endocrine - thyroid Flashcards
0
Q
DIT plus DIT
A
Tetraiodithyronine or T4
1
Q
Biosynthesis of T3 and T4
A
- Dietary iodide ingestion by follicular cells
- Active transport and uptake of iodide into colloid by thyroid gland
- Oxidation of I and iodination of Tg tyrosine residues
- Coupling of Iodotyrosine residues (MIT & DIT) to form T3 and T4
- Proteolytic of Tg with release of T3 and t4 into circulation
2
Q
DIT plus MIT
A
Triiodothyronine T3
3
Q
Indispensable component of thyroid hormone comprising 65% of T4 and 58% of T3’s weight.
A
Iodine
4
Q
Required daily intake of iodine in 0-7y/o.
A
90 ug/d
5
Q
Required daily intake of iodine in 7-12y/o.
A
120 ug/d
6
Q
Required daily intake of iodine in teenager and adults
A
150 ug/d
7
Q
Required daily intake of iodine in pregnant and lactating women
A
25o ug/d
8
Q
Iodine intake not more than
A
1100 ug/d
9
Q
Excess iodine
A
Wolff chaikoff effect
Jodbasedow phenomenon
10
Q
Excess iodine with transient shut down of thyroid hormone production (normally).
When increasing doses of iodide inhibit organification and hormonogenesis of thyroid hormone.
A
Wolff chaikoff effect
11
Q
In some pts with HAshimoto’s thyroiditis, they may stay hypothyroid because of inability to escape this effect
A
Wolff-chaikoff effect
12
Q
Thyroid hyperfunction induced by excess iodine ingestion in pts with various thyroid disorder (grave’s disease)
A
Jod-basedow phenomenon
13
Q
Dietary iodine reaches the circulation as
A
Iodide anion
14
Q
Iodide active transport by thyroid Is mediated by this membrane protein
A
Sodium-iodide symporter or NIS
15
Q
It functions as iodide concentrating mechanism that enables iodide to enter the thyroid for hormone biosynthesis
A
NIS
16
Q
Iodide trapping by the aid of
A
NIS
17
Q
Iodide must be first ___ to be able to iodinate tyro sly residues of Tg
A
Oxidized
18
Q
Iodination of tyrosyl residues then forms monoiodotyrosine and diiodotyrosine which are then coupled to form either T3 or T4. Both reactions are catalyzed by
A
Thyroperoxidase
19
Q
Thyroperoxidase Catalyzes oxidation steps involved in:
A
I- activation
Iodination of Tg tyrosyl residues
Coupling of iodotyrosyl residues
20
Q
TPO uses ___ as the oxidant to activate I- to hypoiodate the iodination species
A
H2O2
21
Q
To liberate t3 and t4, Tg is resorted into follicular cells in the form of ___ which fuse with lysosomes to form phagolysosome
A
colloid droplets
22
Q
Primary secretory product of thyroid gland
A
T4
23
Q
Thyroid secretes approximately how many grams of thyroxine daily
A
70-90 ug/d
24
Total daily production rate of t3
15-30 ug/d
25
T3 is derived from 2 processes
1. 80% of circulating T3 comes from deiodination of T4 on peripheral cells
2. 20% comes directly from thyroid secretion.
26
Pro hormone for T3
T4
27
T4 is biologically inactive in target tissues
True. Until converted to T3
28
T4 is converted to T3 by
5-deiodination of outer ring of T4
29
T3/T4 which is biologically active responsible for the majority of thyroid hormone effects
T3
30
Major extrathyroidal T4 conversion site for production of T3
Liver
| Some occurs in kidney and other tissue
31
Normal disposition of T4
41% is converter to T3
38% is converter to rT3
21% is metabolized via other pathways (conjugation on liver and excretion in bile)
32
Normal circulating concentration of t4
4.5-11 ug/dl
33
Normal circulating concentration of t3
60-180 ng/dl
34
T3/4: Produced only in thyroid gland
T4
35
T3/4: 80% are from peripheral conversion
T3
36
Half life of t4
7 days
37
Half life of t3
One day
38
T3/4: only free hormones are active
T4
39
3-8x more potent
T3
40
More than 99% of circulating T3 and t4 is bound to plasma protein Carrier proteins which are
TBG 75%
Transthyretin TTR / thyroxine-binding prealbumin TBPA 10-15%
Albumin 7%
HDL 3%
41
Decrease or increase TBG effects on total serum T3 and T4 level and free T3 and T4.
