1. Introduction and FEEDBACK LOOPS
Homeostasis
Introduction and FEEDBACK LOOPS

2. Introduction Conditions in the body must be kept within a narrow range
Homeostasis:
The maintenance of a consistent internal environment despite external changes (keeping the environment between set ranges or maintaining a dynamic equilibrium)

3. Main Internal Dynamic Equilibriums
Body Temperature
Water Balance/Blood Pressure
Water/Ion Balance
Blood Glucose Levels
Blood O2/CO2 levels (pH)

4. Forms of Regulation Voluntary:
Control the internal environment by conscious control (think about it)
Ex. Put on warm clothes in the winter, swim in the summer
Involuntary:
control of the internal environment without conscious thought
Ex. Increased respiration when exercising

5. Regulation Mechanisms
1. Osmotic Pressure differential between 2 solutions on opposite sides of semi-permeable membrane Ex. Kidney & urine formation 2. Hormonal: Chemical messenger Slow communication, long term Ex. Growth hormone

6. Regulation Mechanisms continued
3. Nervous ▫
Fast
Often works with endocrine system (hormones into bloodstream)
Ex. Shivering
4. Immune
Defends body against microorganisms & viruses
Ex. Fever

7. Feedback Loops
Any homeostatic control system has three functional components: a receptor, a control center, and an effector.
RECEPTORS:
detects a change in some variable in the animal’s internal environment, such as a change in temperature.
CONTROL CENTRE (Integrator):
processes the information it receives from the receptor and directs an appropriate response
EFFECTOR:
Molecule, signal or vessel that directs the change (restores balance)

8. Control systems help maintain homeostasis.
1. sensors gather data
2. control center receives data, sends messages
3. communication system delivers messages to target organs, tissues (EFFECTORS)
4. targets respond to change
pore
sweat
glands
hair
follicle
muscle
goose
bump

9. Negative Feedback Loops
Negative feedback counteracts change as the effector will trigger responses that return conditions to the standard state
In this case, the control center, called a thermostat, also contains the receptor, a thermometer.
When room temperature falls, the thermostat switches on the heater, the effector.

10. Positive Feedback Loops
Positive feedback involves a change in some variable that trigger mechanisms that amplify rather than reverse the change.
For example, during childbirth, the pressure of the baby’s head against sensors near the opening of the uterus stimulates uterine contractions.
These cause greater pressure against the uterine opening, heightening the contractions, which cause still greater pressure.
Positive feedback brings childbirth to completion, a very different sort of process from maintaining a steady state.

11. Positive feedback increases change.

12. Do we always maintain?
Most systems try to maintain a standard range although some regulated change is allowed
Cyclic change: ex. Menstruation cycle in women
Reaction to Challenge: ex. Fever if sick

13. How is Homeostasis Disrupted
Homeostasis can be disrupted for several reasons.
sensors fail
targets do not receive messages
injury
illness
Prolonged disruption can cause injury or severe problems therefore a considerable amount of the energy gained from food is used to maintain an organisms internal environment.