1. * Maintaining of a stable internal environment
Homeostasis
* Maintaining of a stable internal environment
Homeostasis must be maintained for normal body functioning and to sustain life
Homeostatic imbalance – a disturbance in homeostasis resulting in disease
“physiological normal”
involves maintaining the volume and composition of body fluids
intracellular (ICF)
extracellular (ECF)

2. Homeostatic Control Mechanisms
COMPONENTS
receptor
monitors changes
input to control center
control center
evaluates input and generates output
effector
receives output from control center
produces a response

3. Homeostatic Control Mechanisms
continually disrupted by internal and external environments
balance regulated by
nervous
action potentials
rapid
endocrine
hormones
slow

4. Homeostatic Control Mechanisms
Control center
The hypothalamus
detects the deviation
from the set point and
signals effector organs.
Receptors
Thermo receptors
send signals to the
control center.
Effectors
Skin blood vessels
dilate and sweat glands
secrete.
Stimulus
Body temperature
rises above normal.
Response
Body heat is lost to
surroundings, temperature
drops toward normal.
too high
Normal body
temperature
37°C (98.6°F)
too low
Response
Body heat is conserved,
temperature rises toward normal.
Stimulus
Body temperature
drops below normal.
Receptors
Thermoreceptors
send signals to the
control center.
Effectors
Skin blood
vessels constrict
and sweat glands
remain inactive.
Effectors
Muscle
activity
generates
body heat.
Control center
The hypothalamus
detects the deviation
from the set point and
signals effector organs.
If body temperature
continues to drop,
control center signals
muscles to contract
Involuntarily. 4

5. Homeostatic Control Mechanisms
Negative feedback summary:
Prevents sudden, severe changes in the body
Reduces the actions of the effectors
Corrects the set point
Causes opposite of bodily disruption to occur, i.e. the ‘negative’
Limits chaos in the body by creating stability
Most common type of feedback loop
Examples: body temperature, blood pressure & glucose regulation

6. Homeostatic Control Mechanisms
Positive feedback summary: Increases (accelerates) the actions of the body. Positive feedback mechanisms are short-lived . Examples: blood clotting and child birth

7. The Body’s Environment
Interior of body separated from external environment by a layer of epithelial tissue
Lumen of respiratory system, gastrointestinal system, and urinary system are part of external environment
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8. Body fluid compartments
Two main compartments
Intracellular
Extracellular.
Extracellular composed of two sub compartments.
Blood plasma
Interstitial fluid (between cells/ within tissues).
Also considered part of the interstitial fluid are lymph, cerebrospinal fluid, humors of the eye, synovial fluid, serous fluid in pericardial, pleural and peritoneal spaces and secretions of the gastrointestinal tract. These are referred to as Transcellular fluids

9. Body fluid compartments

10. Body Fluid Compartments
Figure 1.5
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11. Fluid movement between compartments.
There is a continuous exchange and mixing of body fluids between fluid compartments.
This is regulated by osmotic and hydrostatic pressures.
Water can move freely between compartments along osmotic gradients.
Solutes are unequally distributed because of their size, electrical charge, or dependence on transport proteins.

12. Water balance
Homeostasis is the combination of processes occurring within the body facilitating maintenance of the composition of interstitial fluid .
For the body to remain properly hydrated, water intake must equal water output.
These processes ensure a constancy within the body internal environment.
Maintenance of homeostasis includes two major tasks:
Maintaining water balance within the cells (ICF). This ensures adequate functioning of cells.
Maintaining water balance in the plasma. This ensures the tissues of the body are adequately perfused.
Both are achieved by maintaining the correct level of water in the ECF.

13. Water balance Feedback mechanisms that facilitate maintenance of a stable internal environment.

14. Water balance
The influence of ADH

15. Disorders of water balance: Dehydration.
Results in body water which leads to plasma osmolarity.
Water moves from intracellular space to extracellular spaces.
Cells dehydrate.
Cell functioning impaired

16. II. Homeostasis: A Central Organizing Principle of Physiology
Negative Feedback Controls and
Thermoregulation
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17. Negative Feedback Control in Homeostasis
Primary mechanism for maintaining homeostasis.
External change  triggers change in regulated variable in internal environment  triggers reaction to oppose the change and return regulated variable toward normal (set point)
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18. Negative Feedback Mechanisms
Set point = desired level of regulated variable
Sensors detect level of regulated variable and provide input to integrating center
Integrating center compares set point to actual level of regulated variable
Error signal = difference between actual level and set point
Integrating center sends output to effectors to return regulated variable toward set point
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19. Negative Feedback Control of Body Temperature
Figure 1.6c, d
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20. Negative Feedback Loop
Figure 1.7
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21. Positive Feedback Loop
Positive feedback loops cause a rapid change in a variable.
Figure 1.8
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22. Thermoregulation
Homeothermic animals – regulate body temperature within a narrow range
Poikilothermic animals – do not regulate body temperature
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23. Homeothermic Animals Normal body temperature = set point
Differs in animal species
Humans: 37oC (98.6oF)
Hypothermia = decrease in body temperature
Hyperthermia = increase in body temperature
above 41oC, dangerous
above 43oC, deadly
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24. 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
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25. Components of Thermoregulatory System
Thermoregulatory system maintains core body temperature
Detectors - thermoreceptors (central and peripheral)
Integrator - hypothalamus
Effectors - sweat glands, blood vessels in skin, skeletal muscles
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26. Thermoneutral Zone
Range of outside temperature where alterations in blood flow alone regulates body temperature oC
Body temperature increase:blood flow to skin increases
Body temperature decrease:blood flow to skin decreases
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27. Thermoregulation Figure 1.9c
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28. Fever Fever accompanies infections White blood cells secrete pyrogens
Body temperature set point increases
Fever enhances immune response
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