LESSON ASSIGNMENT LESSON 11 The Human Endocrine System. LESSON ASSIGNMENT Paragraphs 11-1 through 11-18. LESSON OBJECTIVES After completing this lesson, you should be able to: 11-1. Given a hormone, identify the endocrine organ that produces it. 11-2. Match the names or types of hormones with the body functions affected. SUGGESTION After completing the assignment, complete the exercises at the end of this lesson. These exercises will help you to achieve the lesson objectives. MD0007 11-1
LESSON 11 THE HUMAN ENDOCRINE SYSTEM Section I. INTRODUCTION 11-1. ENDOCRINE ORGANS ENDO = within CRINE = secrete The endocrine system (Figure 11-1) is a loose collection of organs called endocrine glands. Figure 11-1. The endocrine glands of the human body and their locations. MD0007 11-2
a. The endocrine glands are organs of internal secretion. Since they lack a duct system, they are often referred to as ductless glands. b. Since their secretions pass into the blood, they are usually well supplied with blood vessels. 11-2. HORMONE The secretion of an endocrine organ is called a hormone. The hormone is a chemical required in very small amounts for the proper development and/or functioning of the body. (Note the similarity of this definition to that of a vitamin. However, the hormone is produced within the body, and the vitamin is acquired from without.) 11-3. TARGET ORGAN AND FEEDBACK MECHANISM When the hormone is secreted by the endocrine organ, it is carried by the blood to the appropriate organ, the target organ. In addition, the level of activity of the target organ often affects the activity of the endocrine organ. Thus, there is a feedback mechanism that causes the endocrine organ to secrete just the right amount of hormone. Section II. THE PITUITARY BODY 11-4. GENERAL a. The pituitary body is located immediately under the brain. It is in a special hollow of the floor of the cranial cavity. The pituitary body is actually two glands: the posterior pituitary gland and the anterior pituitary gland. b. As a whole, the pituitary body produces a large number of hormones. These affect many tissues of the body. Many of these hormones are referred to as tropins (or trophins) because they cause development or activity of the tissues. 11-5. POSTERIOR PITUITARY GLAND In the embryo, the posterior pituitary gland develops as an outcropping (hypophysis) of the inferior part of the brain. Later in life, the posterior pituitary gland remains connected to the forebrain-stem. There is a series of nuclei in the forebrainstem which are together referred to as the hypothalamus. The hormones of the posterior pituitary gland are actually produced in the hypothalamus. The hormones pass from the hypothalamus to the posterior pituitary gland by way of neurosecretory fibers. From the posterior pituitary gland, the hormones are secreted into the blood. The main hormones of the posterior pituitary gland are: MD0007 11-3
a. Antidiuretic hormone (ADH). ADH is involved with the resorption or salvaging of water within the kidneys. Antidiuretic hormone is produced under thirst conditions. b. Oxytocin. Oxytocin has several specific effects, particularly upon smooth muscle. It is involved with contractions of smooth muscle in the uterus and with milk secretion. 11-6. ANTERIOR PITUITARY GLAND In the embryo, the anterior pituitary gland develops from the roof of the pharynx. Eventually, it lies in front of and attached to the posterior pituitary gland. Certain cells of the hypothalamus produce specific secretions called releasing factors. A special venous portal system carries these releasing factors to the anterior pituitary gland. There, they stimulate the cells of the anterior pituitary gland to secrete their specific hormones. a. Somatotropin (Somatotrophic Hormone; Growth Hormone). Somatotropin stimulates the growth of the body in general. When this hormone is deficient, dwarfism results. When it is present in excess amounts, giantism results. b. Thyrotropin. Thyrotropin stimulates the thyroid gland to produce its hormones. c. Adrenocorticotropic Hormone (ACTH). Adrenocorticotropic hormone stimulates the adrenal (suprarenal) cortex to produce its hormones. d. Luteinizing Hormone (LH). Luteinizing hormone stimulates ovulation and luteinization of ovarian follicles in females and promotes testosterone production in males. e. Follicle-Stimulating Hormone (FSH). Follicle-stimulating hormone stimulates ovarian follicle growth in females and stimulates spermatogenesis in males. f. Prolactin. Prolactin stimulates milk production and maternal behavior in females. Section III. THE PINEAL GLAND 11-7. LOCATION The pineal gland is located just above the brainstem. It is between the cerebral hemispheres. MD0007 11-4
