How the Endocrine System affects Chronic Disease

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Choose one of the CDC’s five most common chronic diseases (heart disease, stroke, cancer, diabetes, or arthritis) and describe the anatomical and physiological changes associated with the endocrine system. Describe normal function of the system and how the disease alters the normal function. List signs and symptoms that indicate the disease has developed, specific to the system being covered. Identify and describe steps people can take to reduce their risk of developing the chronic disease.

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10 The Endocrine System The Body’s Other Control Center Here we are again, talking about control. We have already visited one of the control systems—the complex structure of cells and connections known as the nervous system. Now we visit yet another control system—the endocrine system. These two control systems may seem like separate systems, but they are interconnected and always monitor each other’s activities. The nervous system collects information and sends orders with a speed that is truly mind-boggling. Whereas the endocrine system also collects information and sends orders, it’s a slower, more subtle control system. The endocrine system’s orders to the body also last much longer than those made by the nervous system. You might think of the endocrine system as sending “standing orders,” or orders meant to be obeyed inde initely unless changed by another set of orders. The orders change subtly on a regular basis, but their intention is constant. The nervous system, on the other hand, issues orders that are to be obeyed instantaneously but are used for short-term situations. The endocrine system demands organs to “carry on,” whereas the nervous system expects them to respond immediately. On our journey, suppose we stop at an amusement park to ride a roller coaster. Afterward, en route to our next destination, we are forced off the road because of a near miss with a truck. Even after the roller coaster ride is over or the truck is long gone, your legs still shake, your heart continues to race, and your blood pressure remains elevated, even though you are no longer in danger. We call such lingering effects the “adrenaline rush.” These lingering effects are not due to continued activity of the nervous system, but rather to endocrine activity deliberately triggered by the autonomic nervous system. LEARNING OUTCOMES At the completion of your journey through this chapter, you will be able to: ● Discuss the functions of the various endocrine glands ● Describe the purpose and effects of hormones within the body ● Discuss the process of homeostatic control and feedback mechanisms of hormone levels ● Differentiate between hormonal control, humoral control, and neural control of hormones ● Explain common diseases of the endocrine system Pronunciation Guide Correct pronunciation is important in any journey so that you and others are completely understood. Here is a “see and say” Pronunciation Guide for the more dif icult terms to pronounce in this chapter. In addition, the Audio Glossary includes an audio pronunciation and de inition of each of these terms. Please note that pronunciations given are referenced to medical dictionaries, and regional variations may exist. adrenal cortex (ah DREE nal KOR teks) adrenal medulla (ah DREE nal meh DULL lah) antidiuretic hormone (AN tye dye yoo RET ick) endocrine (EHN doh krin) epinephrine (EP ih NEFF rin) homeostasis (HOH mee oh STAY sis) hormone (HOR moan) hypercholesterolemia (HIGH per koh LESS ter ohl EE me ah) hyperpituitarism (HIGH per peh TOO eh tair izm) hypopituitarism (HIGH poh peh TOO eh tair izm) hypothalamus (HIGH poh THAL ah mus) melatonin (MELL ah TOH nin) norepinephrine (nor EP ih NEFF rin) oxytocin (AHK see TOH sin) pancreas (PAN kree ass) parathyroid gland (PAIR ah THIGH royd) pineal gland (PIN ee al) pituitary (pih TOO ih tair ee) prolactin (proh LAK tin) testes (TESS teez) thymus (THIGH mus) thyroid (THIGH royd) 10.1 ORGANIZATION OF THE ENDOCRINE SYSTEM The endocrine system has many organs that secrete a variety of chemical substances. Let’s begin by looking at the basic organization of the system. Endocrine Organs The endocrine system (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss412) is a series of organs and ductless glands (see FIGURE 10-1 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec1#ch10 ig1) ) in your body that secrete chemical messengers called hormones (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss599) into your bloodstream. (Note that endo means “into,” and crine means “to secrete.”) In contrast, exocrine (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss455) glands and organs such as the pancreas and the sweat, salivary, and lacrimal glands produce secretions that must exit that particular gland through a duct. We have already discussed some of the endocrine glands, such as the hypothalamus, pituitary, and pineal glands, because they are part of the nervous system and provide a link between the two control systems. We will visit some of the other endocrine glands later when we journey through the urinary, reproductive, and digestive systems. Many endocrine glands, like the hypothalamus and pancreas, have multiple functions. It may seem like an overwhelming task to learn all the endocrine glands and their associated hormones. Therefore, we will begin our discussion with a concise overview to lay a foundation on which to build. As we journey through this chapter, these concepts are reinforced and expanded. For now, see TABLE 10-1 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec1#ch10tab1) , which lists the wide variety of functions of endocrine organs. Amazing Body Facts Lesser-Known Endocrine Glands Did you know that many organs, such as the heart, small intestine, kidneys, stomach, and placenta, can also secrete hormones and therefore have endocrine-like functions? These and many other organs are not listed as endocrine glands because their primary jobs are focused on other tasks, like pumping blood, storing and digesting food, or nourishing an embryo. But the hormones secreted by other organs are still an important part of the body’s control systems. Hormones The chemical messengers released by endocrine glands are called hormones (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss599) . We have already seen one type of chemical messenger: the neurotransmitter. Neurotransmitters are released by neurons at chemical synapses. They diffuse across the synapse (a very tiny space) to a cell on the other side, and they bind to that cell. They are cleaned up quickly, so their effects are localized and short-lived. Hormones, on the other hand, are released into the bloodstream and travel all over your body. Some hormones can affect millions of cells simultaneously. Their effects last for minutes or even hours or days. Many hormones are secreted constantly, and the amount secreted changes as needed. To help clarify the similarities and differences between a neurotransmitter and hormone, please see TABLE 10-2 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec1#ch10tab2) . FIGURE 10-1 ▲ The endocrine glands and their hormones. TABLE 10-1 ENDOCRINE ORGAN FUNCTIONS ENDOCRINE ORGAN HORMONE RELEASED EFFECT Hypothalamus A variety of hormones; see Table 10-3 Controls (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10tab3) pituitary hormone levels Pineal Melatonin Believed to regulate sleep Pituitary A variety of hormones; see Table 10-3 Controls other (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10tab3) endocrine organs Thyroid Parathyroid glands Thyroxine, triiodothyronine Controls cellular metabolism Calcitonin Decreases blood calcium Parathyroid hormone Increases blood calcium ENDOCRINE ORGAN HORMONE RELEASED EFFECT Pancreas Insulin Lowers blood sugar Glucagon Raises blood sugar Epinephrine, norepinephrine Flight-or- ight response Adrenocorticosteroids Many different effects Ovaries Estrogen, progesterone Control sexual reproduction and secondary sexual characteristics, such as pubic hair and axillary hair Testes Testosterone Control secondary sexual characteristics, such as growth of beard and other hair, deepening of voice, increase in musculature, production of sperm Thymus Thymosin Immune system, causing maturation of white blood cells Adrenal glands TABLE 10-2 COMPARISON OF NEUROTRANSMITTERS AND HORMONES NEUROTRANSMITTERS HORMONES Chemical messengers Chemical messengers Bind to receiving cell Bind to receiving cell Control cell excitation Control cell activities Released by neurons Released by neurons, glands, or organs Released at chemical synapse Released into bloodstream Intended target very close Travel to distant target Effects happen quickly (less than a second) Effects take time (seconds or minutes) Effects wear off quickly (few seconds) Effects long lasting (minutes or hours) Affect single cell Can affect many cells How Hormones Work Like neurotransmitters, hormones work by binding to receptors on target cells. But hormones may bind not only to sites on the outside of the cell, like neurotransmitters, but also to sites inside the cell. If hormones bind to the outside of the cell, they can have several different effects, either changing cellular permeability or sending the target cell a message that changes enzyme activity inside the cell. Thus, the target cell changes what it has been doing, usually by making a new protein or turning off a protein it has been making. One special class of hormones, steroids (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1289) , is particularly powerful because steroids can bind to sites inside cells. (Thyroid hormones also enter cells, but many other hormones do not.) Steroids are lipid molecules that can pass easily through the target cell membrane. These hormones can then interact directly with the cell’s DNA, the genetic material, to change cell activity. These hormones are carefully regulated by the body because of their ability, even in very small amounts, to control target cells. See the section “The