Thyroid: Science and Diseases Flashcards
(131 cards)
1
Q
Where do the thyroid lobes attach?
A
thyroid and cricoid cartilages
2
Q
Which cartilages does the thyroid attach? Which is superior and which is inferior?
A
Thyroid (superior), Cricoid (inferior)
3
Q
Where does the isthmus of the thyroid gland lie?
A
2-3rd tracheal cartilages – C5-T1 vertebrae
4
Q
Where does the thyroid gland originally develop?
A
between the anterior and posterior parts of the tongue, where the foramen caecum is found in adults
5
Q
How does the thyroid migrate to its adult location?
A
via the thyroglossal duct - around week 7
6
Q
Working anteriorly to posteriorly, what is the first level of fascia found at the neck?
A
Superficial fascia
7
Q
What does the superficial fascia of the neck contain?
A
platysmus
8
Q
Working anteriorly to posteriorly, what is found after the superficial fascia in the neck?
A
anterior investing fascia
9
Q
What does the anterior investing fascia contain?
A
the sternocleidomastoid muscles
10
Q
Working anteriorly to posteriorly, what is found after the anterior investing fascia in the neck?
A
pretracheal fascia
11
Q
What is found within the pretracheal fascia? (5)
A
strap muscles, trachea, oesophagus, recurrent laryngeal nerves, thyroid gland
12
Q
What is found bilaterally to the pretracheal fascia in the neck?
A
carotid sheath
13
Q
What is found within the carotid sheath? (4)
A
internal jugular vein, deep cervical lymph nodes, vagus nerves, carotid arteries
14
Q
Which fascia is found beyond the pre-tracheal fascia?
A
pre-vertebral fascia
15
Q
What is found within the pre-vertebral fascia?
A
c-vertebrae, postural neck muscles
16
Q
What muscle is found within the posterior investing fascia?
A
the trapezius muscles (bilaterally)
17
Q
Which arteries supply the thyroid gland? (2)
A
superior and inferior thyroid arteries
18
Q
What are the origins of the superior and inferior thyroid arteries?
A
superior - external carotid; inferior - branch of subclavian
19
Q
Which veins does the thyroid gland drain? (3)
A
the superior (2), middle (2) and inferior thyroid (1) veins
20
Q
Where do the veins from the thyroid gland drain?
A
superior and middle –> internal jugular –> brachiocephalic; inferior –> brachiocephalic
21
Q
Which lymph nodes does the thyroid gland drain into? (4)
A
the inferior pretracheal node; paratrachial nodes; superior deep cervical nodes and deep cervical nodes
22
Q
Which aortic arch is the subclavian artery formed from?
A
4th
23
Q
Which aortic arch is the arch of the aorta formed from?
A
4th
24
Q
Name the 4 strap muscles
A
Omohyoid, sternohyoid, sternothyroid, thyrohyoid
25
What 3 things does the thyroid gland secrete?
T4 (thyroxine), T3 (triiodothyronine), calcitonin
26
What naturally causes an increase in the size of the thyroid gland?
menstruation and pregnancy
27
Innervation of the thyroid gland (2)
ANS including Vagus nerve (Parasympathetic) and the sympathetic trunk
28
Describe the structure of the thyroid gland
follicles surround by follicular cells; parafollicular C cells found dotted about
29
What is found within the follicle of the thyroid gland?
colloid - tyrosine containing thyroglobulin
30
How are T3/T4 secreted into the blood stream?
via pinocytosis
31
How is T3 made?
Iodine taken into the follicle is attached to tyrosine residues in the form of mono-iodotyrosine (MIT) or di-iodotyrosine (DIT). T3 is made up of MIT+DIT
32
How is T4 made?
Iodine taken into the follicle is attached to tyrosine residues in the form of mono-iodotyrosine (MIT) or di-iodotyrosine (DIT). T4 is made up of DIT + DIT
33
Which thyroid hormone is more potent?
T3
34
Which thyroid hormone is more biologically active?
T3
35
Which thyroid hormone is most commonly secreted?
T4
36
Where is T4 converted to T3?
the liver and kidney
37
What stimulates the release of T3 and T4 from the follicular cell?
TSH
38
How are T3/T4 carried within the blood stream and why?
