thyroid physiology

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2. THYROID HORMONE FUNCTIONS AND ABNORMALITIES
THYROID HORMONE FUNCTIONS
AND ABNORMALITIES
Dr. Sidra Shaukat
PG Trainee MPhil
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3. Genomic & Nongenomic Actions of
Thyroid Hormones
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

4. Thyroid Hormone
Functions
• Calorigenic effect
• Effect on growth
• Metabolic effects
• Systemic effects
• Endocrine effects
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

5. Functions of Thyroid Hormone
• Calorigenic effect
• Increased BMR
• Increased oxygen consumption
• Increased number, size and surface
area of mitochondria
• Increased Na-K ATPase activity
• Un coupling of oxidative
phosphorylation in brown fat
• Catecholamine induced increased
cellular activity
Calorigenic effects are not present in
gonads, spleen, lymph nodes and brain
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

6. Functions of Thyroid Hormone
• Effect on growth
• Effects both brain and skeletal growth
• Growth rate of bone, cartilage and teeth is
increased
• Causes metabolic activation of osteo and
chondroblasts
• In adult brain it causes myelination and branching
of neurons
• In fetus it causes brain development like basal
ganglia, cochlea and cerebral cortex
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

7. Functions of Thyroid Hormone
• Systemic effects
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8. Functions of Thyroid Hormone
• Renal System
• GFR is increased
• Urinary uric acid &urea levels raised
• Na & K loss is increased
• Cardio Vascular System
• Heart rate ---increased
• Blood pressure ----pulse pressure increased, mean BP
normal
• Cardiac output ----increased
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

9. THYROID HORMONE FUNCTIONS AND ABNORMALITIES
Functions of Thyroid Hormone
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Increased heart
rate &
contractility
Direct action;
Raised Na-K ATPase
Sarcoplasmic reticulum Ca- ATPase
Gs to Gi ratio is increased
Beta adrenergic receptor density
Increased ventricular contractility
In Direct action;
decreased diastolic blood pressure and
peripheral vascular resistance
Reflex increase in adrenergic stimulation

10. Functions of Thyroid Hormone
• Central Nervous System
• Mental development in fetus ( basal ganglia, cochlea)
• Brisk tendon reflexes
• Lack of sleep ----RAS is activated
• Increased cerebration (irritability, insomnia, lack of sleep)
• Reproduction
Menstrual cycle, fertility & lactation
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

11. Functions of Thyroid Hormone
• Gastrointestinal tract
• Increases motility
• Increase secretions
• Increases absorption of nutrients
• Increased appetite
• Respiratory System
• Increased rate and depth of respiration
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

12. Functions of Thyroid Hormone
• Metabolic effects
• Glucose metabolism
• Protein metabolism
• Lipid metabolism
• Effect on endocrine system
• Increases levels of growth hormone, Cortisol, ACTH, PTH
• T3+ GH+ prolactin----needed for lactation
• T3 +cortisol----needed for catecholamine action on
increasing BMR and androgen induced growth hormone
release
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

13. Thyroid Hormones
• Hyperthyroidism
• Primary hyperthyroidism(T3, T4 raised )(TSH, TRH reduced)
• Secondary hyperthyroidism
• Tertiary hyperthyroidism
• Hypothyroidism
• Hypothyroidism in adults
• Hypothyroidism in children
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Abnormalities
THYROID HORMONE FUNCTIONS AND ABNORMALITIES

14. Abnormalities of Thyroid Hormones
Hyperthyroidism
Primary hyperthyroidism
(toxic goiter, thyrotoxicosis, Graves
disease)
Signs and Symptoms
• Heat intolerance
• Weight loss and fatigue
• Muscle weakness
• Nervousness and tremors in hand
• Exophthalmos (immunoglobulin against
eye muscles)
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Hyperthyroidism
THYROID HORMONE FUNCTIONS AND ABNORMALITIES

15. Hyperthyroidism
Cause
Diagnosis
T3, T4, BMR and TSI’s increased, TSH reduced
Treatment
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TSI against TSH receptors that mimic the actions of TSH
Continuous stimulation of the gland cells
Continuous production of T3 and T4
• Radioactive iodine
Medical
• Propylthiouracil and iodides
Surgical
THYROID HORMONE FUNCTIONS AND ABNORMALITIES

