Control Of Internal Environment PDF

CONTROL OF INTERNAL ENVIRONME NT Dr. Raheela  Outline: ◦ EXERCISE/PHYSICAL ACTIVITY ◦ EXERCISE PHYSIOLOGY ◦ HOMEOSTASIS ◦ CONTROL SYSTEM ◦ FEEDBACKS PHYSICAL ATIVITY..???. ◦ ◦ EXERCISE…????  The term homeostasis is defined as the maintenance...

CONTROL OF INTERNAL ENVIRONME NT Dr. Raheela  Outline: ◦ EXERCISE/PHYSICAL ACTIVITY ◦ EXERCISE PHYSIOLOGY ◦ HOMEOSTASIS ◦ CONTROL SYSTEM ◦ FEEDBACKS PHYSICAL ATIVITY..???. ◦ ◦ EXERCISE…????  The term homeostasis is defined as the maintenance of a constant internal environment. A similar term, steady state , is often used to denote a HOMEOSTASI steady and unchanging level S of some physiological variable. Therefore, the term homeostasis is generally reserved for describing normal resting conditions, and the term steady state is often applied to exercise.  ◦ Changes in body core temperature during sixty minutes of constant-load submaximal exercise in a thermo-neutral environment , low humidity and low temperature. ◦ Note that core temperature Difference reaches a new and steady level within forty minutes after commencement of exercise. ◦ This plateau of core temperature represents a steady state, since temperature is constant; this constant temperature is above the normal resting body temperature.  BIOLOGICAL CONTROL SYSTEM CONTROL SYSTEM: MECHANICAL CONTROL SYSTEM CONTROL SYSTEMS OF THE BODY The body has literally hundreds of different control systems, and the overall goal of most is to regulate some physiological variable at or near a constant value The most intricate of these control systems reside inside the cell itself. These cellular control systems regulate cell activities such as protein breakdown and synthesis, energy production, and maintenance of the appropriate amounts of stored nutrients  The fact that the The lungs (pulmonary system) cardiopulmonary system is and heart (circulatory system) usually able to maintain normal work together to replenish levels of oxygen and carbon oxygen and to remove carbon dioxide even during periods of dioxide from the extracellular strenuous exercise is not an fluid. accident but the end result of a good control system. ◦ Suppose the thermostat is set at 20° C. Any change in room temperature away from the 20° C “set point” results in the appropriate response by either the furnace or the air conditioner to return the room temperature to 20° C. If the room temperature rises above the set NATURE point, the thermostat signals the air OF THE conditioner to start, which returns the room temperature to 20° C. In contrast, CONTROL a decrease in temperature below the set point results in the thermostat signaling SYSTEMS the heating system to begin operation. ◦ In both cases the response by the heating and cooling system was to correct the condition, low or high temperature, that initially turned it on. Like the example of a mechanical control system, a biological control system is a series of interconnected components that maintain a chemical or physical parameter of the body near a constant value. Biological control systems are composed of three elements: 1. a sensor (or receptor) 2. a control center(brain) 3. effectors (organs that produce the desired effect) ◦ The signal to begin the operation of a control ◦ system is the stimulus that represents a change in the internal environment. ◦ The stimulus excites a sensor that is a receptor in the body capable of detecting change in the variable in question. ◦ The excited sensor then sends a message to the control center. The control center integrates the strength of the incoming signal from the sensor and sends an appropriate message to the effectors to bring about the appropriate response to correct the disturbance. ◦ POSITIVE FEEDBCK ◦ The return of the internal environment to normal results in a decrease in the original stimulus that triggered the control system into action. This type of feedback loop is termed negative feedback and is the primary method responsible for maintaining homeostasis in the body. … ◦ Positive feedback control mechanisms act to increase the original stimulus. ◦ This type of feedback is termed positive because the response is in the same direction as the stimulus. POITIVE FEEDBCK: ◦ A classic example of a positive feedback mechanism involves the enhancement of labor contractions when a woman gives birth. For example, when the head of the baby moves into the birth canal, the increased pressure on the cervix (narrow end of the uterus) stimulates