27 synthesis, mode of action and regulatory effects of thyroid hormone

Question 1

what is the thyroid follicle

Answer 1

a small spherical group of cells containing a cavity

Question 2

what do follicular cells secrete

Answer 2

thyroid hormones

Question 3

what do C-cells secrete

Answer 3

calcitonin

Question 4

is colloid a glycoprotein

Answer 4

yes

Question 5

what does the thyroid gland produce

Answer 5

• T3 and T4 hormones
• calcitonin

Question 6

why must sufficient iodine be taken in to maintain thyroid hormone synthesis

Answer 6

as T3 and T4 incorporate iodine

Question 7

is iodine more concentrated in the follicular cells or the plasma

Answer 7

the follicular cells, 20-50x more

Question 8

what does the sodium/iodine symporter do

Answer 8

transport 2Na+ for every iodine ion

Question 9

what does the Na+ electrochemical gradient provide

Answer 9

the energy for secondary active transport of iodine

Question 10

what are T3 and T4 synthesised on

Answer 10

thyroglobulin

Question 11

what is thyroglobulin

Answer 11

a glycoprotein synthesised by follicular cells and released into the colloid by exocytosis

Question 12

what happen s to tyrosine residues on thyroglobulin

Answer 12

they get iodinated by oxidised iodine (very reactive) giving monoiodotryosine (MIT) or diiodotyrosine DIT)

Question 13

what does conjugation lead to

Answer 13

adjacent tyrosyl residues being paired together

Question 14

what makes up ac colloid

Answer 14

thyroglobulin bound to T3 and/or T4

Question 15

can the complex be taken back up into follicular cells

Answer 15

yes, this is where proteases liberate T3 and T4 for release into blood

Question 16

how is thyroglobulin taken up into follicular cells

Answer 16

by endocytosis

endoscopes fuse with lysosomes, thyroglobulin is degraded liberating T3 and T4

Question 17

synthesis of T3 and T4 from pituitary gland to thyroid gland

Answer 17

the hypothalamus releases (TRH)

causing the anterior pituitary to release TSH)

causing the thyroid gland to release thyroid hormones T3 and T4

Question 18

what stimulates endocytosis of thyroglobulin into follicular cells

Answer 18

TSH

Question 19

what stimulates release of the thyroid hormone into the bloodstream

Answer 19

TSH

Question 20

what stimulates synthesis of thyroglobulin and Na/I transporter

Answer 20

TSH

Question 21

what is secretion of TSH/TRH subject to

Answer 21

feedback regulation by T3 and T4

Question 22

what proteins are T3 and T4 associated with

Answer 22

binding proteins in the blood

• thyroid hormone-binding globulin
• transthyretin
• albumin

Question 23

do T3 and T4 have high or low solubility in water

Answer 23

low

Question 24

is there more T3 or T4 secreted from the thyroid

Answer 24

more T4 (10x more)

Question 25

is T3 or T4 more active

Answer 25

T3 is more active (up to 10x more)

Question 26

what does monodeiodination in target cells do

Answer 26

convert much of the secreted T4 to T3 regulating cell sensitivity to thyroid hormone

Question 27

what does expression diodinase enzymes do

Answer 27

affects the response of cells to thyroid hormone by regulating the conversion of T4 to active or inactive T3

Question 28

what do deiodinase enzymes regulate

Answer 28

the activity of thyroid hormones

Question 29

what do thyroid hormones activate

Answer 29

nuclear receptors

Question 30

are thyroid hormones hydrophobic

Answer 30

yes

Question 31

what do thyroid hormones require for movement across the plasma membrane

Answer 31

transporter proteins

Question 32

what specific receptor does thyroid hormones act on

Answer 32

nuclear TR, a hormone sensitive transcription factor

Question 33

metabolic effects of thyroid hormone

Answer 33

- increased BMR - increased oxygen consumption - increase thermogenesis

Question 34

cardiovascular effects of thyroid hormone

Answer 34

- increased CO - increase HR and SV

Question 35

neurological effects of thyroid hormone

Answer 35

- enhances wakefulness - enhances memory - enhances alertness - enhances reflexes

Question 36

growth and developmental effects of thyroid hormone

Answer 36

- essential for foetal neural and bone development - essential for normal bone growth after birth - essential for normal tooth development

Question 37

does thyroid hormone increase sensitivity of body to catecholamines

Answer 37

yes

Question 38

what do thyroid hormones level correlate with

Answer 38

body weight and energy expenditure

Question 39

what does hyperthyroidism cause

Answer 39

a hyper metabolic state characterised by i - increased resting energy expenditure and weight loss -high HR and BP

Question 40

what does hypothyroidism cause

Answer 40

- reduced resting energy expenditure - weight gain - lethargy and weakness

Question 41

what is the basal metabolic rate

Answer 41

the primary source of energy expenditure in humans