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The Endocrine System

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The Endocrine System Homework Due Tuesday 2/19 Replace a Missing Assignment Due in Lab PreLab #6 Homework 11 in study guide Omit #11 The Endocrine System Part 1 Overview Acts with the nervous system (NS) Influences metabolic activities using hormones Responses occur more slowly but last longer than NS Endocrine glands Pituitary, thyroid, thymus, pancreas, parathyroid, adrenal and pineal glands Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus Adrenal glands Pancreas Ovary (female) Testis (male) Figure 16.1 Making Connections 16.1 Homeostatic Interrelationships Between the Endocrine System and Other Body Systems Copyright © 2010 Pearson Education, Inc. Overview Nervous System Endocrine System Nerve impulses Hormones Neurotransmitters Slower responses Faster responses Longer effects Brief effects Broader influence Acts on specific target Hormones Chemical substances secreted by cells Long-distance chemical signals Travel in the blood or lymph Most are amino-acid based or steroid molecules Hormones Two main classes 1. Amino acid-based hormones Amines, thyroxine, peptides and proteins 2. Steroids Synthesized from cholesterol Gonadal and adrenocortical hormones Figure 16.4 Three types of endocrine gland stimuli. (a) Humoral Stimulus (b) Neural Stimulus (c) Hormonal Stimulus 1 Capillary blood contains 1 Preganglionic sympathetic 1 The hypothalamus secretes low concentration of Ca2+, fibers stimulate adrenal hormones that... which stimulates... medulla cells... Hypothalamus Capillary (low CNS (spinal cord) Ca2+ in blood) 2 …stimulate Thyroid gland the anterior Parathyroid (posterior view) pituitary gland glands to secrete Pituitary hormones gland Preganglionic that… sympathetic fibers Thyroid Adrenal Gonad Medulla of gland cortex (Testis) adrenal Parathyroid gland PTH glands Capillary 2 …secretion of 2 …to secrete catechola- parathyroid hormone (PTH) mines (epinephrine and 3 …stimulate other endocrine by parathyroid glands* norepinephrine) glands to secrete hormones Copyright © 2010 Pearson Education, Inc. Target Cell Specificity A hormone may have more than one type of target cell Specific receptors Hormone effects are due to alteration of cell’s activity Effects vary Target Cell Specificity Target cell interaction depends on three factors 1. Blood levels of the hormone 2. Relative number of receptors on or in the target cell 3. Affinity of binding between receptor and hormone Target Cell Specificity Hormones influence the number of their receptors Up-regulation Target cells form more receptors in response to the hormone Down-regulation Target cells lose receptors in response to the hormone Target Cell Specificity Hormone concentration depends on Rate of release and synthesis Speed of inactivation Mechanism of Action Slow acting Fatty acids or steroids Fast acting Proteins or peptides Slow Acting Hormones lipid soluble cross cell membrane enters nucleus interacts with DNA changes cell function by initiating gene transcription Relatively long lasting effects Examples: testosterone and estrogen Steroid hormone Plasma Extracellular fluid membrane 1 The steroid hormone diffuses through the plasma membrane and binds an Cytoplasm intracellular receptor. Receptor Receptor- protein hormone complex 2 The receptor- Hormone hormone complex enters Nucleus response the nucleus. elements 3 The receptor- hormone complex binds a hormone DNA response element (a specific DNA sequence). mRNA 4 Binding initiates transcription of the gene to mRNA. 5 The mRNA directs protein synthesis. New protein Figure 16.3 Fast Acting Hormones bind to receptor protein (hormone is first messenger) second messenger (cyclic-AMP) activates enzymes rapid change in cell function Relatively short term effects May be greatly amplified 1 Hormone (1st messenger) Adenylate cyclase Extracellular fluid binds receptor. G protein (GS) 5 cAMP acti- vates protein Receptor kinases. GDP Inactive Active protein kinase protein 2 Receptor 3 G protein 4 Adenylate Hormones that kinase act via cAMP activates G activates cyclase Triggers responses of mechanisms: protein (GS). adenylate converts ATP target cell (activates cyclase. to cAMP (2nd enzymes, stimulates Epinephrine Glucagon messenger). ACTH PTH cellular secretion, FSH TSH opens ion channel, etc.) LH Calcitonin Cytoplasm Figure 16.2 Cellular Hormones Some cells have endocrine capacity Intestine secretin and cholecystokinin Kidney erythropoeitin Pituitary Gland 2 lobes 1. Anterior pituitary lobe (adenohypophysis) Glandular tissue Releases hormones formed within pituitary 2. Posterior pituitary lobe (neurohyophysis) Glial-like supporting cells and nerve fibers Releases hormones formed within hypothalamus