infrahyoid muscles and thyroid gland

Question 1

the thyroid gland begins where?

Answer 1

in floor of pharynx as an invagination at foramen cecum and then descends inferiorly alongside larynx

Question 2

thyroid gland may be connected to foramen cecum by what?

Answer 2

thyroglossal duct

Question 3

thyroid gland is divided into?

Answer 3

two lateral lobes connected by an isthmus

Question 4

follicular cells are derived from?

Answer 4

endoderm

Question 5

parafollicular cells are derived from?

Answer 5

ultimobranchial body (4-6 pouch)

Question 6

where is the thyroid gland ?

Answer 6

between the 5th cervical and 1st thoracic vertebrae

Question 7

arterial supply of thyroid

Answer 7

from superior and inferior thyroid arteries

Question 8

superior thyroid artery

Answer 8

• the first branch to arise from the **external carotid artery
• glandular branches (lateral and anterior)
• thryoid ima artery (from brachiocephalic trunk)

Question 9

**the inferior thyroid artery is from?

Answer 9

branch of thyrocervical trunk

Question 10

venous drainage of thyroid

Answer 10

forms a plexus on surface of thyroid gland that drains into superior, middle, and inferior thyroid veins

Question 11

what innervates the larynx?

Answer 11

superior laryngeal nerve and recurrent laryngeal nerve

Question 12

two branches of vagus nerve

Answer 12

1. superior laryngeal – internal laryngeal (sensory) and external laryngeal (motor)
2. recurrent larygneal– right: behind the right subclavian artery; left: behind the aortic arch

Question 13

the recurrent laryngeal nerve ascends between

Answer 13

trachea and esophagus

Question 14

reccurent laryngeal nerve supplies

Answer 14

• motor innervation to laryngeal muscles (except cricothyroid)
• viscerosensory innervation to the laryngeal mucosa

Question 15

what leads to ipsilateral palsy of vocal folds?

Answer 15

damage to recurrent laryngeal nerve (due to thyroidectomy)

• prevents abduction of vocal folds, causing hoarseness
• bilateral nerve loss causes asphyxiation

Question 16

what is the thyroid gland composed of?

Answer 16

• covered by fibrous capsule from which septa extend into parenchyma dividing it into lobules and carrying blood vessels nerves and lymphatics
• lobules consist of colloid-filled epithelial follicles
• each follicle is filled with colloid of a large gelatinous protein called thyroglobulin

Question 17

lobules are lined by?

Answer 17

cuboidal epithelial cells

Question 18

follicular cells

Answer 18

synthesize and exocytose thyroglobulin into lumen as a component of colloid
-also concentrate iodine from blood

Question 19

follicular cells secrete

Answer 19

• tri-iodothyronine (T3)

- tetra-iodothyronine (T4)

Question 20

overactive follicles

Answer 20

• -reduced colloid content

- -smaller because they release more T3 and T4

Question 21

underactive follicles

Answer 21

• -increased amount of colloid

- -huge because they store more colloid

Question 22

parafollicular cells or C cells

Answer 22

• release calcitonin

- individually or in groups between follicular cells or in connective tissue

Question 23

what triggers release of calcitonin?

Answer 23

triggered by elevated blood Ca levels

inhibits osteoclast activity

Question 24

what does the microvasculature of the parathyoid gland arise from?

Answer 24

inferior thyroid arteries

Question 25

superior parathyroid gland is from?

Answer 25

4th pharyngeal pouch

Question 26

inferior parathyroid gland is from?

Answer 26

3rd pharyngeal pouch

Question 27

parathyroid glands

Answer 27

- secrete parathyroid hormone - stimulated by a decrease in blood calcium levels - PTH is synthesized by chief cells (principal cells) - oxyphil cells (aged chief cells -- no longer secrete PTH)

Question 28

PTH function

Answer 28

- osteoblasts respond to PTH by making RANKL which increases osteoclasts - resulting resorption--> release of Ca --> increases Ca concentration in circulation, which suppresses PTH production - distal convoluted tubules--PTH stimulates Ca reaborption (and inhibits phos reabs in proximal tubules) - indirectly increases Ca absorption in small intestine by stimulating vitamin D activation

Question 29

effect of PTH on blood levels of Ca is opposite of?

Answer 29

calcitonin

Question 30

infrahyoid muscles

Answer 30

- two superficial (omohyoid and sternohyoid) | - two deep (sternothyoid and thyrohyoid)

Question 31

nerve supply of infrahyoid

Answer 31

ansa cervicalis except the thyrohyoid (C1)

Question 32

omohyoid

Answer 32

- superior and inferior belly - inferior originates from superior border of scapula - runs anteriorly and medially across the posterior triangle of neck and narrows down to intermediate tendon - superior belly passes deep to sternocleidomastoid muscle, emerges into anterior triangle, and inserts into body of hyoid bone

Question 33

actions of omohyoid muscle

Answer 33

- depresses hyoid; draws larynx and hyoid down for phonation and terminal phases of swallowing - nerve supply: ansa cervicalis

Question 34

sternohyoid

Answer 34

- arises from posterior aspect of manubirum of sternum and head of clavicle - fibers pass upward, over anterior aspect of trachea and larynx and insert into body of hyoid bone above

Question 35

action of sternohyoid

Answer 35

- depresses hyoid - draws larynx and hyoid down for phonation and terminal stages of swallowing - nerve supply: ansa cervicalis

Question 36

sternothyroid muscle

Answer 36

- deep to sternohyoid - origin from posterior aspect of manubrium of sternum - inserts above into oblique line of thyroid cartilage

Question 37

action of sternothyroid

Answer 37

- depresses hyoid - draws larynx and hyoid down for phonation and swallowing terminally - nerve supply: ansa cervicalis

Question 38

thyrohyoid muscle

Answer 38

- originates from oblique line of thyroid cartilage | - passes upward to insert into body of hyoid bone

Question 39

action of thyrohyoid

Answer 39

- depresses hyoid - raises larynx during swallowing - nerve supply: C1 via CN XII **