Chapter 20 Outline • Endocrine Glands and Hormones • Hypothalamic Control of the Endocrine System • Pituitary Gland • Thyroid Gland • Parathyroid Glands • Adrenal Glands • Pancreas • Pineal Gland and Thymus • Endocrine Functions of the Kidneys, Heart, Gastrointestinal Tract, and Gonads • Aging and the Endocrine System • Development of the Endocrine System Introduction • ______ glands are ductless organs. • They secrete their molecular products (hormones) into the bloodstream. • All endocrine organs have an extensive distribution of many blood vessels. • The endocrine system and the nervous system both function to communicate signals throughout the body to bring about homeostasis. – Table 20.1 lists similarities and differences between the two organ systems. Comparison of the Endocrine and Nervous Systems Organs of the Endocrine System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamus Antidiuretic hormone (ADH) Oxytocin (OT) Regulatory hormones Pineal gland Pituitary gland Melatonin Anterior pituitary secretes: Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Growth hormone (GH) Luteinizing hormone (LH) Thyroid gland Parathyroid glands Melanocyte-stimulating hormone (MSH) Calcitonin (CT) (located on posterior surface Prolactin (PRL) Thyroid hormone (TH) of thyroid) Thyroid-stimulating hormone (TSH) Parathyroid hormone (PTH) Posterior pituitary releases: Antidiuretic hormone (ADH) Thymus Oxytocin (OT) Thymopoietin Thymosins Heart Atriopeptin Adrenal glands Gastrointestinal (GI) tract Cortex: Cholecystokinin (CCK) Corticosteroids Gastric inhibitory peptide (GIP) Medulla: Gastrin Epinephrine (E) Secretin Norepinephrine (NE) Vasoactive intestinal peptide (VIP) Kidney Pancreatic islets Calcitriol Glucagon Erythropoietin (EPO) Insulin Somatostatin Pancreatic polypeptide Testes (male) Androgens Inhibin Ovaries (female) Estrogen Inhibin Progesterone Figure 20.1 Overview of Hormones • Endocrine glands produce informational molecules called ______. • Hormones can only affect cells (target cells) or organs (target organs) that have receptors for a specific hormone. • Cells or organs that do not possess receptors for a specific hormone do not respond to that hormone. Classes of Hormones • The study of the structural components of the endocrine system, the hormones they produce, and the effects of these hormones on target organs is termed endocrinology. • There are three major classes of hormones based on their chemical structure: 1. ______ hormones—growth hormone 2. ______ hormones—estrogen 3. ______ amines—thyroid hormone Control of Hormone Secretion • Hormone secretion is regulated by a self- adjusting mechanism called a feedback loop. • There are two types of feedback loops: 1. ______ feedback loop 2. ______ feedback loop Negative Feedback Loop • In this type of loop, the stimulus starts the process like an elevation in blood glucose (eating a meal). • The hormone secreted in response to elevated glucose is insulin. • Insulin brings about a decrease in blood glucose. Negative Feedback Loop Figure 20.2 Positive Feedback Loop • Only a few examples in the human body • In this type of loop, the stimulus doesn’t produce an opposite and counteracting effect like a negative feedback loop • The stimulus accelerates the process Positive Feedback Loop Figure 20.2 Hypothalamic Control of the Endocrine System • The hypothalamus is the interface between the nervous system and the endocrine system and is the master gland of the endocrine system. • It controls and oversees most endocrine functions. • It is located in the inferior region of the diencephalon just superior to the pituitary gland. Mechanisms of Hypothalamic Control The hypothalamus controls most endocrine activity in three ways: 1. Controls release of ______ hormones from the anterior pituitary gland 2. Secretes oxytocin (OT) and antidiuretic hormone (ADH) from the posterior pituitary gland 3. Controls the stimulation and secretion activities of the adrenal medulla Mechanisms of Hypothalamic Control Figure 20.3 Pituitary Gland • Also called the ______ • Located just inferior to the hypothalamus • Housed within the sella turcica of the sphenoid bone • Connected to the hypothalamus by a thin stalk called the ______ • Divided into ______ and ______ lobes Pituitary Gland Figure 20.4 Anterior Pituitary • Also known as the adenohypophysis • Divided into three distinct areas: 1. Pars ______ 2. Pars ______ 3. Pars ______ Control of Anterior Pituitary Hormone Secretions • Hormones secreted from anterior pituitary gland are regulated by regulatory hormones secreted from the hypothalamus. • These regulatory hormones from the