Thyroid Anatomy and Pathology I

Question 1

thyroid gland forms at the base of the __, then it descends to set at the __ __. there are still connections from where it started to where it ended up called the __ __. If this duct is compromised, the thyroid might be in the ___ ___ position, called an __ __.

A cyst can also develop on the residual duct, called (creatively) a __ ___ ___.

All in all, if there are changes in the embryonic development of the thyroid, it can cause dysfunction and lead to __ __.

Answer 1

thyroid gland forms at the base of the tongue, then it descends to set at the epitracheal rings. there are still connections from where it started to where it ended up called the thyroglossal duct. If this duct is compromised, the thyroid might be in the wrong anatomical position, called an ectopic thyroid.

A cyst can also develop on the residual duct, called (creatively) a thyroglossal duct cyst.

All in all, if there are changes in the embryonic development of the thyroid, it can cause dysfunction and lead to neonatal hypothyroidism.

Question 2

A lingual thyroid is caused by a failure of ___. It can be seen on physical exam and by trapping of radioiodine

Answer 2

A lingual thyroid is caused by a failure of __. It can be seen on physical exam and by trapping of radioiodine

Question 3

Answer 3

a thyroglossal duct cyst

Question 4

Answer 4

Question 5

Thyroid gross anatomy
Normal adult gland weighs 15-20 gm

• ___ lateral lobes, 4 cm long, 2 cm wide
• __ joins the lobes, below the cricoid cartilage.
• lobes extend up to the level of the __ cartilage

Gland is surrounded by a thin __ __ that is
posteriorly attached to the __ & __ (and is __ sensitive- the thyroid doesnt have pain but the capsule does)
– thus, the thyroid gland moves upwards with swallowing

Answer 5

Normal adult gland weighs 15-20 gm

• Two lateral lobes, 4 cm long, 2 cm wide

• Isthmus joins the 2 lobes, below the cricoid cartilage.

• lobes extend up to the level of the thyroid cartilage

Gland is surrounded by a thin fibrous capsule that is
posteriorly attached to the trachea & larynx (and is pain sensitive)
– thus, the thyroid gland moves upwards with swallowing

Question 6

Arterial Drainage;

• Inferior thyroid artery is a branch of the __ artery
• Superior thyroid artery is a branch of the __ carotid

Venous drainage: __, __, __ thyroid veins

Answer 6

Arterial Drainage;

Inferior thyroid artery is a branch of the subclavian artery

Superior thyroid artery is a branch of the external carotid

Venous drainage: superior, middle, inferior thyroid veins

Question 7

__ __ nerve lies adjacent to the postromedial aspect of the thyroid, near the __ between the lateral aspect of the __ & __; this nerve contains the __ __ for the abductor muscles of the true __ __.

Answer 7

Recurrent laryngeal nerve lies adjacent to the postromedial aspect of the thyroid, near the groove between the lateral aspect of the trachea & esophagus; this nerve contains the motor fibers for the abductor muscles of the true vocal cords.

Question 8

A thyroid malignancy may not be palpable on the exam, but you might see it in the ___ ___.

Answer 8

lymph glands. YOU MUST DO A LYMPH EXAM WHEN DOING A THYROID EXMA

Question 9

Answer 9

Question 10

Tracheal blockage would cause what kind of sound while breathing? What would the volume curve show?

Answer 10

inspiratory stridor

Question 11

common symptoms of large goitor

Answer 11

inspiratory stridor

• hoarseness because of recurrent laryngeal nerve impingement

dysphagia because of esophageal compression

Question 12

microscopic anatomy of thyroid:

compartmentalized into __ composed of ___. Around these cells are _____ which contain calcitonin

Answer 12

compartmentalized into lobules composed fo follicles. Around the follicles are parafollicular/C cells that create calcitonin

Question 13

pemberton sign

Answer 13

goiter blocks the thoracic inlet of the jugular veins, preventing blood flow when you raise your arms

Question 14

which laryngeal nerve is affected when the thyroid is enlarged?

Answer 14

only the LEFT!

Question 15

pituitary TSH stimualtes the follicular cells of the thyroid, which releases __

Answer 15

pituitary TSH stimualtes the follicular cells of the thyroid, which releases thyroxin.

In the image, the “colloid” is the stored thyroxin

Question 17

thyroxin is aka

Answer 17

T4

Question 18

Outline the hypothalamic hormonal control of the thyroid

Answer 18

1. hypothalamus releases TRH: thyrotropin releasing hormone
2. TFH stimulates pituitary to release TSH: thyroid stimulating hormone
3. Pituitary TSH stimulates the follicles of the thyroid to release THYROXIN: T4, as well as T3.

Question 19

Outline the how thyroid hormones influnece;
1. heart

2. liver
3. bone
4. CNS

Answer 19

1. heart- increase in contraction
2. liver: increase release
3. bone : growth
4. CNS: works more– wakes up– less sluggish
   - overall, thyroid hormone is a stimulator

Question 20

How is the thyroid involved in negative regulation?

