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

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Flashcards in 2-3-16-Thyroid Gland (Lopez) Deck (53):
1

Thyroid hormones are synthesized by ___ cells.

___ is composed of newly synthesized thyroid hormones attached to thyroglobulin

Follicular epithelial

Colloid (follicular lumen)

2

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

Deiodinase

3

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

-Fasting
-Medical and surgical stress
-Catabolic diseases

4

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

Obesity
Cold exposure
Hyperthyroid

5

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

Pregnancy
Fasting
Beta blockers
Hepatic and renal failure
Aging
Hypothyroid

6

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

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

7

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

Perchlorate, thiocyanate

8

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

T3

9

Deficiency of ___ mimics dietary I- deficiency

Intrathyroidal deiodinase

10

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

Wolff-Chaikoff

11

___ is an effective treatment for hyperthyroidism and inhibits peroxidase

PTU (propylthiouracil)

12

99% of thyroid hormones in the bloodstream are ___

Bound to plasma proteins, the other 1% is free

13

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

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

14

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

T3 resin uptake

15

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

Hyperthyroidism

16

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

Hypothyroidism

17

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

High TBG

18

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

Low TBG

19

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

Hepatic failure

20

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

Pregnancy

21

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

HPT axis

22

TSH is regulated by:

TRH and free T3

23

___ is the 2nd messenger for TSH

Cyclic AMP

24

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

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