sensory receptors. These excited sensors then send a neural message to the brain (i.e., control center), which responds by triggering the release of the hormone oxytocin from the pituitary gland. Oxytocin then travels via the blood to the uterus and promotes increased contractions. ◦ As labor continues, the cervix becomes more stimulated and uterine contractions become even stronger until birth occurs. At this point, the stimulus (i.e., the pressure) for oxytocin release stops and thus shuts off the positive feedback mechanism. NEGTIVE FEEDBCK: ◦ tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances. Most control systems act by way of negative feedback.. Negative Feedback ◦ Most control systems of the body operate via negative feedback. ◦ An example of negative feedback can be seen in the respiratory system's regulation of the CO 2 concentration in extracellular fluid. In this case, an increase in extracellular CO 2 above normal levels triggers a receptor, which sends information to the respiratory control center (integrating center) to increase breathing. The effectors in this example are the respiratory muscles. ◦ This increase in breathing will reduce extracellular CO 2 concentrations back to normal, thus reestablishing homeostasis. Gain of a Control System ◦ The degree to which a control system maintains homeostasis is termed the gain of the system ◦ a control system with a large gain is more capable of correcting a disturbance in homeostasis than a control system with a low gain. As you might predict, the most important control systems of the body have large gains. ◦ For example, control systems that regulate body temperature, breathing (i.e.pulmonary system), and delivery of blood (i.e., cardiovascular system) all have large gains. ◦  EXAMPLES OF HOMEOSTATIC CONTROL Regulation of Body Temperature ◦ An excellent example of a homeostatic control system that uses negative feedback is the regulation of body temperature. The sensors in this system are thermal receptors located in several body locations. ◦ The control center for temperature regulation is located in the brain, and when body temperature increases above normal, temperature sensors send a neural message to the control center that temperature is above normal. ◦ The control center responds to this stimulus by directing a response to promote heat loss (i.e., skin blood vessels dilate and sweating occurs). When body temperature returns to normal, the control center is inactivated. Regulation of Blood Glucose ◦ An example of the endocrine system’s role in the maintenance of homeostasis is the control of blood glucose levels. ◦ Indeed, in health, the blood glucose concentration is ◦ carefully regulated by the endocrine system. ◦ For example, the hormone insulin regulates cellular ◦ uptake and the metabolism of glucose and is therefore important in the regulation of the blood glucose concentration. After a large carbohydrate meal, the blood glucose level increases above normal. ◦ The rise in blood glucose signals the pancreas to release insulin, which then lowers blood glucose by increasing cellular uptake. ◦ Failure of the blood glucose control system results in disease (diabetes). ◦ EXERCISE: A TEST OF HOMEOSTATIC CONTROL ◦ For example, during heavy exercise, ◦ skeletal muscle produces large amounts of lactic acid, ◦ which causes an increase in intracellular and extracellular ◦ acidity. This increase in acidity represents a serious challenge to the body's acid-base control system. ◦ Additionally, heavy exercise results in large increases in muscle O 2 requirements, and large amounts of CO 2 are produced. These changes must be countered by increases in breathing (pulmonary ventilation) and blood flow to increase O 2 delivery to the exercising muscle and remove metabolically produced CO 2. ◦ Further, during heavy exercise the working muscles produce large amounts of heat that must be removed to prevent overheating. The body's control systems must respond rapidly to prevent drastic alterations in the internal environment. ◦ The body rarely maintains true homeostasis while performing intense exercise or during prolonged exercise in a hot or humid environment. ◦ Heavy exercise or prolonged work results in disturbances in the internal environment that are generally too great for even the highest gain control systems to overcome, and thus a steady state is not possible. ◦ Severe disturbances in homeostasis result in fatigue and, ultimately, cessation of exercise.