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Endocrine > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Where is the thyroid located?

A

Immediately below larynx, anterior and to each side of the trachea

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2
Q

How much does the thyroid gland weigh?

A

15-20 grams in adults

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3
Q

What is the #1 and #2 endocrinopathy?

A

DM - #1
Thyroid disease - #2

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4
Q

What does the thyroid gland do?

A

regulates the metabolic rate of the body

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5
Q

What does a complete lack of thyroid secretion result in?

A

Basal metabolic rate decrease of 40-50%

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6
Q

What does an extreme excess of thyroid secretion result in?

A

Increase basal metabolic rate by 60-100% above normal

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7
Q

The SLN and RLN are branches of what nerve?

A

CN X (Vagus nerve)

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8
Q

Where does the phrenic nerve come down from?

A

C3, 4, 5

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9
Q

What hormones does the thyroid produce?

A
  • Thyroxine (T4)
    -Triiodothyronine (T3)
    -reverse T3 (rT3)-inactive
  • calcitonin (important for calcium regulation)
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10
Q

What kind of cells is the thyroid made of?

A

Follicles of cuboidal epithelial cells surrounding colloid matrix

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11
Q

What substance is required for thyroid hormone synthesis?

A

IODINE

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12
Q

What is the colloid matrix?

A

A substance made of a protein called thyroglobulin which is responsible for the formation and storage of thyroid hormone

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13
Q

What is tyrosine?

A

An amino acid
(amino acids are building blocks of protein= tyrosine is the building block of thyroglobulin)

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14
Q

What does iodine combine with to form T3 and T4?

A

Iodine combines w thyroglobulin in the colloid to form T3 and T4

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15
Q

T3 is _______ T4 which occurs in the target tissues

A

T3 is de-iodinated T4 which occurs in the target tissues

(T3 loses and iodine atom)

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16
Q

What two hormones are the most important thyroid hormones for metabolic control?

A

Thyroxine (T4) and Triiodothyronine (T3)

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17
Q

How do T4 and T3 differ?

A

The function of the 2 hormones are qualitatively the same but they differ in their rapidity and intensity of action

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18
Q

In what percentage does the thyroid secrete thyroxine (T4)?

A

93% (though nearly all is converted to T3 in the tissues)

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19
Q

In what percentage does the thyroid secrete triiodothyronine (T3)?

A

7% (T3 is mostly produced outside thyroid gland)

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20
Q

T3 is _________ x more potent than T4, but is more _____and is _______ more rapidly

A

T3 is 4x more potent than T4, but is more scarce and is cleared more rapidly

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21
Q

What is released by the hypothalamus?

A

Thyrotropin-releasing hormone (TRH)

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22
Q

What does TRH cause the release of, and from where?

A

thyroid-stimulating hormone (TSH) by the anterior pituitary

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23
Q

What does TSH cause the release of and from where?

A

Thyroid hormones (T3, T4) from the thyroid gland

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24
Q

What hormones are active?

A

T3 and T4

but over 99% is bound to protein (thyroxine-binding globulin (TBG) or albumin

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25
Q

Peripheral tissues contain enzymes that convert what?

A

T4 to T3 (T3 is more metabolically active)

TH activate intracellular processes, these increase gene transcription, protein and enzyme production which increase metabolic rate

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26
Q

What do T3 and T4 (TH) increase?

A

TH increases the size, and number of mitochondria, which are the energy generators of the cells.

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27
Q

What cells are targets for thyroid hormones?

A

It is likely that all cells in the body are targets for thyroid hormones

  • thyroid hormones effect metabolism, growth, and development
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28
Q

What are the thyroid hormone effects?

A
  • Stimulation of carbohydrate metabolism
    (increased uptake of glucose by cells and GI tract, enhances glycolysis, gluconeogenesis, and insulin secretion)
  • Stimulation of fat metabolism
    (mobilizes lipids, decreases fat stores, decreases cholesterol)

-Increased requirement for vitamins
(Vitamins are needed for increased enzyme synthesis)

  • Increased Basal metabolic rate
    (increased metabolism in almost all cells)
  • Decreased body weight
    (Does not always occur bc appetite is also increased)
  • Brings up blood sugar
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29
Q

What are the cardiovascular effects of thyroid hormones?

A

-Increase blood flow secondary to vasodilation
-Increased CO
-increased heart strength and HR
- Increase SBP, decreased DBP, increase pulse pressure (normal MAP)
-Increase respiration (d/t more CO2 produced)
-Increased number and affinity of beta-adrenergic receptors
-Decreased number of cardiac alpha-adrenergic receptors

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30
Q

What are the CNS effects of thyroid hormone?

A

increased mentation
increased anxiety
increased neurosis

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31
Q

What are the muscular effects of thyroid hormone?

A

Muscles more vigorous, become weak w protein catabolism

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32
Q

What are the effects on sleep by thyroid hormone?

A

causes exhaustive sleep states (Hypo)
excitable effects (hyper) - constantly tired but can’t sleep

Hypothyroid pts can sometimes need 12-14 hrs a day of sleep

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33
Q

What are the endocrine effects of thyroid hormone?