Adrenal Glands” for further discussion of steroid hormones and the dangers of taking steroids. WEBSITE MEDIA EXTRA View a 3-D animation of the endocrine system and try an interactive drag-and-drop exercise. TEST YOUR KNOWLEDGE 10-1 Choose the best answer: 1. What chemical, when secreted into the bloodstream, controls the metabolic processes of target cells? a. neurotransmitter b. secretion c. hormone d. ligand 2. Steroid hormones are very powerful because they: a. are hormones b. are medicine c. interact directly with DNA d. are secreted outside the body 3. Which of the following is true of hormones? a. They last a short time. b. They are fast acting. c. They affect distant targets. d. They leave the body. 10.2 CONTROL OF ENDOCRINE ACTIVITY Many endocrine glands and organs are active all the time. The amount of hormones they secrete changes as the situation demands, but unlike neurons, the cells in the endocrine glands often secrete hormones continuously. How is the activity controlled? How do these glands and organs know how much hormone to secrete? Homeostasis and Negative Feedback To understand how the endocrine system is controlled, we irst have to revisit the concept of homeostasis (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss595) discussed at the beginning of our journey in Chapter 1 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch01#ch01) (see FIGURE 10-2 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec2#ch10 ig2) ). Recall that many of the chemical and physical characteristics of the body have a standard level, or set point (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1230) , that is the ideal level for that particular value. Blood pressure, blood oxygen, heart rate, and blood sugar, for example, all have “normal” ranges. Your control systems, nervous and endocrine, work to keep the levels at or near ideal. There is a way for your body to measure the variable, a place where the “ideal” level is stored, and a way for the body to correct levels that are not near ideal. For example, neurons measure your body temperature. The hypothalamus stores the set point. If your temperature falls below the set point temperature, the hypothalamus causes shivering to produce additional heat. If body temperature rises above the set point, the hypothalamus causes sweating. If any of the body’s dozens of homeostatic values become seriously disrupted, the control systems work to bring them back to set point. This process is called negative feedback (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss869) (see FIGURE 10-3 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec2#ch10 ig3) ). Most of you are familiar with negative feedback in real life. When you pump gas, a sensor in the nozzle turns off the low of gas when the tank is full. That is negative feedback. The gas is lowing, the tank is illing, and when the goal is reached, the gas stops lowing. In the body, negative feedback counteracts a change. As blood pressure rises, for example, your body works to bring it down to normal. If blood pressure falls, your body works to raise it back to the normal set point. Hormones work the same way. As hormone levels rise, negative feedback turns off the endocrine organ that is secreting the hormone. The body is also capable of positive feedback (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1059) , which increases the magnitude of a change. The low of sodium into a neuron during depolarization is a real-life example we have already visited. The more depolarized a neuron becomes, the more sodium lows in, so it becomes more depolarized, so more lows in, and so on. Childbirth also involves an important positive feedback mechanism (see the Clinical Application in this chapter). Therefore, positive feedback is not a way to regulate your body because it increases a change away from set point. What if instead of shivering when you got cold to raise your body temperature, you got colder and colder and colder? Sources of Control of Hormone Levels Hormone levels can be controlled by the nervous system (neural control (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss878) ), by other hormones (hormonal control (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss598) ), or by body luids such as the blood (humoral control (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss603) ). Neural Control FIGURE 10-2 ▲ Homeostasis is analogous to regulation of temperature via a thermostat. Some hormones are directly controlled by the nervous system. For example, the adrenal glands receive signals from the sympathetic nervous system. When the sympathetic nervous system is active (remember the near-wreck), it sends signals to the adrenal glands to release epinephrine and norepinephrine as hormones, prolonging the effects of sympathetic activity (see FIGURE 10-4 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec2#ch10 ig4) ). FIGURE 10-3 ▲ Homeostasis and negative feedback as related to control of body temperature. Hormonal Control FIGURE 10-4 ▲ Sympathetic control of adrenal gland. Other hormones are part of a hierarchy of hormonal control in which one gland is controlled by the release of hormones from another gland higher in the chain, which is controlled by another gland’s release of hormones yet higher in the chain. Orders are sent from one organ to another. This is very similar to a relay race at a track meet where the baton is smoothly handed from one runner to the next to send the baton to the inish line. Negative feedback controls the low of orders via hormones from one part of the “chain of command” to the other. For example, the hypothalamus has control over the pituitary, which has control over the adrenal gland, which secretes the hormone cortisol. Increased cortisol secretion is one way that the body copes with stress, and as cortisol levels rise in the blood, further release of hormones at the hypothalamus is depressed. This is an example of negative feedback. Please see FIGURE 10-5 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec2#ch10 ig5) . Clinical Application CHILDBIRTH AND POSITIVE FEEDBACK Positive feedback is often harmful if the cycle cannot be broken, but sometimes positive feedback is necessary for a process to run to completion. A good example of necessary positive feedback is the continued contraction of the uterus during childbirth. When a baby is ready to be born, a signal tells the hypothalamus to release the hormone oxytocin (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss953) from the posterior pituitary. Oxytocin increases the intensity of uterine contractions. As the uterus contracts, the pressure inside the uterus caused by the baby moving down the birth canal increases the signal to the hypothalamus: More oxytocin is released, and the uterus contracts harder. As pressure gets higher inside the uterus, the hypothalamus is signaled to release more oxytocin, and the uterus contracts even harder. This cycle of ever-increasing uterine contractions due to ever-increasing release of oxytocin from the hypothalamus continues until the pressure inside the uterus decreases— that is, when the baby is born. FIGURE 10-5 ▲ Hormonal control of adrenal gland. CRH = corticotropin releasing hormone; ACTH = adrenocorticotropic hormone. Humoral Control Still other endocrine organs or glands can directly monitor the body’s internal environment by monitoring the body luids, such as the blood, and respond accordingly. Humoral pertains to body luids or substances, and therefore control through body luids is called humoral control (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss603) . For example, the pancreas secretes insulin in response to rising blood sugar, as shown in FIGURE 10-6 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec2#ch10 ig6) . In diabetics, like Maria, this response is impaired due to destruction of the pancreas by the immune system. FIGURE 10-6 ▲ Humoral control of blood sugar levels. TEST YOUR KNOWLEDGE 10-2 Choose the best answer: 1. Which of the following is the least common way that hormones are regulated? a. negative feedback b. chain of command c. positive feedback d. direct control by nervous system 2. The “ideal” value for a body characteristic is called the: a. set point b. average c. goal d. feedback point 3. _____________ feedback enhances a change in body chemistry. a. Negative b. Positive c. Regular d. Cyclic 10.3 THE MAJOR ENDOCRINE ORGANS The endocrine system has several organs, and each has speci ic tasks within the body. The messages to carry out these tasks are related to the hormones they release. The Hypothalamus We already visited the hypothalamus (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss624) when we stopped at the central nervous system. Located in the diencephalon of the brain, this gland is an important link between the two control systems: nervous and endocrine (FIGURE 10-7 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig7) ). (Remember from Chapter 9 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch09#ch09) , the diencephalon is situated between the brainstem and cerebrum and acts as an important regulator of many body processes.) The hypothalamus controls much of the body’s physiology, including hunger, thirst, luid balance, and body temperature, to name only a few of its functions. The hypothalamus is also, in part, the “commander-in-chief” of the endocrine system because it controls the pituitary gland and therefore most of the other glands in the endocrine system. TABLE 10-3 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10tab3) lists the hypothalamic and pituitary hormones. The Pituitary The pituitary (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1027) , also a part of the diencephalon, is a small gland, about the size of a grape, located at the base of the brain. The pituitary is commonly known as the “master gland,” indicating its important role in control of other endocrine glands. However, that name is misleading because the pituitary gland rarely acts on its own. The pituitary acts only under orders from the hypothalamus. If the hypothalamus is the “commander-in-chief,” the pituitary is a high-ranking soldier who carries out the orders. The Posterior Pituitary (or Neurohypophysis) The pituitary is split into two segments: the posterior pituitary (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1063) and the anterior pituitary (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss73) . The posterior pituitary is an extension of the hypothalamus. Hypothalamic neurons, specialized to secrete hormones instead of neurotransmitters, extend their axons through a stalk to the posterior pituitary. Using the posterior pituitary as a sort of launch pad, these neurons secrete two hormones: antidiuretic hormone (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss78) (ADH (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss78) ; also called vasopressin) and oxytocin (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss953) . Both of these hormones are secreted from the posterior pituitary, but they are made by the hypothalamus. LEARNING HINT Hormone Names Most hormones are named according to where they are secreted or what they do. If you learn the meanings of their names, you can usually tell something about the hormone. For example, growth hormone stimulates cells to grow. Prolactin (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1089) increases milk production. (Note that pro means “for,” and lactin means “milk.”) Even a complicated hormone name like adrenocorticotropic hormone can be picked apart fairly easily. Adreno refers to the adrenal gland, and cortico refers to the cortex. Therefore, adrenocorticotropic hormone is a hormone that changes the activity (in this case increases) of the adrenal cortex. Also keep in mind that most hormones are known by their abbreviations, for obvious reasons. Adrenocorticotropic hormone, for example, is abbreviated ACTH, which is much easier to say and write. FIGURE 10-7 ▲ The hypothalamus, anterior and posterior pituitary glands, and their targets and associated hormones. ADH does exactly what its name suggests: It is an antidiuretic. A diuretic is a chemical that increases urination, so an antidiuretic decreases urination. The effect of ADH, then, is to decrease luid lost due to urination, increasing body luid volume. ADH is secreted when the hypothalamus senses decreased blood volume or increased blood osmolarity (more solids suspended in blood). ADH circulates through the bloodstream and targets the kidneys speci ically, causing them to absorb more water. It is very important in long-term control of blood pressure, especially during dehydration. (For more information on ADH, see Chapter 16 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch16#ch16) , “The Urinary System.”) TABLE 10-3 SELECTED HYPOTHALAMIC AND PITUITARY HORMONES HORMONE FUNCTION Hypothalamus Growth hormone-releasing hormone (GHRH) Increases the release of growth hormone from the pituitary gland HORMONE FUNCTION Growth hormone-inhibiting hormone (GHIH) Decreases the release of growth hormone from the pituitary gland Corticotropin-releasing hormone (CRH) Increases the release of adrenocorticotropic hormone from the pituitary gland Gonadotropin-releasing hormone (GRH) Increases the release of luteinizing hormone and follicle-stimulating hormone from the pituitary gland Thyrotropin-releasing hormone (TRH) Increases the release of thyroid-stimulating hormone from pituitary gland Posterior Pituitary Antidiuretic hormone (ADH), also known Dilutes blood and increases luid volume by increasing water reabsorption as vasopressin in the kidney Oxytocin Increases uterine contractions Anterior Pituitary Growth hormone (GH) Increases tissue growth Thyroid-stimulating hormone (TSH) Increases secretion of thyroid hormones Adrenocorticotropic hormone (ACTH) Increases steroid secretion from adrenal gland Prolactin Increases milk production Luteinizing hormone (LH) Stimulates ovaries and testes for ovulation and sperm production Follicle-stimulating hormone (FSH) Stimulates estrogen secretion and sperm production As we discussed in the section on positive feedback, the second hypothalamic hormone released from the posterior pituitary is oxytocin. Oxytocin is important in maintaining uterine contractions during labor in women and is involved in milk ejection in nursing mothers. Oxytocin’s function in males is unknown. The Anterior Pituitary (or Adenohypophysis) The anterior pituitary (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss73) is also controlled by the hypothalamus, but is an endocrine gland in its own right. The anterior pituitary makes and secretes a number of hormones, under hormonal control by the hypothalamus, that control other endocrine glands. (Growth hormone and prolactin are exceptions to this rule.) Refer back to Table 10-3 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10tab3) and Figure 10-7 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig7) for a list of hypothalamic and pituitary hormones. We discussed this relationship previously when we talked about hormonal control. The hypothalamus secretes a hormone that controls hormone secretion by the anterior pituitary, which usually controls the secretion of hormones by another endocrine gland. The hormone levels are controlled by negative feedback to both the pituitary and the hypothalamus. Pathology Connection: Posterior Pituitary and Antidiuretic Hormone Drinking too much alcohol can lead to several unpleasant consequences, not the least of which is the development of a hangover. The symptoms of a hangover are due to many side effects from alcohol consumption, but the most important may be that alcohol turns off ADH. The more alcohol you drink, the less ADH you secrete, and the more dehydrated you become. That makes you thirsty, so you drink some more alcohol, and you secrete even less ADH and become even more dehydrated. The more alcohol you drink, the more you urinate and the more dehydrated you are. This is part of the reason why consuming too much alcohol on Friday night can make you miserable on Saturday morning. Diabetes Insipidus Diabetes Insipidus (DI) (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss348) is a condition characterized by the production of large amounts of very dilute urine. It is typically caused by underproduction of ADH due to non-cancerous pituitary tumors. Generally, excessive urination is the only symptom of DI because thirst compensates for luid loss. In severe cases, DI can be treated by taking medications which function like ADH. Syndrome of Inappropriate Antidiuretic Hormone Secretion Syndrome of inappropriate antidiuretic hormone (SIADH) is a condition characterized by severe hyponatremia (low blood sodium), usually due to overproduction of ADH regardless of blood osmolarity. It leads to luid retention and very dilute plasma. The dilution of plasma leads to dangerously low sodium levels in the blood. Causes of SIADH include pulmonary disease, cancer, medications, and central nervous system disorders. One of the most common causes of SIADH is traumatic brain injury. Symptoms of SIADH include confusion, altered consciousness, fatigue, nausea, muscle cramps, and loss of appetite. Untreated hyponatremia can lead to brain herniation and coma and can be fatal. Given that the symptoms of SIADH overlap with those of TBI it is often dif icult to diagnose SIADH. Also, since this is a disorder caused by too much water retention, giving IV luids may exacerbate the problem. Current research is aimed at inding better ways to diagnose SIADH especially in brain injured patients. Pathology Connection: Anterior Pituitary Hypopituitarism Hypopituitarism (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss623) is a decrease in pituitary function caused by tumors, surgery, radiation, or head injury. Hypopituitarism is characterized by loss of any or all of the anterior pituitary hormones including ACTH, GH, LH, and TSH, causing a variety of symptoms. LH and GH are usually the most severely affected. Hypopituitarism is dif icult to diagnose and treat because symptoms are often vague or subtle. In one study, one quarter of patients with traumatic brain injuries had symptoms of hypopituitarism that were untreated one year after injury, even though they had recovered enough to be released from rehabilitation. If hypopituitarism is caused by a pituitary tumor, the tumor may be removed. No matter the cause, hormone replacement is the treatment of choice. Effective replacement of pituitary hormones is dif icult, and it often takes months to adjust the medication to appropriate therapeutic levels. Hyperpituitarism Hyperpituitarism, overproduction of pituitary hormones, is usually cased by benign pituitary tumors. Symptoms include reproductive abnormalities, acromegaly, cardiac dysfunction, sleep apnea, Cushing’s syndrome (see section on the adrenal gland for detailed discussion), and hyperthyroidism. Like many hormonal disorders, hyperpituitarism is dif icult to diagnose due to the vagueness of symptoms. Imaging studies and hormone levels are generally used. Hyperpituitarism is treated by decreasing the size of the tumor or removing it. Stature Disorders Stature disorders are those disorders that result in well-below-average height (called dwar ism (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss379) ) or well-above-normal height (called giantism or gigantism (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss529) ). Some of these disorders are caused by abnormalities in skeletal development or nutritional de iciencies. However, growth hormone (GH) problems are often implicated. If GH secretion is insuf icient during childhood, children do not grow to “standard” height. This type of dwar ism results in stunted adult height. However, if GH de iciency is diagnosed before closure of the growth zones of the long bones, it can be treated with GH injections. Children treated with GH injection may attain full height. On the other end of the spectrum are those who secrete too much GH. If the oversecretion happens during childhood, people get extremely tall. (The current record in the Guinness Book of World Records is more than 8 feet tall.) Gigantism causes many