4U, December 12th, 2012

2. Maintaining an Internal Balance
Ray Zahab vs. Fennec Fox
Fennec fox  ears allow for efficient hearing and act as radiator

3. Maintaining and Internal Balance
Homeostasis: the physiological state of the body in which the internal physical and chemical conditions are maintained within an acceptable or tolerable range that is suitable for essential biological processes
Dynamic state

4. Maintaining an Internal Balance
Body has several conditions that must be monitored. Such as:
-internal temperature
-hormone levels
-pH
-flow and concentration of glucose and other solutes
*some tolerable ranges are narrow, while others are more broad*

5. The Internal Environment
Purpose of homeostasis: to maintain internal physical and chemical conditions that are appropriate for the cells to function properly
Internal environment: the extracellular fluid, which consists of the fluid that surrounds the cells and tissues in the body and the plasma portion of the blood
Focus on fluid outside of the cells

6. Organ Systems Involved in Homeostasis
Nervous System
Endocrine System
Muscular System
Integumentary System
Excretory System
Reproductive System

7. Organ Systems Involved in Homeostasis
All of the organ systems are coordinated to carry out the tasks necessary for the survival of the organism. No matter how simple or complex the animal, these functions include:
Taking in nutrients and other required chemicals, processing and excreting
Synthesizing proteins, fats and carbs
Sensing and responding to changes in external environment
Protecting body
Reproducing, protecting and feeding offspring

8. Organ Systems Involved in Homeostasis
Homeostatic Mechanisms: a system that monitors internal and external conditions and changes bodily functions to maintain homeostasis
Ex: shivering in response to cold weather

9. Negative Feedback Mechanisms
Primary mechanism of homeostasis
Negative feedback: the response of a system that acts to maintain equilibrium by compensating for any changes made to the system
3 components: sensor, integrator and effector

10. Negative Feedback Mechanisms
Sensor: consists of tissues or organs that detect any change in external or internal factors
Info transmitted to integrator  acts as a processing or control centre. Compares environmental conditions with the optimal function conditions called set points
Integrator activates the effector  the element of a feedback system that acts to return the system to its optimal state

11. Negative Feedback Mechanisms
Antagonistic effects  response opposite to change
Ex: thermostat
Sensor measures temperature
Integrator compares the measures temperature to set point
Integrator activates electrical effector (furnace or air conditioner)
Temperature returned to normal state

12. Negative Feedback in Animals
Ex: humans
Neurons in preoptic region of hypothalamus receive info from thermoreceptors
Hypothalamus compares info to set point
Hypothalamus activates effectors that induce vasoconstriction in skin. Less thermal energy lost. Body temperature increases

13. Positive Feedback Mechanisms
Positive Feedback: the response of a system that acts to increase the effect of any changes made to the system
Do not result in homeostasis
Operate when a continuous increase in some internal variable is required (ex: fight or flight)
Ex: childbirth contractions  release of oxytocin