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The Role of Hormones and Endocrine Glands

Discuss about the Medical Physiology for Biology (Endocrine System).

1. The endocrine system consists of a collection of different glands, which are concerned, with the secretion of hormones. This system is considered as one of the most integrative systems within the human body since the hormones that are produced by the endocrine glands act at a distance and several of these hormones act in diverse organs of the body (Melmed et al. 2015). This essay aims to describe the role of the main hormones and the endocrine glands that produce different hormones. It will explain the role of the blood stream in the process. In addition, it will also explain the role of the target cells and several other mechanisms that are associated with the endocrine system.

This system is responsible for signaling the information. Its mechanisms as well as effects are slow in initiation but are extended in response as they last from a small number of hours to weeks. The study of the endocrine system and the disorders which are associated with it is known as endocrinology, which is a branch of internal medicine (Fuxe 2013).  The important glands of the endocrine system include the thyroid gland, pituitary gland, parathyroid gland, adrenal glands, pineal gland, hypothalamus, testes, ovaries and pancreas. The distinctive features of these glands include their ductless nature, presence of intracellular vacuoles and their vascular nature (Boron and Boulpaep 2016). 

“Hormones are the effectors of the endocrine system”. The different glands of the endocrine system secrete them and they are collected through circulation. Some of the hormones are proteins as for e.g. glucagon and insulin while other hormones are derived from proteins or in other words, they are modified amino acids, for e.g. noradrenaline and adrenaline. A few of the hormones are steroids, such as estrogen and corticosteroids (Melmed et al. 2015). The hormone melatonin is secreted by the pineal gland is produced at night and is associated with the circadian rhythm circulation (Axelrod 2013). This hormone has an important function in regulating the several functions of the body that are associated with the night-day cycle. The hormones that are secreted by the thyroid gland includes three hormones namely, triiodothyronine, Thyroxine, and calcitonin. Thyroxine is concerned with the stimulation of body oxygen and consumption of energy. It increases the basal metabolic rate and promotes protein synthesis. Triiodothyronine performs similar functions like thyroxine. Calcitonin is responsible for the stimulation of osteoblasts. The pancreas is a mixed gland and secretes the hormones such as glucagon, insulin, pancreatic polypeptide and somatostatin (Zarrow 2012). Glucagon enhances the blood glucose level. Insulin helps in glycolysis and glycogenesis in muscle and liver from the blood. Somatostatin inhibits the release of glucagon and insulin. Pancreatic polypeptide is concerned with the regulation of the activities of pancreatic secretion. The adrenal glands secrete adrenaline and noradrenaline. Adrenaline boosts glucose and oxygen supply to the muscles and brain, dilation of pupils. Noradrenaline improves the readiness of the skeletal muscles. The testes secrete the hormones like testosterone and estradiol. Testesterone helps in the maturation of sex organs, scrotum formation and growth of axillary hairs and beard. Estradiol prevents apoptosis of the germ cells. The ovaries secrete progesterone and estrogen. Progesterone plays a significant role during pregnancy while estrogen is concerned with several functions of the body (Sherwood 2015). 

Distinctive Features of Endocrine Glands

The blood stream plays a significant role in the endocrine system as the blood collects the different hormones that are produced by the endocrine glands and they reach to the target organs through circulation (Fuxe 2013). Hence, for the proper functioning of the endocrine system, circulatory system is essential. In the absence of the circulatory system, the feature of “action at distance” of the endocrine system would not take place. After passing through the blood stream, the communication of the hormones with the body occurs which is headed towards the target cells for bringing about a specific effect or alteration to the cell. The hormones can also lead to alterations in the cells of the adjacent tissues (Norris and Carr 2013). 

Receptors are present on the target cells, these receptors are specific for every hormone, and their activation is carried out either through water-soluble hormones or lipid/fat soluble hormones. The diffusion of lipid/fat soluble hormones occurs through the plasma membrane for entering into the target cell and binding with a receptor protein on the cell’s plasma membrane. On the other hand, the water-soluble hormones bind with a receptor protein on the cell’s plasma membrane (Labhart 2012). 

