Thyroid

Question 1

What does the hypothalamus secrete

Answer 1

TRH

Question 2

What does TRH do?

Answer 2

stimulates thyroid-stimulating hormone (TSH) from ant pit

Question 3

What does TSH do?

Answer 3

stimulates T3 and T4 production in the thyroid gland

Question 4

Where is most of the negative feedback in the hypothalamus-pituitary-thyroid axis?

Answer 4

at the level of the ant pit via TH (T3/T4)

Question 5

describe the histology of the thyroid gland

Answer 5

parafollicular cells, follicle cells, and luminous colloid spaces

Question 6

What are parafollicular cells called

Answer 6

C cells

Question 7

What do C cells do

Answer 7

important for calcium regulation, not necessarily thyroid function. secrete calcitonin

Question 8

What do follicle cells do

Answer 8

Synthesize thyroglobulin and secrete it into the follicle lumen for iodination and storage

Question 9

What type of hormone is TH

Answer 9

amine hormone that acts like a steroid

Question 10

what is thyroglobulin

Answer 10

binding protein that attaches to DIT and MIT so they can be manipulated and eventually be secreted from the cell

Question 11

What is thyroglobulin made of

Answer 11

tyrosine backbone that needs to interact with I to make TH

Question 12

How does TSH affect thyroglobulin secretion

Answer 12

more TSH = more thyroglobulin secretion

Question 13

What transporter brings I- into follicle cell

Answer 13

Na/I symporter

Question 14

what transporter moves I- across the luminal border into the colloid

Answer 14

pendrin

Question 15

what are the three functions of thyroid peroxidase

Answer 15

oxidation- iodide to iodine
iodination- attaching iodine to thyroglobulin backbones in colloid to make MIT and DIT
conjugation- attaching MIT and DIT to DIT to create T3 and T4

Question 16

where does thyroglobulin come from? what does it do?

Answer 16

made in follicle cell, secreted to colloid, used for TH synthesis (backbone)

Question 17

That is made in higher quantities and why? T3 or T4

Answer 17

T4 is made more frequently than T3, because it has a longer half-life and is therefore more stable, even though T3 is more biologically active.

Question 18

How does the thyroglobulin backbone with T3 and T4 leave the colloid?

Answer 18

it is exocytosed into the follicle cell

Question 19

How do T3 and T4 leave the cell without their thyroglobinin backbones?

Answer 19

lysosomal enzymes in the follicle cell liberate T3 and T4 from TG backbone. Then TG is recycled and T3/T4 leave the cell via the MCT transport protein, where they go into circulation and bind to carrier proteins.

Question 20

What is the T3/T4 carrier protein in the blood?

Answer 20

Thyroxine binding globulin (TBG)

Question 21

Where is T4 converted to T3 and by what enzyme?

Answer 21

Converted at target tissues by 5’-deiodinase

Question 22

Where is type 1 deiodinase and what does it produce

Answer 22

in liver, produces T3 and rT3 (excreted by kidney)

Question 23

where is type 2 deiodinase and what does it produce

Answer 23

ant pituitary, brain, and placenta, produces T3 only

Question 24

Which ring is deiodinated to create T3? rT3?

Answer 24

T3- outer ring deiodination
rT3- inner ring deiodination

Question 25

What hormone stimulates the thyroid to make TH

Answer 25

TSH

Question 26

TSH does 4 things to follicular cells...

Answer 26

1)increases iodide transport into follicular cells 2)increases production and iodination of thyroglobulin 3)increases endocytosis of colloid (with thyroglobulin) from lumen into follicular cells 4)increases size of follicular cells

Question 27

What does TH do? (4 things)

Answer 27

1)increases number and activity of mitochondria 2)increases oxygen consumption 3)increases cardiac output 4)increases activity of Na/K ATPase, increases basal metabolic rate, increases body temp

Question 28

If we have high TH, what do we need in order for it to work effectivly

Answer 28

lots of ATP

Question 29

What parts of development is TH important for

Answer 29

muscle, bone, neurologic, metabolic

Question 30

in pregnancy, hCG mimics what other hormone?

