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Learning Outcomes of Session
• Understand the principles of homeostasis
• Describe physiological events under homeostasis control
• Describe the systems involved in homeostasis
• Explore the mechanism of homeostatic control
What is Homeostasis?The traditional spelling of homoeostasisgives us a clue to the word’s meaning
HOMO – the same STASIS – staying
Literally – staying the sameHomeostasis refers to the various mechanisms that
maintain the body’s stable internal environment
Homeostasis‘Maintenance of a constant internal environment
despite fluctuations in the external world’ Walter Cannon
A state of body equilibrium / stable internal environment of the body
Physiological factors under Homeostasis
Can you think of some physiological factors that need controlling?
How homeostasis works
60mmHg
120mmHg
Blood pressure
90 mmHg Mean arterial pressure
Homeostatic control mechanisms
All homeostatic control mechanisms have at least three components:• Receptor• Control centre• Effector
RECEPTOR
Detects stimulus
CONTROLLER
Interprets stimulus and coordinates response
EFFECTOR
Outputs response
1.
Imbalance
2. Change detected by receptor
Control Centre
Receptor Effector
3. Input information 4. Output information
5. Feeds back to the system
Types of Sensory Receptors
Negative Feedback MechanismThis type of feedback system inhibits the direction of the initial inputs
output output
input input
receptor receptor
controller
- -
Positive Feedback Mechanisms
This type of feedback system intensifies the input.
output output
input input
receptor receptor
controller
+ +
Regulatory systems in the bodyEndocrine system Nervous systemAmplitude FrequencyResponse [hormone] Response frequency of APs∝ ∝Slow Rapid
Blo
od [h
orm
one]
(mV)
Time(mins – hrs)
Time(msec – sec)
Water-balance Homeostasis
Water makes up a high proportion (60%) of the adult human body.
Water in the body is distributed between two compartments:
• Intracellular fluid (ICF) - water inside cells
• Extracellular fluid (ECF) - water outside cells.
Homeostasis through the neuroendocrine reflex,maintains body fluid volume, distribution and composition.
Intracellular fluid 66%
Plasma 8%
Interstitial 26%
Extracelllular 34%
blood vessel
red blood cell
Fluid Compartments
Water-balance Homeostasis
Water-balance Homeostasis
• Increased plasma osmolality either due to dehydration, increased salt intake or blood volume stimulated osmoreceptors in hypothalamus
• Hypothalamus generates action potential through the paraventricular and supraoptic nuclei to the posterior pituitary causing the release of ADH
• ADH acts on kidneys to retain water causing decrease in osmolality and increase in blood volume
Cover this in detail during HPA session
• Homeostasis restores any changes to internal environment of the body to equilibrium
• Allows normal function of the human body• Uses the endocrine and nervous system to help
regulate these changes
In Summary
Any Questions
