Thyroid & Parathyroid glands

Question 1

What are the three layers of the cervical viscera, superficial to deep?

Answer 1

1. Endocrine layer: the thyroid and parathyroid glands.
2. Respiratory layer: the larynx and trachea.
3. Alimentary layer: the pharynx and esophagus

Question 2

What 2 hormones are produced by the thyroid + what are their functions?

Answer 2

thyroid hormone (T3,T4), which controls the rate of metabolism

calcitonin, a hormone decreasing calcium metabolism.

Question 3

What hormone is produced by the parathyroid glands + what is its function?

Answer 3

parathormone (PTH), controls the metabolism of phosphorus and calcium in the blood; increases calcium level in blood.

Question 4

The parathyroid glands targets what 3 regions/structures in the body?

Answer 4

skeleton

kidneys

bones

Question 5

The thyroid gland lies deep to which 2 muscles located anteriorly in the neck?

It lies at the level of which vertebrae?

Answer 5

• sternothyroid + sternohyoid muscles
• C5 - T1

Question 6

The right and left lobes of the thyroid lie where, in relation to the larynx and trachea?

What connects the 2 lobes and at what level?

Answer 6

• anterolateral to the larynx + trachea
• thin isthmus; usually anterior to the 2nd + 3rd tracheal rings.

Question 7

Dense connective tissue attaches the fibrous thyroid capsule to which 2 structures?

•External to the capsule is a loose sheath formed by …?

Answer 7

• the cricoid cartilage and **superior tracheal rings. **
• the visceral portion of the pretracheal fascia (deep cervical fascia)

Question 8

Which 2 arteries lie between the fibrous capsule + the loose fascial sheath supplying blood to the thyroid?

Answer 8

• superior + inferior thyroid arteries

*1st branch of ECA = superior thyroid artery: descends to superior poles of gland, pierce pretracheal fascia, +divides into anterior + posterior branches supplying mainly the antero-superior aspect of the gland

** accompanied by External Laryngeal Nerve –> innervates cricothyroid m.

Question 9

•The inferior thyroid arteries are the largest branches of what?

Answer 9

• thyrocervical trunks (fr. subclavian arteries)
• * run superomedially posterior to the carotid sheaths to reach the posterior aspect of the thyroid gland. *
• **divide into several branches that pierce the pretracheal layer of the deep cervical fascia + supply the posteroinferior aspect, including the inferior poles of the gland. *
• *** right + left superior / inferior thyroid arteries anastomose extensively within the gland*

Question 10

Thyroid Ima Artery

• found in what percentage of people?
• usually arises from what artery?
• location?
• supplies blood to…?

Answer 10

• 10% of people
• brachiocephalic trunk
• (may arise fr. arch of the aorta or from the right common carotid, subclavian, or internal thoracic arteries)*
• -* ascends on the anterior surface of the trachea
• divides and supplies the isthmus

*artery must be considered when performing procedures in the midline of the neck inferior to the isthmus (tracheotomy) because it is a potential source of bleeding

Question 11

What are the three pairs of thyroid veins (usually forming a thyroid plexus of vv.) on the anterior surface of the thyroid gland (anterior to the trachea)?

Answer 11

• superior thyroid veins: accompany superior thyroid arteries; drain the superior poles of the thyroid gland; drains into IJV
• middle thyroid veins: do not accompany but run essentially parallel courses with the inferior thyroid arteries; they drain the middle of the lobes; drains into** IJV**
• Inferior thyroid veins: usually independent; drain the inferior poles; drains into **brachiocephalic v. **(posterior to the manubrium)

Question 12

THYROID ARTERIES

Answer 12

THYROID VEINS

Question 13

Lymphatic vessels from thyroid gland run where?

The vessels pass into the prelaryngeal, pretracheal, + paratracheal nodes, whic hdrain into..?

Answer 13

• in the interlobular connective tissue
• *(they communicate with a capsular network of lymphatic vessels)*
• superior deep cervical nodes (from the prelaryngeal nodes) + inferior deep cervical nodes (from the pretracheal and paratracheal nodes).
• **Laterally, vessels along superior thyroid veins pass directly to inferior deep cervical lymph nodes; some nodes may drain into the brachiocephalic lymph nodes or thoracic duct.*

Question 14

thyroid cancer

• most common type of endocrine cancer
• Low iodine, high radiation all contribute to increased incidence
• Prognosis serious b/c lymph nodes located in close proximity to carotid sheath.. difficult to remove without injuring these vessel; life expectancy usually 1-2 years MAX.
• May also metastasize to the lungs

Answer 14

Question 15

• Nerves of the thyroid gland are derived from the …(3) ganglion?
• They reach the gland through which 3 plexuses?
• Are the fibers vasomotor or secretomotor?
• Endocrine secretion from the thyroid gland is hormonally regulated by the ..?