health problems. The body gets so big that it cannot support itself. Most cases are caused by non-cancerous pituitary tumors. Treatment is often dif icult. Surgery is the treatment of choice for this disorder, but must often be supplemented by radiation and drug therapies. Oversecretion of GH in adults, after bones have stopped growing, causes acromegaly (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss12) , a painful, often crippling disorder characterized by excess growth of body tissue, especially those of the face and extremities. Bones become deformed, and organs may malfunction due to excess growth. Like gigantism, acromegaly is usually caused by noncancerous pituitary tumors. Treatment for acromegaly is the same as for gigantism. Acromegaly is one of the potential side effects of using growth hormone for performance enhancement. WEBSITE MEDIA EXTRA The endocrine system, like all systems, is affected by the aging process. Watch a video on the effects of aging on the endocrine system. TEST YOUR KNOWLEDGE 10-3 Choose the best answer: 1. Oxytocin: a. is secreted by the anterior pituitary b. decreases uterine contractions c. is secreted from the posterior pituitary d. is a way to get more oxygen to your toes 2. The _____________ is controlled by hormones from the hypothalamus, whereas the _____________ actually secretes hypothalamic hormones. a. posterior pituitary; posterior pituitary b. anterior pituitary; anterior pituitary c. anterior pituitary; posterior pituitary d. posterior pituitary; anterior pituitary 3. This gland, under orders from the hypothalamus, releases hormones that control other endocrine glands: a. adrenal gland b. anterior pituitary c. thyroid gland d. pancreas 4. Which gland does ACTH control? a. adrenal gland b. anterior pituitary c. thyroid gland d. pancreas 5. SIADH is caused by excess secretion of: a. cholesterol b. epinephrine c. growth hormone d. antidiuretic hormone 6. Alcohol inhibits secretion of ADH. This causes: a. headache b. lots of dilute urine c. decreased urination d. stupidity The Thyroid Gland The thyroid (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1363) gland, located in the anterior portion of your neck on either side of the larynx over the trachea, is a butter ly-shaped (H-shaped) organ. The thyroid gland is responsible for secreting the hormones thyroxine (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1365) (T4) and triiodothyronine (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1386) (T3), under orders from the pituitary gland (see FIGURE 10-8 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig8) ). Thyroxine is controlled by secretion of TSH. The designations T4 and T3 refer to the number of iodine atoms in the hormone. The importance of these hormones is so great that in many countries, table salt contains added iodine to ensure that people get enough iodine in their diets to make adequate amounts of thyroid hormones. T4 and T3 control cell metabolism and growth. Maintenance of these hormone levels takes place in a negative feedback loop. Control of T4 and T3 is an example of hormonal control. When blood levels of T4 or T3 drop, neurons in the hypothalamus sense the drop and produce thyrotropin-releasing hormone, or TRH. TRH stimulates the pituitary gland to produce TSH, or thyroid-stimulating hormone. TSH binds to cells on the thyroid gland and stimulates the thyroid to produce T4 and T3. Neurons in the hypothalamus sense when T4 and T3 blood levels are back to normal, and they produce less TRH. This decreases the secretion of TSH in the pituitary gland. With less TSH to trigger the thyroid gland, the production of T4 and T3 decreases. When levels of thyroid hormone get too low, the cycle starts again. T4 and T3 are generally referred to as “thyroid hormones” and are of great clinical importance. Overproduction (hyperthyroidism) or underproduction (hypothyroidism) can cause a variety of clinical symptoms because the level of these hormones is essential in controlling growth and metabolism of body tissues, particularly in the nervous system. The thyroid gland also secretes a third hormone, calcitonin, which decreases blood calcium by stimulating bone-building cells. This prevents hypercalcemia (high blood calcium levels), which can cause conditions such as arrhythmia, kidney stones, and osteoporosis. The Thymus Gland The thymus gland is both an endocrine gland and a lymphatic organ. It is located in the upper thorax behind the sternum and plays an important function in the immune system. It produces a hormone called thymosin (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1360) , which helps with the maturation of white blood cells to ight infections. It begins to disappear during puberty. This gland is further discussed in Chapter 14 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch14#ch14) , “The Lymphatic and Immune System.” The Pineal Gland The tiny pineal gland (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1023) is found in the brain, and its full function still remains unknown. However, it has been shown to produce the hormone melatonin (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss788) , which rises and falls during the waking and sleeping hours. It is believed this hormone is what triggers our sleep by peaking at night and causing drowsiness. The Pancreas The pancreas (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss957) is an accessory organ of the digestive system. It is located in the upper abdomen, near the stomach. Part of the pancreas acts as an exocrine organ. This part produces and secretes digestive enzymes that help to break down starches, fats, and proteins, and this will be further discussed in Chapter 15 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch15#ch15) on the gastrointestinal system. The other part of the pancreas acts as an endocrine organ. This part produces hormones that regulate blood sugar. FIGURE 10-8 ▲ The thyroid and parathyroid glands. Pathology Connection: The Thyroid Gland Hypothyroidism Hypothyroidism (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss625) occurs when too little thyroid hormone is produced. It can be caused by decreased production of hypothalamic (TRH), pituitary (TSH), or thyroid (T4 or T3) hormones. Symptoms of hypothyroidism include fatigue, feeling cold, brittle or thinning hair, constipation, brittle nails, bradycardia, leg cramps, muscle pain, weight gain, hyperlipidemia, hypercholesterolemia (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss612) , forgetfulness, depression, sexual dysfunction, and dry, itchy skin. Hashimoto’s thyroiditis (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss567) is the most common cause of hypothyroidism. It is caused by autoimmune attack on the thyroid gland. For unknown reasons, the immune system begins to attack the cells in the thyroid, causing in lammation and damage to the gland. This damage eventually leads to decreased production of thyroid hormones—hypothyroidism. In addition, the thyroid may swell, causing pain and dif iculty swallowing. Hashimoto’s thyroiditis, like many autoimmune disorders, is most common in women between 30 and 50 years old. Hashimoto’s thyroiditis can be distinguished from other kinds of thyroid disorders by blood tests. The disease is characterized by high TSH levels and low T4 levels. It can be treated by daily doses of synthetic T4. Congenital hypothyroidism is hypothyroidism present at birth, occurring in about 1 in 4,000 live births. Congenital hypothyroidism is caused by anatomical thyroid abnormalities (no thyroid present in some cases), thyroid metabolism errors, or iodine de iciency. Untreated congenital hypothyroidism causes severe intellectual disabilities and short stature. It is the most common preventable cause of mental retardation. Newborn screening for congenital hypothyroidism is standard in developed countries. If treated early most babies with congenital hypothyroidism have the potential to grow up without learning problems. Hyperthyroidism Hyperthyroidism (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss617) is the overproduction of thyroid hormone. Symptoms of hyperthyroidism include feeling hot, muscle tremors, sweating, muscle weakness, tachycardia, cardiac arrhythmia, loose bowels, infertility, nervousness, irritability, and enlarged, bulging eyes. Patients with hyperthyroidism are often hypersensitive to the effects of the sympathetic hormones norepinephrine and epinephrine. People with hyperthyroidism eat large quantities of food, but continue to lose weight. See FIGURE 10-9 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig9) , which contrasts signs and symptoms of hypothyroidism and hyperthyroidism. Graves’ disease (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss558) , the most common cause of hyper-thyroidism, is also an autoimmune disorder. In this case, the immune system binds to TSH receptors, stimulating the thyroid to produce excess thyroid hormone. Like Hashimoto’s thyroiditis, Graves’ disease is more common in women of childbearing age. Acute Graves’ disease can often result in a potentially fatal form of hyperthyroidism called a thyroid storm (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1364) . FIGURE 10-9 ▲ A comparison of the signs and symptoms of A. hypothyroidism and B. hyperthyroidism. Diagnosis of Graves’ disease is made by blood tests (low TSH levels with high T4 levels) and increased levels of radioactive iodine uptake by the thyroid. Patients may also have a condition called exophthalmos, in which swelling of tissue behind the eyes makes the eyeballs bulge, giving the appearance of “bug eyes.” There are three treatment options for Graves’ disease: anti-thyroid medications to decrease thyroid activity or beta-blockers to decrease the activity of epinephrine and norepinephrine, treatment with radioactive iodine to kill thyroid cells, and removal of the thyroid gland. If the thyroid gland is removed or destroyed, daily doses of thyroid hormones are required. Goiter (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss549) is the enlargement of the thyroid and can be the result