Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: The Body’s Long-Distance Regulators Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body Hormones reach all parts of the body, but only target cells are equipped to respond Hormones convey information via the bloodstream to target cells throughout the body

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Control Pathways and Feedback Loops The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior A common feature is a feedback loop connecting the response to the initial stimulus Negative feedback regulates many hormonal pathways involved in homeostasis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Signaling by any of these hormones involves three key events: – Reception – Signal transduction – Response

LE 45-3 SECRETORY CELL Hormone molecule Signal receptor VIA BLOOD VIA BLOOD TARGET CELL TARGET CELL Signal transduction pathway OR Cytoplasmic response DNA NUCLEUS Nuclear response Receptor in plasma membraneReceptor in cell nucleus DNA NUCLEUS mRNA Synthesis of specific proteins Signal transduction and response Signal receptor Hormone molecule SECRETORY CELL

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm or a change in gene expression The same hormone may have different effects on target cells that have – Different receptors for the hormone – Different signal transduction pathways – Different proteins for carrying out the response

LE 45-4 Different receptors different cell responses Epinephrine  receptor Epinephrine  receptor Epinephrine  receptor Vessel constricts Vessel dilates Intestinal blood vessel Skeletal muscle blood vessel Liver cell Different intracellular proteins different cell responses Glycogen deposits Glycogen breaks down and glucose is released from cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Paracrine Signaling by Local Regulators In paracrine signaling, nonhormonal chemical signals called local regulators elicit responses in nearby target cells Types of local regulators: – Neurotransmitters – Cytokines and growth factors – Prostaglandins help regulate aggregation of platelets, an early step in formation of blood clots

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The hypothalamus and the pituitary gland control much of the endocrine system Tropic hormones, hormones that regulate endocrine organs Tropic hormones are secreted into the blood and transported to the anterior pituitary The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system

LE 45-7 Mammary glands, uterine muscles Hypothalamus Kidney tubules Oxytocin HORMONE TARGET ADH Posterior pituitary Neurosecretory cells of the hypothalamus Axon Anterior pituitary

LE 45-8 Neurosecretory cells of the hypothalamus Endocrine cells of the anterior pituitary Portal vessels Pituitary hormones (blue dots) Pain receptors in the brain EndorphinGrowth hormone Bones Liver MSH Melanocytes Prolactin Mammary glands ACTH Adrenal cortex TSH Thyroid Testes or ovaries FSH and LH TARGET HORMONE Hypothalamic releasing hormones (red dots) Tropic Effects Only FSH, follicle-stimulating hormone LH, luteinizing hormone TSH, thyroid-stimulating hormone ACTH, adrenocorticotropic hormone Nontropic Effects Only Prolactin MSH, melanocyte-stimulating hormone Endorphin Nontropic and Tropic Effects Growth hormone

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Posterior Pituitary Hormones The two hormones released from the posterior pituitary act directly on nonendocrine tissues Oxytocin induces uterine contractions and milk ejection Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anterior Pituitary Hormones The anterior pituitary produces both tropic and nontropic hormones

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tropic Hormones The four strictly tropic hormones are – Follicle-stimulating hormone (FSH) – Luteinizing hormone (LH) – Thyroid-stimulating hormone (TSH) – Adrenocorticotropic hormone (ACTH) Each tropic hormone acts on its target endocrine tissue to stimulate release of hormone(s) with direct metabolic or developmental effects

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nontropic Hormones Nontropic hormones produced by the anterior pituitary: Prolactin stimulates lactation in mammals but has diverse effects in different vertebrates MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals Endorphins inhibit pain

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Growth Hormone Growth hormone (GH) has tropic and nontropic actions It promotes growth directly and has diverse metabolic effects It stimulates production of growth factors

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The thyroid gland produces calcitonin, which functions in calcium homeostasis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parathyroid Hormone and Calcitonin: Control of Blood Calcium Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin, play the major role in calcium (Ca 2+ ) homeostasis in mammals. Calcitonin stimulates Ca 2+ deposition in bones and secretion by kidneys, lowering blood Ca 2+ levels

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE STIMULUS: Rising blood Ca 2+ level Thyroid gland releases calcitonin. Calcitonin Stimulates Ca 2+ deposition in bones Reduces Ca 2+ uptake in kidneys Blood Ca 2+ level declines to set point Homoeostasis: Blood Ca 2+ level (about 10 mg/100 mL) STIMULUS: Falling blood Ca 2+ level Blood Ca 2+ level rises to set point Stimulates Ca 2+ release from bones PTH Parathyroid gland Stimulates Ca 2+ uptake in kidneys Active vitamin D Increases Ca 2+ uptake in intestines

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Insulin and Glucagon: Control of Blood Glucose The pancreas secretes insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis Glucagon is produced by alpha cells Insulin is produced by beta cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE Beta cells of pancreas release insulin into the blood. Insulin Liver takes up glucose and stores it as glycogen. STIMULUS: Rising blood glucose level (for instance, after eating a carbohydrate- rich meal) Blood glucose level declines to set point; stimulus for insulin release diminishes. Homeostasis: Blood glucose level (about 90 mg/100 mL) STIMULUS: Dropping blood glucose level (for instance, after skipping a meal) Blood glucose level rises to set point; stimulus for glucagon release diminishes. Liver breaks down glycogen and releases glucose into the blood. Body cells take up more glucose. Alpha cells of pancreas release glucagon into the blood. Glucagon

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Target Tissues for Insulin and Glucagon Insulin reduces blood glucose levels by – Promoting the cellular uptake of glucose – Slowing glycogen breakdown in the liver – Promoting fat storage

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glucagon increases blood glucose levels by – Stimulating conversion of glycogen to glucose in the liver – Stimulating breakdown of fat and protein into glucose

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diabetes Mellitus Diabetes mellitus is perhaps the best-known endocrine disorder It is caused by a deficiency of insulin or a decreased response to insulin in target tissues It is marked by elevated blood glucose levels

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The adrenal glands are adjacent to the kidneys The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) They are secreted in response to stress-activated impulses from the nervous system They mediate various fight-or-flight responses Adrenal Hormones: Response to Stress

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Melatonin and Biorhythms The pineal gland, located in the brain, secretes melatonin Light/dark cycles control release of melatonin Primary functions of melatonin appear to relate to biological rhythms associated with reproduction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Invertebrate regulatory systems also involve endocrine and nervous system interactions Diverse hormones regulate homeostasis in invertebrates In insects, molting and development are controlled by three main hormones: – Brain hormone stimulates release of ecdysone from the prothoracic glands – Ecdysone promotes molting and development of adult characteristics – Juvenile hormone promotes retention of larval characteristics

LE 45-15_3 Brain hormone (BH) Brain Neurosecretory cells Corpus cardiacum Corpus allatum Prothoracic gland Ecdysone EARLY LARVA LATER LARVA PUPA ADULT Juvenile hormone (JH) Low JH