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Briefly describe the hormones and factors involved in production of normal blood levels of the thyroid hormones T3 and T4.
the hypothalamus detects circulating blood levels of T4. when blood T4 levels drop low enough, the hypothalamus detects this and sends TRH (thyrotropin releasing hormone) to the pituitary gland. this causes the pituitary gland to release TSH (thyroid stimulating hormone) which stimulates the thyroid to produce T3 and T4 then T4 blood levels rise and the hypothalamus detects the rise in blood T4 levels, and stops sending out TRH (negative feedback).
What do thyroid hormones regulate in the body?
metabolic rate, growht and development, body temperature, heart rate, metabolism of nutrients, resistance to infection, etc.
List the 2 thyroid hormones and describe their main functions.
- T3 - tri-iodothyronine - the form that is active at the cellular level. causes the actual effects, do the actual regulating.
- T4 - tetra-iodothyronine - the form detected by the hypothalamus in the negative feedback loop. also is converted by different tissues to T3 as needed.
Do all tissues of the body need the same level of T3? What tissue has a high demand for T3?
no - needs vary between tissue. the CNS has a high demand for T3.
What is hypothyroidism?
lack of T3 and T4
Is hypothyroidism most common in dogs or in cats?
What are the clinical signs of hypothyroidism?
- weight gain with normal eating
- cold-intolerance - heat-seeking behavior
- dry hair coat and skin
What is the difference between primary, secondary, and tertiary hypothyroidism?
- primary: thyroid itself does not function
- secondary: piuitary problems - decreased TSH production
- tertiary: hypothalamus problem - lack of TRH
Once a patient is being treated for hypothyroidism, how long does he have to be treated?
for the rest of his life
What are the 3 categories of drugs used to treat hypothyroidism?
- thyroid extract
- synthetic levothyroxine (T4)
- synthetic liothyronine (T3)
What is thyroid extract, and why is it not used much to treat hypothyroidism?
ground - up animal thyroid glands. inconsistent quality, concentrations, and results
Which is better for treating hypothyroidism - T3 or T4? Why?
T4 - allows tissues to convert T4 to T3 as needed, less chance for T3 overdose. more natural, triggers negative feedback mechanism.
What is the drug of choice for treatment of hypothyroidism?
synthetic levothyroxine - T4. Synthroid, Soloxine, L-thyroxin etc.
Once a patient has been regulated on a certain bran of T4 thyroid supplement, it is OK to switch back and forth between brands. True or false? Why?
false - the patient may respond differently to the new brand, need to be re-regulated.
Name a synthetic liothyronine - T3 drug. Is it commonly used? Why or why not?
Cytobin. not commonly used - is T3, easier to overdose, needs to be administered more frequently, is expensive.
What is hyperthyroidism?
thyroid hormone levels are too high.
Is hyperthyroidsim most common in dogs or in cats?
What are the clinical signs of hyperthyroidism?
restlessness, hyperactive, diarrhea (due to increased GI motility), weight loss, voracious appetite, tachycardia, PU/PD.
What is a commone cause of hyperthyroidism?
functional thyroid tumors. functional means that the tumor cells are still capable of making thyroid hormone.
What are the 3 ways to treat hyperthyroidism?
- radioactive iodine
What is the best therapy for hyperthyroidism in cats?
surgery - thyroidectomy
What are some reasons not to do a thyroidectomy on a hyperthyroid cat?
poor body condition, expense. also amy be difficult to regulate blood calcium levels if a bilateral thyroidectomy is done, and the parathyroid glands are removed also
How does radioactive iodine work to treat thyroid tumors?
the radioactive iodine is concentrated in the thyroid gland at a high enough level to destroy it
Radioactive iodine therapy or thyroid tumors is effective. Why is it not as commonly done?
radioactivity is dangerous. need special facilities, period of isolation. is expensive
Drugs are not the therapy of choice for hyperthyroidism. When are drugs used?
when the owners cannot afford surgery or radioactive iodine treatment. or drugs may be used to get a debilitated patient into better shape to withstand surgery
What is the drug of choice for medical therapy of hyperthyroidism?
methimazole - Tapazole
How does methimazole - Tapazole work? If the patient does not receive surgery or radioactive iodine therapy, how long must methimazole be given?
prevents incorporation of iodine into T3 and T4 molecules - are non-functional. is given for the rest of the patient's life.
