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172 Chapter 9 Answers: Endocrine System
9.2 Introduction to the Endocrine System
What is the endocrine system? What is its general function? The endocrine system is a system of glands that release chemical messenger molecules called hormones into the bloodstream. The general function of the endocrine system is to control cellular processes throughout the body.
Describe the role of the pituitary gland in the endocrine system. The pituitary gland is the master gland of the endocrine system. Most of its hormones control other endocrine glands.
List three endocrine glands other than the pituitary gland. Identify their functions. Answers may vary. Sample answer: Three endocrine glands are the thyroid gland, which controls the rate of metabolism; the pineal gland, which controls the sleep-wake cycle; and the pancreas, which controls the level of glucose in the blood.
Which endocrine gland has an important function in the immune system? What is that function? The thymus gland has an important function in the immune system. Its function is to mature immune system cells called T cells, which are critical to the adaptive immune response.
Name an endocrine disorder in which too much of a hormone is produced. Answers may vary. Sample answer: An endocrine disorder caused by hypersecretion of a hormone is gigantism, in which too much growth hormone is produced.
What are two reasons people with diabetes might have signs and symptoms of inadequate insulin? They might have hyposecretion of insulin because insulin-secreting cells of the pancreas have been destroyed, or they might have hormone resistance in which other cells throughout the body have become resistant to insulin.
Besides location, what is the main difference between the anterior lobe of the pituitary and the posterior lobe of the pituitary? The anterior lobe of the pituitary synthesizes and secretes its own endocrine hormones, while the posterior lobe of the pituitary stores and secretes hormones synthesized by the hypothalamus.
9.3 Endocrine Hormones: Review Questions and Answers
Explain how steroid hormones influence target cells. Steroid hormones pass through the plasma membrane of target cells and bind with receptors in the cytoplasm. The hormones and receptors form steroid complexes that move into the nucleus where they influence gene expression.
How do non-steroid hormones affect target cells? Non-steroid hormones affect target cells by binding with receptors on the plasma membrane of the cells. This activates an enzyme in the cell membrane to trigger a second messenger, which affects cell processes.
Compare and contrast negative and positive feedback loops. Both negative and positive feedback loops involve a gland or other structure producing a substance that feeds back to influence its own production. In a negative feedback loop, rising levels of a substance feed back to stop its own production, whereas falling levels of the substance feed back to stimulate its own production. In a positive feedback loop, rising levels of a substance feed back to stimulate continued production of the substance.
Outline the way feedback controls the production of thyroid hormones. As thyroid hormone levels start to rise too high, the rising levels feed back to stop the hypothalamus from producing TRH (thyrotropin releasing hormone) and the pituitary gland from producing TSH (thyroid stimulating hormone). As a result, the thyroid gland is no longer stimulated to produce its hormones, so their levels fall. The opposite occurs as thyroid hormone levels start to fall too low.
Describe the feedback mechanism that controls milk production by the mammary glands. When an infant suckles on a nipple, nerve impulses travel to the hypothalamus, which stimulates the pituitary gland to secrete prolactin. Prolactin travels in the blood to the mammary glands and stimulates them to produce milk. The release of milk causes the baby to continue suckling, which causes more prolactin to be secreted and more milk to be produced. The positive feedback loop continues until the baby stops suckling at the breast.
People with a condition called hyperthyroidism produce too much thyroid hormone. What do you think this does to the level of TSH? Explain your answer. When someone produces too much thyroid hormone, it negatively feeds back to the hypothalamus and pituitary to lower the level of TSH. This is because TSH normally stimulates the production of thyroid hormones, and in this case, the body is trying to bring the level of thyroid hormone back down to a normal range.
Which is more likely to maintain homeostasis— negative feedback or positive feedback? Explain your answer. Negative feedback is more likely to maintain homeostasis because in negative feedback, a substance shuts off its own production, keeping the level within a narrow, normal range (i.e. homeostasis). Positive feedback, on the other hand, causes a substance to keep increasing its own production.
Does testosterone bind to receptors on the plasma membrane of target cells or in the cytoplasm of target cells? Explain your answer. Testosterone binds to receptors in the cytoplasm of target cells because it is a sex hormone, and sex hormones are steroid hormones. Steroid hormones are lipids, so they cross the plasma membrane of target cells and bind to receptors in the cytoplasm.
9.4 Pituitary Gland: Review Questions and Answers
Explain why the pituitary gland is called the master gland of the endocrine system. The pituitary gland is called the master gland of the endocrine system because most of the hormones of the anterior lobe of the pituitary gland control other endocrine glands.
Compare and contrast the two lobes of the pituitary gland and their general functions. The anterior lobe of the pituitary gland is the front part of the gland. The posterior lobe is the back part of the gland. The anterior lobe synthesizes and secretes several endocrine hormones, most of which influence other endocrine glands. The posterior lobe stores and secretes hormones that travel to the posterior pituitary from the hypothalamus.
Identify two hormones released by the anterior pituitary, their targets, and their effects. Answers will vary. Sample answer: Two hormones released by the anterior pituitary are growth hormone and prolactin. Growth hormone targets cells throughout the body and stimulates them to grow. Prolactin targets mammary gland cells in the breast and stimulates them to produce milk.
Explain how the hypothalamus influences the output of hormones by the anterior lobe of the pituitary gland. The hypothalamus influences the output of hormones by the anterior lobe of the pituitary gland by secreting releasing hormones and inhibiting hormones that travel to the anterior lobe. The hormones stimulate the anterior pituitary to either release or stop releasing particular pituitary hormones.
Name and give the function of two hypothalamic hormones released by the posterior pituitary gland. Answers may vary. Sample answer: Two hypothalamic hormones released by the posterior pituitary gland are vasopressin, which helps maintain homeostasis in body water; and oxytocin, which stimulates uterine contractions during childbirth and the letdown of milk during lactation.
Answer the following questions about prolactin releasing hormone (PRH) and prolactin inhibiting hormone (PIH).
Where are these hormones produced? The hypothalamus
Where are their target cells located? The anterior pituitary
What are their effects on their target cells? PRH causes the release of prolactin from the pituitary and PIH inhibits, or stops, release of prolactin from the pituitary.
What are their ultimate effects on milk production? Explain your answer. PRH increases milk production while PIH decreases milk production. This is because prolactin increases milk production and PRH increases prolactin while PIH lowers it.
When a baby nurses, which of these hormones is most likely released in the mother? Explain your answer. When a baby nurses, PRH is most likely released in the mother because the stimulation of nursing increases prolactin to increase milk production, and PRH increases prolactin.
For each of the following hormones, state whether it is synthesized in the pituitary or the hypothalamus.
Describe the structure and location of the thyroid gland. The thyroid gland is one of the largest endocrine glands in the body. It is located in the front of the neck below the Adam’s apple. It is shaped like a butterfly and composed of two lobes connected by a narrow band of thyroid tissues called an isthmus.
Identify the types of cells within the thyroid gland that produce hormones. Follicles within the thyroid gland are small clusters of cells that are specialized to absorb iodide ions and use them to make thyroid hormones (T4 and T3). Parafollicular cells scattered among the follicles synthesize and secrete the hormone calcitonin.
Compare and contrast T4 and T3. Both T4 (thyroxine) and T3 (triiodothyronine) regulate gene expression in cells and control the rate of cellular metabolism throughout the body. Each molecule of T4 contains four iodide ions, whereas each molecule of T3 contains three iodide ions. The thyroid gland produces much more T4 than T3, but most of the T4 is converted to T3 by target tissues. T3 is much more powerful than T4.
How do T4 and T3 affect body cells? T4 and T3 cross cell membranes everywhere in the body and bind to intracellular receptors to regulate gene expression. The hormones turn on genes that control protein synthesis. They increase the rate of cellular metabolism body-wide and also increase the rate and force of the heartbeat. In addition, T4 and T3 increase the sensitivity of cells to fight-or-flight hormones.
Explain how T4 and T3 production is regulated. The production of T4 and T3 is regulated by a negative feedback loop that includes the pituitary gland and hypothalamus in addition to the thyroid gland. Low blood levels of T4 and T3 stimulate the hypothalamus and pituitary gland to secrete thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH), respectively. TSH stimulates the thyroid to produce more of its hormones. High blood levels of T4 and T3 have the opposite effects on the hypothalamus and pituitary gland and decrease the production of thyroid hormones.
