Homeostasis

Homeostasis

·         Introduction:

The human organism consists of trillions of cells all working together for the maintenance of the entire organism. While cells may perform very different functions, all the cells are quite similar in their metabolic requirements.

Maintaining a constant internal environment with all that the cells need to survive (oxygen, glucose, mineral ions, waste removal, and so forth) is necessary for the

Well-being of individual cells and the well-being of the entire body. The varied processes by which the body regulates its internal environment are collectively

referred to as homeostasis.

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·         Meaning of Homeostasis?

Homeostasis in a general sense refers to stability, balance or equilibrium. It is the

body's attempt to maintain a constant internal environment. Maintaining a stable internal environment requires constant monitoring and adjustments as conditions change. This adjusting of physiological systems within the body is called homeostatic regulation.

Homeostatic regulation involves three parts or mechanisms:

1) the receptor, 2) the control center and 3) the effector.

-The receptor receives information that something in the environment is changing.

-The control center or integration center receives and processes information from the receptor.

-The effector responds to the commands of the control center by either opposing or enhancing the stimulus. This is an ongoing process that continually works to restore and maintain homeostasis.

For example, in regulating body temperature there are temperature receptors in the skin, which communicate information to the brain, which is

the control center and the effector is our blood vessels and sweat glands in our skin.

Because the internal and external environments of the body are constantly changing and adjustments must be made continuously to stay at or near the set point, homeostasis can be thought of as a synthetic equilibrium.

Since homeostasis is an attempt to maintain the internal conditions of an environment by limiting fluctuations, it must involve a series of negative feedback loops.

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·         Positive and Negative Feedback

When a change of variable occurs, there are two main types of feedback to which the system reacts:

• Negative feedback:

a reaction in which the system responds in such a way as to reverse the direction of change. Since this tends to keep things constant, it allows the maintenance of homeostasis. For instance, when the concentration of carbon dioxide in the human body increases, the lungs are signaled to increase their activity and expel more carbon dioxide.

Thermoregulation is another example of negative feedback. When body temperature

rises (or falls), receptors in the skin and the hypothalamus sense a change, triggering a command from the brain. This command, in turn, effects the correct response, in this

case a decrease in body temperature.

Home Heating System Vs. Negative Feedback

When you are at home, you set your thermostat to a desired temperature. Let's say today you set it at 70 degrees. The thermometer in the thermostat waits to sense a temperature change either too high above or too far below the 70 degree set point. When this change happens the thermometer will send a message to the "Control Center", or thermostat, Which in turn will then send a message to the furnace to either shut off if the temperature is too high or kick back on if the temperature is too low.

In the home-heating example the air temperature is the (Negative Feedback). When the Control Center receives negative feedback it triggers a chain reaction in order to maintain room temperature.

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• Positive feedback:

a response is to amplify the change in the variable.

This has a destabilizing effect, so does not result in homeostasis. Positive feedback is less common in naturally occurring systems than negative feedback, but it has its applications.

For example, in nerves, a threshold electric potential triggers the generation of a much larger action potential. Blood clotting in which the platelets process mechanisms to transform blood liquid to solidify is an example of positive feedback loop.

Another example, is the secretion of oxytocin which provides a pathway for the uterus to contract, leading to child birth.

- Harmful Positive Feedback:

Although Positive Feedback is needed within Homeostasis it also can be harmful at times. When you have a high fever it causes a metabolic change that can push the fever higher and higher. In rare occurrences the body temperature reaches 113 degrees and the cellular proteins stop working and the metabolism stops, resulting in death.

Summary: Sustainable systems require combinations of both kinds of feedback. Generally with the recognition of divergence from the homeostatic condition, positive feedbacks are called into play, whereas once the homeostatic condition is approached, negative feedback is used for "fine tuning" responses. This creates a situation of (metastability), in which homeostatic conditions are maintained within fixed limits, but once these limits are exceeded, the system can shift wildly to a wholly new (and possibly less desirable) situation of homeostasis.

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·         Properties of Homeostatic systems:

• They are ultra-stable, meaning the system is capable of testing which way its variables should be adjusted.

• Their whole organization (internal, structural, and functional) contributes to the maintenance of balance.

• Physiology is largely a study of processes related to homeostasis. Some of the functions you will learn about in this book are not specifically about homeostasis

(e.g. how muscles 4 Pathways That Alter Homeostasis contract),

but in order for all bodily processes to function there must be a suitable internal environment. Homeostasis is, therefore, a fitting framework for the introductory

study of physiology.

