Homeostasis: Plasma Glucose Concentration and Thermoregulation

The existence of each cell observed in the human body depends on the composition and steadiness of the chemical and physical characteristics of the surrounding exterior environment. The cell gets oxygen and vitamins for their survival and removes wastes products via the extracellular fluid referred to as the internal environment. The extracellular fluid gets in many instances monitored by varies control structures in the body. The variables of the fluid surrounding the cell and which needs manipulate include temperature, concentrations of glucose, sodium ion, calcium ion, osmolality, and so forth. Regulation of the internal surroundings is known as homeostasis. Favorable internal conditions keep the cell alive and enable it to contribute its activity to the tissue to which it belongs. Similarly, tissues contribute to organs of which they are part of systems as illustrated bellow in diagram 1. Therefore, homeostasis refers to the process of maintaining relatively constant internal physiological conditions in response to changes in the environment.

Homeostasis comprises of four components namely stimuli, receptor, control center and effector Chiras, (2013, 204). The stimulus causes a change in the system while the change gets detected by the receptor or sensor. Control center produces a response to the change detected so as to bring a constant condition by the effector. Homeostasis processes get regulated through feedback mechanisms whereby the effector regulates the process by either reducing the stimulus or by reinforcing it. Feedback mechanisms occur by either negative or positive mechanism. In positive feedback mechanisms, the effector enhances the stimulus thereby moving the system away from its set point. Blood clotting is an example of positive feedback mechanism. Negative feedback involves the effector reducing the effect of stimulus which in turn brings back the system to its set point. Examples of negative feedback mechanisms include thermoregulation and regulation of plasma glucose concentration as discussed below.

Thermoregulation

All metabolic reactions in the body are enzymatic. Therefore, if the body temperature decreases below the standard value, the rate of an enzyme-controlled reaction decreases. Temperature beyond optimum denatures hence metabolic reactions fails to proceed. Khanday, (2014, 153) states that the human body regulates the body’s temperature by maintaining an equilibrium between heat gain and heat loss. The average internal temperatures at rest vary between 36.5 to 37.5oC. Temperatures in the human body get regulated by the thermoregulatory center found in the hypothalamus which gets impulses from two groups of thermoreceptors. The first receptors are located in the hypothalamus and keep check of the blood temperature as it flows over the brain, that is, the core or internal temperature. The second receptors located in the skin known as hot and cold receptors, and they monitor external temperature. Thermoreceptors then send impulses to various effectors that adjust the body temperature.
For instance, on a hot day, thermoreceptors located in the skin conduct signals to the hypothalamus. The hypothalamus responds by distributing nerve impulses to the skin to raise heat loss from the surface of the body by three different ways. The first method is through sweating. Once the body gets too hot, glands found underneath the skin produce sweat on the skin surface. It increases the heat loss through evaporation. Excretion of sweat ends when the body temperature gets back to usual. The second method involves the hairs found on the skin. Relaxation of erector muscles causes the hair to flatten on the surface of the skin, therefore, increasing heat loss. The final method of heat loss involves the vasodilation of the arterioles. Vasodilation happens by relaxation of the muscles found on the walls of the arterioles resulting in widening of the lumen. Therefore, more blood flow in the capillary beds near the skin surface thereby losing heat from the blood by radiation, conduction, and convection. The blood flowing from the skin get to lose more heat to the external environment Gunga, et.al. (2015, 161).

During a cold temperature, thermoregulation gets achieved through the following ways. Muscles get nerve impulses from the brain and respond by shivering associated with rapid contraction and relaxation of skeletal muscles. Shivering warms up the body. Also, the hair erector muscles contracts pulling the hair to a more upright position in the follicle. The standing hair traps a thick layer of air thereby insulating the body against heat loss. Finally. The blood flow pattern switches with less blood flowing in the capillary beds closer to the skin surface, but more blood gets retained deeper in the skin. Heat gain gets achieved by vasoconstriction associated with contraction of muscles found on the arterioles that supply blood to capillary beds near the skin surface Anochie, (2013, 040).

