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13 Cards in this Set

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Describe the hypothalamic-pituitary-thyroid axis.
The H-P-T refers to communication pathways b/t the hypothalamus, anterior pituitary, and thyroid gland. It is comprised not only the direct stimulatory b/t these tissues, but the (-) feedback loops as well.
List all chemicals released and the Feedback mechanisms operating in the hypothalamic-pituitary-thyroid axis scheme.
- TRH (thyrotropin releasing hormone)

- TSH (thyroid stimulating hormone)

- T3 (Triiodothyroninie)

- T4 (Thyroxine or Tetraiodothyronine)Negative feedback
List the systemic effects of thyroid hormone on the body.
– increases in cardiac output, heart rate, stroke volume

– increase in respiratory rate

– increase in RBC count

– promotes normal growth

– promotes development and maturation of the nervous system
Describe the action of PTU and its effects on the thyroid gland and on the target cells.
PTU reduces both the production of thyroid hormone at the thyroid gland and the effectiveness of T3 and T4 at the target tissues.Physiological Effects of PTU:

- Inside the thyroid follicle cells: PTU prevents the synthesis of T4 and T3 (inhibits oxidation of I and coupling of MIT and DIT)

- Peripherally in target cells, PTU interferes with the conversion of T4 to T3 in the cells (specifically inhibits 5’ deiodinase)
Describe the process of T3 and T4 production in the thyroid gland
1. tyrosine-containing thyroglobulin is exported from the follicular cells into the colloid by exocytosis.

2. Thyroid captures iodine form the blood.

3. Iodine is quickly attached to a tyrosine. (1 iodine + 1 tyrosine = MIT monoiodothyrosine; 2 iodine + 1 tyrosine = DIT di-iodotyrosine.

4. Coupling process b/t iodinated tyrosine molecule to form the thyroid hormones. 1 MIT + 1 DIT = T3 ( tri-iodothryonine); 1 DIT + 1 DIT = T4 (tyroxine)
Compare and contrast hyperthyroid, hypothyroid, and euthyroid mice.
Hyper:• cannot tolerate warm temperatures (faster BMR/heat production) •often lose weight •highly responsive to external stimuli (often to the point of extreme nervousness)

Hypo: • cannot tolerate cold temperatures (slower BMR/heat production) •often gain weight -mentally and physically sluggish

Eu: normal, used as a control
Describe how each mouse was induced in lab and the general characteristics of each.
Hyper: thyroxine in food
Hypo: PTU in water
Explain the results attained with the different experimentalmouse groups concerning oxygen consumption, weight gain, and metabolic rate.
Calculate the “% change” from “pre-treatment” and “post-treatment” data.
Post - pre / pre *100
What are the primary effects of thyroid hormones?
• Primary effect is stimulation of calorigenesis (heat production) in the body

– causes increases in catabolism and anabolism of proteins, lipids, and carbohydrates

– response is reflected by an increase in oxygen consumption in most tissues (except the brain, spleen, and testes)
What is the most common disease of hyperthyroidism and its causes?
Graves disease It is an abnormality of the immune system which produces antibodies that recognize and bind onto the TSH sites of the thyroid cells, stimulating the TSH receptors causing an increase in thyroid hormone production.
What is the most common disease of hypothyroidism and its causes?
In most cases hypothyroidism results from a defect in the thyroid gland itself. Most instances of hypothyroidism are from an autoimmune condition where antibodies are directed against the thyroid gland, destroying the gland.
What is a goiter and what is it caused from?
In the absence of iodide , thyroid hormones cannot be produced. Therefore, negative feedback effects are absent. This allows for continual release of TRH and TSH thus the growth promoting effects of TSH causing the glad to grow in size.