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Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What 2 categories of hormone are synthesized from Tyrosine?

A
  • Catecholamines

- Thyroid hormones

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2
Q

Describe the functional unit of the thyroid gland.

A
  • A follicle is the functional unit
  • picture each follicle as a balloon
  • the balloon is made of follicular cells, the air inside is Colloid, outside the balloon are BVs
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3
Q

What is the active thyroid hormone?

A

T3 (triiodothyronine)

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4
Q

What is the most prevalent form of thyroid hormone in the serum?

A

T4 (thyroxine; converted to T3 in tissues)

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5
Q

Describe the combinations of DIT and MIT.

A

DIT+DIT= T4

MIT+DIT=T3

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6
Q

Describe how Iodide gets into follicular cells.

A
  • Na+/I- symporter (NIS) brings I- in

- NIS is secondary transport, uses Na+ gradient from Na/K ATPase

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7
Q

How does Iodide get thru the apical membrane of follicular cells?

A

-Pendrin

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8
Q

Where is Thyroperoxidase (TPO) located?

A

-on the colloid-apical membrane of the follicular cells

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9
Q

What are the 3 functions of TPO?

A
  • Oxidize Iodide (I-) to Iodine (I0)
  • Organification of Iodine (add I to tyr residue on Tg)
  • Conjugates/couples DIT+MIT, or DIT+DIT
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10
Q

Describe the synthesis and exocytosis of Thyroglobulin.

A
  • synthesized on the rER
  • glycosylation: improves water solubility
  • immediately exocytosed to colloid space
  • very few tyr residues are available for Iodination
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11
Q

What class of drug is a competitive inhibitor for TPO?

A

Thiocarbamides

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12
Q

Describe the process of thyroid hormone SECRETION (after TPO conjugated MIT, DIT)

A
  • the Iodinated Thyroglobulin is sitting in the colloid
  • TSH stimulates Endocytosis of Thyroglobulin
  • proteases chop Thyroglobulin up
  • MIT and DIT are recycled
  • Exocytosis of T3 and T4 into blood
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13
Q

Describe the TSH-R and its signal transduction.

A

G protein coupled receptor

G(as): (works with cAMP+pkA)

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14
Q

If lab results reveal increased MIT:DIT and T3:T4 ratios, what will you suspect?

A

-some type of Iodine deficiency

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15
Q

What the hell is the Wolff-Chaikoff effect?

A

-in situation of hyperthyroidism = temporary inhibition of TPO (can lead to hypothyroidism)

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16
Q

What step of thyroid hormone synthesis will be inhibited by the administration of Iodide?

A

-Uptake of Iodide from the blood by the follicular cell (slows action of Na/I symporter)

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17
Q

What step of thyroid hormone synthesis will be inhibited by the administration of Methimazole?

A

-all 3 steps done by TPO

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18
Q

What step of thyroid hormone synthesis will be inhibited by the administration of Propylthiouracil (PTU)?

A
  • all 3 steps done by TPO

- PLUS peripheral conversion of T4 to T3 (via 5’-deiodinase)

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19
Q

What step of thyroid hormone synthesis will be inhibited by the administration of Dexamethasone?

A

-peripheral conversion of T4 to T3

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20
Q

What amino acid is integral for organification of Iodine?

A

-Tyrosine

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21
Q

Describe the relationship of thyroid function and Iodide uptake.

A

-higher activity of gland = higher uptake of tagged I (diagnostic test)

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22
Q

What is the difference between T3 and reverse T3?

A
  • T3: distal ring has one Iodine

- reverse T3: distal ring has 2 Iodines

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23
Q

How do peripheral tissues regulate their metabolism?

A

-by fooling with the proportion of T4 converted into T3 (active) vs. that converted into reverse T3 (inactive)

24
Q

All Steroid hormones except what are carried around by proteins in the blood?

A

DHEA (its sulfated)

25
Q

A cell’s T3/T4 Receptor is found _________.

A

in the nucleus!

26
Q

All tissues in the body can regulate their metabolic activity by thyroid hormones EXCEPT:

A
  • brain

- gonads

27
Q

Describe the relationship of thyroid hormones and neural tissue.

A
  • thyroid hormone ESSENTIAL for neural development

- however, mature neural tissue does not need/use thyroid hormones

28
Q

What specific neural defects occur in the perinatal period if the mother/infant has hypothyroidism?

A

-abnormal synapses
-decreased dendritic branching and myelination
= CRETINISM

29
Q

Describe thyroid hormone’s effects on cardiac tissue.

A
  • increases # of beta receptors

- permissive effect on catecholamines

30
Q

What is the connection between Primary Hypothyroidism and hyperprolactinemia?

A
  • Hashimoto’s: lo T4, thus hi TSH and TRH
  • recall: TRH also stimulates PRL!
  • therefore, Hashimoto’s can present additionally with Prolactinoma signs (dry men, wet women)
31
Q

Describe how a thyroglossal duct cyst forms.

