Endocrine > 2-3-16-Thyroid Gland (Lopez) > Flashcards

2-3-16-Thyroid Gland (Lopez) Flashcards

(53 cards)

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1
Q

Thyroid hormones are synthesized by ___ cells.

___ is composed of newly synthesized thyroid hormones attached to thyroglobulin

A

Follicular epithelial

Colloid (follicular lumen)

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2
Q

Peripheral conversion of T4 to T3 occurs through the action of __ enzyme

A

Deiodinase

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3
Q

There may be reduction in the conversion of T4 to T3 in what clinical states?

A
  • Fasting
  • Medical and surgical stress
  • Catabolic diseases
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4
Q

What are some factors that lead to an INCREASE in the conversion of T4 to T3?

A

Obesity
Cold exposure
Hyperthyroid

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5
Q

What are some factors that lead to a DECREASE in T4 to T3 conversion?

A 
Pregnancy
Fasting
Beta blockers
Hepatic and renal failure
Aging
Hypothyroid
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6
Q

Describe the “I- trap” on the basolateral membrane of the follicular epithelial cell

A

It is an I-/2Na+ co-transporter –> active transport

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7
Q

What compounds can inhibit the “I trap” (I-/2Na+ cotransporter)?

A

Perchlorate, thiocyanate

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8
Q

When the availability of iodide is restricted, the formation of __ is favored

A

T3

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9
Q

Deficiency of ___ mimics dietary I- deficiency

A

Intrathyroidal deiodinase

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10
Q

High levels of I- inhibit organification and synthesis of thyroid hormones. This is known as the ___ effect

A

Wolff-Chaikoff

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11
Q

___ is an effective treatment for hyperthyroidism and inhibits peroxidase

A

PTU (propylthiouracil)

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12
Q

99% of thyroid hormones in the bloodstream are ___

A

Bound to plasma proteins, the other 1% is free

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13
Q

The main binding protein of thyroid hormones is ____

A

Thyroxine-Binding protein (TBG) –> synthesized in the liver, binds 1 molecule of T3 or T4, has a higher affinity for T4 than T3

TTR (10-15%)
Albumin( 15-20%)

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14
Q

Circulating levels of TBG can be indirectly assessed with a ___ test

A

T3 resin uptake

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15
Q

Increased blood levels of T4 and increased blood levels of T3 resin uptake indicate ____

A

Hyperthyroidism

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16
Q

Decreased blood levels of T4 and decreased blood levels of T3 resin uptake indicate ____

A

Hypothyroidism

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17
Q

Increased blood levels of T4 and decreased blood levels of T3 resin uptake indicate ___

A

High TBG

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18
Q

Decreased blood levels of T4 and increased blood levels of T3 resin uptake indicate ___

A

Low TBG

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19
Q

Decreased levels of TBG and increased blood levels of T3 resin uptake indicate ___

A

Hepatic failure

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20
Q

Increased blood levels of TBG and decreased levels of T3 resin uptake indicate ____

A

Pregnancy

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21
Q

The major control of the synthesis and secretion of thyroid hormones is via the ___

A

HPT axis

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22
Q

TSH is regulated by:

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A

TRH and free T3

23
Q

___ is the 2nd messenger for TSH

24
Q

TSH has these 2 types of actions on the thyroid gland:

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A

Increase synthesis and secretion of thyroid hormones

Trophic effect on thyroid gland

25
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
26
What are some stimulatory factors affecting thyroid hormone secretion?
TSH Thyroid-stimulating Ig's Increased TBG levels (i.e., pregnancy)
27
What are some inhibitory factors affecting thyroid hormone secretion?
Iodide and/or deiodinase deficiency Excessive Iodide intake (wolff-chaikoff effect) Perchlorate, thiocyanate PTU Decreased TBG levels (i.e., liver disease)
28
T4 ----> T3 is done by this enzyme:
Iodinase
29
In most tissues, synthesis of the ___ is stimulated by thyroid hormones
Na/K ATPase
30
In cardiac muscle cells, ___ is synthesized under the direction of thyroid hormones
Myosin B1-adrenergic receptors Ca ATPase
31
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
32
Hyperthyroidism leads to a ___ BMR while hypothyroidism causes a ___ BMR
High Low
33
Plasma concentration of cholesterol and triglycerides are ___ correlated with thyroid hormones
Inversely There is an increase in blood cholesterol concentration in hypothyroidism
34
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
35
How do thyroid hormones affect carbohydrate metabolism?
Increased gluconeogenesis and glycogenolysis to generate free glucose Enhancement of insulin-dependent entry of glucose into cells
36
Thyroid hormones stimulate the synthesis of cardiac __ receptors
B1-adrenergic (Sympathetics --> Norepi --> B1 receptor --> Positive chronotropy and inotropy)
37
When thyroid hormone levels are high, the myocardium has an increased number of __ receptors and is more sensitive to stimulation by sympathetics
B1 adrenergic
38
Thyroid hormones act synergistically with ___ to promote bone formation
GH and somatomedins
39
What are some primary causes of hypothyroidism?
- Agenesis - 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)
40
What are secondary causes of hypothyroidism?
- Hypothalamic disease - Pituitary disease (Sheehan's syndrome) - Resistance to thyroid hormones
41
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)
Hashimoto's thyroiditis
42
___ 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
Cretinism
43
Untreated postnatal hypothyroidism results in ___
Cretinism
44
Primary hyperthyroidism is AKA ___ disease
Graves
45
The presence of ___ helps distinguish Graves disease from adenoma of pituitary thyrotrophs (a secondary endocrine disease)
Circulating thyroid-stimulating Ig's
46
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
47
Indicate the following levels relative to normal for Grave disease: A-TSH levels B-T3/T4 levels C-TSI D-Radioactive Iodine uptake test
A-Decrease B-increase C-Positive D-Increase
48
Indicate the following levels relative to normal for thyroiditis: A-TSH B-T3/T4 C-TSI D-Radioactive iodine uptake test
A-decrease B-increase C-negative D-decrease
49
Indicate the following levels relative to normal for thyroid nodules (hot or toxic): A-TSH B-T3/T4 C-TSI D-Radioactive iodine uptake test
A-decrease B-Increase C-negative D-Increase or norma
50
Indicate the following levels relative to normal for Hashimotos (early stage): A-TSH B-T3/T4 C-Antithyroid Ab
A-Increase B-Decrease or normal C-Positive
51
Indicate the following levels relative to normal for Hashimotos (late stage): A-TSH B-T3/T4 C-Antithyroid Ab
A-Increase B-decreased C-Positive
52
Indicate the following levels relative to normal for Pituitary abnormality (hypothyroidism): A-TSH B-T3/T4 C-Antithyroid Ab
A-Decrease B-decrease C-Negative
53
The ___ is the functional unit of the thyroid gland The thyroid gland contains __ cells that secrete calcitonin
thyroid follicle C cells or parafollicular cells
Endocrine
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