The thyroglossal tract arises form a median bud in the pharynx, it passes from foramen caecum at junction of anterior 2/3 and posterior 1/3 of the tongue and descend toward the root of the neck forming two lobes linked by isthmus. The fourth or fifth pharyngeal pouch gives rise to parafollicular cells ( C cell) which amalgamate with the lobes of the gland.
It is composed of 2 lobes linked by isthmus lying over the second, third and fourth tracheal rings. WT is about 20 to 25 gm. its heavier in female, its just visible in normal person.
The functioning unit is the lobule, which composed of follicles lined by cubical epithelium.
The T.G secretes 3 hormones: Thyroxin T4 Tri-iodothyronine T3 Calcitonin (regulates Ca and ph. Levels) An adequate supply of iodine is required for the synthesis of these hormones (100 microgram). The most common source is table salt and fish.
Functions of thyroid Hormones 1- Growth and development 2- Carbohydrate, protein and fat metabolism 3- Vitamin metabolism 4- Basal metabolic rate 5- Effect on the cardiovascular system 6- Increase oxygen consumption by the tissue 7- Increase oxygen release from Hb 8- Effect on muscle function 9- Increase oxidative phosphorylation 10- Induce hyperglycemia. 11- Augmentation of adrenalin and noradrenalin function
HYPOTHALAMUS
Thyrotropin releasing hormone (TRH)PITUITARY
Thyroid stimulating hormone (TSH)
THYROID GLAND
Secretes T4 (main hormone) and T3.
Metabolic demands Drugs Infection Surgery Trauma Low temperature Pit. disorders Age stress Sleep
-VE FEEDBACK MECHANISM
As blood concentrations of thyroid hormones increase, they inhibit both TSH and TRH, leading to "shutdown" of thyroid epithelial cells. Later, when blood levels of thyroid hormone have decayed, the negative feedback signal fades, and the system wakes up again.
T3 is four times more powerful than T4 T3 less adherent to the binding protein.(98% in comparison with 99.9% for T4) Half life of T3 is 3 days (8 to14 days for T4). All T4 change to T3 at the cellular level. The normal thyroid gland produces about 80% T4 and about 20% T3. Every cell in the body depends upon thyroid hormones for regulation of their metabolism.
A- Hormone measurement 1- Total T3 1.2 to 2.8 nmol\L 2- Total T4 150 nmol\L 3- TSH 0.5 to 5 mU\L B- Measurement of thyroid-pituitary-hypothalamic axis (TSH stimulation test, TRH stimulation test). C-Thyroid scanning: use of RAI131 then the gland is scanned to see its uptake. D- Biopsy (FNA ,Core biopsy, Incisional biopsy, excisional biopsy. E-Imaging study 1-Ultrasound 2-MRI 3- CT scan.
Due to either hypo- or hyper function of glandThey are the second most common endocrine disorder – mostly in woman
Congenital (Agenesis / Ectopic as lingual, supra or infrahyoid , mediastinal ) / persistent thyroglossal duct result in cyst or fistula Hypofunction (hypothyroidism) Hyperfunction (thyrotoxicosis) Thyroiditis. Thyroid gland neoplasm.
The enlargement may be diffuse, nodular, singular, functional or non-functional.
