The Thyroid Gland Flashcards Preview

Regulatory Physiology and Pharmacology > The Thyroid Gland > Flashcards

Flashcards in The Thyroid Gland Deck (60)
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31

How do T3 and T4 act during development and growth?

promote growth of neurons and maturation of the CNS
essential between week 11 and birth
correct mental development and body growth

32

How do T3 and T4 act on the sympathetic system?

increase responsiveness to catecholamines by increasing the no. of receptors in tissue

33

How do T3 and T4 act on the respiratory and cardiovascular system?

alters expression of ryanodine Ca channels in SR and promote calcium release
enhances sensitivity and expression of adrenoceptors to stimulation by noradrenaline (esp. B1 receptors)

34

How do T3 and T4 act on the BMR?

adjust heat loss through sweating and ventilation
accelerates response to starvation

35

How do T3 and T4 act on the ANS and catecholamines??

increase the no. of b-adrenergic Rs in the heart
increase the generation of intracellular second messengers

36

How do T3 and T4 act on the nervous system?

development
enhances wakefullness, alertness, responsiveness to various stimuli

37

What are the possible causes of hyperthyroidism?

Autoimmune disease such as Graves
Benign tumour causing enlargement of gland
Excessive TSH secretion from a TSH producing tumour

38

What are the possible causes of hypothyroidism?

Autoimmune disease such as Hashimoto disease
Dietary Iodine Deficiency
Defective hypothalamic and pituitary function resulting in insufficient thyrotropin secretion for thyroid gland stimulation

39

What is Goitre?

An enlarged thyroid gland - with 90% of cases caused by iodine deficiency

40

Why does iodine deficiency cause Goitre?

TSH secretion increases and thryoid cells proliferate to try and make more TH

41

What is another cause of Goitre?

Hyperthyroidism - Graves and excess TSH from pituitary tumour

42

What are the symptoms of Graves disease?

weight loss, excessive sweating, HR trouble, periorbital oedema, difficulty swallowing due to Goitre

43

How do you distinguish between Graves and a pituitary adenoma?

Graves has increase TSI and decreased TSH
Adenoma has decrease TSI and increased TSH

44

What are the possible treatments for hyperthryoidism?

Surgery - partial or complete removal
Drugs - thioureylenes, iodine contatining preparations, b-adrenoceptor antagonists

45

What do thiourelyenes require?

Thiocarbamide - S-C-N for activity

46

What are the effects of thiourelyenes?

Inhibit thyroid hormone synthesis - prevent iodination of tyrosine, and prevent coupling reactions of mono-iodo and di-iodo

47

What are some common thioureylenes used?

Carbimazole, Methimazole and Propylthiouracil which also inhibits deiodinases in peripheral tissues converting T4 to T3

48

Why do hormone changes and effects take so long in treating hyperthyroidism?

hormone stores and T4 bound to binding proteins

49

What is the effect of iodine containing preparations?

Radioiodine given as Na I, or I-131 produces y-rays and b-particle causing localised damage to follicular cells
half life of 8 days

50

How does KI preparation work and what is the effect called?

suppresses NADPH oxidase activity and peroxidase genes
Wolff-Chaikoff effect
inhibitory effect for up to 2 weeks then tolerant
used frequently before surgery or treatment of thyroid storm

51

How do b-adrenoceptors work to reduce hyperthyroidism?

no direct on synthesis or release but blocks cardiac b-adrenoceptors normalising HR
used in patients waiting for surgery or waiting for thiouryelenes to work

52

How is hypothyroidism treated?

synthetic T4 and T3 as replacement

53

Why is T4 first choice for replacement therapy?

builds up over days to max effects as it binds to plasma proteins and binding sites need to saturate for free hormone to become available
T3 is only used in emergencies such as coma as they have rapid action

54

What is the issue of replacement therapy?

If it is too high may cause cardiac dysregulation

55

How does T3 enter the brain?

T4 enters a glial cell where it is converted to T3 by D2
T3 exits cell and transported into neuron by MCT8
Enters the nucleus, binds a TR or inactivated to T2 by D3 iodinase

56

What is the molecule that converts T4 to T3 in the glial cell?

D2

57

What is the molecule that converts T3 to T2?

D3 iodinase

58

Where is the MCT8 gene located?

X chromosome

59

What does MCT8 deletions result in males?

Allan-Herndon-Dudley syndrome - abnormal plasma TH, global developmental delay, spastic quadraplegia, impaired gaze and hearing, hypotonia

60

What does MCT8 deletion result in females?

have two copies of gene
heterozygous mutants have mild thyroid phenotype and no neurological defects
50% chance of passing onto son