2. Dr. MUNAZA KHATTAK ASISTANT PROFESSOR PHYSIOLOGY DEPARTMENT PMC
HOMEOSTASIS
Dr. MUNAZA KHATTAK
ASISTANT PROFESSOR
PHYSIOLOGY DEPARTMENT
PMC

3. HOMEOSTASIS Greek word for ‘same’ and ‘steady’
Any process that living things use to actively maintain fairly stable conditions necessary for survival.

4. Homeostasis
Maintenance of nearly constant conditions of internal environment
Maintenance of environment compatible with life
Essential for survival of each cell
Each cell contribute its part in homeostasis

5. The Internal Environment
The internal environment or milieu interieur
-Blood plasma
-Intracellular fluid
-Extracellular fluid
The maintenance of a steady state in these fluids is essential to living things

6. Homeostasis : Terms Set point Expected value of regulated variable
Examples
Core body temperature = 37º C
Blood glucose (sugar) = 100 mg/dL
Blood pH = 7.4
Error signal
Difference between value of set point and regulated variable

8. Homeostasis: Components
Structures enabling homeostasis
Components include
Receptors(sensors that detect stimuli)
Thermoreceptors
Chemoreceptors
Baroreceptors
Integrating Centers
Effectors(Responsible for body responses)
Muscles (smooth, striated, and cardiac)
Glands
Signals

9. Signals
Allow components to communicate
Input signal is from a receptor to an integrating center
Output signal is from an integrating center to an effector
Signals are chemical or via neurons

10. Examples of Homeostasis
Body water regulation by osmoreceptors and kidneys
Excretion of waste products by kidneys and respiration
Temperature regulation
Blood glucose regulation
Constant supply of nutrients
Maintenance of pH

11. Osmoreceptors, sense change in osmotic pressure.
When the osmotic pressure of blood changes (i.e. it is more or less dilute), water diffusion into and out of the osmoreceptor cells changes.
That is, they expand when the blood plasma is more dilute and contract with higher concentration.
This causes an afferent neural signal to be sent to the hypothalamus, which increases or decreases vasopressin (ADH) secretion from the posterior pituitary to return blood concentration to normal.

12. REGULATORY MECHANISM Intrinsic (local)controls
Built in or inherent to an organ e.g CO2 in exercising muscles increase blood flow in the muscle
Extrinsic controls
Initiated outside the organ
Nervous system
Endocrine system

13. Action can be voluntary
1.Drink when thirsty
2.Eat when hungry
3.Put on clothing when cold
4.Open a window when one is too warm
Action can be Involuntary
1.Shivering
2.Sweating

14. SECTIONS OF HOMEOSTASIS
External environment
The Internal environment
Control system

15. Control Systems have two components:
Sensor which detects the change
Effector which corrects the change
Most physiological systems in the body use feedback to maintain the body's internal environment exactly balanced

16. Control of homeostasis
Feedback Systems in Homeostasis
Negative feed back system
Positive feed back system

17. Regulatory Mechanism Negative feed back control
Change in controlled variable triggers a response opposite to the change.
Positive feed back control
Change in controlled variable continues to move in the direction of the change enhancing the change

19. Positive feedback loops cause a rapid change in a variable.

20. Homeostasis: Thermoregulation
Core body temperature
Humans: 37º C (98.6º F)
Hypothermia = decrease in body temperature
Hyperthermia = increase in body temperature
Above 41º C is dangerous
Above 43º C is deadly

21. Mechanisms of heat transfer between body and external environment
Radiation—thermal energy as electromagnetic waves.
Conduction—thermal energy through contact.
Evaporation—heat loss through evaporation of water
Insensible water loss
Sweating
Convection—heat transfer by movement of fluid or air

22. Thermoregulation: Components
Receptors = thermoreceptors
Central: found in CNS (hypothalamus)
Peripheral: found in PNS (mainly skin)
Effectors
Glands: sweat glands
Muscles: skeletal muscles, and smooth muscle of cutaneous blood vessels

23. Thermoregulation: Components
Integrating center
Thermoregulatory center in hypothalamus
Signals
Nerve impulses via neurons
Chemicals via hormones

24. Thermoneutral Zone
Range of outside temperature where alterations in blood flow alone regulates body temperature—25-30ºC
Body temperature increase
Blood flow to skin increases
Body temperature decrease
Blood flow to skin decreases

25. Negative feedback control of body temperature

26. Thermoregulation

27. FEVER Rise in core body temperature Accompanies infection
White blood cells secrete pyrogens
Body temperature set point increases
Fever enhances immune response

28. Feedback Systems in Homeostasis
Negative feedback
Used by most of the body's systems
The response caused by the feedback is opposite to the change (stimulus).
↑ Thyroxin → → → → ↓ TSH → ↓ Thyroxin
↓ Thyroxin → → → → ↑ TSH → ↑ Thyroxin

29. -ve feed back control of thyroxin

30. Feedback Systems in Homeostasis
Positive feedback
Control is used in some cases.
The response caused by the feedback is in the direction of the change (stimulus).
Input increases or accelerates the response.

31. Labor
Oxytocin →↑ uterine contraction →↑Oxytocin

32. Pathophysiology Disruption of Homeostasis Disease
Failure of homeostasis
Death

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