Download - Nomad: Thyroid Physiology

04/07/2304/07/23 NOMAD:ENDOPHYSIOL: THYNOMAD:ENDOPHYSIOL: THYROID PARAROID PARA

11

THYROID GLAND ITHYROID GLAND I

ByBy

Dr. M. Anthony David, MDDr. M. Anthony David, MD

Professor of PhysiologyProfessor of Physiology


22

THE THYROID GLANDTHE THYROID GLAND ““ThyreosThyreos” Greek for ” Greek for ShieldShield.. Morphology:Morphology:

Largest Endocrine gland: 15 – 25 Gms Largest Endocrine gland: 15 – 25 Gms

in weight.in weight. Anatomy:Anatomy:

Has two lobes connected by an IsthmusHas two lobes connected by an Isthmus Is richly vascular; 4 -6ml/g/minIs richly vascular; 4 -6ml/g/min Has sympathetic innervationHas sympathetic innervation


33

THYROID

GLAND


44

THYROID GLANDTHYROID GLAND EMBRYOLOGY:EMBRYOLOGY:

Begins development in the Begins development in the 44ththwk of wk of IULIUL

Hormones secreted from the Hormones secreted from the 1212thth weekweek..

Fetal Thyroid Hormones useful for:Fetal Thyroid Hormones useful for: Normal Fetal Bone maturation.Normal Fetal Bone maturation. Normal development of the CNS.Normal development of the CNS.


55

HISTOLOGY:HISTOLOGY: 3 Million spherical follicles3 Million spherical follicles 50 - 500µ in diameter 50 - 500µ in diameter Each follicle has clear viscid Each follicle has clear viscid

protein colloid called protein colloid called ThyroglobulinThyroglobulin

The Parafollicular ‘C’ cells secrete The Parafollicular ‘C’ cells secrete (Thyro) (Thyro) Calcitonin.Calcitonin.

THYROID GLANDTHYROID GLAND


66


77

BIOSYNTHESIS OF THYROID BIOSYNTHESIS OF THYROID HORMONESHORMONES

IODINE UPTAKE & TRAPPINGIODINE UPTAKE & TRAPPING IODINATION & COUPLINGIODINATION & COUPLING

Tyrosine + Iodine = Mono Iodo Tyrosine + Iodine = Mono Iodo Tyrosine (MIT)Tyrosine (MIT)

MIT + MIT = Di Iodo Tyrosine (DIT)MIT + MIT = Di Iodo Tyrosine (DIT) MIT + DIT = Tri Iodo Tyrosine TMIT + DIT = Tri Iodo Tyrosine T33

DIT + DIT = Tetra Iodo Thyronine (TDIT + DIT = Tetra Iodo Thyronine (T44))


88

IODINATION&COUPLING


99

COUPLED HORMONES COUPLED HORMONES COMBINE WITH COMBINE WITH THYROGLOBULIN, COLLOID.THYROGLOBULIN, COLLOID.

ARE FREED BY ARE FREED BY PROTEOLYSISPROTEOLYSIS THE FREE THYROID THE FREE THYROID

HORMONES ARE THEN HORMONES ARE THEN RELEASED INTO THE BLOODRELEASED INTO THE BLOOD

BIOSYNTHESIS OF THYROID BIOSYNTHESIS OF THYROID HORMONESHORMONES


1010

TRANSPORT OF THYROID TRANSPORT OF THYROID HORMONESHORMONES

60% : THYROXIN 60% : THYROXIN BINDING GLOBULIN BINDING GLOBULIN (TBG)(TBG)

30% : THYROXIN 30% : THYROXIN BINDING PRE BINDING PRE ALBUMIN (TBPA)ALBUMIN (TBPA)

10% : ALBUMIN10% : ALBUMIN


1111

EFFECTS OF THYROID HORMONES: EFFECTS OF THYROID HORMONES: MetabolicMetabolic

CALORIGENESIS:CALORIGENESIS:Heat Production.Heat Production.

REGULATIONREGULATION:: Transport:Transport:

IonsIons WaterWater

Intermediary Intermediary metabolisms:metabolisms:

CHOCHO FatsFats ProteinsProteins

BMRBMR


1212

REGULATION:REGULATION: Growth in HomeothermsGrowth in Homeotherms Metamorphosis in Poikilotherms.Metamorphosis in Poikilotherms.

CONTROL:CONTROL: Protein Synthesis.Protein Synthesis.