of either hypothyroidism or hyperthyroidism. A goiter can interfere with swallowing or breathing and can produce tightness in the throat. The swelling itself may not be painful. Medications or radioactive iodine treatment may shrink a goiter. A goiter may also be removed surgically. A simple goiter is caused by lack of dietary intake of iodine. See FIGURE 10-10 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig10) for examples of goiter and Graves’ disease. FIGURE 10-10 ▲ A. Examples of various goiters. (Sources: Photolibrary/Peter Arnold, Inc.; Custom Medical Stock Photo, Inc.; Marka/Custom Medical Stock Photo, Inc.) B. Ocular changes in Grave’s disease. (Source: Dr. P. Marazzi/Photo Researchers, Inc.; NMSB/Custom Medical Stock Photo, Inc.) Parathyroid Glands The thyroid gland has two small pairs of glands embedded in its posterior surface. These glands are called the parathyroid glands (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss965) , and they produce parathyroid hormone (PTH) (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss966) , which regulates the levels of calcium in the bloodstream. There are four parathyroid glands, and each is the size of a grain of rice. If calcium levels get too low, the parathyroid glands are stimulated to release PTH, which stimulates bone-dissolving cells and thereby releases needed calcium in the bloodstream. Again, see Figure 10-8 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig8) . Damage to the parathyroid glands (during surgery or, in rare instances, during radioactive iodine treatment for hyperthyroidism) can reduce the production of parathyroid hormone. Hypoparathyroidism, or insuf icient production of parathyroid hormone, can lead to a drop in calcium levels in the blood. Low blood calcium can interfere with nerve function and cause the condition called tetany (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1350) . Patients with tetany may experience muscle spasms, cramps, uncontrolled twitching, or seizures. Spasms of respiratory muscles, including those in the larynx, can cut off air supply and cause death. Tetany can be treated with calcium and vitamin D supplements. Parathyroid hormone treatment may also be used. If the tetany is severe, the patient may be treated with intravenous calcium to restore blood calcium levels. The pancreas is largely responsible for maintaining blood sugar (glucose) levels at or near a set point. The normal clinical range for blood glucose levels is 70 to 105 mg/dL (milligrams per deciliter). The pancreas can measure blood sugar, and if the blood glucose is high or low, the pancreas releases a hormone to correct the level. Control of blood sugar by the pancreas is perhaps the best example of humoral control of hormone levels. To understand the importance of the pancreas, let’s go back in your journey to the chapter on cells. Why does it matter how much glucose is in your blood? Why devote much of an organ, and a pretty big one at that, to controlling blood sugar? There are two reasons why blood glucose is important. Too much glucose loating around in your blood causes many problems with the luid balance of your cells. Recall that if the concentration of the luid outside a cell is high in solutes, the cell will lose water to its surroundings. If the solute concentration is low outside the cell, the cell will ill with water. Obviously, that’s a serious problem. It does not matter if the solids are salts or glucose, the result is the same. Blood glucose must therefore be maintained at a certain level for cells to neither gain nor lose water. Why else is glucose important? Glucose is vital for cellular respiration. Cellular respiration is needed to get energy, by making adenosine triphosphate (ATP). Remember from Chapter 3 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch03#ch03) that the chief way most cells make ATP, the energy that powers cells, is by breaking down glucose during cellular respiration. Therefore, cells need to have enough glucose that they can make suf icient ATP to carry out their daily activities. The pancreas makes two hormones that control blood glucose: insulin (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss653) , which most of you have heard of before, and glucagon (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss541) . These hormones are produced by two specialized groups of cells in pancreatic tissue called the islets of Langerhans (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss680) . Beta cells in the islets secrete insulin, whereas alpha cells secrete glucagon. Insulin, the hormone that is missing or ineffective in diabetes mellitus (diabetes), removes glucose from the blood by directing the liver to store excess glucose and by helping glucose to get inside the cells (facilitated diffusion) so it can be used to make ATP. (Remember that glucose, a carbohydrate, is water soluble, so it cannot get into cells by itself.) When would insulin be secreted by the pancreas: when blood glucose is high or when blood glucose is low? Because insulin removes glucose from the blood, it lowers blood sugar, so it is released when blood sugar is high (hyperglycemia), like right after a meal. Glucagon does the opposite of insulin. Glucagon puts glucose into the bloodstream mainly by directing the liver to release glucose that was stored in the form of glycogen (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss546) . Glucagon is released typically several hours after a meal to prevent blood glucose from dropping too low (hypoglycemia). These two hormones control blood glucose very tightly in healthy humans (see FIGURE 10-11 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig11) ). Other hormones, like the adrenal hormone cortisol, also aid in the control of blood sugar. The Adrenal Glands The adrenal (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss25) glands are a pair of small glands that sit on top of your kidneys like baseball hats. The adrenal glands are split into two regions: the adrenal cortex (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss26) , an outer layer, and the adrenal medulla (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss27) , the middle of the gland. (Note that it is best to be speci ic when talking about the adrenal cortex because your cerebrum has a cortex too.) The Adrenal Medulla The adrenal medulla releases two hormones: epinephrine (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss437) (also known as adrenaline (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss28) ) and norepinephrine (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss892) . These hormones increase the duration of the effects of your sympathetic nervous system. Remember your friend’s snarling dog? Cells of the adrenal medulla receive the neurotransmitter norepinephrine from the sympathetic nervous system. (It is both a hormone and a neurotransmitter, depending on where it is released.) The neurotransmitter triggers the release of norepinephrine and epinephrine into the bloodstream, increasing heart rate, blood pressure, and respiration rate and giving you sweaty palms and dry mouth. Again, the effects of the hormones last much longer than effects of the neurotransmitter. FIGURE 10-11 ▲ Control of blood glucose by pancreatic hormones. The Adrenal Cortex The adrenal cortex (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss26) makes dozens of steroid hormones known collectively as adrenocorticosteroids (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss29) (steroids in the adrenal cortex). The adrenal cortex releases steroid hormones under the direction of the anterior pituitary. Many of these steroid hormones are so important that a decrease in their production could be fatal relatively quickly. Some of these hormones, the mineralocorticoids (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss815) , regulate electrolyte and luid balance. The glucocorticoids (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss542) regulate blood sugar. Others are in part responsible for regulation of reproduction and secondary sexual characteristics, and still others control cell metabolism, growth, and immune system function. Pathology Connection: Diabetes Mellitus Diabetes mellitus (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss349) is a condition characterized by abnormally high blood glucose (hyperglycemia) because of the decreased secretion of insulin or the body’s insensitivity to insulin. Type 1 or juvenile onset is caused by the immune system’s destruction of the insulin-producing cells of the pancreas and is generally diagnosed in people under the age of 40. Patients with type 1 diabetes, such as our patient Maria, do not produce enough insulin. They are always dependent on daily doses of insulin. Type 2 (sometimes called late onset) is caused by insensitivity of the body’s tissues to insulin and has typically been diagnosed in patients over 50, particularly those with other complicating conditions like obesity. Currently there is a trend of seeing type 2 diabetes in children and becoming more common in adolescents and young adults. Patients in early stages of type 2 diabetes can often be treated with a carefully controlled diet and weight-loss regimen or antidiabetic drugs, which help maintain glucose levels. Some type 2 patients become insulin dependent as the disease progresses and evidence suggests that some type 2 patients may actually have delayed-onset autoimmune diabetes. Diagnosis is usually accomplished using blood tests and urinalysis. Some blood substances, such as glucose, will “spill” over into the urine. This is why diabetics, like Maria, sometimes have glucose in their urine. Sugar (glucose) tests can be used to detect diabetes, con irm the diagnosis of diabetes, or determine the effectiveness of the treatment for diabetes. Note that sugar in urine, known as glucosuria or glycosuria, is not always abnormal. Situations of emotional stress, diet, or a low reabsorption rate by the kidneys with normal blood levels of glucose may cause high readings. However, you will ind that in most cases, sugar in