DISCUSS THE CONCEPT OF HOMEOSTASIS PARTICULARLY IN RELATION TO TEMPERATURE CONTROL
DISCUSS THE CONCEPT OF HOMEOSTASIS PARTICULARLY IN RELATION TO TEMPERATURE CONTROL
In complex organisms organs are united to form organ systems such as the digestive, reproductive, nervous and muscular systems. The fact that all of the organ systems generally work in a highly coordinated manner suggests strongly that organisms possess distinct physiological control mechanisms that make the coordination of such highly complex processes possible. One of the most interesting features of such control mechanisms is that they are built into the system to regulate it. The controls are self-adjusting and do not require constant monitoring from an outside agent. Such controls maintain the system in equilibrium. Maintaining a constant internal environment is a struggle which of course is one that every physiological system ultimately loses; death being the final failure of the bodies system. By internal environment we mean the immediate vacinity of the cells, mammalian tissue cells are surrounded by tiny channels and spaces filled with fluid, these provide the cells with the medium in which they have to live and this represents the organs internal environment. It must be kept constant if the cells are to continue their vital functions. The importance of preserving the internal environment, despite considerable fluctuations in the external environment was first pointed out by the great 19th century French physiologist Claude Bernard, in his book he quoted, "It is the fixity of the internal environment which is the condition of free and independent life. All the vital mechanisms, however varied they may be have only one objective; that of preserving constant the conditions of life in the internal environment." The early 20th century American physiologist Walter Bradford Cannon coined the term homeostasis (derived from the Greek word homeo- meaning the same, and stasis meaning maintenance) to refer to the processes that maintain a constant internal environment. Factors that must be kept constant include chemical constituents, osmotic pressure, carbon dioxide and temperature, the latter being the main feature of this discussion. Many physiological processes are homeostatic in that they are directly or indirectly responsible for regulating the internal environment
All animals produce body heat as the result of metabolic processes. Even in the most efficient animal most of the energy released is lost for useful work. Some animals are able to use this waste heat, to rise above the restrictions of the environmental temperature variation and remain active all year round. There are two types of animal categories, homeotherms and poikilotherms. More useful and well-known terms are ectothermic and endothermic respectfully. Endotherms are warm-blooded animals, which are mammals and birds. Their body temperature is individual to the environmental temperature; this is regulated by physiological and behavioral means. ...
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All animals produce body heat as the result of metabolic processes. Even in the most efficient animal most of the energy released is lost for useful work. Some animals are able to use this waste heat, to rise above the restrictions of the environmental temperature variation and remain active all year round. There are two types of animal categories, homeotherms and poikilotherms. More useful and well-known terms are ectothermic and endothermic respectfully. Endotherms are warm-blooded animals, which are mammals and birds. Their body temperature is individual to the environmental temperature; this is regulated by physiological and behavioral means. An advantage of being endothermic is considerable, by maintaining a steady body temperature they are free to exploit a wider range of environmental habitats. The temperature of all warm-blooded animals is not the same, but it never varies more than 2-3 degrees from an average unless some major upset occurs, such as a fever. In humans a constant body temperature of 37 c is necessary because it is the optimum temperature for the action of enzymes, which the organized functioning of the cells depend upon. Ectotherms are cold-blooded animals, their body temperature changes with the fluctuations of the environmental temperature. They rely on external heat generation, such as heat from the sun and from behavioral changes. Heat that is released from their metabolism is not retained and homeostatically balanced within their bodies, it dissipates to the outside environment. At rest such animals body temperatures is the same as the surrounding medium. The body temperature of warm-blooded animals does not remain perfectly constant; it continually fluctuates about an average point that we call "normal". Every adjustment in one direction or the other tends to overshoot the mark; this brings the alternative response into play. Such fluctuations are characteristic of any living system existing in a steady state.
Homeostatic mechanisms achieve their effect by modification of the processes that occur continually. All homeostatic systems have a feedback mechanism by which part of the output of the system is fed back into the system as an instruction telling it what to do. There are two types of feedback mechanisms, negative and positive. The control of body processes often occurs through the operation of negative feedback; movement away from an ideal state causes a return back to the ideal state, or "set point". One example of this is sweating, when a change in the system in one direction (sweating) is converted into a command to change that system in another direction (reduce sweating). In body temperature control, increased sweating lowers the body temperature, a decrease in the body temperature is converted to a command to decrease the amount of water excreted through the sweat glands. This contributes to a rise in body temperature and thus increases sweating. Using such control mechanisms the body acts to counteract disturbances in order to restore homeostasis. Positive feedback however may destroy the equilibrium. It may occur when the normal control mechanism in the body breaks down. If body temperature rises much above 42 c the negative feedback mechanism breaks down and is replaced by positive feedback. The high temperature brings about an increase in the metabolic rate; this produces more heat, which raises the temperature, and so on. The ultimate result if left unchecked is death. Not all positive feedback is destructive, certain kinds are highly adapted for organisms. For the body to maintain a constant temperature heat loss must equal heat gain. Three components for any homeostasis mechanism to work effectively are-:
) Receptors capable of detecting a change.
