Thyroid gland

Question 1

what cells secrete calcitonin?

Answer 1

C (clear) cells / parafollicular C cells

Question 2

what is the structure of the thyroid gland histologically?

Answer 2

follicular cells surrounding a follicle which is filled with colloid (glycoprotein matrix containing TH)
between follicles is parafollicular C cells

Question 3

what important nutrient is required for thyroid hormone synthesis?

Answer 3

iodine

Question 4

what forms the thyroid hormones?

Answer 4

iodide + tyrosine residues

Question 5

what enzymes catalyses the conversion of tyrosine to TH’s?

Answer 5

thyroid peroxidase (thyroperoxidase)

Question 6

where is thyroperoxidase located?

Answer 6

located on the apical membrane of the follicular cell

Question 7

tyrosine + 1 iodide?

Answer 7

MIT = moniodotyrosine (T3)

Question 8

tyrosine + 2 iodide?

Answer 8

DIT = diiodotyrosine (T4 / thyroxine)

Question 9

what plasma proteins does T3 and T4 bind to when they enter back into the plasma?

Answer 9

thyroxine binding globulin

Question 10

what is the movement of TH from the colloid into the plasma under the control of?

Answer 10

TSH release

Question 11

what accounts for the long half life of thyroxine (T4)

Answer 11

thyroxine binding globulin has a high affinity for T4 compared to T3 which accounts for its slow release into the plasma

Question 12

what thyroid hormone is more physiologically active and why?

Answer 12

T3

because thyroid hormone receptor has a higher affinity for T3

Question 13

because T3 is more physiologically active than T4, how is the efficiency of T4 utilised?

Answer 13

T4 is deionised to T3 by deiodinase enzymes

Question 14

what factors can increase TRH release from the hypothalamus?

Answer 14

cold
pregnancy
exercise

Question 15

what hormones are inhibitory to TSH release?

Answer 15

glucocorticoids

somatostatin (GHIH)

Question 16

what is the function of thyroid hormones in the body?

Answer 16

raise metabolic rate and promote thermogenesis
increase hepatic gluconeogenesis
net increase in proteolysis
net increase in lipolyisis
required for foetal brain development
critical for growth (permissive effects of GH)

Question 17

what can be the causes of hypothyroidism?

Answer 17

iodine deficiency
hashimotos disease
idiopathic - linked to thyroididits

Question 18

what cna be the cause of hyperthyroidism?

Answer 18

graves disease

thyroid adenoma

Question 19

what is graves disease?

Answer 19

autoimmune disease which causes hyperthyroidism

autoantibodies which mimic TSH and bind to and activate the thyroid gland

Question 20

what are the symptoms of hyperthyroidism?

Answer 20

increased HR/ contractile/ CO and cardiac failure
weight loss, heat intolerence
hyperexcitable reflexes, psychological disturbances
muscle weakness

Question 21

what are the symptoms of hypothyroidism?

Answer 21

weight gain, cold intolerence
brittle nails, thin skin
sow speech & reflexes, fatigue
slow HR / weaker pulse

Question 22

how does thyroid hormone dysfunction cause goitre?

Answer 22

increased trophic action of TSH on thyroid follicular cells (hypothyroidsim)
over activity of the gland (hyperthyroidism)

Question 23

hashimotos and graves disease are an example of primary/secondary/tertiary disorders?

Answer 23

primary

Question 24

How long would it take before the thyroid gland ran out of thyroid hormone if it stopped producing more?

Answer 24

2-3 months