Hyperthyroidism Hypothyroidism Euthyroid (normal levels)
Failure of thyroid gland to produce adequate level of H. It is either 1- Congenital 2-Acquired ( primary or secondary) In adults called myxedema In children called cretinismA- Idiopathic (spontaneous) B- Autoimmune C- Thyroiditis C- Surgery (partial, sub-total or total ) D- Radioactive iodine E- Drugs (thiocyanate, propyl-thiouracil -PTU, lithium, phenylbutazone. F- Post- thyroiditis (Hashimotos) G- Iodine deficiency H- Secondary to pituitary gland failure. Treatment is replacement therapy (Levothyroxine)
Hypothyroidism
The commonest causes are Primary hyperthyroidism –toxic diffuse goiter - (Graves disease) Toxic nodular goiter Toxic solitary noduleHashimotos thyroiditis Jud-basedow syndrome (excessive iodine intake)Factitious Thyrotoxicosis (excessive thyroxin intake)Ectopic thyroid H secretion (teratoma)Thyroid carcinomaMalignancies with thyroid stimulatorsPitutary adenoma stimulating TSH (Thyroid - stimulating hormone)
THYROTOXICOSIS
IMPORTANT NOTE 1- Thyrotoxicosis may be confused with acute anxiety 2- In thyrotoxicosis, hands are sweaty and warm 3- In acute anxiety, palms are cold and clammy1-Anti-thyroid drugs Inhibit synthesis of thyroxin by interference with trapping, oxidation and coupling of iodide. Most commonly used drugs are carbimazole and propylthiouracil (PTU)
2- Radioactive iodine: I131 is commonest isotope used and the aim is to destroy the thyroid tissue. 3- Surgery : The aim is to remove the thyroid tissue by Subtotal thyroidectomy (Preserves about 4g (10%) of thyroid tissue). Patients must be euthyroid prior to operation
Detection of undiagnosed disease Symptoms Signs Referral Patient with diagnosed disease Determine original disease Past therapy Current medication Assessment of clinical status Referral if necessary
Prevent the occurrence of life threatening situations ( Myxedema coma or thyroid storm) Prevent the exacerbation of complications associated with them as cardiovascular diseases
Avoidance of the following in untreated or poorly treated patients: Surgical procedures Acute infection Epinephrine in local anesthetic solutions and gingival retraction cords
Patient under good medical treatment: Supine position Patient on PTU should be given stress management medications as diazepam, lorazepam For local anesthesia, use mepivicaine only If patient is off the anti-thyroid drug, THEN you can use lidocaine,prilocaine , bupivicaine (max= 2 carpules) Epinephrine concentration as low as possible (1:200.000) over (1:100.000) over (1:50.000) In block injections, aspiration before injection Implement normal procedures and management Avoid atropine since it may lead to increase in heart rate and precipitate a thyroid storm
Patient under good medical treatment Avoid acute infection Treat all chronic infections Patient on PTU causes agranulocytosis, thrombocytopenia and has an anti-vitamin k activity Always check the complete blood picture (CBC), platelet count , prothrombin time and NR (normalized ratio)
Thyroid storm Life-threatening exacerbation of thyrotoxicosis. Has a mortality of 50%. Precipitating factors Thyroid surgery, Radioiodine ,Withdrawal of antithyroid drugs, Acute illness (e.g. stroke, infection, trauma) Clinical features Severe thyrotoxicosis, fever, delirium ,seizure or coma, tachycardia, congestive heart disease, profuse sweating, .
Treatment ABC (BASIC LIFE SUPPORT) Patency of airway (Head tilt-chin lift) Assessment of breathing Administration of O2 ( 100% - FLOW RATE 10L/ MIN) Assessment of adequacy of circulation If available , establish an IV LINE for 5% dextrose and water or normal saline Wet or ice packs Medical assistance at once High antithyroid drugs, beta- blockers, 200-300mg hydrocortisone to prevent adrenal insufficiency Sedation, hydration and electrolyte balance
Detection of undiagnosed disease Symptoms Signs Referral Patient with diagnosed disease Determine original diagnosis Past therapy Current medication Assessment of clinical status Referral if necessary
Avoidance of the following in untreated or poorly treated patients Surgical procedures Acute infection CNS depressants (opioid analgesics, sedative hypnotics as barbiturates and other anianxiety drugs Administration of such drugs may become an overdose---- respiratory / or cardiovascular depression
Patient under good medical treatment: Avoid acute infection Implement normal procedures and management
An exacerbation of hypothyroid signs and symptomsUsually in old peopleSeek medical aidBasic life support measures (BLPM)Oxygen – 100%- flow rate 10L/Min)I.V or i.m Hydrocortisone (100-300mg) Myxedematous crisis:
Thyrotoxicosis Osteoporosis of alveolar bone Dental caries and PDD Teeth and jaw develop rapidly Premature loss of deciduous teeth Early eruption of permanent teeth Lingual thyroid
Hypothyroidism Infants with hypothyroidism may demonstrate thick lips, enlarged tongue, delayed eruption of teeth, malocclusion In adults there is macroglossia