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What is the apical transport for Iodine
Pendrin
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Pendrin syndrome
- Absence of Pendrin used for transporting Iodine into the follicular cells for thyroid hormones
- It causes hearing problems and hypothyroidism
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What are the two essential ingredients to T3 and T4
Protein bound tyrosine and iodine
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Iodine trap
Active transport on the basal side of the follicular cells that transports Iodine and Na into the cell
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What are the ways that iodine can get into the follicular cells to make thyroid hormones
- Pendrin transport
- Iodine trap
- Break down of MIT and DIT
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What the 7 steps for making T3 and T4
- 1. ER in the Follicular cell makes Thyroglobulin then the Golgi glycosylates it
- 2. Thyroglobulin is exocytosed into the lumen colloid
- 3. Iodide is oxidized to Iodine by thyroperoxidase and binds to Thyroglobulin making MIT and DIT
- 4. Binding of DIT and MIT makes protein bound T3 and T4
- 5. Protein bound T3 and T4 are pinocytosed back into cell
- 6. Hormones and thyroglobulin are separated by lysosymes
- 7. MIT and DIT are recycled while T3 and T4 are released into blood stream
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Iodide is oxidized to Iodine by
Thyroperoxidase
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What lies between follicular cells
Tight junctions
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Thyroglobulin in the thyroid gland contains a supply of
Hormone sufficient for three months
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How do T3 and T4 compare
- T3 is 3-4 times more potent then T4
- Half life of T4 is 6 days
- Half life of T3 is 1.5 days
- 95% of released hormone is T4
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How much of T3 and T4 is bound to proteins in the blood
99%
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In large target tissues, what happens to the T4
Some is activated to T3 and some to reverse T3 (rT3)
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Most of the T3 in the system comes from
T4 broken down in tissues outside the thyroid gland
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What are the proteins that T3 an T4 are bound to in the blood stream
- Thyroxin binding protein (TBG) (80%)
- Transthyretin (10%)
- Albumin (10%)
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What happens if a patient has a lack of Thyroxin binding globulin (TBG)
The patient is normal, T3 and T4 will simply float around freely till it arrives at a target organ
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What benefit is the binding of the transport protein to T3 and T4
- It has a longer half life
- It can't be excreted while bound to a protein
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Transcortin
Protein transport and binding agent for glucocorticoids
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What is the binding protein for Estrogens and Androgens
Sex hormone binding globulin
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The biological action of a given hormone is proportional to
The level of unbound hormone in the blood, not the total hormone
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The pituitary gland in the negative feedback system only recognizes
Free Hormones
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Myxedema
- Hypothyroidism in adults
- - reduced metabolic rate
- - Subcutaneous edema (caused by excess hyaluronic acid)
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What are the two most common endocrine issues
Diabetes and Thyroid deficiency
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Hashimoto disease
Autoimmune disease in which the thyroid is gradually destroyed
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In what geographical areas are people more prone to hypothyroidism and less prone, why
- Prone in mountainous areas (lack of iodine)
- Less prone near sea (its packed with iodine)
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What are the signs of hyperthyroidism
- Increased metabolic rate
- Palpitations
- Restlessness
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What is it called when there is an enlargement of the thyroid gland
Goiter
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What kinds of problems cause goiter
- Iodine deficiency which causes a raise TSH levels
- Antibody stimulating the thyroid (Graves disease)
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Wolff-Chaikoff affect
High doses of iodine inhibit hormone release, used only for short term treatment
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What are some inorganic anions that inhibit iodine uptake into the thyroid gland
- Thiocyanate
- Nitrate
- Pertechnetate
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