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12: The Endocrine System (Hormones)ContentsFunctions of the Endocrine SystemThe Endocrine system (along with the nervous system) controls and regulates the complex activities of the body. The Endocrine system regulates the activities of the body by secreting complex chemical substances (hormones) into the blood stream. These secretions come from a variety of glands which control various organs of the body. The key functions are:
About HormonesHormonesare secreted from the glands of the endocrine system, they are specific in that each hormone causes a response in a specific target organ or group of cells, rather than on the body as a whole. Exocrine hormones are secreted via a duct into the blood and usually effect a distant organ or tissue. Endocrine hormones are secreted within the tissue (rather than via a duct) and enter the blood stream via capillaries.Hormones can be grouped into three main types:
The Pituitary GlandThis is known as the "master gland" because it exerts control over all of the other glands of the endocrine system. Despite its importance the pituitary gland is no larger than a small pea. The Pituitary gland is made up of two separate glands: the Anterior lobe which is an outgrowth of the pharynx, and the Posterior lobe which is an outgrowth of the brain composed of neural (nerve) tissue. The Anterior Lobe of the pituitary plays the 'master' role secreting six major hormones that affect most of the body, including the other Endocrine glands:
The Posterior Lobe of the Pituitary Gland (or neurophpophysis) stores and releases hormones secreted by the hypothalamus section of the brain including:
The Thyroid glandThe thyroid is a butterfly shaped gland which is located at the base of the throat . It has two lobes separated in the middle by a strip of tissue (the isthmus). The Thyroid itself secretes three main hormones:
People who have surgery to remove the thyroid gland (thyroidectomy) for cancer or other thyroid problems usually need to take thyroxine supplements in order to maintain normal weigh and body functions. The ParathyroidsThere are four Parathyroid glands which are small and rounded, arranged in two pairs usually located above and below the thyroid. Each Parathyroid is small, yellow and smooth, sometimes they imbed themselves in the thyroid itself. Parathyroid hormone increases the blood concentrations of calcium and phosphorous, working to balance the Calcitonin which is secreted by the thyroid to maintain the body's balance of calcium. The PancreasThe pancreas is a long, narrow, lobed gland located behind the stomach. The Pancreas has two types of cells: exocrine and endocrine cells. The exocrine cells secrete Pancreatic juices which are used in the duodenum as an important part in the digestive system. The endocrine cells are arranged in clusters throughout the Pancreas, these known as Islets of Langerhans . There are three types of endocrine cells; alpha cells which secrete glucagon, beta cells which secrete insulin, and delta cells which inhibit the secretion on glucagon and insulin:
The Adrenal GlandsThe adrenal glands resemble small caps perched on top of each kidney. The Adrenal is actually a combination of two glands the adrenal cortex and the adrenal medulla. The adrenal cortex is essential for life, as opposed to the adrenal medulla which is important but not indispensable. The anterior pituitary controls the adrenal cortex by secreting the hormone ACTH. All of the secretions of the adrenal cortex are known as steroids, many of which can now be manufactured synthetically. The adrenal cortex is made up of three layers associated with three classes of hormones:
The Adrenal Medulla is the inner part of the adrenal gland. The hormones secreted effect the structures in the body that are under the control of the sympathetic nervous system, aiding the body to deal with stressful situations such as fright, attack or pursuit. They are both associated with an increased heart beat, higher blood pressure, and higher blood glucose levels, thus preparing the body for quick action.
The GonadsThe gonads consist of ovaries in the female and testes in the male. These glands produce hormones important in the development and functioning of the reproductive organs. they are under the control of the pituitary gland, and produce the secondary sexual traits. Male testes are egg shaped glands located in the sac like scrotum, and serve two main functions: (i) The production of sperm cells, and (ii) The secretion of testosterone. Testosterone is the masculizing hormone inducing male secondary sexual characteristics after puberty. Female ovaries are two almond shaped glands on each side of the uterus. They have three main functions; (i) Containing immature ova (eggs), (ii) The secretion of oestrogen, and (ii) the secretion of progesterone. Ostrogen is secreted by the adrenal cortex as well as the ovaries, and is present in the blood of all females from puberty through to the menopause. oestrogen acts on the structure of the reproductive organs, especially during the menstrual cycle. This induces and maintains female secondary sexual characteristics. Progesterone works on the uterus to prepare it for the implantation of a fertilised ovum (egg). It causes the development of the breasts, and is essential for the complete development of the maternal proportion of the placenta. Giantism too much HGH is secreted before puberty. Diabetes Mellitus is a condition with under-secretion of insulin, causing the cells to loose their permeability to glucose preventing them from getting sugar needed for energy. Sugar remains in the blood and often the body will try and remove this leading to a high sugar content in the urine, causing polyuria (passing of large volumes of urine) and polydipsia (excessive thirst). Roots, suffixes, and prefixesMost medical terms are comprised of a root word plus a suffix (word ending) and/or a prefix (beginning of the word). Here are some examples related to the Endocrine System. For more details see Chapter 4: Understanding the Components of Medical Terminology
Cancer FocusOverview of Endocrine System CancersTumours can arise in the endocrine system, e.g. pituitary tumours, thyroid cancers and neuroendocrine tumours of the pancreas. As a consequence of the position of these tumours, they may cause destruction of the normal gland and subsequent hormonal deficiency. Occasionally these tumours can also lead to an overproduction or secretion of hormone e.g. some pituitary tumours may lead to precocious puberty. The adrenal medulla is a common site for the development of neuroblastoma.Neuroblastoma may be associated with hypertension as a result of the oversecretion of catecholamines.Radiation therapy given to children may lead to reduced growth in the bones and muscles in the affected area, for example when the patient reaches adulthood one limb might be slightly shorter than the other. Related Abbreviations and Acronyms
Further Resources (3 links)SEER, National Cancer Institute WebAnatomy, University of Minnesota Paul Andersen This guide by Simon Cotterill First created 4th March 1996 Which glands secrete hormones that regulate metabolism?Adrenal gland.
The adrenal glands make and release corticosteroid hormones and epinephrine that maintain blood pressure and regulate metabolism.
Which hormone regulates the metabolism of carbohydrates fats and proteins in the body quizlet?Insulin helps control carbohydrate, protein, and fat metabolism in the cell. Insulin stimulates the breakdown of glucose (glycolysis) for energy and stimulates the liver and skeletal muscles to store excess glucose as glycogen (glycogenesis).
Which hormone regulates the metabolism of carbohydrates fats and proteins in the body and also has an anti inflammatory action?Cortisol is known as a stress hormone involved in the response to physical and/or emotional stress. Cortisol also participates in various homeostatic maintenance actions: blood pressure; immune system; metabolism of protein, carbohydrate, and adipose; and anti-inflammatory action.
Which gland secretes hormones that regulate the body's metabolism quizlet?The thyroid gland has a major role in regulating the body's metabolism. The gonads serve two important function; the production of gametes and the secretion of sex hormones.
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