Thyroid Flashcards
1
Q
what does the thyroid secrete
A
Thyroxine (T4)
Tri-iodothyronine (T3)
Calcitonin
2
Q
what does the parathyroid secrete
A
PTH
3
Q
what cells secrete calcitonin
A
Parafollicular C cells
4
Q
steps of synthesis and storage of T3 and T4
A
1 - Iodine taken up by follicle cells
2 - iodine attached to tyrosine residues on thyroglobulin to form (MIT) & (DIT)
3 - coupling of MIT+ DIT = T3
and DIT + DIT = T4
4 - stored in COLLOID thyroglobulin till required
5
Q
how many iodine units does DIT and MIT contain
A
DIT - 2
MIT - 1
6
Q
what does CARBIMAZOLE & PROPYLTHIOURACIL inhibit
A
Iodine attaching to tyrosine
7
Q
what is the major biologically active thyroid hormone
A
T3
8
Q
what thyroid hormone is produced the most by the thyroid
A
T4 - thyroxine
9
Q
where is T4 converted to T3
A
liver and kidney
10
Q
what triggers the release of T3 and T4
A
the TSH from the pituitary gland
11
Q
what form of T3/T4 is the biologically active form
A
unbound/free
12
Q
what are the plasma protein binding molecules of T3/T4
A
Thyroxine binding globulin (TBG – approx 70%)
Thyroxine binding prealbumin (TBPA- approx 20%)
Albumin
13
Q
Metabolic state correlates LESS closely with the free than with the total concentration in the plasma - true or false
A
False
Correlates MORE with free/unbound concentration
14
Q
is thyroid hormone important for growth ?
A
yes
15
Q
what is needed to treat symptoms in initial stages on therapy for hyperthyroidism
A
Beta blocker e.g. Propranolol
16
Q
what stimulates the release of TSH from the ANTERIOR pituitary
A
TRH from the hypothalamus
17
Q
what can inhibit TRH and TSH release
A
stress
18
Q
what type of rhythm does thyroid hormone release have
A
circadian rhythm
- highest late at night, lowest AM
19
Q
severe complication of hypothyroidism
A
adults - myxoedema (puffy face/hands/feet)
babies - cretinism (dwarfism and limited mental function)
20
Q
when would there be a lingual thyroid
A
failure of descent - embryological abnormality
21
Q
where can the thyroid be found if there has been excessive descent
A
retrosternal in mediastinum
22
Q
where does the thyroid descend from
A
foramen caecum
23
Q
what is the thyroid composed of
A
follicles
24
Q
what is each follicle surrounded by
A
cuboidal follicular epithelial cells.
25
what is in the centre of follicle cells
thyroglobulin - dense amorphic pink material
26
pathway of release of T3 and T4
- TSH binds to TSH receptor
- G proteins activated
- GTP to GDP
- production of cAMP
- increased production and release of T3 and T4
27
what are the antibodies of Grave's Disease
Anti TSH receptor antibodies
- Thyroid stimulating immunoglobulin (most specific for Graves)
- Thyroid growth stimulating immunoglobulin
- TSH binding inhibitor immunoglobulins
28
what is the triad of features associated with Graves
- Hyperthyroidism with diffuse enlargement of the thyroid
- Eye changes (exophthalmos)
- Pretibial myxoedema.
29
why is there eye changes in Graves disease
fibroblasts (etc.) in the eye expressing TSH receptors
30
what antibodies are associated with Hashimotos' thyroiditis
Anti-thyroid antibodies
- Anti-thyroglobulin
- anti-peroxidase
31
what is Hashimoto's associated with
Middle aged women
Other Autoimmune disease
HLA – DR3 and DR5
32
what causes the destruction of the thyroid in Hashimoto's
CD8 +ve cells - cytotoxic destruction
cytokine mediated cell death
33
what polymorphisms in what genes are associated with Hashimoto's
CTLA-4
- polymorphisms increase risk of auto-immune diseases
PTPN -22
- inhibits T cell function
34
what may precede Hashimoto's
Transient hyperfunction (Hashitoxicosis)
35
what is a goitre
any enlargement of the thyroid gland
36
what commonly causes multi nodular goitre
lack of dietary iodine
37
what does a lack of iodine cause
cannot produce T3 and T4; causes thyroid to work harder resulting in increase in size due to rise in TSH
38
what does diffuse goitre normal present with
mess effect i.e. neck lump
| T3/T4 normal so euthyroid even if TSH is high
39
how can multi-nodular goitre develop
evolution from long standing simple goitre i.e. recurrent hyperplasia
40
what is the pathology seen in multi-nodular goitre
Rupture of follicles, haemorrhage, scarring, calcification
41
what are the benign neoplasms of the thyroid
Follicular adenoma
42
what are the malignant neoplasms of the thyroid (most to least common)
- papillary
- follicular
- medullary
- anaplastic
43
pathology of adenoma
Discrete solitary mass
- incidental finding normally
- can cause local symptoms
Encapsulated by collagen cuff
Composed of neoplastic thyroid follicles
44
features of adenoma
normally non- functional
| can secrete thyroid hormones - thyrotoxicosis
45
what mutations are commonly seen in adenomas
TSHR signalling pathway
46
what are most malignant thyroid cancers derived from
follicular epithelium
47
Pathology of papillary carcinoma
usually solitary nodule in thyroid (can be multi)
Cystic
Calcified; psammoma body
48
survival rates for papillary carcinoma
good - 10 yrs 95%+
49
what can be the local effects of a cancer in the thyroid
hoarseness
dysphadia
cough
dyspnoea
50
