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Endocrinology > Anatomy of the thyroid gland > Flashcards

Anatomy of the thyroid gland Flashcards

1
Q

What are the borders of the posterior triangle of the neck?

A

Trapezius - Posterior
Clavicular head of sternocleidomastoid - Anterior
Clavicle - Base

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2
Q

What are the borders of the anterior triangle of the neck?

A

Midline - Anterior
Sternal head of sternocleidomastoid - Posterior
Mandible - Roof

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3
Q

What is the origin of the sternocleidomastoid?

A

Mastoid process of temporal bone

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4
Q

What are the 2 insertions of the sternocleidomastoid?

A

Sternal head -> Manubrium
Clavicular head -> Medial clavicle

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5
Q

What nerve innervates both the trapezius and sternocleidomastoid?

A

Spinal accessory nerve (CN XI)

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6
Q

What is the name for the thin sheet of muscle located in the anterior neck, within the superficial fascia?

A

Platysma muscles

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7
Q

What is the function of the platysma muscles?

A

They belong to the muscles that control facial expression

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8
Q

What nerve innervates the platysma muscles?

A

Cranial nerve VII (Facial)

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9
Q

What are the 2 main veins that drain each side of the neck?

A

External jugular vein
Anterior jugular vein

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10
Q

Where does the external jugular vein pass?

A

It runs within the superficial fascia of the neck and drains into the subclavian vein

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11
Q

Where does the anterior jugular vein pass?

A

It runs within the superficial fascia of the neck and drains into the external jugular vein

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12
Q

What are the 4 main fascial compartments of the neck?

A
  • Investing fascia
  • Prevertebral (Deep) fascia
  • Carotid sheath (x2)
  • Pretracheal fascia
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13
Q

What is contained in the investing fascia?

A

The investing fascia encloses all other neck fascial compartment and encloses 2 pairs of muscles, the trapezius and the sternocleidomastoid

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14
Q

What is contained in the pre-vertebral fascia?

A

The prevertebral fascia is located posteriorly and encloses the postural neck muscles and cervical vertebrae

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15
Q

What is contained in the carotid sheaths?

A
  • Deep cervical lymph nodes
  • Vagus nerve
  • Common carotid artery
  • Internal jugular vein
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16
Q

Where do the carotid sheaths attach?

A

These carotid sheaths attach to the base of the skull around the jugular foramen, blending inferiorly with the mediastinal fascia

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17
Q

What is contained in the pre-tracheal fascia?

A
  • Oesophagus
  • Trachea
  • Thyroid gland
  • Strap muscles
  • Recurrent laryngeal nerves
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18
Q

What are the strap (Intrahyoid) muscles?

A

These are a group of 4 muscles found between the sternum and hyoid

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19
Q

What are the 4 strap muscles?

A

Thyrohyoid (Thyroid cart. -> Hyoid)
Sternohyoid (Sternum -> Hyoid)
Sternothyroid (Sternum -> Thyroid cart.)
Omohyoid (Shoulder (Omo) -> Hyoid)

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20
Q

Describe the structure of the omohyoid

A

The omohyoid contains 2 bellies, the superior belly and inferior belly with an intermediate tendon connecting the 2

A fascial sling attaches the intermediate tendon of the omohyoid to the clavicle

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21
Q

What is the name given to the space found between the carotid sheath and pre-vertebral fascia?

A

Retropharyngeal space

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22
Q

Where does the thyroid gland develop?

A

It develops as a midline epithelial proliferation at the junction between the anterior 2/3rds and posterior 1/3rd of the tongue (Foramen caecum in an adult)

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23
Q

Describe the migration of the thyroid gland during development

A

The thyroid gland moves from the tongue inferiorly, while remaining attached to the tongue via the thyroglossal ct
The gland then reaches its final position in relation to the larynx in the 7th week of development

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24
Q

What structure connects the 2 lobes of the thyroid gland?

A

The isthmus

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25
Q

What do the thyroid lobes attach to?

