Medical Terminology: The Endocrine System

1. What is The Endocrine System?
The endocrine system is comprised of several glands, scattered throughout the body. The glands release hormones that are chemical messengers, substances that control and regulate the activity of target cells and organs.
Together, these hormones influence growth, development, and digestion, and regulate metabolism and reproduction. The glands generally release the hormones into the blood because of a stimulus, another hormone, or a threshold. The signal to turn off the hormone production is regulated by a process called direct feedback. Direct feedback is necessary to maintain homeostasis. The body receives feedback about changes in hormone levels and impacts organs or body systems to adjust the hormone production to tell the body to return to homeostasis. When the concentration of the substance reaches a threshold, the gland and its production are turned off. The glands, the hormones they produce, and the effects are discussed below.
The thyroid gland is located in the anterior neck, overlying the trachea. It makes three hormones: thyroxine (T4), triiodothyronine (T3), and calcitonin, which affects the blood calcium and phosphate release from the bones. Thyroid hormones affect metabolism, muscles, the heart, and many other body organs and systems. They help regulate carbohydrate metabolism, lipids, proteins, and growth and development.
Anterior pituitary glands are controlled by hormones from the hypothyroid and direct feedback.
The adrenal glands are bilateral glands that cap each kidney. They are located in the retroperitoneum. The glands are composed of two parts: the cortex and the adrenal medulla. The cortex secretes (1) aldosterone, which is responsible for renal reabsorption of sodium and excretion of potassium; (2) cortisol, which maintains glucose control, increases hepatic gluconeogenesis (the making of glucose), and manages the body’s stress response; and (3) androgens, which are sex hormones. The adrenal medulla produces, stores, and secretes epinephrine and norepinephrine, which are called catecholamines. When they are released, heart and respiratory rates increase, blood pressure rises, airways dilate, and an increase in the metabolic rate is seen.
The parathyroid glands are composed of usually four, but sometimes six or more small glands that are found on the posterior side of the thyroid gland. Their function is to produce parathyroid hormone (PTH). Parathyroid hormone maintains the calcium level in the blood. It also regulates the phosphorus level in the body. If the serum calcium level falls, PTH is released, which causes bones to break down, releasing calcium into the blood. It also causes the kidneys to decrease the calcium released in the urine, and increases phosphate excretion.

2. Hypothyroidism (Myxedema)
Hypothyroidism is a lack of, or too little, thyroid hormone commonly caused by Hashimoto’s thyroiditis. Hashimoto’s thyroiditis is a chronic disorder caused by abnormal antibodies that attack the thyroid gland. Hypothyroidism can also be caused by decreased production of the thyroid-stimlating hormone (TSH) from the pituitary gland, a side effect of surgery, inflammation of the thyroid gland, and treatment for hyperthyroidism.

3. Hyperthyroidism (Graves’ Disease)
This is an overproduction of T3. and T4. by the thyroid gland that can be caused by an autoimmune disease in which the body’s immune system attacks the thyroid gland. Other causes can be a benign tumor (adenoma), resulting in an enlarged thyroid gland (goiter), or an overproduction of thyroid-stimulating hormone (TSH) by the pituitary gland, caused by a pituitary tumor.

4. Simple Goiter
A lack of iodine in the patient’s diet (endemic, simple goiter) causes the thyroid gland to become enlarged. This is seen less today because iodine is added to table salt. The thyroid gland can also become enlarged by ingesting large amounts of goitrogenic drugs or goitrogenic foods that decrease production of thyroxine (goitrogenic), such as strawberries, cabbage, peanuts, peas, peaches, and spinach. This results in sporadic simple goiter. A simple goiter is not caused by inflammation or neoplasm.

5. Hypopituitarism
Hypopituitarism results when the pituitary gland is unable to secrete a normal amount of pituitary hormones. Primary causes are pituitary tumors, inadequate blood supply to the pituitary gland, infection, radiation therapy, or surgical removal of a portion of the pituitary gland. Secondary causes affect the hypothalamus, which regulates the pituitary gland.

6. Hyperpituitarism (Acromegaly and Gigantism)
The pituitary gland produces an excessive amount of growth hormone. If hyperpituitarism occurs before epiphy-seal closure, the patient (infants and children) has gigantism, resulting in an overgrowth of all body tissues. If hyperpituitarism occurs after epiphyseal closure, which is rare, the patient has acromegaly, resulting in bone thickening, growth in width (transverse growth), and enlarged organs (visceromegaly).

7. Hyperprolactinemia
This is an overproduction of the prolactin hormone that promotes lactation. Excessive secretion is usually caused by a pituitary tumor (prolactinoma) and may also be caused by hypothyroidism, chronic kidney disease, and medications that affect the pituitary gland.

