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MBBS 2: Endocrine Anatomy > Anatomy of Thyroid and Parathyroid Glands > Flashcards

Anatomy of Thyroid and Parathyroid Glands Flashcards

(55 cards)

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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?

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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?

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A
  1. superior + middle veins - drain into internal jugular veins 2. inferior veins - drain into left brachiocephalic vein
25
Describe the lymphatic drainage?
lateral deep cervical lymph nodes
26
Describe the nerve supply?
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
The thyroid gland is covered by?
1. thin connective tissue capsule 2. the connective tissue capsule sends septa (trabeculae) into the gland to divide it into lobes and lobules
28
Thyroid tissue is composed of?
follicles - formed by simple epithelium : functional unit of the thyroid gland
29
Describe the lumen of the follicles?
have colloid - rich in thyroglobulin (iodinated glycoprotein)
30
Describe the histology of follicular cells?
squamous, cuboidal + columnar with variable diameter
31
When is the gland considered hypoactive?
when the average composition of follicular cells is squamous
32
Which hormone regulates anatomical and functional state of thyroid?
thyrotropin
33
State 3 functions of thyrotropin?
1. Stimulates synthesis of thyroid hormone 2. Increases height of follicular epithelium 3. Decreases quantity of colloid & size of follicles
34
Describe the structure of follicular cells?
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
Describe thyroid epithelium?
epithelium rests on basal lamina
36
Describe characteristics of follicular epithelium?
characteristics of a cell that synthesizes, secrets, absorbs & digests proteins - basal part of these cells are rich in rough endoplasmic reticulum
37
How is thyroxine formed?
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
Describe the thyroid in dietary iodide deficiency?
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
Describe the importance of thyroxine?
1. the bodys metabolic hormone 2. controls the rate at which glucose is oxidized 3. important for tissue growth and development
40
What is goitre?
enlargement of thyroid gland due to iodine deficiency
41
Describe the consequences of hyposecretion of thyroxine in early childhood?
cretinism (dwarfism)
42
Describe the consequences of hyposecretion of thyroxine in adulthood?
myxedema (physical and mental slaggishness), obesity
43
Follicular epithelium also contain what other kind of cells?
10% of scattered parafollicular cells - are within the follicle in the simple cuboidal epithelium and between the follicles
44
Parafollicular cells are derived from?
neural crest cells
45
Describe parafollicular cells in a thyroid section?
widely dispersed large, rounded pale-staining cells with central spherical nuclei
46
Describe the parathyroid gland?
four small glands on the thyroid gland - sometimes they are embedded
47
Parathyroid glands are derived from?
pharyngeal pouches : 1. superior glands - 4th pouch 2. inferior glands - 3rd pouch
48
Describe the arterial supply of the parathyroid glands?
superior + inferior thyroid arteries
49
Each gland is contained in a?
capsule
50
Name the 2 types of cells in parathyroid glands?
1. chief cells 2. oxyphil cells
51
Describe chief cells?
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
Describe oxyphil cells?
1. smaller in population 2. larger polygonal cells 3. Cytoplasm has many acidophilic mitochondria with abundant cristae 4. their function is not known
53
What happens to the glands with increasing age?
With increasing age, secretory cells are replaced with adipocytes - Adipose cells constitute more than 50% of the gland in older people
54
Describe functions of parathyroid hormone?
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
State 3 congenital anomalies of the thyroid?
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

MBBS 2: Endocrine Anatomy (5 decks)

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