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Endocrine > Iodine metabolism and thyroid hormones > Flashcards

Iodine metabolism and thyroid hormones Flashcards

1
Q

Describe the abundance of iodine?

A

High abundance in sea

Low abundance on land

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2
Q

What is the RDI for iodine?

A

150 ug

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3
Q

What is iodine required for in the body?

A

Synthesis of thyroid hormones T3 and T4

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4
Q

What can iodine deficiency lead to?

A

Decreased thyroid hormone synthesis > feedback to increase production of TSH > induces thyroid cell proliferation > goitre

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5
Q

What is the cause of cretinism?

A

Congenital condition due to maternal iodine defciciency

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6
Q

Which radioactive substance can destroy the thyroid?

A

Radiation from I-131

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7
Q

Why are iodine deficiencies common in humans and land animals?

A

Absence from soils

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8
Q

Describe the difference between an antiseptic and a disinfectant?

A

Antispetic: antimicrobial that reduces the risk of infection, applied externally to living surfaces

Disinfectant: antimicrobial that is applied to non-living objects

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9
Q

Can iodine be used as an antibiotic, antiseptic, or disinfectant?

A

Antiseptic

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10
Q

What are the advantages of using iodine as an antiseptic?

A

Wide spectrum of antimicrobial activity

When brown - can see where it is and inidicates that it is active

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11
Q

Describe why iodine has an antimicrobial action?

A

Active form, I2, is a potent oxidiser

Reacts in electrophilic reactions with enzymes of respiratory chain and amino acids in cell membrane and cell wall > cell integrity destroyed

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12
Q

Why is iodine used as an X-ray contrast material?

A

High atomic number

Low toxicity

Ease of attachment to organic compounds

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13
Q

Is iodine a major mineral or a trace mineral in the body?

A

Trace mineral (20mg/body)

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14
Q

Which substance has the highest concentration of iodine?

A

Kelp

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15
Q

What is the recommended upper level of iodine intake per day?

A

1100 ug/day

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16
Q

What are the most significant sources of iodine in the human diet?

A

Iodised salt

Seafood

Bread

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17
Q

Briefly describe the symptoms of iodine deficiency?

A

Underactive thyroid gland

Goitre

Cretinism

18
Q

Describe the symptoms associated with iodine toxicity?

A

Underactive thyroid gland

Elevated TSH

Goitre

19
Q

What are goitrogens?

Where are they found?

A

Substances that inhibit iodide uptake in the thyroid and magnify the severity of any iodine deficiency

Found in soy, cabbage, kale, brussel sprouts

20
Q

How many people in the world are affected by iodine deficiency?

A

2 billion

21
Q

How many people are affected by goitre?

A

200 million

22
Q

How many people worldwide are affected by cretinism?

A

6 million

Most common form of mental retardation

Also most preventable

23
Q

What is the most common and also most preventable form of mental retardation?

A

Cretinism

24
Q

Describe the hypothalamic-pituitary-thyroid axis?

A
25
Q

What controls the release of thyroid hormones?

A

TSH from pituitary

26
Q

Describe the action of thyroid hormones?

A

Increase mental alertness

Increase basal metabolic rate

Elevate number of catecholamine receptors > enhance catecholamine effects

Stimulate differentiation and function of brown adipose tissue > generate heat

27
Q

Why does every cell in the body rely upon thyroid hormones?

A

Required for regulation of metabolism

28
Q

Describe the proportion in which the normal thyroid produces T3 and T4?

A

80% T4

20% T3

29
Q

Describe the relative activity of T3 and T4 in the body?

A

T3 has about four times the activity of T4

30
Q

Describe the half-lives of T3 and T4?

A

T3: 6-9 days

T4: 24-36 hours

31
Q

Describe the synthesis of T3 and T4?

A

Iodide oxidised by thyroperoxidase > iodine reacts with tyrsosines in thyroglobulin > iodinated tyrosines on surface of thyroglobulin enzymatically condensed by thyroperoxidase > modified thyroglobulin taken up into thyroid cell > peptide links hydrolysed > free amino acids and T3/T4 liberated

32
Q

Where is thyroperoxidase located?

A

Embedded in thyroid cell membrane

33
Q

Describe the process of T3 and T4 secretion from the thyroid gland?

A
34
Q

Describe uptake of iodide by the thyroid gland?

A

TSH stimulates TSH receptor > cAMP activated > activates NIS (Na iodide symport) > Na and I enter cell at same time

35
Q

What drives the NIS in thyroid cells?

A

Na gradient maintained by 3Na/2K ATPase

36
Q

Describe the use of radioactive iodine as treatment for goitre?

A

Iodine-131 can be used to reduce thyroid mass

37
Q

Describe the treatment options for goitre?

A

Radioactive iodine treatment

Antithyroid drug therapy

Surgery/thyroidectomy

Thyroid arterial embolization

38
Q

How are thyroid hormones transported in the plasma?

Why?

A

70-80% carried in plasma bound to thyroid binding globulin (TBG)

Remainder divided between transthyretin and serum albumin

Because it is lipophilic

39
Q

Describe how thyroid hormones elicit their actions?

A

Receptors bind DNA > transcritptional repression in absence of hormone

Hormone binds receptor > transcription activated

40
Q

Compare the effects of hypothyroidism and hyperthyroidism?

A

Endocrine (17 decks)

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