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Thyroid, straddles the trachea. Contain 2 cells: Follicular cells- thyroid…
Thyroid, straddles the trachea. Contain 2 cells: Follicular cells- thyroid hormones. Parafollicular C cells--produces calcitonin.
- Follicle cells produce thyroid hormones (T3 & T4), Follicular cell synthesizes thyroglobulin
- Follicle colloid stores thyroglobulin
- C cells produce calcitonin
Func: sets the heart’s tempo, produce muscles and bones to grow, determines how quickly the electrical impulses speeds along the nerves
Thyroid is thyronines, not protein
99%T3/T4 are protein bound. Only free T3/T4 are active (free T3 0.4%, T4 0.04%)
80% of T4 are converted into T3 or inactive T3 (rT3) (Competes for T3 receptor binding sites). (by liver/kidneys)
T3 is 3-8x more active than T4, less tightly bound to protein. greater affinity to target tissue receptors.
70% bound to thyroxine-binding globulin (TBG). 15% bound to thyroxine-binding prealbumin (TBPA), 15%bound to albumin
So, increase binding proteins -- decrease free thyroid hormone but increase total T3 & total T4
In pregnancy, estrogen increase TBG production in liver
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Hypothalamic （TRH）-Pituitary (TSH)-Thyroid (t3,t4)Axis (HPTA
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Hypothyroidism: lowered metabolism, edema and constipation. apathy. weight gain, fatigue,
cold intolerance
Hyperthyroidism: thyrotoxicosis: bulging eyes, tachycardia, tremors), weight loss, anxiety, Insomnia,perspiration
1 degree hypothyroidism (low T3,T4 + high TSH)
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Thyroid evalu. test; TSH, T4,T3, Thyroglobulin. Nuclear medicine
Nuclear medicine evalu.: Assessing metabolic activity of thyroid tissue and Assists in treatment of thyroid cancer. if radioactive iodine high uptake: metabolically active. Low uptake: not active. low TSH turns off I2 uptake . if Low TSH + high uptake thyroid acting alone(not responsive to HPTA) or have TSH surrogate. ex. Grave’s Disease:
Hypoythyroidism
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Secondary: pituitary gland dysfunction. TSH decrease. ex Sheehan’s syndrome aka postpartum hypopituitarism : hypovolemic shock during and after childbirth
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Severe Hypothyroidism in adults-- Myxedema - dermatological change (skin & tissue disorder) due to severe prolonged severe hypothyroidism. clinic: puffy face (swelling), swelling of skin, anemia, coma, crisis
treatment: Levothyroxine (T4) is treatment of choice. T½ = 7 days, so need to wait at least 5 half-lives before re-checking thyroid functions
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Calcitonin: Opposes action of parathyroid hormone. Reduces ca level. Inhibits osteoclast activity (Breakdown). Decrease ca reabsorption in kidneys- increase excretion
even though T3 ,T4 synthsis, still back thyrogloulin matrix until get TSH signals.
Painful thyroiditis: Characterized by: neck pain, low grade fever, myalgia, tender diffused goiter. by viral infections. Anti-TPO Ab usually absent; increase TG & RBC ESR
Euthyroid sick syndrome: decline in FT3 and TT3. normal/low TSH, low T3, low FT4.
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