Homeostatic Systems in Humans

Homeostasis is a biological term derived from two Greek words for “steady” and “same” and it refers to any manner used by living organisms for superb maintenance of relatively steady body conditions essential for their survival. Any system of the body that is in dynamic equilibrium tends to gain a steady state, which is a balance succesful of resisting outside change forces. The disturbance of such structures ignites a response from the built-in regulatory devices so as to create a new balance via a feedback control process. The human body uses homeostasis to maintain steady levels of the body temperature and other critical conditions like sugar, fat, salt, calcium, oxygen, as well as protein contents (Heer and Egert 2015, p. 18). The brain, the kidneys, and the liver all play critical roles in maintaining homeostasis. Additionally, all the homeostatic systems use negative feedback for the maintenance of a constant value known as the set point (Klinke 2009, p. 1888). Negative feedback implies that the occurrence of a change in a system automatically causes the start of a corrective mechanism, thereby reversing the original change and bringing the system back to normal (set point) (Klinke 2009, p. 1889). This paper gives a description of glucose concentration balance and temperature balance as two of the examples of homeostatic systems in humans.

Body Glucose Homeostasis

Glucose concentration in the body refers to the amount of blood sugar (glucose) present in the blood stream. The human body makes use of glucose as the primary energy source (Thorens 2014, p. 221). However, too large or too small quantities of glucose in the bloodstream can lead to serious complications in the body. Various body hormones play the role of regulating glucose concentration (Thorens 2014, p. 222). Insulin helps in the reduction of the glucose concentration in the bloodstream while glucagon, catecholamine, and cortisol assist in lowering the glucose level (Thorens 2014, p. 224).

Glucose forms the transport carbohydrate in the human body and its level of concentration greatly affects all body cells (Klinke 2009, p. 1889). Glucose concentration is, therefore, controlled through a homeostatic process within the range of 0.8 to 1 gram per dm3 of blood. Additionally, glucose concentration in very high levels (hyperglycaemia) or very low levels (hypoglycaemia) is dangerous and can lead to death (Klinke 2009, p. 1891). The pancreas has an essential role to play in the control of blood glucose concentration. The pancreas has both the endocrine cells and the glucose receptor cells which assist in the secretion of hormones and monitoring the blood glucose concentration respectively (Klinke 2009, p. 1892).

The hormone glucagon is secreted by the α-cells while the hormone insulin is secreted by the β-cells (Ozanne 2010, p. 43). However, the hormones are antagonistic and lead to reverse effects on the blood glucose. While insulin decreases blood glucose, glucagon increases it. Insulin stimulates glucose uptake by respiratory cells, as well as the conversion of glucose to glycogen through the glycogenesis process (Ozanne 2010, p. 44). Glucagon, on the other hand, stimulates the breaking down of glycogen to glucose, through the glycogenolysis process, in the liver. In extreme cases, glucagon can also stimulate glucose synthesis from pyruvate (Heer and Egert 2015, p. 25). Figure 1 below illustrates a summary of the processes involved in the glucose concentration balance in the bloodstream.

After the consumption of a meal, glucose gets absorbed into the hepatic portal vein from the gut, thereby increasing the concentration of glucose in the bloodstream (Thorens 2014, p. 225). The pancreas then detects the change in the glucose concentration and, in response, secretes insulin hormone from its β-cells. Insulin stimulates the uptake of glucose by the liver as well as its conversion to glycogen (Thorens 2014, p. 227). The blood glucose then gets reduced, making the pancreas stop the insulin secretion. If the glucose concentration falls too far, the change is detected by the pancreas, making it release or produce glucagon from its α-cells. Glucagon, in turn, makes the liver break down part of its stored glycogen into glucose, which is absorbed into the bloodstream (Thorens 2014, p. 228). The blood glucose then increases and causes the pancreas to stop glucagon production. Since the levels of blood glucose can deviate from the set point by approximately 20 percent before the activation of any corrective mechanism, the secretion of glucagon and insulin can never occur simultaneously. Figure 2 below shows a summary of glucose homeostasis (Thorens 2014, p. 229).

