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unit 6: physiology > Thyroid Physiology (11) > Flashcards

Thyroid Physiology (11) Flashcards

1
Q

What is the main role of the thyroid gland?

A

Regulates vertebrate growth, development and metabolism

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2
Q

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

A

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

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3
Q

How is TH stored?

A

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

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4
Q

Within the thyroid, where is calcitonin synthesized and released?

A

In scattered parafollicular C-cells

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5
Q

What are the biologically active forms of TH?

A

Thyroxine (T4), Triiodothyronine (T3)

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6
Q

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

A

Tyrosine, and dietary Iodide

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7
Q

What is T4?

A

Thyroxine

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8
Q

What is T3

A

Triiodothyroxine

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9
Q

Which TH is preferentially synthesized in the thyroid?

A

T4

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10
Q

How is iodide stored in the thyroid/

A

In association with thyroglobulin (TG)

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11
Q

How is Iodide concentrated in the thyroid?

A

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

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12
Q

What can chronic iodide deficiency lead to?

A

Hypothyroidism that can be corrected by providing adequate dietary Iodide

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13
Q

What regulates TH synthesis, storage regulation and release?

A

TSH

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14
Q

How is the release of TSH regulated?

A

Negative feedback control by the thyroid hormones

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15
Q

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

A

T4…so T4 acts as a prohormone

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16
Q

What are the two functions of the Thyroid Peroxidase?

A

1- Oxidize I- to Iodide

2- Couple together DIT to another DIT to form T4

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17
Q

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

T4, T3, DIT, MIT

A

MIT, DIT, T4, T3

18
Q

What is organification?

A

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

19
Q

What is circulating TH bound to ?

A

1- Thyroid-binding globulin (70%)

2- Transthyretin

3- Albumin

20
Q

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

A

Peripheral Deiodinases

21
Q

Which TH has the longer half life?

A

T3 (1 day)

T4 (days)

22
Q

Which TH is more potent?

A

T3 is more potent

23
Q

Which TH is usually sued to treat hypothyroidism?

A

T4 because of its longer half life and greater stability

24
Q

Where are TH receptors expressed?

A

virtually all tissues of teh boy

25
Q

What type of metabolism does TH regulate?

A

Carbohydrates, proteins and lipids

26
Q

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

A

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

27
Q

What do thyroid hormone receptors form heterodimers with?

A

Retinod X receptors

28
Q

What TH usually binds the thyroid hormone receptor

A

T3

29
Q

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

A

cytoplasmic 5’/3’ monodeiodinase

30
Q

Describe the onset and duration of THs?

A

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

31
Q

Which has a faster action time…T4 or T3?

A

T3 acts 4X as rapidly as T4

32
Q

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
A

Increases them all

33
Q

How does TH regulate normal growth and development?

A

acts synergistically with growth hormone to promote bone formation

also promotes ossification and fusion of bone plates and bone maturation

34
Q

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

A

Mental retardation (cretinism) and growth retardation

Treated with T4 shortly after birth

35
Q

Which condition increases BMR? Hyper- or Hypothyroidism?

A

Hyperthyroidism

36
Q

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

A

Hypothyroidism

37
Q

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

A

Hyperthyroidism

38
Q

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

A

Hypothalamic THR (+)

Anterior Pituitary TSH (+)

Circulating TH (-)

39
Q

How does TRH stimulate TSH release?

A

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

40
Q

How does TSH stimulate the synthesis/ release of TH?

A

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

unit 6: physiology (13 decks)

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