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Endocrine System 3-May-17 Introduction to Endocrine system 1 Introduction Endocrine One system of the system involved In coordination of body functions Systems 1. involved include Neural system Release chemical substances (neurotransmitters) at axon terminals Act locally to control cell function 3-May-17 Introduction to Endocrine system 2 Introduction 2. Endocrine system Glands or specialized cells Release chemicals (hormones) 3. Into blood Have influence on cell function at another location Neuro-endocrine Neurons secrete substances (neurohormone) 3-May-17 Introduction to Endocrine system 3 Introduction Reach circulating blood Influence cell function at another location 4. Paracrine Cells secrete substances Diffuse in ECF Affect neighboring cells 3-May-17 Introduction to Endocrine system 4 Introduction 5. Autocrine Cells 3-May-17 secrete substances Affect the functioning of the same cell Introduction to Endocrine system 5 Hormones Working definition Hormone is chemical substance Serve as regulators & coordinators of Various biologic functions in the body Highly potent, specialized organic molecules Produced by endocrine cells In response to specific stimuli 3-May-17 Introduction to Endocrine system 6 Hormones They exert their actions on specific target cells The target cells are equipped with Receptor that bind hormones With high affinity & specificity When bound hormone Initiate characteristic biological responses by target cells 3-May-17 Introduction to Endocrine system 7 Principal Endocrine Organs Organ Hormone Pituitary gland Tropic hormones (ACTH, GH, prolactin) Hypothalamus Hypophysiotropic hormones (releasing hormones, TRH); ADH, oxytocin Thyroid gland Thyroxin , triiodothyronin Adrenal glands Mineralocorticoids (aldosterone), glucocorticoids (cortisol), catecholamines (epinephrine, norepinephrine) Parathyroid gland Parathtyroid hormone (PTH) Gonads Testosterone, estrogen, progesterone Pancreatic islets Insulin, glucagon, somatostatin 3-May-17 Introduction to Endocrine system 8 Principal Endocrine Organs Other organs Hormone Heart Atrial natriuretic peptide (ANP) Kidney 1,25-dihydroxycholecalciferol (calcitriol), erythropoeitin Liver 25-hydroxycholecalciferol (calcidiol), somatomedin Pineal gland Melatonin Skin Calciferol (vitamin D) GIT Gastrin, cholecyctokinin (CCK), secretin, vasoactive intestinal peptide (VIP) etc 3-May-17 Introduction to Endocrine system 9 Structure & Synthesis 3 1. general classes of hormone Protein & polypeptides Include hormones secreted by Anterior pituitary The pancreas (insulin, glucagon) Parathyroid gland (PTH) 3-May-17 Introduction to Endocrine system 10 Structure & Synthesis 2. Steroids, include hormones secreted by Adrenal cortex Ovaries Oestrogen, progesterone Testes Cortisol, aldosterone Testosterone Placenta 3-May-17 Oestrogen, progesterone Introduction to Endocrine system 11 Structure & Synthesis 3. Derivatives of amino acid tyrosine Thyroid Thyroxin, tri-iodothyronin Adrenal 3-May-17 gland medulla Epinephrine & norepinephrine Introduction to Endocrine system 12 Peptide Hormones Preprohormone Synthesis in RER Cleaved into prohormone in ER Prohormone 3-May-17 Polypeptides and protein hormone Packaging in Golgi, cleaved into active hormone Hormone & Inactive fragments Synthesized on Rough endplasmic reticulum of the endocrine cells Usually synthesized as preprohormone Larger protein Has no biological activity Introduction to Endocrine system 13 Peptide Hormones Preprohormone Synthesis in RER This is then cleaved Cleaved into prohormone in ER To a prohormone In endoplasmic reticulum Prohormone Packaging in Golgi, cleaved into active hormone Hormone & Inactive fragments 3-May-17 Introduction to Endocrine system 14 Peptide Hormones Preprohormone Synthesis in RER Cleaved into prohormone in ER Packaging in Golgi, cleaved into active hormone Hormone & Inactive fragments 3-May-17 Prohormone The prohormone is then Transferred to Golgi apparatus For packaging In the process enzymes cleave it into An active hormone & A larger inactive fragment Introduction to Endocrine system 15 Peptide Hormones Ca++ Secretion of peptide hormones Ca++ Occur by exocytosis when 3-May-17 Active hormone & inactive fragment secretory vesicles fuse with cell membrane Introduction to Endocrine system 16 Peptide Hormones Ca++ Ca++ a) Stimulation In many cases the stimulus for the exocytosis is 3-May-17 Granular content are then extruded into Interstitial fluid Blood stream Ca++ in cytosol as a result of Depolarization of plasma membrane Introduction to Endocrine system 17 Peptide Hormones Activation Receptor 2. cAMP Prot kinase In other cases Stimulation of the endocrine cell surface receptors 3-May-17 cAMP Activation of protein kinase Initiate release of the hormone Introduction to Endocrine system 18 Peptide Hormones Activation Receptor cAMP Prot kinase Peptide hormone are water soluble 3-May-17 Enter the circulatory system easily Carried to target tissues Introduction to Endocrine system 19 Steroid Hormones Usually synthesized from cholesterol Chemical structure Similar They to that of cholesterol are lipid soluble,consist of 3 cyclohexyl ring and 1 cyclopentyl ring 3-May-17 Introduction to Endocrine system 20 Structure of Steroid Hormones Derivative of cholesterol Have 3 cyclohexyl rings( A, B, C) One cyclopentyl ring (D) 18 19 2 10 A 4 12 5 17 16 14 9 B 13 D C 1 3 11 8 15 7 6 Cyclopentanoperhydrophenanthrene 3-May-17 Introduction to Endocrine system 21 Steroid Hormones There In But is little hormone stored steroid forming cells there are large stores Of cholesterol esters Can be rapidly mobilized for steroid synthesis 3-May-17 Introduction to Endocrine system 22 Steroid Hormones Most of the cholesterol Come from plasma But cells have the ability to synthesize it 3-May-17 Introduction to Endocrine system 23 Steroid Hormones Steroid hormones are lipid soluble Once they are synthesized They diffuse across cell membrane 3-May-17 Into interstitial fluid Introduction to Endocrine system 24 Amine Hormones Derivatives of tyrosine From the thyroid & adrenal medulla glands Formed by the action Of 3-May-17 cytoplasmic enzymes Introduction to Endocrine system 25 Amine Hormones Thyroid hormones Synthesized and stored in thyroid gland Incorporated in thyroglobulin Stored in large follicle within the gland Secretion occurs when The amines are split from thyroglobulin 3-May-17 Free hormone released in blood Bound to thyroxine binding globulin (TBG) Which slowly releases the hormone to target tissues Introduction to Endocrine system 26 Amine Hormones Epinephrine & norepinephrine Formed in the adrenal medulla Stored in vesicles Secrete 4 times more epinephrine than norepinephrine Secreted by exocytosis In plasma can exist Free form or in conjugation with other substances 3-May-17 Introduction to Endocrine system 27