Homeostasis

Pathology

1. Homeostasis K Krupa Sagar Dept. of Pharmacology

2. Homeostasis A condition in which the internal environment of the body remains relatively constant despite changes in the external environment. Examples would be the maintenance of “body temperature” and “levels of glucose in the blood”

3. Homeostatic mechanisms Homeostasis is achieved through negative or positive feedback mechanism. Negative feedback: Includes most homeostatic control mechanisms . Shuts off or decreases the original stimulus , or reduces its intensity. Works like a household thermostat. Examples include control of blood pressure and temperature regulation. Secretion of Insulin when blood sugars levels are high

4. Homeostatic mechanisms Positive feedback: Increases the original stimulus to push the variable farther e.g. in blood clotting during blood vessel injury. Homeostatic mechanisms are designed to reestablish homeostasis when there is an imbalance .

5. The Home Heating System 1. When the temperature of a room decreases below a set point, the thermostat electrically starts the furnace. 2. As the temperature of the room rises to the set point, the thermostat shuts down the furnace. 3. As the room cools, step one is repeated. There are three components to this system: 1. The Sensor which detects the stress. 2. The Control Center which receives information from the sensor and sends a message to the Effector. 3. The Effector which receives the message from the control center and produces the response which reestablishes homeostasis.

6. There are three components to a homeostatic system: 1. The Sensor which detects the stress. 2. The Control Center which receives information from the sensor and sends a message to adjust the stress. 3. The Effector which receives the message from the control center and produces the response which reestablishes homeostasis It should be noticed that 1. the heat produced by the furnace shuts the furnace down through the thermostat. 2. the original stress is reduced, i.e., the room warms up. Homeostatic mechanisms that show these two characteristics are operating by negative feedback

7. Homeostasis Using a Neural Pathway Many homeostatic mechanisms use a nerve pathway in which to produce their effects. These pathways involve an afferent path which brings sensory messages into the brain and an efferent path which carries outgoing nerve messages to effectors.

8. Harmful Effects of Positive Feedback Positive feedback can be harmful. Two specific examples of these harmful outcomes would be: 1. Fever can cause a positive feedback within homeostasis that pushes the body temperature continually higher. If the temperature reaches 45 degrees centigrade cellular proteins denature bringing metabolism to a stop and death. 2. Chronic hypertension can favor the process of atherosclerosis which causes the openings of blood vessels to narrow. This, in turn, will intensify the hypertension bring on more damage to the walls of blood vessels.