1. Homeostasis

2. Homeostasis is like your home’s thermostat
Thermostat’s set point is 75ºF
heat
Inside temperature =
75ºF
74ºF
73ºF
72ºF

3. Defined: Process where the body maintains a constant internal environment
Importance: Internal reactions & enzymes work best in specific conditions
Control systems adjust to internal/external changes
Changes controlled: pH, temp, fluids

4. Control Systems Sensors (aka: receptors)
!*%!?%&#
Sensors (aka: receptors)
Gather information about the body and external environment
Ex: skin senses pressure
Communication Center
Messages sent throughout the body to respond
Ex: Impulse travel through your nerves
Control Center
Receives information from the sensors
Ex: Brain interprets the impulse
Targets
Body part that changes its activity
Ex: Muscles in foot stretch/contract abruptly

5. Negative Feedback Loops
Regulates most of the body
Reverses any change that moves conditions from a set point
Ex: if your temp drops…you will shiver to generate heat
97.5
97.7
98.4
98.6
97.2
98.1
97.2
98.4
98.6
98.1
97.7
97.5
96.8

6. Negative Feedback Loops
Regulates most of the body
Reverses any change that moves conditions from a set point
Ex: if your temp drops…you will shiver to generate heat
Ex: If your temp rises…you will sweat to cool down
99.5
99.2
98.8
98.6
99.7
99.7
98.6
98.8
99.2
99.5
100.1

7. Negative Feedback Loop: Cold Response

8. Negative Feedback Loop: Breathing

9. Positive Feedback Loop
Increases the changes away from set points
Important when rapid change is needed
Ex: Pregnancy contractions
Uterus contractions begin slowly
Oxytocin released to speed up the contractions
Negative feedback would reverse and stop the contractions. But if the contractions stopped, would the baby be delivered?
Ask yourself…
If this was negative feedback, what would happen next?
So how will the body respond to the contractions if it’s positive feedback?

10. Positive Feedback Loop
More examples…
Growth hormones stimulate cell division
Torn vessel stimulates release of clotting factors
platelets
fibrin
white blood cell
red blood cell
blood vessel
clot

11. Working Together Thermoregulation: Maintenance of body temperature
Skin (sensors): sensors detect cold
Nervous system (communication system): electrical impulse sent to brain
Hypothalamus (endocrine system) in brain (control center): releases hormones into blood stream
Muscles (target) : Hormones cause shivering

12. Homeostasis disruption
Beck Weathers, thought to be dead, survived a night exposed to Mt. Everest cold.
Some disruptions are temporary
Infections, fever, sore throats, muscle soreness
Some disruptions are too great for your body to control
Frost bite: Sensors are destroyed
Paralysis: Messages from brain can’t reach target
Can lead to death

13. Diabetes Defined: Inability to control blood sugar Normally
Glucose in blood rises after meals
Pancreas releases insulin
Cells remove the glucose
Type 1
Immune system destroys pancreas cells
Pancreas unable to make insulin
Blood pH decreases as glucose builds up
Type 2
Pancreas does not make enough insulin
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
insulin
insulin
insulin
insulin
insulin
insulin
insulin
glucose
glucose
glucose
glucose

14. Review Define homeostasis.
Name and describe the four parts of the “control system.”
What is negative feedback?
What is positive feedback?
Is the following example positive or negative feedback?
During heavy exercise your body loses water when you sweat. As a result of water loss, your body redirects the remaining water inside your body to vital parts of your body to replenish these vital organs.
What is diabetes?
Which organ releases insulin?
How does Type I and Type II diabetes differ?
What happens when blood glucose levels are too high ?