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18 Cards in this Set
- Front
- Back
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What does the thyroid make?
Diff bw Active and Inactive thyroid on histo? |
Follicular cells - Thyroid Hormone
C-cells - Calcitonin Active - Cuboidal, less colloid Inactive - flattened, more colloid |
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How is Thyroid Hormone synthesized?
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Dietary Iodine --> follicular cells --> colloid, binds thyroglobulin --(thyroid peroxidae)--> T3/T4 --> follicular cells --> bloodstream (99% bound to plasma proteins - FREE 1% is physio Active)
(T3>T4... T4 is deiodinated to become T3) |
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What suppresses TRH?
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T3, T4, and Glucocorticoids
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Hyperthyroidism
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Common in Cats
Adenomatous hyperplasia - functional Adenomas - functional or nonfunctional (Carcinoma in dogs, rare, and usually nonfunctional) Elevated T3/T4 Weight loss, nervous, tachycardic, weak Cardiomegaly -> arrythmia -> saddle thrombi and death |
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Hypercalcitonism
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RARE
(most in Bulls - some in human, rat, dog) Can occur in Aged Bulls with a Calcium-Rich Diet |
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Hypothyroidism (2 main types)?
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Most common Endocrinopathy of DOG
1. Idiopathic Atrophy - may be 10% normal size, glandular tissue replaced by fat and CT... may be end stage of #2 below. 2. Lymphocytic Thyroiditis = immune-mediated, gland infiltrated by lymphocytes, Mphages, plasma cells Clinical Signs not until 75% destroyed Genetic Component in Beau's |
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Clinical Signs of Hypothyroidism
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Slow Metabolism --> Lethargy, exercise intolerance, heat seeking, dull, weight gain, slow pulse, Anemia, Hypercholesterolemia
Derm --> scaling, "rat tail", myxedema (xs gags) causing "tragic face", pyoderma |
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Goiter
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Bilateral enlargement of thyroid due to NON-neoplastic and NON-inflammatory causes
Impaired synth of thyroid hormone -> low T3/T4 -> inc.TSH -> Hyperplasia and Hypertrophy (can cause Euthyroid or Hypothyroid state) |
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Causes of Goiter
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1. Iodine Def.
2. Ingest Goitrogenics (Bassica - cabbage, cauliflower, brussel sprouts) 3. xs Dietary Iodine (rare) 4. Hereditary dfx in enzymes/thyroglobulin -> no synth of T3/T4 -> inc.TSH |
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Other Thyroid Conditions
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1. Neoplasia
a. Carcinoma (some in Dog, rare in cat) - invasive, metastasize to lung b. Adenoma (common in old horses) 2. Cysts - common in Dog - incidental |
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Composition of the Parathyroid Glands?
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ONE cell type - Chief Cells
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What contributes to Calcium Homeostasis?
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1. PTH from Chief cells
Bone - inc. resorption Kidney - inc. Ca resorb, dec. P resorb, inc. VitD GI - inc Ca absorb 2. Calcitonin from C-cells inhibits bone resorb 3. Cholecalciferol (VitD) ProD3 (skin) + UV = D3 --> 25D3 (Liver) --> 1,25D3 (Kidney) |
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Primary Hyperparathyroidism
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Fnxnl Parathyroid Adenoma in Aged Dogs (uncommon)
anorexic, weak, high PTH can Ca, thick mandible, loose teeth |
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Secondary Hyperparathyroidism
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Chronic Renal Dz
low GFR -> low P excretion -> hyperphosphatemia -> lowers serum Ca -> PTH -> bone release of Ca PU/PD, dehydrate, vomit, FOD - rubber jaw |
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Nutritional Hyperparathyroidism
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see bone notes... lame
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Pseudohyperparathyroidism
(hypercalcemia of malignancy) |
Tumors that make PTHrP -- causes PTH levels to drop and atrophy of the parathyroid gland
Lymphosarcoma (esp dogs) Apocrine gland adenocarcinma of the anal sac (older female dogs) |
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Name 2 other forms of pseudohyperparathyroidism
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Bone related:
Malignant tumor growing in bone -> bone resportion Malignant neoplams metastasizing to bone -> bone resportion *both through prodxn of PGs and Cytokines leading to tissue destrxn |
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Hypofunction of Parathyroid
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Iatrogenic and/or Idiopathic
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