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2H. IM > ENDOC- THYROID intro > Flashcards

ENDOC- THYROID intro Flashcards

1
Q

The thyroid (Greek thyreos , shield, plus eidos , form) consists of two lobes connected by an_______________

A
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2
Q

The thyroid gland is located where?

A

It is located anterior to the trachea between the cricoid cartilage and the suprasternal notch.

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3
Q

What is the weight of thyroid?

A

The normal thyroid is 12–20 g in size, highly vascular, and soft in consistency.

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4
Q

What is located posterior to the thyroid gland?

A

Four parathyroid glands, which produce parathyroid hormone (Chap. 353) , are located posterior to each pole of the thyroid.

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5
Q

The _______________ traverse the lateral borders of the thyroid gland and must be identified during thyroid surgery to avoid injury and vocal cord paralysis.

A

recurrent laryngeal nerves

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6
Q

The thyroid gland produces two related hormones, _____________

A

thyroxine (T 4 ) and triiodothyronine (T 3 )

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7
Q

T3 and T4 acting through thyroid hormone receptors α and β, these hormones play a critical role in ____________________________

A
  1. cell differentiation during development
  2. and help maintain thermogenic and metabolic homeostasis in the adult.
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8
Q

Thyroid hormones are derived from____________ a large iodinated glycoprotein

A

Tg,

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9
Q

What happens after secretion into the thyroid follicle, _______________

A

Tg is iodinated on tyrosine residues that are subsequently coupled via an ether linkage.

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10
Q

________________ cell allows proteolysis and the release of newly synthesized T 4 and T 3 .

A

Reuptake of Tg into the thyroid follicular

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11
Q

____________ is a critical first step in thyroid hormone synthesis

A

Iodide uptake

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12
Q

. Ingested iodine is bound to serum proteins, particularly _________. Unbound iodine is excreted in the urine.

A

albumin

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13
Q

The thyroid gland extracts iodine from the circulation in a highly efficient manner. For example, 10–25% of radioactive tracer (e.g., 123 I) is taken up by the normal thyroid gland over 24 hours; this value can rise to **70–90% in Graves’ disease. **

A
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14
Q

Iodide uptake is mediated by _________________-, which is expressed at the basolateral membrane of thyroid follicular cells.

A

NIS

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15
Q

recommended average daily intake of iodine is _____________for adults

A

150–250 μg/d

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16
Q

recommended average daily intake of iodine is______________for children,

A

90–120 μg/d

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17
Q

recommended average daily intake of iodine is______________ ____________- for pregnant and lactating women

A

250 μg/d

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18
Q
A
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19
Q

. Urinary iodine is _______________in iodine-sufficient populations.

A

>10 μg/dL

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20
Q

After iodide enters the thyroid, it is trapped and transported to the____________of thyroid follicular cells, where it is oxidized in an organification reaction that involves TPO and hydrogen peroxide.

The reactive iodine atom is added to selected tyrosyl residues within Tg, a large (660 kDa) dimeric protein that consists of 2769 amino acids.

A

**apical membrane **

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21
Q

The iodotyrosines in Tg are then coupled via an_____________ in a reaction that is also catalyzed by TPO.

Either T 4 or T 3 can be produced by this reaction, depending on the number of iodine atoms present in the iodotyrosines.

A

ether linkage

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22
Q

After coupling, Tg is taken back into the thyroid cell, where it is processed in_____________to release T 4 and T 3

.

A

lysosomes

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23
Q

Uncoupled mono- and diiodotyrosines (MIT, DIT) are deiodinated by the enzyme ____________, thereby recycling any iodide that is not converted into thyroid hormones.

A

dehalogenase

24
Q

What are the steps in the process of thyroid synthesis?

