Thyroid Gland Flashcards
1
Q
At what gestational age does the thyroid gland first appear?
A
3-4 weeks
2
Q
Where in the foetus does the thyroid gland first appear?
A
At the base of the tongue where the foramen caecum will exist
3
Q
The thyroid descends as the thyroglossal duct via the hyoid bone and the proximal part regresses by which point in gestation?
A
5-7 weeks
4
Q
From where do the parafollicular cells appear in the foetus?
A
4th and 5th branchial pouches
5
Q
Sometimes, an additional lobe is present in the thyroid. What is the name of this lobe?
A
Pyramidal lobe
6
Q
What is the name of the part of the thyroid which connects the right and left lobes?
A
Isthmus
7
Q
What is the name of the extracellular substance which exists in the lumen of the follicles of the thyroid gland?
A
Colloid
8
Q
Where in the thyroid gland do C cells exist?
A
Interspersed between follicular cells in the follicles and also in spaces between the follicles
9
Q
Describe the arrangement of the follicular cells of the thyroid?
A
These are arranged in a single layer of cells to form a spheroidal follicle
10
Q
What is produced by the parafollicular cells of the thyroid gland?
A
Calcitonin
11
Q
What is produced by the follicular cells of the thyroid gland?
A
Triiodothyronine (T3)
Thyroxine / Tetraiodothyronine (T4)
12
Q
The majority of T3 and T4 are bound to what protein in the blood?
A
Thyroxine binding globulin
13
Q
What type of hypothyroidism is caused by Sheehan’s syndrome?
A
Secondary hypothyroidism
14
Q
What is the name for the dwarfism and severe mental retardation cause by hypothyroidism in infancy?
A
Cretinism
15
Q
In adults, what are the clinical features of hypothyroidism?
A
Myxoedema slowed physical and mental activity fatigue cold intolerance periorbital oedema coarsening of skin and facial features cardiomegaly effusions hair loss
16
Q
What antibodies are involved in Hashimoto’s thyroiditis?
A
Anti-TSH receptor antibodies
anti-thyroglobulin antibodies
Antithyroid peroxidase antibodies
17
Q
Hashimoto’s thyroiditis is usually a diffuse process. T/F?
A
True
18
Q
You would expect to see a goitre in Hashimoto’s thyroiditis. T/F?
A
True - although a person could still have the condition even if a goitre was not present
19
Q
What pathohistological changes in the thyroid would you expect to see with Hashimoto’s thyroiditis?
A
Paler
resembling a lymph node on section - lymphocytes, plasma cells, macrophages and germinal centre formation
oncocytic change in the epithelium (Hurthle cells)
fibrosis
20
Q
What percentage of men and women are affected by thyroid disorders?
A
5% of women
0.5% of men
21
Q
What is the approximate weight of the thyroid glands?
A
10-20g
22
Q
When stimulated, what shape are the follicular cells of the thyroid gland and what affect does stimulation have on the colloid?
A
Columnar cells and the lumen is depleted of colloid
23
Q
When the thyroid gland is stimulated, what shape are the follicular cells and what affect does this have on the colloid?
A
Flat cells
Colloid accumulates in the lumen
24
Q
Iodine is necessary for thyroid hormone synthesis. Iodine is obtained in the diet from…?
A
Seawater
Fruit
Vegetables
25
How much iodine is required in the diet each day?
150-300micrograms
26
What public health measure has reduced iodine deficiency?
Iodine supplementation of salt
27
Oral iodine is reduced to iodide in the GI tract before absorption. T/F?
True
28
Iodide ions are actively transported into the follicular cells of the thyroid by co-transport with which electrolyte?
Sodium
29
What is the name of the transport protein which carried iodide into vesicles on the apical membrane of follicular cells in the thyroid?
Pendrin
30
Which enzymes catalyses the oxidation of iodide to iodine and the binding of this iodine to tyrosine residues on thyroglobulin?
Thyroid peroxidase
31
Once T3 and T4 has been produced, what happens to the thyroglobulin?
It is hydrolysed
32
Where in the cell are T3 and T4 cleaved from thyroglobulin?
Lysosome
33
The combination of iodine and tyrosine forms...?
mono iodinated thyronine (MIT) and di iodinated thyronine (DIT)
34
T3 is released in greater quantities from the thyroid gland than T4. T/F?
False- the opposite is true
35
T4 can be converted to T3 in the periphery by the process of...?
5' deionisation of T4
36
T3 is more potent than T4. T/F?
True
37
99.5% of circulating thyroid hormones are protein bound. To what proteins are they bound?
Globulin
Transthyretin
Albumin
38
The free component of circulating thyroid hormone is the active and regulated component. T/F?
