The Thyroid Gland

Question 1

What are the two physiologically active forms of thyroid hormones?

Answer 1

T3 and T4

Question 2

What are the two cell types found in the thyroid gland? What is the function of each?

Answer 2

C cells- secrete calcitonin

Follicular cells- support thyroid hormone synthesis and surround hollow follicles

Question 3

What make the thyroid follicles made of and what are they filled with?

Answer 3

Walls made of follicular cells

Centre filled with colloid

Question 4

What do follicular cells produce?

Answer 4

The enzymes that make thyroid hormones and thyroglobulin

Question 5

How are the thyroid hormones formed?

Answer 5

Follicular cells actively concentrate iodide from the plasma and transport it into the colloid where it combines with the tyrosine residues to form the thyroid hormones

Question 6

How does iodide enter the follicular cells?

Answer 6

Via a Na+/I- transporter

Question 7

How is iodide transported from the follicular cells into the colloid?

Answer 7

Via the pendin transporter

Question 8

What enzyme catalyses the addition of iodide to tyrosine?

Answer 8

Thyroid peroxidase

Question 9

What occurs within the follicles in repsonse to TSH?

Answer 9

Portions of the colloid are taken back up into the follicular cell by endocytosis. Within the cells they form vesicles which contain proteolytic enzymes that cut the thyroglobulin to release thyroid hormones

Question 10

How do T3 and T4 circulate in the plasma?

Answer 10

Bound to protein as they are lipophilic

Question 11

Which of the thyroid hormones is more physiologically active and which is more common in the plasma?

Answer 11

Physiologically active- T3

T4 more common in plasma

Question 12

What is the mechanism of thyroid hormone function?

Answer 12

TH binds to nuclear receptors in target cells where they change transcription and translation to alter protein synthesis

Question 13

What are the effects of thyroid hormone?

Answer 13

Raises metabolic rate and promotes thermogenesis 
Increase hepatic gluconeogenesis 
Net increase in proteolysis
Net increase in lipolysis
Critical for growth 
Essential for brain development

Question 14

What are the most common causes of hyperthyroidism?

Answer 14

Graves’ disease

Thyroid adenoma

Question 15

What are the symptoms of hyperthyroidism?

Answer 15

Weight loss 
Heat intolerance 
Muscle weakness 
Hyperreflexia
Psychological disturbances 
Increased HR
Cardiac failure

Question 16

What are the common causes of hypothyroidism?

Answer 16

Hashimotos disease
Deficiency in dietary iodine
Idiopathic

Question 17

What are the symptoms of hypothyroidism?

Answer 17

Weight gain 
Cold intolerance 
Brittle nails
Thin skin 
Slow speech/reflexes 
Fatigue 
Slow heart rate 
Weaker pulse

Question 18

What are the possible causes of goitre?

Answer 18

Increased trophic action of TSH on thyroid follicular cells

Over acidity of autoimmune disease