Hypothalamus 1 When appropriately stimulated, hypothalamic neurons Hypothalamic neuron secrete releasing and cell bodies inhibiting hormones into the primary Superior capillary plexus. hypophyseal artery Hypophyseal portal system 2 Hypothalamic hormones • Primary capillary travel through the portal plexus veins to the anterior pituitary • Hypophyseal where they stimulate or portal veins inhibit release of hormones • Secondary from the anterior pituitary. capillary plexus Anterior lobe 3 Anterior pituitary of pituitary hormones are secreted TSH, FSH, into the secondary LH, ACTH, capillary plexus. GH, PRL, MSH (b) Relationship between the anterior pituitary and the hypothalamus Copyright © 2010 Pearson Education, Inc. Figure 16.5b Anterior Pituitary Hormones • Growth hormone (GH) • Thyroid stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Follicle stimulating hormone (FSH) • Luteinizing hormone (LH) • Prolactin (PRL) • Melanocyte stimulating hormone (MSH) Growth Hormone (GH) Stimulates most cells Main targets = bone & skeletal muscle Functions Promotes protein synthesis Encourages use of fats for fuel Breakdown of glycogen Imbalances of Growth Hormone Hypersecretion Gigantism Acromegaly Hyposecretion Pituitary dwarfism Simmond’s disease Acromegaly Hypothalamus secretes growth Feedback Inhibits GHRH release Stimulates GHIH hormone—releasing Anterior release hormone (GHRH), and pituitary Inhibits GH synthesis somatostatin (GHIH) and release Growth hormone Indirect actions Direct actions (growth- (metabolic, promoting) anti-insulin) Liver and other tissues Produce Insulin-like growth factors (IGFs) Effects Effects Carbohydrate Skeletal Extraskeletal Fat metabolism Increases, stimulates Increased protein Reduces, inhibits Increased cartilage Increased Increased blood synthesis, and Initial stimulus formation and fat breakdown glucose and other cell growth and skeletal growth and release anti-insulin effects Physiological response proliferation Result Figure 16.6 Thyroid-Stimulating Hormone (TSH) Produced by the anterior pituitary Stimulates the normal development and secretory activity of the thyroid Regulation of TSH release Stimulated by hypothalamus Inhibited by rising blood levels of thyroid hormones Hypothalamus TRH Anterior pituitary TSH Thyroid gland Thyroid hormones Stimulates Target cells Inhibits Copyright © 2010 Pearson Education, Inc. Figure 16.7 Adrenocorticotropic Hormone (ACTH) Secreted by the anterior pituitary Stimulates the adrenal cortex to release corticosteroids Gonadotropins (FSH & LH) Follicle-stimulating hormone (FSH) and luteinizing hormone (LH or ICSH) Secreted by the anterior pituitary Regulate function of ovaries and testes Gonadotropins (FSH & LH) Regulation of gonadotropin release Triggered by the gonadotropin-releasing hormone (GnRH) Absent from the blood in prepubertal boys and girls Suppressed by gonadal hormones Prolactin Secreted by the anterior pituitary Stimulates milk production Blood levels rise toward the end of pregnancy Suckling stimulates PRH release and promotes continued milk production Presence in men not well understood Hypersecretion Melanocyte Stimulating Hormone Stimulates melanocytes • Unknown role in humans • May influence brain activity Control of Anterior Pituitary Hormones Pituitary-Hypothalamic Relationships Hypophyseal portal system Capillary plexuses Hypophyseal portal veins Hypothalamus 1 When appropriately stimulated, hypothalamic neurons Hypothalamic neuron secrete releasing and cell bodies inhibiting hormones into the primary Superior capillary plexus. hypophyseal artery Hypophyseal portal system 2 Hypothalamic hormones • Primary capillary travel through the portal plexus veins to the anterior pituitary • Hypophyseal where they stimulate or portal veins inhibit release of hormones • Secondary from the anterior pituitary. capillary plexus Anterior lobe 3 Anterior pituitary of pituitary hormones are secreted TSH, FSH, into the secondary LH, ACTH, capillary plexus. GH, PRL, MSH (b) Relationship between the anterior pituitary and the hypothalamus Copyright © 2010 Pearson Education, Inc. Figure 16.5b Releasing Factors Releasing factors Growth Hormone Releasing Factor/Hormone Thyroid Hormone Releasing Factor/Hormone Inhibiting factors Identified for prolactin and GH Negative feedback Posterior Pituitary Contains axons of hypothalamic neurons Hormones produced by hypothalamus Stores antidiuretic hormone (ADH) and oxytocin Released in response to nerve impulses 1 Hypothalamic neurons synthesize oxytocin Paraventricular and ADH. Hypothalamus nucleus Supraoptic 2 Oxytocin and ADH are nucleus transported along the Optic chiasma hypothalamic-hypophyseal Infundibulum tract to the posterior (connecting stalk) pituitary.
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