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JMP Semester 2 > Week 23 > Flashcards

Week 23 Flashcards

1
Q

What are some sources of dietary iodine?

A

Seafood, dairy, eggs, meat, iodised salt

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2
Q

What is iodine needed for in the body?

A

It is a hormone precursor for thyroid hormones

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3
Q

Where is iodine absorbed?

A

From the GIT into circulation

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4
Q

How is iodine excreted?

A

98% by kidneys into urine

Rest into faeces

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5
Q

How can environmental position relate to iodine deficiency?

A

More likely to see iodine deficiency inland compared to coastal areas

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6
Q

How can the distribution of dietary iodine be described in the body?

A

Mostly excreted in urine, portion that is absorbed large chunk to thyroid for T3 and T4 production.

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7
Q

What is thyroglobulin?

A

Precursor for T3 and T4

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8
Q

Where is thyroglobulin stored?

A

Colloid

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9
Q

What is the difference of secretion of T3 and T4?

A

T4 in the main secreted form.

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10
Q

What is the general differences between T3 and T4?

A

T3 is more potent

T4 has a longer half-life

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11
Q

What happens to T4 when it reaches target cells?

A

It is enzymatically cleaved to T3 at target tissues.

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12
Q

How can the activity of thyroid cells be investigated clinically?

A
  1. Hormone levels (T3 and T4, TSH, TRH)

2. Labeled Iodine accumulation in thyroid cells is proportional to activity.

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13
Q

What are all the steps in the manufacture of T3 and T4:

A
  1. Follicle cells produce thyroglobulin –> transported into the lumen of the follicle (colloid)
    1. TSH binds to receptors
    2. Binding stimulates the production of T3 and T4 (at all points pretty much G protein coupled response)
    3. Iodine is brought into the follicular cells cell via the Na+ I+ symporter –> then into the lumen (colloid)
    4. Iodine in then converted to Iodide by thyroperoxidase
    5. Iodine and thyroglobulin comes together –> to be MIT or DIT
    6. MIT + DIT = T3
    7. DIT + DIT = T4
    8. These thyroglobulin reenter the follicular cells to be cleaved into individual T3 and T4 to then be released into the blood stream.
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14
Q

How do lipid soluble hormones travel in circulation?

A

Associated with solubilizing carrier peptides (increases hormone half-life and prevents inappropriate diffusion)

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15
Q

How is T4 transported in the blood?

A

Free - 0.04%

Bound 99.96% (various proteins (TBG, albumin other liver carrier proteins)

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16
Q

What are the areas involved in the HPT axis?

A

Hypothalamus
Anterior pituitary
Thyroid

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17
Q

What are the hormones produced and their effects on the different parts of the HPT axis?

A
  1. Hypothalamus produces (thyrotropin releasing hormone) TRH which acts on the Anterior pituitary
    1. Anterior pituitary produces Thyroid stimulating hormone (TSH) which acts on the thyroid
    2. Thyroid produces T3 and T4 which can negatively feedback on the hypothalamus and the anterior pituitary to reduce production of itself.
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18
Q

What is the mechanism of TRH produced by the hypothalamus?

A
  1. Low thyroid hormone concentrations drive TRH release
    1. TRH acts on receptors
    2. Receptor action increases intracellular Ca2+ concentration
    3. Elevated Ca2+ concentration increases TSH secretion
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19
Q

What is the mechanism of TSH activity?

A
  1. Increases activity of thyroid follicular cells
    1. Increases thyroglobulin synthesis (colloid) - which is a hormone precursor
    2. Increases follicular uptake of iodine (if available)
    3. Production of T3 and T4
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20
Q

What happens if TSH activity is increased and there is no available iodine?

A

Hyperplasia - Goitre formation- hyperthyroidism

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21
Q

What is usually the problem is someone has increased TSH levels?

A

Lack of negative feedback loop function.

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22
Q

What are some effects of thyroxine (T3,T4) signalling?