Does methimazole immediately cause improvement of clinical signs when it is first given to the patient?
no. existing, circulating bloo levels of T3 and T4 must be depleted first.
What are some side effects of methimazole therapy?
- skin eruptions
- liver problems
- bleeding disorders
- WBC count changes
What drug is sometimes given to hyperthyroid cats to slow down their heart rate?
propranolol - beta blocker
What is goiter? How is it treated?
enlarge thyroid gland due to lack of dietary idodine. no T4 causes hypothalamus release TRH which then causes the pituitary to release TSH this then tries to stimulate the thyroid to make T4 and causes and enlarged thyroid gland. treat by adding iodine to the diet.
Where in the body is insulin normally produced?
by the beta cells in the islets of Langerhans in the pancreas
What is the main function of insulin?
glucose metabolism and distribution. decreases blood glucose concentration by distributing glucose into tissues. move glucose from blood into cells, utilizing insulin receptors on cell membranes. also makes the liver stor glucose as glycogen. facilitates fat deposition. inhibits breakdown of fat, protein, and glycogen for energy.
What is diabetes mellitus (DM)?
a disease state characterized by high blood glucose levels and high urine glucose levels.
Briefly name the 2 types of diabetes mellitus.
- Type I diabetes - IDDM - insulin dependant diabetes mellitus.
- Type II diabetes - NIDDM - non-insulin dependent diabetes mellitus.
Describe Type I diabetes - IDDM.
lack of insulin - patient needs insulin injections. juvenile onset human form, most common form in dogs and cats
Describe Type II diabetes - NIDDM.
tissue is resistant to insulin. may be due to decareased numbers of insulin receptors, decreased senstitivity of insulin receptors, or decreased sensitivity of beta cells to hyperglycemia. adult onset human form. seen occasionally in cats, very rare in dogs. regulated by diet and oral hypoglycemic drugs.
Name an oral hypoglycemic drug.
glipizide - Glucotrol.
List the clinical signs of diabetes mellitus.
- weight loss
- diabetic ketoacidosis
Do we have to be concerned about drug interactions in a diabetic patient?
yes - look up cautions and interactions
By what routes is insulin administered?
by SQ injection for daily maintenance. may be given IV or IM for faster emergency regulation
Is insulin give PO? Why or why not?
no - insulin is a protein, will be broken down in the digestive tract into amino acids
How should insulin be stored?
in the refrigerator
Should insulin be mixed? If so, how?
yes - mix by rolling between the hands. because vigorous shaking can destroy the insulin molecules
In what forms is insulin available?
available as units per ml. U-100 and U-40 are available. be sure to use the syringe type that corresponds to the insulin concentration
What do you need to tell the owner of a diabetic patient?
- the owner needs to understand the disease
- how to store, mix and administer insulin
- how to monitor the patient's blood or uring glucose
- how much insulin to give
- how often to return to the vet office for rechecks
- to keep the injections, diet, and exercise regular
- to watch for hypoglycemia, etc.
How can a diabetic patient on insulin get hypoglycemia?
- insulin overdose
- lack of eating
- maybe increased exercise
What are the clinical signs of hypoglycemia?
What should the owner do if he diabetic pet on insulin shows clinical signs of hypoglycemia?
call his vet or emergency center immediately and follow their advice, bring the patient into the vet hospital immediately, may need to administer a little Karo syrup or something similar - rub small amounts inside cheek
What are the 3 types of insulin, classified according to origin?
- recombinant human insulin
Which origin insulin is best for dogs? Which is next best?
pork origin insulin is best, recombinant human origin is next best
How could a dissimilar insulin (beef insulin in a canine patient, for example) be a problem?
patient can develop antibodies to the forein sinsulin, interfering with the insulin, for more erratic results
What are the 3 types of insulin, classified according to duration of action?
- short acting
- intermediate acting
- long acting
List 2 examples of short-acting insulin.
regular (crystalline) insulin, Semilente insulin
Which insulin is u sed for initial treatment of diabetic ketoacidosis?
regular (crystalline) insulin
List 2 examples of intermediate acting insulin.
NPH (isophane) insulin, Lente insulin
Which insulin is the insulin of choice for treating uncomplicated diabetes?
NPH (isophane) insulin
List 2 examples of long acting insulin.
Ultralente, PZI - protamine zinc insulin