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Endocrine Glands: Secretion and Action of Hormones IVMS Endocrinology 1 of 4

Endocrine Glands: Secretion and Action of Hormones IVMS Endocrinology 1 of 4
Marc Imhotep Cray, M.D. BMS & ICM Professor/ USMLE Steps 1 & 2 Review Tutor

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IVMS Endocrine Secretion and Action I IVMS Endocrine Secretion and Action I Presentation Transcript

  • Endocrine Glands: Secretion and Action of Hormones IVMS Endocrinology 1 of 4 Marc Imhotep Cray, M.D. BMS & ICM Professor/ USMLE Steps 1 & 2 Review TutorCorrelative study / review:Histology Endocrine Glands
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endocrine Learning Concepts Outline (1)Normal processes •embryonic development, fetal maturation, and perinatal changes •organ structure and function ohypothalamus, posterior and anterior pituitary gland othyroid gland oparathyroid glands oadrenal cortex, adrenal medulla opancreatic islets oovary and testis oadipose tissue •cell/tissue structure and function, including hormone synthesis, secretion, action, and metabolism opeptide hormones osteroid hormones, including vitamin D othyroid hormones ocatecholamine hormones orenin-angiotensin system •repair, regeneration, and changes associated with stage of life 2
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endocrine Learning Concepts Outline (2)Abnormal processes •infectious, inflammatory, and immunologic disorders •traumatic and mechanical disorders •neoplastic disorders (including pituitary, thyroid, parathyroid, adrenal cortex, pancreatic islets, neural crest, pheochromocytoma) •metabolic and regulatory processes (including diabetes mellitus, pituitary, hypothalamus, thyroid, parathyroid, pancreatic islet disorders, adrenal disorders) •vascular disorders •systemic disorders affecting the endocrine system •idiopathic disorders •degenerative disorders •drug-induced adverse effects on the endocrine system •congenital and genetic disorders affecting the endocrine system 3
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endocrine Learning Concepts Outline (3)Principles of therapeutics •mechanisms of action and use of drugs for treatment of disorders of the endocrine system ohormones and hormone analogs ostimulators of hormone production oinhibitors of hormone production ohormone antagonists opotentiators of hormone action oantiobesity agents ononhormonal therapy for endocrine disorders oother treatment for diabetes •other therapeutic modalities 4
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endocrine Learning Concepts Outline (4)Gender, ethnic, and behavioral considerations affecting diseasetreatment and prevention, including psychosocial, cultural,occupational, and environmental •emotional and behavioral factors •influence on person, family, and society •occupational and other environmental risk factors •gender and ethnic factors 5
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endocrine Glands and Hormones Secrete biologically active molecules into the blood.  Lack ducts. Carry hormones to target cells that contain specific receptor proteins for that hormone. Target cells can respond in a specific fashion. 6
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Endocrine Glands and Hormones(continued) Neurohormone:  Specialized neurons that secrete chemicals into the blood rather than synaptic cleft.  Chemical secreted is called neurohormone. Hormones:  Affect metabolism of target organs.  Help regulate total body metabolism, growth, and reproduction. 7
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Chemical Classification ofHormones Amines:  Hormones derived from tyrosine and tryptophan.  NE, Epi, T4. Polypeptides and proteins:  Polypeptides:  Chains of < 100 amino acids in length.  ADH.  Protein hormones:  Polypeptide chains with > 100 amino acids.  Growth hormone. 8
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Classification of Hormones (continued) Lipids derived from cholesterol.  Are lipophilic hormones.  Testosterone.  Estradiol.  Cortisol.  Progesterone. 9
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Chemical Classification ofHormones (continued) 10
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Classification of Hormones (continued) Glycoproteins:  Long polypeptides (>100) bound to 1 or more carbohydrate (CHO) groups.  FSH and LH. Hormones can also be divided into:  Polar:  H20 soluble.  Nonpolar (lipophilic):  H20 insoluble.  Can gain entry into target cells.  Steroid hormones and T4.  Pineal gland secretes melatonin:  Has properties of both H20 soluble and lipophilic hormones. 11