the urine of your patient is a result of diabetes mellitus. Normal urine glucose: < 0.5 mg/dL. See FIGURE 10-12 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10 ig12) , which shows various effects of diabetes mellitus. In both types of diabetes, abnormally high blood glucose (hyperglycemia) must be resolved. If blood glucose remains high, the kidneys work overtime to excrete the excess sugar. Increased urination and dehydration are the most obvious symptoms. The stress of trying to get rid of the excess blood sugar eventually causes kidney damage. In addition, if insulin is not effective, glucose cannot get into cells. Cells must have glucose in order to make ATP. If cells can’t get glucose and can’t make ATP, they will look for other sources of energy. Untreated diabetics often lose weight as their body searches for other energy sources. Often, their blood becomes increasingly acidic due to their abnormal metabolism. There is often dif iculty in wound healing and permanent damage to the peripheral nervous system. The changes in blood chemistry lead to tissue and organ damage. Left untreated, diabetes mellitus may lead to coma and death. Even diabetics who follow a strict treatment regimen often have poorly controlled blood glucose levels due to the complexity of our blood glucose control system. TABLE 10-4 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec3#ch10tab4) compares type 1 and type 2 diabetes. Blood glucose that is too low, hypoglycemia, is actually a more acute problem than hyperglycemia for most diabetics and is the primary side effect of insulin therapy. Tight glucose control increases the risk of hypoglycemia. The early symptoms of hypoglycemia include hunger, nervousness, dizziness, anxiety, dif iculty speaking, and weakness. If not resolved, hypoglycemia can progress to cause mental confusion, seizures, coma, and even death. Too little blood glucose causes luid balance problems. In addition, too little blood glucose also means that cells, particularly those in the brain, cannot get the glucose they need to produce energy. WEBSITE MEDIA EXTRA View videos and animations spotlighting the pathology of diabetes. Therefore, the body has an elaborate defense mechanism against hypoglycemia. If blood glucose drops too low, the pancreas decreases its insulin secretion and increases secretion of glucagon. In addition, the adrenal medulla secretes epinephrine. The hypothalamus is involved in that it senses the decrease in blood sugar and triggers the action of the adrenal gland via sympathetic control. (Remember from our discussion of neural control of hormone levels that the hypothalamus has some control over the sympathetic nervous system, which controls epinephrine release by the adrenal gland.) The hypothalamus also triggers feelings of hunger during hypoglycemia, so patients will eat food, increasing glucose levels. For some diabetics, hypoglycemia becomes a recurrent problem. It is thought that damage to the autonomic nervous system or decreased CNS sensitivity caused by repeated hypoglycemic incidents makes it dif icult for the body to defend against future hypoglycemic episodes and even decreases awareness of symptoms of hypoglycemia. In some patients this effect can be reversed or diminished by a proper diabetic-approved diet. The only way to treat acute hypoglycemia is to get sugar quickly into the bloodstream. For patients in early hypoglycemia, sugar consumption, sugar-sweetened sodas, orange juice, or hard candy are among the best ways to increase blood sugar. Severe hypoglycemia requires medical attention. People who are not diabetic may also experience symptoms of hypoglycemia if blood glucose drops too low. A person experiencing hypoglycemic symptoms must get medical treatment immediately. FIGURE 10-12 ▲ Various effects of diabetes mellitus. TABLE 10-4 COMPARISON OF TYPE 1 AND TYPE 2 DIABETE TYPE 1 DIABETES TYPE 2 DIABETES Cause Autoimmune destruction of pancreas; not enough insulin is produced Insulin resistance, obesity and sedentary lifestyle; insulin produced by pancreas does not work effectively Age at onset Typically before the age of 40 Typically later in life, though some obese and/or sedentary children are being diagnosed Treatment Insulin injections, insulin pump, pancreas transplant, stem cells Diet and exercise, medications, insulin in later stages TYPE 1 DIABETES Symptoms Usually sudden and severe, excess urination, extreme thirst, weight loss TYPE 2 DIABETES Often more subtle than type 1 symptoms, excess urination, thirst Pathology Connection: Steroid-Related Conditions Addison’s Disease Addison’s disease is caused by insuf icient production of adrenocorticosteroids, particularly cortisol, a glucocorticoid, and aldosterone, a mineralocorticoid. The disease can be fatal if not treated. Symptoms include weight loss, muscle weakness, fatigue, low blood pressure, hypoglycemia, irritability, depression, and excessive skin pigmentation. (Compare these to the symptoms of Cushing’s disease, which is characterized by the oversecretion of cortisol.) Many cases of Addison’s disease are autoimmune (body attacking itself), but other causes may include infection and cancer. Abnormalities of the hypothalamus and pituitary may also cause Addison’s disease. It is diagnosed with blood tests and imaging studies and is treated with hormone replacement. Cushing’s Syndrome Cushing’s syndrome (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss320) is caused by oversecretion of cortisol. Symptoms include upper body obesity, round face, easy bruising, osteoporosis, fatigue, depression, hypertension, and hyperglycemia (high blood glucose). Women may have excess facial hair and irregular periods; men may have decreased fertility and decreased sex drive. Cushing’s syndrome may be a side effect of medical use of steroids, like prednisone, or may be due to pituitary tumors, adrenal tumors, or one of several genetic disorders. New data suggests that some cases of metabolic syndrome (abdominal obesity occurring with high cholesterol, high blood pressure, and hyperglycemia or insulin resistance) may be minor or subtle cases of Cushing’s syndrome. Diagnosis of Cushing’s, particularly telling pituitary causes of Cushing’s apart from other causes, is relatively complicated. Techniques include MRI, blood cortisol levels, clinical pro ile, 24-hour urine cortisol testing, hormone levels, dexamethasone suppression tests, genetic testing, and pituitary sampling. Treatment depends on the underlying cause of the disorder. Classic Cushing’s is due to a pituitary tumor that produces too much ACTH, stimulating the adrenal gland to produce too much cortisol. There are no approved drug therapies for classic Cushing’s, though several clinical trials are underway. The tumor must be removed, and in the case of a pituitary tumor, damage to the pituitary usually requires hormone replacement for the rest of the patient’s life. Other cases of Cushing’s are caused by overproduction of cortisol by the adrenal gland independent of what the pituitary and/or hypothalamus are doing. Surgery may be necessary, but in many cases the disease can be managed by drug therapy to decrease cortisol secretion. Side Effects of Therapeutic Steroids Prednisone is clinically important in the treatment of in lammation, organ transplant rejection, and immune disorders, but prescription steroids are a double-edged sword. These medications are so powerful that they can cause dangerous side effects, such as bone density loss, weight gain, fat deposits, and delayed wound healing, much like Cushing’s syndrome. In addition, these drugs, even when taken for a short time, cannot be discontinued suddenly. Patients must be weaned off their medication slowly. Why? We aren’t really sure. One hypothesis suggests that when a patient takes a steroid medication, the adrenal gland decreases steroid production in response. (Remember negative feedback: As hormone levels rise, hormone secretion decreases.) Other suggested mechanisms are biochemical changes, changes in the adrenal gland itself, and even changes in the immune system caused by steroid use. In any case, if the medication is removed suddenly, patients are left with serious withdrawal symptoms. Steroids, even those used for a short time, must be tapered off slowly to avoid withdrawal. Steroid Abuse It is no surprise, then, that taking steroid medications for the purpose of increasing athletic performance is prohibited by amateur and professional sports organizations. Anabolic steroids (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss53) are a class of steroid molecules that cause large increases in muscle mass when compared to working out without steroids. Some athletes use anabolic steroids to enhance performance or to get big muscles much faster than they would without steroids. Because steroid hormone levels are so tightly controlled by the body, anabolic steroids have a number of side effects. (Think back to the discussion of prednisone at therapeutic levels; abuse levels are much higher.) Men abusing steroids may experience changes in sperm production, enlarged breasts, and shrinking of their testicles. Women may experience deepening of the voice, decreased breast size, and excessive body hair growth. Steroid abuse may lead to cardiovascular diseases and increased cholesterol levels. Many steroids suppress immune function, and because steroid use is illegal, many abusers expose themselves to hepatitis B and HIV when sharing needles. Steroid abuse has also been linked to increased aggressive behavior. All major professional and amateur athletic organizations ban the use of steroids. Cortisol and the Stress Response The typical cortisol secretion pattern is peak cortisol levels just before waking with cortisol decreasing as the day goes on. During the day, there are peaks and valleys superimposed on the overall levels. Cortisol levels also peak during times of stress. Your body has a set response to any stressor, whether physiological—such as hypothermia, decreased blood volume, or hyperglycemia—or psychological—such as a big exam or a near collision. When you are exposed to stressors, both