True
39
Where in the cell do the receptors for thyroid hormones exist?
In the nucleus
40
Almost all tissues have nuclear receptors for T3. T/F?
True
41
In primary hypothyroidism there is low T4 but high TSH. How is this different in secondary hypothyroidism?
In secondary hyperthyroidism there is both low TSH and T4
42
What factors may cause hyperthyroidism?
Autoimmune reactions such as Graves' disease
Toxic adenoma
Multinodular goitre
Thyroiditis
43
Excess administration of thyroxine will cause an excess of thyroid hormone. Why is this not classed as hyperthyroidism?
This is thyrotoxicosis - an increase in the level of thyroid hormone. Hyperthyroidism comes under the umbrella of thyrotoxicosis but specifically refers to increased thyroid hormone levels due to overactivity of the thyroid gland.
44
What are the clinical features of hyperthyroidism?
```
Weight loss
Tremor
heat intolerance
diarrhoea
tachycardia
hypertension
palpations
sweating
```
45
What percentage of patients with Graves' disease will develop dermopathy?
1-2%
46
What eye problems may occur in Graves' disease?
```
Lid lag
periorbital oedema
proptosis
diplopia
Nerve compression
erythema
conjunctivitis
```
47
What are the features of dermopathy as seen in Graves' disease?
Soft tissue swelling
| Clubbing of the finger
48
What are the treatment options for hyperthyroidism?
Antithyroid drugs
Surgery
Radio iodine
49
What is the rare and severe side effect of the use of carbimazole and Propylthiouracil?
Agranulocytosis
50
Conception should be delayed for at least how may months after receiving radio iodine therapy?
4 months
51
Radio iodine therapy may worsen eye disease in people with Graves' disease. T/F?
True
52
What is the most common side effect of radio iodine therapy?
Hypothyroidism
53
What complications may result from thyroidectomy?
```
Haemorrhage
recurrent laryngeal palsy
permanent hypocalcaemia
hypothyroidism
hypoparathyroidism
infection
keloid formation
```
54
Hashimoto's disease is more common in men than in women. T/F?
False the opposite is true
55
Other than hashimotot;s thyroiditis, what factors could cause hypothyroidism?
```
Thyroidectomy
Thyroiditis (often viral)
Drug induced
Pituitary disease
Severe iodine deficiency
```
56
What are the symptoms of hypothyroidism?
```
weight gain
depression
thin hair
anaemia
lethargy
constipation
cold intolerance
poor concentration
hoarseness
menorrhagia
bradycardia
dry skin
slow relaxing reflexes
```
57
What does of levothyroxine is usually given to patients with hypothyroidism?
1.7-2.0 mg/kg/day
58
In what patients is levothyroxine started on lower doses?
Elderly patients
| Patients with CV disease
59
What other medications may interfere with levothyroxine?
Proton pump inhibitors
Ferrous sulphate
Calcium
60
What is the normal TSH range?
0.5-5mU/L
61
Atrial fibrillation and osteoporosis are possible side effects of levothyroxine. T/F?
True
62
Thyroid cancer can be differentiated or undifferentiated. Which has the better prognosis?
Differentiated
63
Papillary cancer comprises what percentage of cases of differentiated thyroid cancer?
17%
64
Follicular cancer comprises what percentage of cases of differentiated thyroid cancer?
13-20%
65
Medullary carcinoma of the thyroid comprises what percentage of cases of differentiated thyroid cancer?
6%
66
Mixed differentiated thyroid cancer comprises what percentage of cases of differentiated thyroid cancer?
50%
67
The isthmus of the thyroid lies on top of which tracheal cartilages?
2nd - 4th tracheal cartilages
68
Some people also have a pyramidal lobe of the thyroid. What embryological structure is this a remnant of?
Thyroglossal duct
69
When the larynx rises during swallowing, the thyroid gland rises with it. Why does this happen?
The connective tissue capsule of the thyroid adheres to the larynx
70
Which nerve lies behind the thyroid and thus can become damaged in thyroid surgery causing hoarseness and impaired function of the voice?
Recurrent laryngeal nerve
71
The thyroid receives blood supply from the superior and inferior thyroid arteries. Where do these arise from?
Superior thyroid artery arises from the external carotid
| Inferior thyroid artery arises from the subclavian artery
72
The thyroid is drained by the superior, middle and inferior veins. Where do each of these veins drain to?
Superior and middle thyroid veins drain to the internal jugular vein
Inferior thyroid vein drains to the brachiocephalic vein
73
To what nodes do the lymph vessels of the thyroid drain to?
Deep cervical nodes
74
Which vein are the deep cervical nodes associated with?