Body Temperature Homeostasis

Regulation of the body temperature is another example of homeostatic systems in the human body. The normal body temperature is usually 98.6 degrees F or 37 degrees C and, therefore, the temperatures way below or above the normal levels result in serious complications (Adair 2008, p. 588). For example, muscle failure can occur at a body temperature of 82.4 degrees F, or 28 degrees C, while the loss of consciousness can occur at 91.4 degrees F or 33 degrees C. Additionally, the central nervous system can begin to break down at body temperatures of about 107.6 degrees F or 42 degrees C (Chaperon and Seuront 2010, p. 1741). However, too high body temperatures of 111.2 degrees Fahrenheit or 44 degrees C can cause death. The body, therefore, ensures the body temperature balance either by producing heat or releasing excess heat (Chaperon and Seuront 2010, p. 1742).

Humans are warm-blooded, meaning that they maintain almost a constant body temperature. The process of thermoregulation forms an important aspect of human temperature homeostasis (Nisha and Nina 2016, p. 77). Muscle contraction and the liver are the main sources of heat in the body, and the thermoregulation process makes it easy for humans to adapt to various climates, including hot arid and hot humid (Adair 2008, p. 590). High body temperatures pose stresses to the body and may put the body into great danger leading to injury or even death (Adair 2008, p. 590). The cultural and physiological adaptations developed by the human body, therefore, contribute significantly to dealing with different climatic conditions (Nisha and Nina 2016, p. 76). At extreme body temperatures of 45°C (113°F), the body temperature may enter the positive feedback circle. At such extreme temperatures, proteins get denatured, thereby causing a change in the active site of proteins, hence, stopping the metabolism processes and ultimately causing death (Nisha and Nina 2016, p. 76).

In the human body, the temperature gets controlled in the hypothalamus by the thermoregulatory centre (Adair 2008, p. 593). The thermoregulatory centre receives input from two sets of thermoreceptors. The skin receptors help in monitoring the external temperature while the hypothalamus receptors assist in monitoring the blood temperature as the blood passes through the brain (Adair 2008, p. 594). Both information sets from the two receptors are necessary for the body to make appropriate temperature adjustments (Adair 2008, p. 594). Besides, the thermoregulatory centre sends impulses to various effectors to allow for body temperature adjustment as shown in Figure 3 below.

The first response of the body to encountering colder or hotter condition is involuntary. If too cold, one may decide to turn up the heating or put on extra clothes; if too hot, one may decide to take off come clothes (Nisha and Nina 2016, p. 77). The thermoregulatory centre only gets stimulated when such responses are not enough. When the body gets too hot, the hypothalamus’ heat loss centre becomes stimulated. However, when the body gets too cold, it is the hypothalamus’ heat conservation centre that gets stimulated. Some of the low-temperature responses cause heat generation while others lead to heat conservation (Nisha and Nina 2016, p. 79). Similarly, some responses to high body temperatures result in active cooling of the body while others just reduce the production of heat or move the heat to the surface (Chaperon and Seuront 2010, p. 1746). The body, therefore, has a broad range of responses, depending on the external and internal temperatures. Figure 4 below shows a summary of various processes involved in the body temperature homeostasis.

Conclusion

Homeostasis is a process of great importance in the human body as it allows for the fine-tuning of enzymes to a given set of conditions so as to make the body function more efficiently. Additionally, homeostatic systems and processes help keep the body environment under control as well as keep the conditions favorable for the body cells to live and function. The homeostatic systems, therefore, play a vital role in ensuring that all body processes remain in their right conditions.

References

Adair, R. (2008). Reminiscences of a journeyman scientist: studies of thermoregulation in non-human primates and humans. Bioelectromagnetics, 29(8): 586-597.

Chaperon, C., and Seuront, L. (2010). Behavioral thermoregulation in a tropical gastropod: links to climate change scenarios. Global Change Biology, 17(4): 1740-1749.

Heer, M., and Egert, S. (2015). Nutrients other than carbohydrates: their effects on glucose homeostasis in humans. Diabetes/Metabolism Research and Reviews, 31(1): 14-35.

Klinke, D. (2009). Validating a dimensionless number for glucose homeostasis in humans. Annals of Biomedical Engineering, 37(9): 1886-1896.

Nisha, C., and Nina, S. (2016). Sex hormone effects on autonomic mechanisms of thermoregulation in humans. Autonomic Neuroscience, 196, pp. 75-80.

Ozanne, S. (2010). Experimental consequences of IUGR on body weight and glucose homeostasis. Journal of Perinatal Medicine, 38(1): 36-47.

Thorens, B. (2014). GLUT2, glucose sensing and glucose homeostasis. Diabetologia, 58(2): 221-232.