Thyroid gland

Question 1

describe the structure of the thyroid gland

Answer 1

2 lobes joined by the isthmus

Question 2

describe the embryological development of thyroid gland

Answer 2

• originates from foramen caecum
• thyroid diverticulum grows down > thyroglossal duct
• as thyroid descends the thyroglossal duct breaks down

Question 3

describe the microscopic structure of thyroid glands

Answer 3

• thyroid follicles - follicular cells in spheres
• filled with colloid - deposition of thyroglobin

Question 4

what do thyroid follicular cells produce?

Answer 4

thyroid hormone

Question 5

what do parafollicular cells produce?

Answer 5

calcitonin

Question 6

what are the principal cells of the parathyroid gland?
what do they produce?

Answer 6

chief cells
parathyroid hormone

Question 7

how are thyroid hormones formed?

Answer 7

2 iodinated tyrosine molecules are linked together with iodine at 3 or 4 positions on aromatic rings

Question 8

what is needed to make T3?

Answer 8

monoiodotyrosine + diiodotyrosine > triiodotyrosine

Question 9

what is needed to make T4?

Answer 9

diiodotyrosine + diiodotyrosine > tetraiodotyrosine/thyroxine

Question 10

what is the role of thyroglobulin in thyroid hormone formation?

Answer 10

acts as a scaffold on which thyroid hormones are produced

Question 11

what is thyroid peroxidase?

Answer 11

membrane bound enzyme that regulates thyroid hormone synthesis

Question 12

what does thyroid peroxidase regulate to thyroid hormone synthesis?

Answer 12

• oxidation of iodide to iodine
• addition of iodine to tyrosine acceptor residues on thyroglobulin
• coupling of MIT/DIT to generate thyroid hormones

Question 13

outline the absorption of dietary iodine in the thyroid gland

Answer 13

• dietary iodine reduced to iodide
• iodide absorbed by small intestines
• iodide taken up from blood by thyroid epithelial cells via Na/I- symport

Question 14

sources of iodine

Answer 14

dairy products
meat
vegetables
eggs
grains

Question 15

where is T4 converted to T3?

Answer 15

liver + kidneys

Question 16

how are thyroid hormones transported in the blood?

Answer 16

lipid soluble
bound to thyroxine-binding globulin

Question 17

what thyroid hormone is more biologically active?

Answer 17

T3

Question 18

Actions of thyroid hormones

Answer 18

• increased BMR
• affects growth in children (bone + CNS development)
• increased HR + CO
• increase thermogenesis
• important for normal reproductive function

Question 19

describe the structure of TSH

Answer 19

glycoprotein hormone
composed of 2 non-covalently bound subunits aB

Question 20

what does TSH stimulate?

Answer 20

• iodide uptake
• oxidation of iodide to iodine
• thyroglobulin synthesis
• thyroglobulin iodination
• colloid pinocytosis into cells
• proteolysis of thyroglobulin
• cell metabolism + growth

Question 21

how do thyroid hormones increase BMR + heat production?

Answer 21

• increase number + size of mitochondria
• stimulate synthesis of enzymes in respiratory chain

Question 22

what metabolic pathways are stimulated by thyroid hormone?

Answer 22

• lipid metabolism - lipolysis + B-oxidation
• carb metabolism - gluconeogenesis, glycogenolysis, insulin dependent entry of glucose into cells

Question 23

effect of thyroid hormones on CVS

Answer 23

• increases hearts responsiveness to catecholamines:
• increase CO (HR and force of contraction) + peripheral vasodilation

Question 24

effect of thyroid hormones on nervous system

Answer 24

• increased development of neurones
• increased myelination of nerves

Question 25

What affect would lack of dietary iodine have on?
- T3+4
- TSH
- goitre present?

Answer 25

• decreased T3+4
• increased TSH
• yes, goitre present

Question 26

Blood supply to the thyroid

Answer 26

Superior + inferior thyroid artery

Question 27

Venous drainage of the thyroid

Answer 27

• superior + middle thyroid veins drain into internal jugular vein
• inferior thyroid vein: drains into left brachiocephalic vein

Question 28

Origin of the superior thyroid artery

Answer 28

Branches from external carotid artery

Question 29

Origin of the inferior thyroid artery

Answer 29

subclavian artery > thyrocervical trunk > inferior thyroid artery