Hormones Presentation PDF

Chapter 41 Chemical Signals in Animals Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education Ltd....

Chapter 41 Chemical Signals in Animals Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education Ltd. Kathleen Fitzpatrick Figure 41.1a Male Female Male and female elephant seals differ greatly in appearance and behavior. The male is much larger, and only he has the prominent proboscis. The male is also far more territorial. Underlying each of these differences is a single hormone — testosterone. © 2021 Pearson Education Ltd. CONCEPT 41.1: Hormones and other signaling molecules bind to target receptors, triggering specific response pathways A hormone is a secreted molecule that circulates through the body and stimulates specific cells Hormones reach all parts of the body, but only target cells have receptors for that hormone © 2021 Pearson Education Ltd. Figure 41.1b © 2021 Pearson Education Ltd. CONCEPT 41.1: Hormones and other signaling molecules bind to target receptors, triggering specific response pathways Chemical signaling by hormones is the function of the endocrine system The nervous system is a network of specialized cells—neurons—that transmit signals along dedicated pathways The nervous and endocrine systems often overlap in function © 2021 Pearson Education Ltd. Intercellular Information Flow Communication between animal cells through secreted signals can be classified by two criteria: – The type of secreting cell – The route taken by the signal in reaching its target © 2021 Pearson Education Ltd. Figure 41.2 © 2021 Pearson Education Ltd. Endocrine Signaling Hormones secreted into extracellular fluids by endocrine cells reach their targets via the bloodstream Endocrine signaling: – maintains homeostasis – mediates responses to stimuli – regulates growth and development – triggers changes underlying sexual maturity and reproduction © 2021 Pearson Education Ltd. Paracrine and Autocrine Signaling Local regulators are molecules that act over short distances, reaching target cells solely by diffusion Paracrine and autocrine signaling play roles in processes such as blood pressure regulation, nervous system function, and reproduction © 2021 Pearson Education Ltd.  In paracrine signaling, the target cells lie near the secreting cells In autocrine signaling, the target cell is also the secreting cell Local regulators that mediate such signaling include the prostaglandins Prostaglandins function in the immune system and blood clotting © 2021 Pearson Education Ltd.  Some local regulators, such as nitric oxide (NO) are gases When the level of oxygen in the blood falls, cells in blood vessel walls release NO After diffusing into the surrounding smooth muscle cells, NO activates an enzyme that relaxes the cells This vasodilation increases blood flow to tissues © 2021 Pearson Education Ltd. Synaptic and Neuroendocrine Signaling Neurons communicate with target cells via specialized junctions called synapses At synapses, secreted molecules called neurotransmitters diffuse short distances and bind to receptors on target cells In neuroendocrine signaling, specialized neurosecretory cells secrete neurohormones that diffuse from nerve endings into the bloodstream © 2021 Pearson Education Ltd. Signaling by Pheromones Members of some animal species may communicate with pheromones, chemicals that are released into the environment Pheromones serve many functions, including marking trails leading to food, defining territories, warning of predators, and attracting potential mates © 2021 Pearson Education Ltd. Figure 41.3 © 2021 Pearson Education Ltd. Chemical Classes of Hormones Hormones fall into three major chemical classes – Polypeptides – Steroids – Amines Polypeptides and most amines are water-soluble Steroid hormones and other largely nonpolar hormones are lipid-soluble © 2021 Pearson Education Ltd. Figure 41.4 © 2021 Pearson Education Ltd. Cellular Hormone Response Pathways Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells They bind to receptors in the cytoplasm or nucleus of the target cells © 2021 Pearson Education Ltd. Figure 41.5 © 2021 Pearson Education Ltd. Mastering Biology Animation: Binding of Hormones © 2021 Pearson Education Ltd. Response Pathway for Water-Soluble Hormones Binding of a hormone to its receptor initiates a cellular response The chain of events that converts the chemical signal to an intracellular response is called signal transduction The response may be activation of an enzyme, change in uptake or secretion of certain molecules, or rearrangement of the cytoskeleton In some cases, the signal may initiate changes in transcription of certain genes © 2021 Pearson Education Ltd.  