16. Hyperthyroidism
Secondary Hyperthyroidism
• Pituitary hyperthyroidism
• Tumor of the gland
Tertiary Hyperthyroidism
• Hypothalamic hyperthyroidism
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

17. Hypothyroidism
Primary Hypothyroidism (T3 and T4 reduced)
(TSH &TRH increased)
• Endemic colloid goitre
• Idiopathic non toxic colloid goitre
• Hashimotos thyroiditis
• Myxoedema
• Drug induced
• Post surgery
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Hypothyroidism in Adults
THYROID HORMONE FUNCTIONS AND ABNORMALITIES

18. Hypothyroidism in Adults
Endemic Colloid Goitre (Iodine Deficiency)
LACK OF IODINE
decreased T3 and T4
increased TSH because of no feedback inhibition
increased TSH causes increased gland size by increasing
Idiopathic non toxic colloid goitre
Thyroiditis nodular appearance of enlargements
Enzymatic deficiency (deiodinase lack, peroxidase deficiency, deficient
iodide trapping)
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

19. Hypothyroidism in Adults
Hashimotos Thyroiditis
Auto immune cause (antibodies are formed against the
thyroid gland)
Drug Induced Hypothyroidism
Destruction of the gland by drugs
Post Surgery Hypothyroidism
Removal of gland by any surgical procedure
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

20. Hypothyroidism in Adults
Clinical features
• Somnolence, poor memory , excess sleep
• Myopathies, hyporeflexia
• Cold intolerance
• Reduced BP &CO
• Atherosclerosis
• Bagginess under the eyes
• Non pitting Edema,
• Pale coarse skin and frog like husky voice
Diagnosis
• BMR decreased (-30 to -50)
• Thyroxin reduced
• TSH increased in response to TRH
Treatment
• Oral Thyroxin
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Myxoedema
THYROID HORMONE FUNCTIONS AND ABNORMALITIES

21. Hypothyroidism in Adults
Secondary Hypothyroidism
• Decreased T3,T4 &TSH
• Increased TRH
• Pituitary hypothyroidism (tumour removal)
Tertiary Hypothyroidism
• T3,T4,TSH &TRH decreased
• Hypothalamic hypothyroidism
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THYROID HORMONE FUNCTIONS AND ABNORMALITIES

22. Hypothyroidism in Children
Causes
• Genetic defect of gland
• Congenital lack of thyroid gland (congenital
cretinism)
• Lack of iodine in diet (endemic cretinism)
Signs & Symptoms
• Retarded physical and mental growth
• Sluggish movements
• Skeletal growth is more effected than soft tissue
Treatment
• Iodine
• Thyroxin
• Mental defects might never be reversed
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Cretinism
THYROID HORMONE FUNCTIONS AND ABNORMALITIES

23. Hypothyroidism in Children
Causes
• Idiopathic
• Auto immune
Signs and Symptoms
• Slow Growth
• Delayed Tooth Development
• Lack Of Energy
• Inactivity
• Hoarse Speech
• Droopy Eyelids
Treatment
• Restoration of normal hormone levels
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Juvenile Hypothyroidism
THYROID HORMONE FUNCTIONS AND ABNORMALITIES

24. Goiter
Euthyroid Goiters Hypothyroid
Goitre
Hyperthyroid Goitre Puberty Goitre
T3 ,T4 levels
normal
T3 &T4 Levels are
decreased
T3&T4 are raised T3 & T4 levels
normal
Lack of iodine
cause transient
decrease in T3,T4
levels
Severe dietary
deficiency of iodine
causes low levels
Pituitary tumor Raised estrogens
and progesterone
at puberty causes
raised TBGs
TSH release is
stimulated
TSH release is
stimulated
Raised levels of TSH TSH levels rise due
to decreased T3
&T4 (due to binding
with TBGs)
Increased TSH
causes T3 & T4 to
rise towards normal
and also goiter
T3 &T4 levels do
not rise despite rise
of TSH. This
results in
hypothyroid goiter
T3&T4 rise in
response to TSH.
The high levels of
TSH cause
hyperthyroid goiter
TSH release
causes goiter of
puberty
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25. THYROID HORMONE FUNCTIONS AND ABNORMALITIES
Thank You
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