Answer 20

TSH secretion (made by th epituitar) is regulated by the T4 and T3 from the thyroid and from TRH of the hypohalamus.

• response to elevated levels of thyroid hormones shuts off the production cascade

Question 21

What is the mechanism of action of TSH peptide on thyroid?

Answer 21

the TSH (from pituitary) have alpha and beta subunits. Beta is unique– there are different beta units in FSH, LH, and betaHCG). it binds to G protien receptor on the thyoid.

Question 22

What happens inside the thyroid gland?

All in response to the stimulation by TSH:

1.Uptake of __ into the follicular cell

2.Synthesis of _ (and __) within the __ cell
(and stored)
3.Release of ready-made stored T4 (and T3) from the _ of the follicle into the circulation

Answer 22

All in response to the stimulation by TSH:

1.Uptake of iodine into the follicular cell

2.Synthesis of T4 (and T3) within the follicular cell
(and stored)
3.Release of ready-made stored T4 (and T3) from the colloid of the follicle into the circulation

Question 23

you need __ to create T4 and T3.

Answer 23

you need iodine to create T4 and T3.

Question 24

synthesis of T4 and T3 happen on the __ protein, which uses __ to differentiate between different thyroid hormones. It is then stored in the __.

Answer 24

synthesis of T4 and T3 happen on the THYROGLOBULIN protein, which uses iodine to differentiate between different thyroid hormones. It is then stored in the colloid.

ex/ Tyrosine on the TGP adds 1 Iodine to create mono-iodotyrosine (MIT). If tehrea re 3 iodines, it’s T3, and if its 4 iodines, it’s T4.

Question 25

___is the main secreted form of thyroid hormone, and the main form transported in __;

__ is mainly an intracellular product of T4 in the target cells

Answer 25

T4 is the main secreted form, and the main form transported in blood;

T3 is mainly an intracellular product of T4 in the target cells

Question 26

Which form of thyroid hormone acts on the DNA of the cell that it gets engulfed in?

Answer 26

T4 is the main circulator, but when it gets endocytosesd by the receiving cell, it gets de-iodinated to become T3. T3 acts inside the cell.

Question 27

otuline the release of thyroxin (and some T3) into the blood from the thyroid

Answer 27

thyroxin is contained in the colloid (middle of the follicle). It gest endocytosed into the thyroid follicular cell, where lysosomes degrade the colloid vesible and the thyroglobulin component is cleaved by proteolysis to releas T3 and T4

Question 28

Question 29

Outline the peripheral metabolism of thyroxine, when it gets absorbed by the peripheral target cell

Answer 29

T4 goes in, where D2 cleaves it to T3. T3 enters the nucleus and affects transcription by binding to the Tr-RXR activator, causing transcription of the T3 resposnive gene.

MrnA is created which causes protein synthesis and overall T3 effects. Depending on the cell, growth, temperature incrase, oxygen consumption, increase in metabolism, cardiovascular effects

Question 30

Outline the Wolff Charikoff Effect

Answer 30

During the first day of iodine xposure, the sodium-iodide symporter transports the excess iosine into the thyroid, resulting in transient inhibition of thyroid peroxidase (TPO) and a decrease in thyroid hormone synthesis.

• the decrease in sodium-iodide symporter expression results in decreased iodine transport and the subsequent resumption of thyroid hormone synthesis.

The Wolff–Chaikoff effect is an effective means of rejecting a large quantity of imbibed iodide, and therefore preventing the thyroid from synthesizing large quantities of thyroid hormone.

Question 31

outline the general mechanism for how iodine deficinecy causes goiter

Answer 31

Question 32

T/F when assessing T4 levels, you should measure total levels

Answer 32

false. only measure FREE t4, because many are protein bound which renders bound T4 inactive.

Question 33

Serum ___ is the most sensitive screening test for primary hyperthyroidism and primary hypothyroidism

Answer 33

Serum TSH is the most sensitive screening test for primary hyperthyroidism and primary hypothyroidism

Question 34

serum TSH is high in ____ ___
serum TSH is low in ____ ____

Answer 34

serum TSH is high in PRIMARY HYPOTHYROIDISM
serum TSH is low in PRIMARY HYPERTHYROIDISM

Question 35

Serum TSH is the BEST initial test for primary thyroid disease, since it lets the pituitary tell you how the thyroid is doing.

What test should be done to confirm a THYROID disease after the serum TSH is found to be abnormal?

Answer 35

SERUM FREE THYROXIN (non-protein bound)

Question 37

Miscellaneous Lab Measurements;

Hashimotos’ thyroiditis:

Graves disease:

A test done in the absence of the thyroid gland:

Answer 37

Hashimotos’ thyroiditis: Anti-thyroid antibodies

Graves disease: Antibody to TSH receptor

A test done in the absence of the thyroid gland: Serum thyroglubulin

Question 38

Question 39

note; outline the diagnostic approach for primary thyroid dysfunction