The hormone epinephrine (or adrenaline) regulates many organs in response to stressful situations Epinephrine binds to G protein-coupled receptors on the plasma membrane of target cells This triggers a cascade of events involving synthesis of cyclic AMP (cAMP) This leads to activation of enzymes responsible for (for example) the breakdown of glycogen into glucose © 2021 Pearson Education Ltd. Figure 41.6 © 2021 Pearson Education Ltd. Mastering Biology Animation: Water-Soluble Hormone Pathway © 2021 Pearson Education Ltd. Response Pathway for Lipid-Soluble Hormones In most cases, the response to a lipid-soluble hormone is a change in gene expression When a steroid hormone binds to its cytosolic receptor, a hormone-receptor complex forms that moves into the nucleus There, the receptor part of the complex acts as a transcriptional regulator of specific target genes © 2021 Pearson Education Ltd.  The steroid hormone receptors that bind to estrogens are well-characterized In female birds and frogs, estradiol, a form of estrogen, binds to a cytoplasmic receptor in liver cells The estradiol-bound receptor activates transcription of the vitellogenin gene, needed to produce egg yolk © 2021 Pearson Education Ltd.  Thyroxine, vitamin D, and other lipid soluble hormones that are not steroids typically have receptors in the nucleus These hormone molecules diffuse across the plasma membrane and the nuclear envelope Once bound to a hormone, the receptor binds to sites in the cell’s DNA and stimulates transcription of specific genes © 2021 Pearson Education Ltd. Mastering Biology Animation: Steroid Hormone Pathway © 2021 Pearson Education Ltd. Figure 41.7 © 2021 Pearson Education Ltd. Animation: Lipid-Soluble Hormone © 2021 Pearson Education Ltd. Multiple Responses to a Single Hormone The same hormone may have different effects on target cells that have – Different receptors for the hormone – Different signal transduction pathways For example, the hormone epinephrine has multiple effects that form the basis of the “fight-or- flight” response, a rapid response to stress © 2021 Pearson Education Ltd. Endocrine Tissues and Organs Endocrine cells are often grouped in ductless organs called endocrine glands, such as the thyroid and parathyroid glands and testes or ovaries In contrast, exocrine glands, such as salivary glands, have ducts to carry secreted substances onto body surfaces or into body cavities © 2021 Pearson Education Ltd. Figure 41.8 © 2021 Pearson Education Ltd. CONCEPT 41.2: Feedback regulation and coordination with the nervous system are common in hormone pathways Hormones are assembled into regulatory pathways © 2021 Pearson Education Ltd. Simple Endocrine Pathways In a simple endocrine pathway, endocrine cells respond directly to a stimulus by secreting a particular hormone The hormone travels in the bloodstream to target cells, where it interacts with its specific receptors Signal transduction within target cells brings about a physiological response © 2021 Pearson Education Ltd.  The release of acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete secretin This causes target cells in the pancreas to secrete bicarbonate into ducts that lead to the duodenum This causes a raise in the pH in the duodenum © 2021 Pearson Education Ltd. Figure 41.9 © 2021 Pearson Education Ltd. Simple Neuroendocrine Pathways In a simple neuroendocrine pathway, the stimulus is received by a sensory neuron, which stimulates a neurosecretory cell The neurosecretory cell secretes a neurohormone, which enters the bloodstream and travels to target cells © 2021 Pearson Education Ltd. Figure 41.10 © 2021 Pearson Education Ltd.  For example, the suckling of an infant stimulates signals in the nervous systems of the mother, that reach the hypothalamus Nerve impulses from the hypothalamus trigger the release of oxytocin from the posterior pituitary This causes the mammary glands to secrete milk © 2021 Pearson Education Ltd. Feedback Regulation In a negative feedback loop, the response reduces the initial stimulus For example, the increase in pH in the intestine caused by secretin release shuts off further secretin release Positive feedback reinforces a stimulus to produce an even greater response For example, in mammals oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin © 2021 Pearson Education Ltd. Coordination of Endocrine and Nervous Systems In a wide range of animals, endocrine organs in the brain integrate