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Diabetes & Endocrinology > The thyroid gland > Flashcards

The thyroid gland Flashcards

1
Q

Describe the appearance of the thyroid gland

A

butterfly - heavy (15-20g) - lies across trachea at base of larynx
not palpable or visible in health

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2
Q

What are the 2 physiologically active hormones which the thyroid gland secretes?

A

T3 and T4(thyroxine)

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3
Q

What are the 2 types of cells found in the thyroid gland?

A

follilcular cells

clear cells

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4
Q

What do clear cells secrete?

A

calcitonin

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5
Q

What do follicular cells do?

A

support thyroid hormone synthesis

surround hollow follicles

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6
Q

What is the middle of the follicle filled with?

A

colloid

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7
Q

What does the colloid contain?

A

sticky glycoprotein matrix containing 2-3 month supply of TH

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8
Q

What do follicular cells make?

A

enzymes

thyroglobulin

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9
Q

What do follicular cells do in terms of thyroid hormone (and iodide)

A

concentrate iodide from the plasma and transport it into the colloid where it combines with tyrosine residues to form thyroid hormone

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10
Q

Describe the thyroglobulin molecule?

A

Large protein residues rich in tyrosine residues

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11
Q

Where do you get tyrosine and iodide from?

A

the diet

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12
Q

What differentiates T3 and T4?

A

T3 has 3 iodide ions from the 2 tyrosine molecules

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13
Q

What enzyme catalyses the reaction to form thyroid hormone and where is it found?

A

thyroid peroxidase

apical membrane of follicular cells

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14
Q

How does iodide enter the follicular cells from the plasma?

A

Na+/I- transporter –> symport

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15
Q

What is the advantage of coupling iodide to sodium for transport?

A

Can uptake against the concentration gradient

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16
Q

How is iodide transported from the follicular cells to the colloid?

A

pendrin transporter

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17
Q

What inhibits iodide transport into follicular cells and where is this found in daily life?

A

thiocyanates

cigarette smoke

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18
Q

What does thyroperoxidase catalyse?

A

iodide to tyrosine residues in thyroglobulin

19
Q

After T3 and T4 are made what happens to release them into the blood?

A

TSH stimulates endocytosis of parts of the colloid into follicular cells and form vesicles with proteolytic enzymes to cut thyroglobulin to release thyroid hormones

20
Q

What plasma proteins do thyroid hormones bind to?

A

thyroxine binding hormone

21
Q

Does TBG have a particularly high affinity for T3 or T4?

22
Q

What does TBG do in terms of T4 half life?

A

make it longer by releasing it slowly into the plasma

23
Q

What does the thyroid hormone need to be to exert an inhibitory effect on TSH and TRH?

A

free (physiologically active and not bound to plasma proteins)

24
Q

Does most TH circulate as T3 or T4?

25
Q

Do most of TH binding to intracellular receptors T3 or T4?

26
Q

Does TH receptor have higher affinity for T3 or T4?

27
Q

Is T3 or T4 more physiologically active?

28
Q

How is T4 converted to T3?

A

deiodinated by deiodinase enzymes

29
Q

Where is T4 deiodinated?

A

half in plasma

half inside target cells

30
Q

Can levels of deiodinase of T4 be changed?

A

yes in response to suit demand

31
Q

Positive inputs to TRH?

A

cold, exercise and pregnancy

32
Q

What does glucocorticoids inhibit in terms of thyroid hormones?

A

TSH and conversion of T4–>T3

33
Q

What does GHIH inhibit in terms of thyroid hormones?

34
Q

Thyroid hormone functions

A

increase lipolysis
increase proteolysis
raise metabolic rate and promote thermogenesis
increase hepatic gluconeogenesis
Growth - stimulate GH receptor expression and anabolic
foetal brain development

35
Q

2 causes of hyperthyroidism

A

Graves disease - autoimmune

adenoma of thyroid

36
Q

Graves disease

A

Autoimmune stimulation of thyroid hormone due to antibodies mimic TSH and increase negative feedback and turn off TSH from anterior pituitary so plasma TSH is low
large thyroid gland –> hyperplasia
hyperactivity

37
Q

Thyroid adenoma

A

rare

hormone secreting thyroid tumour

38
Q

Link hyperthyroidism symptoms to what has happened

A

increased metabolic rate and heat production - weight loss and heat intolerance
protein catabolism - loss of muscle and weight
altered nervous system function - hyperexcitable reflexes and psychological
Elevated CV function as TH is permissive to epinephrine so increased HR, palpitations

39
Q

3 causes of hypothyroidism

A

hashimotos disease
iatrogenic
iodine deficiency

40
Q

Hashimotos disease

A

autoimmune destruction of thyroid gland

41
Q

Symptoms of hypothyroidism

A

weight gain, tiredness, slow heart rate, brittle nails and skin, slow speech and reflexes

42
Q

What is Goitre?

A

enlarged thyroid gland - hypo and hyperthyroidism

43
Q

Where do primary, secondary and tertiary thyroid disorders occur?

A

primary - thyroid gland
secondary - anterior pituitary
tertiary - hypothalamus

Diabetes & Endocrinology (24 decks)

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