T3/T4 are hydrophobic so are carried in the plasma bound to plasma proteins - when they are in the free form they are biologically active
39
Name the 3 proteins which T3/T4 are most commonly bound to
Thyroxine binding globulin (TBG) ~70%; Transthyretin thyroxine binding pre-albumin (TTR); Albumin (5%)
40
Which form of T3/T4 is more closely correlated to the metabolic state?
free T3 and free T4
41
What is the result of increasing TBG?
increased total T4, not free T4
42
States where there may be increased TBG (4/7)
pregnancy, newborn, hepatitis, biliary cirrohosis, oral contraceptive pill (or other sources of oestrogen), acute intermittent porphyrias, heroin
43
What is the result of decreasing TBG?
decreased total T4, not free T4
44
States where there may be a decrease in TBG (4/7)
androgens, large doses of glucocorticoids, active acromegaly, severe systemic illness, chronic liver disease, phenytoin, carbemazepine
45
Physiological effect of increasing thyroid hormones (5/8)
increased BMR; increased thermogenesis; increased carbohydrate/lipid metabolism; increased protein synthesis; growth; development of foetal/neonatal brain; normal CNS activity
46
How does thyroid hormone affect the response to adrenaline?
increases responsiveness to adrenaline and NA by increasing the number of receptors --> increase in HR and force
47
Why is propanolol an initial treatment of hyperthyroidism?
It antagonises the adrenoreceptors to reduce HR and force which can be found in hyperthyroidism
48
How does thyroid hormone increase BMR?
increases the number and size of mitochondria, increases oxygen use and ATP hyrdolysis and increases the synthesis of respiratory chain enzymes
49
How much of temperature regulation is affected by thyroid hormone?
30%
50
How does thyroid hormone affect carbohydrate metabolism?
increased blood glucose through glycogenolysis and gluconeogenesis while increasing insulin dependent uptake into cells
51
How does thyroid hormone affect growth?
GHRH production and secretion requires TH
52
How does thyroid hormone affec the development of the neonatal brain?
increases myelinogenesis and axonal growth
53
How is thyroid hormone release regulated?
Thyrotropin RH is released from the hypothalamus and stimulates TSH release from the anterior pituitary
54
How do T3/T4 impact the release of TRH?
negative feedback system: T3/T4 inhibit the release of TRH and TSH
55
What kind of receptor is the TSH receptor?
A GPCR which stimulates cAMP in the follicular cell
56
When is TH highest in the day?
Late at night; lowest in the morning
57
How many types of de-iodinase enzymes are there?
3
58
Which de-iodinase enzyme is most important for converting T4 to T3 ?
type 2
59
Where is type 2 de-iodinase enzyme mostly found?
within the heart, skeletal muscle, CNS, fat, thyroid and pituitary
60
Where is type 3 de-iodinase enzyme mostly found?
foetal tissue, the placenta and brain (-pituitary)
61
Where is type 1 de-iodinase enzyme mostly found?
liver and kidneys
62
How does T3 activate the TH receptor?
TH receptor is activated and travels to the nucleus of the cell where it binds with the RXR and a transcription factor
63
What are the 4 thyroid hormone receptor isoforms?
TRa1, TRa2, TRb1, TRb2
64
Which is the predominant form of thyroid hormone receptor in most tissues?
TRa
65
Which tissues is TRb the predominant form of thyroid hormone receptor?
liver and negative feedback loop
66
Test results show: high TSH, low fT4...diagnosis is...
primary hypothyroidism
67
Test results show: high TSH, normal fT4...diagnosis is...
subclinical hypothyroidism
68
Test results show: high TSH, high fT4...diagnosis is...
TSH secreting tumour or TH resistance
69
Test results show: high TSH, high fT4/ low fT3..diagnosis is...
deiodinase deficiency, TH antibody
70
Test results show: low TSH, high fT4/T3...diagnosis is...
primary hyperthyroidism
71
Test results show: low TSH, normal fT4...diagnosis is...
subclinical hyperthyroidism
72
Test results show: low TSH, low fT4...diagnosis is...
secondary hypothyroidism
73
Test results show: low TSH, lowfT4/T3...diagnosis is...
sick euthyroid or pituitary disease
74
Test results show: normal TSH, abnormal fT4...diagnosis is...
consider TBG, amiodarone, pituitary TSH tumour
75
Chief cause of hypothyroidism worldwide
iodine deficiency
76
Chief cause of hypothyroidism in the UK
Hashimotos disease
77
Clinical features of hypothyroidism that might be seen in the hair and skin (4+)
coarse, sparse hair; dull expressionless face; periorbital puffiness; pale cool skin that feels doughy
78
Clinical features involving thermogenesis of hypothyroidism
cold intolerance
79
Cardiac features of hypothyroidism
bradycardia, worsening heart failure
80
Metabolic features of hypothyroidism
hyperlipidaemia, weight gain, decreased appetite
81
Common GI feature of hypothyroidism
constipation
82
Common neurological features of hypothyroidism
depression, psychosis, carpal tunnel syndrome and decreased visual acuity
83
Common gynae features of hypothyroidism
menorrhagia follows by amenorrhoea
84
Goitrous causes of primary hypothyroidism (4)
chronic thyroiditis (Hashimotos), iodine deficiency, drug induced (lithium, amiodarone), maternally transmitted
85
Non-goitrous causes of primary hypothyroidism (3)
atrophic thyroiditis (autoimmune), post-ablative, congenital developmental defect
86
Subclinical hypothyroidism may present with what blood test features?
high TSH, normal T4
87
Common clinical investigations other than thyroid function tests which may be ordered when considering hypothyroidism
MCV - macrocytosis, increased CK, increased LDL and cholesterol, hyponatraemia, hyperprolactinaemia
88
Main drug treatment of hypothyroidism
levothyroxine (T4) - taken before breakfast
89
Why might levothyroxine dose need to be increased in pregnancy?
due to increased TBG produced by the liver
90
Why is it important to slowly restore normal thyroid function in hypothyroidism?
it may cause cardiac arrhythmias
91
Dose of levothyroxine in young person?
