1. HOMEOSTASIS

2. 2nd Law of Thermodynamics
One of the fundamental laws of nature.
It states that the universe and everything in it is always moving in the direction of increasing disorder
Any Other Examples

3. 2nd Law of Thermodynamics
Yet, life appears to be the exact opposite of this, for life is very organized and living organisms maintain that organization until they die.
This is this property that separates life from non-life.

4. HOMEO – THE SAME, STASIS – TO STAY
The ability of life to maintain a constant, stable, and organized internal environment is called HOMEOSTASIS.
Along with evolution, this is one of the guiding principles of modern biology.

5. Even the simplest life form, an amoeba, maintains a distinctly ordered internal environment separate from its external environment. Why?
The more complex the life form, the more elaborate and efficient are the homeostatic mechanisms they have evolved.

7. In humans, we have (as much as possible) physically separated all of our cells from the external environment; thus, improving the quality of our ‘internal seawater’.
We have evolved ‘physiology’ which allows us to monitor and adjust our internal environment within very narrow parameters.

8. Homeostatic Mechanisms
Sensitive receptors monitor each condition under homeostatic control
For example:
37oC
Blood 120/80
Sugar 0.07%
Osmolarity (salt 0.1M 7

9. 2. These monitors are linked in someway (usually by nerves or hormones) to mechanisms capable of correcting changes in the particular state (ie: warm the body temperature).
3. A linked series (of receptors and corrective mechanisms) is called a FEEDBACK LOOP.

10. Feedback Loops There are two types of feedback loops:
Negative Feedback Loops
Positive Feedback Loops

11. Negative Feedback Loops
This type of a feedback loop occurs where the output from some body system inhibits itself (shuts itself off) at a certain set point.
Example: with both a thermostat in furnace or in the brain (hypothalamus)
When the heat increases, the furnace is shut off
When the heat decreases, the furnace is turned on
In humans temperature homeostasis is controlled by the thermoregulatory centre in the hypothalamus. It receives input from two sets of thermoreceptors: receptors in the hypothalamus itself monitor the temperature of the blood as it passes through the brain (the core temperature), and receptors in the skin monitor the external temperature. Both pieces of information are needed so that the body can make appropriate adjustments. The thermoregulatory centre sends impulses to several different effectors to adjust body temperature:

13. The hypothalamus maintains a set point of 37. 5 ± 0
The hypothalamus maintains a set point of 37.5 ± 0.5 °C in most mammals.
The temperature is regulated within a range determined by a ‘high’ and ‘low’ set point (± 0.5 °C )
Whenever a change occurs in a system, the change automatically causes a corrective mechanism to start, which reverses the original change and brings the system back to normal.

14. How It Works
STIMULUS

15. How It Works
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16. How It Works
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RECEPTOR

17. How It Works
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18. How It Works
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RECEPTOR
REGULATORY CENTER

19. How It Works
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REGULATORY CENTER

20. How It Works
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RECEPTOR
REGULATORY CENTER
EFFECTOR

21. How It Works
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22. How It Works
STIMULUS
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REGULATORY CENTER
RESPONSE
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23. How It Works
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24. How It Works
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RESPONSE
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25. STIMULUS: Body Temperature rises above 37oC
How It Works: an example
STIMULUS: Body Temperature rises above 37oC

26. STIMULUS: Body Temperature rises above 37oC
How It Works: an example
STIMULUS: Body Temperature rises above 37oC

27. STIMULUS: Body Temperature rises above 37oC RECEPTOR: thermoreceptor
How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor

28. STIMULUS: Body Temperature rises above 37oC RECEPTOR: thermoreceptor
How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor

29. How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor
REGULATORY CENTER: hypothalamus

30. How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor
REGULATORY CENTER: hypothalamus

31. How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor
REGULATORY CENTER: hypothalamus
EFFECTOR: smooth muscle in arterioles, sweat glands, muscles in skin, skeletal muscles, and thyroid gland

32. How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor
REGULATORY CENTER: hypothalamus
EFFECTOR: smooth muscle in arterioles, sweat glands, muscles in skin, skeletal muscles, and thyroid gland

33. How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor
REGULATORY CENTER: hypothalamus
RESPONSE: arterioles dilate (blood moves to extremities), sweat, thyroid gland decreases metabolism
EFFECTOR: smooth muscle in arterioles, sweat glands, muscles in skin, skeletal muscles, and thyroid gland

34. How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor
REGULATORY CENTER: hypothalamus
RESPONSE: arterioles dilate (blood moves to extremities), sweat, thyroid gland decreases metabolism
EFFECTOR: smooth muscle in arterioles, sweat glands, muscles in skin, skeletal muscles, and thyroid gland

35. How It Works: an example
STIMULUS: Body Temperature rises above 37oC
RECEPTOR: thermoreceptor
REGULATORY CENTER: hypothalamus
RESPONSE: arterioles dilate (blood moves to extremities), sweat, thyroid gland decreases metabolism
EFFECTOR: smooth muscle in arterioles, sweat glands, muscles in skin, skeletal muscles, and thyroid gland

36. FEVERS
Chemicals called pyrogens are released by white blood cells to raise the set point. This causes body temp. to increase by 2-3 °C.
This helps to kill bacteria (+ white blood cells work best at this temperature) and explains why you shiver even though you are hot.

38. Hibernation
Some mammals release hormones that reduce their set point to around 5°C while they hibernate. This drastically reduces their metabolic rate and so conserves their food reserves.

39. Another Example:
Blood Sugar Control

40. Positive Feedback Loops
This type of a feedback loop occurs when the product of one pathway stimulates or causes another pathway to increase activity.
Example: Labour (the pressure of the babies head on the uterus) stimulates the pituitary gland in the brain to release the hormone oxytocin.
The oxytocin causes the uterus to contract, which leads to increased pressure.
Contractions cause the pituitary to produce more oxytocin and the cycle continues until you give birth.