Download Module 7 / Introduction to Homeostasis

- [ S IGN IN ]
Anatomy & Physiology (Open + Free)
Sy lla bu s
Unit 3:: Homeostasis
Hom eostasis and Feedback
Loops
Module 7 /
| Ou t lin e
| Help
|
Mor e
This course is not led by an instructor
Hom eostatic Maintenance
Integration of Sy stem s
Search this course
Introduction to Homeostasis
Define hom eostasis and describe
the m ultiple lev els of
hom eostatic m aintenance in
phy siology .
Homeostasis relates to dynamic physiological processes that help us maintain a stable internal environment.
Homeostasis is not the same as equilibrium. Equilibrium occurs when everything is equal: add milk to the
coffee and eventually, when equilibrium is achieved, all of the coffee will be the same color. Homeostasis,
however, is the mechanism by which internal variables are kept at or near values appropriate to the system.
Consider that when the temperature drops, the body does not just "equilibrate" with (become the same as)
the environment. Multiple systems work together to help maintain the body’s temperature: we shiver, blood
flow is altered, and our brain says “get out of the cold.”
Many conditions and diseases result from altered homeostasis. This section will review the terminology, and
explain the physiological mechanisms, that are associated with homeostasis. We will discuss homeostasis in
every subsequent system. Many aspects of the body are in a constant state of change—blood flows, that rate
at which substances are exchanged between cells and the environment, and the rate at which cells are
growing, dividing, and dying are all examples. But these changes actually contribute to keeping many of the
body's variables, and thus the body's overall internal conditions, within relatively narrow ranges. For
example, blood flow will increase to a tissue when it becomes more active. This is done to ensure that the
tissue will have enough oxygen to support its higher level of metabolism. Maintaining internal conditions in
the body is called homeostasis (from homeo-, meaning similar, and stasis, meaning standing still). The
root "stasis" of the term "homeostasis" may seem to imply that nothing is happening. But if you think about
anatomy and physiology, even standing still requires a lot of effort. Stabilizing muscles hold you upright, and
your brain incorporates information from your tendons, inner ear and eyes to maintain balance. If you think
that it’s easy to stand still, look at a baby who is just learning to stand. Similarly, the process of homeostasis is
an active process to maintain the ‘same-ness’ of our body processes.
homeostasis
(definition) Homeostasis is the tendency of biological systems to maintain relatively constant
conditions in the internal environment while continuously interacting with and adjusting to
changes originating within or outside the system.
EXAMPLE
Exercise
We can consider the maintenance of homeostasis on a number of different levels. For example, consider
what happens when you exercise. At the whole-body level, you notice some specific changes: your
breathing and heart rate increase, your skin may flush, and you may sweat. If you continue to exercise,
you may feel thirsty. These effects are all the result of your body trying to maintain its internal balance:
62
Your muscle cells use oxygen to convert the energy stored in glucose into the energy stored in ATP
(adenosine triphosphate), which they then use to drive muscle contractions. When you exercise, your
muscles need more oxygen. Therefore, to maintain an adequate oxygen level in all of the tissues in
your body, you breathe more deeply and at a higher rate when you exercise. This allows you to take
in more oxygen. Your heart also pumps faster and harder, which allows it to bring more oxygenated
blood to your muscles and other organs that will need more oxygen.
As your muscles carry out cellular respiration to release the energy from glucose, they produce
carbon dioxide and water as waste products. These wastes must be eliminated to help your body
maintain its fluid and pH balance. Your increased breathing and heart rates also help eliminate a
great deal of carbon dioxide and some of the excess water.
Your muscles use the energy stored in ATP molecules to generate the force they need to contract. A
byproduct of releasing that energy is heat, so exercising increases your body temperature. To
maintain temperature balance, your body compensates for the extra heat by causing blood vessels
near your skin to dilate and by causing sweat glands in your skin to release sweat. These actions
allow heat to more easily dissipate into the air through evaporation of the water in sweat into the air.
As you exercise for longer periods of time, you lose more and more water and salts to sweat (and, to
a smaller extent, from breathing more). If you exercise too long, your body may lose enough water
and salt that its other functions begin to be affected. Low concentrations of water in the blood prompt
the release of hormones that make you feel thirsty. Your kidneys also remove less water from urine if
your fluid levels are low. These actions help you maintain fluid balance.
Open Learning Initiativ e
Unless otherwise noted this work is licensed under a Creativ e Com m ons Attribution 3 .0 Unported License.
62