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SF3-EXAM 4 (CAMELITA) > Thyroid Physiology > Flashcards

Thyroid Physiology Flashcards

1
Q

The lumen of the thyroid gland is filled with ______.

A

Thyroglobulin

NOTE: Thyroglobulin gene is transcribed and translated within the follicular cell. After post-translational modification and packaging, it is exocytosed into the lumen.

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2
Q

Where are iodide molecules concentrated?

A

Thyroid gland

Salivary glands

Gastric glands

Lacrimal glands

Mammary glands

Choroid plexus

NOTE: Iodiine uptake by the sodium/iodide symporter (NIS) on the basal membrane of the thyroid gland can raise I- within the cell as much as 250 times that of the plasma.

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3
Q

I- is transported to the lumen by ______.

A

Pendrin

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4
Q

Circulating thyroglobulin is minimal in healthy individuals. In what instances is thyroglobulin seen in circulation?

A

Thyroiditis

Nodular goiter

Cancerous thyroid tissue

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5
Q

Mechanism by which Tyrosine is converted to T4 and T4 is converted to T3

A

NOTE: The catalystic enzyme is TPO

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6
Q

Pieces of colloid are endocytosed back into follicle and fuse with _________.

A

Lysosomes

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7
Q

Moving toward the basal membrane, thyroglobulin is broken into free amino acids. What components are released?

A

T4, T3, MIT, and DIT

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8
Q

Where are thyroglobulin and peroxidase synthesized?

A

Rough ER

Golgi

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9
Q

What are the inhibitors of the Na+-I+ trnasport NIS symporter?

A

Perchlorate

Thiocynate

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10
Q

What enzyme catalyzes the oxidation of I- to I2?

A

PTU, Methimazole (used to treat an overactive thyroid)

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11
Q

Which steps of thyroid hormone synthesis are inhibited by PTU and methimazole?

A
  • Oxidation of I- to I2
  • Organification of I2 into MIT and DIT
  • Coupling of MIT and DIT
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12
Q

Which hormone is most frequently secreted from the thyroid?

A

T4 (90%)

T3 (10%)

RT3 (less than 1%)

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13
Q

Which thyroid hormone has the greater affinity for nuclear receptors TRa and TRb?

A

T3

NOTE: TRa transduces thyroid hormone action on the heart

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14
Q

In the extracellular fluid thyroid hormones circulate bound. What hormones do the hormones bind to ?

A

Thyroxine-binding globulin (TBG)- 70%

Transthyretin (TTR) - 10-15%

  • TTR provides thyroid hormones to the CNS.
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15
Q

What immediate affects does TSH have on the thyroid?

A
  • Endocytosis of colloid
  • Iodide uptake
  • Increase TPO activity
  • Stimulates generation of peroxidase
  • Stimulates proteolysis of thyroglobulin
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16
Q

Which enzymes induce the formation of T3 and RT3 from T4?

A

T3- Deiodinases 1 and 2

RT3- Deiodinase 3

NOTE: The brain maintains constant intracellular levels of T3

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17
Q

What intermediate (hrs to days) affect does TSH have on the thyroid?

A
  • Stimulation of protein synthesis and expression f genes including NIS, thyroglobulin, TPO
18
Q

What long-term (sustained TSH secretion) affect does TSH have on the thyroid?

A

Hypertrophy and hyperplasia of follicular cells

19
Q

In what organs is T4 converted to T3?

A

Liver kidneys

20
Q

TSH has an alpha and beta subunit, but the _ subunit is what gives us specificity.

A

Beta

21
Q

What is the body’s response to a deficient iodine intake?

A
  • The thyroid gland makes more T3 and less T4. The decrease in T4 stimulates TSH secretion
  • It increases iodine trapping, maintains T3 secretion and causes formation of a goiter

REMEMBER: T4 is responsible to negative feedback and feedback is mainly on the pituatary and to a lesser extent on the hypothalamus

22
Q

What effect would excessive intake of iodide have?