8. Diabetes Insipidus
Either a decrease in antidiuretic hormone (ADH) production by the hypothalamus or the increased ADH by the pituitary gland causes a decreased ability of the kidneys to concentrate urine. This results in the excretion of large amounts of diluted urine. The patient then drinks large amounts of fluid to replace the increased urine output.

9. Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH)
The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is caused by too much ADH being secreted by the posterior pituitary gland. Antidiuretic hormone (ADH) is responsible for controlling the amount of water reabsorbed by the kidney; it prevents the loss of too much fluid. When too much water is detected, ADH production or secretion is halted. SIADH may be caused by damage to the hypothalamus or pituitary, inflammation of the brain, some medications such as selective serotonin reuptake inhibitors (SSRIs), carbamazepine, cyclophosphamides, and chlorpropamide. Certain cancers, especially lung, may produce ADH.

10. Addison’s Disease
Addison’s disease is inadequate secretion of corticosteroids from the adrenal cortex, resulting from damage to the adrenal cortex. Autoimmune destruction of the adrenal gland and tuberculosis are two common causes of Addison’s disease. A patient can experience Addisonian crisis when infection, surgery, or other stressful events result in a decrease in the production of cortisol and aldosterone. Addisonian crisis is a medical emergency.

11. Cushing’s Syndrome
The adrenal cortex secretes an excess of glucocorticoids or the pituitary gland an excess of adrenocorticotropic hormone (ACTH) as a result of a pituitary tumor, adrenal tumor, or from ongoing glucocorticoid therapy.

12. Primary Aldosteronism (Conn’s Syndrome)
The adrenal cortex is secreting an excessive amount of aldosterone caused by an adrenal tumor, a malfunctioning adrenal cortex, or sources outside the adrenal gland producing aldosterone. Some medications such as calcium channel blockers can lower aldosterone levels, which can confuse the diagnosis.

13. Pheochromocytoma
A tumor on the adrenal medulla secretes excessive amounts of epinephrine and norepinephrine.

14. Hypoparathyroidism
Hypoparathyroidism is diminished functioning of the parathyroid glands leading to low levels of parathyroid hormone (PTH), which causes hypocalcemia. The primary cause of hypoparathyroidism is destruction of the glands by an autoimmune cause. Parathyroidectomy is no longer a major cause, since surgery now removes only the gland that is malfunctioning. Occasionally the gland(s) may be accidentally removed during thyroidectomy.

15. Hyperparathyroidism
Overactivity of the parathyroid glands caused by a tumor produces too much PTH, resulting in hypercalcemia and hypophosphatemia. Excess calcium is reabsorbed by the kidneys and may result in kidney stones; however, malfunction in the feedback mechanism prevents detection of excessive calcium levels in the blood, thereby failing to adjust the secretion of PTH. Parathyroid tumors are usually benign.

16. Diabetes Mellitus
Our body converts certain foods into glucose, which is the body’s primary energy supply. Insulin from the beta cells of the pancreas is necessary to transport glucose into cells where it is used for cell metabolism. Diabetes mellitus occurs when beta cells either are unable to produce insulin (type I diabetes mellitus) or produce an insufficient amount of insulin (type II diabetes mellitus).
As a result, glucose does not enter cells but remains in the blood. Increased glucose levels in the blood signal to the patient to increase intake of fluid in an effort to flush glucose out of the body in urine. Patients then experience increased thirst and urination.
Cells become starved for energy because of the lack of glucose and signal to the patient to eat, causing the patient to experience an increase in hunger. There are three types of diabetes mellitus: (1) type I, known as insulin-dependent (IDDM), where beta cells are destroyed by an autoimmune process; (2) type II, known as non-insulin-dependent (NIDDM), where beta cells produce insufficient insulin; and (3) gestational diabetes mellitus, which occurs during pregnancy.

17. Metabolic Syndrome (Syndrome X/Dysmetabolic Syndrome)
These patients have a collection of symptoms that include high blood glucose, obesity, high blood pressure, and high triglycerides based on family history. Beta cells in the pancreas are unable to produce sufficient insulin; therefore, the liver produces a higher level of glucose. The patient is also insulin resistant. This syndrome leads to cardiovascular disease.

Basic Questions
Endocrine System

1. What are hormones?
Hormones are chemical messengers that control and regulate the activity of target cells and organs.

2. What is direct feedback?
Direct feedback is necessary to maintain homeostasis. The body receives feedback about changes in hormone levels and impacts organs or body systems to adjust the hormone production to tell the body to return to homeostasis.

