The Endocrine System Similar in fxn to the Nervous System Both send a message-Δ fxn of cell Nervous System-quick on, quick off Endocrine System-slow on, slow off © 2012 Pearson Education, Inc.

Figure 18-1 Organs and Tissues of the Endocrine System Hypothalamus Production of ADH, oxytocin, and regulatory hormones Pituitary Gland Anterior lobe: ACTH, TSH, GH, PRL, FSH, LH, and MSH Posterior lobe: Release of oxytocin and ADH Parathyroid Glands (located on the posterior surface of the thyroid gland) Parathyroid hormone (PTH) Pineal Gland Melatonin p.597

© 2012 Pearson Education, Inc. Figure 18-1 Organs and Tissues of the Endocrine System Thyroid Gland Thyroxine (T 4 ) Triiodothyronine (T 3 ) Calcitonin (CT) Adrenal Glands Adrenal medulla: Epinephrine (E) Norepinephrine (NE) Adrenal cortex: Cortisol, corticosterone, aldosterone, androgens Insulin Glucagon Pancreas (Pancreatic Islets) Testis Ovary Thymus: (Undergoes atrophy during adulthood) Secretes thymosins Adipose Tissue: Secretes Leptin Digestive Tract: Secretes numerous hormones involved in the coordination of system functions, glucose metabolism, and appetite Kidneys: Secrete Erythropoietin (EPO) Calcitriol Gonads: Testes (male): Androgens (especially testosterone), inhibin Ovaries (female): Estrogens, progestins, inhibin Organs with Secondary Endocrine Functions Heart: Secretes natriuretic peptides. Atrial natriuretic peptide (ANP) Brain natriuretic peptide (BNP) See Chapter 21 See Chapter 22 See Chapter 25 See Chapters 19 and 26 See Chapters 28 and 29 p.597

Hormone: organic chemical that changes the function of its target cell – Autocrine- – Paracrine- – Endocrine- – exocrine Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings © 2012 Pearson Education, Inc. p.595

Maintenance of Homeostasis – Water/electrolytes – Enzyme function – Transport Regulate long term processes Development Growth Reproduction © 2012 Pearson Education, Inc.

Circulate freely-don’t last long – Bind to receptor – b.d. by liver or kidneys – b.d. by enzymes in plasma or interstitial fluid Bound to a carrier-last a long time – Reserves in the blood stream – Once released from carrier-don’t last long – Same reasons as above © 2012 Pearson Education, Inc.

Hormones Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings p.598 © 2012 Pearson Education, Inc.

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings © 2012 Pearson Education, Inc. p.601

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings © 2012 Pearson Education, Inc. p.601

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings p.600

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mechanisms of Hormone Action The Process of Amplification – Is the binding of a small number of hormone molecules to membrane receptors – Leads to thousands of second messengers in cell – Magnifies effect of hormone on target cell © 2012 Pearson Education, Inc.

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mechanisms of Hormone Action Down-regulation – Presence of a hormone triggers decrease in number of hormone receptors – When levels of particular hormone are high, cells become less sensitive Up-regulation – Absence of a hormone triggers increase in number of hormone receptors – When levels of particular hormone are low, cells become more sensitive © 2012 Pearson Education, Inc.

Figure 18-3 G Proteins and Hormone Activity Hormone Protein receptor G protein activated Hormone Protein receptor G protein activated Effects on cAMP Levels Many G proteins, once activated, exert their effects by changing the concentration of cyclic-AMP, which acts as the second messenger within the cell. Increased production of cAMP adenylate cyclase Acts as second messenger kinase Activates enzymes Opens ion channels If levels of cAMP increase, enzymes may be activated or ion channels may be opened, accelerating the metabolic activity of the cell. Examples: Epinephrine and norepinephrine (β receptors) Calcitonin Parathyroid hormone ADh, ACTH, FSH, LH, TSH Glucagon Examples: Epinephrine and norepineph- rine (α 2 receptors) In some instances, G protein activation results in decreased levels of cAMP in the cytoplasm. This decrease has an inhibitory effect on the cell. Enhanced breakdown of cAMP PDE Reduced enzyme activity Hormone Protein receptor G protein (inactive) G protein activated p.600

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings © 2012 Pearson Education, Inc. p.600

© 2012 Pearson Education, Inc. Figure 18-3 G Proteins and Hormone Activity Hormone Protein receptor G protein (inactive) G protein activated Hormone Protein receptor G protein activated Effects on Ca 2+ Levels Some G proteins use Ca 2+ as a second messenger. Examples: Epinephrine and norepinephrine (α 1 receptors) Oxytocin Regulatory hormones of hypothalamus Several eicosanoids Activates enzymes Calmodulin PLC, DAG, and IP 3 Opening of Ca 2+ channels Release of stored Ca 2+ from ER or SER Ca 2+ acts as second messenger p.600

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings © 2012 Pearson Education, Inc. p.600

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Endocrine Reflexes – Functional counterparts of neural reflexes – In most cases, controlled by negative feedback mechanisms Stimulus triggers production of hormone whose effects reduce intensity of the stimulus © 2012 Pearson Education, Inc.

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Endocrine Reflexes Endocrine reflexes can be triggered by – Humoral stimuli Changes in composition of extracellular fluid – Hormonal stimuli Arrival or removal of specific hormone – Neural stimuli Arrival of neurotransmitters at neuroglandular junctions © 2012 Pearson Education, Inc.

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Endocrine Reflexes Simple Endocrine Reflex – Involves only one hormone – Controls hormone secretion by the heart, pancreas, parathyroid gland, and digestive tract Complex Endocrine Reflex – Involves One or more intermediary steps Two or more hormones The hypothalamus © 2012 Pearson Education, Inc.

Figure 18-5 Three Mechanisms of Hypothalamic Control over Endocrine Function Production of ADH and oxytocin HYPOTHALAMUS Control of sympathetic output to adrenal medullae Secretion of regulatory hormones to control activity of the anterior lobe of the pituitary gland Preganglionic motor fibers Adrenal gland Secretion of epinephrine and norepinephrine Adrenal medulla Adrenal cortex Posterior lobe of pituitary gland Release of ADH and oxytocin Hormones secreted by the anterior lobe control other endocrine organs Anterior lobe of pituitary gland Infundibulum p.602

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Endocrine Reflexes Neuroendocrine Reflexes – Pathways include both neural and endocrine components Complex Commands – Issued by changing Amount of hormone secreted Pattern of hormone release: – hypothalamic and pituitary hormones released in sudden bursts – frequency changes response of target cells © 2012 Pearson Education, Inc.