Polypeptide/protein hormones act on the cells which act as specific targets. Binding occurs with the receptors that are located on cell surface. These receptors are glycoproteins and proteins that are fixed in the cell membrane (Sherwood 2015).  Examples of polypeptide/protein hormones comprise insulin secreted from the pancreas and adrenocorticotropin secreted from the pituitary gland. Eicosanoids like prostaglandins and Catecholamines such as epinephrine discover their receptors sticked to the cell membrane of the target cells. Polypeptide and steroid hormones both are concerned with the regulation of gene expression by involving a communication with the core complex of transcription through the similar injector. The receptor of polypeptide hormones is exceptional to the specific target cell. The polypeptide receptors use three different classes of cell surface receptors namely, Ligand-gated ion channels, G-protein receptors and catalytic receptors. On the other hand, the receptors of steroid hormones occur in all the nucleated cells. They work at a slower pace and require elevated concentrations (Zarrow 2012).

To conclude, the endocrine system plays an important role and has several functions overall. It is responsible for secretion of hormones, metabolism, growth and several other activities of the cells. It acts as an information signal system. This system is considered to be one of the most integrative systems within the human body since the hormones that are produced by the endocrine glands act at a distance and numerous of these hormones act in diverse organs of the body. It is also responsible for maintaining homeostasis of the body. If this system lacks a proper functioning, then it leads to the development of several diseases associated with growth and metabolism.

Blood Stream and Endocrine System

Homeostasis refers to the way by which a stable environment is maintained by the body. It is essential for our body to maintain a stable environment for the cells for functioning in a correct manner (Hardie 2015).  It keeps the internal environment of the body balanced. The well-recognized homeostats in the human body and other mammalians are the regulators that are concerned in keeping the composition of the internal environment constituting of extracellular fluids constant, particularly with respect to pH, temperature, osmolality and Ca2+, K+, Na+, O2, CO2 and Glucose concentrations (Ramsay and Woods 2014). The control mechanisms of homeostasis have at least three components that are dependent on each other, namely, receptor, effector and integrating center. The receptor is responsible for sensing the environmental stimuli and sends the information to the integrating center (Waugh and Grant 2014). This center is usually a region in the brain known as the hypothalamus, which is concerned with the signaling of an effector for responding to the stimuli. An effector refers to any tissue or organ, which receives information from the integrating center and works to result in the changes required for maintaining homeostasis. Negative and positive feedbacks are central to understand the process of homeostasis (Ramsay and Woods 2014).

Negative feedback

Almost all the control mechanisms of homeostasis are negative feedback mechanisms. It occurs when the systems require slowing down or completely stopping a process, which is taking place (Hardie 2015). For example, when food substances are consumed, they travel in the stomach. After this, the process of digestion commences. It works by involving different hormones together with the nerve impulses for stopping as well as starting the acids secretion in the stomach. An additional instance of negative feedback is sweating (Waugh and Grant 2014). 

Positive Feedback

In positive feedback mechanism for maintaining homeostasis, the enhancement of an output occurs. It is responsible for amplifying the action of a system or encouraging a physiological process (Ramsay and Woods 2014). Positive feedback involves a cyclic process, which can continue for amplifying the response of the body to stimuli until there is a takeover of response of negative feedback (Waugh and Grant 2014).  A very good illustration of positive feedback can also take place inside the stomach. It usually secretes pepsinogen, which is an inactive enzyme (Waugh and Grant 2014).  Since pepsinogen is converted to pepsin by the body, it activates a process that aids in the conversion of the molecules of pepsinogen to pepsin. After the occurrence of this cascade effect, the stomach gets sufficient molecules of pepsin for digesting proteins (Hall 2015).  

Role of Target Cells

Homeostasis of blood Glucose levels

In our bodies, glucose acts as a fuel for the cells but for diffusing into the cells, it is too big. Instead, it requires to be transported into the cells. Pancreas produces a hormone, namely insulin, which facilitates the transport of glucose into the cells (Hall 2015). Insulin reduces the levels of blood glucose as a result of facilitating the transport of glucose into the cells via bloodstream (Hardie 2015). It also slows down the production of glucose from the amino acids glycogen and fatty acids. Insulin is responsible for the stimulation of formation of glycogen from glucose. These functions of insulin assist in lowering the blood glucose levels (Waugh and Grant 2014).  

