HOMEOSTASIS
Imagine that you are driving a car. To reach your destination, you cannot just put the car in gear and then sit back, relax, and expect it automatically to take you there. You have to be actively involved in the process.
You must accelerate to the proper speed, monitor and avoid other traffic, steer as the road twists and turns, accelerate up hills, brake while going down hills, stop when necessary, and generally oversee conditions and make adjustments throughout the journey. This description is an analogy for homeostasis in the body. The road is life, the car is the animal's body, and homeostasis is all the little inputs and corrections necessary to keep the body (car) alive (on the road).Homeostasis is the maintenance of a dynamic equilibrium in the body. The word dynamic implies activity, energy, and work, and equilibrium refers to balance. Together they summarize all the physiological processes that actively maintain balance in the various structures, functions, and properties of the body. Consider this: An animal's body temperature cannot vary more than a few degrees from either side of the normal range without starting to interfere with other body functions. Or consider how acid-base balance, fluid balance, hormone levels, nutrient levels, and oxygen levels cannot vary by much if the body is to operate normally; they must be kept within fairly narrow operational ranges. The processes that monitor and adjust all the various essential parameters of the body are summarized by the term homeostasis.
Is some particular part of the body responsible for homeostasis? The answer is no. The whole body is responsible for homeostasis. All the body systems are involved in the many mechanisms of homeostasis, which require a lot of energy and work. Like all the little inputs and corrections teheapt k a car safely traveling down the road, the various homeostatic mechanisms in the body keep it functioning iasmtsid the tw and turns of life.
To put it more mechanisti- rcoalcleys, stehse p of homeostasis help maintain a fairlyceronasltant int environment in the body as conditions
inside and outside the animal change. Along with normal functioning of the body's cells, tissues, organs, and systems, trhoecepsses of homeostasis make life possible.
TEST YOURSELF 1-5
1. How doesthe normal Onatomyandphysiology of cells in nn nnianl's body iapnct the health of the nnianl ns n whole? How does the noranl nnntoay nnd physiology of the nnianl's body ns n whole iapnct the health of ench of its cells?
2. How olo homaestatin mechanieas i nfleenen the health of nn nnianl?
of you are beginning to view the concepts of life and health as a little less ordinary and more unique, you are starting to appreciate the amazing complexity of the animal body. Only by undosstanding what is normal in the body can we hope to help sick or injured animals. With this in mind, we can iptrhoceed w our examination of the fascinating machine that is the animal body.
CLINICAL APPLICATION
Homeostasis and Congestive Heart Failure
Thie peocesses in the body that try to maintain the functioning of a failing heart offer some excellent illustrations of how important homeostasis is as it attempts to maintain the health and life of an animal. Congestive heart failure is a clinical term used to describe a heart that is not pumping adequate amounts of blood. This results in blood “backing up” in the body, which produces congestion, or abnormal fluid accumulation, oumpstream fr the failing heart. There are many causes and forms of congestive heart failure, but the overall homeostatic mechanisms that attempt to maintain normal blood circulation in the body are basically the same.
The fi rso indication that the heart is starting to fail is a drop iahnredtiac c output, that is, the amount of blood the heart uptumps o per minute. The decreased blood flow and blood rperessure a picked up by receptors in the vascular system and relayed to foe central nervous system.
Signals then go out to ahcetivate t sympathetic portion of the nervous system. This system, ato called the fight-or-flight system, helpe prepare the body for intense physical activity. Its effect on the cardiovascular system is to increase blood flow and blood pressure by stimulating the heart to beat harder and faster and by constricting blood vhnessels. I t short term, these mechanisms help bring blood lnfloodowd a b pressure back up to normal levels.Unfortunately, these compensatory mechanisms cause the toweak hear t work harder, which is kind of like whipping an exhausted horse to get it to move faster or pull harder. The result is a further weakening of the heart and further decreases in cardiac output. This causes more sympathetic nervous ismysutelamtiostn. The cycle continues to repeat until either
the heart gives up completely or we intervene with medical therapy. Homeostatic mechanisms cannot change the basic defects that are causing the heart to fail, but they help the damaged heart maintain vital blood flow to the rest of the body for as long as possible. By adding good medical care to the body’s natural homeostatic mechanisms, we can often extend the length and quality of life of an animal in congestive hureea.rt fail