Control Of Internal Environment PDF

CONTROL OF THE INTERNAL ENVIRONMENT DR ARSHEEN (PT) 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 re...

CONTROL OF THE INTERNAL ENVIRONMENT DR ARSHEEN (PT) 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.  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.  When body temperature falls below normal, temperature sensors send these data to the control center in the brain, which responds by preventing the loss of body heat (e.g., blood vessels in the skin constrict) This action serves to conserve heat Again, when body temperature returns to normal, the control center becomes inactive. REGULATION OF BLOOD GLUCOSE Maintaining homeostasis is an important function of the endocrine system. The body contains eight major endocrine glands, which synthesize and secrete blood- borne chemical substances called hormones. Hormones are transported via the circulatory system throughout the body as an aid to regulate circulatory and metabolic functions An example of the endocrine system’s role in the maintenance of homeostasis is the control of blood glucose levels. 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 consuming a large carbohydrate meal, blood glucose levels increase above normal. This 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 Muscular exercise presents a dramatic test of the body’s homeostatic control systems because exercise has the potential to disrupt many homeostatic variables. For example, during heavy exercise, skeletal muscle produces large amounts of heat, which pose a challenge for the body to prevent overheating. Additionally, heavy exercise results in large increases in muscle O2 requirements, and large amounts of CO2 are produced.  These changes must be countered by increases in breathing (pulmonary ventilation) and blood flow to increase O2 delivery to the exercising muscle and remove metabolically produced CO2. The body’s control systems must respond rapidly to prevent drastic alterations in the internal environment.  In a strict sense, 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. Improved exercise performance following exercise training is largely due to training adaptations that result in a better maintenance of homeostasis EXERCISE IMPROVES HOMEOSTATIC CONTROL VIA CELLULAR ADAPTATION The term adaptation refers to a change in the structure and function of a cell or an organ system that results in an improved ability to maintain homeostasis during stressful conditions. cell’s ability to respond to a challenge is not fixed and can be improved by prolonged exposure to a specific stress (e.g., regular bouts of exercise)  Also, cells can adapt to environmental stresses, such as heat stress due to a hot environment. Acclimation: This type of environmental adaptation—the improved function of an existing homeostatic system—is known as acclimation.  Regular bouts of exercise promote cellular changes that result in an improved ability to preserve homeostasis during the “stress” of exercise. This improved ability of cells and organ systems to maintain homeostasis occurs via a variety of cell signaling mechanisms.  The term cell signaling refers to a system of communication between cells that coordinates cellular activities. The ability of cells to detect changes in their internal environment and correctly respond to this change is essential in the maintenance of homeostasis. It should be no surprise that a variety of cell signaling mechanisms coordinate all the different functions of the body. SIGNALING MECHANISMS 1) Intracrine signaling skeletal muscle adaptation to exercise training. 2) Juxtacrine signaling heart contracts in a smooth and effective manner. 3) Autocrine signaling protein synthesis in cells (Size of muscle) 4) Paracrine signaling immune cells communication 5) Endocrine signaling hormones STRESS PROTEINS ASSIST IN THE REGULATION OF CELLULAR HOMEOSTASIS A disturbance in cellular homeostasis occurs when a cell is faced with a “stress” that surpasses its ability to defend against this particular type of disturbance cellular stress response proteins are important in maintaining homeostasis. For example, proteins play critical roles in normal cell function by serving as intracellular transporters or as enzymes that catalyze chemical reactions. Damage to cellular proteins by stress (e.g., low pH or free radicals) can result in cell damage and a disturbance in homeostasis.  cells respond by rapidly manufacturing protective proteins called stress proteins One of the most important families of stress proteins are called heat shock proteins exercise training results in significant increases in the production of numerous heat shock proteins within the heart and the trained skeletal muscle production of heat shock proteins can also be triggered by other types of stress such as free radical production, low pH, and inflammation.  The process of synthesizing heat shock proteins begins with a stressor that promotes protein damage heat shock proteins go to work to protect the cell by repairing damaged proteins and restoring homeostasis.