Homeostasis of plasma glucose

Glucose is the form in which carbohydrates get transported in humans, and its concentration affects body cells. Glucose concentration should, therefore, get controlled in the range of 0.8-1g per dm3 of plasma. High levels (hyperglycemia) and low levels (hypoglycemia) of glucose can cause death. The concentration of blood glucose gets regulated by glucagon and insulin hormones secreted by the islets of Langerhans cells in the pancreas.
Stanford, et.al. emphasizes that after a meal time, glucose gets absorbed from the gut into the hepatic portal vein. Therefore, blood glucose level rises and gets sensed by the pancreas an organ that secretes insulin from beta cells. Insulin then binds to the receptor proteins present in cell membranes. More protein passages also get to open permitting more glucose to get into the cells where it gets used for respiration. Moreover, inside the liver insulin encourages an enzymatic change of glucose to glycogen for storage thereby decreasing blood glucose.

During exercise or starvation where glucose concentration gets too low in the blood, the pancreas produces glucagon from alpha cells in response. Glucagon leads to the release of an enzyme found in the liver, which breaks glycogen to glucose. Glucose then diffuses into the blood thus raising the blood sugar level. During extreme cases like strenuous exercises synthesis of glucose could be stimulated from pyruvate. However, blood glucose levels are permitted to deviate from the standard by about 20% before the activation of any control mechanism, and glucagon and insulin can never get secreted at the same time Sherwood, (2016, 371).

Homeostasis brings about a restricted range of conditions where cellular operations work efficiently to sustain life. In humans nervous and endocrine systems regulate homeostasis. Both organs and organ systems offer a response to the brain. The body sustains homeostasis by maintaining conditions like temperature and blood glucose levels. Therefore homeostasis is important because living cells relies on chemical movements around the body. Chemicals like dissolved food, oxygen and carbon dioxide get transported inside and outside the cells which occur by osmosis and diffusion. Also, cells rely on the enzyme to speed up the many metabolic processes that keep the cell alive. The enzymes work best at optimum temperatures, and therefore homeostasis is crucial to cells.
Both thermoregulation and blood sugar control are negative feedback mechanisms. They change the variable to its optimum level. For example, insulin gets produced during high levels of blood sugar. Its production results in the conversion of glucose to glycogen thereby maintaining the sugar level at an optimum. Also during cold the body shivers which results in warming up the body which restores body’s optimum temperature.

Bibliography

Anochie, I.P., 2013. Mechanisms of fever in humans. International Journal of Microbiology and Immunology Research, 2(5), pp.037-043.
Chiras, D. D. (2013). Human Biology. Burlington, Jones & Bartlett Learning, LLC. http://public.eblib.com/choice/PublicFullRecord.aspx?p=4441207.
Gunga, H.-C., Opatz, O., Steinach, M., & Stahn, A. C. (2015). Human physiology in extreme environments. http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=565090.
Khanday, M.A., 2014. Numerical study of partial differential equations to estimate thermoregulation in human dermal regions for temperature-dependent thermal conductivity. Journal of the Egyptian Mathematical Society, 22(1), pp.152-155.
Liang, J., Liu, C., Qiao, A., Cui, Y., Zhang, H., Cui, A., Zhang, S., Yang, Y., Xiao, X., Chen, Y. and Fang, F., 2013. MicroRNA-29a-c decrease fasting blood glucose levels by negatively regulating hepatic gluconeogenesis. Journal of Hepatology, 58(3), pp.535-542.
Sherwood, L. (2016). Human physiology: from cells to systems. http://www.myilibrary.com?id=815632.
Stanford, K.I., Middelbeek, R.J., Townsend, K.L., An, D., Nygaard, E.B., Hitchcox, K.M., Markan, K.R., Nakano, K., Hirshman, M.F., Tseng, Y.H. and Goodyear, L.J., 2013. Brown adipose tissue regulates glucose homeostasis and insulin sensitivity. The Journal of clinical investigation, 123(1), pp.215-223.