function of the endocrine system with that of the nervous system © 2021 Pearson Education Ltd. Invertebrates The endocrine pathway that controls the molting of larva originates in the larval brain, where neurosecretory cells produce PTTH In the prothoracic gland, PTTH directs the release of ecdysteroid Bursts of ecdysteroid trigger each successive molt as well as metamorphosis Metamorphosis is not triggered until the level of another hormone, JH (juvenile hormone), drops © 2021 Pearson Education Ltd. Figure 41.11 © 2021 Pearson Education Ltd. Figure 41.12 © 2021 Pearson Education Ltd. Vertebrates The hypothalamus coordinates endocrine signaling It receives information from nerves throughout the body and initiates appropriate neuroendocrine signals Signals from the hypothalamus travel to the pituitary gland, composed of the posterior pituitary and anterior pituitary © 2021 Pearson Education Ltd.  The posterior pituitary stores and secretes hormones that are made in the hypothalamus The anterior pituitary makes and releases hormones under regulation of the hypothalamus © 2021 Pearson Education Ltd. Figure 41.13 © 2021 Pearson Education Ltd.  Posterior Pituitary Hormones Neurosecretory cells of the hypothalamus synthesize the two posterior pituitary hormones – Antidiuretic hormone (ADH) regulates physiology and behavior – Oxytocin regulates milk secretion by the mammary glands © 2021 Pearson Education Ltd. Figure 41.14 © 2021 Pearson Education Ltd.  Anterior Pituitary Hormones The anterior pituitary controls diverse processes, such as metabolism, osmoregulation, and reproduction Hormones secreted by the hypothalamus control release of all anterior pituitary hormones For example, prolactin-releasing hormone from the hypothalamus stimulates the anterior pituitary to secrete prolactin (PRL), which has a role in milk production © 2021 Pearson Education Ltd. Figure 41.15 © 2021 Pearson Education Ltd.  Sets of hormones from the hypothalamus, anterior pituitary, and a target endocrine gland are often organized into a hormone cascade The anterior pituitary hormones in these pathways are called tropic hormones © 2021 Pearson Education Ltd. Thyroid Regulation: A Hormone Cascade Pathway In mammals, thyroid hormone regulates many functions If thyroid hormone level drops in the blood, the hypothalamus secretes thyrotropin-releasing hormone (TRH), causing the anterior pituitary to secrete thyroid-stimulating hormone (TSH) TSH stimulates release of thyroid hormone by the thyroid gland © 2021 Pearson Education Ltd. Figure 41.16 © 2021 Pearson Education Ltd. Disorders of Thyroid Function and Regulation Disruption of thyroid hormone production and regulation can result in serious disorders Thyroid hormone is the only iodine-containing molecule synthesized in the body With low levels of thyroid hormone, due to insufficient iodine, the pituitary continues to secrete TSH This causes the thyroid to enlarge, resulting in a goiter, a marked swelling of the neck © 2021 Pearson Education Ltd. Hormonal Regulation of Growth Growth hormone (GH) is secreted by the anterior pituitary gland, and has tropic and nontropic effects The liver, a major target, responds to GH by releasing insulin-like growth factors (IGFs) These stimulate bone and cartilage growth An excess of GH can cause gigantism, while a lack of GH can cause dwarfism © 2021 Pearson Education Ltd. Figure 41.17 © 2021 Pearson Education Ltd. CONCEPT 41.3: Endocrine glands respond to diverse stimuli in regulating homeostasis, development, and behavior Endocrine signaling regulates homeostasis, development, and behavior © 2021 Pearson Education Ltd. Parathyroid Hormone and Vitamin D: Control of Blood Calcium Homeostatic regulation of calcium (Ca2+) in the blood is vital In mammals, parathyroid hormone (PTH) is released by the parathyroid glands when Ca2+ levels fall below a set point © 2021 Pearson Education Ltd.  PTH increases the level of blood Ca2+ – It releases Ca2+ from bone and stimulates reabsorption of Ca2+ in the kidneys – It indirectly affects Ca2+ by promoting production of vitamin D Calcitonin decreases the level of blood Ca2+ – It stimulates Ca2+ deposition in bones and secretion by kidneys © 2021 Pearson Education Ltd. Figure 41.18 © 2021 Pearson Education Ltd. Adrenal Hormones: Response to Stress The adrenal glands are located atop the kidneys Each adrenal gland consists of two glands: the adrenal medulla (inner portion) and adrenal cortex (outer portion) © 2021 Pearson Education Ltd. The Role of the Adrenal Medulla The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) These hormones are members of a class of compounds called catecholamines They coordinate a set of physiological responses that comprise the “fight-or-flight” response © 2021 Pearson Education Ltd.  