1. 28.2 & 28.3: Homeostasis
Key Concept: Homeostasis is the regulation and maintenance of the internal environment.
Key Concept: Body systems interact to maintain homeostasis

2.
What is homeostasis by the amoeba sisters.
Homeostasis is the regulation and maintenance of a stable internal environment – this includes temperature, fluids, salts, pH, nutrients, and gases.
Homeostasis is maintained through internal control systems that respond to change.

3. Control Systems have 4 parts
1. Sensors, aka receptors, gather information about conditions in & out of the body.
2. Control center, often the brain, receives info from the sensors and compares these values to the ideal values.
If they are out a range, a message is sent through the communication system.
3. Communication system: Communication is controlled by the nervous system and endocrine system which carry messages to all parts of the body and tells them how to respond to changes.
4. Target: Any organ, tissue, or cell that changes its level of activity in response to a message.

4. Control systems work together through feedback
Feedback: Information from sensor that allows a control center to compare current conditions to a set of ideal values.
Feedback loop: Sensorcontrol centertargetsensor….
Negative feedback loops: control system counteracts any change in the body that moves conditions above or below a set point (reversing change to return conditions to their set points)-most functions in the body are regulated this way.
Ex.: Thermostats, holding your breath
Positive feedback loops: Control center uses information to increase rate of change away from set points.
Ex.: Cut finger increases clotting factors in blood.

5. Negative Feedback Loop

6. Negative Feedback Loop

7. Positive Feedback Loop

8. Body systems interact to maintain homeostasis
Example: Thermoregulation – the process of maintaining a
steady body temperature. (Sweating, shivering)
Requires closer interaction of the
respiratory, circulatory, nervous,
and endocrine systems.
Example: Osmoregulation: maintaining the proper water levels. Keeps fluid levels from becoming too concentrated and too diluted. (excretion (urination), sweating, water vapor in breath).

9. Homeostasis can be disrupted for several reasons
Sensors fail to detect changes in internal or external environment
Wrong messages sent or correct ones fail to reach targets.
Serious injuries overwhelm homeostatic mechanisms.
Viruses or bacteria change body’s internal chemistry.
Overview of homeostasis:

10. Homeostasis in Plants
ALL living things must maintain stable internal conditions.
Examples in plants:
Opening & closing of tiny pores called stomata to regulate water loss.
Cacti adaptations:
No leaves: reduced surface area for both thermoregulation and osmoregulation.
Waxy coating retains moisture.
Thick stem acts as water reservoir.