11-8. FUNCTIONS The details of the secretions and functions of the pineal gland are still not fully understood. Apparently, they are associated with sexual drive and reproduction. At least in lower animals, the pineal gland is influenced by the cumulative number of hours of light passing into the eyes each day. Section IV. THE THYROID AND PARATHYROID GLANDS 11-9. THE THYROID GLAND a. Location and Structure. The thyroid gland is located around the trachea, just below the larynx. It consists of two lobes, left and right. They are connected across the front of the trachea by an isthmus. b. Hormones. (1) Thyroxin. The most important hormone produced by the thyroid gland is thyroxin. Thyroxin affects the basal metabolic rate (BMR), the level of activity of the body. Since iodine is an important element in the structure of thyroxin, the dietary intake of iodine is very important. When the gland is not functioning properly, it may become enlarged (goiter). Insufficient or excess thyroxin has serious effects on the body. (2) Calcitonin. A second hormone of the thyroid gland is calcitonin. It is involved with calcium metabolism in the body. 11-10. THE PARATHYROID GLANDS On the posterior side of each thyroid lobe is a pair (2 + 2 = 4) of tiny bodies called the parathyroid glands. The hormone of the parathyroid glands is parathoromone. It is important in maintaining the calcium levels of the body. When excess thyroid tissue is removed in surgery, the surgeon takes care not to remove the parathyroid glands. Section V. THE PANCREATIC ISLETS (ISLANDS OF LANGERHANS) 11-11. LOCATION AND STRUCTURE There are small groups of cells, known as islets, distributed through the substance of the pancreas. These cells function independently of the pancreas and produce their own hormones. MD0007 11-5
11-12. HORMONES Insulin and glucagon are two important hormones of the islets. These hormones are concerned with the glucose levels in the body. Section VI. THE ADRENAL (SUPRARENAL)GLANDS 11-13. LOCATION AND STRUCTURE As seen in a previous lesson, the kidneys are attached to the upper posterior abdominal wall by a combination of fat and fascia. The adrenal (suprarenal) gland is embedded in the fat immediately above each kidney. Each is triangular or crescent shaped. Each adrenal gland has a central medulla and an outer cortex. 11-14. HORMONES OF THE ADRENAL MEDULLA The central portion of the adrenal gland produces two hormones: epinephrine (Adrenalin) and norepinephrine (noradrenalin). These hormones mobilize the energy-producing organs of the body and immobilize the others. This is important during the stress reaction ("fight or flight"). 11-15. HORMONES OF THE ADRENAL CORTEX The outer portion (the cortex) of the adrenal gland produces a variety of hormones which can be grouped into three categories: a. Mineralocorticoids (for example, aldosterone), which are concerned with the electrolyte and water balance of the body. b. Glucocorticoids (for example, cortisol), which are concerned with many metabolic functions. They are especially known for their anti-inflammatory effects. c. Sex Hormones (adrenal androgens and estrogens). Section VII. THE GONADS AS ENDOCRINE GLANDS 11-16. GENERAL We have already seen that the primary sex organs (gonads) produce sex hormones in addition to sex cells (gametes). These hormones help to determine an individual's actual sex (male or female) and promote the sexual development of the individual. MD0007 11-6
11-17. MALE SEX HORMONES In the male, certain cells of the testes produce the male sex hormones, known as androgens (for example, testosterone). Androgens are concerned with male sexuality. 11-18. FEMALE SEX HORMONES The sex hormones of the female are known as the estrogens and progesterone. In the female, these hormones are secreted in a cyclic sequence, the menstrual cycle. During this cycle, the hormones affect a number of tissues of the female body. These tissues include the endometrium of the uterus, the milk-producing portions of the mammary glands, and so forth. During pregnancy, the placenta continues the production of progesterone. Continue with Exercises MD0007 11-7
EXERCISES, LESSON 11 REQUIREMENT. The following exercises are to be answered by completing the incomplete statements. After you have completed all the exercises, turn to "Solutions to Exercises" at the end of the lesson, and check your answers with the Academy solutions. 1. The endocrine glands are organs of internal n. Since they lack a duct system, they are often called less glands. They are usually well supplied with blood vessels to facilitate the release of their secretions into the d. 2. A hormone is a chemical required in very small amounts for the proper ment or f g of the body. Unlike a vitamin, a hormone is produced within the body. The blood carries each hormone to its t organ, whose level of activity in turn affects the e organ. Thus, to ensure the secretion of just the right amount of hormone, there is a k mechanism. 