Introduction to Physiology-Homeostasis
Interactive Physiology MediaPhysio3:
Download this folder if you don’t have already. Download folder from drop down menu of MediaPhysio3. This link can be helpful. Read “Read me before run the MediaPhys3” and follow the required steps. Double clicks on “index” or "index" located within "data" folder to run the program. You can explore the following modules:
1. Introduction to Physiology.
2. Body Fluids.
3. Human Cell.
4. Nerve Cells.
5. Muscles.
6. Nervous System.
7. Sensory Systems.
8. Circulatory System 1: Heart.
9. Circulatory System 2: Blood Vessels.
10. Respiratory System.
11. Renal System, Water and Electrolyte Balance.
12. Acid-Base Balance.
13. Endocrine System.
14. Reproductive System.
15. Digestive System.
16. Metabolism.
17. PhysSkill
Homeostasis: Homeostasis refers to the maintenance of constant
internal environment of the body (homeo = same; stasis = standing).
Internal environment in the body is the extracellular fluid (ECF) in
which the cells live. It is the fluid outside the cell and it constantly
moves throughout the body. It includes blood, which circulates in the
vascular system and fluid present in between the cells called
interstitial fluid. ECF contains nutrients, ions and all other substances
necessary for the survival of the cells. Normal healthy living of large
organisms including human beings depends upon the constant maintenance
of internal environment within the physiological limits. If the internal
environment deviates beyond the set limits, body suffers from
malfunction or dysfunction. Therefore, the ultimate goal of an organism
is to have a normal healthy living, which is achieved by the maintenance
of internal environment within set limits. For the functioning of
homeostatic mechanism, the body must recognize the deviation of any
physiological activity from the normal limits. Fortunately, body is
provided with appropriate detectors or sensors, which recognize the
deviation. These detectors sense the deviation and alert the integrating
center. The integrating center immediately sends information to the
concerned effectors to either accelerate or inhibit the activity so that
the normalcy is restored. One or more systems are involved in
homeostatic mechanism of each function. Some of the functions in which
the homeostatic mechanism is well established are given below:
2. Body temperature must be maintained at 37.5°C. Increase or decrease in temperature alters the metabolic activities of the cells.
3. Adequate amount of nutrients must be supplied to the cells.
4. Adequate amount of oxygen should be made available to the cells for the metabolism of the nutrients. Simultaneously, the carbon dioxide and other metabolic end products must be removed.
5. Many hormones are essential for the metabolism of nutrients and other substances necessary for the cells.
6. Water and electrolyte balance should be maintained optimally.
7. For all these functions, the blood, which forms the major part of internal environment, must be normal. It should contain required number of normal red blood cells and adequate amount of plasma with normal composition.
8. Skeletal muscles are also involved in homeostasis. This system helps the organism to move around in search of food. It also helps to protect the organism from adverse surroundings, thus preventing damage or destruction.
9. Central nervous system, which includes brain and spinal cord also, plays an important role in homeostasis. Sensory system detects the state of the body or surroundings. Brain integrates and interprets the pros and cons of these information and commands the body to act accordingly through motor system so that, the body can avoid the damage.
10. Autonomic nervous system regulates all the vegetative functions of the body essential for homeostasis.
Components of homeostatic system: Homeostatic system in the body acts through self-regulating devices, which operate in a cyclic manner (Figure & Figure). This cycle includes four components: 1. Sensors or detectors, which recognize the deviation 2. Transmission of this message to a control center 3. Transmission of information from the control center to the effectors for correcting the deviation. Transmission of the message or information may be an electrical process in the form of impulses through nerves or a chemical process mainly in the form of hormones through blood and body fluids 4. Effectors, which correct the deviation.
Mechanism of action of homeostatic system: Homeostatic mechanism in the body is responsible for maintaining the normalcy of various body systems. Whenever there is any change in behavioral pattern of any system, the effectors bring back the normalcy either by inhibiting and reversing the change or by supporting and accelerating the change depending upon requirement of the situation. This is achieved by means of feedback signals. Feedback is a process in which some proportion of the output signal of a system is fed (passed) back to the input. This is done more often intentionally in order to control the behavior pattern of the system. Whenever any change occurs, system receives and reacts to two types of feedback:
1. Negative feedback
2. Positive feedback.
Negative feedback (see figure & figure ): Negative feedback is the one to which the system reacts in such a way as to arrest the change or reverse the direction of change. After receiving a message, effectors send negative feedback signals back to the system. Now, the system stabilizes its own function and makes an attempt to maintain homeostasis. Most systems supporting homeostasis operate by negative feedback. Because positive feedback is stimulatory, there are only a few situations in which it is beneficial to the body (such as during childbirth or in blood clotting). More often, positive feedback is harmful (such as when a high fever continues to rise).
Positive feedback (see figure): Positive feedback is the one to which the system reacts in such a way as to increase the intensity of the change in the same direction. Positive feedback is less common than the negative feedback. However, it has its own significance particularly during emergency conditions.