A
  1. Increases mitochondrial activity
    1. Increases transcription
    2. Roles in growth, Beta adrenergic receptor expression
    3. Negative feedback at hypothalamus/anterior pituitary
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23
Q

What are the main actions of thyroid hormones?

A
  1. Normal brain development
    1. Sustain cell growth and differentiation
  2. Increases in basal metabolic rate
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24
Q

What is the consequences of a deficiency in thyroid hormone?

A

Decreased metabolism (hypothyroidism)

25
Q

What is the most common causes for hypothyroidism?

A
  1. Iodine deficiency
    1. Autoimmune
    2. Surgery
    3. Drugs
    4. Congenital
26
Q

What is some clinical signs of hypothyroidism?

A
  1. Usually high TSH as there is low/decreased synthesis of T4/T3 to try to increase the levels of T4/T3 to restore homeostasis.
    1. Weight gain, cold intolerance, bradycardia
      What is the consequences of thyroid hormone excess?
      Increased metabolism (hyperthyroidism)
27
Q

What is the most common causes for hyperthyroidism?

A
  1. Graves disease (auto immune)
    1. Iodine excess or synthetic T4 excess
    2. Cancer
    3. Thyroiditis
28
Q

What is some clinical signs of hyperthyroidism?

A
  1. Usually elevated T4/T3 and decreased TSH levels. Feedback loop non functioning.
    1. Weight loss
    2. Sweating, hot, tachycardia
29
Q

What is the relationship between Thyroid hormone and adrenalin?

A

Thyroid hormone initiated an overexpression of Beta-adrenoceptors leading to increased sensitivity to catecholamines (like adrenalin)

30
Q

What would be the effect of hyperthyroidism on the bodies reaction to adrenaline?

A

The body would be more sensitised to adrenaline from increased receptor expression

31
Q

What is the differences between Hypo and Hyperthyroidism?

A

Hypo - not enough thyroid hormone

Hyper - too much thyroid hormone

32
Q

What is atrophy?

A

Body tissue or an organ that waste away - cell degeneration or evolution driving them to be vestigial.

33
Q

What are the different aspects for clinical inspection of a lump?

A
  1. Anatomical position
    1. Size
    2. Shape
    3. Contours (well defined edge or irregular)
    4. Consistency (soft, hard, rubbery etc
    5. Tenderness
    6. What tissue layer it is in - (skin - will move when skin is moved, subcutaneous tissue- will not move with the skin,
34
Q

What are some common disorders of the thyroid?

A
  1. Hyperthyroidism
    1. Hypothyroidism
    2. Thyroid nodules
    3. Goitre
    4. Graves disease
35
Q

How would a person present with hyperthyroidism?

A 
Fatigue
Heart palpitations
Heat intolerance
Sweating
Weight loss
Etc
36
Q

What is biological issue with hyperthyroidism?

A
  1. Too much thyroid hormones
37
Q

What is some of the causes of too much thyroid hormone (hyperthyroidism)?

A
  1. Graves disease- B cells produce antibodies against thyroid proteins - they then bind to the TSH receptors on the follicular cells in the thyroid to imitate TSH - causing a high level of T3/T4.
    1. Toxic nodular goiter- follicles generate lots of TSH- usually from a mutated TSH receptor that keeps follicles active.
    2. Hyperfunctioning Thyroid adenoma- benign tumour - produces excess thyroid hormones.
38
Q

What is the biological issue with hypothyroidism?

A
  1. Too little thyroid hormone
39
Q

What is some of the causes of too little thyroid hormone (hypothyroidism)?

A
  1. Autoimmune (Hashimotos thyroiditis) - damage thyroids ability to produce T3/T4
    1. Thyroid surgery - removal of all or part of the thyroid gland.
    2. Medications - (eg lithium for depression)
    3. Iodine deficiency- needed for production of hormone- will cause goiter.
40
Q

What is the biological cause of thyroid nodules?