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Prohormones and Prehormones Prohormone:  Precursor is a longer chained polypeptide that is cut and spliced together to make the hormone.  Proinsulin. Preprohormone:  Prohormone derived from larger precursor molecule.  Preproinsulin. Prehormone:  Molecules secreted by endocrine glands that are inactive until changed into hormones by target cells.  T4 converted to T3. 12
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Common Aspects of Neural andEndocrine Regulation APs are chemical events produced by diffusion of ions through neuron plasma membrane. Action of some hormones are accompanied by ion diffusion and electrical changes in the target cell.  Nerve axon boutons release NTs.  Some chemicals are secreted as hormones, and also are NTs. In order for either a NT or hormone to function in physiological regulation:  Target cell must have specific receptor proteins.  Combination of the regulatory molecule with its receptor proteins must cause a specific sequence of changes.  There must be a mechanism to quickly turn off the action of a regulator. 13
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Synergistic:  Two hormones work together to produce a result.  Additive:  Each hormone separately produces response, together at same concentrations stimulate even greater effect.  NE and Epi.  Complementary:  Each hormone stimulates different step in the process.  FSH and testosterone. 14
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Hormonal Interactions (continued)  Permissive effects:  Hormone enhances the responsiveness of a target organ to second hormone.  Increases the activity of a second hormone.  Prior exposure of uterus to estrogen induces formation of receptors for progesterone.  Antagonistic effects:  Action of one hormone antagonizes the effects of another.  Insulin and glucagon. 15
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effects of [Hormone] on Tissue Response [Hormone] in blood reflects the rate of secretion. Half-life:  Time required for the blood [hormone] to be reduced to ½ reference level.  Minutes to days. Normal tissue responses are produced only when [hormone] are present within physiological range. Varying [hormone] within normal, physiological range can affect the responsiveness of target cells. 16
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effects of [Hormone] on Tissue Response (continued) Priming effect (upregulation):  Increase number of receptors formed on target cells in response to particular hormone.  Greater response by the target cell. Desensitization (downregulation):  Prolonged exposure to high [polypeptide hormone].  Subsequent exposure to the same [hormone] produces less response.  Decrease in number of receptors on target cells.  Insulin in adipose cells.  Pulsatile secretion may prevent downregulation. 17
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanisms of Hormone Action Hormones of same chemical class have similar mechanisms of action.  Similarities include:  Location of cellular receptor proteins depends on the chemical nature of the hormone.  Events that occur in the target cells. To respond to a hormone:  Target cell must have specific receptors for that hormone (specificity).  Hormones exhibit:  Affinity (bind to receptors with high bond strength).  Saturation (low capacity of receptors). 18
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hormones That Bind to Nuclear Receptor Proteins Lipophilic steroid and thyroid hormones are attached to plasma carrier proteins.  Hormones dissociate from carrier proteins to pass through lipid component of the target plasma membrane. Receptors for the lipophilic hormones are known as nuclear hormone receptors. 19
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nuclear Hormone Receptors Steroid receptors are located in cytoplasm and in the nucleus. Function within cell to activate genetic transcription.  Messenger RNA directs synthesis of specific enzyme proteins that change metabolism. Each nuclear hormone receptor has 2 regions:  A ligand (hormone)-binding domain.  DNA-binding domain. Receptor must be activated by binding to hormone before binding to specific region of DNA called HRE (hormone responsive element).  Located adjacent to gene that will be transcribed. 20
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanisms of Steroid Hormone Action Cytoplasmic receptor binds to steroid hormone. Translocates to nucleus. DNA-binding domain binds to specific HRE of the DNA. Dimerization occurs.  Process of 2 receptor units coming together at the 2 half-sites. Stimulates transcription of particular genes. 21
