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Endocrine Anatomy > Anatomy of Thyroid and Parathyroid Glands > Flashcards

Anatomy of Thyroid and Parathyroid Glands Flashcards

1
Q

Describe the thyroid gland?

A

bow-tie shaped thryroid producing hormone

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2
Q

What kind of cells make up the thyroid?

A

follicular and parafollicular cells

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3
Q

Follicular cells synthesize?

A
  1. thyroxine 2. tetraiodothyronine - T4 3. triiodothyronine - T3
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4
Q

Function of the hormones synthesized by follicular cells?

A
  1. controls how quickly the body uses energy and makes proteins 2. controls how sensitive the body should be to other hormones
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5
Q

Parafollicular cells synthesize?

A

calcitonin

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6
Q

Function of calcitonin?

A

lower calcium - antagonistic in action to parathyroid hormone

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7
Q

What is the first endocrine gland to develop in an embryo?

A

thyroid gland

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8
Q

When does the throid gland first appear?

A

3 - 4 weeks

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9
Q

What does it appear as?

A

as an epithelial proliferation on the floor of primordial pharynx – endoderm

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10
Q

Where does it appear?

A

at the level of 2nd pharyngeal arch, at base of tongue

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11
Q

Describe the course of the thyroid gland in development?

A
  1. Thyroid descends through thyroglossal duct, connected to the tongue (foramen cecum) 2. migrates to the base of the neck
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12
Q

Parafollicular cells are derived from?

A

derived from ultimobranchial (ultimopharyngeal) body - from 4th pharyngeal pouch endoderm (also believed to have been derived from neural crest cells)

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13
Q

What happens to the ultimopharyngeal body?

A

join primordial thyroid gland during its decent to its final location in the anterior neck

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14
Q

Where is the thyroid located?

A

cervical region

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15
Q

Describe the relations of the thyroid in the cervical region?

A
  1. anterior to the larynx in the neck 2. inferior to the thyroid cartilage (Adams apple) - at the same level as the cricoid cartilage
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16
Q

Describe the structure of the thyroid?

A

2 lobes united by an isthmus - one lobe on either side of the trachea

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17
Q

What covers the thyroid?

A

fibrous sheath

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18
Q

Which muscles cover the thyroid?

A
  1. anterioly - infrahyoid muscles 2. laterally - sternocleidomastoid muscles
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19
Q

Describe the posterior relations of the thyroid?

A
  1. posterior suspensory ligament of Berry - the gland is fixed to the cricoid and tracheal cartilages and cricopharyngeus muscle by a thickening of the fascia
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20
Q

Describe the posterior lateral relations?

A

carotid sheath - 1. common carotid artery 2. external carotid artery 3. internal jugular vein 4. vagus nerve

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21
Q

Describe the medial relations?

A
  1. larynx 2. trachea 3. inferior constrictor of pharynx 4. esophagus 5. cricothyroid muscle 6. laryngeal nerve
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22
Q

Describe the relations of the isthmus?

A
  1. anteriorly - sternothyroid’s, sternohyoids, anterior jugular veins, fascia and skin 2. posteriorly - 2nd to 4th rings of trachea; terminal branches of thyroid arteries
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23
Q

Describe the arterial supply of the thyroid?

A
  1. superior thyroid artery - branch of external carotid artery 2. inferior thyroid artery - branch of thyrocervical trunk 3. thyroidea ima - branch of brachiocephalic artery : the arteries anastomose over surface of the gland
24
Q

Describe the venous drainage?

A
  1. superior + middle veins - drain into internal jugular veins 2. inferior veins - drain into left brachiocephalic vein
25
Q

Describe the lymphatic drainage?

A

lateral deep cervical lymph nodes

26
Q

Describe the nerve supply?

A
  1. Superior laryngeal nerve - paralysis (cough reflex)
    NB. Also related to superior thyroid artery especially the external branch 2. Recurrent laryngeal nerve - paralysis (vocal cords) - surgeons check preoperative state
    NB. Also related to inferior thyroid artery
27
Q

The thyroid gland is covered by?

A
  1. thin connective tissue capsule 2. the connective tissue capsule sends septa (trabeculae) into the gland to divide it into lobes and lobules
28
Q

Thyroid tissue is composed of?

A

follicles - formed by simple epithelium : functional unit of the thyroid gland

29
Q

Describe the lumen of the follicles?

