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S & F 4 Test 2 > McCumbee - Thyroid Hormones > Flashcards

McCumbee - Thyroid Hormones Flashcards

1
Q

Enlarged thyroid gland

A

Goiter

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2
Q

The functional unit of the thyroid gland is the ?

A

Follicle

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3
Q

The principle component of the thyroid follicle is within the colloid, it a glycoprotein called _____

A

Thyroglobulin

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4
Q

Principle thyroid hormone secreted by thyroid follicles _

A

Thyroxine (T4)

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5
Q

Parafollicular (C cells) are in the stroma of the thyroid, surround the follicles. These cells secrete ______

A

Calcitonin

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6
Q

The thyroid gland removes Iodide from circulation by ?

A

Iodine trapping

Uses a Na-Iodide symporter

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7
Q

In a normal euthyroid individual. The NIS pump maintains a T/S ratio of idodide (ratio of concentration in follicle cell to that in serum) that is_____

A

About 30

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8
Q

Anions that can competitively interfere with the NIS transporter are ? (X3)

A

Perchlorate (HClO4-)
Thiocyanate(CNS-)
Pertechnetate (TcO4-)

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9
Q

As the iodide molecules into the follicular lumen of in the thyroid _________ catalyzes their oxidation.

A

Thyroid peroxidase (TPO)

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10
Q

What does thyroid oxidase do ?

A

In the creation of thyroid hormones, when iodide is oxidated by thyroid peroxidase when crossing the apical membrane of the follicular cell, Thyroid oxidase facilitates H2O2 accepting the extra electron.

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11
Q

T3 and T4 are stored where?

A

Outside the cell within the colloid of the follicular lumen

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12
Q

Thyroglobulin is an important reservoir of iodide in the form of ____ and ____

A

MIT

DIT

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13
Q

The coupling reaction of MIT and DIT forms T4 and T3

This reaction is catalyzed by ?

A

Thyroid peroxidase

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14
Q

Coupling DIT and DIT forms

A

T4

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15
Q

Coupling DIT and MIT forms

A

T3

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16
Q

In a normal adult, there is enough thyroid hormone stored as thyroglobulin to maintain euthyroid condition for ___

A

2 to 3 months

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17
Q

Thyroid hormone release into circulation requires _____ of thyroglobulin from the colloid

A

Proteolysis

The colloid fragments are then endocytosed at apical surface of follicle cell

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18
Q

What happens in people that are deficient in the microsomal deiodinase “idotyrosine deiodinase”.

A

This enzyme is involved in recycling MIT and DIT.

People deficient in it have hypothyroidism and elevated serum and urine DIT and MIT

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19
Q

Most circulating T3 and T4 are bound to plasma proteins (T4 .03% free T3 0.3% free)
What are the 3 binding proteins?

A

Thyroxine-binding globulin

Transthyretin

Albumin

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20
Q

TBG levels decreases in response to _____ (x3)

A

Malnutrition

Liver disease (decreased synthesis)

Kidney disease (increased loss in urine)

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21
Q

Hepatic TBG synthesis is stimulated by _______

A

Estrogens

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22
Q

_______ cause decreased thyroid hormone binding to TBG

A

Salicylates

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23
Q

What are the roles of thyroid hormone binding proteins/

A

Serve as a reserve capacity

Increase amount carried in plasma since these hormones are insoluble

Decrease amount of the small T3 and T4 molecules lost in urine.

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24
Q

Circulatory half life of T4 is ____

Circulatory half life of T3 is ___

A

6-7 days

1 days

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25
Q

The majority of the circulating T3 comes from ____

A

The peripheral metabolism of T4

Mostly converted at the kidney and liver

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26
Q

The major source of serum T3 (metabolized from T4) is the _____ and ____-

A

Liver

Kidney

27
Q

What are the important physiological roles of peripheral iodothyronine deiodinases (x3)

A

Maintain circulatory pool of T3

Regulation of iodothyronine deiodinases at specific tissues allows for independent regulation of T3 levels at different tissues

Thyroid hormone inactivation

28
Q

The most important hormone regulating the thyroid gland is _____

A

TSH

29
Q

Due to actions of _____ and _____, thyroid deficient patients being treated w/ T4 usually have normal levels of T3

A

D1 and D2

Deiodinaes

30
Q

Thyroid stimulating hormone (TSH) secretion is _______ by thyrotropin releasing hormone

A

Stimulated

31
Q

TSH (thyroid stimulating hormone) secretion is __—-_- by T4 and T3

A

Inhibited

32
Q

TSH stimulates:

A

Iodide trapping

Endocytosis and proteolysis of colloid

Expression of genes for thyroglobulin, thyroid peroxidase, and NIS

Increase in size and number of follicle cells

Increase in capillary. Proliferation and blood flow thru the thyroid

33
Q

How does TSH work?

A

The TSH receptor is coupled to a Gs protein which activates adenylyl cyclase and makes cAMP which induces the various responses to TSH

34
Q

Chronic TSH stimulation will lead to ?