A

Lots of causes - iodine deficiency, cancer, cyst, inflammation of the thyroid.

41
Q

What are the biological causes of goitre?

A
  1. Iodine deficiency - hyperplasia in an effort to obtain more iodine.
    1. Graves disease- (overactive thyroid) increased stimulation of thyroid cells - gland swells as it produces more T3/T4
    2. Hashimotos disease- (underactive thyroid)- thyroid cannot produce enough T3/T4- causes increased levels of TSH- TSH stimulated thyroid - thyroid grows even though not producing.
    3. Cancer
    4. Inflammation
    5. Nodules
    6. Pregnancy- Human growth hormone can cause thyroid gland enlargement.
42
Q

What is the biological cause of Graves disease?

A

Auto immune- antibodies bind to TSH receptors and mimic TSH - causing overstimulation - lots of T3/T4 and hyperplasia of the thyroid.

43
Q

What are some physical signs of hyperthyroidism?

A
  1. Goiter
    1. Weight loss
    2. Sweating
    3. Heat intolerance
    4. Tachycardic
    5. Anxiety
    6. Tremors
44
Q

What are some physical signs of hypothyroidism?

A
  1. Goiter
    1. Weight gain
    2. Dry skin
    3. Cold sensitivity
    4. Bradycardia
  2. Muscle weakness
45
Q

What is the mechanism of action for carbimazole?

A
  1. A HYPERTHYROID MEDICATION
    1. Pro-drug –> converted to methimazole
    2. Prevents thyroid peroxidase enzyme from coupling and iodinating tyrosine residues
    3. Hence reduces the production of thyroid hormones T3/T4
46
Q

What is the mechanism of action for propylthiouracil?

A
  1. inhibits iodine and peroxidase from their normal interactions with thyroglobulin to form T4 and T3.
    1. This action decreases production of thyroid hormone.
    2. Cn also reduce the peripheral conversion of T4 to T3
47
Q

Why are carbimazole and propylthiouracil similar?

A

They both lower amounts of T3/T4 (used for hyperthyroidism)

48
Q

What is the significance of high TSH and low-normal FT4/FT3?

A

Mild- Hypothyroidism

49
Q

What is the significance of low TSH and High-normal FT4/FT3?

A

Mild-Hyperthyroidism

50
Q

What is the significance of Low TSH and low FT4/FT3?

A

Rare pituitary hypothyroidism. - issue with anterior pituitary

51
Q

What are the significance of thyroid antibodies present in the blood?

A

Suggests autoimmune thyroid involvement

52
Q

What is the significance of no thyroid antibodies present in blood?

A

Non autoimmune cause.

53
Q

What is thyroid scintigraphy and how does it work?

A

Thyroid scintigraphy is a nuclear medicine procedure that produces a visual display of functional thyroid tissue based on the selective uptake of various radionuclides by thyroid tissue. (usually labelling iodine is used)

54
Q

How can thyroid scintigraphy distinguish between common causes of hyperthyroidism?

A
  1. Can determine functional level of thyroid tissue
    1. The presence of hot (autonomous function) warm normal function and cold (low function) nodules.
    2. Can also be used to detect cancers they are not usually hot (most likely cold and warm)
55
Q

What are the most common nutritional deficits globally?

A 
Iron
B12 deficiency 
Vitamin A
Zinc
Iodine
56
Q

Where is iodine deficiency a risk across the world?

A

Low income countries

Particularly in Sudan etc

57
Q

What are the main sources of iodine in an Australian diet?

A
  1. Seafood
    1. Iodised table salt
    2. Bread
    3. Some plants and vegetables (depending on soil)
    4. Dairy
    5. Eggs
58
Q

How has iodized salt impacted on thyroid disease?

A

Its increased spread worldwide has reduced the prevalence of hypothyroidism.

JMP Semester 2 (8 decks)

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