2. Learning objectives:
• Understand the synthesis, factors controlling, release of thyroid
hormone
• Know what thyroid hormone does, as well as what happen if excess
or deficient levels
• Understand the role of iodine in thyroid hormone
• Know the basics of thyroid medications
3. General Information:
• One of the largest endocrine gland
• Butterfly shaped bi-lobed structure, weight 15-20gms.
• It not only synthesis, releases but also store
• Basic unit is follicle, surrounded by colloid (semifluid material).
• Colloid contains thyroglobulin (TGB), which is a high molecular weight
glycoprotein containing 115 tyrosine residues
• A few cells lie embedded between the follicles c/s parafollicular cells (C cells )
8. *Mechanism of action:
• Free form diffuse across the cell bind to intra cellular thyroid receptor.
• T3 bound to receptor change connformation, the co-repressor
complex is suppressed while co-activator complex is recruited.
• This stimulates transcription resulting in synthesis of proteins
produce many action
9. Know what thyroid hormone does, as well as what happen if excess or deficient levels:
(decrease mentioned, opposite excess)
Regulates growth (Growth retardation)
Regulates metabolic rate (dec BMI Body weight gain)
Increase cholesterol synthesis & cholesterol excretion into the bile
On GIT: Increase GI motility and secretion of gastric fluids (Constipation)
On CVS:
• Enhance tissue sensitivity to catecholamine
• Increase or decrease need for oxygen in the periphery leading to an increase or decrease
in cardiac output (Angina, Bradycardia, Cardiac failure)
10. CHO metabolism:
• Increase glycogenlysis & gluconeogenesis, Increase glucose absorption from GIT
• Enhance glycolysis – rapid uptake of glucose by the cell.
• Net effect increased blood glucose level
On fat metabolism:
• Increase mobilization of fat
• oxidation of FA increase FFA
On nervous system:
• Iodine is required for myelination of CNS neurons
• Excitable effect
• Has role on development of brain in fetal & 1st few weeks of postnatal life depend
on mother T3 and T4
Muscle weakness due to protein catabolism (Increased protein catabolism)
Know what thyroid hormone does, as well as what happen if excess or deficient levels:
(decrease mentioned opposite excess)
11. • Helps regulate temperature (low body temperature Cold
intolerance)
• Helps maintain & release of egg from ovum (Infertility)
Know what thyroid hormone does, as well as what happen if excess or deficient levels:
(decrease mentioned opposite excess)
12. Thyroid disorders:
Hypothyroidism
• Cretinism (in children)
• Myxoedema (in adult)
Hyperthyroidism
• Thyrotoxicosis
• Grave’s disease
Subclinical hypothyroidism: no symptom, only abnormality is an inc. TSH
13. HYPOTHYROIDISM: Resulting from deficiency of thyroid
• Primary hypothyroidism: Inability of thyroid gland itself produce T3 and T4
Causes:
• Autoimmune hypothyroidism (Hashimoto’s (scientist): thyroid gland is attacked by a variety of cell- and
antibody-mediated immune processes.
• Iatrogenic (I123 treatment, thyroidectomy, external irradiation of the neck)
• Drugs: iodine excess, lithium, antithyroid drugs Decrease iodine trapping
• Iodine deficiency
• Infiltrative disorders of the thyroid: amyloidosis, sarcoidosis, haemochromatosis
• Post thyroidectomy
• Secondary hypothyroidism: Hypothalamic or pituitary disease
14. Symptoms: General
• Goitre: Due inactivity compensatory mechanism enlarge
• Tiredness and weakness: Muscle weakness and fatigue
• Feeling cold: Dec body temperature and intolerance to cold
• Bradycardia: Due to weak muscle and dec sensitivity of catecholamine’s
• Angina: decrease cardiac output , Serous cavity effusions (pericardial )
• Constipation: Due decrease movement of intestine muscle
• Weight gain with poor appetite : Due decrease BMR
• Hoarse voice: Due enlargement it press voice box
• Anemia: Due to decxrease erythroposis
• Infertility: Due to decrease release of egg from ovum
• Difficulty in concentrating, psychosis and poor memory CNS
• Impaired hearing
• Puffy face, hands and feet (accumulation of interstitial fluid)
• Delayed tendon reflex relaxation
• Carpal tunnel syndrome : Feeling numbness, tingling, or weakness in hand due to compression of nerve
• Dry skin ( dec BMI, dec tissue activity)
• Galactorrhoea (elevated TSH)
