18.7 THYROID GLAND

Question 1

butterfly-shaped thyroid gland is located inferior to the?

Answer 1

larynx (voice box)

Question 2

It is composed of right & left lateral lobes on each side of the trachea and are connected by what

Answer 2

an isthmus (narrow passage) anterior to the trachea

Question 3

about 50% of thyroid glands have a small 3rd lobe called ?

Answer 3

pyramidal lobe (extends superiorly from the isthmus)

Question 4

microscopic spherical sacs that make up most of the thyroid gland are called?

Answer 4

thyroid follicles

Question 5

the wall of each follicle consists of cells called what?

Answer 5

follicular cells - extend to the lumen (internal space) of follicle

Question 6

what surrounds each follicle

Answer 6

a basement membrane

Question 7

when follicular cells are inactive their shape is?

Answer 7

low cuboidal to squamous

Question 8

under the influence of TSH they become active in secretion and their shape becomes?

Answer 8

range from cuboidal to low columnar

Question 9

which 2 hormones do the follicular cells produce? (THYROID HORMONES)

Answer 9

thyroxine (tetraiothyronine) T4 - 4 atoms iodine
triiodothyronine T3 - 3 forms of iodine

Question 10

A few cells called what lie between follicles?

Answer 10

parafollicular cells or C cells

Question 11

What hormone do the parafollicular cells or C cells produce ?

Answer 11

calcitonin which helps regulate calcium homeostasis

Question 12

how do thyroid follicular cells trap iodine ions? What happens as a result of this?

Answer 12

By actively transporting them from the blood into the cytosol
Result - thyroid gland normally contains most of the iodine in the body

Question 13

While follicular cells trap iodine, they also synthesize thyroglobulin (TGB) which is

Answer 13

a large glycoprotein produced in the rough ER, modified in golgi complex and packaged into secretory vesicles

Question 14

some amino acids in TGB are tyrosines that will become donated. Negatively charged iodine ions cannot bind to tyrosine until they undergo what?

Answer 14

oxidation -> removal of electrons to iodine

Question 15

as iodine atoms (I0) form after oxidation, they react with?

Answer 15

tyrosines that are part of thyroglobulin molecules

Question 16

the thyroglobulin (TGB) with attached iodine atoms, a sticky material that accumulates and is stored n the lumen of the thyroid follicle is termed?

Answer 16

colloid

Question 17

in the last step of synthesis of thyroid hrmone two T2 molecules join to form __? or one T1 and one T2 join to form __?

Answer 17

T4 T3

Question 18

How do droplets of colloid reenter follicular cells ?

Answer 18

pinocytosis

Question 19

after colloid reenters, they merge with?

Answer 19

lysosomes

Question 20

how do T3 and T4 go into the PM into inserstial fluid into the blood

Answer 20

they diffuse because they are lipid-soluble

Question 21

is T3 or T4 secreted in greater quantity ?

Answer 21

T4

Question 22

is T3 or T4 more potent?

Answer 22

T3

Question 23

AFTER t4 enters a body cell, what happens

Answer 23

it is converted to T3 by removal of one iodine

Question 24

1 function of thyroid hormones is increasing the basal metabolic rate, what is this?

Answer 24

the rate of energy expenditure under standard or basal conditions (awake, at rest, fasting)

Question 25

when the basal metabolic rate increases, cellular metobolism of carbs, lipids, and proteins

Answer 25

increases

Question 26

How do thyroid hormones increase the basal metabolic rate?

Answer 26

1. stimulate synthesis of additional sodium potassium pumps
   2/ increase concentrations of enzymes in cellular respirations which increases breakdown of organic fuels and APT production
2. increase number and activity of mitochondria in cells - increases ATP

Question 27

CALORIGENIC EFFECT

Answer 27

as cells produce & use more ATP, BMR increases and more heat is given off = body temp rises

Question 28

symptoms of excess levels of thyroid hormone?

Answer 28

increase HR, more forceful heartbeats, increased BP (due to thyroid hormones having permissive effects on catecholamines which bind to adreginc receptors promote sympathetic responses)

Question 29

what stimulates the hypothalamus to secrete thyrotropin-releasing hormone (TRH)

Answer 29

low levels of t3 and t4 or a low metabolic rate

Question 30

conditions that increase the ATP demand which insect the secretion of the thyroid hormones?

Answer 30

cold environmentt, hypoglycaemia, high altitude, pregnancy

Question 31

the hormone produced by the parafollicular cells of the thyroid gland are?

Answer 31

calcitonin

Question 32

when level of calcium is high in the blood how does calcitonin lower the amount of blood calcium & phosphates?

Answer 32

by inhibiting bone resorption (breakdown of bone extracellular matrix) by osteoclasts and accelerating the uptake of calcium and phosphates into the bone extracellular matrix

Question 33

high blood calcium levels ___ secretion, low blood calcium levels ____ secretion

Answer 33

high - stimulate
low - inhibit