Thyroid hormones Structures of the major circulating thyroid hormones Dynamics of Thyroid Hormone Production Thyroid hormone metabolism Type1 (D1) Type2 (D2) Type3 (D3) 5’-deiodinase I 5’-deiodinase II 5-deiodinase
certain beta blockerscorticosteroids starvation, amiodarone
All family members contain the novel amino acid selenocysteine (SeC) in their catalytic center. The Hypothalamic-Pitutary Gland- Thyroid Gland Axis The Effects of TSH Ca2+ + PLC Immediate effects Long term effects (trophic effects) Hormone synthesis
Endocythosis of colloidProteolysis of thyreoglobulinGlucose oxidationNADPH generation
Circadian rhythm: peak serum TSH at night, usually between 0.00 and 4.00 AM
Antithyroid Drugs II. Block of organic binding of iodineIV. The effect of large doses of iodidesV. Naturally occurring thyroid inhibitorEffects of Antith n and Coupling thiocarbamides methimazole propylthiouracil lithium ion Alteration of iodide trapping chlorate perchlorate pertechnetate periodate biiodate nitrate propylthiouracil thyocyanate acids dinitrotyro T propylthiouracil Antithyroid Drugs IV Wolff-Chaikoff effect
Increasing doses of Iodine increase hormone synthesis initially
Large dose of Iodide inhibits the hormone production.
– inhibits the organic binding of iodide
– inhibits proteolysis of thyroglobulin
– decreases the vascularity of the hyperplastic gland
– this inhibitory effect can be explained by the down-regulation of the
Antithyroid Drugs II. Block of organic binding of iodineIV. The effect of large doses of iodidesV. Naturally occurring thyroid inhibitor
- Thiocyanates are sometimes ingested with food
- It occurs as progoitrin in vegetables of Brassicaceae family
(cabbage, turnips, kale, kohlrabi, rutabaga)
- there are progoitrin activators in the intestine
- Goitrin intake on a normal mixed diet is usually not harmful
Mechanism of Thyroid Hormone Action I
- T3 and T4 enter target cells by carrier mediated energy-dependent, Na+ coupled transport
- Unliganded high-affinity nuclear T3 receptors are bound to
The receptor function requires zinc ions.
- Because thyroid hormones act trough gene transcription the
hormone effects become evident several hours later and lasts more days.
- Elevated serum thyroid hormone level and fasting decrease the number and
binding capacity of thyroid hormone receptors. Mechanism of Thyroid Hormone Action II
- increase the number of “pump units”
- stimulate oxygen consumption (except in brain)
- increase the basal metabolic rate (calorigenic action)
except in brain, gonads and spleen (low concentration of T receptors)
Effects on intermediary metabolism Carbohydrate metabolism blood glucose level is slightly increased Lipid metabolism Protein metabolism
- low doses of thyroid hormone stimulate protein synthesis- large doses of thyroid hormone accelerate protein catabolism
Effects of Thyroid hormones Thermoregulation
- extra heat production- slight rise in body temperature- activation of heat dissipating mechanisms (sweating, cutaneous vasodilation)
Effects on cardiovascular system
- ↑ number of βAR- ↑ heart rate- ↑ force of contraction- ↑ stroke volume- ↑ cardiac output- ↑ P
Effects on respiration Effects of Thyroid hormones Effects on blood
- Increased production of erythropoietin- The need for all vitamin is increased due to the increased
Effects on the nervous system
- Thyroid transport across the blood-brain barrier- Thyroid hormone excess causes rapid mentation,
- reaction time of stretch reflexes shortened
Effects on skeletal muscle
- large doses of thyroid hormone causes myopathy
Effects on the gonads
- to the normal process of sperm production- to the ovarian cycle of follicular development- to the maintenance of healthy pregnancy
Effects of Thyroid hormones
- thyroid hormones promote skeletal maturation
cartilage ossification, maturation of epiphyses
- thyroid hormones change the process of bone remodelling
Effects on growth and development
- it requires the presence of thyroid hormone, GH and insulin
- thyroid hormone potentiates the effects of GH on the tissues- thyroid hormone stimulates linear growth and maturation of bone
- growth of cerebral and cerebellar cortex - proliferation of axons- branching of dendrites- myelinization
Alteration of thyroid gland functionThyroid gland enlargement (goiter)
- dietary deficiency of Iodide- thyroiditis- excess Iodide- malignancy
Thyroid Hormone Deficiency In infancy - cretenism, mental and growth retardation - dwarfism, limbs are disproportionately short compared
- neurologic signs of pyramidal and extrapyramidal tract
In childhood - less prominent mental retardation - impairment of linear growth - child who appears younger than his or her chronological age - epiphyseal development is delayed Thyroid Hormone Deficiency
nonspecific symptoms and signs appear over month or years-cold intolerance- hair loss, -dry, coarse skin
accumulation of mucopolisacharids in subcutaneous tissues
- delayed muscle contraction and relaxation
- SV and heart rate are reduced - altered mental function
impaired memory, slow speech, decreased initiative, somnolencelethargy
Thyroid Hormone Excess
nervousnessirritabilityemotional instability
- weight loss despite normal or increased food intake
- heat intolerance, increased sweting, increased ventillation
, tachycardia, atrial arrhythmias may develop
- fatigue, muscle weakness, osteoporosis
- women have decreased or absent menstrual flow
Measurement of TSH level "Full thyroid function tests" Measurement of total T4 levels Measurement of antithyroglobulin antibodies TRH stimulation test
Year 2 OSCE 2013 Station 16 Candidate Instructions Clinical scenario You are a junior doctor at a general practice. Mr Tate, aged 56 has atrial fibril ation. He was started on warfarin 12 months ago and needs a sample of venous blood to be taken to check his INR. Task In a total of five minutes: • briefly explain the procedure to him [Mr Tate’s left arm wil be
Manual do Paciente A proposta deste texto é fornecer orientação a pessoas que desejam algum tipo de cirurgia plástica. Embora a maioria das respostas esteja incluída nestes textos, qualquer dúvida em relação ao tratamento deve ser discutida com o médico escolhido, pois o sucesso do tratamento depende da comunicação adequada e cooperação entre o paciente e a equipe médica. Af