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Endocrine - MSI Spring > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

The size of the epithelial cells and amount of colloid change with what?

A

activity

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2
Q

What are C cells?

A

contained in thyroid follicle

Parafollicular cells that secrete calcitonin

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3
Q

What is colloid composed of ?

A

newly synthesized thyroid hormones attached to thyroglobulin

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4
Q

What is the outermost part of the follicle?

A

basal lamina

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5
Q

What are the secretory products of the thyroid gland?

A

iodothyronines

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6
Q

How much of circulating T3 comes from direct secretion from thyroid gland ?

A

10-20%

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7
Q

What does the peripheral conversion of T4 to T3 ?

A

Deiodinase
80-90% produced this way
Provides circulating T3 for uptake by other tissues in which T3 supply is too low

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8
Q

What are the clinical states associated with a reduction in the conversion of T4 into T3?

A 
Fasting
Medical and surgical stress
Catabolic diseases 
Pregnancy
Beta-blockers
Hepatic and renal failure
Aging
Hypothyroid
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9
Q

What are factors affecting the conversion of T4 to T3?

A

Obesity
Cold exposure
Hyperthyroid

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10
Q

Deficiency of ________ mimics dietary I- deficiency

A

Deiodinase

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11
Q

When the availability of iodide is restricted the formation of _____ is favored

A

T3

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12
Q

What is an effective treatment for hyperthyrodism?

A

PTU

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13
Q

What is Wolff-chaikoff effect?

A

High levels of I- inhibit organification and synthesis of thyroid hormones

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14
Q

How is iodine stored?

A

iodinated as tyrosines of thyroglobulin

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15
Q

Enough hormones is stored as iodinated TG in the follicular colloid to last the body for ________

A

2-3 months

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16
Q

The activity of the thyroid gland can be assessed by what?

A

radioactive iodine uptake

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17
Q

What disease is an example of Extreme stimulation of thyroid gland with high turnover of I

A

Graves’ disease - associated thyrotoxicosis

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18
Q

Describe TBG

A

synthesized in the liver
Binds 1 molecule of T3 or T4
Has higher affinity for T4 than T3
Binds 70% of thyroid hormones

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19
Q

What can circulating levels of TBG be indirectly assessed with?

A 
T3 resin uptake test
TBG w bound T4 from serum
Unbound T3 added
Anti T3 antibody added - free T3 precipitates 
Bound T3 remains in solution
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20
Q

Describe levels of T4 and T3 resin uptake in hyperthyroidism in T3 resin uptake test

A

High T4

High T3 resin uptake

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21
Q

Describe levels of T4 and T3 resin uptake in hypothyroidism in T3 resin uptake test

A

Decreased T4

Decreased T3 resin uptake

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22
Q

Describe levels of T4 and T3 resin uptake in High TBG patients in T3 resin uptake test

A

High T4

Low T3 resin uptake

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23
Q

Describe levels of T4 and T3 resin uptake in Low TBG patients in T3 resin uptake test

A

Low T4

High T3 resin uptake

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24
Q

Describe levels of T4 and T3 resin uptake in heptaic failure pt in T3 resin uptake test

A

Low TBG

High T3 resin uptake

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25
Q

Describe levels of T4 and T3 resin uptake in pregnant pt in T3 resin uptake test

A

Increase TBG

Low T3 resin uptake

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26
Q

Describe the levels of TGB in blood in hepatic failure pt. What will result?

A

Decreased blood levels of TBG
Transient increase in the level of free T3, T4
Followed by inhibition of synthesis of T3, T4 - negative feedback

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27
Q

Describe the levels of TGB in blood in pregnant pt. What will result?

A

Increased levels of TBG
Increased bound T3, T4
Decreased free T3, T4
The transient decrease in free T3, T4 causes an increase in synthesis and secretion of T3, T4
Increase total levels of T3 and T4 but levels of free, physiologically active hormones are normal

*clinically euthyroid

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28
Q

What is the major control of the synthesis and secretion of thyroid hormones ?

