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SUGER > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What is the weight of the thyroid

A

25-30g

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2
Q

What is the role of thyroid hormones

A

Control of metabolism - energy generation and use

Regulation of growth

Multiple roles in development

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3
Q

Describe thyroid hormone synthesis

A

Produced by follicular thyroid cells

Synthesised from thyroglobulin precursor

Iodine is absorbed from bloodstream and concentrated in follicles

Thyroperoxidase binds to iodine to tyrosine residues in thyroglobin molecules to form MIT + DIT

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4
Q

What are the two thyroid hormones

A

T3 - Triiodothyronine

T4 - Thyroxine

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5
Q

What is the enzyme involved in thyroid synthesis

A

Thyroid peroxidase

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6
Q

Describe T3

A

Biologically active hormone

Produced by mono-deiodination of T4 which is most abundant

Deiodinase (D1,2,3) enzymes present in peripheral tissue

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7
Q

What does MIT + DIT make

A

T3

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8
Q

What does DIT + DIT make

A

T4

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9
Q

How does T4 become T3

A

Deiodination

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10
Q

What % of T4 is free

A

0.03%

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11
Q

What % of T3 is free

A

0.3%

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12
Q

What is T3 and T4 bound to

A

Thyroxine binding globulin

Transthyretin

Albumin

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13
Q

What would hyperthyroidism show

A

Low serum TSH

High Serum free T4

High serum free T3

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14
Q

What would hypothyroidism show

A

High serum TSH

Low serum free T4

Low serum free T3

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15
Q

What is the function of the parathyroid gland

A

Regulate calcium and phosphate levels

Secrete parathyroid hormone in response to
- low calcium
OR
- high phosphate

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16
Q

What are the actions of PTH

A

Increases calcium reabsorption in renal distal tubule

Increases intestinal calcium absorption (via activation of vitamin D)

Increases calcium release from bone (stimulates osteoclast activity)

Decreases phosphate reabsorption

17
Q

What is the normal reference range for PTH

A

1.6 - 6.9 pmol/L

18
Q

What are the metabolic processes increased by thyroid hormones

A

Basal metabolic rate

Gluconeogenesis

Glycogenolysis

Protein synthesis

Lipogenesis

Thermogenesis

19
Q

What is the production of thyroid hormone

A

Hypothalamus - release TRH

To anterior pituitary - thyrotropes respond to TRH

Secrete TSH

TSH circulates through the blood to the thyroid gland

Production of T3 and T4 (thyroid hormone)

20
Q

What is the feedback of the thyroid hormone

A

Too much T3 and T4 - negative feedback to hypothalamus

Low T3 and T4 - feedback to increase hypothalamus

21
Q

How do T3 and T4 circulate

A

Via TBG (thyroid binding globule - protein)

22
Q

What is thyroxine

A

T4

23
Q

Describe the production of T3

A

Can pass into lipid bilayer into cell

5’-deidoinsase - removes iodine off thyroxine

Removal of the iodine molecule on the 5’ of thyroxine (T4)

Produces T3 - active form

24
Q

Describe the role of T3

A

T3 binds to a transcription factor/receptor and retinoic acid (RXR) binds

Active transcription factor can move into nucleus

Protein synthesis

Na/k ATPase on the surface - T3 increases expression of these

Due to increase of ATP usage = increase metabolism (metabolic rate)

25
Q

What is the active form of thyroid hormone

A

T3

26
Q

What is the role of thyroxine (T4) on the liver

A

Stimulates

Glycogen conversion to glucose - glycogenolysis

Gluconeogenesis

Increases number of LDL receptors to decrease LDL in the blood (bad cholesterol)

27
Q

What is the effect of thyroid hormone in the heart

A

Increase contractility of the heart due to expression of binding sites as well as on the SA node (increases number of action potentials)

Increase HR = Increase in blood pressure

28
Q

What is the effect of the thyroid hormone on the CNS

A

Increases dendrite formation

Increase myelination - faster action potentials

Increase synapses

29
Q

What is the effect of thyroid hormone in the bone

A

Regulates osteoblast and osteoclast balance

Stimulate interstitial growth

Stimulating endochondral ossification

Role in bone remodelling

30
Q

What is the effect of thyroid hormone on the adipose tissue

A

Lipolysis - fatty acid chain and glycerol

31
Q

What is the effect of thyroid hormone on the muscle

A

Regulates activity of catabolism and anabolism

32
Q

What is the effect of the thyroid hormone on the skin

A

Metabolic rate increases body temperature

Sweat and vasodilation

33
Q

What is the effect of the thyroid hormone on the GI tract

A

Normal motility

Secretions

SUGER (15 decks)

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