the sympathetic nervous system and the adrenal cortex are activated. Epinephrine and norepinephrine are released from the adrenal medulla, raising blood pressure and heart rate, raising respiration rate, increasing blood glucose, and decreasing digestion and other nonessential physiological responses. The adrenal cortex, under orders from the hypo-thalamus and pituitary, releases cortisol, a glucocorticoid hormone, causing increased blood glucose, and changes in immune response. This initial stress response is appropriate and useful, allowing your body to be ready to expend energy. If the stress continues, this response also continues, entering a phase of adaptation in which there is a balance between stress response and homeostatic mechanisms, and homeostasis is maintained. This is still a useful and healthy response to stress. However, if stress becomes chronic, the secretion of epinephrine, and cortisol in particular, becomes pathological. The response of the body to chronic stress is also in luenced by many other factors, including psychological factors. Increased optimism, greater social support mechanisms, and lower perceived stress are all associated with lower cortisol levels, whereas depression and anxiety are associated with higher levels of cortisol. In some overweight people, high cortisol levels are associated with increased risk of type 2 diabetes, heart disease, and stroke. However, these are only associations. That cortisol causes these conditions has not been shown. It is a “chicken versus egg” problem. Does high cortisol cause these problems or do these problems cause high cortisol? Results are complicated due to the complexity of hormonal regulation, studies are often con licting, and age, gender, and the effects of other conditions complicate the picture. There is much more research to be done before we understand the complex relationship between cortisol levels and disease. 10.4 THE GONADS The chief function of the gonads—the testes in males and the ovaries in females—is to produce and store gametes (reproductive cells), eggs, and sperm. However, the gonads also produce a number of sex hormones that control reproduction in both males and females, including testosterone in males and estrogen and progesterone in females. For more details on the sexual hormones produced by the gonads, see Chapter 17 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch17#ch17) . Clinical Application CORTISOL BUSTERS AND WEIGHT LOSS It is clear that very high cortisol levels, such as in Cushing’s disease, cause weight gain, and that very low cortisol, such as in Addison’s disease, causes weight loss. There is evidence that chronic high cortisol is associated with risk factors for metabolic syndrome: abdominal obesity, hypercholesterolemia, hyperglycemia, and hypertension. However, this association is more apparent only in a subset of people who are overweight. Conversely some overweight people have low cortisol levels. Perhaps the combination of high body mass index and high cortisol is the culprit, but the interaction of hormone levels, blood chemistry, and body fat is also complicated by gender, age, and, no great surprise, stress levels. At this time there is no clear picture of how cortisol is related to obesity and risk factors for health problems associated with increased body weight, although high cortisol combined with obesity and other risk factors is often a sign of problems to come. You may have all seen the advertisements for “cortisol busters,” which claim to cause signi icant, rapid weight loss simply by decreasing blood cortisol levels. These products claim that abdominal fat is caused by high cortisol levels, regardless of what you are eating or how much you are exercising. (They do, however, suggest a sensible diet and exercise plan while taking their product.) Given the available scienti ic information, it seems unlikely that simply decreasing cortisol will cause rapid, healthy weight loss. You are better off exercising more and eating more nutritiously if you wish to lose weight, though it’s probably not a bad idea to decrease your overall stress levels. Chronic secretion of cortisol has a number of effects on metabolism, including increased appetite, changes in the immune system that increase autoimmunity and decrease defense against infection, increased heart rate, hypertension, hyperglycemia, hypercholesterolemia, increased abdominal fat, anxiety, and depression. (Remember the symptoms of Cushing’s syndrome?) So there appears to be a trade-off at work. A certain amount of stress is productive and useful, sharpening awareness and increasing energy levels, but chronic stress causes detrimental physiological and psychological changes. Estrogen, produced by the ovary in the female, is responsible for the development of both the reproductive organs and the secondary sex characteristics in females. Progesterone, also produced by the ovary, helps to regulate the menstrual cycle in females. In the male, the testes (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/bm01#gloss1347) produce testosterone, which is responsible for development of the reproductive organs and secondary sex characteristics, such as the male’s deep voice. For more details on these hormones, see Chapter 17 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch17#ch17) . 10.5 PROSTAGLANDINS Prostaglandins are molecules that act like hormones. Many different body tissues produce prostaglandins. These molecules have a variety of functions, depending on where they were produced. Some prostaglandins help to constrict and dilate smooth muscle—in the blood vessels, digestive tract, or the bronchial tubes of the lungs. Others help with contraction of the uterus during childbirth. Other prostaglandins respond to tissue in lammation. Each prostaglandin generally acts in a small area of the body—on the cells or tissues where it was produced. Prostaglandins have a shortterm but powerful effect on these local tissues. FIGURE 10-13 (http://content.thuzelearning.com/books/Colbert.3997.17.1/sections/ch10lev1sec5#ch10 ig13) shows examples of some common endocrine disorders. WEBSITE MEDIA EXTRA It is critically important to monitor blood glucose levels and maintain an appropriate diet patients with diabetes. Phlebotomists are specially trained allied health professionals who draw blood for testing. Dieticians are intensively involved in the design of specialized diets for diabetes and many other illnesses. Learn more about these important allied health professions. FIGURE 10-13 ▲ Examples of Endocrine Disorders. A. An infant with congenital hypothyroidism. (Source: Bettina Cirrone/Photo Researchers, Inc.) B. A patient with Cushing’s syndrome. (Source: Biophoto Associates/Photo Researchers, Inc.) C. A patient with gigantism. (Source: Bettina Cirrone/Photo Researchers, Inc.) A QUICK TRIP THROUGH THE DISEASES OF THE ENDOCRINE SYSTEM DISORDER ETIOLOGY SIGNS AND SYMPTOMS Diabetes insipidus ADH de iciency. Copious, dilute urine. DIAGNOSTIC TEST(S) TREATMENTS Rule out diabetes mellitus, ADH levels. If caused by a medication, eliminate the medication. If low ADH, give synthetic vasopressin. DISORDER ETIOLOGY Syndrome of inappropriate antidiuretic hormone (SIADH) Excess ADH production usually caused by pulmonary disease, cancer, medications, and central nervous system disorders leading to severe hyponatremia. SIGNS AND SYMPTOMS DIAGNOSTIC TEST(S) TREATMENTS Confusion, altered Rule out TBI, evaluate consciousness, fatigue, volume status. nausea, muscle cramps and loss of appetite. Restrict water, infusion of hypertonic saline. Gigantism/acromegaly Excess growth hormone from hyperfunction of pituitary, often due to pituitary tumor. In children, Imaging, blood tests overgrowth of long for hormone levels. bones results in rapid growth to height in great excess of normal height, in adults, excess growth and deformity of body tissues. Removal of pituitary tumor, followed by hormone replacement therapy. Dwar ism Growth hormone de iciency from hypofunction of pituitary in childhood. In children, failure to attain normal height, abnormally slow growth. Early diagnosis, growth hormone injections. Graves’ disease Hyperthyroidism due Tremors, sweating, Blood tests—low TSH to autoimmune attack weakness, tachycardia, levels but high T4 on thyroid. arrhythmia, levels, radioactive irritability. iodine uptake. Removal or destruction of thyroid or anti-thyroid medication, followed by daily thyroid hormone. Congenital hypothyroidism Hypothyroidism present at birth due to anatomical thyroid abnormalities, thyroid metabolism errors, or iodine de iciency. Early treatment is critical and includes daily thyroid hormone. Dull look, puffy face, thick tongue that sticks out; many newborns exhibit no symptoms. Blood tests, rule out other causes of dwar ism. Newborn screening, including x-ray, thyroid scan. SIGNS AND SYMPTOMS DISORDER ETIOLOGY Hashimoto’s thyroiditis Hypothyroidism due Fatigue, thinning hair, Blood tests—high TSH Daily thyroid to autoimmune attack bradycardia, with low T4. hormone. on thyroid. hypercholesterolemia, depression. Diabetes mellitus Insulin de iciency Excess urination and Urine glucose, blood caused by increased thirst due to glucose, glucose autoimmune attack on high blood glucose. tolerance testing. pancreas, or insulin resistance. Diet, exercise, antidiabetic medications, insulin injections. Addison’s disease De iciency of adrenocorticosteroids due to autoimmune attack on adrenal cortex. Imaging and blood tests for corticosteroids. Hormone replacement. Cushing’s disease Excess cortisol usually Abdominal obesity, due to benign easy bruising, pituitary tumor. hypertension, hyperglycemia, hypercholesterolemia, depression. Imaging, blood cortisol levels, urine cortisol, CTH levels, dexamethasone suppression test, pituitary biopsy. Tumor removal followed by hormone replacement. If caused by overuse of steroids, decrease or eliminate use. Chronic stress Excess cortisol in response to stressors. Weakness, fatigue, hypotension, hypoglycemia, depression. DIAGNOSTIC TEST(S) TREATMENTS Depression, anxiety, No good test. Effects of Decrease stress, perhaps