A

increases secretion by glands but also the need for hormone from peripheral tissues

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34
Q

What are the reproductive effects of thyroid hormone?

A

lack of thyroid hormone causes loss of libido
excess causes impotence
- inconsistent menstrual changes occur

35
Q

What are the symptoms of Hypothyroidism?

A

-Cold intolerance (body not producing heat)
-constipation
-depression
-fatigue
-muscle/joint pain
-paleness
-thin, brittle fingernails
-thin, brittle hair
-weakness
-wt gain
-decreased taste and smell
-hoarseness
-menstrual disorders
-puffy face, hands, and feet- d/t loss of proteins (can also see pleural/pericardial effusions)
- slow speech
-thickening of skin
-thinning of eyebrows

More common in females

36
Q

What is Primary hypothyroidism?

A

T3, T4 are not produced bc of problems w thyroid gland

Causes:
Hashimoto’s
Surgical removal
Inadequate iodine
Radiation exposure
Lithium

TSH elevated
Low T4

37
Q

What is secondary hypothyroidism? (5-10% of cases)

A

Inadequate T3, t4 d/t TSH not being released from the pituitary

TSH low

38
Q

What is Tertiary Hypothyroidism (<5% of cases)

A

inadequate T3, t4 d/t Thyrotropin-releasing hormone (TRH) from the hypothalamus

39
Q

Hypothyroidism that occurs in infancy leads to?

A

mental retardation and growth defects (cretinism)

40
Q

What is the most severe form of hypothyroidism?

A

Myxedema coma

  • Triggered by illness, stroke, infection/sepsis, exposure to the cold, medicines

Myxedema Coma is a state of decompensated hypothyroidism. All symptoms of a slow metabolism. Most cases of hypothyroidism are mild symptoms unlike myxedema coma. Myxedema coma is named after the symptoms it causes- Myxedema (non-pitting edema) Coma (altered state of consciousness/ mental status, hyper somnolent *not necessarily a coma)

41
Q

What are the symptoms of Myxedema coma?

A
  • coma
    -decreased breathing
    -decreased blood sugar
    -decrease BP
    -decreased temperature

Near total or total lack of thyroid hormone

42
Q

What medications can cause myxedema coma?

A

Amiodarone or lithium can cause myxedema coma d/t iodine richness

43
Q

How do you test for hypothyroidism?

A

Serum T4 assay is the standard test for thyroid gland function.

44
Q

When are blood levels of rT3 high?

A

Euthyroid sick states (critical illness)

45
Q

What is Levothyroxine (Synthroid)?

A

T4 (most commonly used)

46
Q

what is Armour thyroid?

A

both T3 and T4

47
Q

When do Thyroxine binding globulin (TBG) levels change?

A

liver disease and pregnancy

48
Q

When should surgery be done?

A

Once the euthyroid state is achieved

49
Q

What are some problems that can occur with a pt with hypothyroidism and anesthesia?

A

-lethargy
-HoTN
- bradycardia
-CHF
-gastroparesis
-hypoglycemia
-Hypothermia
-hypoventilation
-Hyponatremia

50
Q

What induction is ideal to use in the hypothyroid pt?

A

Ketamine (but all meds can be used)

51
Q

Anesthetic management of hypothyroidism:

A

-Be aware of the “crash on induction” possibility
-Ketamine “ideal” but all meds can be used
-MAC is usually not affected, potent volatile agents may worsen myocardial depression
-Regional anesthesia preferred if surgery permits
-Pancuronium/Rocuronium have vagolytic/sympathomimetic effects
-Aline is indicated with PA catheter in setting of cardiac failure
-Hypoventilation is very serious. Avoid any pre-op sedation prior to going to OR. Diminished response to hypoxia and hypercarbia

52
Q

What is Hashimotos?

A

form of hypothyroidism. Associated w other forms of autoimmune (DM, adrenal insufficiency, myasthenia gravis)

53
Q

What is thyroiditis?

A

-Thyroiditis: inflammation of the thyroid which causes release of excessive hormone but not increased production

Hyperthyroid is excess gland activity and thyrotoxicosis is increased hormones

54
Q

What is thyrotoxicosis?

A

oversupply of thyroid hormones on peripheral tissues

55
Q

What are the symptoms of hyperthyroidism?

A
  • Palpitations
    -Nervousness
    -breathlessness
    -fatigue
    -tachycardia
    -muscle weakness
    -hair loss
    -heat intolerance
    -insomnia
    -increased bowel movements
  • light or absent menstrual periods
    -trembling hands
    -warm moist skin
    -staring gase (exophthalmos)

Tachycardia/ a-fib common. CO can double or triple normal

56
Q

What’s the most common cause of hyperthyroidism?

A

Grave’s disease (60-90% of cases) - an autoimmune disease

-Autoantibodies activate the TSH receptor.
-Causes multinodular goiter
-Stimulates thyroid hormone synthesis, secretion and thyroid growth (goiter formation)
-Exophthalmos is caused by inflammation of the eye muscles by attacking autoantibodies.

More common in females 40-60 years old (caused by genetics, stress, or cigarette smoking)

57
Q

What is the treatment for hyperthyroidism?