A

via the HPT axis

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29
Q

What is the role of TSH?

A

regulate the growth of thyroid gland (trophic effect)

The secretion of thyroid hormones

30
Q

TSH is regulated by what?

A

Thyrotropin-releasing hormone (TRH)

Free T3

31
Q

Does TSH secretion occur at an unsteady rate?

A

No, unlike GH secretion, it occurs at a steady rate

32
Q

What is the second messenger for TSH ?

A

cAMP

33
Q

What are the two types of actions of the thyroid gland by TSH?

A

Increases the synthesis and secretion of thyroid hormones

Trophic effect on thyroid gland

34
Q

Describe the levels of TSH in Graves’ disease

A

Levels are lower than lower bc the high circulating levels of thyroid hormones inhibits TSH secretion

Thyroid-stimulating immunoglobulins stimulate TSH receptor causing overproduction of thyroid hormones

35
Q

What are the stimulatory factors of thyroid hormone secretion ?

A

TSH
Thyroid-stimulating immunoglobulins
Increased TBG levels (pregnancy)

36
Q

What are the inhibitory factors of thyroid hormone secretion?

A 
iodide deficiency 
Deiodinase deficiency
Excessive iodide intake (wolff-chaikoff effect)
Perchlorate, thiocyanate
Propylthiouracil (PTU)
Decreased TBG levels
37
Q

What proteins are synthesized under the direction of thyroid hormones ?

A 
Na/K ATPase: in most tissues
Transport proteins
B1-adrenergic receptors, Mysoin, Ca ATPase in cardiac m
Lysosomal enzymes
Proteolytic proteins
Structural proteins
38
Q

What role do thyroid hormones have in Growth and CNS?

A

Growth formation
Bone maturation
Maturation of CNS

39
Q

What roles do thyroid hormones have in BMR and Cardiovascular?

A

Increase in Na/K ATPase, O2 consumption, Heat production and BMR

Increase in cardiac output by increasing thermogenesis->decrease peripheral vascular resistance -> decrease diastolic BP-> renin-angio-aldos->increase preload
and decrease afterload

40
Q

What roles do thyroid hormones have in metabolism?

A

Increase glucose absorption, glycogenolysis, gluconeogenesis, lipolysis, lipogenesis, insulin resistance, protein synthesis and degradation (net catabolic), bile acid synthesis

41
Q

What does the increased activity of Na/K ATPase accout for ?

A

most of the increase in metabolic rate

Leads to increase consumption and heat production

42
Q

The increase in BMR produced by a single dose of thyroxine (T4) occurs after ________ but is long lasting for _____

A

several hours

> or equal to 6 hr

43
Q

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

A

high

Low

44
Q

What role do thyroid hormones play in lipid metabolism?

A

stimulate fat mobilization -> increased concentration of Fa in plasma
Enhance oxidation of FA
Fequired for conversion of carotene to vitamin A

45
Q

Plasma concentration of cholesterol and TGs are ______ correlated with thyroid hormones

A

inversely

Increase in blood cholesterol concentration in hypothyroidism

46
Q

Hypothyroid patients can suffer from what symptoms due to low Vit A?

A

Blindness and yellowing of the skin

47
Q

What role do thyroid hormones play in carbohydrate metabolism?

A

Increased gluconeogenesis and glycogenolysis to generate free glucose
Enhancement of insulin-dependent entry of glucose into cells

48
Q

When thyroid hormone levels are high, the myocardium has an increased # of _____ receptors and is more sensitive to stimulation by _______ nervous system

A

Beta-1

Sympathetic

*PNS->ACh->M2

49
Q

What effect do thyroid hormones have on growth?

A

thyroid hormones act synergistically with GH and somatomedins to promote bone formation

50
Q

What does deficiency of thyroid hormone during perinatal period lead to?

