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Endocrinology > The thyroid gland > Flashcards

The thyroid gland Flashcards

1
Q

What is the name for a greatly enlarged thyroid?

A

Goitre

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2
Q

What is TSH?

A

a pituitary dimeric glycoprotein composed of an alpha and a beta subunit.

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3
Q

The alpha subunit is the same as:

A

TSH
LH
FSH
hCG

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4
Q

TSH binds to a G-protein couple receptor on thyroid follicle epithelial cells, which activates both:

A
  • Adenylate Cyclse = cAMP/PKA dependant pathway

- Phospholipase C = PI turnover = DAG and IP3

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5
Q

iodine is actively taken up from the blood into follicular cells and transporter into the lumen. in the lumen the enzyme ________ ________ converts iodine to free iodine.

A

Thyroid peroxidase

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6
Q

Thyroglobulin contains a high content of what?

A

tyrosine

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7
Q

Iodine atoms are incorporated into?

A

Tyrosine residues

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8
Q

MIT stands for:

A

mono-iodotyrosine = one iodine per tyrosine

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9
Q

DIT stands for:

A

Di-iodotryrosine = two iodine per tyrosine

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10
Q

DIT + DIT =

A

T4

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11
Q

MIT + DIT =

A

T3

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12
Q

Two ____ do NOT couple

A

MIT

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13
Q

what do lysosomal cells in the follicular cells do?

A

break down the iodinated thyroglobulin liberating free T3 and T4

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14
Q

How does T3 and T4 enter the blood?

A

Diffuse through the plasma membrane of the follicular cells

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15
Q

Inactive DIT and MIT are rapidly?

A

de-ionated and the released iodine is recycled back to the lumen for further use

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16
Q

follicular cells take up a portion of the _____ in the lumen (________)

A

Colloid

Endocytosis

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17
Q

What does TBG stand for?

A

Thyroxine binding globulin

18
Q

What does TBG circulate bound to?

A

T3 AND T4, because they have poor solubility in water

19
Q

What does TBG prevent?

A

Urinary secretion of T3 andT4

20
Q

TBG ____ against ____ changes in the ______ functions

A

buffers
acute
thyroid

21
Q

before exerting a biological effect what must T3/T4 do?

A

dissociate from TBG

22
Q

what is secreted 90%; T3 or T4?

A

T4, T3 is secreted 10%

23
Q

What is more potent T3 or T4?

A

T3 is 3 fold more potent than T4

24
Q

how is most of secreted T4 activated?

A

by the removal of an iodine in target peripheral tissues

25
Q

T3 and T4 bind to

A

intracellular thyroid hormone receptors

26
Q

the receptor that T3 and T4 bind to is a:

A

HORMONE REPSONSIVE TRANSCRIPTION FACTOR, T3 is more active as it binds with a higher affinity

27
Q

what are the effects of thyroid hormone?

A 
-Increases basa metabolic rate (BMR)
   raised CO2 consumption 
   CO2 production
   Heat production
-Cardiovascular system
    increased hear force and contraction
-Nervous system
   increases activity of sympathetic nervous system
    enhances the sensitivity to catecholamines
-Growth and maturation
   embryo development
   CNS development
   Linear growth
28
Q

How does a goitre come about?

A

hypertrophy of thyroid gland caused by excessive stimulation by TSH
associated with certain forms of hypo or hyper thyroids
often associated with autoimmune disease

29
Q

Effects of Hypothyroidism in Adults:

A 
weight gain
cold intolerance
lethargy
depression
puffiness of skin and muscles
sluggish reflexes
muscular weakness
reduced pulse rate and cardiac output
30
Q

Effects of hypothyroidism in foetus/child

A

brain damage - permanent if not treated early enough
shortness
obesity
mental retardation

31
Q

What is done to prevent foetus/child hypothyroidism?

A

routine neonatal screening for elevated TSH.

High TSH indicated low T3/T4 due to reduced -ve feedback on hypo. pit

32
Q

Iodine Deficiency Disorder (IDD) is the worlds most prevalent cause of?

A

brain damage

33
Q

how many people worldwide does it effect?

A

740 million, 200 million with goitre

34
Q

IDD is easily avoided by?

A

use of iodised cooking salt/supplementary iodine in foods

35
Q

What is the treatment for HYPOthyroidism?

A

lifelong replacement of T4 (adult ~150ug/day), unless due to chronic dietary iodine deficiency in which case increased supplementary iodine is given in diet.

36
Q

What are the causes of hypothyroidism?

A
  • Primary failure of thyroid gland
  • Secondary due to hypothalamic or anterior pituitary failure
  • Secondary due to autoimmune damage to gland
  • Secondary due to chronic lack of dietary iodine
37
Q

What is HYPERthyroidism?

A

excess thyroid hormone

38
Q

what are the symptoms of hyperthyroidism?

A 
weight loss
nervousness
heat intolerance
high cardiac output
hand tremors
eyeball protusion
39
Q

50% of hyperthyroidism are due to _________

A

Grave’s disease

40
Q

What causes graves disease?

A

autoimmune disease
thyroid stimulating Ab that mimics TSH:
Primary = hyper secreting thyroid tumour
secondary= excessive hypothalamic/anterior pituitary secretion

41
Q

What is the treatment for hyperthyroidism?

A

anti-thyroid drugs that interfere with thyroid hormone synthesis
surgical resection of thyroid
thyroid ablation using radioactive iodine

42
Q

Elevated ___ inhibits the release of ___ and ___ = _______ __________

A

T3
TSH
TRH
negative feedback

Endocrinology (12 decks)

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