Internal jugular vein
75
Other than iodide, what electrolyte does pendrin transport?
Chloride
76
Thyroglobulin is synthesised by the follicular cells. How does it reach the colloid?
By exocytosis
77
T3 and T4 must be cleaved from thyroglobulin before secretion into the blood - this occurs inside the cell. How is the T3/4 containing thyroglobulin moved from the colloid back into the follicular cell?
By endocytosis
78
Other than stimulating T3/4 production, what effects does TSH have on the thyroid?
It increases DNA replication, cell devision and increases the amount of rough ER and other cellular machinery required by the follicular cells for protein synthesis. I.e. TSH induces hypertrophy of the follicular cells
79
What effect do thyroid hormones have on metabolism?
Increase metabolic rate
Increase carbohydrate absorption in small intestine
Increase gluconeogenesis
Increase fatty acid release from adipocytes
Increases action of Na/K-ATPases
80
Thyroid hormones increases sympathetic nervous system activity. How do they accomplish this?
Up regulate beta adrenergic receptors in many tissues
81
T3 is required for the normal production of which hormone from the anterior pituitary gland?
Growth hormone
82
T3 is important in the development of which body system?
Nervous system - involved in the formation of action potentials, the production of synapses and the growth of dendrites
83
T3 is important for normal nerve and muscle reflexes and cognition. T/F?
True
84
What is the most common cause of hypothyroidism in Western countries?
Hashimoto's (autoimmune) thyroiditis)
85
What antibodies may be present in Hashimoto's thyroiditis?
Anti-thyroglobulin
Anti-thyroid peroxidase
Inhibitory TSH receptor binding antibodies
86
Other than iodine deficiency or autoimmune conditions, what else can result in hypothyroidism?
```
Thyroidectomy
Radio iodine therapy
Radiotherapy
Toxic exposure to certain drugs
Infiltrative diseases
```
87
Explain how non-pitting oedema may occur in patients with hypothyroidism?
In severe, untreated hypothyroidism, glycasoaminoglycans can accumulate in the interstitial space (T3 normally acts to prevent over expression of these) and water becomes trapped within these molecules. This causes a characteristic non-pitting oedema
88
Cretinism is reversible if thyroid replacement therapy is started rapidly. t/f?
True - if not started soon enough then it is not reversible
89
What dose of levothyroxine is usually given to patients?
1.7-2.0 mg/kg/day
90
The main complication of treatment of hypothyroidism with levothyroxine is over-replacement. This increases the risk of what conditions?
Osteoporosis
| Atrial fibrillation
91
What is the most common cause of hyperthyroidism?
Graves' disease
92
What class of antibody is present in Graves' disease?
IgG
93
What is the name for the antibody which is present in Graves' disease and what is its action?
Long acting thyroid stimulator (LATS). This is analogous to normal TSH and binds to the TSH receptor on follicular cells to cause an increase in production of T3/4 by the thyroid which is not subject to normal negative feedback inhibition
94
What clinical features of Graves' disease may be present in the eyes?
```
Lid lag
erythema
conjunctivitis
proptosis
periobital oedema
diplopia
nerve compression
```
95
What are the signs of dermopathy which can occur in Graves' disease?
Soft tissue swelling
| Clubbing of the fingers
96
Other than Graves', what conditions can cause hyperthyroidism?
Toxic adenoma
Multinodular goitre
thyroiditis
97
What medications are used to control the cardiovascular symptoms of hyperthyroidism?
Beta blockers or calcium channel blockers
98
What are the possible side effects of antithyroid drugs?
Skin rash
| Very rarely agranulocytosis can occur
99
What is a goitre?
An enlarged thyroid gland
100
Why might a goitre be present in primary hypothyroidism?
Thyroid gland failure or iodine deficiency causes a decrease in circulating levels of thyroid hormone meaning there is little negative feedback on the anterior pituitary and hypothalamus meaning that TSH levels are high. TSH levels normally stimulate thyroid hormone production and hypertrophy and hyperplasia of the follicular cells. TSH cannot in this case work to produce more thyroid hormone but still exhibits its other functions resulting in enlargement of the thyroid even though the gland is still underproducing
101
Why might goitre be present in hyperthyroidism?
Excessive secretion of TSH from hypothalamic or anterior pituitary defects results in overstimulation of thyroid growth and secretion
In Graves; the goitre occurs because LATS (the Graves' antibody) also stimulates thyroid gland growth as well as enhancing secretion of thyroid hormone
102
Hyperthyroidism does not always result in goitre formation. In what causes of hyperthyroidism would you least expect to find a goitre?
Any cause of hyperthyroidism resulting from overactivity of the thyroid in the absence of overstimulation such as an uncontrolled thyroid tumour
