Thyroid physiology

Question 1

Follicular cells function in Thyroid synthesis

Answer 1

Synthesise thyroglobulin, secrete into the colloid of thyroid follicles

Question 2

Colloid function

Answer 2

Stores thyroglobulin (attached to iodine atoms)

Question 3

Parafollicular cells function

Answer 3

Secrete calcitonin (decrease Calcium levels in blood)

Question 4

2 types of thyroid hormone and what are they made up of

Answer 4

T3, T4
Tyrosine amino acid with 3 or 4 iodine atoms

Question 5

Process of Thyroid Hormone Synthesis (write out)

Answer 5

refer to notes

Question 6

2 sites of TH storage

Answer 6

In colloid and Bound to plasma proteins in blood

Question 7

Which TH is made more, and which is more effective

Answer 7

Make more T4, converted to T3 in pituitary, T3 is biologically active and more potent

Question 8

How is TH regulated

Answer 8

Negative feedback, Thyroid gland to Hypothalamus (produce more Thyrotropin Releasing Hormone) and Anterior Pituitary (produce more Thyroid Stimulating Hormone)

Question 9

6 Physiological effects of T3 and T4

Answer 9

1) Control Basal Metabolic Rate (BMR)
BMR is proportional to amount of O2 a person is consuming.
Increase size and no. of mitochondria + Increase enzymes that regulate oxidative phosphorylation → Increase O2 consumption and energy use under resting conditions
Increase metabolic activity → Increase heat production

2) Sympathomimetic effect - Mimic sympathetic NS activation
Thyroid hormones proliferate catecholamines (E, NE) cell receptors → Increase cell responsiveness to catecholamines

3) Cardiovascular effect
Increase heart responsiveness to catecholamines → Increase HR and force of contraction → Increase cardiac output

4) Bone growth

5) Development of nervous system eg. brain during childhood, normal CNS activity

6) Increase metabolism (synthesis and degradation) of proteins, lipids and carbs

Question 10

3 causes of Hypothyroidism

Answer 10

1) Primary failure of thyroid gland

2) Secondary to deficiency of TRH (Thyrotropin Releasing Hormone), TSH (Thyroid Stimulating Hormone).
Hypothalamus and Pituitary gland not making enough hormones

3) Inadequate dietary iodine

Question 11

Symptoms of Hypothyroidism

Answer 11

Intolerance to cold
Extreme fatigue
Brittle nails and hair (no proteins to make these)
Constipation
Weight gain
Cardiac complications

Question 12

3 causes of Hyperthyroidism

Answer 12

1) Production of TSI (Thyroid Stimulating Immunoglobulin)
2) Secondary to excess TSH, TRH
3) Hypersecreting thyroid hormone

Question 13

Symptoms of Hyperthyroidism

Answer 13

Intolerance to heat
Bulging eyes
Enlarged thyroid
Increased systolic BP
Weight loss
Muscle wasting
Tremors
Diarrhea

Question 14

What is Grave’s disease?

Answer 14

Autoimmune disease
Body producing TSI (immunoglobulin) →TSI binds to TSH receptor → Secretion and growth of thyroid hormone
TSI is not subjected to (-) feedback, thyroid secretion and growth continues unchecked

Question 15

What is Goiter? How does it occur in both Hyperthyroidism and Hypothyroidism

Answer 15

(enlarged thyroid gland)
Caused by high TSH or TSI
Can occur in hyperthyroidism and hypothyroidism
Hyperthyroidism: Excessive TSI acting on TSH receptor
Hypothyroidism: Not enough iodine → Low TH production → Negative feedback to increase TSH production in pituitary

Question 16

3 types of Treatment for Hyperthyroidism

Answer 16

1) Anti-thyroid drugs
interfere with TH synthesis (Block I- uptake or Inhibit TPO)

2) Surgical removal of over secreting thyroid gland
May result in Hypothyroidism

3) Administer radioactive iodine

Question 17

How is thyroid hormone metabolised

Answer 17

Conjugation with glucuronic acid in liver