A

These lobes attach to lateral aspects of the thyroid and cricoid cartilages and to the trachea

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26
Q

Which cartilages of the trachea does the thyroid gland lie anterior to?

A

2nd and 3rd cartilage rings

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27
Q

How will a goitre move during swallowing?

A

Superiorly and then inferiorly

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28
Q

Between which vertebrae does the thyroid gland lie?

A

C5 and T1

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29
Q

How many parathyroid glands are there?

A

4

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30
Q

Where are the parathyroid glands found?

A

On the posterior surfaces of the thyroid glands

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31
Q

What is a pyramidal lobe?

A

This is a physiological abnormality occurring in between 28 and 55% of people, in which there is a long, superiorly branching lobe of the thyroid gland

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32
Q

What is the most common lobe to give rise to a pyramidal lobe?

A

Left lobe

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33
Q

What arteries supply the thyroid and parathyroid glands?

A

Inferior and superior thyroid arteries

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34
Q

From which arteries do the superior thyroid arteries arise?

A

Left and right external carotid arteries

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35
Q

From which arteries do the inferior thyroid arteries arise from?

A

Left and right subclavian arteries

36
Q

What are the 3 pairs of veins that drain the thyroid and parathyroid glands?

A
  • Superior thyroid vein
  • Middle thyroid vein
  • Inferior thyroid vein
37
Q

Where do the superior and middle thyroid veins drain into?

A

Internal jugular veins

38
Q

Where do the inferior thyroid veins drain into?

A

Left brachiocephalic vein

39
Q

What are some of the lymph nodes into which the thyroid and parathyroid glands drain into?

A
  • Pre-tracheal node (Only 1)
  • Para-tracheal nodes
  • Superior deep cervical lymph nodes
  • Inferior deep cervical lymph nodes
40
Q

From where in the brain does the vagus nerve emerge?

A

Medulla oblongata

41
Q

Describe the route of the right vagus nerve splitting into the right recurrent laryngeal nerve

A

Medulla oblongata
Jugular foramen
Carotid sheaths
Splits into recurrent laryngeal nerve
Wrap around the brachiocephalic artery
To thyroid and larynx

42
Q

Describe the route of the left vagus nerve splitting into the right recurrent laryngeal nerve

A

Medulla oblongata
Jugular foramen
Carotid sheaths
Splits into recurrent laryngeal nerve
Wrap around the arch of aorta
To thyroid and larynx

43
Q

What are Langer’s lines?

A

Langer’s lines are a number of body-wide lines used by surgeons which show the ideal direction in which an incision should be made to reduce scarring and tension

44
Q

How is access to the thyroid gland gained in a classical thyroidectomy?

A

A collar incision is made with these Langer’s lines, just superior to the clavicles and jugular notch, going through the skin and platysma

45
Q

What will occur if one recurrent laryngeal nerve is damaged during thyroidectomy?

A

Unilateral damage will cause hoarseness or weakness of the voice

46
Q

What will occur if both recurrent laryngeal nerves are damaged in thyroidectomy?

A

Bilateral damage will cause aphonia (Inability to produce sound) and inability to close the rima glottidis, increasing risk of aspiration

47
Q

Describe the histology of the thyroid gland?

A

It contains may follicles, containing colloid, surrounded by follicular cells
Parafollicular C cells then surround the follicular cells

48
Q

What is secreted by the parafollicular C cells?

A

Calcitonin

49
Q

What is colloid?

A

A tyrosine-containing thyroglobulin

50
Q

What is secreted by the follicular cells?

A

T3 and T4

51
Q

What are the 3 glands involved in thyroid hormone synthesis and release?

A

Hypothalamus
Pituitary gland
Thyroid gland

52
Q

What hormone is secreted by the hypothalamus in the HPT axis?

A

Thyrotropin releasing hormone (TRH)

53
Q

What gland does TRH release stimulate?

A

The pituitary gland

54
Q

What is released by the pituitary gland in the HPT axis?

A

TSH (Thyroid stimulating hormone)

55
Q

What gland does TSH stimulate?