Answer 30

TSH

Question 31

That is the T3/T4 carrier in the blood

Answer 31

TBG

Question 32

how do T3 and T4 enter the cell

Answer 32

via MCT8 carrier-mediated transport mechanism

Question 33

What enzyme co3nverts T4 to T3 and where does it happen?

Answer 33

3'/5' Monodeiodinase converts T4 to T3 in target tissues cytoplasm

Question 34

How does T3 work as a transcription factor? What else does it need?

Answer 34

TH binds to TH receptor which uses retinoid X receptor as a binding partner. They work together to act as a transcription factor. Together they are called the thyroid response element (TRE)

Question 35

what type of receptor is a TH receptor (where is it)

Answer 35

nuclear receptor (in the nucleus)

Question 36

What is more potent and why? T3 or T4

Answer 36

T3 is more potent because it has a much higher affinity for the thyroid hormone receptor (TR)

Question 37

What are the two main causes of hypothyroidism?

Answer 37

congenital and autoimmune disorders

Question 38

What are some less common causes of hypothyroidism

Answer 38

Iodine deficiency, viral infection, drugs, irradiation, thyroid surgery

Question 39

What is a goiter

Answer 39

An enlarged thyroid gland caused by the overstimulation of the thyroid gland

Question 40

What states of thyroid function could someone have a goiter in?

Answer 40

any

Question 41

In an iodine deficient diet, would a goiter present? Why?

Answer 41

yes a goiter could be present because TSH is not being regulated via negative feedback (no TH produced) and TSH stimulation on follicular cells would cause the cells to enlarge

Question 42

What do we do in america to make sure that everyone has enough iodine

Answer 42

we supplement iodine into salt

Question 43

Who needs the most iodine

Answer 43

pregnant/lactating women

Question 44

What is cretinism

Answer 44

when an infant or child has a TH deficiency from birth caused by extreme hypothyroidism during fetal life, infancy or childhood

Question 45

What are the three types of cretinism, what causes them?

Answer 45

1)congenital- absence of thyroid gland from birth 2)Genetic defect- thyroid gland can't produce something due to genetic defect (ex. pendred syndrome body can't produce pendrin 3)endemic- iodine lacking in diet

Question 46

What is Hashimoto's

Answer 46

Thyroid autoimmune disease

Question 47

Who makes up 85% of hashimoto's patients

Answer 47

females

Question 48

What would you give someone with Hoshimoto's as treatment

Answer 48

T4 (stable)

Question 49

What are TSH levels like in someone with hoshimoto's

Answer 49

high TSH (low feedback -> not effective at TH production due to damaged cells)

Question 50

Could a person with Hashimoto's have a goiter?

Answer 50

yes, high TSH stimulation

Question 51

What are symptoms of hypothyroidism

Answer 51

thin hair, goiter, puffy face, dry skin, slow heartbeat, low O2 sat, low metabolism, constipation, infertility, poor appetite, cold extremities, weight gain, memory loss, tiredness

Question 52

What is hyperthyroidism

Answer 52

increased TH secretions

Question 53

What are primary causes of hyperthyroidism

Answer 53

graves disease, thyroid tumor, excessive iodine intake, exogenous TH

Question 54

What are secondary causes of hyperthyroidism?

Answer 54

ant pit tumor, hypothalamic tumor

Question 55

What type of disease is Grave's disease?

Answer 55

autoimmune (antibodies against TSH receptors, stimulating those receptors)

Question 56

What are TSG and TH levels like in a patient with Grave's disease

Answer 56

TH is very high. TSH is very low

Question 57

What could be used to treat Grave's disease

Answer 57

therapeutic doses of radioactive I2, thyroid gland removal, immune system suppressants, drugs that inactivate thyroid peroxidase, low I2 consumption

Question 58

What are some grave's disease symptoms

Answer 58

exophthalmos (bulging eyes), goiter, warm extremeties, arrhythmia/tachycardia, muscle weakness

Question 59

Children who drink local milk after I-131 is released into the air develop what?

Answer 59

hypothyroidism because of I-131 trapped in milk

Question 60

What can a person do during a nuclear disaster to prevent being affected by irradiated iodine

Answer 60

take KI so that thyroid gland takes up unaffected iodine and I-131 passes through body