Epinephrine and norepinephrine – Increase the rate of glycogen breakdown in liver cells – Trigger the release of glucose and fatty acids into the blood – Increase the rate of oxygen delivery to body cells – Direct blood toward heart, brain, and skeletal muscles and away from skin, digestive system, and kidneys © 2021 Pearson Education Ltd. Animation: Hormonal Response to Stress © 2021 Pearson Education Ltd. Figure 41.19 © 2021 Pearson Education Ltd. BioFlix® Animation: Homeostasis © 2021 Pearson Education Ltd.  Epinephrine’s Multiple Effects: A Closer Look Epinephrine coordinates a response in a range of target cells – In liver cells, it binds to a receptor that activates protein kinase A, which regulates glycogen metabolism (increase breakdown to glucose and secretion of glucose into the blood) – In smooth muscle cells lining blood vessels supplying skeletal muscle, it leads to vasodilation to increase blood supply – In smooth muscle of blood vessels of the intestines, it leads to vasoconstriction and reduced blood flow © 2021 Pearson Education Ltd. Figure 41.20 © 2021 Pearson Education Ltd. The Role of the Adrenal Cortex The adrenal cortex becomes active under stressful conditions including low blood sugar, decreased blood volume and pressure, and shock A series of hormonal signals lead to production and secretion of a family of steroids called corticosteroids Humans produce two types of corticosteroids: 1. Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system 2. Mineralocorticoids, such as aldosterone, affect salt and water balance © 2021 Pearson Education Ltd. Sex Hormones The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progesterone All three types are found in both males and females, but in different proportions © 2021 Pearson Education Ltd.  The testes primarily synthesize androgens, mainly testosterone, which promote development of male reproductive structures Testosterone is responsible for male secondary sex characteristics © 2021 Pearson Education Ltd.  Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system They are also responsible for development of female secondary sex characteristics In mammals, progesterone is primarily involved in preparing and maintaining the uterus © 2021 Pearson Education Ltd.  Synthesis of the sex hormones is controlled by the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary Gonadotropin secretion is controlled by gonadotropin-releasing hormone (GnRH) from the hypothalamus © 2021 Pearson Education Ltd. Figure 41.21 Sex hormones regulate formation of internal reproductive structures in human development © 2021 Pearson Education Ltd. Endocrine Disruptors Between 1938 and 1971, some pregnant women at risk for complications were prescribed a synthetic estrogen called diethylstilbestrol (DES) Daughters of women treated with DES are at higher risk for reproductive abnormalities, including miscarriage, structural changes, and cervical and vaginal cancers DES is an endocrine disruptor, a molecule that interrupts the normal function of a hormone pathway, in this case, that of estrogen © 2021 Pearson Education Ltd. Hormones and Biological Rhythms The pineal gland, located in the brain, secretes melatonin Primary functions of melatonin relate to biological rhythms associated with reproduction and with daily activity levels The release of melatonin by the pineal gland is controlled by a group of neurons in the hypothalamus called the suprachiasmatic nucleus (SCN) The SCN functions as a biological clock © 2021 Pearson Education Ltd. Evolution of Hormone Function Over the course of evolution, the functions of particular hormones have diverged For example, thyroid hormone plays a role in metabolism across many lineages, but in frogs has taken on a unique function: stimulating the resorption of the tadpole tail during metamorphosis Prolactin also has a broad range of activities in vertebrates © 2021 Pearson Education Ltd. Figure 41.22 © 2021 Pearson Education Ltd.  Melanocyte-stimulating hormone (MSH) regulates skin color in amphibians, fish, and reptiles by controlling pigment distribution in melanocytes In mammals, MSH plays roles in hunger and metabolism in addition to coloration © 2021 Pearson Education Ltd. Figure 41.UN02 Summary © 2021 Pearson Education Ltd. Figure 41.UN03 Summary © 2021 Pearson Education Ltd. Figure 41.UN04 Summary © 2021 Pearson Education Ltd.