What is calcitonin’s function? The function of calcitonin is to help regulate blood calcium levels by stimulating the movement of calcium into bone. It is secreted in response to rising blood calcium levels. It decreases blood calcium levels by enhancing calcium absorption and deposition in bone.
Identify the chief cause and effects of hyperthyroidism. The chief cause of hyperthyroidism is Graves’ disease, which is an autoimmune disorder in which abnormal antibodies produced by the immune system stimulate the thyroid to secrete excessive quantities of its hormones. The effects of hyperthyroidism may include the development of a goiter as well as such signs and symptoms as protruding eyes, heart palpitations, excessive sweating, diarrhea, weight loss despite increased appetite, muscle weakness, and unusual sensitivity to heat.
What are two possible causes of hypothyroidism? Two possible causes of hypothyroidism are dietary iodine deficiency and Hashimoto’s thyroiditis, which is an autoimmune disorder that attacks and destroys the thyroid gland.
List signs and symptoms of hypothyroidism. Signs and symptoms of hypothyroidism may include the development of a goiter as well as signs and symptoms such as abnormal weight gain, tiredness, baldness, cold intolerance, and slow heart rate.
Why is it that both hyperthyroidism and hypothyroidism cause goiters? Both hyperthyroidism and hypothyroidism may cause goiters because in both conditions, but for different reasons, the thyroid gland is stimulated to produce more of its hormones, to which it responds by increasing in size.
Choose one symptom each for hyperthyroidism and hypothyroidism. Based on the functions of thyroid hormones, explain why each symptom occurs. Answers will vary. Sample answer: Hyperthyroidism causes weight loss despite increased appetite because it results from an excess of thyroid hormones, which increase cellular metabolism. Hypothyroidism, on the other hand, causes weight gain because the lack of thyroid hormones slows the body’s metabolism.
In cases of hypothyroidism caused by Hashimoto’s thyroiditis or removal of the thyroid gland to treat hyperthyroidism, patients are often given medication to replace the missing thyroid hormone. Explain why the level of replacement thyroid hormone must be carefully monitored and adjusted if needed. Answers may vary. Sample answer: In thyroid hormone replacement therapy, the levels must be carefully monitored and adjusted if needed because they need to stay within a certain range for the patient to be healthy. This is normally taken care of by a negative feedback loop involving the hypothalamus, pituitary, and thyroid gland. When the thyroid gland is damaged, as in the case of Hashimoto’s thyroiditis, or removed surgically, the level of thyroid hormone must be monitored and adjusted externally by a physician.
9.6 Adrenal Glands: Review Questions and Answers
Describe the structure and location of the adrenal glands. The two adrenal glands are located on both sides of the body, just above the kidneys. The right adrenal gland is smaller and has a pyramidal shape. The left adrenal gland is larger and has a half-moon shape. Each adrenal gland has two distinct parts: an outer layer called the adrenal cortex and an inner layer called the medulla.
Compare and contrast the adrenal cortex and adrenal medulla. The adrenal cortex and adrenal medulla both synthesize and secrete endocrine hormones. The adrenal cortex produces three different types of steroid hormones, whereas the adrenal medulla produces non-steroid catecholamine hormones.
Identify the three layers of the adrenal cortex and the type of hormones each layer produces. The three layers of the adrenal cortex are the zona glomerulosa, which is the outermost layer of the cortex and produces mineralocorticoids; zona fasciculata, which is the middle layer and produces glucocorticoids; and zona reticularis, which is the innermost layer and produces androgens.
Give an example of each type of corticosteroid and state its function. An example of a mineralocorticoid is aldosterone, which helps control the body’s electrolyte balance as well as blood volume and blood pressure. An example of a glucocorticoid is cortisol, which helps control the rate of metabolism and also suppresses the immune system. An example of an androgen is DHEA, which serves as a precursor for both male and female sex hormones.
Explain how the production of glucocorticoids is regulated. The production of glucocorticoids is stimulated by adrenocorticotropic hormone (ACTH) from the anterior pituitary, which in turn is stimulated by corticotropin releasing hormone (CRH) from the hypothalamus. When levels of glucocorticoids start to rise too high, they provide negative feedback to the hypothalamus and pituitary gland to stop secreting CRH and ACTH, respectively. The opposite occurs when levels of glucocorticoids start to fall too low.
