1) Homeostasis refers to the body's ability to regulate its internal environment to maintain stable conditions, despite changes in the external environment. 2) The concept was first described by Claude Bernard in the 1860s, and the term "homeostasis" was coined by Walter Cannon in 1932 to describe the coordinated physiological processes that maintain steady states. 3) Homeostasis involves negative feedback loops, where a deviation from the normal setpoint is detected by receptors, signaling the control center to activate effectors to correct the deviation and restore the normal condition. Positive feedback also occurs in some cases, like childbirth, to amplify a process.

1. Homeostasis
Roger Watson
Twitter: @rwatson1955

2. Homeostasis
Homeostasis refers to the body's ability to regulate physiologically its
inner environment to ensure its stability in response to fluctuations in
the outside environment.

3. Homeostasis
The concept was first articulated by [Frenchman] Claude Bernard in
1860s

5. Bernard:
‘I think I was the first to urge the belief that animals have really two
environments: a milieu extérieur in which the organism is situated,
and a milieu intérieur in which the tissue elements live.’

6. Homeostasis
Term coined by Walter Cannon (1932)

8. Cannon:
The coordinated physiological processes which maintain most of the
steady states in the organism are so complex and so peculiar to living
beings--involving, as they may, the brain and nerves, the heart, lungs,
kidneys and spleen, all working cooperatively—that I have suggested
a special designation for these states, homeostasis. The word does
not imply something set and immobile, a stagnation. It means a
condition—a condition which may vary, but which is relatively
constant.

9. Bozeman biology You Tube link
Homeostasis

11. Fishbowl Human Body Function
Water Body fluid Internal environment
Glass bowl Skin Barrier (internal vs. external)
Fish Cells Stay alive
Air pump Lungs Keep O2 level constant (high)
Filter Kidneys Keep nitrogen wastes constant (low)
Heater Muscles Keep temperature constant (high)
Feeder Digestive system Keep nutrient levels contant (high)
Everything working together Relatively constant conditions

12. Homeostasis: how does it work?
Feedback:

14. Homeostasis: how does it work?
Feedback:
•Negative
•Positive

15. Negative feedback
Example:
•Thermostat

16. Engineered control system (thermostat) model
Example: thermostatic heating system in a home
Components of an automatic control system
Variable is the characteristic of the internal environment that is
controlled by this mechanism (internal temp in this example)
Sensor (receptor) detects changes in variable and feeds that
information back to the integrator (control center) (thermometer in this
example)
Integrator (control centre) integrates (puts together) data from sensor
and stored "setpoint" data (thermostat in this example)
Setpoint is the "ideal" or "normal" value of the variable that is previously
"set" or "stored" in memory
Effector is the mechanism (furnace in this example) that has an "effect"
on the variable (internal temperature in this example)

20. Components of a negative feedback loop
•Stimulus
•Condition
•Receptors
•Control centre
•Effector
•Response

22. Example: blood pressure control

24. Components of blood pressure negative
feedback loop
•Stimulus drop in blood pressure
•Condition constant blood pressure
•Receptors carotid artery receptors
•Control centre brain
•Effector cardiovascular system
•Response increased blood pressure

25. Positive feedback
Example:
•Audiofeedback

28. Positive feedback
Physiological example:
•Labour in childbirth

30. Labour in childbirth
Foetus's head moves into birth canal (vagina) at start of labour, which
causes the birth canal to stretch beyond its setpoint amount of stretch,
which is detected by sensors (stretch receptors) in the vaginal wall
and fed back to hypothalamus of brain, which releases oxytocin,
which stimulates stronger and more frequent uterine (womb)
contractions, which pushes the foetus, which causes more vaginal
stretch, which produces more oxytocin, and so on -- greatly amplifying
and speeding up labour contractions…until birth!

31. Homeostasis: what goes wrong without it?
JUST ABOUT EVERYTHING!
•Hypothermia
•Diabetes
•Hypo/hyperglycaemia
•Hypo/hypertension
•Haemorrhage
•Acidosis
•Ketosis
•Hypoxia
•Hypercapnia..etc etc

32. Homeostasis: what compromises it?
•Disease
•Neonatal
•Ageing
•Environmental extremes
•Trauma
•Malnutrition
•Drugs/alcohol

33. Homeostasis
Homeostasis refers to the body's ability to regulate physiologically its
inner environment to ensure its stability in response to fluctuations in
the outside environment.

34. Questions
1. Define 'homeostasis'.
2. What are the components of a homeostatic system?
3. Using blood glucose as an example explain how negative feedback
works in the restoration of blood glucose levels after ingesting
carbohydrates.
4. Using blood pressure as an example identify the following: sensor
or receptor; control centre; effector; variable.
5. Using falling blood pressure as an example explain how negative
feedback works.

35. r.watson@hull.ac.uk
Four things about…(a simple approach to
anatomy and physiology)
Homeostasis