Homeostasis of Blood Glucose Levels                      

Homeostasis of Blood Glucose Levels

(Negative Feedback)                                           

Oxytocin in a normal labour- Homeostasis

Oxytocin is a hormone, which is produced by the endocrine system and is responsible to stimulating uterus contraction. This leads to the development of pain, which is sensed through the nervous system (Kenkel, Yee and Carter 2014). Instead of minimizing, the oxytocin and causing the pain to drop, additional production of oxytocin occurs until the contractions become powerful enough leading to the birth of the child. During labor in females, this hormone is released and is responsible for intensification and speeding up of the contractions. The birth of the child ends oxytocin release and the mechanism of positive feedback ends too (Burgos et al. 2016).

Oxytocin in a normal labour- Positive feedback (Flowchart)

3. This study aims to critically analyse the use of Hormone Replacement Therapy (HRT) in the human body. It is a type of hormone therapy in which the patients during their course of medical treatment are made to receive hormones either for supplementing a shortage of hormones that occur naturally or for substituting other hormones in place of the naturally occurring hormones (Tucker et al. 2016). This therapy utilizes normal concentrations of hormone supplements for returning the hormone levels within the normal ranges. The common types hormone replacement therapy comprise of the following:

Hormone Replacement Therapy for Menopause- It utilizes one or more medication groups that are designed for boosting the hormone levels artificially and is based on the thought that the treatment may lead to the prevention of discomfort, which is caused by reducing the circulating progesterone and estrogen hormones. The major hormones that are involved with this therapy include progesterone, estrogen and in some cases testosterone. This therapy is often referred to as “treatment” (Jordahl et al.  2015).

Androgen Replacement Therapy- Involves treatment by hormones frequently prescribes to contradict male hypogonadism effects (Kotsopoulos et al. 2016). It is also prescribed for delaying the onset of aging in males. In addition, this therapy is utilized for the males with reduced testicular functions, cancer, along with some other reasons (Jordahl et al.  2015).  

Hormone Replacement Therapy for Transgender individuals – This therapy is involved with the introduction of hormones that are associated with the sexual category identified by the patient (for trans women estrogen is used and for trans men testosterone is used). A number of intersex individuals may receive HRT. For transgender people, Cross-sex hormone treatment is divided into two- hormone replacement therapy (male-to-female), hormone replacement therapy (female-to-male) (Hou et al. 2013).

Polypeptide/Protein Hormones and Steroid Hormones

Hormone replacement therapy was first discovered in the year 1940 but it became more prominent in the year 1960 and had created a revolution in menopause management in women (Kuh et al., 2016). It was prescribed generally for the relief symptoms of the menopausal women such as genito-urinary and psychological problems, night sweats, hot flushes, sleep disturbances, vaginal dryness, reduced sexual drive and mood swings (Shapiro et al. 2013).

This therapy has been revealed to possess several beneficial effects (Kuh et al., 2016). A study carried out in women demonstrated that the women who took estrogen through HRT revealed that the prefrontal cortex is positively affected by estrogen by enhancing the working memory (Jordahl et al.  2015). It proposes that estrogen play a significant role in certain functions of the frontal lobe in women. The women who utilized HRT subsequent to menopause did not gained additional weight in comparison to the women who did not utilize HRT (Kuh et al., 2016). In addition, the women who used HRT together with a component of estrogen exhibited positive effects in their sexual life, as their sexual sensitivity and sexual drive increased but the effects were contradictory across women (Kotsopoulos et al. 2016).

In addition to the benefits, there are also some identified risks of this therapy as some researchers have proved that some HRT forms enhance the risk of womb (endometrial) cancer. (Tucker et al. 2016). Nonetheless, previous research has revealed that the integrated form of HRT poses a bigger risk of developing breast cancer in comparison to estrogen or tibolone. It can result in side effects such as headaches, indigestion, nausea, vaginal bleeding and abdominal pain (Shapiro et al. 2013).

A study in the menopausal women utilizing HRT along with progestin as the main constituent of the therapy revealed some negative effects with respect to hearing that highlighted the significance of selecting bioidentical progesterone rather than synthetic progestin. It has also been revealed in some of the situations that menopausal women who had a role of caregiving and receiving HRT are more prone to suffer from cardiovascular diseases (Kuh et al., 2016).

To avoid the risks of HRT, it is necessary to utilize the most efficient delivery method of progesterone as well as estrogen. The patients and the healthcare providers should discuss the benefit and risks of the individuals particularly the women. If the individuals decided to take HRT, then it should be of a lowest dose and that assists for the shortest time required. It is a kind of hormone therapy in which the patients during their course of medical treatment are made to receive hormones either for supplementing a shortage of hormones that occur naturally or for substituting other hormones in place of the naturally occurring hormones (Shapiro et al. 2013).