Decrease or increase TBG will decrease/increase total serum T3 and T4 level.
While free T3 and T4 remain unchanged
42
Drugs that increase TBG
```
Oral contraceptives
Methadone
Clofibrate
5-fluorouracil
Heroin
Tamoxifen
```
43
Conditions that increase TBG
```
Pregnancy
Infectious/chronic active hepatitis
HIV infection
Biliary cirrhosis
Acute intermittent porphyria
Genetic factors
```
44
Drugs that decrease serum t3 and t4 by decreasing TBG conc
```
Glucocorticoids
Androgens
L-asparaginase
Mefenamic acid
Furosemide
```
45
Drugs that decrease serum t3 and t4 by decreasing binding
Antiseizure medications
| Salicylates
46
Decreased thyroid hormone concentration may lead to alteration of ___. May develop impairment of attention, slowed motor function, and poor memory
cognitive function.
47
Thyroid hormone influences cv hemodynamics by
```
Increase HR and decrease systemic vascular resistance thus increase CO = improve cardiac performance
Elevate blood volume
Local vasodilators
Decrease diastolic blood pressure
Cardiac chronotropy and inotropy
```
48
Thyroid hormone is critical for normal bone Growth and development
T3 regulates sk maturation at growth plate.
T3 participates in osteoblasts differentiation and proliferation and chondrocytes maturation loading to bone ossification.
49
Major regulator of mitochondrial activity
T3
50
Thyroid hormone is a major regulator of mitochondria activity
T3 induces early transcription and increases TFA expression.
T3 stimulates O2 consumption.
51
Thyroid hormone stimulates mitochondrial activity in most tissue
T3 increases basal metabolic rate, body heat production and O2 consumption.
52
Metabolic effects of T3
1. Lipolysis- FA + glycerol
2. expression of lipogenic enzymes
3. cholesterol catabolism into BA
4. Rapid removal of LDL from plasma
5. Carbohydrate and protein catabolism
53
Thyroid hormone influences the female repro system
Hypothyroidism may be asso with menstrual disorder, infertility, risk of miscarriage and other complications of pregnancy.
54
AOG when fetus is completely dependent on maternal thyroid hormones
First 3 mos
55
AOG when fetal thyroid begins to conc iodine and synthesize Iodothyronines
10-12wks
56
AOG when fetal pituitary gland differentiates
10-12 wks
57
Thyroid hormones that appear in fetal serum
TSH
| T4
58
Placental transfer without difficulty
Iodide
Thionamides
Thyroid ab
TRH
59
Some placental transfer
T3
| T4
60
Little or no placental transfer
TSH
61
Increased thyroid hormone requirements during pregnancy
Increase free TH binding to TBG - marked fall in serum free T4 - if no compensatory increase in thyroid secretion leads to hypo.
Transplacental transfer of T4 - placental degradation of T4 - if no compensatory increase in thyroid secretion leads to hypo.
62
During first trimester, ___ is at its highest conc and can stimulate thyroid cells to produce new thyroid hormones.
B-HCG
63
There is transient low TSH during 1st trimester due to increased thyroid hormone production.
True
64
During pregnancy, there is an increased Renal iodine clearance, therefore..
Increased 24-hr RAIU
65
During pregnancy, there is an decreased plasma iodine and placental iodine transport to the fetus, therefore..
In deficient women, decreased T4, increases TSH then leads to goiter formation
66
During pregnancy, there is an increased O2 consumption, therefore..