What is a catecholamine? Give an example of a catecholamine and state its function. A catecholamine is a non-steroid, water-soluble hormone synthesized and secreted by the adrenal medulla. An example of a catecholamine is adrenaline, which is a fight-or-flight hormone that brings about such changes as increased heart rate, more rapid breathing, constriction of blood vessels in certain parts of the body, and an increase in blood pressure.
Compare and contrast Cushing’s syndrome and Addison’s disease. Both Cushing’s syndrome and Addison’s disease are adrenal gland disorders associated with abnormal production of adrenal hormones. Cushing’s syndrome involves hypersecretion of the adrenal hormone cortisol and is most commonly caused by a pituitary tumor. It leads to such signs and symptoms as obesity, diabetes, high blood pressure, and excessive body hair. Addison’s disease, in contrast, involves hyposecretion of the adrenal hormone cortisol and is generally caused by the immune system attacking cells of the adrenal cortex. It leads to such signs and symptoms as hyperpigmentation of the skin and excessive fatigue.
What are two ways in which the nervous system (which includes the brain, spinal cord, and nerves) controls the adrenal gland? Answers may vary. Sample answer: One way in which the nervous system controls the adrenal gland is that the hypothalamus of the brain influences the secretion of hormones from the adrenal cortex via the pituitary gland. A second way is that the sympathetic division of the autonomic nervous system influences the secretion of catecholamines from the adrenal medulla.
Explain why a pituitary tumor can cause either hypersecretion or hyposecretion of cortisol. Answers may vary. Sample answer: A pituitary tumor can cause either increased or decreased secretion of ACTH. This, in turn, causes hypersecretion or hyposecretion of cortisol, respectively.
9.7 Pancreas: Review Questions and Answers
Describe the structure and location of the pancreas. The pancreas is about 15 centimetres (6 in.) long, and it has a flat, oblong shape. Structurally, it is divided into a head, body, and tail. The pancreas is located in the upper left abdomen behind the stomach and near the upper part of the small intestine.
Distinguish between the endocrine and exocrine functions of the pancreas. As an endocrine gland, the pancreas releases hormones such as insulin directly into the bloodstream for transport to cells throughout the body. The endocrine hormones of the pancreas are all involved in glucose metabolism and homeostasis of blood glucose levels. As an exocrine gland, the pancreas releases digestive enzymes into ducts that carry the enzymes to the gastrointestinal tract where they assist with digestion.
What is pancreatitis? What are possible causes and effects of pancreatitis? Pancreatitis is inflammation of the pancreas. It has a variety of possible causes including gallstones and chronic alcohol use. It occurs when pancreatic digestive enzymes damage the gland’s tissues, causing problems with fat digestion. Signs and symptoms usually include intense pain and jaundice.
Describe the incidence, prognosis, and risk factors of cancer of the endocrine tissues of the pancreas. Cancer of the endocrine tissues of the pancreas is rare, but its incidence has been rising sharply. It occurs most often in later adulthood. Pancreatic cancer is generally diagnosed at a relatively late stage when it is too late for surgery, which is the only cure. Factors that increase the risk of pancreatic cancer include smoking, chronic pancreatitis, and diabetes.
Compare and contrast type 1 and type 2 diabetes. Both type 1 and type 2 diabetes are characterized by inadequate activity of insulin, which leads to high blood levels of glucose. Early symptoms of both types of diabetes include excessive urination and thirst. Type 1 diabetes is caused by the immune system attacking the insulin-secreting beta cells of the pancreas. It may develop in people of any age but is most often diagnosed before adulthood. For type 1 diabetics, insulin injections are critical for survival. Type 2 diabetes is usually caused by a combination of insulin resistance and impaired insulin secretion that occur due to both genetic and environmental factors. It develops most commonly in adults. Management of type 2 diabetes typically includes changes in diet and physical activity as well as non-insulin medications. Treatment of type 2 diabetes may or may not include insulin injections.
If the alpha islet cells of the pancreas were damaged to the point that they no longer functioned, how would this affect blood glucose levels? Assume that no outside regulation of this system is occurring and explain your answer. Further, would administration of insulin be more likely to help or hurt this condition? Explain your answer. Blood glucose levels would probably drop because the alpha cells secrete glucagon which normally raises blood glucose levels. Administration of more insulin would probably make this condition worse, because it would lower blood glucose levels even further.