A
  • thryoid gland starts as pouch from proximal esophagus (@base of tongue)
  • it moves inferiorly as fetus grows
  • thyroglossal duct is the ‘trail’, may persist as cyst or pyramidal extra lobe
32
Q

How can a thyroglossal duct cyst be diagnosed?

A
  • midline anterior neck mass

- moves with swallowing

33
Q

Increased levels of thyroid hormone will increase synthesis of __________, which directly increases BMI in nearly every tissue.

A

Na/K ATPase

34
Q

Hashimoto’s thyroiditis is associated with HLA ______ and may increase risk of what type of cancer?

A
  • HLA-DR5

- hi risk for Non-Hodgkin’s lymophoma (in the thyroid)

35
Q

Name 4 causes of hypothyroidism.

A
  • Iodine deficiency
  • Hashimoto’s
  • drugs (ex Li)
  • surgical removal or radioablation
36
Q

Since Hashimoto’s is an autoimmune condition, what cell type will infiltrate the thyroid?

A

Lymphocytes (may see Germinal Centers)

37
Q

Lack of maternal Iodine will cause a baby to present how?

A

-pot bellied, mentally retarted, short, protruding umbilicus, puffy face, protruding fat tongue

aka cretinism

38
Q

Pt presents with hypothyroidism following a VIRAL infection, and has a VERY TENDER THYROID. What’s the name and inflammatory pattern seen.

A
  • Subacute (de Quervain’s) Thyroiditis

- granulomatous inflammation

39
Q

Patient comes in with hypothyroidism, and a ROCK HARD THYROID. It is found that the surrounding areas, as well as the thyroid itself, are fibrotic. What 2 disorders do we need to differentiate here?

A
  • Riedel’s thyroiditis (YOUNG females often)

- Anaplastic Carcinoma (only OLD patients)

40
Q

TSI antibody is found in what disease, and what is its function?

A
  • Grave’s dz (primary hyperthyroidism)

- IgG that resembles TSH, stimulates R on thyroid gland

41
Q

What two characteristic external symptoms will be found in Grave’s disease?

A
  • Proptosis/exophthalmos

- Pretibial myxedema (doughy)

42
Q

Describe the development of Exophthalmos in a Grave’s disease patient.

A
  • fibroblasts behind eye have TSH-R
  • TSI Ab will stimulate+cause release of glycosaminoglycans/mucopolysaccharides (push eye fwd)
  • hi symp stimulation from hi thyroxine=stimulation of levator palpebra superioris
43
Q

What is the number one risk in Grave’s disease and the treatment for it?

A
  • thyroid storm (death by arrhythmia)

- Tx: B blocker+PTU+steroids

44
Q

What are some key findings on histo and blood tests in Grave’s disease?

A

-scalloping of follicles (colloid pulls away from epith)

  • hi blood glucose
  • hypocholesterolemia
  • hi radioactive Iodine uptake (due to hi activity)
45
Q

To sample cells from the thyroid, what technique is always used?

A

-Fine needle aspirate (bloody organ!)

46
Q

Name the 4 types of Carcinoma in the thyroid gland.

A

Papillary carcinoma
Follicular carcinoma
Medullary carcinoma
Anaplastic carcinoma

47
Q

What type of carcinoma will you find nuclei with clearnings in the center?

A

-Papillary carcinoma (clearings=ground glass=Orphan Annie nuclei)

48
Q

The 2 follicular cancers of the thyroid have a fibrous capsule. How do you differentiate between them?

A
  • follicular CARCINOMA: cells have spread beyond capsule (malig)
  • follicular ADENOMA: cells within capsule (benign)
49
Q

Medullary carcinomas of the thyroid produce hi levels of ________ from _______ cells.

A
  • Calcitonin

- Parafollicular/C cells

50
Q

Which carcinoma often presents with sheets of cells within Amyloid stroma?

A

Medullary carcinoma (the calcitonin can deposit as Amyloid)

51
Q

Medullary carcinoma has a high association with what 2 conditions?

A
  • MEN 2A

- MEN 2B

52
Q

Follicular carcinoma likes to metastasize where?

A

-to the BLOOD (weird for a carcinoma)

53
Q

What is the difference between MEN 2A and 2B?

A

2A: aka Sipple dz (Parathyroid involved)

2B: Oral ganglioneuromatosis involved (marfan habitus)

54
Q

What are the similarities btw MEN 2A and 2B?

A
  • both involve Medullary Thyroid CA
  • both involve Pheochromocytomas
  • both associated with ret gene
  • both have AD inheritance
55
Q

Which thyroid carcinoma has a high association with childhood radiation, as well as Psammoma bodies?

A

-Papillary carcinoma

56
Q

Carcinomas typically like to spread to the lymph nodes. Name the 4 exceptions that like to go to the blood.

A
  • Renal cell carcinoma (renal v)
  • Hepatocellular carcinoma (portal v)
  • Follicular carcinoma of the thyroid
  • Choreocarcinoma
57
Q

A patient has hyperthyroidism and has a cystic mass of the ovary. What is the dx?

A

Struma ovarii (germ cell teratoma of the ovary that is mostly thyroid tissue)

Endocrinology (7 decks)

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