Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 48 Mechanisms of Endocrine Control

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Functions of the Endocrine System Growth and development Sex differentiation Metabolism Adaptation to an ever-changing environment –Regulation of digestion –Use and storage of nutrients –Electrolyte and water metabolism –Reproductive functions

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Mechanisms of Hormones Hormones interact with high-affinity receptors. –These are linked to one or more effector system in the cell. Some receptors are located on the surface of the cell. –These act through second messenger mechanisms. Others are located in the cell. –They modulate the synthesis of enzymes, transport proteins, or structural proteins.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hypothalamic Hormones Regulating the Secretion of Anterior Pituitary Hormones Hypothalamus is the coordinating center of the brain for endocrine, behavioral, and autonomic nervous system function. GH-releasing hormone (GHRH) Somatostatin Dopamine Thyrotropin-releasing hormone (TRH) Corticotropin-releasing hormone (CRH) Gonadotropin-releasing hormone (GnRH)

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Monitoring Changes in Hormone Levels Positive feedback Negative feedback Level of the substance the hormone regulates

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hormones Function as chemical messengers –Move through the blood to distant target sites of action –Or, act more locally as paracrine or autocrine messengers that incite more local effects –Most are present in body fluids at all times in greater or lesser amounts as needed. Characteristics –A single hormone can exert various effects in different tissues. –A single function can be regulated by several hormones.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Hormone Actions Paracrine Actions –Hormones acting locally on cells other than those that produced the hormone –For example, the action of sex steroids on the ovary Autocrine Actions –Hormones exerting action on the cells from which they were produced –For example, the release of insulin from pancreatic beta cells can inhibit its release from the same cells.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hormone Synthesis and Secretion Protein and polypeptide hormones are synthesized and stored in vesicles in the cytoplasm of the endocrine cell until secretion is required. Steroid hormone are secreted upon synthesis.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Categories of Hormones According to Structure Amines and amino acids Peptides, polypeptides, proteins, and glycoproteins Steroids Fatty acid derivatives

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which of the following is a characteristic of a hormone? –A. A single hormone can exert various effects in different tissues. –B. A single function can be regulated by several hormones. –C. Both

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer C. Both Rationale: These are both characteristic of hormones and are at the heart of the functionality of hormones.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Actions of Hormones Released into the Bloodstream Circulate as free, unbound molecules –Peptide hormones and protein hormones usually circulate unbound in the blood. Circulate as hormones attached to transport carriers –Steroid hormones and thyroid hormone are carried by specific carrier proteins synthesized in the liver. Intracellular and extracellular mechanisms participate in the termination of hormone function.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Factors Affecting Response of a Target Cell to a Hormone Number of receptors present –Up-regulation –Down-regulation Affinity of these receptors for hormones –Affected by a number of conditions –For example, the pH of the body fluids plays an important role in the affinity of insulin receptors.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hormone Receptor Interactions—Second Messenger Glucagon Insulin Epinephrine Parathyroid hormone Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH)

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hormone Receptor Interactions—Second Messenger (cont.) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Antidiuretic hormone (ADH) Secretin

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hormone Receptor Interactions— Intracellular Interactions Estrogens Testosterone Progesterone Adrenal cortical hormones Thyroid hormones

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Control of Hormone Levels Affected by diurnal fluctuations that vary with the sleep– wake cycle –Growth hormone (GH) and adrenocorticotropic hormone (ACTH) Secreted in a complicated cyclic manner –Female sex hormones Regulated by feedback mechanisms that monitor substances such as glucose (insulin) and water (ADH) in the body Regulated by feedback mechanisms that involve the hypothalamic–pituitary target cell system

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Five Cell Types of the Anterior Pituitary Gland Thyrotrophs: produce thyrotropin, also called thyroid stimulating hormone (TSH) Corticotrophs: produce corticotrophin, also called adrenocorticotropic hormone (ACTH) Gonadotrophs: produce the gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) Somatotrophs: produce growth hormone (GH) Lactotrophs: produce prolactin

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Function of Hormones Produced by the Anterior Pituitary Body growth and metabolism (GH) Function of the thyroid gland (TSH) Glucocorticoid hormone levels (ACTH) Function of the gonads (FSH and LH) Breast growth and milk production (prolactin)

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Is the following statement True or False? Most hormones are regulated via positive feedback mechanism.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Rationale: In fact, some are regulated via positive feedback, but the vast majority are regulated by negative feedback mechanisms.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which of the following is a mechanism of hormone regulation? –A. Affinity of cellular receptors –B. Production of intracellular second messengers –C. Number of cell surface receptors –D. Levels of circulating albumin

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer C. Number of cell surface receptors Rationale: Number of cell surface receptors is a direct cellular response and mechanism of regulation of the hormone action.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Measures for assessing Endocrine Function and Hormone Levels Blood tests Urine tests Stimulation and suppression tests Genetic tests Imaging