PBL 6 - Hypothyroidism Flashcards
Name the two hormones secreted by the cuboidal cells of the thyroid gland
follicles. No abbreviations
1) Triiodothyronine (T3)
2) Thyroxine (T4)
Name two consequences of hyperthyroidism on glucose metabolism.
Hyperthyroidism leads to Insulin resistance [1], mainly associated with increased
hepatic gluconeogenesis [1
Explain why the thyroid gland is enlarged in Hashimoto thyroiditis and why TSH
is elevated
Thyroid enlargement is induced by an inflammatory infiltrate of immunocytes that
replace the parenchyma and subsequent fibrosis [1]
Thyroid hormones have a negative feedback action on secretion of TSH by the
anterior pituitary Low plasma levels of T3 / T4 remove this ‘brake’ on TSH
production/release, resulting in high plasma levels of the hormone
What do coeliac disease and Hashimoto disease have in common?
They are both autoimmune disease [1].
Both involve CD4 T cells and B cells, producing auto-immune antibodies targeting
epithelial cells to undergo apoptosis/necrosis [1
) What treatment was Maria given and explain why it was probable the dose
would need adjusting. [
Hormone replacement therapy with thyroxine (tetraiodothyronine, T4), for life [1].
Normally patients started on low dose which is gradually increased [1], the aim
being to reverse S & S of hypothyroidism without causing predictable adverse
effects, especially cardiac [
What is TPO (thyroid peroxidase)
enzyme that oxidises iodide on tyrosine of thyroglobulin –> T3/T4 synthesis.
How are T3 and T4 stimulated
Hypothalamus secretes thyrotropin-releasing hormone –> AP secretes TSH –> Thyroid secreates triiodothyronine + thyroxine
= Negative feedback - too much T3 and T4 –> TRH inhibited
Effects of thyroid hormone
Increase BMR
Enhance fatty acid oxidation and mobilation
Thermogenesis
Insulin effects
How do thyroid hormones enhance FA oxidation and mobilisation
= Increases no LDL receptors
= Breaks down cholesterol
= Increases lipolysis –> removing triglycerides from chylomicrons and VLDL + depositing fat in tissue
How does thyroid hormone affect glucose metabolism
1) Synergistic with insulin - increases uptake of glucose via GLUT4 upregulation in muscles
2) Opposes insulin in the liver- gluconeogenesis/glycogenolysis in liver
How does TH increase thermogenesis
Increases uncoupling by increasing capacity to do more oxidative phosphorylation by increasing the no of mitochondria
TH effects on cardiac myocytes
Increase contractility by increasing no of beta adrenergic receptors
Symptoms of hypothyroidism
Skin, CV, GI, Nerves, renal, endocrine
= Myxoedema, brittle nails, hair falls out, wounds heal slowly
= reduced cutaneous circulation, sensitivity to cold, sinus bradyacrdia,LDL cholesterol up
= Reduced appetite, weight gain, constipation
= Hyponatraemia
= Decreased GLUT 4 stimulation, reduced libido
What is cretinism
Congenital hypothyroidism
What is hashimotos syndrome
Autoimmune disease where the thyroid gland is gradually destroyed
What are autoantibodies against in hashimotos
= Thyroid peroxidase, thyroglobulin, TSH receptors
How can you diagnose hashimotos
Elevated TPO antibodies
Why does a goitre form
Low thyroxine –> Stimulates TSH (Type IV hs)
Hypertrophy/hyperplasia of epithelial cells of follicles
Increased colloid accumulation
Lymphoid filtration + accumulation –> inflammatory cytokines attract more immunocytes –> replace parenchyma –> fibrosis of gland
Cause of goitre
Hashimotos
I2 deficiency
Diagnosis + ant Tx of hypothyroidism
High TSH
Low t4
Give levothyroxine or Iiothyronine
Hyperthyroidism symptoms
Weight loss
intolerance to heat
bone reabsorption
tachycardia
Insulin resistance - hepatic gluconeogenesis
Decreased levels of LDL, ApoB, total cholesterol
Why does the pt have high TSH
Due to positive feedback, low TH would increase the anterior pituitary to release more TSH to compensate for the hypothyroidism
Why high HbA1c in pt
- TH oppose insulin so increase blood sugar by increasing hepatic gluconeogenesis, glycogenolysis (in liver) Work with insulin in muscle, there is insulin resistance and TH dec GLUT4
Why high LDL cholesterol
• Need TH to regulate lipoprotein lipase needed to remove triglycerides from chylomicrons and VLDL as well as depositing fat in adipose → Patient has a lack of TH→ Increase in LDL cholesterol
Why patient weight gain
Decreased BMR
Doesnt burn as many calories per day
Why memory loss in pt
lack of TH slows down neural processes (brain depends on glucose, glucose metabolism affected by low TH)
Why does the pt feel cold
– Decreased BMR due to lack of TH production, less uncoupling –> less thermogenesis
How is levothyroxine given
Orally or via IV
Long term use of levothyroxine
Hyperthyroidism, cardiac failure, angina
Why can levothyroxine not be used as a diet pill
Only help to lose weight if you have hypothyroidism
Can be toxic as can cause hypertension in normal people - sweating, angina, cardiac failure, dysrhythmias
What can trigger hypothalamus to produce TRH
Cold
Acute psychosis
Circaidian rhythm
Severe stress can inhibit
In cells, what receptors do thyroid hormones interact with
Neuclear
What are HbA1c levels
Measure of glycosation of haemoglobin over past 3 months if high