EFFECTS OF THYROID EFFECTS OF THYROID HORMONES: HORMONES: DevelopmentalDevelopmental


1313

CALORIGENESIS: Heat ProductionCALORIGENESIS: Heat Production

How?How? By increasing Oxygen consumption in:By increasing Oxygen consumption in:

HeartHeart Gastric MucosaGastric Mucosa Smooth MusclesSmooth Muscles KidneysKidneys LiverLiver Skeletal Muscles.Skeletal Muscles.


1414

No response to Thyroxine inNo response to Thyroxine in TT: Testes: Testes UU: Uterus: Uterus LL: Lymph nodes: Lymph nodes SS: Spleen: Spleen AA: Anterior Pituitary: Anterior Pituitary

Results:Results: TachycardiaTachycardia Sensitivity to Adrenal Lipolysis.Sensitivity to Adrenal Lipolysis.

CALORIGENESIS: Heat CALORIGENESIS: Heat ProductionProduction


1515

THYROID HORMONES: THYROID HORMONES: PHYSIOLOGIC ACTIONSPHYSIOLOGIC ACTIONS

ON THE HEART:ON THE HEART: POSITIVE CHRONO POSITIVE CHRONO

& IONOTROPIC & IONOTROPIC EFFECTEFFECT No & affinity of No & affinity of ββ

adrenergic receptorsadrenergic receptors Response to Response to

CatecholaminesCatecholamines Proportion of alpha Proportion of alpha

Myosin heavy chains Myosin heavy chains


1616

ON THE ADIPOSE ON THE ADIPOSE TISSUE:TISSUE: Thyroid hormones Thyroid hormones

are catabolic.are catabolic. They cause They cause

Lipolysis.Lipolysis. ON MUSCLES:ON MUSCLES:

CatabolicCatabolic Protein lysis.Protein lysis.



1717

ON THE BONE:ON THE BONE: Developmental Developmental

effect:effect: Normal growth & Normal growth &

development.development.



1818

ON THE NERVOUS ON THE NERVOUS SYSTEM:SYSTEM: DEVELOPMENTALDEVELOPMENTAL Promotes normal Promotes normal

developmentdevelopment



1919

ON THE GUT:ON THE GUT: METABOLIC EFFECT:METABOLIC EFFECT: CHO AbsorptionCHO Absorption



2020

ON LIPOPROTEINS:ON LIPOPROTEINS: METABOLIC EFFECT:METABOLIC EFFECT: LDL Receptor formation.LDL Receptor formation.

OTHER:OTHER: CALORIGENESISCALORIGENESIS BMR:BMR:

Oxygen consumption in most tissues except Oxygen consumption in most tissues except TTestes, estes, UUterus, terus, LLymph nodes, ymph nodes, SSpleen & pleen & AAnterior Pituitary.nterior Pituitary.



2121

CARBOHYDRATES:CARBOHYDRATES: GLUCOSE PRODUCTION GLUCOSE PRODUCTION BY:BY:

GlycogenolysisGlycogenolysis GluconeogenesisGluconeogenesis Hunger - Hunger - Intake of food Intake of food

ANTI INSULIN EFFECTANTI INSULIN EFFECT:: Catabolism of InsulinCatabolism of Insulin Secretion of InsulinSecretion of Insulin

THYROID HORMONES: THYROID HORMONES: METABOLIC EFFECTSMETABOLIC EFFECTS


2222

LIPIDS:LIPIDS: SynthesisSynthesis LysisLysis Hypothyroidism:Hypothyroidism:

S. Cholesterol: 400 – 700 mg%S. Cholesterol: 400 – 700 mg% Hyperthyroidism:Hyperthyroidism:

S. Cholesterol: 100 – 150 mg%S. Cholesterol: 100 – 150 mg%



2323

PROTEINS:PROTEINS: AnabolismAnabolism

VITAMINS:VITAMINS: Converts Converts ββ Carotene to Vit A & Retinene. Carotene to Vit A & Retinene.

MUCOPOLYSACCARIDES:MUCOPOLYSACCARIDES: Metabolism disturbed in HypothyroidismMetabolism disturbed in Hypothyroidism Causes ‘Myxedema’: Dry Coarse Puffy Causes ‘Myxedema’: Dry Coarse Puffy

skin.skin.



2424

BMR:BMR: Increases by 60 to Increases by 60 to 100 %100 % How?How?By increasing the size By increasing the size

and number of and number of MitochondriaMitochondria..