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanism of Thyroid Hormone Action T4 passes into cytoplasm and is converted to T3. Receptor proteins located in nucleus.  T3 binds to ligand-binding domain.  Other half-site is vitamin A derivative (9-cis-retinoic) acid.  DNA-binding domain can then bind to the half-site of the HRE.  Two partners can bind to the DNA to activate HRE.  Stimulate transcription of genes. 22
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hormones That Use 2nd Messengers Hormones cannot pass through plasma membrane use 2nd messengers.  Catecholamine, polypeptide, and glycoprotein hormones bind to receptor proteins on the target plasma membrane. Actions are mediated by 2nd messengers (signal-transduction mechanisms).  Extracellular hormones are transduced into intracellular 2nd messengers. 23
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Adenylate Cyclase-cAMP Polypeptide or glycoprotein hormone binds to receptor protein causing dissociation of a subunit of G-protein. G-protein subunit binds to and activates adenylate cyclase. ATP cAMP + PPi cAMP attaches to inhibitory subunit of protein kinase. Inhibitory subunit dissociates and activates protein kinase. 24
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adenylate Cyclase-cAMP (continued) Phosphorylates enzymes within the cell to produce hormone’s effects. Modulates activity of enzymes present in the cell. Alters metabolism of the cell. cAMP inactivated by phosphodiesterase.  Hydrolyzes cAMP to inactive fragments. 25
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Phospholipase-C-Ca2+ Binding of Epi to a-adrenergic receptor in plasma membrane activates a G- protein intermediate, phospholipase C.  Phospholipase C splits phospholipid into IP3 and DAG.  Both derivatives serve as 2nd messengers. IP3 diffuses through cytoplasm to ER.  Binding of IP3 to receptor protein in ER causes Ca2+ channels to open. 26
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phospholipase-C-Ca2+ (continued) Ca2+ diffuses into the cytoplasm.  Ca2+ binds to calmodulin. Calmodulin activates specific protein kinase enzymes.  Alters the metabolism of the cell, producing the hormone’s effects. 27
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Epi Can Act Through Two 2ndMessenger Systems 28
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tyrosine Kinase Insulin receptor consists of 2 units that dimerize when they bind with insulin.  Insulin binds to ligand–binding site on plasma membrane, activating enzymatic site in the cytoplasm. Autophosphorylation occurs, increasing tyrosine kinase activity. Activates signaling molecules.  Stimulate glycogen, fat and protein synthesis.  Stimulate insertion of GLUT-4 carrier proteins. 29
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Tyrosine Kinase (continued) 30
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pituitary Gland Pituitary gland is located in the diencephalon. Structurally and functionally divided into:  Anterior lobe.  Posterior lobe. 31
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pituitary Gland (continued) Anterior pituitary:  Master gland (adenohypophysis).  Derived from a pouch of epithelial tissue that migrates upward from the mouth.  Consists of 2 parts:  Pars distalis: anterior pituitary.  Pars tuberalis: thin extension in contact with the infundibulum. Posterior pituitary(neurohypophysis):  Formed by downgrowth of the brain during fetal development.  Is in contact with the infundibulum.  Nerve fibers extend through the infundibulum. 32
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pituitary Hormones Anterior Pituitary:  Trophic effects:  High blood [hormone] causes target organ to hypertrophy.  Low blood [hormone] causes target organ to atrophy. 33
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pituitary Hormones (continued) Posterior pituitary:  Stores and releases 2 hormones that are produced in the hypothalamus:  Antidiuretic hormone (ADH/vasopressin):  Promotes the retention of H20 by the kidneys.  Less H20 is excreted in the urine.  Oxytocin:  Stimulates contractions of the uterus during parturition.  Stimulates contractions of the mammary gland alveoli.  Milk-ejection reflex. 34
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamic Control of Posterior Pituitary Hypothalamus neuron cell bodies produce:  ADH: supraoptic nuclei.  Oxytocin: paraventricular nuclei. Transported along the hypothalamo- hypophyseal tract. Stored in posterior pituitary. Release controlled by neuroendocrine reflexes. 35
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamic Control of the Anterior Pituitary Hormonal control rather than neural. Hypothalamus neurons synthesize releasing and inhibiting hormones. Hormones are transported to axon endings of median eminence. Hormones secreted into the hypothalamo- hypophyseal portal system regulate the secretions of the anterior pituitary 36
