denny agustiningsih dept. of physiology. concept of homeostasis was formulated by a french...
TRANSCRIPT
Concept of homeostasis was formulated by a French Physiologist Claude Bernard in 1865
He noticed that La fixité du milieu intérieur est la condition de la vie libre (it is the fixity of milieu intérieur which is the condition of free and independent life)
WHAT IS HOMEOSTASIS
From Greek words
Homeo= same Stasis= to stand
or stay Term proposed
by American Physiologist Walter B Cannon, 1933
WHAT IS HOMEOSTASIS
BASIC CELL FUNCTIONS Sensing and responding to changes in
surrounding environment Control exchange of materials between
cell and its surrounding environmentObtain nutrients and oxygen from surrounding
environmentEliminate carbon dioxide and other wastes to
surrounding environment Perform chemical reactions that provide
energy for the cell Synthesize needed cellular components
HOMEOSTASIS
Homeostasis involves dynamic
mechanisms that detect and respond to
deviations in physiological variables from
their “set point” values by initiating
effector responses that restore the
variables to the optimal physiological
range.
MAINTENANCE OF HOMEOSTASIS Nervous system
Controls and coordinates bodily activities that require rapid responses
Detects and initiates reactions to changes in external environment
Endocrine systemSecreting glands of endocrine regulate
activities that require duration rather than speed
Controls concentration of nutrients and, by adjusting kidney function, controls internal environment’s volume and electrolyte composition
INTERNAL COMPONENTS OF HOMEOSTASIS
Concentration of oxygen and carbon dioxide
pH of the internal environment
Concentration of nutrients and waste products
Concentration of salt and other electrolytes
Volume and pressure of extracellular fluid
CONTROL OF HOMEOSTASIS
Homeostasis is continually being disrupted byExternal stimuli
heat, cold, lack of oxygen, pathogens, toxins
Internal stimuli Body temperature Blood pressure Concentration of water, glucose,
salts, oxygen, etc. Physical and psychological
distresses Disruptions can be mild to
severe If homeostasis is not maintained,
pathological condition even death may result
HOMEOSTATIC CONTROL SYSTEMS In order to maintain homeostasis,
control system must be able toDetect deviations from normal in the
internal environment that need to be held within narrow limits
Integrate this information with other relevant information
Make appropriate adjustments in order to restore factor to its desired value
CONTROL MECHANISMS IN HOMEOSTASIS
The organs and tissues which maintain homeostasis are called control systems.
Autoregulation (local control) when cells, tissues, organs or systems automatically
change in response to signals within themselves. Intrinsic control
controls that generate a response to change that built into the organ.
Extrinsic control changes stimulated by signals from outside of the cell,
organ, or system Mediated by
Nervous system: brain & spinal cord signals cause change; response is rapid but short term.
Endocrine system glands produce hormones that cause changes; response is slower, but lasts longer
HOMEOSTATIC CONTROL SYSTEMS Feedforward - term used for responses
made in anticipation of a change Feedback - refers to responses made
after change has been detectedTypes of feedback systems
Negative Positive
COMPONENTS OF FEEDBACK MECHANISMS Stimulus:
The change from ideal or resting conditions. Receptor:
The cells or tissue which detects the change due to the stimulus
Relay: The transmission of the message, via nerves or
hormones or both, to the effector. Effector:
The cells or tissue, usually a gland or muscles, which cause the response to happen.
Response: An action, at cell, tissue or whole organism level which
would not have occurred in the absence of the stimulus
Feedback: The consequence of the response on the stimulus. May be positive or negative.
NEGATIVE FEEDBACK
A REGULATORY MECHANISM IN WHICH A CHANGE IN A CONTROLLED
VARIABLE TRIGGERS A RESPONSE THAT OPPOSES THE CHANGE.
NEGATIVE FEEDBACK Most common homeostatic feedback
mechanism responses that resists any change from normal range.
Restoration of homeostasis because Negative feedback causes action that a value is falling
too low. Negative feedback causes action that a value is rising
too high. Values fluctuate within Set limits, Values change from hour to hour, sometimes
with regular diurnal cycles ( circadian rhythms). Elevated or reduced changes are corrected
before they become too extreme. Can continue forever Maintains homeostasis
EXAMPLE: body temperature - Set point = 37 C, 98.6 F
Normal limits 36.5-37.5 C, 97.7-99.5 F
Examples:.Body Temperature – Nervous System.Blood Calcium Levels – Endocrine System
When blood calcium level drops, parathyroid glandssense that and secrete hormones that cause releaseof calcium stores from bone. Blood calcium levelsreturn to normal, secretion stops.
HOMEOSTASIS OF BLOOD PRESSURE
Baroreceptors in walls of blood vessels detect an increase in BP
Brain receives input and signals blood vessels and heart
Blood vessels dilate, HR decreases
BP decreases
POSITIVE FEEDBACK
A REGULATORY MECHANISM IN WHICH THE RESPONSE TO A
STIMULUS, IN A CONTROL SYSTEM, CAUSES THE CONTROLLED VARIABLE
TO MOVE FARTHER FROM THESET POINT.
POSITIVE FEEDBACK Rare homeostatic feedback
mechanism The response enhances the
original stimulus Positive feedback promotes
changes that are developing, so they become more extreme
Positive feedback causes action that a value is falling causing it to fall farther.
Positive feedback causes action that a value is rising causing it to rise higher.
Positive feedback in disease - ex. Hypothalamus increases set point. Development of a fever.
Examples:.Hemorrhage.Childbirth.Lactation
POSITIVE FEEDBACK Unstable system It is used to trigger a sudden event or
phenomenon Can not continue forever, always has a
limit Does not result in homeostasis Beneficial only in special circumstances
Example in childbirth, stretching of uterus elicits production of hormones that stimulate contraction of uterine muscles; this leads to more stretching of uterus, more hormone secretion, more muscle contractions; loop is broken upon birth of a baby
POSITIVE FEEDBACK DURING CHILDBIRTH Stretch receptors in walls of uterus send
signals to the brain Brain induces release of hormone (oxytocin)
into bloodstream Uterine smooth muscle contracts more
forcefully More stretch, more hormone, more
contraction etc. Cycle ends with birth of the baby & decrease
in stretch