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Endocrinology > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

What are the 2 physiologically active thyroid hormones?

A

T3

T4

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2
Q

What are the 2 types of cells in the thyroid?

A

C (clear cells)

Follicular cells

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3
Q

What do clear cells secrete?

A

Calcitonin

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4
Q

What does calcitonin regulate?

A

Calcium

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5
Q

What tends to dominate the action of calcitonin?

A

PTH

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6
Q

What are thyroid follicles?

A

Structures surrounded by follicular cells

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7
Q

What is the centre of thyroid follicles filled with?

A

Colloid

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8
Q

What type of hormone are thyroid hormones?

A

Amine derived from tyrosine `

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9
Q

What do follicular cells manufacture?

A

The enzymes that make thyroid hormones as well as thyroglobulin

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10
Q

Where are thyroid hormone and thyroglobulin exported to?

A

The colloid

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11
Q

What do follicular cells concentrate?

A

Iodide

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12
Q

What does iodide combine with?

A

Tyrosine residues to form TH

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13
Q

Which enzyme catalyses the formation of TH>

A

Thyroid peroxidase

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14
Q

How does iodide enter follicular cells from the plasma?

A

via a Na+/I- transporter (symport they both travel in the same direction). The coupling to Na+ enables the follicular cells to take up iodide against a concentration gradient.

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15
Q

How is iodide transported to the colloid?

A

Via the pendrin transporter

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16
Q

How is iodide transport inhibited?

A

by thiocyanates

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17
Q

What does the addition of one iodine to tyrosine form?

A

MIT (monoiodotyrosine)

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18
Q

What does the addition of two iodine to tyrosine form?

A

DIT

Diiodothyrosine

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19
Q

What does DIT + DIT form?

A

tetraiodothyronine or Thyroxine T4

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20
Q

What does DIT + MIT form?

A

triiodothyronine or T3

21
Q

What happens in response to TSH?

A

Portions of the colloid are taken back up into the follicular cell by endocytosis. Within the cells they form vesicles which contain proteolytic enzymes that cut the thyroglobulin to release thyroid hormones.

22
Q

Are T3 and T4 lipid soluble?

A

Yes

23
Q

What do T3 and T4 bind to in the plasma?

A

Thyroxine-binding globulin

Plasma proteins

24
Q

Where do T3 and T4 circulate?

A

In the plasma

25
Q

What is the movement of TH from the colloid to the plasma under the control of?

A

TSH release from the PG

26
Q

Where is TSH released from?

A

PG

27
Q

How much TH circulates bound to plasma proteins?

A

99.8%

28
Q

Which hormone is released from the hypothalamus to stimulate TSH production?

A

TRH

29
Q

Why does T4 have a longer half life?

A

Because it has a higher affinity for thyroxine binding globulin

30
Q

Does bound hormone exert an inhibitory effect on TSH and TRH?

A

no only free hormone does

31
Q

What do TH receptors have a higher affinity for?

A

T3

32
Q

Which TH is more physiologically active?

A

T3

33
Q

Where do thyroid hormones bind?

A

To nuclear receptors in target cells

34
Q

What is the effect of TH binding to receptors?

A

Change transcription and translation to alter protein synthesis

35
Q

What are the effects of TH in the body?

A

Raises metabolic rate and promotes thermogenesis

increase hepatic gluconeogenesis

net increase in proteolysis

net increase in lipolysis

critical for growth (lack of TH results in retarded growth) anabolic

required for foetal brain development

36
Q

What is congenital hypothyroidism?

A

Thyrodism from birth

37
Q

How does TH affect growth?

A

Stimulates GH receptor expression

38
Q

What happens to growth when TH is not present?

A

Receptors are not in adequate numbers and normal growth cannot occur

39
Q

What can cause hyperthyroidism?

A

Graves disease

Thyroid adenoma

40
Q

What causes graves disease?

A

(common) antibodies produced that bind mimic TSH and continually activate the thyroid gland. Increased release of TH switches off TSH release from anterior pituitary so [TSH] plasma is very low

41
Q

What are the symptoms of hyperthyroidism?

A

Increased metabolic rate and head production
- weight loss

Increased protein catabolism - muscle weakness

Altered nervous system function
- hyper excitable reflexes

Elevated CVS function
- increased HR/contractile force

42
Q

What is a main causes of hypothyroidism?

A

Hashmoto’s disease
Iodide deficiency
Idiopathic

43
Q

What causes Hashmoto’s disease?

A

Autoimmune attack of thyroid gland

44
Q

What are the symptoms of hypothyroidism?

A
  1. Decreased metabolic rate and heat production - weight gain/cold intolerance 2. Disrupted protein synthesis - brittle nails/thin skin
  2. Altered nervous system function - slow speech/reflexes, fatigue
  3. Reduced cardiovascular function - slow heart rate/weaker pulse
45
Q

What is Goitre?

A

Enlargement of the thyroid gland

46
Q

What is primary Thyroid disease?

A

When the TG is not working

47
Q

What is secondary thyroid disease?

A

When the problem is with the PG

48
Q

What is tertiary thyroid disease?

A

When the problem is in the hypothalamus

Endocrinology (19 decks)

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