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Feedback Control of the Anterior Pituitary Anterior pituitary and hypothalamic secretions are controlled by the target organs they regulate.  Secretions are controlled by negative feedback inhibition by target gland hormones. Negative feedback at 2 levels:  The target gland hormone can act on the hypothalamus and inhibit secretion of releasing hormones.  The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone. 37
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Feedback Control of the Anterior Pituitary (continued) Short feedback loop:  Retrograde transport of blood from anterior pituitary to the hypothalamus.  Hormone released by anterior pituitary inhibits secretion of releasing hormone. Positive feedback effect:  During the menstrual cycle, estrogen stimulates ―LH surge.‖ 38
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Higher Brain Function andPituitary Secretion Axis:  Relationship between anterior pituitary and a particular target gland.  Pituitary-gonad axis. Hypothalamus receives input from higher brain centers.  Psychological stress affects:  Circadian rhythms.  Menstrual cycle. 39
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Adrenal Glands Paired organs that cap the kidneys. Each gland consists of an outer cortex and inner medulla. Adrenal medulla:  Derived from embryonic neural crest ectoderm (same tissue that produces the sympathetic ganglia).  Synthesizes and secretes:  Catecholamines (mainly Epi but some NE). 40
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adrenal Glands (continued) Adrenal cortex:  Does not receive neural innervation.  Must be stimulated hormonally (ACTH). Consists of 3 zones:  Zona glomerulosa.  Zona fasciculata.  Zona reticularis. Secretes corticosteroids. 41
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Functions of the Adrenal Cortex Zona glomerulosa:  Mineralcorticoids (aldosterone):  Stimulate kidneys to reabsorb Na+ and secrete K+. Zona fasciculata:  Glucocorticoids (cortisol):  Inhibit glucose utilization and stimulate gluconeogenesis. Zona reticularis (DHEA):  Sex steroids:  Supplement sex steroids. 42
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Functions of the AdrenalCortex (continued) 43
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Functions of the AdrenalMedulla Innervated by preganglionic sympathetic axons.  Increase respiratory rate.  Increase HR and cardiac output.  Vasoconstrict blood vessels, thus increasing venous return.  Stimulate glycogenolysis.  Stimulate lipolysis. 44
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stress and the Adrenal Gland Non-specific response to stress produces the general adaptation syndrome (GAS). Alarm phase:  Adrenal glands activated. Stage of resistance:  Stage of readjustment. Stage of exhaustion:  Sickness and/or death if readjustment is not complete. 45
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thyroid Hormones Thyroid gland is located just below the larynx. Thyroid is the largest of the pure endocrine glands. Follicular cells secrete thyroxine. Parafollicular cells secrete calcitonin. 46
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Production of ThyroidHormones Iodide (I-) actively transported into the follicle and secreted into the colloid. Oxidized to iodine (Io). Iodine attached to tyrosine within thyroglobulin chain.  Attachment of 1 iodine produces monoiodotyrosine (MIT).  Attachment of 2 iodines produces diiodotyrosine (DIT). MIT and DIT or 2 DIT molecules coupled together. 47
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Production of Thyroid Hormones (continued) T3 and T4 produced. TSH stimulates pinocytosis into the follicular cell.  Enzymes hydrolyze T3 and T4 from thyroglobulin. Attached to TBG and released into blood. 48
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Production of ThyroidHormones (continued) 49
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Actions of T3 Stimulates protein synthesis. Promotes maturation of nervous system. Stimulates rate of cellular respiration by:  Production of uncoupling proteins.  Increase active transport by Na+/K+ pumps.  Lower cellular [ATP]. Increases metabolic heat. Increases metabolic rate.  Stimulates increased consumption of glucose, fatty acids and other molecules. 50
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diseases of the Thyroid Iodine-deficiency (endemic) goiter:  Abnormal growth of the thyroid gland.  In the absence of sufficient iodine, cannot produce adequate amounts of T4 and T3.  Lack of negative feedback inhibition.  Stimulates TSH, which causes abnormal growth. 51