Increased BMR
67
During 1st tri in pregnancy, there is an increased HCG, therefore
Increased free T4 and T3
| Decreased basal TSH
68
During pregnancy, there is an increased serum TBG, therefore..
Increased total T3 and T4
69
During pregnancy, there is an increased plasma volume, therefore..
Increased T3 and T4 pool size
70
During pregnancy, there is an increased plasma type 3 deiodinase, therefore..
Accelerates rates of t3 and T4 degradation and production.
71
Refers to classic physiologic manifestations if excessive quantities of the thyroid hormones
Thyrotoxicosis
72
RAIU level in thyrotoxicosis
Decreased
73
Most common cause of thyrotoxicosis
Thyroiditis
74
Reserved for disorders that results from sustained overproduction of hormone by the thyroid gland itself
Hyperthyroidism
75
Most common cause of hyperthyroidism
Graves disease
76
Lab diagnosis for thyrotoxicosis and hyperthyroidism
Suppressed TSH <0.1 mU/L
Elevated T4
RAIU
77
Lab diagnosis to differentiate thyrotoxicosis and hyperthyroidism
RAIU
78
```
TSH level and RAIU level of:
Graves disease
Toxic multinodular goiter
Toxic adenoma
Gestational hyperthyroidism
```
Low TSH
| High RAIU
79
```
TSH level and RAIU level of:
Iodine induced hyperthyroidism
Amiodarone- induced hyperthyroidism
Struma ovarii
Metastatic thyroid Ca
Thyroiditis
```
Low TSH
| Low RAIU
80
TSH level and RAIU level of:
TSH-secreting pituitary tumor
TH hormone resistance
Elevated or normal TSH
81
TSH level and free T4 level of:
| Secondary or central hypothyroidism
Low TSH
| Low T4
82
TSH level and T4 level of:
| Sick euthyroid syndrome
Low TSH
| Low T4
83
TSH level and T4 level of:
T3 thyrotoxicosis
Sub clinical hyperthyroidism
Low TSH
| Normal T4
84
TSH level and T4 level of:
| True hyperthyroidism
Low TSH
| High T4
85
TSH level and T4 level of:
| Graves disease
Low TSH
| High T4
86
Graves disease is a syndrome characterized by
Hyperthyroidism
Ophthalmopathy
Dermopathy
Pretibial myxedema
87
Graves disease is an autoimmune disease with a strong familial disposition more common in male/female.
Female
88
Environmental triggers of graves disease
Stress
Tobacco use
Infection
Iodine exposure
89
Most frequent cause thyrotoxicosis in iodine-sufficient countries
Graves disease
90
Main ag in graves disease
TSHR
91
Circulating ab in graves disease
TRAbs
92
Dermopathy in graves disease
```
Plummer's nail
Hyperpigmentation
Hyperhidrosis
Alopecia
Acropachy (triad of digital clubbing, soft tissue swelling of hands and feet and periosteal new bone formation)
```
93
Signs and symptoms of hyperthyroidism
```
Freq bowel movement
Bulging eyes
Sudden paralysis
Weigh loss / gain
Tachycardia
Heat intolerance
Warm, moist palm
Light period
```
Increase sweating
Insomnia
Nervousness, tremors
```
Goiter
Hoarseness
Infertility
Irritability
Dry/sore throat
Dysphagia
```
94
Signs and symptoms in hypothyroidism
```
Constipation
Puffy eyes
Muscle weakness
Weigh loss gain
Bradycardia
Cold intolerance
Dry, patchy skin
Heavy period
```
```
Hairloss
Tiredness
Forgetfulness
Depression
Elevated cholesterol
```
```
Goiter
Hoarseness
Infertility
Irritability
Dry/sore throat
Dysphagia
```
95
Atrial fibrillation is characteristically manifested in what thyroid disorder
Graves disease
96
First line therapy for hyperthyroidism or graves disease
Radioactive iodine
97
Mechanism of action do radioactive iodine
Destroys the thyroid and stops the excess production of hormone
98
Indication for radioactive iodine treatment
Female planning a pregnancy in the future
Pts with increase ping surgical risk
Pts previously operated or externally irradiated neck
Pts with CI to ATD
99
Treatment of choice for recurrent hyperthyroidism after ATD therapy
RAI
100
RAI is used by elderly and cardiac pts
True.
