Homeostasis and Feedback
Homeostasis: Maintaining Limits
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Homeostasis is the maintenance of
relatively stable conditions

Ensures the body’s internal environment
remains steady despite changes both inside
and outside the body
Examples of Maintaining
Homeostasis
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Keeping body temperature around 37oC
Maintaining blood glucose level
Keeping oxygen concentration steady
Dynamic Equilibrium
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Homeostasis can fluctuate over a narrow
range the is compatible with life.
If certain levels fall outside this range for a
prolonged period of time death may result
Control of Homeostasis:
Feedback Systems
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Every body structure contains homeostatic
devices that work to keep the internal
environment within normal limits
2 body systems control most homeostatic
devices (part of the life process called
regulation)
 Endocrine
 Nervous
Nervous Control of Homeostasis

The nervous system detects changes from
the normal state and sends out nerve
impulses to organs to counteract the
change
Endocrine Control of Homeostasis


Corrects changes by secreting chemicals
called hormones into the blood
Hormones affect specific body cells where
they cause responses that restore
homeostasis
Feedback System


AKA feedback loop
Cycle of events in which the status of a
body condition is continually monitored,
evaluated, changed, remonitored, reevaluated and so on…
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Each condition in the body that is
monitored in such a way is called a
controlled condition
Any disruption that causes a change in a
controlled condition is called a stimulus
Components of a Feedback System
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Receptor – monitors change
Control Center – sets a range of
acceptable values, evaluates input from
the receptor and sends output to an
effector
Effector – a body structure that receives
output from the control center and
produces a response or effect that
changes the controlled condition.
Negative Feedback Systems

Reverses the change in a controlled
condition

EX – BP, BGL, HR, Temp
Positive Feedback System

The effector produces a response that
enhances or reinforces the initial change
in the controlled condition.


EX – Childbirth, Ovulation, Blood Clotting
Happens in stimuli that are do not happen
very often
Homeostasis and Disease


If 1 or more components of the body lose
their ability to contribute to homeostasis,
the normal balance among all the body’s
processes may be disturbed.
This may result in a disease, disorder or
even death
Disorder

Any disturbance of the structure or
function of the body
Disease

A more specific term for an illness that is
characterized by a specific set of signs
and symptoms
Symptoms

Subjective changes in body function that
are not apparent to an observer

Ex – nausea or headache
Signs

Objective changes that a clinician can
observe and measure

Ex – bleeding, swelling, fever, rash
Infectious disease

Pathogens invade a host and cause a
disease
Local Disease

Affects one part or region of the body
Systemic Disease

Affects several body parts or the whole
body
Pathology

The science that deals with the nature,
causes and development of abnormal
conditions that occur from the disease
process
Epidemiology

The science that deals with the why, when
and where diseases occur and how they
are transmitted in a human community
Pharmacology

The science that deals with the effects and
uses of drugs in the treatment of disease
Diagnosis

The identification of a disease or disorder
based on a scientific evaluation of a
patient’s signs and symptoms, medical
history, physical examination and
sometimes lab tests
Aging and Homeostasis

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Aging is a normal process characterized
by a progressive decline in the body’s
ability to restore homeostasis.
Produces observable changes in structure
and function and increases vulnerability to
stress and disease