15. LAB INVESTIGATIONS:
• TSH , free T4
• Anti thyroid antibodies – anti-TPO
• S-Cr.Kinase , s-Chol , s-Trigliseride
• Ultrasound of thyroid – little value
• Normochromic or macrocytic anemia
• ECG: Bradycardia with small QRS complexes
16. Basic thyroid evaluation (Nine square game)
TSH Normal Range 0.3 - 4.0 mU/L
Free T4 Normal Range 0.7-2.1 ng/dL
17. Hypothyroid Treatment: T4 why?
Cretinism:
• Due to failure of thyroid development or defect hormone synthesis or
due to extreme iodine deficiency
• ℞ Thyroxine (8-12µg/kg)
• should be started as early as possible, because mental retardation that has
already caused is only partially reversible
Adult thyroidism (Myxoedema):
• ℞ L- thyroxine 50 µg daily
• Change the dose according response
• Liotrix(4:1)
18. Myxoedema coma:
• It is an emergency characterised by progressive mental deterioration,
caries significant mortality.
• Emergency condition so direct T3 will produce fast good response
• ℞ Liothyronine 100 µg loading dose Followed by 25 µg every six hours
or
℞ L- thyroxine 200-500 µg IV followed by 100 µg Oral therapy daily
Hypothyroid Treatment: T3 why?
19. • Thyroid nodules:
• Certain benign function modules regress when TSH is suppressed by T4
• Papillary carcinoma of thyroid:
• Surgery is the definitive management of thyroid cancer.
• In non resectable cases full dose of T4 supress endogenous TSH production
and may induce temporary remission.
Hypothyroid Treatment:
20. Hyperthyroidism: Due to excessive secretion of thyroid hormone
Causes: Gravis disease and toxic nodular goiter
• Grave’s disease: An autoimmune disorder
• Most common type
• TSH stimulating antibodies in response to T3 and T4 over production
• Normal negative feedback mechanism ( false TSH action)
• T3 and T4, TSH R-Ab elevated while TSH low
Toxic uni or multinodular goiter: Autonomas toxic adenomas of thyroid
21. Hyper thyroidism Symptoms:
• Increased BMR
• Heat intolerance
• Tachycardia, Increased CO, cardiac arrhythmias
• Warm moist skin
• Weight loss (increased appetite)
• Diarrhoea,
• Skeletal muscle weakness with muscle wasting
• Insomnia, hyperreflexia, nervousness
• Hyperglycemia, fine tremors
• Menstrual irregularities
• In addition exopthalmos and dermopathy (peritibial myxoedema) are
characteristic features of Graves’ disease
23. Other : anti thyroid drugs
• In addition, certain drugs used in high doses for prolonged periods cause
hypothyroidism/goiter as a side effect:
• Sulfonamides, Para-aminosalicyhc acid: inhibit thyroglobulin iodination
and coupling reaction.
• Lithium: inhibits thyroid hormone release
• Amiodarone: inhibits peripheral conversion of T4 to T3; also interferes with
thyroid hormone action
• Phenobarbitone, phenytoin, carbamazepine, rifampin: induce metabolic
degradation of T4/T3
24. Inhibit iodide trapping: Thiocyanates, perchlorates, Nitrates
• Inhibit iodide trapping (Anion inhibitors): Competitive inhibitors of
NA/I symporter .
• They are toxic and not clinically used now.
• Thiocynates associated with liver, kidney, bone marrow and brain
toxicity.
• Perchlorates produce rashes, fever, aplastic anaemia, agranulocytosis
25. Thioamides:
• All drugs have a thiocarbamide group
• Act by inhibiting thyroid peroxidase enzyme. (Step 2,3,4 and PTU additional step 7)
• Perioxidation enzyme and DID I (PTU)
• Clinical improvement starts after 1-2 weeks or more (depending on hormone content
of thyroid gland).
26. Comparison
Propylthiouracil Carbimazole
Don’t cross placenta * Pregnancy Cross placenta
Protein binding 75% Protein binding less
Less potent More potent (*10 time grater that PTU)
No active metabolite Active metabolite (Methimazole)
Half-life 75min 4-6 hours
Peripheral T4- T3 conversion inhibitor No peripheral T4- T3 conversion inhibitor
Side effects higher ( less frequent but high
mortality) Fulminant hepatitis
Less ( Regular use)
Not secreted through the milk
28. Therapeutic Uses:
Grave’s disease:
• Remission may occur in up to half of the patients of grave’s disease after 1-2 years of
treatment.
