Physiology ofThyroid gland

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Thyroid gland:

Thyroid gland Dr.Zafar


Introduction Two lobed Roof of neck 20-40gm Females/males Disease are more in females

Histology :

Histology Follicles Cuboidal epithelial Thyroglobulin Para follicular cells

Hormones :

Hormones Tetraiodothyronine(90%) Tri- iodothyronine (10%) Calcitonin

Characteristics :

Characteristics T3 is four times more potent than T4 Duration of action of T4 is four times than T3 T4 has more affinity with proteins T3 has rapid action T4 has longer half life(7 days)& T3 has 10-24 hrs


synthesis Site Follicular activity Raw material Iodine &tyrosine(both are absorbed from GIT)

Stages :

Stages Thyroglobulin synthesis Iodide pump Oxidation of iodide Iodination of tyrosine Coupling reaction

Thyroglobulin synthesis :

Thyroglobulin synthesis Endoplasmic reticulum & Golgi apparatus Glycoprotein Stored in follicular cells

Iodide pump :

Iodide pump Iodine is converted into iodide and absorbed into blood from GIT From blood into follicular cells via active transport Sodium-iodide symporter Iodide- Cholride pump

Oxidation of iodide :

Oxidation of iodide Iodide is oxidized to iodine by enzyme thyroid peroxidase present in the follicular cells

Iodination of tyrosine:

Iodination of tyrosine Iodine is released from follicular cells into cavity Iodine binds Thyroglobulin( organification of Thyroglobulin) Iodination requires iodinase which speed it up MIT DIT

Coupling reaction :

Coupling reaction Iodotyrosin residues MIT+DIT DIT+DIT


Storage Vesicles within Thyroglobulin 1:10 For four months storage

Release :

Release Membrane of follicular cells produces pseudopodes Conversion of T-H complex into pinocytic vesicles lysosomes

Transport :

Transport TBG TBPA Albumin

Metabolism :

Metabolism Deamination Decarboxylase Conjugation with sulfate and glucuronic acid

Mode of action:

Mode of action Conversion of T4 into T3 T3 has high affinity for receptors H-R complex Transcription


functions BMR Increase oxygen consumption Utilization of foodstuff Brain ,retina, lungs, testes

Metabolism of carbohydrates:

Metabolism of carbohydrates Increase in absorption from GIT Accelerate transport of glucose Increase breakdown of glycogen Accelerate gluconeogensis

Metabolism of fat:

Metabolism of fat Catabolic Mobilize fat from adipose tissues Convert fat into free fatty acids

Metabolism of proteins:

Metabolism of proteins Anabolic & catabolic Increase translation of RNA Increase in transcription Increase in number and activity of mitochondria

Fats of plasma and liver:

Fats of plasma and liver Decrease in concentration of cholesterol phospholipids Fatty liver

Vitamin metasbolism:

Vitamin metasbolism Increases enzyme production Vitamin deficiency occurs

Body temperature:

Body temperature Thermogentic Excessive sweating


growth Growth enhancer Height reducer

Body weight :

Body weight Decrease body weight as fat consumption


blood Increase in production of RBC’s Increase in blood volume


cvs H.rate Force of contraction Vasodilatation Systolic BP increases Diastolic BP decreases


respiration Increase in the rate and force of inspiration


GIT Appetitizers Secretion and motility is increased


cns Development of CNS Stimulant Increase in blood flow to brain


sleep Stimulant so it causes exhausted , person feels Sleepy but cannot sleep

Skeletal muscle:

Skeletal muscle Need for normal skeletal muscle activity fatigue

Sexual function:

Sexual function Hyposecretion causes loss of libido Hyper secretion causes impotence Oligimenorrhea in hyper Irregular menstruation in hypo


hypothalamus Thyrotropic releasing hormone Nerve endings of hypothalamus Hypothalamo-hypophyseal vessel Regulate secretion of TSH


tsh Anterior pituitary gland Increases number of thyroid cells Increases size and secreting activity of cell Iodide pump and iodine trapping Secretion of Thyroglobulin Iodination Proteolysis of T-H complex

Feedback control:

Feedback control Autoregulation

Role of iodide:

Role of iodide High intake of iodine Inhibition of enzymes necessary for synthesis(wolf- chaikoff effect)


HYPERTHYROIDISM Grave’s disease is an autoimmune disease Most common cause TSH binds with thyroid cells Plasma cells secretes BTSAB BTSAB acts as TSH(12:1)

Thyroid adenoma:

Thyroid adenoma Local tumor

Signs & Symptoms:

Signs & Symptoms Heat intolerance Increased sweating Body weight decrease Increases motility of GIT Polycythemia Tachycardia Systolic hypertension CNS Goiter Exophthalamus oligomenorrhea


exophthlamos Protrusion of eye balls Swelling of retro-orbital Degenerative changes in extra ocular muscle Stretching & demaging of optic nerve Due to incomplete closure of eyelids constant exposure to environment of eyeball


myxedema Generalized edematous appearance due to hypothyroidism Iodine deficiency Genetic disorder Deficiency of TSH or TRH Hashimoto’s thyroiditis

Signs & symptoms:

Signs & symptoms Swelling of face Bagging under the eyes Nonpitting type of edema Atherosclerosis Anemia


cretinism Stunted growth in children due to hypothyroidism Genetic disorder Congenital absence of thyroid gland Lack of iodine in diet

Signs & symptoms:

Signs & symptoms After few weeks sluggish movements, croaking sound during cry Tongue becomes so long that it hangs down with dripping of saliva Difficulty in breathing Skeletal muscle growth is stunted Disproportionate body Reproductive system abnormility


goiter Enlargement of thyroid glands Toxic goiter(tumor) Non toxic goiter Endemic colloid goiter(iodine deficiency) Idiopathic nontoxic goiter Unknown Enzymes deficiency Goitrogens


Manshor-e- zeast Serve the people live as long as it can