PBL 6 - Hypothyroidism

Question 1

Name the two hormones secreted by the cuboidal cells of the thyroid gland
follicles. No abbreviations

Answer 1

1) Triiodothyronine (T3)

2) Thyroxine (T4)

Question 2

Name two consequences of hyperthyroidism on glucose metabolism.

Answer 2

Hyperthyroidism leads to Insulin resistance [1], mainly associated with increased
hepatic gluconeogenesis [1

Question 3

Explain why the thyroid gland is enlarged in Hashimoto thyroiditis and why TSH
is elevated

Answer 3

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

Question 4

What do coeliac disease and Hashimoto disease have in common?

Answer 4

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

Question 5

) What treatment was Maria given and explain why it was probable the dose
would need adjusting. [

Answer 5

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 [

Question 6

What is TPO (thyroid peroxidase)

Answer 6

enzyme that oxidises iodide on tyrosine of thyroglobulin –> T3/T4 synthesis.

Question 7

How are T3 and T4 stimulated

Answer 7

Hypothalamus secretes thyrotropin-releasing hormone –> AP secretes TSH –> Thyroid secreates triiodothyronine + thyroxine
= Negative feedback - too much T3 and T4 –> TRH inhibited

Question 8

Effects of thyroid hormone

Answer 8

Increase BMR
Enhance fatty acid oxidation and mobilation
Thermogenesis
Insulin effects

Question 9

How do thyroid hormones enhance FA oxidation and mobilisation

Answer 9

= Increases no LDL receptors
= Breaks down cholesterol
= Increases lipolysis –> removing triglycerides from chylomicrons and VLDL + depositing fat in tissue

Question 10

How does thyroid hormone affect glucose metabolism

Answer 10

1) Synergistic with insulin - increases uptake of glucose via GLUT4 upregulation in muscles
2) Opposes insulin in the liver- gluconeogenesis/glycogenolysis in liver

Question 11

How does TH increase thermogenesis

Answer 11

Increases uncoupling by increasing capacity to do more oxidative phosphorylation by increasing the no of mitochondria

Question 12

TH effects on cardiac myocytes

Answer 12

Increase contractility by increasing no of beta adrenergic receptors

Question 13

Symptoms of hypothyroidism

Skin, CV, GI, Nerves, renal, endocrine

Answer 13

= 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

Question 14

What is cretinism

Answer 14

Congenital hypothyroidism

Question 15

What is hashimotos syndrome

Answer 15

Autoimmune disease where the thyroid gland is gradually destroyed

Question 16

What are autoantibodies against in hashimotos

Answer 16

= Thyroid peroxidase, thyroglobulin, TSH receptors

Question 17

How can you diagnose hashimotos

Answer 17

Elevated TPO antibodies

Question 18

Why does a goitre form

Answer 18

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

Question 19

Cause of goitre

Answer 19

Hashimotos

I2 deficiency

Question 20

Diagnosis + ant Tx of hypothyroidism

Answer 20

High TSH
Low t4
Give levothyroxine or Iiothyronine

Question 21

Hyperthyroidism symptoms

Answer 21

Weight loss
intolerance to heat
bone reabsorption
tachycardia
Insulin resistance - hepatic gluconeogenesis
Decreased levels of LDL, ApoB, total cholesterol

Question 22

Why does the pt have high TSH

Answer 22

Due to positive feedback, low TH would increase the anterior pituitary to release more TSH to compensate for the hypothyroidism

Question 23

Why high HbA1c in pt

Answer 23

• 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

Question 24

Why high LDL cholesterol

Answer 24

• 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

Question 25

Why patient weight gain

Answer 25

Decreased BMR

Doesnt burn as many calories per day

Question 26

Why memory loss in pt

Answer 26

lack of TH slows down neural processes (brain depends on glucose, glucose metabolism affected by low TH)

Question 27

Why does the pt feel cold

Answer 27

– Decreased BMR due to lack of TH production, less uncoupling –> less thermogenesis

Question 28

How is levothyroxine given

Answer 28

Orally or via IV

Question 29

Long term use of levothyroxine

Answer 29

Hyperthyroidism, cardiac failure, angina

Question 30

Why can levothyroxine not be used as a diet pill

Answer 30

Only help to lose weight if you have hypothyroidism

Can be toxic as can cause hypertension in normal people - sweating, angina, cardiac failure, dysrhythmias

Question 31

What can trigger hypothalamus to produce TRH

Answer 31

Cold
Acute psychosis
Circaidian rhythm

Severe stress can inhibit

Question 32

In cells, what receptors do thyroid hormones interact with

Answer 32

Neuclear

Question 33

What are HbA1c levels

Answer 33

Measure of glycosation of haemoglobin over past 3 months if high