LEC 2 - Thyroid Hormones + Anti-Thyroid Hormones Flashcards
What are the two hormones that the thyroid release?
T4/T3
Calcitionin
What cells release T4/T3?
Follicle cells
What cells release calcitonin?
C Cells
What is the process by which T4/T3 get into the blood stream?
Iodine comes from blood via Na+ channel then pendrin
Thyroid peroxidase puts I- onto thyroglobulin
Carries T3/T4 into cytoplasm
Broken down by lysosome
What are the neuroendocrine effects of TH?
Increased sensitivity of SNS stimulation
Increased stimulation of all other endocrine organs
What are the cardiac effects of TH?
Increased CO
via HR + contractility + BP
What are the respiratory/metabolic effects of TH?
Increased O2 + energy consumption
Increased erythropoiesis leading to O2 delivery
What are the regulatory hormones of the thryoid?
TRH
– and –
TSH
Diagnostics: Hypothyroid
decreased T4
Increased TSH
Diagnostics: Hyperthyroid
Increased T4
Decreased TSH
What are the four effects of TSH?
Stimulate Iodine symport (NIS)
Activates thyroglobulin synthesis
Activates throid peroxidase
Stimulates lysosomal breakdown of Thyroglobulin
What are the signs a dog is hypothyroid?
Alopecia
Lethargy
Overall sad appearance
What are the four major reasons for hypothryoidism?
Lymphocytic thyroiditis
Congenital
Nutritional status/Underlying disease
Drug-induced
What drugs can induce hypothyroidism?
Trimehtoprim/sulfonamides
Glucocorticoids
Phenobarbital
Which of the drugs that cause hypothyroidism cause there to actually be clinical symptoms?
Trimethoprim/sulfonamides
What is the drug for hypothyroid?
Levothyroixine
How is levo absorped/given?
Orally
Bioavaliblity decreased with food
How is levo handled in the body?
Most bound to plasma protein
How is levo metabolized?
Hepativ
Glucoronnylation
Sulfation
Deamination
What are the contrindications for levo?
Thyrotoxicosis
Acute myocardial infarction
Untreated adrenal insufficency
What are the adverse side effects of levo?
Iatrogenic hyperthyroidism
erythema multiforme
What are the signs of hyperthryoid in a cat?
Weight loss with atrophy
PU/PD
Hyperactive
Can feel thyroid lobes
What can cause adenomatous hyperplasia of the thyroid?
Associated with altered signaling sensivity to TSH
High levels of dietary Iodine/soy may be the cause
When starting to treat a cat with hyperthyroid what is important to remember?
Unmasking CKD in older cats
Increased CO leads to better perfusion of the kidneys, therefor increased GFR
What are the signs of renal failure?
Increased:
Creatinine
BUN
What is the drug of choice for hyperthyroid? Where does it work?
Methimazole
Inhibits production of Thyroid peroxidase
Inhibits binding of T4/T3 to Thyroglobulin
How is methimazole given?
PO
or
Transdermally
What are the adverse effects of methimazole?
Unmasking CKD
Forming anti-nuclear bodies
Vomiting/Lethargy
Thrombocytopenia/Leukopenia
Hepatopathy
What should be done if you are seeing GI effects of methimazole?
Give transdermally
What is the rate at which methimazole works?
SLOW
takes 3 to 4 weeks to normalize T4 levels
How is I131 used?
Irreversible treatment of hyperthryoid
Destroys the cells but aren’t powerful enough to destroy C cells
