Term
| What embryonic layer is the thyroid derived from? |
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Definition
The thyroid is derived from endoderm of the first and second branchial pouch, and descends through the tongue into the neck. Foramen cecum is the remnant of the thyroid at the base of the tongue, and the thyroglossal duct is the anatomic remnant of this migration. |
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Term
| T4 & T3 and derived from what amino acid? |
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Definition
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Term
| This is the biologically active form of Thyronine. |
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Definition
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Term
| What kind of enzymes add Iodine and what kind of enzymes remove it? |
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Definition
| Iodine is added by peroxidases; removed by de-iodinases or halogenases. |
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Term
| ______________ is an enormous, (660,000 Mr), thyroid-specific glycoprotein which serves as the tyrosine-containing substrate for iodination of tyrosine. |
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Definition
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Term
| After synthesis of thyroglobulin, there are 6 steps to thyroid hormone synthesis. What are they? |
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Definition
1. Iodide uptake. 2. Iodide export. 3. Oxidation of iodide to iodine. 4. Coupling. 5. Pioncytosis. 6. Dehalogination. |
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Term
| What is the key regulatory step of Thyroid hormone synthesis? |
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Definition
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Term
| How does uptake of iodide ion take place? |
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Definition
| Via sodium-iodide symporter on the basolateral side of thyrocytes. |
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Term
| Iodide is taken up at the basolateral membrane, transits the thyrocyte to the apical brush border membrane facing the colloid. It then must exit the cell into the colloid. How do thyrocytes accomplish that? |
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Definition
| This is accomplished by an iodide-chloride transporter named “pendrin.” |
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Term
| “Oxidation” of iodide to iodine is performed by____________. |
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Definition
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Term
| This binding of iodine to TG is called _________________. |
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Definition
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Term
| What does "Coupling" refer to during the process of thyroid hormone formation? |
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Definition
| “Coupling” refers to a still mysterious process in which TG folds upon itself allowing iodo-tyrosines in its N- and C-regions to come in contact, transferring the iodo-phenyl group of one tyrosine to the phenyl ring of another iodo-tyrosine within TG. |
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Term
| _____________is the active process through which colloid is engulfed by apical membrane pseudopods and internalized. This is followed by fusion with lysosomes and degradation of TG by proteases. |
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Definition
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Term
| _________ is the process through which the salvage enzyme “dehalogenase” cleaves iodine off of MIT and DIT and returns this to the thyroid iodine pool for re-incorparation into TG and long term storage. |
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Definition
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Term
| What feeds back on the secretion of TRH &TSH? |
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Definition
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Term
| What are the 2 major functions of TSH? |
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Definition
- TSH enters the systemic circulation and goes to the thyroid where it stimulates the thyroid to produce and secrete T4 and T3.
- In addition, over the long term, it stimulates the growth of the thyroid gland and leads to diffuse thyroid enlargement or “goiter”.
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Term
| What are the major steps of thyroid hormone synthesis that are directly regulated by TSH? |
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Definition
The major steps regulated by TSH are: - iodine uptake,
- organification and oxidation (one step), and
- pinocytosis/secretion of T4 and T3.
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Term
| What is the major secretory product of the Thyroid gland? |
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Definition
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Term
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Definition
| Peripheral conversion of T4 to T3 via hepatic deiodinases. |
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Term
True or False T3 and T4 are very hydrophobic and are bound to other carrier proteins most of the time. |
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Definition
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Term
| What are the 3 proteins mainly transporting T3 & T4 in the blood? |
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Definition
- Thyroxine-binding globulin (high affinity).
- Transthyretin (AKA pre-albumin, minor player).
- Albumin (low affinity, high capacity)
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Term
| What are some disorders that increase TBG (Thyroxine binding globulin) and therefore lead to abnormalities in total T4 and T3, but not necessarily, the real free, active T3? |
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Definition
| Hepatitis, estrogen treatment, birth control pills, pregnancy. |
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Term
| which disorders decrease TBG and albumin, which may lead to abnormalities in total T4 and T3, but not necessarily, the real free, active T3? |
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Definition
| hepatic cirrhosis, nephrotic syndrome, androgen use |
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Term
| Upon delivery to a cell by circulating binding proteins, T4 and T3 enter all cells of the body via a cell membrane T4 or T3 transporter named _______________. |
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Definition
| MCT8 (monocarboxylate transporter-8). |
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Term
True or False T3 passes thru the nuclear envelope and binds to specific thyroid hormone receptors (TRs) which are actually transcription factors and which therefore regulate the expression of genes. They are in the same superfamily of nuclear receptors as the steroid hormone receptors. There are at least two major TRs, alpha and beta, and there are subclasses of these. |
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Definition
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Term
| Many mammalian gene promoters contain thyroid hormone-response elements (TREs), and therefore T3 regulates the expression of a myriad of genes, most of which are not fully known or understood. Their concerted actions maintain homeostasis. |
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Definition
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Term
The following are signs of what? Adrenergic Metabolic Miscellaneous
Anxiety, nervousness Heat intolerance Myopathy
Tremor Wt loss despite increased appetite Oligo- or amenorrhea
Tachycardia Fever Psychosis
Perspiration
Oily skin
Wide pulse pressure
Hyperdefecation
Lid retraction hyperreflexia |
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Definition
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Term
The following are signs of what? Adrenergic Metabolic Miscellaneous
Tiredness, apathy Cold intolerance Myopathy
Bradycardia Wt gain despite decreased appetite Oligo- or amenorrhea
Dry skin Hypothermia psychosis
Constipation, ileus Myxedema
Hyporeflexia Periorbital edema
Low voltage on EKG Galactorrhea
Reduced myocardial contractility Hoarseness
Hypercholesterolemia
Hyponatremia
Pleural effusion, Ascites Pericardial effusion
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Definition
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