A

abnormal development of synapses
Decreased dendritic branching and myelination

Irreversible and lead to cretinism unless replacement therapy is started soon after birth

51
Q

In metabolism, what does an excess of thyroid hormones cause? what does a deficiency cause?

A

Excess: heat intolerance, weight loss, increase BMR
Deficiency: Cold intolerance, weight gain, decrease BMR

52
Q

What does an excess of thyroid hormones do to bone? What does a deficiency cause?

A

Excess: osteoporosis
Def: stunted growth

53
Q

What does an excess of thyroid hormones do to CNS? What does a deficiency cause?

A

Excess: agitation, anxiety, difficulty concentrating hyperreflexia

Def: cretinism (congenital) , listlessness, slowed, somnolence, impaired memory, decrease mental capacity

54
Q

What does an excess of thyroid hormones do to skin? What does a deficiency cause?

A

Excess: sweating
Def: dry, myxedema

55
Q

What does an excess of thyroid hormones do to CV system? What does a deficiency cause?

A

Excess: tachycardia, atrial fib, palpitations, high-output heart failure

Def: bradycardia, decrease in contractility and cardiac output, heart failure

56
Q

What does an excess of thyroid hormones do to the intestine? What does a deficiency cause?

A

Excess: diarrhea
Def: constipation

57
Q

What are the primary causes of hypothyroidism?

A

Agenesis, gland destruction (Hashimoto’s), inhibition of thyroid hormones synthesis and secretion, transient (postpartum, thryoiditis)

58
Q

What are the secondary causes of hypothyroidism?

A

hypothalamic disease
Pituitary disease (sheehans)
Resistance to thyroid hormones

59
Q

What is the Tx for hypothyroidism?

A

replacement doses of T4
Because metabolism of T4 decreases and the plasma half-life increases with age, higher doses are required in younger pt

In women beyond menopause, overprescribing T4 can contribute to the development of osteoporosis

60
Q

Describe Hashimoto’s thyroiditis

A

Thyroid hormone synthesis is impaired by thryoglobulin or TPO antibodies, which leads to decrease in T3 and T4 secretion
TSH levels are high and have trophic effect (goiter)

61
Q

What causes cretinism?

A

Impaired development of thyroid gland
maternal intake of anti-thyroid medication or excess iodine
inherent deficit in synthesis of thyroid hormones

62
Q

What are the symptoms of cretinism?

A

Feeding problems, respiratory difficulty, protruding tongue, curse facial features, growth retardation, mental retardation, jaundice, dry skin, hypotonia

63
Q

How does iodine deficiency cause hypothyroidism?

A

leads to transient decrease in synthesis of thyroid hormones
TSH levels are elevated
Goiter

64
Q

Describe euthryoid goiter

A

Gland maintains normal blood levels of thyroid hormones, assymptomatic

65
Q

Describe hypothyroid goiter

A

If gland cannot maintain normal blood levels of thyroid hormones

66
Q

What is the most common cause of thyrotoxicosis = hyperthyroidism?

A

Graves disease a primary endocrine disorder

67
Q

What are the major clinical signs of Graves disease?

A

exophthalmos, periorbital edema (due to anti-TSH receptor antibodies w/i orbital cells)

68
Q

What is Graves disease diagnosed by?

A

Elevated serum free and total T4 or T3 level and clinical signs of goiter and ophthalmophaty
TSH levels low doe to negative feedback
Presence of circulating TSI (thyroid-stimulating immunoglobulins help distinguish Graves from adenoma of pituitary thyrotrophs)

69
Q

What would adenoma of the pituitary thyrotrophs be? Whaat are the levels of thyroid hormones?

A

a secondary endocrine disease

If defect is in anterior pituitary, TSH levels are up

70
Q

What hormones does the thyroid gland produce?

A

Prohormone tetraiodothyronine (T4) and active hormone triiodothyronine (T3)

Endocrine - MSI Spring (15 decks)

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