infrahyoid muscles and thyroid gland Flashcards

1
Q

the thyroid gland begins where?

A

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

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2
Q

thyroid gland may be connected to foramen cecum by what?

A

thyroglossal duct

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3
Q

thyroid gland is divided into?

A

two lateral lobes connected by an isthmus

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4
Q

follicular cells are derived from?

A

endoderm

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5
Q

parafollicular cells are derived from?

A

ultimobranchial body (4-6 pouch)

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6
Q

where is the thyroid gland ?

A

between the 5th cervical and 1st thoracic vertebrae

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7
Q

arterial supply of thyroid

A

from superior and inferior thyroid arteries

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8
Q

superior thyroid artery

A
  • the first branch to arise from the **external carotid artery
  • glandular branches (lateral and anterior)
  • thryoid ima artery (from brachiocephalic trunk)
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9
Q

**the inferior thyroid artery is from?

A

branch of thyrocervical trunk

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10
Q

venous drainage of thyroid

A

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

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11
Q

what innervates the larynx?

A

superior laryngeal nerve and recurrent laryngeal nerve

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12
Q

two branches of vagus nerve

A
  1. superior laryngeal – internal laryngeal (sensory) and external laryngeal (motor)
  2. recurrent larygneal– right: behind the right subclavian artery; left: behind the aortic arch
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13
Q

the recurrent laryngeal nerve ascends between

A

trachea and esophagus

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14
Q

reccurent laryngeal nerve supplies

A
  • motor innervation to laryngeal muscles (except cricothyroid)
  • viscerosensory innervation to the laryngeal mucosa
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15
Q

what leads to ipsilateral palsy of vocal folds?

A

damage to recurrent laryngeal nerve (due to thyroidectomy)

  • prevents abduction of vocal folds, causing hoarseness
  • bilateral nerve loss causes asphyxiation
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16
Q

what is the thyroid gland composed of?

A
  • 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
17
Q

lobules are lined by?

A

cuboidal epithelial cells

18
Q

follicular cells

A

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

19
Q

follicular cells secrete

A
  • tri-iodothyronine (T3)

- tetra-iodothyronine (T4)

20
Q

overactive follicles

A
  • -reduced colloid content

- -smaller because they release more T3 and T4

21
Q

underactive follicles

A
  • -increased amount of colloid

- -huge because they store more colloid

22
Q

parafollicular cells or C cells

A
  • release calcitonin

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

23
Q

what triggers release of calcitonin?

A

triggered by elevated blood Ca levels

inhibits osteoclast activity

24
Q

what does the microvasculature of the parathyoid gland arise from?

A

inferior thyroid arteries

25
Q

superior parathyroid gland is from?

A

4th pharyngeal pouch

26
Q

inferior parathyroid gland is from?

A

3rd pharyngeal pouch

27
Q

parathyroid glands

A
  • 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)
28
Q

PTH function

A
  • 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
29
Q

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

A

calcitonin

30
Q

infrahyoid muscles

A
  • two superficial (omohyoid and sternohyoid)

- two deep (sternothyoid and thyrohyoid)

31
Q

nerve supply of infrahyoid

A

ansa cervicalis except the thyrohyoid (C1)

32
Q

omohyoid

A
  • 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
33
Q

actions of omohyoid muscle

A
  • depresses hyoid; draws larynx and hyoid down for phonation and terminal phases of swallowing
  • nerve supply: ansa cervicalis
34
Q

sternohyoid

A
  • 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
35
Q

action of sternohyoid

A
  • depresses hyoid
  • draws larynx and hyoid down for phonation and terminal stages of swallowing
  • nerve supply: ansa cervicalis
36
Q

sternothyroid muscle

A
  • deep to sternohyoid
  • origin from posterior aspect of manubrium of sternum
  • inserts above into oblique line of thyroid cartilage
37
Q

action of sternothyroid

A
  • depresses hyoid
  • draws larynx and hyoid down for phonation and swallowing terminally
  • nerve supply: ansa cervicalis
38
Q

thyrohyoid muscle

A
  • originates from oblique line of thyroid cartilage

- passes upward to insert into body of hyoid bone

39
Q

action of thyrohyoid

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