A

have colloid - rich in thyroglobulin (iodinated glycoprotein)

30
Q

Describe the histology of follicular cells?

A

squamous, cuboidal + columnar with variable diameter

31
Q

When is the gland considered hypoactive?

A

when the average composition of follicular cells is squamous

32
Q

Which hormone regulates anatomical and functional state of thyroid?

A

thyrotropin

33
Q

State 3 functions of thyrotropin?

A
  1. Stimulates synthesis of thyroid hormone
  2. Increases height of follicular epithelium
  3. Decreases quantity of colloid & size of follicles
34
Q

Describe the structure of follicular cells?

A
  1. simple cuboidal epithelial ells that surround follicles 2. have microvilli on their luminal surface 3. dilated cisternae of rER 4. distended Golgi saccules 5. accumulated apical secretory vessicles 6. exhibit active glycoprotein synthesis & excretion characteristics
35
Q

Describe thyroid epithelium?

A

epithelium rests on basal lamina

36
Q

Describe characteristics of follicular epithelium?

A

characteristics of a cell that synthesizes, secrets, absorbs & digests proteins - basal part of these cells are rich in rough endoplasmic reticulum

37
Q

How is thyroxine formed?

A
  1. Follicular cells actively phagocytose iodinated thyroglobulin they have made 2. Then submit it to lysosomal digestion 3. T3 and T4 liberated as intracellular proteolysis products which pass into circulation via fenestrated capillaries
38
Q

Describe the thyroid in dietary iodide deficiency?

A
  1. the thyroid gland is hypoactive - follicles enlarge with colloid 2. Because no T3 or T4 is made to exert a negative feedback, TSH synthesis & secretion increases 3. TSH stimulates growth of thyroid gland - it enlarges
39
Q

Describe the importance of thyroxine?

A
  1. the bodys metabolic hormone 2. controls the rate at which glucose is oxidized 3. important for tissue growth and development
40
Q

What is goitre?

A

enlargement of thyroid gland due to iodine deficiency

41
Q

Describe the consequences of hyposecretion of thyroxine in early childhood?

A

cretinism (dwarfism)

42
Q

Describe the consequences of hyposecretion of thyroxine in adulthood?

A

myxedema (physical and mental slaggishness), obesity

43
Q

Follicular epithelium also contain what other kind of cells?

A

10% of scattered parafollicular cells - are within the follicle in the simple cuboidal epithelium and between the follicles

44
Q

Parafollicular cells are derived from?

A

neural crest cells

45
Q

Describe parafollicular cells in a thyroid section?

A

widely dispersed large, rounded pale-staining cells with central spherical nuclei

46
Q

Describe the parathyroid gland?

A

four small glands on the thyroid gland - sometimes they are embedded

47
Q

Parathyroid glands are derived from?

A

pharyngeal pouches : 1. superior glands - 4th pouch 2. inferior glands - 3rd pouch

48
Q

Describe the arterial supply of the parathyroid glands?

A

superior + inferior thyroid arteries

49
Q

Each gland is contained in a?

A

capsule

50
Q

Name the 2 types of cells in parathyroid glands?

A
  1. chief cells 2. oxyphil cells
51
Q

Describe chief cells?

A
  1. small polygonal cells with vesicular nucleus and pale staining 2. slightly acidophilic cytoplasm with granules that have parathyroid hormone 3. cells appear in cords
52
Q

Describe oxyphil cells?

A
  1. smaller in population 2. larger polygonal cells 3. Cytoplasm has many acidophilic mitochondria with abundant cristae 4. their function is not known
53
Q

What happens to the glands with increasing age?

A

With increasing age, secretory cells are replaced with adipocytes - Adipose cells constitute more than 50% of the gland in older people

54
Q

Describe functions of parathyroid hormone?

A
  1. Signals osteoblasts to produce an osteoclast-stimulating factor - increases number & activity of osteoclast and promotes absorption of calcified bone matrix & release of calcium into blood 2. lowers phosphate concentration in blood by acting on kidney tubule cells Note: Calcitonin from thyroid lowers blood calcium concentration & increases osteogenesis
55
Q

State 3 congenital anomalies of the thyroid?

A
  1. Agenesis of thyroid - commonest cause of cretinism, neurologic damage 2. Incomplete descent of thyroid - lingual thyroid most common 3. Thyroglossal cyst may appear in childhood or adolescence due to persistence of thyroglossal duct

Endocrine Anatomy (5 decks)

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