3. Many of the hormones of the pituitary body are called "tropins" because they cause ment or y of the tissues. 4. Antidiuretic hormone (ADH) and oxytocin are produced by the s and released from the r pituitary gland. Antidiuretic hormone is involved with the r ption or sal g of water within the kidneys. Antidiuretic hormone is produced under t t conditions. Oxytocin is involved with k secretion. s of smooth muscle in the uterus and with 5. Somatotropin, thyrotropin, and adrenocorticotropic hormone (ACTH) are produced by the r pituitary gland. Somatotropin stimulates the Thyrotroin stimulates the ACTH stimulates the a th of the body in general. d gland to produce its hormones. cortex to produce its hormones. MD0007 11-8
6. The pineal gland is apparently associated with l drive and n. 7. Thyroxin and calcitonin are secreted by the d gland. Thyroxin affects the b m rate. Calcitonin is involved with m metabolism. 8. The hormone of the parathyroid gland is parat, important in maintaining the m levels of the body. 9. Two important hormones of the pancreatic islets are i in and g on. These hormones are concerned with the se levels in the body. 10. Epinephrine and norepinephrine are produced by the adrenal. These hormones mobilize the y-producing organs and ze the others. This is important during the stress reaction, " t or t." 11. Mineralocorticoids, glucocorticoids, and some sex hormones are produced by the adrenal. Mineralocorticoids are concerned with e s of the body. Glucocorticoids are known for their anti- y effects. 12. The testes produce male sex hormones, known as s. The female sex hormones are the s and e. The tissues affected by female sex hormones include the m of the uterus and the milk-producing portions of the y glands. During pregnancy, the placenta continues the production of e. Check Your Answers on Next Page MD0007 11-9
SOLUTIONS TO EXERCISES, LESSON 11 1. The endocrine glands are organs of internal secretion. Since they lack a duct system, they are often called ductless glands. They are usually well supplied with blood vessels to facilitate the release of their secretions into the blood. (para 11-1) 2. A hormone is a chemical required in very small amounts for the proper development or functioning of the body. Unlike a vitamin, a hormone is produced within the body. The blood carries each hormone to its target organ, whose level of activity in turn affects the endocrine organ. Thus, to ensure the secretion of just the right amount of hormone, there is a feedback mechanism. (paras 11-2, 11-3) 3. Many of the hormones of the pituitary body are called "tropins" because they cause development or activity of the tissues. (para 11-4b) 4. Antidiuretic hormone, (ADH) and oxytocin are produced by the hypothalamus and released from the posterior pituitary gland. ADH is involved with the resorption or salvaging of water within the kidneys. ADH is produced under thirst conditions. Oxytocin is involved with contractions of smooth muscle in the uterus and with milk secretion. (para 11-5) 5. Somatotropin, thyrotropin, and adrenocorticotropic hormone (ACTH) are produced by the anterior pituitary gland. Somatotropin stimulates the growth of the body in general. Thyrotropin stimulates the thyroid gland to produce its hormones. ACTH stimulates the adrenal cortex to produce its hormones. (para 11-6) 6. The pineal gland is apparently associated with sexual drive and reproduction. (para 11-8) 7. Thyroxin and calcitonin are secreted by the thyroid gland. Thyroxin affects the basal metabolic rate. Calcitonin is involved with calcium metabolism. (para 11-9) 8. The hormone of the parathyroid gland is parathormone, important in maintaining the calcium levels of the body. (para 11-10) MD0007 11-10
9. Two important hormones of the pancreatic islets are insulin and glucagon. These hormones are concerned with the glucose levels in the body. (paras 11-11, 11-12) 10. Epinephrine and norepinephrine are produced by the adrenal medulla. These hormones mobilize the energy-producing organs and immobilize the others. This is important during the stress reaction, "fight or flight." (para 11-14) 11. Mineralocorticoids, glucocorticoids, and some sex hormones are produced by the adrenal cortex. Mineralocorticoids are concerned with electrolytes of the body. Glucocorticoids are known for their anti-inflammatory effects. (para 11-15) 12. The testes produce male sex hormones, known as androgens. The female sex hormones are the estrogens and progesterone. The tissues affected by female sex hormones include the endometrium of the uterus and the milk-producing portions of the mammary glands. During pregnancy, the placenta continues the production of progesterone. (paras 11-17, 11-18) End of Lesson 11 MD0007 11-11