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

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

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:

A

TRH and free T3

23
Q

___ is the 2nd messenger for TSH

A

Cyclic AMP

24
Q

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

A

Increase synthesis and secretion of thyroid hormones

Trophic effect on thyroid gland

25
Q

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?

A

TSH levels are lower than normal b/c the high circulating levels of thyroid hormones inhibits TSH secretion from anterior pituitary

26
Q

What are some stimulatory factors affecting thyroid hormone secretion?

A

TSH
Thyroid-stimulating Ig’s
Increased TBG levels (i.e., pregnancy)

27
Q

What are some inhibitory factors affecting thyroid hormone secretion?

A

Iodide and/or deiodinase deficiency
Excessive Iodide intake (wolff-chaikoff effect)
Perchlorate, thiocyanate
PTU
Decreased TBG levels (i.e., liver disease)

28
Q

T4 —-> T3 is done by this enzyme:

A

Iodinase

29
Q

In most tissues, synthesis of the ___ is stimulated by thyroid hormones

A

Na/K ATPase

30
Q

In cardiac muscle cells, ___ is synthesized under the direction of thyroid hormones

A

Myosin
B1-adrenergic receptors
Ca ATPase

31
Q

The increased activity of the ___ accounts for most of the increase in metabolic rate due to thyroid hormones

A

Na/K ATPase–> leads to O2 consumption and heat production

32
Q

Hyperthyroidism leads to a ___ BMR while hypothyroidism causes a ___ BMR

A

High

Low

33
Q

Plasma concentration of cholesterol and triglycerides are ___ correlated with thyroid hormones

A

Inversely

There is an increase in blood cholesterol concentration in hypothyroidism

34
Q

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:

A

Carotene –> Vitamin A

35
Q

How do thyroid hormones affect carbohydrate metabolism?

A

Increased gluconeogenesis and glycogenolysis to generate free glucose

Enhancement of insulin-dependent entry of glucose into cells

36
Q

Thyroid hormones stimulate the synthesis of cardiac __ receptors

A

B1-adrenergic (Sympathetics –> Norepi –> B1 receptor –> Positive chronotropy and inotropy)

37
Q

When thyroid hormone levels are high, the myocardium has an increased number of __ receptors and is more sensitive to stimulation by sympathetics

A

B1 adrenergic

38
Q

Thyroid hormones act synergistically with ___ to promote bone formation

A

GH and somatomedins

39
Q

What are some primary causes of hypothyroidism?

A
  • 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
Q

What are secondary causes of hypothyroidism?

A
  • Hypothalamic disease
  • Pituitary disease (Sheehan’s syndrome)
  • Resistance to thyroid hormones
41
Q

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)

A

Hashimoto’s thyroiditis

42
Q

___ 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

A

Cretinism

43
Q

Untreated postnatal hypothyroidism results in ___

A

Cretinism

44
Q

Primary hyperthyroidism is AKA ___ disease

A

Graves

45
Q

The presence of ___ helps distinguish Graves disease from adenoma of pituitary thyrotrophs (a secondary endocrine disease)

A

Circulating thyroid-stimulating Ig’s

46
Q

In Grave’s disease, TSH levels are ___

A

Decreased –> due to neg. feedback of T3 on anterior pituitary

If defect is in the anterior pituitary, TSH levels are increased

47
Q

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

A-Decrease
B-increase
C-Positive
D-Increase

48
Q

Indicate the following levels relative to normal for thyroiditis:

A-TSH
B-T3/T4
C-TSI
D-Radioactive iodine uptake test

A

A-decrease
B-increase
C-negative
D-decrease

49
Q

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

A-decrease
B-Increase
C-negative
D-Increase or norma

50
Q

Indicate the following levels relative to normal for Hashimotos (early stage):

A-TSH
B-T3/T4
C-Antithyroid Ab

A

A-Increase
B-Decrease or normal
C-Positive

51
Q

Indicate the following levels relative to normal for Hashimotos (late stage):

A-TSH
B-T3/T4
C-Antithyroid Ab

A

A-Increase
B-decreased
C-Positive

52
Q

Indicate the following levels relative to normal for Pituitary abnormality (hypothyroidism):

A-TSH
B-T3/T4
C-Antithyroid Ab

A

A-Decrease
B-decrease
C-Negative

53
Q

The ___ is the functional unit of the thyroid gland

The thyroid gland contains __ cells that secrete calcitonin

A

thyroid follicle

C cells or parafollicular cells

Endocrine (14 decks)

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