Homeostasis and Its Role

References

Axelrod, J. ed., 2013. The pineal gland and its endocrine role (Vol. 65). Springer Science & Business Media.

Boron, W.F. and Boulpaep, E.L., 2016. Medical physiology. Elsevier Health Sciences.

Burgos, J., Arana, I., Garitano, I., Rodríguez, L., Cobos, P., Osuna, C., del Mar Centeno, M. and Fernández-Llebrez, L., 2016. Induction of labor in breech presentation at term: a retrospective cohort study. Journal of perinatal medicine.

Fuxe, K. ed., 2013. Central regulation of the endocrine system (Vol. 42). Springer Science & Business Media.

Hall, J.E., 2015. Guyton and Hall textbook of medical physiology. Elsevier Health Sciences.

Hardie, D.G., 2015. AMPK: positive and negative regulation, and its role in whole-body energy homeostasis. Current opinion in cell biology, 33, pp.1-7.

Hou, N., Hong, S., Wang, W., Olopade, O.I., Dignam, J.J. and Huo, D., 2013. Hormone replacement therapy and breast cancer: heterogeneous risks by race, weight, and breast density. Journal of the National Cancer Institute,105(18), pp.1365-1372.

Jordahl, K.M., Doody, D.R., Zhang, Y., Yan, D., Randolph, T.W., Johnson, L.G., Li, C.I., Kelsey, K., Houseman, E.A., Wang, P. and Malone, K.E., 2015. Hormone replacement therapy and genome-wide DNA methylation among post-menopausal women. Cancer Research, 75(15 Supplement), pp.2772-2772.

Kenkel, W.M., Yee, J.R. and Carter, C.S., 2014. Is oxytocin a maternal–foetal signalling molecule at birth? Implications for development. Journal of neuroendocrinology, 26(10), pp.739-749.

Kotsopoulos, J., Huzarski, T., Gronwald, J., Moller, P., Lynch, H.T., Neuhausen, S.L., Senter, L., Demsky, R., Foulkes, W.D., Eng, C. and Karlan, B., 2016. Hormone replacement therapy after menopause and risk of breast cancer in BRCA1 mutation carriers: a case–control study. Breast cancer research and treatment, 155(2), pp.365-373.

Kuh, D., Muthuri, S., Cooper, R., Moore, A., MacKinnon, K., Cooper, C., Adams, J.E., Hardy, R. and Ward, K.A., 2016. Menopause, reproductive life, hormone replacement therapy and bone phenotype at age 60–64: a British birth cohort. The Journal of Clinical Endocrinology & Metabolism, pp.jc-2016.

Labhart, A., 2012. Clinical endocrinology: theory and practice. Springer Science & Business Media.

Melmed, S., Polonsky, K.S., Larsen, P.R. and Kronenberg, H.M., 2015.Williams textbook of endocrinology. Elsevier Health Sciences.

Norris, D.O. and Carr, J.A., 2013. Vertebrate endocrinology. Academic Press.

Ramsay, D.S. and Woods, S.C., 2014. Clarifying the roles of homeostasis and allostasis in physiological regulation. Psychological review, 121(2), p.225.

Shapiro, S., Farmer, R.D., Stevenson, J.C., Burger, H.G., Mueck, A.O. and Gompel, A., 2013. Does hormone replacement therapy (HRT) cause breast cancer? An application of causal principles to three studies. Journal of Family Planning and Reproductive Health Care, 39(2), pp.80-88.

Sherwood, L., 2015. Human physiology: from cells to systems. Cengage learning.

Tucker, P.E., Bulsara, M.K., Salfinger, S.G., Tan, J.J.S., Green, H. and Cohen, P.A., 2016. The effects of pre-operative menopausal status and hormone replacement therapy (HRT) on sexuality and quality of life after risk-reducing salpingo-oophorectomy. Maturitas, 85, pp.42-48.

Waugh, A. and Grant, A., 2014. Ross & Wilson anatomy and physiology in health and illness. Elsevier Health Sciences.

Zarrow, M.X., 2012. Experimental endocrinology: a sourcebook of basic techniques. Elsevier.

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