A

Supression of NIS and TPO

*This is known as the Wolff-Chaikoff effect

23
Q

Excess calories (mainly carbohydrates) increase production and amount of circulating ______.

A

T3

NOTE: Fasting has the opposite effect.

24
Q

What are the actions of T3

A
  • Growth
    • ​Growth formation
    • Bone formation
  • CNS
    • ​Maturation of CNS
  • Basal metabolic rate
    • ​Increases O2 consumption
    • Increased heat production
    • Increased BMR
    • Increased Na-K ATPase
  • Cardiovascular
    • ​Increased cardiac output
    • Increased heart rate
    • Increased sweating
    • Increased ventilation
  • Metabolism
    • ​Increased glucose absorption
    • Increased glycogenesis
    • Increased glycolysis
    • Increased glucogenesis
    • Increased Lipolysis; lipogenesis
    • Increased protein synthesis; degradation
25
Q

What effect does hypothypoidism have on the autonomic nervous system?

A

Normal levels of catecholamines

26
Q

What affect does hyperthyroidism have on the autonomic nervous system?

A
  • Increases expression of B-adrenoceptirs
    • Increases sensitivity to catecholamines, which remain at normal levels
27
Q

What test can be used to assess thyroid status?

A
  • Radioactive iodine uptake
  • Thyroid imaging
  • Perichlorate test
  • Tests to thyroid autoantibodies, thyroglobulin, thyroid peroxidase, TSI
28
Q

What are the symptoms of cretinism?

A

Severe hypothyroidsim in infancy

  • Short stature
  • Obesity
  • Malformed legs
  • Mentally challenged
  • Dry scaly skin
  • Delayed puberty
  • Muscle weakness
  • Bradycardia
29
Q

What are the clinical signs and symptoms of cretinism?

A
  • Feeding problems
  • Lethargy
  • Delayed stooling and constipation
  • Enlarged protruding tongue
  • Hoarse cry
  • Protruding abdomen with an umbilical hernia
  • Delayed skeletal maturation for gestational age
30
Q

Myxedema

A

Mucopolysaccharides accumulate under the skin. Non-pitting adema. This produces delayed deep tendon reflex

31
Q

High TSH, high T3/T4

A

Secondary hyperthyroidism

  • Benign tumor of the pituatary
  • Thyroid hormone resistance
32
Q

Low TSH, low T3/T4

A

Secondary hypothyroidism

33
Q

Low TSH, High T3/T4

A

Primary hyperthyroidism

34
Q

High TSH, low T3/T4

A

Primary hypothyroidism

35
Q

What is the most common form of thyrotoxicosis

A

Graves’ disease

36
Q

By what mechanism does hyperthyroidism occur?

A

Thyroid-stimulating immunoglobulins (TSI) recognize and bind to the thyrotropin receptor (TSH receptor) which stimulates the secretion of thyroxine (T4) and triiodothyronine (T3). Thyroxine receptors in the pituitary gland are activated by the surplus hormone, suppressing additional release of TSH in a negative feedback loop. The result is very high levels of circulating thyroid hormones and a low TSH level.

37
Q

Goiters are caused by stimulation of _________ receptors.

A

TSH

38
Q

Onycholysis

A

When nails begin to split away from their nail beds, has to do with proteolysis

39
Q

Exophthalmos

A

Antibodies affect the extraocular muscles and give the eyes a bulging appearance

40
Q

If the free T3/T4 and plasma TSH are normal but the concentration of binding proteins is abnormal, what is the clinical condition?

A

Euthyroid

NOTE: Drugs and pregnancy can affect levels of binding protein

41
Q

Eurothyroid Sick Syndrome

A
  • A form of hypothyroidism that occurs during illness
    • Seen instarvation, sepsis, surgery, myocardial infarction, bypass, bone marrow transplantation

NOTE: When T4 falls to <4 µg/dl, the risk of death rises to ~50%. When T4 falls to <2 µg/dl, the probability of mortality increases to~80%

SF3-EXAM 4 (CAMELITA) (23 decks)

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