Homeostasis

Definition
Homeostasis is the process by which the internal systems of the body maintain a balance, despite external conditions. There are 6 factors that are constantly homeostatically regulated by the systems of the human body. These factors must remain within certain limits at all times, otherwise adverse effects on the body will result.

Discovery
Roots of current conceptions of the regulation of states of the body that is the mechanisms of homeostasis is traced back to Bernard's ideas on active stabilization of bodily states against disturbances from the outside, revived by Henderson and Haldane, and crystallized in Cannon's concept of homeostasis 1. The term "homeostasis" was first used by Walter Bradford Cannon in 1920s. Walter B. Cannon established homeostasis as a unifying concept of human physiology .

Mode of Action
There are three interdependent components for the variable in all homeostatic control mechanisms are being regulated: The receptor, is the sensing component that recognize and responds to environmental changes. Receptor upon sensing a stimulus sends information to a control center, the component that defines the range at which a variable is maintained. The control center sets an appropriate response to the stimulus. Brain is the control center for most homeostatic mechanisms. The control center that is brain then sends signals to an effector, which could be muscles, organs or other structures correct the deviation by either enhancing it with positive feedback or depressing it with negative feedback mechanism. Positive Feedback, Positive feedback is a mechanism by which an output is increased, eg, protein levels, hormone levels etc. The positive feedback mechanisms are designed to push levels out of normal ranges. To achieve positive feedback, a series of events initiates a cascading process that builds to increase the effect of the stimulus. Positive feedback occurs in the body during blood platelet accumulation, which causes blood clotting in response to a break or tear in the lining of blood vessels. Release of oxytocin to intensify the contractions that take place during childbirth is also a positive feedback mechanism. Negative Feedback Control, In animals the internal environment must have certain conditions within tolerable limits to continue the healthy functioning. In negative feedback control, receptors and effectors bring about a reaction (reduce levels from normal ranges) to ensure that such conditions remain favorable.

Functions
Homeostasis has survival value because it means an animal can adapt to a changing environment. Water Regulation, a change in water concentration leads to active via negative feedback control. Osmoreceptors that are capable of detecting water concentration are situated on the hypothalamus next to the circulatory system. The hypothalamus sends chemical messages to the pituitary gland next to it. The pituitary gland secretes anti-diuretic hormone (ADH), which targets the kidney responsible for maintaining water levels. When the hormone reaches its target tissue, it alters the tubules of the kidney to become more / less permeable to water. If more water is required in the blood stream, high concentrations of ADH make the tubules more permeable. If less water is required in the blood stream, low concentrations of ADH make the tubules less permeable . Sugar Homeostasis: The body requires volumes of glucose in order to create ATP. The amount of ATP demanded will fluctuate, and therefore the body regulates the availability of glucose to maximize its energy making potential. Two hormones are responsible for controlling the concentration of glucose in the blood. These are insulin and glucagon. Among the specialized cell types in the gastrointestinal mucosa, enteroendocrine cells have important roles in regulating energy intake and glucose homeostasis through their actions on peripheral target organs, including the endocrine pancreas . Temperature Regulation in Animals, animals capable of temperature regulation within a given range are deemed homeotherms (alternatively homiotherms or homotherms). They have the ability to regulate temperature via negative feedback control. The hypothalamus once again acts as a receptor in regulation, by detecting fluctuations in temperature. These receptors are better known as thermoreceptors. Skin also possesses thermoreceptors which can detect the temperature of the external environment. This information is relayed to the hypothalamus which can in turn transmit nerve pulses for corrective mechanisms to occur . Angiogenesis, the growth of blood vessels, is a fundamental biological process that controls embryonic development and is also involved in numerous life-threatening human diseases. Much work in the field of angiogenesis research has centred on the vascular endothelial growth factor (VEGF)-VEGF receptor system. The Tie receptors and their angiopoietin (Ang) ligands have been identified as the second vascular tissue-specific receptor Tyr kinase system. Ang-Tie signalling is essential during embryonic vessel assembly and maturation, and functions as a key regulator of adult vascular homeostasis 2.

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