A
  1. Iodide uptake
  2. •Organification
  3. •Coupling
  4. •Storage
  5. •Release
25
– most useful physiologic marker of thyroid hormone action –31kDa
•TSH
26
–\_\_\_\_\_\_\_\_\_ common to other glycoprotein hormones (**LH, FSH, hCG)**
α subunit:
27
\_\_\_\_\_\_\_\_\_\_\_: this subunit is unique to thyroid hormone
–β subunit
28
what suppress TSH
–Dopamine, glucocorticoids, and somatostatin
29
\_\_\_\_\_\_\_\_\_\_\_\_ stimulates pituitary production of **TSH**,
Hypothalamic TRH
30
\_\_\_\_\_\_\_\_\_\_\_- stimulates thyroid hormone synthesis and secretion.
TSH
31
Thyroid hormones, acting predominantly through thyroid hormone receptor \_\_\_\_\_\_\_\_\_\_\_, feed back to **inhibit TRH and TSH production.**
β2 (TRβ2)
32
\_\_\_\_\_\_\_\_\_\_\_\_\_secreted by the **thyrotrope cells** of the anterior pituitary, plays a pivotal role in **control of the thyroid axis and serves as** the **most useful physiologic marker of thyroid hormone action. ** It is a 31-kDa hormone composed of **α and β subunits**; the **α subunit** is common to the o**ther glycoprotein hormones [luteinizing hormone, follicle-stimulating hormone, human chorionic gonadotropin (hCG)],** whereas the **TSH β subunit is unique to TSH.**
TSH,
33
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_-suppress TSH but are **not of major physiologic importance except when these agents are administered in pharmacologic doses.**
Dopamine, glucocorticoids, and somatostatin
34
TSH regulates thyroid gland function through the \_\_\_\_\_\_\_\_\_\_\_\_\_\_, a seventransmembrane G protein–coupled receptor (GPCR). Most of these activating mutations occur in the transmembrane domain of the receptor. They mimic the conformational changes induced by TSH binding or the interactions of thyroid-stimulating immunoglobulins (TSI) in Graves’ disease.
TSH-R
35
Thyroid follicles are formed by **thyroid epithelial cells** surrounding **proteinaceous colloid**, which **contains**\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
thyroglobulin
36
\_\_\_\_\_\_\_\_\_\_\_\_\_\_- which are polarized, synthesize thyroglobulin and carry out thyroid hormone biosynthesis (see text for details).
**Follicular cells**,
37
**T4** is secreted from the thyroid gland in **about\_\_\_\_\_\_\_\_\_\_\_excess over T3** (Table 341-2) .
** twentyfold **
38
Thyroid hormones bind to what proteins?
* thyroxine-binding globulin (TBG), * transthyretin (TTR, formerly known as thyroxine-binding prealbumin, or TBPA), and * albumin.
39
What is the purpose of the plasma-binding proteins\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
* increase the pool of circulating hormone, * delay hormone clearance, * and may modulate hormone delivery to selected tissue sites.
40
When the effects of the various binding proteins are combined, approximately **99.98% of T 4** and **99.7% of T 3 are protein-bound.’**
41
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ may be thought of as a precursor for the **more potent T 3**.
T 4
42
T4 is converted to T 3 by the\_\_\_\_\_\_\_\_\_\_\_\_\_ (see slide 3)
deiodinase enzymes.
43
T 3 is bound with **10–15 times greater affinity than T4** , which explains its\_\_\_\_\_\_\_\_\_\_\_\_-. **Though T 4 is produced in excess of** T 3 , **receptors are occupied mainly by T 3** , **reflecting T 4 → T 3 conversion by peripheral tissues, greater T 3 bioavailability in the plasma, and receptors’ greater affinity for T 3 .**
increased hormonal potency
44
Plasma proteins: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ - carries about **80% of the bound hormones**
Thyroxine-binding globulin
45
• - \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_-carries about **10% of T 4** but **little T3**
Transthyretin
46
\_\_\_\_\_\_\_\_\_\_\_\_\_\_ - **binds up to 10% of T 4** and **30% of T3**
•Albumin
47
The deiodinases
* Type I * Type II * Type III
48
Type I deiodinase, which is located **primarily in\_\_\_\_\_\_\_\_\_\_\_, ___________ and \_\_\_\_\_\_\_\_\_\_\_** has a relatively **low affinity for T 4**.
* ** thyroid,** * **liver,** * **and kidneys**,
49
Type II deiodinase has a **higher affinity for T 4** and is found primarily in the \_\_\_\_\_\_\_\_\_\_, \_\_\_\_\_\_\_\_\_\_\_\_-, ____________ and \_\_\_\_\_\_\_\_\_
* pituitary gland, * brain, * brown fat, * and thyroid gland.
50
Expression of type II deiodinase allows it to\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_-, a property that may be important in the **context of levothyroxine (T 4 ) replacement.** Type II deiodinase is also **regulated by thyroid hormone;** **hypothyroidism** induces the enzyme, resulting **in enhanced T 4 → T 3 conversion** in tissues such as **brain and pituitary**
regulate T 3 concentrations locally,
51
. T 4 → T 3 conversion is impaired by\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
* fasting, * systemic illness * or acute trauma, * oral contrast agents, * and a variety of medications (e.g., **propylthiouracil, propranolol, amiodarone, glucocorticoids)**.
52
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_- **inactivates** T 4 and T 3 and is the **most important source of reverse T 3 (rT 3** ).
Type III deiodinase
53
\_\_\_\_\_\_\_\_\_\_\_\_\_- that **express type III deiodinase** are a **rare** cause of **hypothyroidism in infants.**
Massive hemangiomas
54
Measurement of thyroid hormones * TSH levels change dynamically in **response to alterations of T4 and T3** * **finding of an abnormal TSH** level must be followed by **measurements of circulating thyroid hormone levels **
55
Because TSH levels change dynamically in response to alterations of T 4 and T 3 , a **logical approach** to thyroid testing is to **first determine whether TSH is \_\_\_\_\_\_\_\_\_\_\_\_, _________ and \_\_\_\_\_\_\_**
**suppressed**, normal, or elevated.
56
The **finding of an abnormal TSH level** must be followed by \_\_\_\_\_\_\_\_\_\_\_\_\_to **confirm the diagnosis of hyperthyroidism** (suppressed TSH) or **hypothyroidism (elevated TSH).**
measurements of circulating thyroid hormone levels
57

2H. IM (13 decks)

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