Homeostasis
Updated: Aug 23
INTRODUCTION
Homeostasis term comes from the Greek words for "same" and "steady, “. It refers to any process that living things use to actively maintain stable conditions necessary for survival. The term was coined in 1930 by the physician Walter Cannon. He describes in his book,” The Wisdom of the Body” how the human body maintains steady levels of temperature and other vital conditions such as the water, salt, sugar, protein, fat, calcium and oxygen contents of the blood. Similar processes dynamically maintain steady-state conditions in the Earth's environment.
The homeostasis is the ability of the body to maintain stable internal conditions even though the outside world is continuously changing. This dynamic state of equilibrium is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance, being kept within certain limits. Other variables include the pH of extracellular fluid, the concentrations of sodium, potassium and calcium ions, as well as that of the blood sugar level, and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life. Communication within the body is essential for homeostasis and is accomplished chiefly by the nervous and endocrine systems, which use electrical signals delivered by nerves or blood borne hormones, respectively, as information carriers.
COMPONENTS
All homeostatic control mechanisms have at least three components: The receptor is a type of sensor that monitors and responds to changes in the environment. It responds to such changes, called stimuli, by sending information (input) to the second component, the control center. Information flows from the receptor to the control center along the afferent pathway. The control center determines the level at which a variable is to be maintained. This component analyzes the information it receives and then determines the appropriate response or course of action. The third component, the effector, provides the means for the control center’s response (output) to the stimulus.
FEEDBACK
Information flows from the control center to the effector along the efferent pathway. The results of the response then feedback to influence the stimulus (the original change), either by reducing the amount of change (negative feedback), so that the whole control mechanism is shut off; or by increasing the amount of change (positive feedback), so that the reaction continues at an even faster rate.
NEGATIVE FEEDBACK
It is the most homeostatic control mechanism. In such systems, the net effect of the response to the stimulus is to either shut off the original stimulus or reduce it. A good example of a nonbiological negative feedback system is a home heating system connected to a thermostat. In this situation, the thermostat contains both the receptor and the control center. If the thermostat is set at 20°C (68°F), the heating system (effector) will be triggered ON when the house temperature drops below that setting. As the furnace produces heat, the air is warmed. When the temperature reaches 20°C or slightly higher, the thermostat sends a signal to shut off the furnace. Your body “thermostat” operates in a similar way to regulate body temperature. Other negative feedback mechanisms regulate heart rate, blood pressure, breathing rate, the release of hormones, and blood levels of glucose (blood sugar), oxygen, carbon dioxide, and minerals.
POSITIVE FEEDBACK
It intensifies a change in the body’s physiological condition rather than reversing it. This mechanism is rare in the body because they tend to increase the original disturbance (stimulus) and to push the variable farther from its original value. Typically, these mechanisms control infrequent events that occur explosively and do not require continuous adjustments. Blood clotting and the birth of a baby are the most familiar examples of positive feedback mechanisms.
INTEGRATING SYSTEMS
Each organ system performs specific functions for the body, and each organ system is typically studied independently. However, the organ systems also work together to help the body maintain homeostasis. For example, the cardiovascular, urinary, and lymphatic systems all help the body control water balance. The cardiovascular and lymphatic systems transport fluids throughout the body and help sense both solute and water levels and regulate pressure. If the water level gets too high, the urinary system produces more dilute urine (urine with a higher water content) to help eliminate the excess water. If the water level gets too low, more concentrated urine is produced so that water is conserved. The digestive system also plays a role with variable water absorption. Water can be lost through the integumentary and respiratory systems, but that loss is not directly involved in maintaining body fluids and is usually associated with other homeostatic mechanisms.
Similarly, the cardiovascular, integumentary, respiratory, and muscular systems work together to help the body maintain a stable internal temperature. If body temperature rises, blood vessels in the skin dilate, allowing more blood to flow near the skin’s surface. This allows heat to dissipate through the skin and into the surrounding air. The skin may also produce sweat if the body gets too hot; when the sweat evaporates, it helps to cool the body. Rapid breathing can also help the body eliminate excess heat. Together, these responses to increased body temperature explain why you sweat, pant, and become red in the face when you exercise hard. Heavy breathing during exercise is also one way the body gets more oxygen to your muscles and gets rid of the extra carbon dioxide produced by the muscles.) Conversely, if your body is too cold, blood vessels in the skin contract, and blood flow to the extremities (arms and legs) slows. Muscles contract and relax rapidly, which generates heat to keep you warm. The hair on your skin rises, trapping more air, which is a good insulator, near your skin. These responses to decreased body temperature explain why you shiver, get goose bumps, and have cold, pale extremities when you are cold.
HOMEOSTATIC IMBALANCE
Homeostasis is so important that most disease can be regarded as being the result of its disturbance, a condition called homeostatic imbalance. As we age, our body organs become less efficient, and our internal conditions become less and less stable. These events place us at an increasing risk for illness and produce the changes we associate with aging.
Comments