Thyroid Gland

Question 1

For the Thyroid hormone axis, what does the hypothalamus release?

Answer 1

TRH

Question 2

For the Thyroid hormone axis, what does the anterior pituitary release?

Answer 2

TSH

Question 3

What are the 2 types of thyroid hormones?

Answer 3

T3 and T4

Question 4

What thyroid hormone is the active form?

Answer 4

T3

Question 5

What is the main thyroid hormone secreted?

Answer 5

T4

Question 6

What must 80-90% of T4 undergo in order to create T3?

Answer 6

Peripheral conversion

Question 7

For peripheral conversion, what takes T4 to T3’s active form?

Answer 7

Deiodinase type 1 and 2

Question 8

For peripheral conversion, what takes T4 to T3’s inactive form?

Answer 8

Deiodinase type 3

Question 9

What can inhibit peripheral conversion of T4 to T3?

Answer 9

Fasting, medical stress, catabolic diseases

Question 10

How does Iodide, get into the follicular cell of the thyroid from the blood?

Answer 10

Iodide trap - comes into the cell with sodium

Question 11

What pump takes Iodide from the follicular cell into the colloid?

Answer 11

Pendrin

Question 12

Once in the colloid, what enzyme takes Iodide to Iodine and attaches to tyrosine residues within Thyroglobulin, as well as coupling?

Answer 12

Thyroid Peroxidase (TPO)

Question 13

What is the storage from of T3 and T4?

Answer 13

Attached to Thyroglobulin tyrosine residues in colloid

Question 14

Once TSH stimulates thyroid gland, how does it release T3 and T4?

Answer 14

Endocytosis

Question 15

T3 and T4 are normally bound to what protein in the blood?

Answer 15

Thyroxine Binding Globulin (TBG)

Question 16

Thyroxine Binding Globulin (TBG) has a higher affinity for which thyroid hormone?

Answer 16

T4

Question 17

DIT

Answer 17

1 tyrosine residue plus 2 iodines

Question 18

MIT

Answer 18

1 tyrosine residue plus 1 iodine

Question 19

How do you make T4?

Answer 19

DIT + DIT

Question 20

How do you make T3?

Answer 20

DIT + MIT

Question 21

What is the result of a mutation in pendrin?

Answer 21

Sensorineural hearing loss, goiter, hypothyroidism

Question 22

High levels of iodide that inhibit the synthesis of T3 and T4

Answer 22

Wolff-Chaikoff Effect

Question 23

Effective treatment for hyperthyroidism?

Answer 23

PTU

Question 24

How do you measure the activity of the thyroid gland?

Answer 24

Measuring radioactive iodine uptake

Question 25

Steady increase of radioactive iodine uptake

Answer 25

Hyperthyroidism

Question 26

Extremely fast increase of radioactive iodine uptake that starts to decrease after 24 hours due to high turnover

Answer 26

Grave's Disease

Question 27

TBG has a higher affinity for T4, what does this do to the half life of T4?

Answer 27

Increases it compared to the half life of T3

Question 28

How do you measure circulating levels of TBG?

Answer 28

T3 resin uptake

Question 29

High TBG means?

Answer 29

Increased T4 and decreased T3 resin uptake

Question 30

Low TBG means?

Answer 30

Decreased T4 and increased T3 resin uptake

Question 31

Hepatic failure does what to levels of TBG?

Answer 31

Decreases

Question 32

Pregnancy can do what to level of TBG?

Answer 32

Increase

Question 33

Describe the results of pregnancy increasing TBG

Answer 33

This decreases free T3 and T4 because there will be more bound to TBG. There will be a transient increase in secretion of T3 and T4, but free levels will remain normal due to higher binding proteins = clinically euthyroid

Question 34

Summarize the synthesis of T3 and T4

Answer 34

- Iodide transported into the follicular cell from the blood due to iodide trap with sodium - Pendrin transports Iodide into colloid - Thyroid Peroxidase converts it to Iodine, attaches them to tyrosine residues of Thyroglublin and couples DITs/MITs - When TSH stimulates, endocytosis will occur to release T3 and T4 from thyroglobulin so they can bind TBG in the blood stream

Question 35

List 3 proteins that are synthesized under direction of thyroid hormones

Answer 35

1. Na+/K+ ATPase 2. Beta1 adrenergic receptors in cardiac cells 3. Metabolic enzymes in liver/adipose tissue

Question 36

What is the effect of thyroid hormones on cardiac cells?

Answer 36

Increases the number of beta1 adrenergic receptors which INCREASES the total cardiac output!!

Question 37

What is the effect of thyroid hormones stimulating more Na+/K+ ATPase?

Answer 37

Increased basal metabolic rate (BMR)

Question 38

Increased BMR

Answer 38

Hyperthyroidism

Question 39

Decreased BMR

Answer 39

Hypothyroidism

Question 40

Hypothyroidism does what to cholesterol?

Answer 40

Increases it

Question 41

General symptoms of hyperthryoidism

Answer 41

Increased BMR, weight loss, sweating, increased HR, exopthalmos

Question 42

General symptoms of hypothyroidism

Answer 42

Decreased BMR, weight gain, lethargy, coldness

Question 43

Thyroid hormones are essential for ____ maturation

Answer 43

CNS

Question 44

Thyroid hormones work with what to stimulate bone formation?

Answer 44

GH

Question 45

Another name for hyperthyroidism

Answer 45

Thyrotoxicosis

Question 46

Describe Grave's disease

Answer 46

Antibodies stimulate TSH receptor that causes an overproduction of T3 and T4 - levels of TSH are low due to negative feedback from high levels of T3 and T4 - Presence of TSI - Thyroid stimulating immunoglobulins

Question 47

TSH-secreting pituitary

Answer 47

Secondary hyperthyroidism

Question 48

Most common cause of hypothyroidism in iodine-sufficient areas of the world

Answer 48

Hashimoto's thyroiditis

Question 49

Describe Hashimoto's Thyroiditis

Answer 49

Antibodies to Thyroglobulin or Thyroid Peroxidase (TPO) which impairs thyroid hormone synthesis even if TSH levels are HIGH

Question 50

What can cause congenital hypothyroidism?

Answer 50

Iodide deficiency, maternal intake of anti-thyroid meds

Question 51

Signs of hypothyroidism in babies?

Answer 51

Feeding problems, protruding tongue, retardation, breathing problems

Question 52

Sheehan syndrome

Answer 52

Necrosis of pituitary gland postpartum - causes difficulty with lactation and may impair other endocrine glands

Question 53

Can you have a goiter with hyperthyroidism and hypothyroidism?

Answer 53

Yes