THYROID GLAND IBy Dr. M. Anthony David, MD Professor of Physiology02/09/08 NOMAD:ENDOPHYSIOL: THYROID PARA 1

THE THYROID GLAND

Thyreos Greek for Shield. Morphology:

Largest Endocrine gland: 15 25 Gms in weight. Has two lobes connected by an Isthmus Is richly vascular; 4 -6ml/g/min Has sympathetic innervationNOMAD:ENDOPHYSIOL: THYROID PARA 2

Anatomy:

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THYROID GLAND

EMBRYOLOGY:Begins development in the 4thwk of IUL Hormones secreted from the 12th week. Fetal Thyroid Hormones useful for: Normal

Fetal Bone maturation. Normal development of the CNS.02/09/08 NOMAD:ENDOPHYSIOL: THYROID PARA 4

THYROID GLAND HISTOLOGY:3

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Million spherical follicles 50 - 500 in diameter Each follicle has clear viscid protein colloid called Thyroglobulin The Parafollicular C cells secrete (Thyro) Calcitonin.NOMAD:ENDOPHYSIOL: THYROID PARA

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BIOSYNTHESIS OF THYROID HORMONESIODINE UPTAKE & TRAPPING IODINATION & COUPLING

Tyrosine + Iodine = Mono Iodo Tyrosine (MIT) MIT + MIT = Di Iodo Tyrosine (DIT) MIT + DIT = Tri Iodo Tyrosine T 3

DIT + DIT = Tetra Iodo Thyronine 02/09/08 (T4) NOMAD:ENDOPHYSIOL: THYROID PARA

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I O D I N A T I O N & C O U P L I N G02/09/08 NOMAD:ENDOPHYSIOL: THYROID PARA 8

BIOSYNTHESIS OF THYROID HORMONES COUPLED

HORMONES COMBINE WITH THYROGLOBULIN, COLLOID. ARE FREED BY PROTEOLYSIS THE FREE THYROID HORMONES ARE THEN RELEASED INTO THE BLOOD02/09/08 NOMAD:ENDOPHYSIOL: THYROID PARA

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TRANSPORT OF THYROID HORMONES

60% : THYROXIN BINDING GLOBULIN (TBG) 30% : THYROXIN BINDING PRE ALBUMIN (TBPA) 10% : ALBUMIN

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EFFECTS OF THYROID HORMONES: Metabolic

CALORIGENESIS:Heat Production.

REGULATION:

Transport:Ions Water

Intermediary metabolisms:CHO Fats Proteins

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EFFECTS OF THYROID HORMONES: Developmental REGULATION: Growth

in Homeotherms Metamorphosis in Poikilotherms. CONTROL: Protein 02/09/08

Synthesis.

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CALORIGENESIS: Heat Production

How? By increasing Oxygen consumption in:

Heart Gastric Mucosa Smooth Muscles Kidneys Liver Skeletal Muscles.NOMAD:ENDOPHYSIOL: THYROID PARA 13

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CALORIGENESIS: Heat Production

No response to Thyroxine in

T: Testes U: Uterus L: Lymph nodes S: Spleen A: Anterior Pituitary Tachycardia Sensitivity to Adrenal Lipolysis.NOMAD:ENDOPHYSIOL: THYROID PARA 14

Results:

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THYROID HORMONES: PHYSIOLOGIC ACTIONS

ON THE HEART: POSITIVE CHRONO & IONOTROPIC EFFECT

No & affinity of adrenergic receptors Response to Catecholamines Proportion of 02/09/08 alpha Myosin heavy NOMAD:ENDOPHYSIOL: THYROID PARA

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THYROID HORMONES: PHYSIOLOGIC ACTIONS

ON THE ADIPOSE TISSUE:

Thyroid hormones are catabolic. They cause Lipolysis. Catabolic Protein lysis.16

ON MUSCLES:

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THYROID HORMONES: PHYSIOLOGIC ACTIONS

ON THE BONE:

Developmental effect: Normal growth & development.

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THYROID HORMONES: PHYSIOLOGIC ACTIONS

ON THE NERVOUS SYSTEM:

DEVELOPMENTAL Promotes normal development

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THYROID HORMONES: PHYSIOLOGIC ACTIONS

ON THE GUT:

METABOLIC EFFECT: CHO Absorption

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THYROID HORMONES: PHYSIOLOGIC ACTIONS

ON LIPOPROTEINS:

METABOLIC EFFECT: LDL Receptor formation.