3. What is calcitonin?
Calcitonin is a hormone released by the thyroid gland that affects the blood calcium and phosphate release from the bones.

4. What controls the anterior pituitary glands?
Anterior pituitary glands are controlled by hormones from the hypothyroid and direct feedback.

5. What is aldosterone?
Aldosterone is a hormone produced by the adrenal glands that is responsible for renal reabsorption of sodium and excretion of potassium.

6. What is cortisol?
Cortisol is a hormone produced by the adrenal glands that maintains glucose control, increases hepatic gluconeogenesis (the making of glucose), and manages the body’s stress response.

7. What are catecholamines?
Catecholamines are a hormone produced by the adrenal glands that cause the heart and respiratory rates to increase, blood pressure to rise, airways to dilate, and the metabolic rate to increase.

8. What is the function of the parathyroid hormone?
The parathyroid hormone (PTH) maintains the calcium level in the blood. It also regulates the phosphorus level in the body.

9. What is myxedema?
Myxedema (hypothyroidism) is a lack of, or too little, thyroid hormone.

10. What is Hashimoto’s thyroiditis?
Hashimoto’s thyroiditis is a chronic disorder caused by abnormal antibodies that attack the thyroid gland. Hypothyroidism can also be caused by decreased production of TSH from the pituitary gland, a side effect of surgery, inflammation of the thyroid gland, and treatment for hyperthyroidism.

11. What is Graves’ disease?
Graves’ disease (hyperthyroidism) is an overproduction of T3. and T4. by the thyroid gland that can be caused by an autoimmune disease in which the body’s immune system attacks the thyroid gland. Other causes can be a benign tumor (adenoma) resulting in an enlarged thyroid gland (goiter) or an overproduction of thyroid-stimulating hormone (TSH) by the pituitary gland, caused by a pituitary tumor.

12. What is a simple goiter?
A lack of iodine in the patient’s diet (endemic, simple goiter) causes the thyroid gland to become enlarged.

13. Why is a simple goiter not common today?
This is seen less today because iodine is added to table salt.

14. What is hypopituitarism?
Hypopituitarism results when the pituitary gland is unable to secrete a normal amount of pituitary hormones.

15. What is hyperpituitarism?
The pituitary gland produces an excessive amount of growth hormone.

16. What is gigantism?
If hyperpituitarism occurs before epiphyseal closure, the patient (infants and children) has gigantism, resulting in an overgrowth of all body tissues.

17. What is acromegaly?
If hyperpituitarism occurs after epiphyseal closure, which is rare, the patient has acromegaly, resulting in bone thickening, growth in width (transverse growth), and enlarged organs (visceromegaly).

18. What is hyperprolactinemia?
This is an overproduction of the prolactin hormone that promotes lactation.

19. What is a common cause of hyperprolactinemia?
Excessive secretion is usually caused by a pituitary tumor (prolactinoma) and may also be caused by hypothyroidism, chronic kidney disease, and medications that affect the pituitary gland.

20. What is diabetes insipidus?
Either a decrease in antidiuretic hormone (ADH) production by the hypothalamus or the increased ADH by the pituitary gland causes a decreased ability of the kidneys to concentrate urine. This results in the excretion of large amounts of diluted urine. The patient then drinks large amounts of fluid to replace the increased urine output.

21. What is metabolic syndrome?
These patients have a collection of symptoms that include high blood glucose, obesity, high blood pressure, and high triglycerides based on family history. Beta cells in the pancreas are unable to produce sufficient insulin, whereas the liver produces a higher level of glucose. The patient is also insulin resistant. This syndrome leads to cardiovascular disease.

22. What is the syndrome of inappropriate secretion of antidiuretic hormone (SIADH)?
SIADH is caused by too much ADH being secreted by the posterior pituitary gland. ADH is responsible for controlling the amount of water reabsorbed by the kidney; it prevents the loss of too much fluid. When too much water is detected, ADH production or secretion is halted.

23. What is Addison’s disease?
Addison’s disease is inadequate secretion of corticosteroids from the adrenal cortex, resulting from damage to the adrenal cortex.

24. What is Cushing’s syndrome?
The adrenal cortex secretes an excess of glucocorticoids or the pituitary gland an excess of adrenocorticotropic hormone (ACTH) as a result of a pituitary tumor, adrenal tumor, or from ongoing glucocorticoid therapy.

25. What is Conn’s syndrome?
Conn’s syndrome (primary aldosteronism) occurs when the adrenal cortex is secreting an excessive amount of aldosterone caused by an adrenal tumor, a malfunctioning adrenal cortex, or sources outside the adrenal gland producing aldosterone.