Thyroid Physiology (11)

Question 1

What is the main role of the thyroid gland?

Answer 1

Regulates vertebrate growth, development and metabolism

Question 2

Within the thyroid gland…where is TH synthesized and released from?

Answer 2

Follicular epithelial cells (follicles are the functional unit of the gland)

Question 3

How is TH stored?

Answer 3

In the colloid (the inner area of follicles) in association with Thyroglobulin (TG)

Question 4

Within the thyroid, where is calcitonin synthesized and released?

Answer 4

In scattered parafollicular C-cells

Question 5

What are the biologically active forms of TH?

Answer 5

Thyroxine (T4), Triiodothyronine (T3)

Question 6

What amino acid leads to the production of TH’s? What do you need from the diet?

Answer 6

Tyrosine, and dietary Iodide

Question 7

What is T4?

Answer 7

Thyroxine

Question 8

What is T3

Answer 8

Triiodothyroxine

Question 9

Which TH is preferentially synthesized in the thyroid?

Answer 9

T4

Question 10

How is iodide stored in the thyroid/

Answer 10

In association with thyroglobulin (TG)

Question 11

How is Iodide concentrated in the thyroid?

Answer 11

By a specific transport potion (2Na+/ I- Symporter) that uses the inwardly directed electrochemical Na+ gradient as a driving force

Question 12

What can chronic iodide deficiency lead to?

Answer 12

Hypothyroidism that can be corrected by providing adequate dietary Iodide

Question 13

What regulates TH synthesis, storage regulation and release?

Answer 13

TSH

Question 14

How is the release of TSH regulated?

Answer 14

Negative feedback control by the thyroid hormones

Question 15

What is the majority of circulating or tissue T3 derived from?

Answer 15

T4…so T4 acts as a prohormone

Question 16

What are the two functions of the Thyroid Peroxidase?

Answer 16

1- Oxidize I- to Iodide

2- Couple together DIT to another DIT to form T4

Question 17

In a mature TG list the following in order of greatest to least abundance:

T4, T3, DIT, MIT

Answer 17

MIT, DIT, T4, T3

Question 18

What is organification?

Answer 18

binding of iodine to the TG to form either MIT or DIT

Question 19

What is circulating TH bound to ?

Answer 19

1- Thyroid-binding globulin (70%)

2- Transthyretin

3- Albumin

Question 20

In the periphery, what enzyme is responsible for generating T3 and reverse T3 from T4?

Answer 20

Peripheral Deiodinases

Question 21

Which TH has the longer half life?

Answer 21

T3 (1 day)

T4 (days)

Question 22

Which TH is more potent?

Answer 22

T3 is more potent

Question 23

Which TH is usually sued to treat hypothyroidism?

Answer 23

T4 because of its longer half life and greater stability

Question 24

Where are TH receptors expressed?

Answer 24

virtually all tissues of teh boy

Question 25

What type of metabolism does TH regulate?

Answer 25

Carbohydrates, proteins and lipids

Question 26

Within the cell, what do thyroid hormone receptors bind to?

Answer 26

Nuclear DNA at thyroid response elements in the promoter region of genes regulated by thyroid hormones

Question 27

What do thyroid hormone receptors form heterodimers with?

Answer 27

Retinod X receptors

Question 28

What TH usually binds the thyroid hormone receptor

Answer 28

T3

Question 29

Within target cells, what allows for the conversion of T4 to T3?

Answer 29

cytoplasmic 5'/3' monodeiodinase

Question 30

Describe the onset and duration of THs?

Answer 30

THs have slow onsets and long durations (so there is a latency period)

Question 31

Which has a faster action time...T4 or T3?

Answer 31

T3 acts 4X as rapidly as T4

Question 32

What is the effect of TH on the following: ``` 1- BMR 2- Cardiac Output 3- Urea and Renal Function 4- Ventilation 5- Gluconeogenesis and Glycogenolysis 6- Lipolysis 7- Glucose absorption in the Gut ```

Answer 32

Increases them all

Question 33

How does TH regulate normal growth and development?

Answer 33

acts synergistically with growth hormone to promote bone formation also promotes ossification and fusion of bone plates and bone maturation

Question 34

What does TH deficiency in infants result in? How is it treated?

Answer 34

Mental retardation (cretinism) and growth retardation Treated with T4 shortly after birth

Question 35

Which condition increases BMR? Hyper- or Hypothyroidism?

Answer 35

Hyperthyroidism

Question 36

Which condition has increased serum cholesterol? Hyper- or Hypothyroidism?

Answer 36

Hypothyroidism

Question 37

Which condition has an increased expression of Beta adrenergic receptors? Hyper- or Hypothyroidism?

Answer 37

Hyperthyroidism

Question 38

What is a positive regulator of thyroid function? A negative regulator?

Answer 38

Hypothalamic THR (+) Anterior Pituitary TSH (+) Circulating TH (-)

Question 39

How does TRH stimulate TSH release?

Answer 39

Activation of a GPCR linked to PLC which leads to the generation o IP3 and mobilisation of intracellular calcium

Question 40

How does TSH stimulate the synthesis/ release of TH?

Answer 40

Activating an GPCR linc\ked to adelylate cyclase, which generates cAMP