2) A control mechanism capable of initiating the appropriate corrective measures.
3) Effectors that carry out the corrective measures.
The brain tells our bodies when to switch on our heating or cooling devices. The hypothalamus is situated in the brain and the thermo-regulatory center situated in the hypothalamus acts as a thermostat. It is sensitive to the temperature of the blood perfusing through it and responds by sending nerve impulses to the appropriate effectors. The body possesses millions of microscopically small receptors that are sensitive to temperature. They are located in the skin and connect with the central nervous system by different nerves through which they signal changes in the environmental temperature to the brain. There are two centers in the hypothalamus, the anterior part contains a group of cells designated "the heat loss center". It promotes heat-dissipating responses such as sweating and panting and serves to inhibit heat production and conservation. This center responds directly to an increase in the hypothalamic temperature. The control in the posterior of the hypothalamus initiates heat production responses such as shivering, and the releasing of thyroxin and adrenaline. It serves to minimize heat loss and also to inhibit the heat loss center. This center responds directly as a result of activity in cold receptors in the skin. While the hypothalamus detects fluctuations of temperature inside the body it is the skin receptors that detect temperature changes on the surface of the body.
If body temperature exceeds the temperature of its surroundings it may lose heat energy by four physical processes, conduction, radiation, evaporation and convection. The skin is pivotal in detecting body temperature changes and making the necessary adjustments to maintain homeostasis. When the hypothalamus detects a drop in blood temperature there are four main physiological responses that occur, vasoconstriction, shivering, piloerection and an increase in metabolism. The arterioles leading to the superficial capillaries constrict, the blood flow to the surface of the skin is reduced which cuts down the loss of heat energy from the blood to the surrounding atmosphere, and this is known as vasoconstriction. Shivering occurs when muscles contract and relax rapidly. This is an involuntary tremor of skeletal muscles produced by impulses passing down somatic motor nerves to the muscle. Shivering produces four to five times as much heat as resting muscles. Piloerection means "erection of hairs" and refers to a reflex in hairy animals that makes their hairs stand erect which in turn traps air to provide an insulation layer. In humans the erector pili muscles in the skin pull our tiny hairs upright, but only succeed in producing goose bumps. The body secretes the hormone adrenaline, which raises the metabolic rate and therefore increases heat production.
If the environment is hotter than blood temperature there are also four physiological responses that occur, sweating, vasodilation, a decrease in metabolism and the lowering of hairs by relaxation of the erector pili muscles. The responses involve the reverse of those concerned with cold conditions. The arterioles which lead to the skin capillaries dilate which causes the blood flow to the surface of the skin to be increased, this means that more heat energy is lost to the environment, this is known as vasodilation. The hypothalamus stimulates the production of sweat which is a watery fluid secreted from the sweat glands in the skin. The evaporation of the sweat cools the skin and the blood perfusing through it. As cooler blood flows back to the central regions of the body some passes through the hypothalamus and conveys a message to it that the blood temperature has decreased. The hypothalamus responds by reducing its stimulation of the sweat glands. As a means of dissipating heat sweating is extremely important, there is no other means of getting rid of excess heat.
As we can see from the above information temperature control through homeostasis is an essential function, without which our bodies and other living organisms would not be able to survive.
BIBLIOGRAPHY
HARDY, RICHARD N.
TEMPERATURE AND ANIMAL LIFE.
HARDY, RICHARD N.
HOMEOSTASIS.
BAKER, JEFFREY J. W. & ALLEN, GARLAND E.
THE STUDY OF BIOLOGY.
ROBERTS, M. B. V.
BIOLOGY A FUNCTIONAL APPROACH.
ALLAN, RICHARD. & GREENWOOD, TRACEY.
ADVANCED BIOLOGY 1 2000
ROBERTS, MICHAEL. & REISS, MICHAEL. & MONGER, GRACE.
BIOLOGY PRINCIPLES AND PROCESSES
BARBOR, MARCUS. & BOYLE, MIKE. & CASSIDY, MIKE. & SENIOR, KATHRYN.
BIOLOGY
