© 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc.

Figure 18-1 Organs and Tissues of the Endocrine System (Part 1 of 2). Hypothalamus Pineal Gland Production of ADH, OXT, and regulatory hormones Melatonin Parathyroid Glands Pituitary Gland (located on the posterior surface of the thyroid gland) Anterior lobe ACTH, TSH, GH, PRL, FSH, LH, and MSH Parathyroid hormone (PTH) Posterior lobe Release of oxytocin (OXT) and antidiuretic hormone (ADH) 612

Figure 18-1 Organs and Tissues of the Endocrine System (Part 2 of 2). Organs with Secondary Endocrine Functions Heart See Chapter 21 • Atrial natriuretic peptide (ANP) Thyroid Gland • Brain natriuretic peptide (BNP) Thyroxine (T4) Triiodothyronine (T3) Calcitonin (CT) Thymus (Undergoes atrophy during adulthood) See Chapter 22 • Thymosins Adrenal Gland Adipose Tissue Medulla • Leptin Epinephrine (E) Norepinephrine (NE) Digestive Tract See Chapter 25 Cortex Secretes numerous hormones involved in the coordination of system functions, glucose metabolism, and appetite Cortisol, corticosterone, aldosterone, androgens Pancreatic Islets Kidneys See Chapters 19 and 26 • Erythropoietin (EPO) • Calcitriol Insulin, glucagon Gonads See Chapters 28 and 29 KEY TO PITUITARY HORMONES Testes (male) Androgens (especially testosterone), inhibin ACTH Adrenocorticotropic hormone TSH Thyroid-stimulating hormone Testis GH Growth hormone PRL Prolactin FSH Follicle-stimulating hormone Ovaries (female) Estrogens, progesterone, inhibin Ovary LH Luteinizing hormone MSH Melanocyte-stimulating hormone 612

© 2015 Pearson Education, Inc. Hormone: organic chemical that changes the function of its target cell Autocrine- Paracrine- Endocrine- exocrine 610 © 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc. Maintenance of Homeostasis Water/electrolytes Enzyme function Transport Regulate long term processes Development Growth Reproduction © 2015 Pearson Education, Inc.

© 2015 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 © 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc. Hormones 613 © 2015 Pearson Education, Inc.

Figure 18-4a Effects of Intracellular Hormone Binding. Steroid hormones diffuse through the plasma membrane and bind to receptors in the cytoplasm or nucleus. The complex then binds to DNA in the nucleus, activating specific genes. 1 Diffusion through membrane lipids Target cell response CYTOPLASM Alteration of cellular structure or activity 6 Translation and protein synthesis Receptor 2 Binding of hormone to cytoplasmic or nuclear receptors 5 616 Transcription and mRNA production Receptor 4 Gene activation Nuclear pore 3 Nuclear envelope Binding of hormone–receptor complex to DNA

Figure 18-4b Effects of Intracellular Hormone Binding. Thyroid hormones enter the cytoplasm and bind to receptors in the nucleus to activate specific genes. They also bind to receptors on mitochondria and accelerate ATP production. 1 Transport across plasma membrane Target cell response Target cell response Increased Alteration of cellular structure or activity ATP production Receptor 6 Translation and protein synthesis 2 Binding of receptors at mitochondria and nucleus 5 616 Transcription and mRNA production Receptor 4 Gene activation 3 Binding of hormone–receptor complex to DNA

615

Figure 18-3 G Proteins and Second Messengers (Part 1 of 2). The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein. A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger. 615 Hormone Hormone Protein receptor Protein receptor G protein (inactive) 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. Hormone Hormone Protein receptor Protein receptor G protein activated Increased production of cAMP G protein activated Enhanced breakdown of cAMP Acts as second messenger adenylate cyclase PDE cAMP ATP cAMP AMP kinase Reduced enzyme activity Opens ion channels Activates enzymes If levels of cAMP increase, enzymes may be activated or ion channels may be opened, accelerating the metabolic activity of the cell. In some instances, G protein activation results in decreased levels of cAMP in the cytoplasm. This decrease has an inhibitory effect on the cell. First Messenger Examples • Epinephrine and norepinephrine (β receptors) • Calcitonin • Parathyroid hormone • ADH, ACTH, FSH, LH, TSH First Messenger Examples • Epinephrine and norepineph- rine (α2 receptors)

Figure 18-3 G Proteins and Second Messengers (Part 2 of 2). The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein. A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger. 615 Hormone Hormone Protein receptor Protein receptor G protein (inactive) G protein activated Effects on Ca2+ Levels Some G proteins use Ca2+ as a second messenger. Ca2+ Hormone Protein receptor G protein activated PLC, DAG, and IP3 Opening of Ca2+ channels Release of stored Ca2+ from ER or SER Ca2+ Ca2+ Ca2+ acts as second messenger Ca2+ Calmodulin Activates enzymes First Messenger Examples • Epinephrine and norepinephrine (α1 receptors) • Oxytocin • Regulatory hormones of hypothalamus • Several eicosaoids

A&P Flix Animation: Mechanism of Hormone Action: Second Messenger cAMP

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

Figure 18-3 G Proteins and Second Messengers (Part 1 of 2). The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein. A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger. 615 Hormone Hormone Protein receptor Protein receptor G protein (inactive) 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. Hormone Hormone Protein receptor Protein receptor G protein activated Increased production of cAMP G protein activated Enhanced breakdown of cAMP Acts as second messenger adenylate cyclase PDE cAMP ATP cAMP AMP kinase Reduced enzyme activity Opens ion channels Activates enzymes If levels of cAMP increase, enzymes may be activated or ion channels may be opened, accelerating the metabolic activity of the cell. In some instances, G protein activation results in decreased levels of cAMP in the cytoplasm. This decrease has an inhibitory effect on the cell. First Messenger Examples • Epinephrine and norepinephrine (β receptors) • Calcitonin • Parathyroid hormone • ADH, ACTH, FSH, LH, TSH First Messenger Examples • Epinephrine and norepineph- rine (α2 receptors)

© 2015 Pearson Education, Inc. 615 © 2015 Pearson Education, Inc.

Figure 18-3 G Proteins and Second Messengers (Part 2 of 2). The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein. A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger. 615 Hormone Hormone Protein receptor Protein receptor G protein (inactive) G protein activated Effects on Ca2+ Levels Some G proteins use Ca2+ as a second messenger. Ca2+ Hormone Protein receptor G protein activated PLC, DAG, and IP3 Opening of Ca2+ channels Release of stored Ca2+ from ER or SER Ca2+ Ca2+ Ca2+ acts as second messenger Ca2+ Calmodulin Activates enzymes First Messenger Examples • Epinephrine and norepinephrine (α1 receptors) • Oxytocin • Regulatory hormones of hypothalamus • Several eicosaoids

© 2015 Pearson Education, Inc. 615 © 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc. Endocrine Reflexes 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 © 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc.

Figure 18-5 Three Mechanisms of Hypothalamic Control over Endocrine Function Production of ADH and oxytocin Secretion of regulatory hormones to control activity of the anterior lobe of the pituitary gland Control of sympathetic output to adrenal medullae HYPOTHALAMUS Preganglionic motor fibers 618 Adrenal cortex Infundibulum Adrenal medulla Posterior lobe of pituitary gland Anterior lobe of pituitary gland Adrenal gland Hormones secreted by the anterior lobe control other endocrine organs Release of ADH and oxytocin Secretion of epinephrine and norepinephrine 23

© 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc.