1. Introduction to Homeostasis

2. Homeostasis Homeostasis maintaining internal balance in the body
organism must keep internal conditions stable even if environment changes
also called “dynamic equilibrium” or “steady state”
example: body temperature
humans:
too cold = shiver
too warm = sweat
lizard:
too cold = bask in sun
too warm = hide in shade

3. Regulation How we maintain homeostasis nervous system endocrine system
nerve signals control body functions
endocrine system
hormones
chemical signals control body functions

4. Hormones Why are hormones needed?
chemical messages from one body part to cells in other parts of body
communication needed to coordinate whole body
growth hormones

5. What do they do? Maintain homeostasis Start a new process
Body Temperature
Maintain homeostasis
blood sugar level
temperature control
Start a new process
growth
fetal development
sexual development

6. Homeostasis
To maintain a steady state our body uses feedback regulation.

7. Homeostasis
Our bodies contain several kinds of cells all with their own specific functions.
For all of them to work cooperatively they require a relatively constant environment.
Such things as pH, O2 concentration, glucose and chemical concentrations, and temperature must be maintained within a very narrow range (set points).
Specific limits are necessary for survival.

8. Homeostasis
Recall; the ongoing exchange between cells and their surrounding ECF (extra cellular fluid)
Nutrients
Gases
Wastes
Heat
Cells are always attempting to maintain homeostasis so that they can function optimally.

9. Homeostasis
Our ‘set points’ mark the upper and lower limits of our tolerance for survival.
Feedback regulation – a regulatory mechanism whereby a biochemical pathway is regulated by the amount of the product produced by that pathway,

10. Positive Feedback
Positive feedback loops are rare. They are usually associated with disease and abnormal functioning.

11. General Control System
Afferent
Carrying toward. Vein = blood toward the heart, Nerve that carries impulses toward the central nervous system
Efferent
Carrying away. Artery = blood away from the heart, Nerve that carries impulses away from the central nervous system

12. Positive Feedback Example: Labour (child birth)
contraction – disturbance in normal body function they are maintained & prolonged by oxytocin (hormone)
hypothalamus (in brain) releases oxytocin as long as the baby’s head is exerting pressure on the birth canal
after birth, no pressure, therefore oxytocin is no longer released (slows) and contractions stop

13. Negative Feedback Response to changed body condition
if body is high or low from normal level
signal tells body to make changes that will bring body back to normal level
once body is back to normal level, signal is turned off

14. Maintaining homeostasis
hormone 1
gland
lowers body condition
high
specific body condition
low
raises body condition
gland
Negative Feedback Model
hormone 2

15. Example 1: Blood Sugar
Body’s attempt to maintain a balance in glucose level
high blood sugar levels stimulate the pancreas to release insulin into the blood, therefore glucose enters body cells & Liver (glycogen)
now low blood sugar levels cause release of glucagon (from the pancreas) and glycogen (from the liver), therefore blood sugar levels rise again

16. Regulation of Blood Sugar
Endocrine System Control
Feedback
Regulation of Blood Sugar
islets of Langerhans beta islet cells
insulin
body cells take up sugar from blood
liver stores glycogen
reduces appetite
pancreas
liver
high
blood sugar level
(90mg/100ml)
low
liver releases glucose
triggers hunger
pancreas
liver
islets of Langerhans alpha islet cells
glucagon

17. Thermoregulation
Thermoregulation is the maintenance of body temperature within a range that enables cells to function efficiently.

18. Thermoregulation
Invertebrates and most fish, amphibians, and reptiles, are referred to as ectotherms. These animals depend on air temperature to regulate metabolic rates.
Some of these animals have adapted specific habits like sunning themselves on rocks or hiding in the shade to help them regulate their temperature.

19. Thermoregulation
Mammals and birds are referred to as endotherms; they are able to maintain a constant body temperature regardless of their surroundings.
Endotherms adjust to decreases in environmental temperatures by increasing the rate of cellular respiration to generate heat.

20. Thermoregulation The hypothalamus is the body’s internal thermostat.
The hypothalamus region of the vertebrate’s brain responsible for coordinating many nerve and hormone functions.

21. Controlling Body Temperature
Nervous System Control
Feedback
Controlling Body Temperature
nerve signals
hypothalamus
sweat
dilates surface blood vessels
high
body temperature
(37°C)
low
hypothalamus
constricts surface blood vessels
shiver
nerve signals

22. Sending Signals
Signals, in response to stimuli, can be sent in 2 different ways
Fast – transient – via the nervous system
Slow – persistant – via the endocrine system (hormones – chemical signals)

23. Negative Feedback Negative feedback
every time body is high or low from normal level a signal tells the body to make changes that will bring body back
body temperature
control of blood sugar