Flashcards in 2-3-16-Thyroid Gland (Lopez) Deck (53):
Thyroid hormones are synthesized by ___ cells.
___ is composed of newly synthesized thyroid hormones attached to thyroglobulin
Colloid (follicular lumen)
Peripheral conversion of T4 to T3 occurs through the action of __ enzyme
There may be reduction in the conversion of T4 to T3 in what clinical states?
-Medical and surgical stress
What are some factors that lead to an INCREASE in the conversion of T4 to T3?
What are some factors that lead to a DECREASE in T4 to T3 conversion?
Hepatic and renal failure
Describe the "I- trap" on the basolateral membrane of the follicular epithelial cell
It is an I-/2Na+ co-transporter --> active transport
What compounds can inhibit the "I trap" (I-/2Na+ cotransporter)?
When the availability of iodide is restricted, the formation of __ is favored
Deficiency of ___ mimics dietary I- deficiency
High levels of I- inhibit organification and synthesis of thyroid hormones. This is known as the ___ effect
___ is an effective treatment for hyperthyroidism and inhibits peroxidase
99% of thyroid hormones in the bloodstream are ___
Bound to plasma proteins, the other 1% is free
The main binding protein of thyroid hormones is ____
Thyroxine-Binding protein (TBG) --> synthesized in the liver, binds 1 molecule of T3 or T4, has a higher affinity for T4 than T3
Circulating levels of TBG can be indirectly assessed with a ___ test
T3 resin uptake
Increased blood levels of T4 and increased blood levels of T3 resin uptake indicate ____
Decreased blood levels of T4 and decreased blood levels of T3 resin uptake indicate ____
Increased blood levels of T4 and decreased blood levels of T3 resin uptake indicate ___
Decreased blood levels of T4 and increased blood levels of T3 resin uptake indicate ___
Decreased levels of TBG and increased blood levels of T3 resin uptake indicate ___
Increased blood levels of TBG and decreased levels of T3 resin uptake indicate ____
The major control of the synthesis and secretion of thyroid hormones is via the ___
TSH is regulated by:
TRH and free T3
___ is the 2nd messenger for TSH
TSH has these 2 types of actions on the thyroid gland:
Increase synthesis and secretion of thyroid hormones
Trophic effect on thyroid gland
In graves disease, thyroid-stimulated immunoglobulins bind to TSH receptors resulting in unregulated overproduction of thyroid hormones. Why are TSH levels lower than normal in this scenario?
TSH levels are lower than normal b/c the high circulating levels of thyroid hormones inhibits TSH secretion from anterior pituitary
What are some stimulatory factors affecting thyroid hormone secretion?
Increased TBG levels (i.e., pregnancy)
What are some inhibitory factors affecting thyroid hormone secretion?
Iodide and/or deiodinase deficiency
Excessive Iodide intake (wolff-chaikoff effect)
Decreased TBG levels (i.e., liver disease)
T4 ----> T3 is done by this enzyme:
In most tissues, synthesis of the ___ is stimulated by thyroid hormones
In cardiac muscle cells, ___ is synthesized under the direction of thyroid hormones
The increased activity of the ___ accounts for most of the increase in metabolic rate due to thyroid hormones
Na/K ATPase--> leads to O2 consumption and heat production
Hyperthyroidism leads to a ___ BMR while hypothyroidism causes a ___ BMR
Plasma concentration of cholesterol and triglycerides are ___ correlated with thyroid hormones
There is an increase in blood cholesterol concentration in hypothyroidism
Hypothyroid patients can suffer from blindness and yellowing of the skin due to the lack of thyroid hormones not being able to do this specific conversion:
Carotene --> Vitamin A
How do thyroid hormones affect carbohydrate metabolism?
Increased gluconeogenesis and glycogenolysis to generate free glucose
Enhancement of insulin-dependent entry of glucose into cells
Thyroid hormones stimulate the synthesis of cardiac __ receptors
B1-adrenergic (Sympathetics --> Norepi --> B1 receptor --> Positive chronotropy and inotropy)
When thyroid hormone levels are high, the myocardium has an increased number of __ receptors and is more sensitive to stimulation by sympathetics
Thyroid hormones act synergistically with ___ to promote bone formation
GH and somatomedins
What are some primary causes of hypothyroidism?
-Gland destruction (surgical removal, irradiation, autoimmune disease, idiopathic atrophy) --> Hashimoto's disease
-Inhibition of thyroid hormone synthesis and release (iodine deficiency , inherited enzyme defects, drugs that interfere with thyroid homeostasis)
-Transient (after surgery or therapeutic radioiodine, postpartum, thyroiditis)
What are secondary causes of hypothyroidism?
-Pituitary disease (Sheehan's syndrome)
-Resistance to thyroid hormones
In ___, thyroid hormone synthesis is impaired by thyroglobulin or TPO Abs, which leads to decreased T3 and T4 secretion. TSH levels are high and there is a trophic effect (goiter)
___ is caused by impaired development of the thyroid gland, maternal intake of anti-thyroid medication or excess Iodine, and/or and inherent deficit in the synthesis of thyroid hormones. Symptoms include: feeding problems, resp. Difficulty, protruding tongue, growth and mental retardation, jaundice, dry skin, hypotonia
Untreated postnatal hypothyroidism results in ___
Primary hyperthyroidism is AKA ___ disease
The presence of ___ helps distinguish Graves disease from adenoma of pituitary thyrotrophs (a secondary endocrine disease)
Circulating thyroid-stimulating Ig's
In Grave's disease, TSH levels are ___
Decreased --> due to neg. feedback of T3 on anterior pituitary
If defect is in the anterior pituitary, TSH levels are increased
Indicate the following levels relative to normal for Grave disease:
D-Radioactive Iodine uptake test
Indicate the following levels relative to normal for thyroiditis:
D-Radioactive iodine uptake test
Indicate the following levels relative to normal for thyroid nodules (hot or toxic):
D-Radioactive iodine uptake test
D-Increase or norma
Indicate the following levels relative to normal for Hashimotos (early stage):
B-Decrease or normal
Indicate the following levels relative to normal for Hashimotos (late stage):
Indicate the following levels relative to normal for Pituitary abnormality (hypothyroidism):