pathology of Follicular carcinoma
Usually single nodule
- Slowly enlarging, painless, non-functional
- often haematogenous spread
- more likely to invade other areas
51
prognosis of follicular carcinoma
Depends on Extent of invasion and stage at presentation
50% mortality at 10yrs
52
pathology of Medullary Thyroid Carcinoma (MTC)
Derived from C-Cells (neuroendocrine)
- Can secrete calcitonin
Composed of spindle or polygonal cells arranged in nests, trabeculae or follicles
Sporadic cases - solitary nodule
Familial cases - bilateral
53
what is MTC associated with
MEN IIA or IIB
| Familial medullary carcinoma
54
features of anaplastic carcinomas
Undifferentiated and aggressive tumours
Usually older patients
May occur in people with a history of differentiated thyroid cancer
Rapid growth and involvement of neck structures and death
55
what is the parathyroid composed on
chief cells
56
what are the actions of chief cells
secrete PTH
| act on Ca homeostasis
57
what supports the chief cells
oxyphil cells
58
what is the most common cause of hyperparathyroidism
small adenomas
59
what is hyperplasia of the parathyroid gland associated with
MEN I and MEN IIa
60
what leads to secondary hyperparathyroidism and what can cause this
Chronic hypocalcaemia causes compensatory over activity of the parathyroid glands
e.g. renal failure, Vit D deficiency
61
what is Tertiary hyoerparathyroidism associated with
hypercalcaemia
62
what does hyperparathyroidism cause
hypercalcaemia
63
what are the symptoms of hyperparathyroidism
STONES
- gall stones, renal stones
MOANS
- depression, lethargy, seizures
GROANS
- Constipation, nausea, peptic ulcer disease, pancreatitis,
BONES
- pain, fracture, osteoporosis
64
when can hypoparathyroidism happen
Post-op
| Di George syndrome
65
what are the surgical options of the treatment of thyroid
Thyroid lobectomy with isthmusectomy
Sub-total thyroidectomy
Total thyroidectomy
66
what is papillary thyroid cancer associated with
Hashimoto's thyroiditis
67
where does thyroid cancer spread to
lungs, bones, liver, brain
via lymphatics
(via haematogenously for Follicular carcinoma)
68
Ix of suspected thyroid cancer
1st - US guided FNA of lesion
| 2nd - excision biopsy of lymph node
69
what is not useful Ix for thyroid cancer
CT/MRI
| Isotope thyroid scan
70
what are clinical predictors of malignancy
```
New thyroid nodule age 50
Male
Nodule increasing in size
lesion > 4cm in diameter
History of head and neck irradiation
Vocal cord palsy
```
71
what is Tx for thyroid cancer
surgery
72
what system is used to identify if patient is high or low risk in thyroid cancer
AMES system
A - age
M - mets
E - extend of primary tumour
S - size of primary tumour
73
when is sub-total or total thyroidectomy done
- DTC with extra-thyroidal spread
- Bilateral / multifocal DTC
- DTC with distant metastases
- DTC with nodal involvement
- Patients in AMES high risk group
74
what type of thyroid cancer had a higher percentage of lymph node spread
Papillary
75
what is checked and monitored after thyroid removal
calcium levels
76
Tx post op
T3 or T4
77
when is whole body iodine scanning used
in patients who have undergone sub-total or total thyroidectomy
78
what is administered in thyroid remnant ablation
I - 131
79
in primary hyperthyroidism what are the TFT results
TSH low
| T4/T3 high
80
in primary hypothyroidism what are the TFT results
TSH high
| T4/T3 low
81
in secondary hypothyroidism what are the TFT results
TSH low
| T4/T3 low
82
what can cause secondary hypothyroidism
pituitary gland failure
83
in secondary hyperthyroidism what are the TFT results
TSH high
| T4/T3 high
84
what can severe hypothyroidism cause
myxoedema coma
85
what organs can play a part in secondary hypothyroidism
hypothalamus
| pituitary
86
what antibody is linked to Hashimoto's
Thyroid Peroxidase Antibodies
87
what blood condition is common in hypothyroidism
Macrocytosis - enlarged RBC
88
why is hyponatraemia seen in hypothyroidism
reduced renal tubular water loss
89
why is hyperprolactinaemia seen in hypothyroidism
↑TRH leads to ↑ prolactin secretion
90
what is Mx for hypothyroid
Thyroxine (T4)
50-100 in younger patients
25-50 in elderly
91
what measurement is used as an index of therapeutic success and potential toxicity in primary hypothyroidism
TSH levels
92
when is T4 used to monitor treatment in hypothyroid
in secondary hypothyroidism
93
Tx for hyperthyroidism
Carbimazole
| Propylthiouracil
94
when would Propylthiouracil be used over Carbimazole
in pregnancy
95
what are the precautions in radio-iodine
```
Avoid close prolonged contact with young children/pregnant women
Don’t share a bed for x days
Avoid Pregnancy for 6 months
Ensure not Pregnant
High Risk of Hypothyroidism
```
96
what are risks in removing thyroid through surgery
Scar
Risk to recurrent laryngeal nerve palsy
Hypothyroidism
Hypo-parathyroidism
97
what type of hyperthyroidism can be triggered by a virus
De Quervains
| Sub-Acute Thyroiditis
98
what antiarrhythmic agent can cause thyroid dysfunction
Amiodarone
99
if there is subclinical thyroid disease where will the abnormality in results be
TSH
T4/3 will be normal
