1. HOMEOSTASIS
How does the body maintain body temperature, blood calcium or glucose levels, or the right amount of water?

2. Factors in the external environmental may change but body parts function best when internal conditions are maintained within a range
Ex: Oxygen levels, glucose levels, pH, temperature
Homeostasis - Maintenance of a stable internal environment (around a set point)
In general, organ systems participate in a negative FEEDBACK LOOP designed to maintain the status quo of internal environment

4. 3 Components of a feedback system:
Receptor: provide information about specific conditions in the internal environment (e.g. body temperature)

5. 3 Components of a feedback system:
Control Center – Maintains a “Set Point”: Compare current value to set point value (normal body temp: 37ºC or 98.6ºF); Send message to correct.

6. 3 Components of a feedback system:
Effectors: cause responses that alter conditions in the internal environment (always a muscle or a gland – ex: muscles cause shivering/goosebumps or sweat glands release sweat)

8. Types of Feedback Loops
1) Negative feedback loop: maintains homeostasis!
Prevents sudden, severe changes in the body
Corrects the set point
Causes opposite of bodily disruption to occur, i.e. the ‘negative’ of the disruption
Most common type of feedback loop
Examples: body temperature, blood pressure & glucose regulation

9. **Negative feedback maintains HOMEOSTASIS!**
Change in internal environment
Receptor
Set point in Control Center
Effectors
Oxygen level in blood decreases due to exercise
Cells in carotid artery detect levels of oxygen in blood
Medulla (in the brain stem) recognizes that oxygen levels are too low
Nerve impulses from medulla cause muscles surrounding lungs & diaphragm to contract more often so repiratory rate increases

10. Types of Feedback Loops
2) Positive feedback loop: (moves body away from homeostasis)
Increases (accelerates) the actions of the body
short-lived
do not require continuous adjustments
Examples: blood clotting and child birth

11. POSITIVE FEEDBACK Heightens or elevates a response Example of
childbirth (body needs
to achieve a heightened
state of exertion…
LABOR!)
pressure  uterine  more  more  more etc.
of baby’s contractions pressure contractions pressure
head

12. A more complex feedback loop example: glucose, insulin, & glucagon
You gain glucose through the food that you eat
Digest carbohydrates into glucose and other sugars
Amount of sugar in blood increases

13. Two Hormones Regulate Blood Sugar
High blood sugar - Insulin (protein) stimulates sugar uptake by cells and converts extra glucose into glycogen (stored in your liver); insulin, therefore, decreases your blood sugar level
Like a key that causes the glucose door to open so glucose can leave the blood and enter the cell
Low blood sugar - Glucagon (protein) stimulates the conversion of glycogen back into glucose and therefore, raises your blood sugar level

14. Feedback cycle to control blood glucose levels:
body cells &
liver cells take
up glucose
cells
secrete
insulin
blood glucose
level drops
High glucose
level
Blood Glucose
Level (90 mg/100 mL)
blood glucose
level rises
Low glucose
level
liver cells break
down glycogen
& release glucose
Cells secrete
glucagon

15. Is insulin/glucagon an example of positive or negative feedback?
Homeostasis Video