A

Increased thyroid gland size (bigger follicle cells, more proliferation))

And

Increased capillary perfusion

35
Q

Immediate effects of TSH stimulation are:

A

Increased endocytosis and proteolysis of colloids

Uptake of iodide

Release of thyroid hormone

Activation of thyroid peroxidase

36
Q

In the pituitary, what does TRH do?

A

It stimulates the synthesis and release of TSH

37
Q

T3 and T4 do what to the pituitary release of TSH?

A

Inhibit it thru negative feedback mechanism.

38
Q

Thyroid hormone receptors are ligand activated _______

A

Transcription factors

39
Q

Thyroid hormone receptors are ________ sensitive to T4 than to T3

A

Less

40
Q

What do Thyroid hormone receptors do once bound by T3?

A

Bind DNA sequences called thyroid hormone response elements (TRE’s) in regulatory regions of genes.

They bind as monomers, homodimers, or heterodimers.

Highest affinity is w/ Retinoid X receptor paired TRE’s

41
Q

When is the highest affinity binding of T3?

A

When heterodimers of THR-Retinoid x receptors are found

42
Q

Where are THR usually at when not bound to T3?

A

Usually bound to the TRE segment on DNA, working as an inhibitor of transcription

43
Q

At the cellular level, thyroid hormones work primarily by?

A

Regulating the transcription of genes

44
Q

Thyroid hormone will _________ the transcription of the Na/K ATPase

A

Activate

45
Q

Thyroid hormone will ________ the beta-adrenergic receptor

A

Activate

46
Q

TH _______ the sensitivity of various tissues to catecholamine stimulations

A

Increases

(by increasing synthesis of beta-adrenergic receptors)

[TH can mimic the effects of the catecholamines]

47
Q

The energy required to maintain bodily functions at a state of complete rest

A

Basal metabolic rate (BMR)

Determined by heat production or indirectly by measuring O2 consumption.

48
Q

TH works directly and indirectly to _______ cardiac output and respiratory rate

A

Increase

49
Q

How does thyroid hormone increase basal metabolic rate?

A

By increasing gluconeogenesis, glycogenolysis, lipolysis, and proteolysis.

Also indirectly by increasing cardiac output and respiratory rate

50
Q

How does TH effect cardiovascular system?

A

TH increases transcription of beta adrenergic receptors. This winds up increasing the force and rate of cardiac contraction.

51
Q

What are causes of congenital hypothyroidism?

A

Infants w/ little-no thyroid tissue (80-85% of cases)

Infants who lack proper enzymes for TH synthesis or metabolism

Infants whose mothers have autoimmune dz and pass THR-antibodies to baby.

Places w/ endemic iodide deficiency

52
Q

What proteins do the antibodies produced in hashimoto thyroiditis interact with?

A

Thyroid peroxidase (TPO)

Thyroid globulin (TG)

TSH-receptor

53
Q

Most common cause of hypothyroidism in the US

A

Hashimoto thyroiditis (95%)

54
Q

Explain hashimoto thyroiditis

A

Autoimmune dz. Body makes antibodies for TPO, TG, and TSH-R proteins. Follicle cells eventually destroyed, leading to hypothyroidism. Most common cause of hypothyroid in US.

55
Q

What is the cause of secondary hypothyroidism?

A

Hypofunctional pituitary;
Isolated TSH deficiency
Second to surgery, trauma, infiltrative disorders

56
Q

Early s/s of hypothyroidism

*(x9)

A 
Tiredness
Weight gain
Brittle hair/ nails
Reduced muscle tone
Increased muscle cramps
Joint pain
Carpal tunnel syndrome.
Insensitivity to cold (increased)
Constipation
57
Q

Generalized non-pitting edema caused by the accumulation of mucopolysaccharides in CT. Produces thickened skin and facial features, enlarged tongue, periorbital edema, hoarseness, and joint stiffness

A

Myxedema

58
Q

Later symptoms of hypothyroidism

X3

A

Slowed speech

Myxedema

Women may have irregular periods

59
Q

What are the symptoms of thyrotoxicosis

A

Increased metabolic activity in T3 sensitive tissue

Increased catecholamine sensitivity

60
Q

What is Graves disease?

A

Graves disease is the number 1 cause of thyrotoxicosis.
It has a characteristic hyperplastic goiter as well as thyrotoxicosis s/s.
80% of patients have thyroid-related opthalmopathy
.
Patients have a Thyroid-stimulating immunoglobulin (TSI) which has the same effects TSH on the TSH-R.

61
Q

What are the characteristics of thyroid - associated opthalmopathy?

A

Periorbital edema and proptosis

62
Q

Bulging of the eyeyballs

A

Proptosis

63
Q

Causes of thyrotoxicosis?

A

Graves disease (thyroid stimulating immunoglobulin)

Toxic adenoma

Toxic multinodular goiter

TSH secreting pituitary adenoma

64
Q

Explain toxic Adenomas

A

You get a solitary, hyperfunctioning adenoma in the thyroid, most patients have gain in function mutations of the TSH receptor

S & F 4 Test 2 (15 decks)

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