Explain why diabetes causes excessive thirst. Diabetes causes excessive thirst because the body is trying to flush excess glucose out of the blood by causing the kidneys to excrete more urine. The person then gets thirsty, signaling them to drink more to replace the lost water.
9.8 Case Study Conclusion: Review Questions and Answers
The pituitary gland is considered the master gland of the endocrine system, because its hormones control other endocrine glands. For each of the glands below, describe one way in which it is controlled by the pituitary gland.
the thyroid gland The pituitary secretes TSH, which stimulates the thyroid gland to produce T3 and T4.
the adrenal gland The pituitary secretes ACTH, which stimulates the adrenal gland to produce cortisol.
the gonads (ovaries and testes) The pituitary secretes LH, which stimulates the gonads to produce sex hormones.
Give an example of an endocrine disorder involving hyposecretion. Be sure to include the name of the hormone involved. Give an example of an endocrine disorder involving hypersecretion. Be sure to include the name of the hormone involved. Examples may vary. Sample answer: Hyposecretion is when the body does not produce enough of a hormone. An example is Addison’s disease, where too little cortisol (and sometimes mineralocorticoids) is produced. Hypersecretion is when the body produces too much of a hormone. An example is gigantism, where too much growth hormone is produced.
Explain why non-steroid hormones typically require the activation of second messenger molecules to have their effects, instead of directly affecting intracellular processes themselves. Non-steroid hormones typically cannot pass through the plasma membrane of target cells, so they cannot directly affect intracellular processes. Instead, they bind to receptors on the plasma membrane that then activate second messenger molecules, which affect processes inside the cell.
Explain what it means that endocrine hormones are “chemical messengers.” Answers may vary. Sample answer: Endocrine hormones are chemical messengers because they are chemical molecules that are released into the bloodstream from certain cells, which then affect the processes of other cells. Their “message” is the way they influence the activity of other cells.
If you were a physician, and a patient came to you complaining of excessive thirst and urination, what endocrine disorder might you suspect the patient has? In order to diagnose this disorder, what would you want to check for in the patient’s blood? Explain your answer. Answers may vary. Sample answer: Diabetes. I would want to check the patient’s blood glucose levels because both types of diabetes cause a problem in the regulation of blood glucose, either due to a lack of insulin or because of insulin resistance.
Give one example of negative feedback in the endocrine system. Answers may vary. Sample answer: Glucocorticoids negatively feed back to the hypothalamus and pituitary to regulate the production of CRH and ACTH, respectively. This lowers the level of glucocorticoid production when the level gets too high.
Explain the circumstances in which organs and hormones in a negative feedback loop can actually increase the level of a hormone. Organs and hormones in a negative feedback loop can increase the level of a hormone when the level gets too low. The organs and hormones in this system then act to increase production of the hormone.
Explain why giving iodine can treat some cases of hypothyroidism, but is not usually helpful when someone has hypothyroidism due to Hashimoto’s thyroiditis. Answers may vary. Sample answer: In cases of hypothyroidism due to iodine deficiency, giving iodine will help because it will allow the thyroid gland to use the iodine to make thyroid hormones. In the case of Hashimoto’s thyroiditis, the thyroid gland is damaged or destroyed due to an autoimmune reaction, so it has trouble producing thyroid hormone at all.
For each disease below, identify the hormone involved and whether the problem involves hyposecretion or hypersecretion of this hormone.
Addison’s disease – Hyposecretion of cortisol
Graves’ disease – Hypersecretion of thyroid hormones
Cushing’s syndrome – Hypersecretion of cortisol
Type 1 diabetes – Hyposecretion of insulin
What is an example of a disease caused by hormone resistance? Answers may vary. Sample answer: Type 2 diabetes.
Explain generally how autoimmune disorders can disrupt the endocrine system. Give one example. Answers will vary. Sample answer: Autoimmune disorders produce antibodies that can attack or otherwise alter the functioning of endocrine glands, which can cause hyposecretion or hypersecretion of hormones. One example is Type 1 diabetes, where the immune system attacks the insulin-producing beta cells of the pancreas, which causes hyposecretion of insulin.