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Endocrine > Thyroid Physiology > Flashcards

Thyroid Physiology Flashcards

1
Q

What is secreted from thyroid gland tissue?

A

Thyroxin
Tri-iodothyronine
Calcitonin

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2
Q

What is secreted from the parathyroid glands?

A

Parathyroid hormone

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3
Q

What ion is the parathyroid gland in control of?

A

Calcium

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4
Q

Where does the thyroid sit?

A

Between the 5th cervical and 1st thoracic vertebrae

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5
Q

What is the blood supply to the thyroid gland?

A

Superior and inferior thyroid arteries from the external caroti
Thyroidea ima in some people

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6
Q

What nerve runs alongside the thyroid gland?

A

Recurrent laryngeal nerve

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7
Q

What drains the thyroid gland?

A

Superior/ middle thyroid vein which drain into internal jugular
Inferior thyroid that drains into braciocephalic vein

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8
Q

What are the thyroid producing cells?

A

Follicular cells

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9
Q

What is a colloid?

A

Tyrosine containing thyroglobulin filled spheres enclosed by follicular cells

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10
Q

What cell produces calcitonin?

A

Parafollicular C cells

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11
Q

What is the action of calcitonin?

A

Opposite of PTH - it reduces calcium levels

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12
Q

What ion is needed to make thyroid hormones?

A

Iodine

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13
Q

In what cell is iodine found in inside follicualr cells?

A

Pinocytosis

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14
Q

What is the building blocks of thyroid hormones?

A

Iodine attached to tyrosine residuces on thyroglobulin

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15
Q

Which hormone is more potent - T3 or T4?

A

T3 is 4x more potent

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16
Q

Where is T4 converted to T3?

A

In the liver and kidneys - but can be converted in any cell in the body

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17
Q

Which hormone is the major biologically active thyroid hormone?

A

T3

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18
Q

What does TSH do?

A

Stimulates the follicualr cell to secrete thyriod hormones

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19
Q

How do T3 and T4 travel around the blood?

A

Bound to plasma proteins due to the hydoophobic nature

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20
Q

What are the main plasma proteins that thyroid hormones bind to?

A

Thyroxin binding globulin
Thyroxine binding prealbumin
Albumin

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21
Q

When will the thyroid hormones be biologically active?

A

When unbound and free in the plasma

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22
Q

How is T4 converted to T3?

A

Removal of an iodine ion

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23
Q

What receptors do thyroid hormones bind to at a cellular level?

A

Hybrid nuclear receptors

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24
Q

What do thyroid blood tests measure?

A

The free levels of T4 and T3

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25
Q

What can increase the total T4 but not free T4?

A

Pregnancy

OCP

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26
Q

What effects does thyroxine have?

A 
Metabolism
Growth
Development
Reproduction
Behaviour
27
Q

What will an overactive thyroid do to the skin?

A

Increased sweat

28
Q

What will an overactive thyroid have to the heart?

A

Increased HR

Palpitations

29
Q

What can increased thyroxine do in gynae?

A

Reduced periods

30
Q

For what organ is thyroxine particularly important for in a developing foetus?

A

Brain

31
Q

What do thyroid hormones do the basal metabolic rate?

A

Increased basal metabolic rate
Increase number and size of mitochondria
Increase oxgen use and rates of ATP hydrolysis
Increased synthesis of resp chain enzymes

32
Q

What effect do thyroid hormones have on thermogenesis?

A

Increased

33
Q

What effect do thyroid hormones have on carbohydrate metabolism?

A

Increase blood glucose

Increase insulin-dependent glucose uptake into cells

34
Q

What effect do thyroid hormones have on lipid metabolism?

A

Mobilise fats from adipose tissue

Increase fatty acid oxidation in tissues

35
Q

What effect do thyroid hormones have on protein metabolism?

A

Increased protein synthesis

36
Q

What effect do thyroid hormones have on growth?

A

Growth hormone releasing hormone (GHRH) production and secretion requires thyroid hormones
Glucocorticoid induced GHRH release also dependent on thyroid hormones

37
Q

What effect do thyroid hormones have on developement of foetal and neonatal brain?

A

Myeliongenesis and axonal growth require thyroid hormones

Particularly imporant in 1st trimester as foetus doesn’t have thyroid gland yet

38
Q

What effect do thyroid hormones have on normal central nervous system activity?

A

Hypothyrodism - slow intellectual function

Hyperthyrodism - nervousness, hyperkinesis, emotional lability

39
Q

What neurotransmitters are affected by thyroid hormones?

A

Thyroid hormones increase the responsivness to adrenaline and sympathetic neurotransmitter noradrenaline by increasing the number of receptors

40
Q

What happens in the heart in increased thyroid production?

A

Increased force and rate of contraction

41
Q

What drug can be used to treat the inital symptoms of hyperthyrodism?

A

Beta blockers such as propanolol

42
Q

What is the effect of stress on thyroid hormone regulation?

A

Inhibitis TRH and TSH release

43
Q

How does the circadian rhythm affect thyroid hormone regulation?

A

Highest late at night and lowest in the morning

44
Q

How do low temps affect thyroid hormone regulation?

A

In babies and young children, expsoure to cold environments stimualtes TRH release, stimulating TSH release increasing T3 and T4 release

45
Q

What is the function of throtrophin releaseing hormone (TRH)?

A

Formed in the hypothalamus and stimulates TSH release from the anterior pituitary

46
Q

What type of feedback is utilised in thyroid hormone regulation?

A

Negative feedback control of release of TRH and TSH

47
Q

What is the function of deiodinase enzymes?

A

Activate and deactivate thyroid hormones via the addition or removal of an iodine atom in the outer ring

48
Q

What is the most important deiodinase enzyme?

A

Type 2 - D2

49
Q

What does D2 do?

A

Converts T4 to T3

50
Q

Where it D1 found?

A

Liver and kidneys

51
Q

Where is D2 found?

A

Heart and skeletal muscle, CNS, fat, thyroid and pituitary

52
Q

Where is D3 found?

A

Fetal tissue and placenta, brain (except pituitary)

53
Q

What can cause hypothyrodism?

A

Primary gland failure - may be associated with goitre - autoimmune disease
Secondary to TRH or TSH (no goitre)
Lack of iodine in diet

54
Q

What are the symptoms of hypothyrodism?

A 
Reduced BMR
Slow pulse rate
Fatigue
Cold-intolerance
Tendency to put on weight easily
55
Q

What is myxoedema?

A

Puffy face, hands and feet

56
Q

What is cretinism?

A

Dwarfism and limited mental function due to deficiency of thyroid hormones at birth

57
Q

What is the most common cause for hypothyrodism?

A

Autoimmune disease

58
Q

What is the most common reason for hyperthyrodism?

A

Graves disease - autoimmune disease where thyroid stimulating immunoglobulin acts like TSH

59
Q

What is exopthalmos?

A

Bulging eyes due to water retaining carbohydrate buld up behind eyes

60
Q

What are the common symptoms of hyperthyrodism?

A 
Increased BMR
Vert fast HR
Increased nervousness and excessively emotional 
Insomnia
Sweating and heat intolerance
Tendency to lose weight easily
61
Q

What is the average weight of the thyroid gland in adults?

A

25-30g

62
Q

What is the main regulator of thyroid hormone release?

A

TSH

63
Q

What is the main binding globulin for thyroxine?

A

TBG - thyroxine binding globulin

64
Q

What effects can thyroxine have on the heart?

A

Cardiomyopathy

AF

Endocrine (35 decks)

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