Homeostasis is the process of maintaining steady internal body conditions when the external environment is altered. The process allows certain body mechanisms to adopt the changed external environment and also to operate more efficiently. The hormone system and nervous system under the coordination of the hypothalamus responds accordingly to homeostasis. To maintain steady values, the homeostasis mechanism uses negative feedback to start a corrective mechanism.
All animals require homeostasis to regulate body temperature. Birds and mammals maintain a fairly constant body temperature and are referred to as endotherms. The rest are able to adapt to the surrounding temperature. These animals are known as ectotherms. Whereas the endothermic animals use internal corrective mechanisms, ectotherms use behavioral mechanisms to maintain their body temperatures.
Thermoregulatory center in the hypothalamus is used to control body temperatures in humans. The thermoregulatory center receives information on body temperature from two receptors. The receptors are situated in the brain and the skin. The receptors are very important because the information they provide helps the body to make the required adjustments. Once the thermoregulatory center receives the message from the receptors, it sends impulses to the different effectors to regulate the body temperature.
In case the external temperature is very hot or so cold, humans respond through taking off some clothes or wearing heavy clothes. If this fails to regulate the body temperature, the thermoregulatory center is stimulated. For example, when it is too hot, the heat loss center in the hypothalamus is stimulated. Conversely, when it is too cold, the heat conservation center in the hypothalamus is stimulated. Some body reactions produce heat while others prevent heat loss. During heat loss mechanism, some reactions cool the body as others reduce the body activities that produce heat.
Animals respond to either high or low body temperature through various mechanisms. First, the body mechanism utilizes Smooth muscles in arterioles in the skin. A drop of the body temperature below the required limit results in the narrowing of the arteries. As a result little heat is carried from the inner body to the surface. This helps in maintaining the body temperature. An increase in the body temperature results in expansion of the arteries. As a result there is more heat reaching the skin surface. Once on the skin surface heat is lost through radiation and convection heat loss processes.
Secondly, when the temperatures are low the sweat glands are stimulated produce no sweat. This ensures that no heat is lost from the body as a result of evaporation. However, when the body is experiencing high temperature, the glands are stimulated to produce sweat. Once on the surface of the skin, water in the sweat evaporates. Evaporation has a cooling effect on the body (IHW, 2006 p. 3).
Another muscle the temperature regulation mechanism utilizes is the electro pili muscles. These muscles link the skin hairs to the body. When the body temperatures are too low, the muscles contract and the skin hair rises. The hair spaces are able to hold some warm air that prevents heat loss from the body. Rise of the body temperatures stimulates the muscles to relax. The hairs fall on the skin allowing free movement of air on the skin surface. The air movement on the skin allows convection and radiation processes to take transfer heat from the body (Fosbery and Mclean, 1996, p. 45).
In addition to the electro pili muscles, the body mechanism also utilizes the skeletal muscles in regulation of the body temperature. When the body temperature is low, the muscles contract and relax repeatedly (shivering). Heat is generated through friction. The metabolic reactions are also increased. The metabolic reactions are increased from about 40% to 60%. The muscles remain calm when the body is experiencing high temperature.
Lastly, Adrenal and Thyroid glands produces important hormones that are important in body temperature regulations. If the body temperature is low, adrenal glands and thyroid glands are stimulated to produce adrenaline and thyroxine hormones respectively. The two increases the metabolic rate in different tissues thereby generating heat. When the temperatures are high the glands are stimulated to stop producing thyroxine.
Blood sugar like the blood temperature also requires regulation. Its concentration affects functioning of all cells in the body. The glucose concentration should be controlled within the range of 0.8 to 1 g per dm3 of blood. Very low levels (hypoglycaemia) and very high levels (hyperglycaemia) of blood sugar are very serious.
The concentration of blood sugar is controlled by the pancreas. The pancreas has glucose receptor cells that observe the concentration of blood sugar in blood. In addition it has endocrine cells which produce hormones (IHW, 2006, p. 4). The α-cells produce hormone glucagon and β-cells produce hormone insulin. Insulin stimulates the uptake of glucose by cells during respiration. Additionally, it stimulates the conversion of glucose to glycogen in the liver. Therefore, insulin decreases blood sugar. On the other hand, glucagon stimulates the breakdown of glycogen into glucose in the liver. It has the effects of increasing the blood sugar. Blood sugar can be higher or lower by 20% from the required margin. For this reason, glucagon and glucose can never occur at the same time.
The corrected condition by the regulation mechanism is referred to as the negative feedback. For example, in blood sugar regulation, after a meal the level of blood sugar increases, the pancreas responds by stimulating the production of insulin by the beta cells. Insulin once produced stimulates most body cells to increase the glucose intake, increases the utilization of glucose in generating energy, it accelerates the transformation of glucose to glycogen in the liver, and it stimulates fat synthesis from glucose. These events cause the decrease in the blood sugar and its concentration returns to normal (Biology References, 2012, par. 3-4).
If the blood sugar falls below the required limit the production of insulin is stopped. The pancreas stimulates the production of glucagon by the alpha cells. Glucagon has the following activities. First, it facilitates the breakdown of glycogen into glucose. Then it increases the breakdown of fats into fatty acids. Lastly, it stimulates the liver cells to increase the synthesis of glycogen into glucose. The flow chart below shows the negative feedback homeostasis in the regulation of blood sugar (IHW, 2006, p. 5)
The blood water concentration needs control to avoid excessive water loss or gain by the body cells. The hypothalamus contains osmosreceptor cells. The cells observe changes in water concentration as the blood passes through the brain. It stimulates antidiuretic hormone stored in the pituitary glands. This hormone causes the water channels to open when the water concentration level in the blood is low. Excess water is lost through the skin as sweat. During respiration the lungs help lose water that is absorbed by carbon dioxide.
According to Jacoby and Youngson (2004 p. 1862), the kidney regulates the amount of water in the body. The kidney also maintains the concentration of body fluids. The kidney extract salts from the waste and the water is then reabsorbed by the body into the blood stream.
Biology References. 2012, Blood Sugar Regulations. Web.
Fosbery, R. and Mclean, J 1996, Biology. Spain: Heinemann.
IHW. 2006, Homeostasis. Web.
Jacoby, D.B. and Youngson, R.M. 2004, Encyclopedia of Family Health. USA: Marshall Cavendish.