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diseases of the Thyroid (continued) [Iodine-deficiency (endemic) goiter—continued]  Adult myxedema:  Accumulation of mucoproteins and fluid in subcutaneous tissue.  Symptoms:  Decreased metabolic rate.  Weight gain.  Decreased ability to adapt to cold.  Lethargy. Grave’s disease:  Autoimmune disorder:  Exerts TSH-like effects on thyroid.  Not affected by negative feedback. Cretinism:  Hypothyroid from end of 1st trimester to 6 months postnatally.  Severe mental retardation. 52
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parathyroid Glands Embedded in the lateral lobes of the thyroid gland. Parathyroid hormone (PTH):  Only hormone secreted by the parathyroid glands. Single most important hormone in the control of blood [Ca2+]. Stimulated by decreased blood [Ca2+]. Promotes rise in blood [Ca2+] by acting on bones, kidney and intestines. 53
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pancreatic Islets (Islets of Langerhans) Alpha cells secrete glucagon.  Stimulus is decrease in blood [glucose].  Stimulates glycogenolysis and lipolysis.  Stimulates conversion of fatty acids to ketones. Beta cells secrete insulin.  Stimulus is increase in blood [glucose].  Promotes entry of glucose into cells.  Converts glucose to glycogen and fat.  Aids entry of amino acids into cells. 54
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pineal Gland Secretes melatonin:  Production stimulated by the suprachiasmatic nucleus (SCN) in hypothalamus.  SCN is primary center for circadian rhythms.  Light/dark changes required to synchronize.  Melatonin secretion increases with darkness and peaks in middle of night.  May inhibit GnRH.  May function in the onset of puberty (controversial). 55
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Pineal Gland (continued) 56
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Thymus Site of production of T cells (thymus- dependent cells), which are lymphocytes.  Lymphocytes are involved in cell-mediated immunity. Secretes hormones that are believed to stimulate T cells after leave thymus.  Thymus gland size is large in newborns and children. Regresses after puberty and becomes infiltrated with strands of fibrous tissue. 57
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Gonads and Placenta Gonads (testes and ovaries):  Secrete sex hormones.  Testosterone.  Estradiol 17-b.  After menopause, produces estrone.  Progesterone. Placenta:  Secretes large amounts of estriol, progesterone, hCG, hCS. 58
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Autocrine and Paracrine Regulation Autocrine:  Produced and act within the same tissue of an organ.  All autocrine regulators control gene expression in target cells. Paracrine:  Produced within one tissue and regulate a different tissue of the same organ. Cytokines (lymphokines):  Regulate different cells (interleukins) . Growth factors:  Promote growth and cell division in any organ. Neutrophins:  Guide regenerating peripheral neurons. 59
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prostaglandins Most diverse group of autocrine regulators. Produced in almost every organ. Wide variety of functions. Different prostaglandins may exert antagonistic effects in some tissues.  Immune system:  Promote inflammatory process.  Reproductive system:  Play role in ovulation.  Digestive system:  Inhibit gastric secretion. 60
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Prostaglandins (continued) 61
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Prostaglandins (continued)  Respiratory system:  May bronchoconstrict or bronchodilate.  Circulatory system:  Vasoconstrictors or vasodilators.  Urinary system:  Vasodilation. Inhibitors of prostaglandin synthesis:  Non-steroidal anti-inflammatory drugs (NSAIDS).  Aspirin, indomethacin, ibuprofen: inhibit COX1.  Celecoxib and rofecoxib: inhibit COX2. 62
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ENDOCRINOLOGY HYPERLINK Photos, Images and Pictures Atlas of the Endocrine System [Peyrin et Vandroux] - Univ de St.Etienne (FR) Endocrine Pathol. images - U of Pittsburg Endocrine Pathol. index [EC Klatt] Some Pictures and illustrations in Endocrinology - Univ of Houston (US) Some Images in Endocrinology - MedStudents (BR) Advanced Imaging of the Diabetic Foot and Its Complications [A Gentili] - UCSD Images related to the Endocrine System - Cushings-Help.com A collection of Thyroid surgery images from the American Thyroid Clinic Some Images of Thyroid Disorders [DW Gardner] Thyroid Imaging .com [G Perrella] 63