Week 4 – Homeostasis 1
Homeostasis – the condition of equilibrium in the body’s internal environment due to the constant interaction of
the body’s many regulatory processes
The body’s equilibrium shifts among points in the narrow range that is required to maintain life
Example: blood glucose level normally stays between 70 to 110 mg of glucose per 100 mL of blood
Every structure contributes in some way to homeostasis
Homeostasis and Body Fluids
Maintain composition and volume of body fluids is important for homeostasis.
Body fluids – dilute, watery solutions containing dissolved chemicals found inside and outside cells
Body fluids - dilute,
chemicals that are found
inside and outside of cells
Extracellular fluid (ECF) - Intracellular fluid (ICF) -
fluid outside cells fluid within cells
Interstitial fluid (ISF) - ECF
that fills narrow spaces ECF differs depending on
between cells of tissues where it is in the body.
Plasma, CSF, synovial fluid,
aquaous humor, vitreous
Proper functioning of body cells depends on the regulation of ISF around them.
Interstitial fluid “body’s internal environment”
Composition of ISF changes as substances move back and forth between it and plasma
o Occurs in the smallest blood vessels blood capillaries
o Provides needed materials (like glucose, O ,2ions, etc) to tissue cells
o Removes wastes like CO fro2 ISF Week 4 – Homeostasis 2
Control of Homeostasis
Homeostasis is continually disturbed.
o External environment (physical insults) – intense heat, lack of oxygen
o Internal environment – low blood glucose level
o Psychological stresses from our social environment – demands of work and school
Most disruptions are mild/temporary, and body cells quickly restore balance in the internal environment.
Some disruptions are intense/prolonged (like overexposure to temperature extremes, a severe infection,
or major surgery)
The nervous system and endocrine system are the “regular” systems used in homeostasis, whether they work
together or independently.
Nervous system – sends nerve impulses (action potentials) to organs that counteract changes
o Rapid changes
Endocrine system – includes glands that secrete hormones into the blood
o Slower changes
Both means work toward the same end, usually through negative feedback systems.
Feedback Systems – a cycle of events in which the status of a body condition is monitored, evaluated,
changed, remonitored, reevaluated, and so on.
Each monitored variable (like blood pressure or body temperature) = controlled condition
Disruption that changes a controlled condition = stimulus
A feedback loop consists of a receptor, a control center, and an effector
HOMEOSTASIS homeostasis by
that bring about
a response that Controlled
alters the condition or
controlled variable that is
condition monitored by...
center that send an INPUT