Answer 15

• superior, middle, + inferior cervical sympathetic ganglia.
• cardiac + superior & inferior thyroid periarterial plexuses (accompany thyroid aa.)
• vasomotor (cause constriction of blood vessels)
• pituitary gland!!!

Question 16

Thyroglossal Duct Cysts

• what is the embryological origin + path of descent of the thyroid gland?
• during the descent, the thyroid gland is attached to the foramen cecum by the..?
• duct normally disappears, but remnants may cause a cyst. Where is it usually located?

Answer 16

• begins in floor of the embryonic pharynx (foramen cecum); dorsum of the postnatal tongue.
• descends from the tongue into the neck, passing anterior to the hyoid and thyroid cartilages; final position = anterolateral to the superior part of the trachea.

- thyroglossal duct.

• usually near or within body of hyoid; swelling in anterior part of neck; always on the midline of the neck!!!!

*Size 1 to 4 cm in diameter
**Lined by stratified squamous epithelium; cyst may harbor lymphoid aggregates or remnants of recognizable thyroid tissue

Question 17

Ectopic Thyroid Gland

What causes an ectopic thyroid gland?

What are 3 common locations?

How do you differentiate between an ectopic thyroid gland and a thyroglossal duct cyst?

Answer 17

• thyroid gland fails to descend from its embryonic origin in the tongue
• lingual; high in the neck; just inferior to thyroid bone
• ectopic thyroid gland in the median plane of the neck is the **only thyroid tissue present; ** thyroglossal duct cyst may not be the only thyroid tissue present
• ** injecting a radioactive isotop (iodine) + scan the area for other potential throid tissue*

Question 18

Accessory Thyroid Glandular Tissue

Accessory thyroid tissue may develop where?

*Although the accessory tissue may be functional, it is often of insufficient size to maintain normal function if the thyroid gland is removed.

Answer 18

may appear anywhere along the embryonic course of the thyroglossal duct; in the neck lateral to the thyroid cartilage; it usually lies on the thyrohyoid muscle

Question 19

Pyramidal Lobe of the Thyroid Gland

• what percentage of thyroid glands have a pyramidal lobe?
• where is it usually located?
• *band of connective tissue, often containing accessory thyroid tissue, may continue from the apex of the pyramidal lobe to the hyoid. *
• The pyramidal lobe and the band develop from what?

Answer 19

• Approximately 50%
• extends superiorly from the isthmus of the thyroid gland, usually to the left of the median plane; the isthmus may be incomplete.
• remnants of the epithelium and connective tissue of the thyroglossal duct.

Question 20

Enlargement of the Thyroid Gland

• A non-neoplastic + non-inflammatory enlargement of the thyroid gland is called…?
• it’s caused by…?
• enlarged gland causes a swelling in the neck that may compress which 3 structures?

Answer 20

• a goiter
• a lack of iodine (N= 150micro g/day)
• trachea, esophagus + recurrent laryngeal nerves.

Question 21

• An enlarged thyroid gland can enlarge in which directions?
• It cannot move superiorly because…?

Answer 21

• anteriorly, posteriorly, inferiorly, or laterally.
• superior attachments of the sternothyroid + sternohyoid muscles.

Question 22

GOITERS
(aka, thyromegaly, diffuse or nodular)

• IODINE deficiency
• Grave’s Disease
• Increased TSH
• Goitrogens, (e.g., cabbage, Brussels sprouts, cauliflower, turnips, cassava) –> interfere w. iodine uptake
• Associated with HYPOthyroidism eventually, NOT hyperthyroidism

Answer 22

• Decreased Iodine –> decreased thyroid hormone –> increased TSH –> increased growth of follicles
• That’s how an iodine deficiency leads to a goiter.
• The probability of having a goiter is DIRECTLY proportional to how far you live from the ocean.

Question 23

What is the adaptive response shown by the thyroid, which causes goiters?

Answer 23

adaptive response

The thyroid enlarges to try to trap more iodine, when serum levels are low –> GOITER

Question 24

2 types of:

DIFFUSE NONTOXIC (SIMPLE) GOITERS ?

Answer 24

Endemic and Sporadic

Question 25

**hypothalamus-pituitary-thyroid axis:** what is the mechanism including TRH, TSH, T3+T4 ?

Answer 25

**negative feedback mechanisms:** Low production of T3, T4 by thyroid gland will cause increased production of TSH in pituitary gland!!!