101
RAI has no effect on fertility, no increased incidence of congenital malformation and no increased risk of cancer
True
102
RAI is contraindicated during
Lactation and pregnancy
103
Pregnancy must be postponed for at least ____ after RAI therapy
6 mos
104
RAI therapy or RAI ablation:
| To destroy some thyroid tissue in graves disease or toxic nodules.
RAI therapy
105
RAI therapy or RAI ablation:
| Low dose
RAI therapy
106
RAI therapy or RAI ablation:
| With intention to destroy all thyroid remnant and metastasis in well diff Ca
RAI ablation
107
Indications for thyroidectomy
```
Planning for pregnancy (<4-6 mos)
Thyroid malignancy
Large goiter (>80gms)
Low RAIU
Coexisting hyperparathyroidism
```
108
Patients undergoing surgery (thyroidectomy) should be rendered
Euthyroid
109
What would be given in immediate preop period in thyroidectomy
Potassium iodide
To diminish vascularity to suppress the thyroid hormone production becoz patients undergoing surgery should be rendered euthyroid.
110
Potential complication of thyroidectomy
Hypoparathyroidism
Hypothyroidism
Vocal cord paralysis
111
Anti thyroid drugs
Methimazole
Propylthiouracil
Carbimazole
Thiamazole
112
PTU / MMI:
| Blocks thyroid hormone production and secretion
Both
113
PTU / MMI:
| Blocks peripheral conversion of T4 to T3
Porpylthiouracil
114
PTU / MMI:
| Long half life
MMI
115
PTU / MMI:
| More binding to albumin
PTU
116
PTU / MMI:
| Less placental passage
PTU
117
PTU / MMI:
| Lower conc in breast milk
PTU
118
PTU / MMI:
| With peculiar toxicity - aplastic cutis embryopathy
MMI
119
Mechanism of action of ATDs
Inhibition of organification (iodine binding to Tg)
Inhibition of coupling of Iodothyronines
Inhibition of T4 to T 3 conversion (PTU)
Possible immunosuppressive effects (MMI)
120
ATD that is used in all patients
MMI
| Except those in 1st tri in pregnancy, treatment for thyroid storm
121
Myxedema is due to
Accumulation of hyaluronic acid which alter the composition of the subs of the dermis and other tissue
122
Life threatening clinical condi in pts with long standing severe untreated hypothyroidism
Myxedema coma
123
Severe hypothyroidism in infancy with irreversible mental and growth retardation
Cretinism
124
TSH level, T3 or t4 level in subclinical hyperthyroidism
Low TSH
Normal t4 and t3
Asymptomatic
125
TSH level, T3 or t4 level in subclinical hypothyroidism
High TSH
| Normal t4 and t3
126
Thyroxine therapy must be considered in subj (age) if TSH is ___ and/or TPO ab is (present/absent)
<65 yrs old if TSH >10mU/L and/or TPO ab is present
127
In cases wherein TSH <10mU/L and/or TPO ab is absent, thyroxine therapy still might be warranted in individual with high background for
Cv risk, pregnancy and infertility
128
Most common case of hypothyroidism in areas wherein dietary iodine is sufficient
HAshimoto's thyroiditis
129
Pathologic feature of HAshimoto's thyroiditis
Presence of both mononuclear cells and thyroid follicle destruction
130
Hallmark of classic HAshimoto's disease
Goiter
131
Treatment of choice in HAshimoto's disease and /or large goiter
Levothyroxine
132
Self limited anti-inflammatory disorder of thyroid and the most common cause of pain from thyroid origin
Subacute thyroiditis
133
Rare disorder of chronic sclerosing thyroiditis
Riedel's thyroiditis