A

Suppressive medicines–> surgical or radioisotope therapy

Antithyroid drugs inhibit the production of Th

-Methimazole and propylthiouracil (PTU)
-Beta-blockers (Propranolol)

High dose iodine deceased thyroid activity

58
Q

How do Methimazole and propylthiouracil (PTU) work?

A

inhibit iodination of thyroglobulin and conversion of T4 to T3

59
Q

How do beta-blockers (propranolol) work in hyperthyroidism?

A

-L-isomer causes beta-blockade, treats tachycardia, tremor, palpitations, anxiety, and heat intolerance

-D-isomer inhibits the conversion of T4 to T3

any beta-blocker can be used but propranolol is most common

60
Q

What is radioactive iodine?

A

one time dose in pill form, results in destruction of thyroid tissue

61
Q

What kind of surgery would be done for hyperthyroidism?

A

Partial or total thyroidectomy

Not used extensively in the absence of cancer as meds are effective and risk of removing parathyroids or recurrent laryngeal nerve

62
Q

What is thyroid storm?

A

An extreme form of hyperthyroidism
occurs 6-18 hrs post-op
80% of pts not suspected of having thyroid probs

63
Q

What are the signs and symptoms of thyroid storm?

A

-Hyperthermia
-tachycardia
-dysrhythmias
-CHF
-Shock

64
Q

What are the causes of thyroid storm?

A

-Surgery (especially of the thyroid gland)
-infection
-trauma
-toxemia
-DKA

65
Q

What is the treatment for thyroid storm?

A

Hyperthyroid: Sodium iodide, Inderal/labetalol, Cortisol (increased utilization of cortisol), PTU

Hyperthermia: acetaminophen, cooling blankets

Hydration: Fluids and glucose (increased metabolism)

66
Q

How do you prepare for surgery for a hyperthyroid pt?

A

-checking the airway
-administering antithyroid drugs,
-treating sxs of hyperdynamism
-treating volume depletion and electrolyte problems
-Check airway for goiter, wheezing, obstruction

67
Q

Treatment for hyperthyroidism before surgery:

A

Sodium iodide and propranolol lead to euthyroidism in about 10 days

Antithyroid drugs 6-8 weeks before surgery include sodium iodide and propylthiouracil

Treat hyperdynamism with beta blockers

Treat hypovolemia with crystalloids

68
Q

What drugs should be avoided in the pt w hyperthyroidism?

A

Avoid sympathomimetic drugs:

Atropine
Robinul
Ketamine
Pancuronium
Halothane

69
Q

how do you prepare your hyperthyroid pt for emergency surgery?

A

-Check for upper airway obstruction

-Administer antithyroid drugs: sodium iodide, cortisol (blocks the peripheral conversion of T4 to T3, making rT3 instead), PTU

-Hydrate to compensate for hypovolemia

-Treat hyperdynamic vitals with propranolol

-Premedicate to decrease anxiety may require larger doses

-Treat heart failure with Digitalis and symptomatic support

70
Q

What causes goiters?

A

Chronic stimulation by TSH
Can occur in iodine deficiency states (table salt contains iodine)
Not always visible

71
Q

What will you be monitoring during a thyroidectomy and with what?

A

EGM with dragonfly nerve monitor or nim tube

72
Q

What are you assessing for post-op thyroidectomy?

A

RLN damage:
unilateral= hoarseness
bilaterally= aphonia, stridor, aspiration

SLN damage: abnormal voice in upper registers

Hematoma: airway emergency–> decompression and intubation

Hypocalcemia: d/t inadvertent removal of parathyroids
can end w cv collapse

Tracheomalacia -tracheal softening= airway collapse w inspiration

73
Q

What can happen with hypocalcemia?

A

Hypocalcemia- monitor Ca+ levels.
Laryngeal stridor can progress to laryngospasm, often an early sign of hypocalcemic tetany.
CV collapse if Ca+ is not replaced.
Tracheomalacia or a tracheal compression from hematoma.

74
Q

What are the functional units of the thyroid gland?

A

follicles (each lobule is composed of 20-40 follicles)

75
Q

How much ingest iodine is required each week to form normal quantities of thyroid hormones?

A

1 mg

76
Q

What’s the most vascular organ?

A

Thyroid

77
Q

Where are hormones made and stored?

A

colloid matrix

78
Q

what do you need in your every day diet?

A

tyrosine and iodine

79
Q

Thyroglobulin is responsible for:

A

the formation and storage of thyroid hormone

80
Q

What are the causes of Primary Hypothyroidism?

A

-Hashimoto’s
-Surgical removal
-inadequate iodine
-radiation exposure
-lithium

81
Q

What are the 2 roles of propranolol?

A

L-isomer causes beta blockade
D-isomer inhibits conversion of T4 to T3

82
Q

What meds should be avoided in Hyperthyroidism?

A

-Halothane
-Atropine
-Robinul (glycopyrrolate)
-Ketamine
-Pancuronium

Sympathomimetic drugs

83
Q

What will you see with hypocalcemia?

A

-Weakness
-Tetany
-Laryngospasm

(24-72hrs later)

Endocrine (7 decks)

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