OTHER: CALORIGENESIS BMR:

Oxygen consumption in most tissues except Testes, Uterus, Lymph nodes, Spleen & Anterior Pituitary.NOMAD:ENDOPHYSIOL: THYROID PARA 20

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THYROID HORMONES: METABOLIC EFFECTS

CARBOHYDRATES:

GLUCOSE PRODUCTION BY: Glycogenolysis Gluconeogenesis Hunger - Intake of food

ANTI INSULIN EFFECT: Catabolism of Insulin Secretion of Insulin

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THYROID HORMONES: METABOLIC EFFECTS

LIPIDS:

Synthesis Lysis Hypothyroidism:

S. Cholesterol: 400 700 mg% S. Cholesterol: 100 150 mg%

Hyperthyroidism:

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THYROID HORMONES: METABOLIC EFFECTS

PROTEINS:

Anabolism Converts Carotene to Vit A & Retinene. Metabolism disturbed in Hypothyroidism Causes Myxedema: Dry Coarse Puffy skin.NOMAD:ENDOPHYSIOL: THYROID PARA 23

VITAMINS:

MUCOPOLYSACCARIDES:

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THYROID HORMONES: METABOLIC EFFECTS

BMR:Increases by 60 to 100 % How? By increasing the size and number of Mitochondria.

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THYROID HORMONES: A NEGATIVE FEEDBACK REGULATIONHYPOTHALAMUS

TRH ANT PIT TSH

STIMULATING INHIBITORY

TARGET TISSUES02/09/08

T3 & T4 THYROID GLANDNOMAD:ENDOPHYSIOL: THYROID PARA 27

APPLIED ASPECTS

EUTHYROIDISM: Normal thyroid status HYPOTHYROIDISM:

In infancy: Cretinism (Thyroid dwarfism) In adults: Myxedema, Hypothyroidism ThyrotoxicosisNOMAD:ENDOPHYSIOL: THYROID PARA 28

HYPERTHYROIDISM:

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HYPOTHYROIDISM

CHILDREN: CRETINISM:

Congenital Hypothyroidism Dwarfism Mentally Subnormal: MR Enlarged, Protruding tongue Pot bellies.

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C R E T I N I S M02/09/08 NOMAD:ENDOPHYSIOL: THYROID PARA

P R O T R U D I N G

T O N G U E30

HYPOTHYROIDISM: ADULTS

MYXEDEMA: CAUSES:

Primary: Thyroid diseases Secondary: Pituitary or Hypothalamic cause.

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MYXEDEMA: CLINICAL FEATURES

Low BMR: - 40 Coarse & Sparse Hair Dry & Yellow skin ( Carotenemia) Poor Cold toleration Voice: Husky & slowNOMAD:ENDOPHYSIOL: THYROID PARA 32

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MYXEDEMA: CLINICAL FEATURES

Plasma Cholesterol Slow mentation Poor memory Severe mental symptoms: Myxedema madness DepressionNOMAD:ENDOPHYSIOL: THYROID PARA 33

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HYPOTHYROIDISM: TREATMENTVery effective treatment available. Replacement of the deficient Tab Eltroxin Thyroxine by Oral One tablet tablets. a day Brand name Life long Eltroxin This causes all the clinical features 02/09/08 NOMAD:ENDOPHYSIOL: THYROID PARA to disappear.

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HYPERTHYROIDISM

Also called Thyrotoxicosis Hyperphagia + Weight loss Heat Intolerance Pulse Pressure Sleeping Pulse Rate >90/minNOMAD:ENDOPHYSIOL: THYROID PARA 35

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HYPERTHYROIDISMNervousness, Anxiety Fine Tremor: Paper test Warm, soft skin Sweating BMR: +10 to +10002/09/08 NOMAD:ENDOPHYSIOL: THYROID PARA 36

HYPERTHYROIDISM: GRAVES DISEASE

EXOPHTHALMIC GOITRE: Exophthalmos: Protruding eyeballs Is an autoimmune disorder Can be also Hashimotos ThyroiditisNOMAD:ENDOPHYSIOL: THYROID PARA 37

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TREATMENT OF HYPERTHYROIDISM

Antithyroid drugs: Most drugs interfere with Iodide trapping. Others block iodisation of Tyrosine. Examples: Perchlorates Thiocyanates Decrease Goitrogen consumption:NOMAD:ENDOPHYSIOL: THYROID PARA 38

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GOITROGENS

Goitrogens: Goitrin & Progoitrin seen in: Cabbage Rutabagas & TurnipsNOMAD:ENDOPHYSIOL: THYROID PARA 39

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