Unit Overview: Defining Homeostasis, what it is, and how it effects the body.

1. Homeostasis was first coined by the American physiologist Walter Cannon in 1932.

Definition: Homeostasis is the ability for the body to regulate its inner environment to ensure stability no matter what is happening in the outside environment.2.

Homeostasis controls many functions like blood pressure, body temperature, respiration rate, and blood glucose levels which are maintained within a range of normal values around a set point despite constantly changing external conditions.

For example the pH of the blood. If the pH is too high (above 7.4), the blood is too alkaline which means above the normal pH level. If the blood is below this value, the blood is too acidic. Both the kidneys and the lungs participate in keeping the pH near the normal value. 5.


1. Negative Feedback & Positive Feedback

Negative feedback is the control mechanism in physiological systems (and non-physiological systems as well) in which a deviation from a set point causes a response that moves the system back to the set point.

A non-physiological example is a thermostat. If the house gets colder than the desired temp, the furnace goes on, raising the temperature back to the set the preferred temp, and then the furnace goes off. That is, the system responds by returning to a desired temperature once the difference has been found. If a house had both a furnace and an air conditioner, the air conditioner would turn on if the temperature got too high, and it would turn off when the temperature returned to normal. 6.

The counterpart to negative feedback is the Positive feedback loop, which is a process in where the body senses a change and activates mechanisms that accelerates or increases that change.

An example of Positive Feedback is seen in blood clotting. Part of the complex pathway of clotting is the production of an enzyme that forms the matrix of the blood clot, but also speeds up the production of still more thrombin. That is, it has a self- catalytic , self-accelerating effect, so that once the clotting process begins, it runs faster and faster until, hopefully, bleeding stops. Showing, this positive feedback loop is part of a larger negative feedback loop, one that is activated by bleeding and ultimately works to stop the bleeding.

Another example of positive feedback is seen in childbirth, where stretching of the uterus triggers the secretion of a hormone, oxytocin, which stimulates uterine contractions and speeds up labor.

Yet, another is seen in protein digestion, where the presence of partially digested protein in the stomach triggers the secretion of hydrochloric acid and pepsin, the enzyme that digests protein. Once digestion begins, it becomes a self-accelerating process. 7.

This video explains what Homeostasis is and how Negative and Positive Feedback works.

2. Our body has four different types of primary tissues. These include: Muscle, Nervous, Epithelial, and Connective Tissue.

The Muscle Tissue is known for its different contractions that help the body do different things. First the muscle tissue is broken down into three different kinds: skeletal, cardiac, and smooth.3
external image dwa5%20muscle%20tissues.gif

Contractions of the skeletal muscles that are attached to your bones help move your body voluntarily.

Smooth muscle is also involuntary and one of its functions is to move food from on digestive tract to another by contracting.

Cardiac muscle is involuntary and is found only around your heart.

The Nervous Tissue is made up of nerve cells that help controls and regulates the functions of your body.

external image neurons.jpg
Spinal cord (nerve tissue)

The Epithelial Tissues are made up of a bunch of different types of membranes that all have their own type of job. For example the simple epithelial membrane transports material between our body's internal and external walls. While the epithelial membranes job is to make the wall between the internal and external environments. One of the appearances of epithelial is the continuous loss and production of cells. Lacrimal glands and sebaceous glands are examples of exocrine glands that result from the cells of the epithelial membranes.

Simple Squamous
Simple Squamous
Simple Cuboidal
Simple Cuboidal

Simple Columnar
Simple Columnar

Stratified Squamous
Stratified Squamous

The Connective Tissue consists of four different types. These include: Blood, Bone, Connective tissue proper, and Cartilage.
Loose Connective Tissue
Loose Connective Tissue
 Bone Tissue
Bone Tissue
Hyaline Cartilage
Hyaline Cartilage

Adipose Tissue
Adipose Tissue
Blood Connective Tissue
Blood Connective Tissue

3. Organs and Systems

ORGANS are anatomical and functional units that are made of two or more primary tissues.
In terms of surface area, the largest organ in the body is the skin.
The different tissues of an organ are composed of cells that are highly specialized or differentiated. Differentiation is a process that begins during embryonic development, when the fertilized egg divides to produce three embryonic tissue layers: ectoderm, mesoderm, and endoderm. Because specialized cells have a limited lifespan, many organs retain small populations of cells that are less differentiated and more able to divide and become specialized cell types. These less-differentiated cells are know as adult stem cells.

SYSTEMS are organs that are located in different regions of the body that perform related functions. These include the integumentary system, nervous system, endocrine system, skeletal system, muscular system, circulatory system, immune system, respiratory system, digestive system, and reproductive system.
Tissues, organs, and systems can be divided into two major parts: intracellular compartment and extracellular compartment. Both consist primarily of water. The compartments are separated by the cell membrane surrounding each cell. The intracellular compartment is the part inside the cells. The extracellular compartment is the part outside the cells and divided into two parts. One part is the blood plasma and the other is interstitial fluid that bathes the cells within the organs of the body.

This is a quick review of our organs and their systems.

Essential Questions:

- Describe negative feedback and how insulin is controlled by a negative feedback inhibition.

When you eat food your blood glucose goes up, which triggers your Pancreatic Islets that makes your insulin increase, which then starts taking out the extra glucose that's in your blood. Once the glucose goes back to the normal level, the Pancreatic Islets stop producing insulin.

- Why is it essential that insulin and other molecules be regulated?

It's essential that insulin and other molecules be regulated because if it's not it can cause many diseases such as Diabetes types 1 or 2 or edema to develop in the extremities, along with blindness, and other diseases and conditions.

How it pertains to PTA:

As PTA's homeostasis is important for your patients because when they are injured or have surgery they are out of balance because of their body trying to heal what was hurt or damaged. So while we are doing therapy we can help bring them back to the closest normal function possible depending on their injury or condition.

1. Fox, Stuart I. "Human Physiology." New York: McGraw-Hill, 2011. Print. pg.5
2. http://en.wikipedia.org/wiki/Human_homeostasis
3. Click on pictures for their links.
4. http://en.wikipedia.org/Nervous_tissue
5. Guyton, Arthur. "Medical Physiology." Saunders Press. Print.
6. Cannon, Walter B. The Wisdom of the Body. New York: W. W. Norton, 1932.
7. Saladin, Kenneth S. Anatomy and Physiology—The Unity of Form and Function, 2nd ed. Dubuque, IA: McGraw-Hill Higher Education, 2001.
8. http://www.youtube.com