the thyroid gland

Question 1

what are the hormones released by this gland

Answer 1

calcitonin and T3, T4

Question 2

what is calcitonin

Answer 2

a polypeptide hormone produced by c cells that functions in regulating blood calcium levels in conjunction with parathyoid hormone

Question 3

what is calcitonin secretion dependent on

Answer 3

blood calcium levels

Question 4

how does calcitonin lower blood calcium levels

Answer 4

inhibit the rate of decalcification of bone by osteoclastic resorption

Question 5

what produces calcitonin

Answer 5

c cells

Question 6

what are T3 and T4

Answer 6

iodine containing hormones

Question 7

what is T3

Answer 7

tri-iodothyronine

Question 8

what is T4

Answer 8

tetraiodothyronine

Question 9

how is T4 converted to T3

Answer 9

in general circulation by removal of one iodothyronine

Question 10

what is the function of T4

Answer 10

regulate basal metabolic rate

Question 11

what is T4 in relation to T3

Answer 11

the metabolically active form of T3

Question 12

what is thyroxine

Answer 12

T4

Question 13

what is secretion of t4 regulated by

Answer 13

thyroid stimulating hormone

Question 14

what does the thyroid hormone do

Answer 14

store lots of inactive hormone within the extracellular compartments in the centre of the follicles

Question 15

what is thyrotoxosis

Answer 15

excess of circulating thyroid hormone which causes symptoms due to systemic effect of the thyroid hormone

Question 16

what can thyrotoxicosis lead to

Answer 16

graves disease

Question 17

what is graves disease

Answer 17

hyperfunction of the thyroid gland, an autoimmune disease

Question 18

what are the symptoms of graves disease

Answer 18

exophthalmos (puffy eyes) and non pitting edema of the lower limbs (fluid accumulation)

Question 19

what is hypothyroidism

Answer 19

lack of production of thyroid hormone leading to weight gain, tiredness and poor tolerance to cold weather

Question 20

what is hashimotos disease

Answer 20

the thyroid acini are destroyed as the gland is infiltrated by lymphocytes and plasma cells. leads to fatigue, weight gain and depression

Question 21

which epithelium lines the thyroid follicles

Answer 21

simple cuboidal

Question 22

what do the septa of the gland convey

Answer 22

blood supply, lymphatics and nerves

Question 23

what do thryoid follicles store

Answer 23

thryoglobulin and iodinated glycoprotein

Question 24

what is the storage form of T4

Answer 24

thyroglobulin

Question 25

what is the storage form of T3

Answer 25

iodinated glycoprotein

Question 26

what is the epithelium of the inactive follicles

Answer 26

simple squamous or cuboidal

Question 27

what is the epithlium of the actively secreting or synthesising follicles

Answer 27

columnar

Question 28

where are the c cells found in the thyroid glands

Answer 28

as scattered individual cells in the follicle lining or as small clumps in the interstices between the follicles

Question 29

how do follicular cells concentrate iodide from the body

Answer 29

iodine pump in the basal plasma membrane

Question 30

how are T3 and T4 formed

Answer 30

iodide taken in from the blood via iodide pump in the plasma membrane of follicular cells and oxidised to iodine to be transported to the follicular plasma membrane where it is released into the follicular lumen where it combines with tyrosine residues of the follicular lumen

Question 31

what is pinocytosis

Answer 31

ingestion of liquid into the cell by budding of small vescicles in the cell membrane

Question 32

describe the process of secretion of thyroxin

Answer 32

ingestion of liquid into the thyroglobulin hormone complex to form cytoplasmic vacuoles which fuse with lysosomes of the follicular cell cytoplasm.
hydrolytic enzymes cleave the hormone from the thryoglobulin and they are released in the basal cytoplasm, where they diffuse into the bloodstream