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·         Where did the term "Homeostasis" come from?

 In first studying of the maintenance of stability in the "milieu interior".

Scientist saids, "All the vital mechanisms, varied as they are, have only one object, that of preserving constant the conditions of life in the internal environment"

Then the term itself was coined by American physiologist Walter Cannon (1932). The word comes from the Greek homoios (same, like, resembling) and stasis

(to stand, posture).

 An example Cruise Control on a car as a simple metaphor for homeostasis When a car is put on cruise control it has a set speed limit that it will travel. At times this speed may vary by a few miles per hour but in general the system will maintain the set speed. If the car starts to go up a hill, the systems will automatically increase the amount of fuel given to maintain the set speed. If the car starts to come down a hill, the car will automatically decrease the amount of fuel given in order to maintain the set speed.

It is the same with homeostasis- the body has a set limit on each environment. If one of these limits increases or decreases, the body will sense and automatically try to fix the problem in order to maintain the pre-set limits.

This is a simple metaphor of how the body operates—constant monitoring of levels, and automatic small adjustments when those levels fall below (or rise above) a set point.

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·         Pathways That Alter Homeostasis

A variety of homeostatic mechanisms maintain the internal environment within tolerable limits. Either homeostasis is maintained through a series of control mechanisms, or the body suffers various illnesses or disease. When the cells in the body begin to malfunction, the homeostatic balance becomes disrupted. Eventually this leads to disease or cell malfunction.

Disease and cellular malfunction can be caused in two basic ways: either, deficiency (cells not getting all they need) or toxicity (cells being poisoned by things they do not need).

When homeostasis is interrupted in your cells, there are pathways to correct or worsen the problem. In addition to the internal control mechanisms, there are external influences based primarily on lifestyle choices and environmental exposures that influence our body's ability to maintain cellular health.

(1)Nutrition:

If your diet is lacking in a specific vitamin or mineral your cells will function

poorly, possibly resulting in a disease condition. For example, a menstruating woman with inadequate dietary intake of iron will become anemic. Lack of hemoglobin, a molecule that requires iron, will result in reduced oxygen-carrying capacity. In mild cases symptoms may be vague (e.g. fatigue), but if the anemia is severe the body will try to compensate by increasing cardiac output, leading to palpitations and sweatiness, and possibly to heart failure.

(2)Toxins:

Any substance that interferes with cellular function, causing cellular malfunction.

This is done through a variety of ways; chemical, plant, insecticides, and/or bites. A

commonly seen example of this is drug overdoses. When a person takes too much of a

drug their vital signs begin to waver; either increasing or decreasing, these vital signs can cause problems including coma, brain damage and even death.

(3)Psychological:

Your physical health and mental health are inseparable. Our thoughts and emotions cause chemical changes to take place either for better as with meditation, or worse as with stress.

(4)Physical: Physical maintenance is essential for our cells and bodies. Adequate rest,

sunlight, and exercise are examples of physical mechanisms for influencing homeostasis. Lack of sleep is related to a number of ailments such as irregular cardiac rhythms, fatigue, anxiety and headaches.

(5)Genetic/Reproductive: Inheriting strengths and weaknesses can be part of our genetic makeup. Genes are sometimes turned off or on due to external factors which we can have some control over, but at other times little can be done to correct or improve genetic diseases.

(6)Medical practices: Because of genetic differences some bodies need help in gaining or maintaining homeostasis. Through modern medicine our bodies can be given different aids, from antibodies to help fight infections, or chemotherapy to kill harmful cancer cells. Traditional and alternative medical practices have many benefits, but like any medical practice the potential for harmful effects is present.

Whether by nosocomial infections, or wrong dosage of medication, homeostasis can be altered by that which is trying to fix it. Trial and error with medications can cause potential harmful reactions and possibly death if not caught soon enough.

The factors listed above all have their effects at the cellular level, whether harmful or

beneficial. Inadequate beneficial pathways (deficiency) will almost always result in a harmful waver in homeostasis.

Too much toxicity also causes homeostatic imbalance, resulting in cellular malfunction.

By removing negative health influences, and providing adequate positive health influences, your body is better able to self-regulate and self-repair, thus maintaining homeostasis.

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