obesity, stress vary widely treatment of hypercholesterolemia, among individuals. symptoms. hypertension, increased susceptibility to infection. Pharmacology Corner Many hormonal disorders can be treated with hormone replacement therapy. For example Synthroid™ (a synthetic hormone) is used in the treatment of hypo-thyroidism. Hydrocortisone, a steroid, is used to replace cortisol in the treatment of Addison’s disease. Prednisone™, which acts like a corticosteroid, can be used to replace corticosteroids or as an anti-in lammatory drug (in patients with normal corticosteroid levels) and to treat severe allergies, rheumatoid arthritis, or other chronic conditions. Children with growth hormone de iciency are treated by growth hormone injections. One of the most commonly used medications in the treatment of diabetes is insulin. There are various ways to administer insulin, including a recently introduced aerosol inhaler that replaces the more invasive daily injections. Often in late-onset diabetes the insulin is functioning but very poorly. Drugs such as Glucophage™ help to potentiate (make stronger) the effect of insulin, making it function more ef iciently. Sometimes hormones need to be inhibited rather than replaced. Mitotane™, a cortisol inhibitor, can be used to treat some kinds of Cushing’s syndrome. Somatostatin™ analogs can be used to decrease growth hormone production in the treatment of acromegaly. In addition, disorders may be treated by blocking the receptors that receive the hormone at the target cell. For example, scientists are experimenting with speci ic aldosterone blockers to treat high blood pressure. WEBSITE MEDIA EXTRA View videos on the importance of nsulin and monitoring and injection techniques. SUMMARY Snapshots from the Journey █ The endocrine system works together with the nervous system to regulate the activities of all the body systems. The endocrine system secretes hormones that act very slowly on distant targets. Their effects are long lasting. █ Most hormones act on cells by binding to external receptors, causing changes in enzyme activity inside the target cell. Steroids, however, can enter cells and interact directly with DNA, which makes steroids very powerful. █ Hormone levels are controlled largely by negative feedback. When hormone levels rise, signals are transmitted to the endocrine organ releasing the hormone, telling the organ to decrease the amount of hormone released. Hormone levels will then decrease. The optimal level of the hormone is called the set point. If the signal brings a hormone back to set point, the action is called negative feedback. If the signal causes the hormone to get further away from set point, the action is positive feedback. █ Hormone levels can be regulated by three mechanisms: changes in the body’s internal environment, control by hormones released by another endocrine gland, and direct control by the nervous system. █ The hypothalamus, a part of the diencephalon, controls much of the endocrine system by controlling the pituitary gland. The pituitary gland has two parts: the posterior pituitary, which is part of the hypothalamus and actually secretes hypothalamic hormones (ADH and oxytocin), and the anterior pituitary, which secretes several different hormones under the in luence of hormones from the hypothalamus. The hormones secreted by the anterior pituitary typically control other endocrine glands. (Growth hormone is an exception.) █ Noncancerous pituitary tumors cause a number of different endocrine disorders, depending on whether hormones are oversecreted or undersecreted. Hyperpituitarism, acromegaly, gigantism, and Cushing’s syndrome are caused by oversecretion of pituitary hormones. █ Several other endocrine glands have important control functions. The thyroid gland secretes the iodine-containing hormones triiodothyronine (T3) and thyroxine (T4), which control growth and cellular metabolism. █ Autoimmune attack on the thyroid can cause serious problems. Hashimoto’s thyroiditis, the most common form of hypothyroidism, causes the typical symptoms of hypothyroidism, including bra-dycardia, thinning hair, leg cramps, fatigue, forgetfulness, and depression. Graves’ disease, the most common cause of hyperthyroidism, causes tremors, anxiety, irritability, cardiac arrhythmia, and excessive sweating. █ The pancreas secretes two hormones: insulin, which lowers blood sugar, and glucagon, which raises blood sugar. Diabetes is caused by a decrease in insulin secretion or decreased sensitivity to insulin. Very high blood sugar is the result. Hypoglycemia (low blood sugar) is also a problem for diabetics and is the chief side effect of insulin therapy. Many diabetics have health problems due to the dif iculty of effectively controlling blood glucose. █ The adrenal glands are split into two parts. The adrenal medulla is an extension of the sympathetic nervous system, releasing epinephrine and norepinephrine as hormones during ight-or- light response. The adrenal cortex releases many different adrenocorticosteroid hormones, which control reproduction, in lammation, tissue growth, and immunity. █ One of the most important hormones released by the adrenal cortex is cortisol, a glucocorticoid, but we do not really understand how it works. It is well known that too much cortisol (Cushing’s) causes weight gain and that too little cortisol (Addison’s) causes weight loss. But these are diseases. Our understanding of how cortisol is involved in obesity and its related conditions that make up metabolic syndrome—hypertension, hypercholesterolemia, and insulin resistance—is not complete. Maria’s Story Let’s revisit Maria’s case. She is a 35-year-old insulin-dependent diabetic who currently takes good care of herself. She did not take good care of herself as a teenager. She is on an insulin pump to try to control her blood sugar, but has recently passed out in public several times. a. What condition causes her to pass out? (hyperglycemia or hypoglycemia) b. Why does this condition develop? c. What is the appropriate treatment for the early stages of this condition? d. Given that she has been a diabetic for so long, why doesn’t Maria realize she is in trouble before she passes out? REVIEW QUESTIONS Matching 1. Match the hormone on the left with its function on the right. _____ADH a. decreases blood sugar _____insulin _____glucagon _____oxytocin _____epinephrine _____thyroxine b. increases thyroid hormone secretion c. regulates cell metabolism d. increases steroid release e. increases uterine contractions f. decreases urination _____prolactin _____ACTH (adrenocorticotropic hormone) _____TSHg _____rowth hormone g. prolongs sympathetic response h. stimulates tissue growth i. increases blood sugar j. increases milk production in females 2. Match the hormone abnormality on the left with the disease on the right. _____too much ADH _____too little insulin _____too little cortisol a. gigantism b. Diabetes mellitus c. Dwar ism _____too little thyroid hormone _____too little growth hormone _____too much thyroxine _____too much cortisol _____too much growth hormone d. SIADH e. Graves’ disease f. Addison’s disease g. changes in sexual characteristics, immune suppression, rage h. Hashimoto’s thyroiditis _____too many steroids i. Cushing’s disease Multiple Choice 1. ADH stands for: a. vasodilate b. antidiuretic hormone c. androdoginin hormone d. all-diglyceride hormone 2. The “master gland” is the: a. adrenals b. pituitary c. thyroid d. pancreas 3. The thymus gland’s main function is: a. reproduction b. growth c. immunity d. RBC levels 4. The pineal gland is located in/on the: a. kidneys b. brain c. thorax d. abdomen 5. Glucagon performs the opposite action of: a. glucose b. insulin c. ATP d. WBCs 6. Anxiety, rapid heartbeat, and sweating are symptoms of: a. Graves’ disease b. Cushing’s syndrome c. Hashimoto’s thyroiditis d. all of the above 7. Glucocorticoid hormones control: a. glucose b. insulin c. ATP d. WBCs 8. This hormone may be involved in metabolic syndrome: a. glucagon b. ADH c. TSH d. cortisol Short Answer 1. Compare and contrast neurotransmitters and hormones. 2. List the sources of control of hormone levels. 3. Explain negative feedback and its role in controlling hormone levels. 4. Discuss why the use of anabolic steroids should be outlawed for performance enhancement. 5. What is the difference between neural control and humoral control of endocrine glands? 6. Explain the difference between type 1 and type 2 diabetes. 7. Why are hormone disorders so dif icult to diagnose? 8. Explain the difference between “good stress” and “bad stress.” Suggested Activities 1. Review the hormones secreted by each endocrine organ and their functions. Make up 3 × 5 cards with the endocrine gland on the front and the hormones it produces on the back. Pick a partner and quiz each other. Once you and your partner can match the gland to the hormones, make up another set of cards with the hormone on the front and its activity or function on the back, and again quiz each other. 2. Review the endocrine diseases listed in this chapter. Make up 3 × 5 cards with the signs and symptoms on the front and the actual disease printed on the back. In a small group or with a partner, try to stump each other in determining the correct disease diagnosis. Use this address to access the Companion Website created for this textbook. Simply select “Basic Health Science” from the choice of disciplines. Find this book and log in using your username and password to access interactive learning games, assessment questions, videos, animations, and much more.
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Running head: THE ENDOCRINE SYSTEM

The Endocrine System
Name
Institution Affiliation

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THE ENDOCRINE SYSTEM

The Endocrine System Chronic Disease
The endocrine system is normally known for working together with the central
nervous system in regulation of every body system. One of such function of the endocrine
systems is or will be secretion of hormones, which function gradually on distantly positioned
targets. ...


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