Question 26

4 effects of Thyroid Hormone Action (T3+T4)?

Answer 26

Both T3 and T4: 1. increase cell metabolism 2. facilitate normal growth 3. facilitate normal mental development 4. increase the local effects of catecholamines *(type of organic compound)*

Question 27

**Hyperthyroidism** Hypermetabolic state + overactivity of the sympathetic NS (info card)

Answer 27

**Skin:** soft, warm, and flushed because of increased blood flow and peripheral vasodilation to increase heat loss. Heat intolerance, increased sweating Weight loss Increased appetite **CVS:** Increase cardiac output, tachycardia, palpitations, and cardiomegaly are common. Arrhythmias, particularly atrial fibrillation Thyrotoxic or hyperthyroid cardiomyopathy and congestive heart failure **Nervous system:** Tremor, hyperactivity, emotional lability, anxiety, inability to concentrate, and insomnia. Proximal muscle weakness and decreased muscle mass - thyroid myopathy. **Eyes:** Wide, staring gaze and lid lag are present because of sympathetic overstimulation of the levator palpebrae superioris, in case of Graves disease - proptosis **GI:** Increased appetite, hypermotility, malabsorption, diarrhea and fatty changes in the hepatocytes **Skeletal system:** osteoporosis , atrophy of skeletal muscles with fatty infiltration

Question 28

**hypothyroidism: cretinism and myxedema** •Most Common cause – iodine deficiency!!! *(info card)*

Answer 28

**•CRETINISM ** hypothyroidism that develops in infancy or early childhood. •**Location**: where dietary iodine deficiency is endemic (mountains) **•Clinical features:** include impaired development of the skeletal system and central nervous system, manifested by severe mental retardation, short stature, coarse facial features, a protruding tongue, and umbilical hernia. •The severity of the mental impairment in cretinism related to the time at which thyroid deficiency occurs in utero. If there is maternal thyroid deficiency before the development of the fetal thyroid gland, mental retardation is severe.

Question 29

**hypothyroidism: MYXEDEMA (Gull disease) ** Chronic autoimmune thyroiditis (most common cause in NA) *(info card)*

Answer 29

•Hypothyroidism developing in the older child or adult. **Clinical features of myxedema:** **•CNS:** slowing of physical and mental activity, fatigue, apathy, and mental sluggishness •Speech and intellectual functions become slowed, deepening in the voice •Patients with myxedema are listless, cold intolerant, and frequently overweight **•GI:** constipation, enlargement of the tongue, unexplained weight gain **•Skin:** decreased sweating, skin cool and pale because of decreased blood flow, non pitting edema (accumulation of glycosaminoglycans), **•CVS:** shortness of breath and decreased exercise capacity, increase in total cholesterol and low-density lipoprotein (LDL) levels

Question 30

Thyroid ADENOMAS (aka. follicular adenomas) * (info card)*

Answer 30

* Clinically - nodules of follicular hyperplasia * Follicular adenomas are not risk factor for to carcinomas; * Although the vast majority of adenomas are nonfunctional, * Hormone production in functional adenomas (“toxic adenomas”) is independent of TSH stimulation and represents another example of thyroid autonomy, analogous to toxic multinodular goiters.

Question 31

thyroid adenoma: Morphology

Answer 31

* The typical thyroid adenoma is a solitary, spherical, encapsulated lesion that is well demarcated from the surrounding thyroid parenchyma * Follicular adenomas average about 3 cm in diameter, but some are much larger (≥10 cm in diameter). * The neoplastic cells are demarcated from the adjacent parenchyma by a well-defined, intact capsule.

Question 32

THYROID CARCINOMAS *(info card)* **•Papillary carcinoma** (most common type) **•Follicular carcinoma •Anaplastic (undifferentiated) carcinoma** (worst type) **Medullary carcinoma**

Answer 32

``` **•1.5% of all cancers.** •A female predominance has been noted among patients who develop thyroid carcinoma in the early and middle adult years. In contrast, cases presenting in childhood and late adult life are distributed equally among males and females. •Most thyroid carcinomas (except medullary carcinomas) are derived from the thyroid follicular epithelium, and of these, the vast majority are well-differentiated lesions. _•The major subtypes of thyroid carcinoma and their relative frequencies include the following:_ **•Papillary carcinoma (\>85% of cases) •Follicular carcinoma (5% to 15% of cases) •Anaplastic (undifferentiated) carcinoma (\<5% of cases) Medullary carcinoma (5% of cases)** ```