1. Balancing the internal environment
Homeostasis
Balancing the internal environment

2. External vs. Internal Environment
What is the difference?

3. External environment:
Your surroundings.
The factors that cause your body to change in order to stay in homeostasis. (Cold outside, working out, bacteria)

4. Internal Environment
Conditions within the fluid surrounding its body cells
Comprised of self-regulating control systems – homeostatic mechanisms

5. Homeostatic Mechanisms
Have three common components:
Receptors –
Set point –
Effectors -
provides information about specific conditions
tells what a particular value should be
Cause the response that alter conditions in the internal environment.

6. Homeostatic Mechanism
Set Point
Control Center
Homeostatic Mechanism
Receptor
Effectors
Stimulus – change in external environment
Response – Change Corrected

7. Negative vs. Positive feedback mechanisms

8. Negative Feedback Systems
There is a change from the set point and negative feedback corrects this change or brings it back to normal.
This correction reduces the action of the effectors until the body is back in homeostasis.

9. WAIT? WHAT? Think of the thermostat in your house..
You set the thermostat to 67o F – this would be the
Your house is warm due to the sun shining on it.
If your house thermometer reads the temperature as 70o F – the thermometer________________ that it is: Or
What do you think the furnace does? There is a choice: or
set point.
senses.
Too hot?
Too cold?
Turns on?
Turns off?

10. WAIT? WHAT? Think of the thermostat in your house..
You set the thermostat to 67o F – this would be the
Your house is cool due to the sun setting
If your house thermometer reads the temperature as 65o F – the thermometer________________ that it is: Or
What do you think the furnace does? There is a choice: or
set point.
senses.
Too hot?
Too cold?
Turns on?
Turns off?

11. Homeostatic Regulation of Body Temperature through Negative Feedback
Your average body temperature is 98.6o F – this would be the
Your body becomes warm sitting in Ms. Neubert’s room.
If your body temperature goes above 98.6o F– the brain________________ that it is: Or
What do you think your body does?
set point.
senses.
Too hot?
Too cold?

12. Answer…
When your body senses that it is too hot the following will most likely happen:
Blood vessels in the skin dilate (blood vessels get larger) allowing heat to be closer to the surface of the skin and thus heat is released.
Nervous system will activate the sweat glands – evaporation of sweat helps to lower the body temperature.
Gradually, your body temperature will return to normal.

13. Homeostatic Regulation of Body Temperature through Negative Feedback
Your average body temperature is 98.6o F – this would be the
Your body is cooled because Ms. Neubert’s room is too cold!
If your body temperature goes below 98.6o F– the brain________________ that it is: Or
What do you think your body does?
set point.
senses.
Too hot?
Too cold?

14. Answer…
When your body senses that it is too cold the following will most likely happen:
Blood vessels in the skin constrict (blood vessels get smaller) allowing heat to be conserved.
Nervous system will activate the skeletal muscles if the body temperature falls lower than normal– shivering helps to raise the body temperature by generating heat.
Gradually, your body temperature will return to normal.

15. Homeostatic Regulation of Body Temperature through Negative Feedback
Heat receptors in the skin
Hypothalamus
Hyperthermia
Stress
Control Center
Sensors
Stress is reduced shutting down mechanism
Increased activity of sweat glands
Perspiration evaporates cooling the skin
Increased blood flow to the skin
Effect
Effectors

16. Homeostasis Using a Neural Pathway
Control center
Many homeostatic mechanisms use a nerve pathway in which to produce their effects. These pathways involve an afferent path which brings sensory messages into the brain and an efferent path which carries outgoing nerve messages to effectors.

17. Positive feedback systems

18. Positive Feedback Systems
Increasing change in the same direction.
Deviation from the set point is accelerated
No correction from the reaction of the effectors
Body will shut down.
however some positive feedback systems work in favor of the body – ie. Childbirth.

19. Positive Feedback Mechanisms Typical Positive Feedback Process
Effector
Intensifies
Sensor
Stress
Control Center

20. Think of your body temperature throughout the day….
Your average body temperature is 98.6o F – this would be the ________________________
Your body becomes hot due to an infection (feverish).
If your body temperature goes above 98.6o F– the brain________________ that it is:
What do you think your body does?
set point.
senses.
Too hot?
Too cold?

21. But what if the effector message does not work?
The fever will cause metabolic functions to change. The body does not cool down and continues to get hotter.
When your body temperature reaches to 113o F, the following will happen:
Death due to cellular proteins breaking down (denaturing) at such high temperatures and metabolism will stop.

22. Think of your body temperature throughout the day….
Your average body temperature is 98.6o F – this would be the _______________________
Your body is cooled because you are stuck outside in the cold weather!
If your body temperature goes below 98.6o F– the brain________________ that it is:
What do you think your body does?
set point.
senses.
Too hot?
Too cold?

23. But what if the effector message does not work?
The extreme cooling of your body will cause metabolic processes to slow down. The body does not warm up and continues to get colder.
When your body senses that it is too cold the following will most likely happen:
The first area to be affected by extreme loss of heat is the brain. You will become disoriented and tired.
Loss of energy will NOT initiate voluntary muscle actions such as shivering to occur.
Eventually your respiratory and cardiovascular systems shut down and ultimately result in death.

24. Homeostatic Regulation of Child Birth through Positive Feedback
Nerve endings in the uterine wall carry afferent messages to the Hypothalamus
Pressure of Fetus on the Uterine Wall
Intensifies
Production and Release of Oxytocin into the Blood
Increasing strength of uterine contractions
The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk letdown and blood clotting.

25. Helpful Effects of Positive Feedback Positive feedback can be helpful
Helpful Effects of Positive Feedback Positive feedback can be helpful. A specific example of these helpful outcomes would be:
Childbirth, where there is an increased release of the hormone oxytocin when the head of the baby presses against the cervical opening in the mother. This pressure stimulates the sensory receptors. Oxytocin stimulates the uterus to contract and will continue to contract when the baby is born.

26. Blood clotting,
where there is a break in the blood vessel wall and bleeding begins to occur. Damage cells release a chemical that initiates the clotting process. These chemicals will continue to be released until the bleeding has stopped.

27. Digestion in the stomach,
where food enters stomach. As more food enters the stomach, the stomach stretches. A stretched stomach releases more pepsinogen. More pepsinogen means more pepsin which then means more protein breakdown. Gastrin levels increase, which control the acid released in the stomach. Thus more secretion occurs, more mucous, more histamine, increased peristalsis and the muscular layer become more active, until the food moves into the intestines.

28. Some examples of what your body can regulate:
Body temperature
Blood pressure
Oxygen needed or Respiration
Heart Rate (or blood delivered to heart)
Glucose level or blood sugar level.

29. Body control center