1. HOMEOSTASIS

2. Survival Needs water food oxygen heat pressure
Life depends on five environmental factors
water
food
oxygen
heat
pressure

3. Survival Needs Food Water - most abundant substance in body
- required for metabolic processes
- required for transport of substances
- regulates body temperature
Life depends on the availability of certain things.
60 – 80 % of body weight is water, it is the most abundant chemical found in the body
Water is required for metabolic reactions, for transport of substances, for temperature regulation
Food provides the chemicals needed for energy and the raw materials for building new living matter
Food
- provides necessary nutrients
- supplies energy
- supplies raw materials

4. Survival Needs Oxygen (Gas) Heat Pressure
- one-fifth of air
- used to release energy from nutrients
Heat
- form of energy
- partly controls rate of metabolic reactions
Oxygen is a key component in those chemical reactions of metabolism, it release energy from food
Heat is a byproduct of metabolism, it controls the rate at which chemical reaction take place in the body
Pressure is the force that helps move air or fluids within the body, Atmospheric pressure helps breathing and Hydrostatic pressure helps blood movements
Pressure
- application of force on an object
- atmospheric pressure – important for breathing
- hydrostatic pressure – keeps blood flowing

5. Homeostasis Maintenance of a stable internal environment
Blood pressure
Temperature
Hydration
Sugar level
Homeostatic imbalance – a disturbance in homeostasis resulting in disease
Homeostasis must be maintained for normal body functioning and to sustain life
Why is a stable internal environment important?
Body parts function only when the concentration of water, nutrients and oxygen and the conditions of heat and pressure remain with certain
narrow limits
What sorts of things need to be controlled or regulated in order to maintain a stable internal environment?
temperature; BP; sugar levels; hydration;
There are mechanisms in place that help maintain homeostasis.
What is the result of not maintaining homeostasis? 5

6. Feedback Mechanisms Negative feedback
Includes most homeostatic control mechanisms
Shuts off the original stimulus, or reduces its intensity
Works like a household thermostat
Many of the homeostatic controls are negative feedback Mechanisms 6

7. Monitor aspects of the internal environment and corrects any changes
Homeostatic Mechanisms
Monitor aspects of the internal environment and corrects any changes
Receptors - provide information about stimuli
Control center - tells what a particular value should be (includes a set point)
Effectors - elicit responses that change conditions in the internal environment

8. The body communicates through neural and hormonal control systems
Receptors provide information about specific conditions in the internal environment
This information is sent to the control center where it is compared to the set point which is what the particular value should be for example
What is the set point on body temperature in humans? – 98.6F
Effectors are what causes responses that alter conditions in the internal environment
What is an example of an effector that might alto the body temperature? – infection, hypothermia
In maintaining homeostasis the feedback to the control center is triggered by changes away from the set point

9. Feedback Mechanisms STIMULUS: DECREASE IN EXTERNAL TEMPERATURE
CONTROL CENTER
RECEPTOR
EFFECTOR
RESPONSE

10. Feedback Mechanisms Positive Feedback
Increases the original stimulus to push the variable farther
In the body this occurs only in blood clotting and child birth
In childbirth it this mechanism is necessary because labor must continue and its intensity increase in order for the uterus to expel the baby
And we all want our blood to continue to clot and stay clotted when we are bleeding so this stimuli also needs to be increased. 10

11. The calcium in the blood should be in the range of 9-11 mg per 100 ml when the calcium level goes above this normal range a signal is sent to the thyroid gland to produce more calcitonin which removes calcium from the blood and puts it in the bone.
If the calcium level in the blood drops below this normal range then the parathyroid glands release the hormone PTH which will remove calcium from the bones and put it into the blood.
In this way the balance of calcium in the blood remains consistent – homeostasis is maintained