• If symptoms recur –treatment is reinstituted.
• This is preferred in young patients with a short history of Graves' disease and a small
goiter.
Thyrotoxicosis: lifelong
Pre operatively:
• To make euthyroid & preparation of patient for surgical subtotal thyroidectomy
• *B blockers used to reduce catecholamine sensitivity induced by hyperthyroidism
Along with 131I:
• Initial control with anti-thyroid drug l to 2 weeks gap Radioiodine dosing of 131
I resume anti thyroid drug after 5-7 days gradually withdraw over 3 months as
the response to 131I develops..
29. Advantage:
• No surgical risk, scar or chances of injury to parathyroid glands or
recurrent laryngeal nerve.
• If hypothyroidism develops then therapy can be stopped normal
function
Side effect common: The most dangerous – agranulocytosis
(granulocyte count <500 cells/mm2)
30. Inhibit hormone release: Iodine
• These are fastest acting but short duration anti-thyroid drugs.
• Iodides are required for thyroid synthesis but at high concentration
limits its own transport (Step1)
• Endocytosis of the colloid and proteolysis of thyroglobulin [step 5]
inhibits release of T3 and T4:inhibited (thyroid constipating agents)
• Also attenuates TSH and cAMP induced thyroid stimulation.
• It makes the gland less vascular and more compact
Preparations and dose:
• Lugol’s iodine (5% iodine in 10% potassium iodide solution).
• Iodide (sodium/potassium): 100-300 mg/day (therapeutic), 5-10
mg/day (prophylactic) in endemic goiter.
31. Uses: preoperatively, thyroid storm, prophylaxis in endemic goiter,
antiseptic
ADRs: Acute reaction:
• Hypersensitivity reaction: Swelling of lips and eyelids, angiooedma of larynx,
fever, joint pain, petichial haemorrhage,
• thrombocytopenia, lymphadenopathy further exposure to iodine should
be stopped immediately.
Chronic overdose (Iodism):
• Major symptoms are inflammation of mucus membrane, increase in
secretions (salivation, lacrimation, rhinorrhoea), headache, rashes,
gastrointestinal distress.
• Flaring up of acne in adolescents
32. Radioactive Iodine
• 131I is the most commonly used radioactive iodine with half life of 8
days.
• Actively taken up by thyroid gland and stored in the colloid (as sodium
salt of 131I orally) emits x rays and β particles
• β particles can penetrate only 0.5-2 mm of the tissue and destroy
the gland from within.( undergo pyknosis, necrosis followed by
fibrosis)
Uses:
• Diagnostic: 25-100 u curie
• Therapeutic: average therapeutic dose 3-6 m curie response is
slow start after 2 weeks, gradually increases peak seen around 3
months repeat if necessary.
33. Advantages:
• Treatment with 131Is simple, conveniently given on outpatient basis and
inexpensive.
• No surgical risk, scar or injury to pararathyroid / recurrent laryngeal nerves.
• Once hyperthyroidism is controlled, cure is permanent
Disadvantages:
• If hypothyroidism develops it is permanent.
• Long latent period of response
• Contraindicated during pregnancy foetal thyroid will also destroyed
resulting in cretinism, other abnormalities if given during 1st trimester.
• Not suitable for young patients
34. Drugs useful in thyroid storm: 5Bs
• Block synthesis: PTU 200-300 mg oral 6 hrly
• Block conversion: PTU
• Block release: Iopanoic acid (0.5 to 1 g OD oral)
• Block entrohepatic circulation: Cholestramine
• Beta blockers : propranolol 1-2 mg iv followed by 60-80 mg oral.
• Rehydrarion, external cooling, anxiolytics, appropriate antibiotics are
the other measures
• Corticosteroids
Notas del editor
Infiltration is the diffusion or accumulation (in a tissue or cells) of foreign substances or in amounts in excess of the normal.
Amyloid is an abnormal protein that is produced in your bone marrow and can be deposited in any tissue or organ
Sarcoidosis is an inflammatory disease
Haemochromatosis: indicates accumulation of iron in the body from any cause.
nonthyroidal illness (NTI)
Regress: return to a former
A toxic thyroid nodule causes hyperthyroidism (an overactive thyroid). This occurs when a single nodule (or lump) grows on the thyroid gland causing it to become enlarged and produce excess thyroid hormones. If the increased hormone production is coming from a single nodule in the gland, this is called toxic adenoma.
Pyknosis, or karyopyknosis, is the irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis or apoptosis.