A

Thyroid gland

56
Q

What are the 2 types of thyroid hormone?

A

Triiodothyronine (T3)
Thyroxine (T4)

57
Q

What are the 6 stages of thyroid hormone synthesis?

A
  1. Thyroglobulin synthesis
  2. Uptake and concentration of iodide into follicular cells
  3. Oxidation of iodide to iodine in follicular cells
  4. Iodination of thyroglobulin
  5. Formation of MIT and DIT
  6. Secretion
58
Q

What is MIT?

A

Monoiodotyrosine unit (1 iodine residue)

59
Q

What is DIT?

A

Diiodotyrosine unit (2 iodine residue)

60
Q

Which 2 thyroid hormone units bind to form T3 (Triiodothyronine)?

A

MIT + DIT (1 + 2 = 3)

61
Q

Which 2 thyroid hormone units bind to form T4 (Thyroxine)?

A

DIT + DIT (2 + 2 = 4)

62
Q

Where is T4 converted to T3?

A

Liver and kidneys

63
Q

Which is more potent, T3 or T4?

A

T3 is 4x more potent than T4

64
Q

How are thyroid hormones transported in the blood?

A

Bound to serum proteins
Unbound

65
Q

What are some examples of serum binding proteins of thyroid hormones?

A

Thyroxine binding globulin (TBG)
Transthyretin (TTR)
Albumin

66
Q

Which form of thyroid hormone is biologically active in the blood?

A

Unbound

67
Q

What processes do thyroid hormones affect?

A

Metabolism
Growth
Development
Reproduction
Behaviour

68
Q

How do thyroid hormones increase BMR?

A

It increases basal metabolic rate by increasing number and size of mitochondria, increasing oxygen use, increasing rate of ATP hydrolysis and increasing synthesis of respiratory chain enzymes

69
Q

How do thyroid hormones affect body heat?

A

They increase thermogenesis

70
Q

How do thyroid hormones affect blood glucose?

A

It increases carbohydrate metabolism, as it increases glycogenolysis (Glycogen breakdown) and gluconeogenesis, and stimulares insulin-dependant glucose uptake into cells

71
Q

How do thyroid hormones affect lipid metabolism?

A

It increases lipid metabolism by mobilising fats from adipose tissue and increasing fatty acid oxidation in tissue

72
Q

How do thyroid hormones stimulate growth?

A

It increases lipid metabolism by mobilising fats from adipose tissue and increasing fatty acid oxidation in tissue

73
Q

How does TSH stimulate thyroid hormone release?

A

TSH binds to TSH receptors, which stimulates ATP to cAMP conversion

74
Q

What are some factors that decrease TRH and TSH release?

A

High T3 and T4 levels
Stress

75
Q

What can stimulate TSH release in babies and young children?

A

Low temperatures

76
Q

How do thyroid hormone levels change with the Circadian rhythm?

A

Thyroid hormones are highest late at night and are lowest in the morning due to the Circadian rhythm

77
Q

What enzymes are responsible for activation and deactivation of thyroid hormones?

A

De-iodinase enzymes

78
Q

How do de-iodinase enzymes activate or deactivate thyroid hormones?

A

They can add or remove an iodine atom from their outer ring

79
Q

What are the 3 types of de-iodinase enzymes?

A

D1
D2
D3

80
Q

Where is D1 commonly found?

A

Liver and kidneys

81
Q

Where is D2 commonly found>

A

Heart, skeletal muscle, CNS, fat, thyroid and pituitary gland

82
Q

Where is D3 commonly found?

A

Foetal tissue, placenta and brain (Except pituitary)

83
Q

Which of the duo-iodinase enzymes is responsible for conversion of T3 - T4?

A

D2

84
Q

What are the main 2 classes of thyroid hormone receptor?

A

THRa
THRß

85
Q

Where is THRa most commonly found?

A

CNS
Muscle
Bone
Intestines
Heart

86
Q

Where is THRß most commonly found?

A

Liver
Hypothalamus
Pituitary gland

87
Q
A

Endocrinology (42 decks)

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