50-100µg/day
92
Dose of levothyroxine in elderly
25-50µg/day
93
Antibodies associated with Hashimoto's thyroiditis
anti-TPO - thyroid peroxidase
94
group most commonly affected by myxoedema coma
elderly women with longstanding or undiagnosed hypothyroidism
95
Signs of myxoedema coma
bradycardia, type 2 resp failure, hypoxia, hypercarbia, co-existing adrenal failure
96
cardiac features of hyperthyroidism
palpitations, AF, rarely cardiac failure
97
General feelings when suffering from hyperthyroidism
anxiety, irritibility, sleep disturbance
98
How might hyperthyroidism affect the sympathetic nervous system?
sweating and tremors
99
Visual features of hyperthyroidism
lid retraction (non-specific), diplopia, proptosis - Graves
100
Gynae features of hyperthyroidism
lighter and less frequent periods
101
Where might a patient experience weakness in hyperthyroidism?
thighs and upper arms
102
Thermogenesis in hyperthryoidism
heat intolerance
103
Weight in hyperthyroidism
decreased despite increased appetite
104
Causes of thyrotoxicosis associated with hyperthyroidism (7)
Graves, Hashitoxicosis, thyrotropinoma, thryoid cancer, toxic solitary nodule, toxic multinodular goitre
105
Causes of thyrotoxicosis associated with hyperthyroidism (3)
thyroid inflammation (post-partum, sub-acute, drug induced), exogenous TH, ectopic thyroid tissue
106
Age associated with Grave's disease
younger patients (20-50years)
107
Is there a genetic component to Graves?
Yes - 70% have susceptibility factors and sisters and children of women with Graves have a 5-8% chance of developing an autoimmune thyroid disease of any kind
108
Key exacerbating factor in Grave's disease
smoking - more severe and difficult to treat in smokers
109
Investigations in Graves disease
```
TFT
LFTs
Calcium
WCC
TSH receptor antibody
```
110
Thyroid function test results expected in Graves disease
Decreased TSH and increased fT3/T4
111
Expected LFTs and calcium results in Graves disease
hypercalcaemia and raised ALP due to increased bone turnover --> association with osteoporosis
112
Expected WCC in Graves disease
leucopaenia - often milk
113
TSH receptor antibody is confirmation of diagnosis of Graves - True/False
True - If this is present then there is no need to image the thyroid gland
114
Clinical signs of Graves disease (4)
Pretibial myxoedema, thyroid acropachy, thyroid bruit, graves eye disease
115
Graves eye disease occurs in what percentage of patients...what group are particularly high risk?
20%, particularly smokers
116
confirmation of graves eye disease on MRI
inflammation behind the eye
117
Which group of patients is most likely to experience nodular thyroid disease?
older patients - occurs with insidious onset
118
What features suggest a thyroid storm?
resp and cardiac collapse, severe hyperthermia, exaggerated reflexes
119
Patients at risk of thyroid storm?
those with acute infection or recent surgery
120
treatment of a thyroid storm?
Lugol's iodine, glucocorticoids, PTU, b-blockers, fluids and monitoring
121
Brief overview of deQuervains thyroiditis
subacture granulomatous thyroiditis, inflammation of thyroid which may be painful and oftern preceeded by a viral illness
122
3 phases of deQuervains thyroiditis
thyrotoxicosis, hypothyroid, euthryroid
123
investigation results confirming deQuervains thyroiditis
raised ESR, CRP and TH levels
124
First line treatment of hyperthyroidism
carbimazole
125
mechanism of action of treatment of hyperthyroidism
inhibition of thyroid peroxidase --> blocks TH synthesis
126
situation where carbimazole is not first line treatment
early pregnancy - may cause aplasia cutis
127
1st line treatment in early pregnancy for hyperthyroidism
polythiouracil (PTU) - 10x less potent than carbimazole
128
mechanism of action of PTU
inhibits DIO1
129
main risk of PTU
1:10000 liver failure
130
in the first 6 weeks of hyperthyroid treatment, what is the biggest side effect risk
agranulocytosis - warn verbally, get urgent FBC if fever, oral ulcer or oropharyngeal infection
131
common side effects of hyperthyroidism treatments
cholestatic jaundic, increased liver enzymes, fulminant liver failure
