Endocrine Thyroid Hormone (TH)

Question 1

State the biological effects of thyroid hormone (4)

Answer 1

1. brain development (dur perinatal period)
2. growth (via effect on GH production) –> TSH increases GH production but GH is able to decrease thyroid hormone production
3. thermogenic action (heat production)
4. synthesis and effects of GH (metabolism)

Question 1

THYROID HORMONE
- Both ____ and ____ are taken up into cells –> ____ is converted into ____ intracellularly
- ____ binds to ____ receptors and activates gene transcription

Answer 1

THYROID HORMONE
- Both T3 and T4 are taken up into cells –> T4 is converted into T3 intracellularly
- T3 binds to NUCLEAR receptors and activates gene transcription

Question 2

State the relationship in the HPT Axis and the hormones involved at each level.

Answer 2

Hypothalamus - secretes TRH (thyrotropin-releasing hormone) which is transported via vascular link to anterior pituitary

Anterior pituitary - stimulated by TRH to secrete TSH (thyroid-stimulating hormone) which is transported via bloodstream to thyroid

Thyroid gland - stimulated by TSH to secrete fT4 + fT3 which is converted to more fT4

Question 3

State the resultant effect on
1. fT4
2. TSH

in primary thyroid pathology and secondary anterior pituitary pathologies during HYPERTHYROIDISM

Answer 3

PRIMARY THYROID PATHOLOGY
- fT4 high, TSH low
- fT4 high due to abnormal TH production, TSH low due to negative feedback aimed at compensating excess fT4

SECONDARY ANTERIOR PITUITARY PATHOLOGY
- fT4 high, TSH normal/high
- TSH normal/high due to anterior pituitary’s inability to recognise/respond to excess fT4
- Physiologically, TSH should be low to signal thyroid gland to produce less fT4

Question 4

State an example of a primary and secondary thyroid pathology which results in HYPERTHYROIDISM.

Answer 4

Primary thyroid patho - grave’s disease

Secondary thyroid patho - anterior pituitary tumour

Question 5

Why is fT3 levels not tested instead of fT4?

Answer 5

Free T3 is less stable and levels vary between tissues. FT3 is only tested when patients are on thyroid hormone replacement to check if T4 is sucessfully converted to T3 + T3 thyrotoxicosis.

Question 6

State the test used to confirm hyperthyroidism.

Answer 6

1. serum thyrotopin-stimulating hormone levels (TSH)
2. serum fT4 levels

Question 7

State the common symptoms of hypothyroidism.

Answer 7

1. cold intolerance
2. bradycardia
3. constipation
4. fatigue
5. goitre
6. muscle stiffness
7. short stature
8. urinary incontinence

Question 8

State the common conditions related to primary and secondary thyroid pathologies for HYPOTHYROIDISM.

Answer 8

primary thyroid pathology - hashimoto’s thyroiditis

secondary thyroid pathology - pituitary gland failure