Ch 2 Thyroid

Question 1

What is the thyroid gland?

Answer 1

An endocrine gland (which releases hormones that go directly into the bloodstream)

Question 2

What does the thyroid gland do?

Answer 2

-Synthesizes, stores + secretes thyroid hormones
-Functions to control the BMI (basal metabolic rate)

Question 3

What shape is the thyroid?

Answer 3

Butterfly shaped (has 2 lobes + an isthmus)

Question 4

Where is the thyroid located?

Answer 4

Lower neck

Question 5

What is the echo texture of the thyroid?

Answer 5

-Very homogeneous (when normal)
-Medium-high level
-Has a fibrous capsule

Question 6

What is the average size of the thyroid?

Answer 6

Length: 4-6cm
AP: 1.3-1.8cm
Isthmus: 4-6mm

Question 7

List the 4 main arteries supplying the thyroid?

Answer 7

-Paired superior thyroid arteries: arise off the ECA

-Paired inferior thyroid arteries: arise from the thyrocervical trunk of the subclavian artery

(sometimes the thyroid ima artery as well - it is an anomaly that only some pt’s have)

Question 8

How many veins drain the thyroid plexus?

Answer 8

3: the superior, middle + inferior thyroid veins

Question 9

The superior + middle thyroid vein come off of which vein?

Answer 9

The internal jugular vein (IJV)

Question 10

The inferior thyroid veins come off of which vein?

Answer 10

The brachiocephalic vein (BCV)

Question 11

What are the 3 thyroid hormones?

Answer 11

-T3 (triiodothyroine)
-T4 (thyroxine)
-Calcitonin (thyrocalcitonin)

Question 12

Which thyroid hormones m/c affect the body’s metabolism?

Answer 12

T3 + T4

Question 13

How is T3 + T4 made?

Answer 13

Follicular cells process iodine to secrete T3 + T4, this increases metabolism

Question 14

Is there more T3 or T4 in the bloodstream?

Answer 14

-There is more T4
-The body converts T4 into T3
-T3 is more potent + is produced in lesser quantity

Question 15

Calcitonin is secreted by what type of cells?

Answer 15

Parafollicular cells (c-cells), this lowers blood calcium levels

Question 16

What are follicles?

Answer 16

-Many small sacs throughout the thyroid
-They are lined with follicular cells and contain colloid in the center

Question 17

How are thyroid hormones made?

Answer 17

-Iodine binds with thyroglobulin (a protein) within the colloid part of a follicle to form thyroid hormones
-The follicular cells reabsorb thyroglobulin + chemically processes T3 + T4

Question 18

Do thyroid hormones circulate freely or when bound to protein (TBG)?

Answer 18

Both!

Question 19

What are thyroid lab tests typically testing for?

Answer 19

-Both free + total T3, T4 + TSH
-Typically testing for conditions such as hyperthyroidism + hypothyroidism

Question 20

When would calcitonin be tested?

Answer 20

Specifically for cancers

Question 21

What does euthyroid mean?

Answer 21

Normal lab values

Question 22

What is thyrotropin-releasing hormone (TRH) released from?

Answer 22

The hypothalamus

Question 23

What is thyrotropin-stimulating hormone (TSH) released from?

Answer 23

The anterior pituitary gland

Question 24

What does TSH do?

Answer 24

Arranges thyroid hormone production

Question 25

TSH is regulated by what?

Answer 25

T3, T4 + TRH

Question 26

Explain the negative feedback loop of the thyroid in 5 steps?

Answer 26

1. Decrease in thyroid hormone causes decreased BMR 2. Decreased BMR stimulates release of TRH 3. TRH induces the release of TSH 4. Thyroid releases T3 + T4 5. BMR returns to normal

Question 27

What is the earliest endocrine gland to form in the human embryo?

Answer 27

The thyroid

Question 28

When is the thyroid fully developed?

Answer 28

By the end of the 1st trimester

Question 29

Development of the thyroid begins at what level?

Answer 29

Level of the primitive pharynx (corresponds to the base of the tongue in adults)

Question 30

As the thyroid develops, the cells migrate downwards in the neck through a canal called what?

Answer 30

The thyroglossal tract/duct (this duct m/c disappears once the thyroid reaches its final position in the neck)

Question 31

What is athyrosis + what is it associated with?

Answer 31

-The most severe abnormality of the thyroid -Associated with cretinism or congenital hypothyroidism

Question 32

What is a pyramidal lobe?

Answer 32

-The m/c variation of the thyroid -Typically extends upward from the isthmus -Can arise from either lobe

Question 33

What is the m/c ectopic location for the thyroid?

Answer 33

Lingual (very rare tho)

Question 34

List 3 other thyroid variations that exclude athyrosis, pyramidal lobe + ectopic locations?

Answer 34

-Absence of isthmus -Absence of 1 lobe (results in compensatory hypertrophy) -Continuity of 1 lobe to the other (no distinguishable isthmus)

Question 35

How common is thyroid pathology?

Answer 35

Very!!!

Question 36

How does the thyroid look when compared to the surrounding muscles?

Answer 36

Homogeneous + echogenic to muscles

Question 37

What are the 3 main hormones produced by the thyroid?

Answer 37

T3, T4 + calcitonin

Question 38

What is the m/c variation of the thyroid?

Answer 38

Pyramidal lobe