W.12: Disturbances of Thyroidal Function Flashcards
What is transporting iodide from follicular cell to colloid?
Pendrin (Na-dependent Cl/I- transporter)
What is transporting T3 and T4 from thyroid follicle into blood?
MCT: Monocarboxylate transporter
Hypothalamus releases what hormone to stimulate the pituitary?
Thyroid releasing hormone (TRH)
Pituitary releases what hormone to stimulate the thryoid?
Thyroid stimulating hormone (TSH)
Free T3 and T4 has ….. feedback on the pituiary and hypothalamus
Negative
T4 can be converted to two other substances..?
T3 and rT3 (reverse T3, ineffecvtive)
Half life of T4
1 week
Half life of T3
1 day
% of T4 bound to TBG
70%
% of T4 bound to TBPA
20%
% of T4 bound to albumin
9.96%
% of T4 unbound (free)
0.04%
Type 1 deiodinase found in?
Liver and kidney
Type 2 deiodinase found in?
Pituitary, placenta, brain
Type 3 deiodinase function?
T4 to rT3
4 actions of TSH on thyroid
- Stimulate iodine uptake
- Hormonogenesis
- Release of T3 and T4 (via cAMP)
- Inc. thyroid gland size and vascularity
How does thyroid hormone affect fetal development?
Affecting neural and skeletal system
How does thyroid hormone affect oxygen consumption and heat production?
Controls BMR, T3 is considered the major regulator of mitochondrial activity
How does thyroid hormone affect the sympathetic system?
Similar to the effects caused by catecholamines
How does thyroid hormone affect the endocrine system?
Inc. cortisol metabolism and clearance
How does thyroid hormone affect the musculoskeletal system?
Inc. the turnover of bone
Values of hormones in hypothryoidism
- TSH > 4.2mIU/L
- Free T4 is low
Values of hormones in subclinical hypothyroidism
- TSH > 4.2mIU/L
- Free T4 is normal
Values of hormones in euthyroid
- TSH 0.3-4.2 mIU/L
- Free T4 normal
Values of hormones in subclinical hyperthyreosis
- TSH <0.3mIU/L
- Free T3/T4 normal
Values of hormones in hyperthyreodism
- TSH < 0.3mIU/L
- Free T3/T4 elevated
How common is hypothyroidism?
Occurs in 3.8-4.6% of the population (10 times more common in women)
Typical symptoms of hypothyroidism
- Slow HR, reduced CO, low voltage, dec. GFR, anemia
- Weight gain, constipation
- Myxoedema, hair loss, dry skin, carotenoderma
- Tiredness, depression, psychosis, memory loss
Primary causes of hypothyroidism (6)
- Hashimoto’s thyroiditis (autoimmune)
- After treatment of hyperthryoidism
- Inflammation
- Iodine def.
- Congenital (incomplete development, enzyme defects)
- Drugs (amiodarone, lithium)
Hashimoto’s thyroiditis
Destruction of the thyroid gland by autoantibodies against thyroglobulin, thyroperoxidase, and other thyroid tissue components
Postpartum thyroiditis
- Usually a transient phenomenon observed following pregnancy
- Believed to result from modifications to the immune system necessary in pregnancy
Subacute thyroiditis
Acute inflammatory disease probably caused by a virus
Progression of subacute thyroiditis
Phase 1: Hyperthyroidism
Phase 2: Euthyroid
Phase 3: Hypothyroidism
Phase 4: Euthyroid
Subclinical hypothyroidism
Isolated elevated TSH level, but normal T3/T4, symptoms may or may not be present
Subclinical hypothyroidism: Prevalence
Worldwide 1-10%, highest rate in women above 60 yrs
8 underlying causes of hyperthyroidism
- Graves disease
- Plummers disease
- Marine-Lenhart syndrome
- Subacute thyroiditis
- Hashimoto thyroiditis hyperthyroid phase
- Thyreotoxicosis Facilita
- Trophoblastic disease
- Struma ovarii
Characteristic symptoms of Graves disease
Opthalmopathy (exophthalmus), dermopathy (pretibial myxedema)