2525


2626


2727

THYROID HORMONES: A NEGATIVE THYROID HORMONES: A NEGATIVE FEEDBACK REGULATIONFEEDBACK REGULATION

HYPOTHALAMUS

TRH

ANTPIT

THYROID GLAND

TSH

T3 & T4TARGETTISSUES

STIMULATING

INHIBITORY


2828

APPLIED ASPECTSAPPLIED ASPECTS EUTHYROIDISM: Normal thyroid statusEUTHYROIDISM: Normal thyroid status HYPOTHYROIDISM:HYPOTHYROIDISM:

In infancy: Cretinism (Thyroid dwarfism)In infancy: Cretinism (Thyroid dwarfism) In adults: Myxedema, HypothyroidismIn adults: Myxedema, Hypothyroidism

HYPERTHYROIDISM:HYPERTHYROIDISM: ThyrotoxicosisThyrotoxicosis


2929

HYPOTHYROIDISM CHILDREN: CHILDREN: CRETINISMCRETINISM::

Congenital HypothyroidismCongenital Hypothyroidism DwarfismDwarfism Mentally Subnormal: MRMentally Subnormal: MR Enlarged, Protruding tongueEnlarged, Protruding tongue Pot bellies.Pot bellies.


3030

CRETINISM

PROTRUDING

TONGUE


3131

HYPOTHYROIDISM: ADULTSHYPOTHYROIDISM: ADULTS

MYXEDEMA:MYXEDEMA: CAUSES:CAUSES:

Primary: Thyroid Primary: Thyroid diseasesdiseases

Secondary: Pituitary Secondary: Pituitary or Hypothalamic or Hypothalamic cause.cause.


3232

MYXEDEMA: CLINICAL MYXEDEMA: CLINICAL FEATURESFEATURES

Low BMR: - 40Low BMR: - 40 Coarse & Sparse Coarse & Sparse

HairHair Dry & Yellow skinDry & Yellow skin

( Carotenemia)( Carotenemia) Poor Cold Poor Cold

tolerationtoleration Voice: Husky & Voice: Husky &

slowslow

Tele diagnosis!Tele diagnosis!


3333

MYXEDEMA: CLINICAL MYXEDEMA: CLINICAL FEATURESFEATURES

Plasma CholesterolPlasma Cholesterol Slow mentationSlow mentation Poor memoryPoor memory Severe mental Severe mental

symptoms: symptoms: Myxedema madnessMyxedema madness

DepressionDepression


3434

HYPOTHYROIDISM: TREATMENTHYPOTHYROIDISM: TREATMENT

Very effective Very effective treatment available.treatment available.

ReplacementReplacement of the of the deficient Thyroxine deficient Thyroxine byby Oral tablets Oral tablets..

Brand name Brand name EltroxinEltroxin This causes This causes allall the the

clinical features clinical features to to disappeardisappear..

Tab EltroxinOne tablet a dayLife long


3535

HYPERTHYROIDISMHYPERTHYROIDISM

Also called Also called ThyrotoxicosisThyrotoxicosis

Hyperphagia + Hyperphagia + Weight lossWeight loss

Heat IntoleranceHeat Intolerance Pulse PressurePulse Pressure Sleeping Pulse Sleeping Pulse

Rate >90/minRate >90/min


3636

HYPERTHYROIDISMHYPERTHYROIDISM Nervousness, Nervousness,

AnxietyAnxiety Fine Tremor: Fine Tremor:

Paper testPaper test Warm, soft skinWarm, soft skin SweatingSweating BMR: +10 to BMR: +10 to

+100+100


3737

HYPERTHYROIDISM: GRAVE’S HYPERTHYROIDISM: GRAVE’S DISEASEDISEASE

EXOPHTHALMIC EXOPHTHALMIC GOITRE:GOITRE: ExophthalmosExophthalmos: :

Protruding eyeballsProtruding eyeballs Is anIs an autoimmuneautoimmune

disorderdisorder Can be also Can be also

Hashimoto’s Hashimoto’s ThyroiditisThyroiditis


3838

TREATMENT OF TREATMENT OF HYPERTHYROIDISMHYPERTHYROIDISM

Antithyroid drugs:Antithyroid drugs: Most drugs interfere with Most drugs interfere with

Iodide trapping.Iodide trapping. Others block iodisation of Others block iodisation of

Tyrosine.Tyrosine. Examples:Examples:

PerchloratesPerchloratesThiocyanatesThiocyanates

Decrease Decrease Goitrogen consumptionGoitrogen consumption::


3939

GOITROGENSGOITROGENS Goitrogens: Goitrogens:

Goitrin & Goitrin & Progoitrin seen Progoitrin seen in:in: CabbageCabbage Rutabagas & Rutabagas &

TurnipsTurnips


4040