hypothalamus to the anterior pituitary travel through a blood vessel network called the hypothalamo-hypophyseal portal system. Regulatory Hormones Secreted by the Hypothalamus Hypothalamo-Hypophyseal Portal System Figure 20.6 Hormones of the Anterior Pituitary There are seven major hormones secreted from the anterior pituitary: 1. ______ stimulating hormone (TSH) 2. ______ (PRL) 3. ______ hormone (ACTH) 4. ______ hormone (GH)—also called somatotropin 5. ______ stimulating hormone (FSH) 6. ______ hormone (LH) 7. ______ hormone (MSH) Anterior Pituitary Hormones, Target Organs, and Effects Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamus Median eminence Infundibulum Anterior pituitary Posterior pituitary Muscle Thyrotropic cells secrete Somatotropic cells secrete thyroid-stimulating hormone growth hormone (GH), which acts (TSH), which acts on the on all body tissues, especially bone, thyroid gland. muscle, and adipose connective tissue. Thyroid Adipose Bone connective tissue Mammary gland Mammotropic cells secrete Gonadotropic cells secrete prolactin (PRL), which acts on follicle-stimulating hormone (FSH) mammary glands and testes. and luteinizing hormone (LH) which acts on the gonads (testes and ovaries). Testis Testis Ovary Corticotropic cells secrete Pars intermedia cells secrete adrenocorticotropic melanocyte-stimulating hormone hormone (ACTH), which acts (MSH), which acts on melanocytes Adrenal on the adrenal cortex. in the epidermis. cortex Adrenal gland Melanocytes Figure 20.7 Posterior Pituitary • Derived from the embryonic diencephalon • Comprised of the following regions: – pars nervosa – infundibular stalk • Neural connection between the hypothalamus and the posterior pituitary is the hypothalamo-hypophyseal tract Hypothalamo-Hypophyseal Tract Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamus Paraventricular nucleus Supraoptic nucleus Hypothalamo-hypophyseal tract Optic chiasm Infundibulum Posterior pituitary Anterior pituitary Telodendria Figure 20.8 Pituitary Gland Hormones Thyroid Gland • The largest gland entirely devoted to endocrine activities • Located just inferior to the thyroid cartilage and anterior to the trachea • Butterfly shape with right and left lobes connected by a midline ______ Thyroid Gland Figure 20.9 Thyroid Follicle • Functional unit of the thyroid gland • Comprised of simple cuboidal cells that produce an iodinated glycoprotein called ______ (TGB) that is stored internally as a colloid • The follicle cells and the internal storage area for TGB is collectively called the ______ follicle Thyroid Follicle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thyrohyoid muscle Thyroid cartilage Common carotid artery Superior thyroid vessels Cricoid cartilage Left lobe of thyroid gland Isthmus of thyroid gland Right lobe of thyroid gland Inferior thyroid artery Trachea Inferior thyroid veins (a) Follicular cells Capillary Parafollicular cell Thyroid follicle Connective tissue capsule Follicle lumen (contains colloid) LM 400x (b) a(right): © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel; b(right): © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser Figure 20.9 Parafollicular Cells • Large endocrine cells located between thyroid follicles called ______ cells • Secrete ______, which helps to regulate serum calcium Thyroid Gland–Pituitary Gland Negative Feedback Loop Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamus stimulatory 1 A stimulus (e.g., low body temperature) causes the hypothalamus to secrete inhibitory thyrotropin-releasing hormone (TRH), Negative feedback which acts on the anterior pituitary. inhibition TRH 5 Increased body temperature is detected by the hypothalamus, and secretion of TRH by the hypothalamus is inhibited. TH also blocks the interactions of TRH from the hypothalamus and anterior pituitary to prevent the formation of TSH. 2 Thyrotropic cells in the anterior pituitary release Anterior thyroid-stimulating pituitary hormone (TSH). Target organs in body TSH 4 TH stimulates target cells to increase metabolic activities, resulting in an increase in basal body temperature. TH 3 TSH stimulates follicular cells of the thyroid gland to release thyroid hormone (TH). Figure 20.10 Parathyroid Glands Small glands (usually four) embedded on the posterior surface of the thyroid gland Figure 20.11 Parathyroid Glands There are two types of cells that are seen in the parathyroid gland: 1. ______ cells (principal cells)—secrete parathyroid hormone (PTH) that helps regulate serum calcium 2. ______ cells—function unknown Cells of the Parathyroid Gland Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction