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Transcript
Bio 257 Day 23 Today’s topic Ch 10 Endocrine System Objectives: • Define endocrine gland, hormone and target tissue. • List the chemical types of hormones • Characterize control of hormone secretions. Objectives: • Describe the structure of the pituitary gland, thyroid gland, parathyroid glands, pancreas, and adrenal glands. Objectives: • List hormones, describe their actions and name the target tissues of the major endocrine glands. • Organs: –Endocrine glands = ductless glands, which secrete hormones into body fluids (blood) Similarity and Differences b/w Nervous and Endocrine Systems control over organs it is in direct contact with indirectly affect many organs of the body at a distance by secreting chemicals into the blood • General Function of the Endocrine System: – Coordinates & regulates body systems to maintain homeostasis • Organs: –Hormone(s) = organic compound, that exerts specific effects on certain organs (target organs) at some distance away Hormone receptors Sites on or in the target tissue (organ) to which a chemical (e.g. hormone) binds to similar to a lock-n-key. Receptors • Membrane-Bound Receptor Responses – Alter membrane permeability by directly opening or closing membrane channels – Activate G proteins that in turn can open or close membrane channels or activate enzymes that produce intracellular chemical signals (2nd messenger) – Alter the activity of enzymes directly leading to an increase or decrease in the level of intracellular chemical signals or add phosphate groups to cellular proteins Polar hormone in blood Cytoplasm ATP E receptor Receptors • Intracellular receptors: – Located in the cytoplasm or nuclei – Regulate the synthesis of specific messenger RNA moleculesProtein Synthesis Lipid Soluble Hormone Overview of Types of Chemical Signals • Intracellular- produced in one part of a cell and travel to another part of the same cell and bind to either cytoplasmic or nuclear receptors. – Often produced at the level of the cell membrane Overview of Types of Chemical Signals • Intercellular chemical signals – Autocrine- released by cells and have a local effect on the same cell or cell type eicosanoids released from smooth muscle and platelets lead to blood vessel dilation and platelet aggregation – Paracrine- released by cells that have effects on other cell types near the cells from which they are released (e.x. somatostatin inhibits release of insulin in the pancreas) Overview of Types of Chemical Signals • Intercellular chemical signals – Neuromodulators and neurotransmitters-secreted by nerve cells function in the nervous system – Pheromones-secreted into the environment may modify the behavior and physiology of other individuals (pheromones produced by humans not fully understood) – Hormones-secreted by endocrine glands into the circulatory system, transported and act on tissues distant from the site of release in a specific way • Neurohormones-hormones secreted from cells of the nervous system Localized chemical signal Hormone Hormone Effects on Target Organs REGULATE: • Growth • Stress • pH of body • Reproduction system • Use of food sources (metabolism) • Water Balance • Uterine contractions/milk release • Heart rate and blood glucose control • Immune system Chemistry of Hormones • 2 classes: – Synthesized from amino acids (AA) • Proteins or peptides (insulin, ADH, oxytocin) • Thyroid hormones derived from AA Tyrosine (throxine, triiodothyronine) • Amines (catecholamines) epinephrine and norepinephrine) – Epinephrine released from the adrenal medulla (ie (Endocrine fxn) – Norepinephrine released more from neurons (not much from adrenal medulla) – Synthesized from cholesterol • Steroids (lipid-like) cortisol, estrogen, testosterone Mechanism of Hormone Action 1. Hormones are released on demand and determined by the body’s need 2. Hormone’s principle action site is its target tissue or organ. 3. The target tissue contains specific receptors, which the hormone binds. 4. Hormones only affect those organs w/ the specific target receptor 5. When a hormone binds to its target tissue receptor, a chain of events are produced that alter the target cell activities Polar Hormone Polar Hormone Polar Hormone Polar Hormone Control of HormoneSecretions • 3 Mechanisms control secretion of hormonesall use negative feedback 1.Hypothalamus/anterior pituitary 2.Nervous system 3.Glands responding to changes in internal environment How do hormones work? • Negative feedback mechanisms –Effects of the hormone on the target gland are “fed back” to the endocrine gland which then decreases the secretion of that hormone How do hormones work? • Many work together = synergistic effects (synergism) • Many work in opposition = antagonistic effects (antagonism) • Hypersecretion = oversecretion of hormone • Hyposecretion = under secretion of hormone Pituitary Gland • Sits in sella turcica • Extends from hypothalamus • Consist of 2 lobes (anterior lobe & posterior lobe) Pituitary gland Relationship of Hypothalamus to Pituitary gland anterior lobe infundibulum posterior lobe Posterior Pituitary Hypothalamus/Posterior Pituitary 1. Neural stimulation of hypothalamic neurons 2. AP carried by axons from hypothalamus to posterior pituitary. The neuron terminal in the posterior pituitary stores hormones 3. AP cause the release of hormones from the axons into the circulatory sytem 4. The hormones pass through the circulatory system and influence the activity of their target tissue Posterior Lobe of Pituitary Gland • 2 hormones (peptide) 1. Oxytocin stimulates contraction of uterine smooth muscle Stimulates milk ejection or milk let-down from mammary glands – target: uterus & mammary glands Posterior Lobe of Pituitary Gland • 2 hormones (peptide) 2. ADH (antidiuretic hormone or vasopressin) = increases reabsorption of water by kidneys resulting in decreased urine output (ie less water lost as urine) target: kidneys Anterior Pituitary Anterior Pituitary Hormones MSH Melanocytes in skin Anterior Lobe of Pituitary Gland • Hormones are called tropic hormones • 7 hormones Anterior Lobe of Pituitary Gland 1. GH (growth hormone) –stimulates growth (increase in cell size & mitosis) by increasing protein synthesis –Increases breakdown of lipidsincrease in free fatty acids –Increases blood glucose levels • target: most body tissues, Anterior Lobe of Pituitary Gland 2. TSH (thyroid stimulating hormone) –stimulates thyroid gland hormone secretions & growth target: thyroid gland Regulation of Thyroid Hormone Secretion Anterior Lobe of Pituitary Gland 3. ACTH (adrenocorticotropic hormone) –stimulates adrenal gland (cortex) secretions • Glucocorticoids cortisol target: adrenal cortex of adrenal gland Regulation of Cortisol Secretion Anterior Lobe of Pituitary Gland 4. Prolactin –stimulates milk production by mammary glands –prolongs progesterone secretion following ovulation/during pregnancy target: mammary glands/ovaries Anterior Lobe Gonadotropins = hormones whose target organs are gonads 5. FSH (follicle-stimulating hormone) stimulate the production of gametes (sperm cells & oocytes) & estrogen target: ovariesfollicles in ovary testisseminiferous tubules Anterior Lobe Gonadotropins 6. LH (luteinizing hormone) stimulates the releases of egg (oocyte) from ovary (ovulation) and progesterone production in ovary. testosterone production from testis target: ovaries & testis Anterior Lobe 7. MSH (melanocyte stimulating hormone) stimulates production of melanin by melanocytes makes the skin darker Pineal Gland • Between cerebrum & cerebellum (epithalamus) • 1 hormone: melatonin = regulates sleep wake cycles, produced at night. may prevent onset of puberty higher amounts in preadolescence children larynx isthmus thyroid gland trachea Thyroid Gland • Lateral to trachea & inferior to larynx (neck) • 2 lobes connected by narrow band of tissue (isthmus) • 3 hormones (thyroxine-T4, triiodothyronine-T3, & calcitonin)