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thyroid gland Flashcards

1
Q

Where is the thyroid gland

what is the structure of the thyroid gland?

A
  • adheres to the trachea
  • 2 large asymmetrical lobes connected by isthmus
  • 4 parathyroid glands on back
    • plasma calcium control
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2
Q

what is the thyroid gland controlled by?

A

regulated by the hypothalamus and pituitary gland

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3
Q

blood supply to the thyroid gland

A

rich blood supply

  • Superior and inferior thyroid arteries
  • External carotid branches
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4
Q

histology of thyroid gland

structrue

A

Functional unit = follicle

  • 1000s in each gland
  • Each follicle consists of layer of follicular cells (simple cuboidal epithelial) surrounding a colloid-filled cavity
  • Follicular cells surrounding colloid
  • C cells - involved in calcium regulation
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5
Q

what hormones does the thyroid secrete

where are they produced

A

Triiodothyronine (T3) and thyroxine (T4)

both produced within the follicles

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6
Q

what is the difference between T4 and T3

A
  • T4 contain four atoms of iodide per molecule
  • T3 contains 3 atoms of iodide per molecule
  • T3 has much higher biological activity
    • yet more T4 is secreted by the thyroid
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7
Q

Why is less than 0.5% of T3 and T4 in ‘free form’??

A

they are bound to plasma proteins: thyroxine-binding globuli and albumin

  • prolongs half life
  • keeps them in circulation
  • prevents them from being exctreded immediately
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8
Q

how are T3 and T4 synthesised?

A

requires tyrosines and iodine

  • tyrosines
    • provided by thyroglobulin
      • makes up colloid
    • secreted by follicular cells into lumen of follicle as colloid
  • iodine
    • pumped into follicular cells against concentration gradient
  1. iodine binds to thyroglobulin
  2. becomes iodinated thyroglobulin
  3. lysosomal enzymes cuts up the molecule
  4. ends up with iodinated tyrosine - T3 and T4
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9
Q

what are monoiodotyrosine (MIT) and diiodotyrosine (DIT)

A
  • Two molecules of iodine bind to 1 tyrosine
    • Diiodotyrosine
  • Opposite -
    • Monoiodotyrosine
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10
Q

how do monoiodotyrosine (MIT) and diiodotyrosine (DIT) make up T3 and T4

A

T3 =

  • 1 monoiodotyrosine (MIT) and 1 diiodotyrosine (DIT)

T4 =

  • 2 diiodotyrosine (DIT)
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11
Q

advantages of gaining thyroid hormone from thyroglobulin and iodine

A
  • The thyroid gland is capable of storing many weeks worth of thyroid hormone within the colloid
    • (coupled to thyroglobulin).
  • Iodine can be stored in the form of iodide also
  • If no iodine is available for this period, thyroid hormone secretion will be maintained.
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12
Q

What must occur for thyroid hormone to be made functional?

A

T4 must be converted into T3

peripheral conversion

done in liver and kidneys after being sent out into circulation

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13
Q

what is given to hypothyroid individuals and why?

A

T4

is then converted into T3

T3 is not given as it is not stable enough to be given as a tablet

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14
Q

effects of thyroid hormone

A
  • Calorigenesis
  • Growth & maturation rate
  • C.N.S. Development & function
  • CHO, fat & protein metabolism
  • Muscle metabolism
  • Electrolyte balance
  • Vitamin metabolism
  • Cardiovascular system
  • Hematopoietic system
  • Gastrointestinal system
  • Pregnancy
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15
Q

principal actions of thyroid hormones

A

Metabolism:

  • Increases mobilization and utilisation of glucose, fat, protein

Heat production (calorigenic effect)

  • Important in temperature regulation and adaptation to cold environments
  • Often those with hypothyroidism
    • Feel cold - cannot regulate temperature well

Growth & Development

  • Essential for normal growth of tissues, including CNS
  • Synergy with growth hormone
  • Thyroid hormone deficiencies can result in mental impairment and short stature

Cardiovascular function

  • Increased cardiac output, heart rate and contractility
  • Increases ventilation rateHypothyroid individuals
    • Low heartrate
  • Hyperthyroid individuals
    • Higher heartrate
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16
Q

draw negative feedback loop of thyroid hormones

A

TRH - thyrotropin releasing hormone

TSH - thyroid stimulating hormone

17
Q

How does TSH affect thyroid function

A
  • including promoting the release of thyroid hormones into blood stream,
  • increasing the activity of the iodide pump and iodination of tyrosine
    • to increase production of thyroid hormones
18
Q

symptoms of hypothyroidism

A
  • Dry, cold skin
  • Sensitivity to cold
  • Weight gain despite loss of appetite
  • Impaired memory
  • Mental dullness
  • Lethargy
  • Myxedema:
    • cutaneous and dermal oedema secondary to increased deposition of connective tissue components
    • Excess fluid tissue under eye
      • Excess GAG deposition
19
Q

how could you tell from a clinical exam that someone has hypothyroidism

A
  • Reduced metabolic rate
  • Slow pulse
  • Reduced cardiac output
20
Q

how would you diagnose someone who has hypothyroidism

A

Low plasma levels of ‘free’ T3 and T4

21
Q

how would you treat hypothyroidism

A

Thyroxine

  • Dose determined by TSH monitoring
    • Individuals with hypothyroidism have increased TSH levels
    • Excess TSH trying to stimulate thyroid gland
    • TSH levels should decrease after supplementations of thyroxine
22
Q

causes of hypothyroidism

A
  • Iodine deficiency
    • Endemic goitre
  • Autoimmune disease
    • Hashimoto’s thyroiditis
  • Others:
    • Congenital
    • Post radiation / surgery
    • Medication
    • stress
23
Q

what is endemic goitre?

what is the treatment?

A
  • iodine deficiency
  • insufficient dietary iodine
  • insufficient T3 and T4
  • Reduction in negative feedback of TSH by the pituitary
    • Abnormally high TSH
  • Abnormal growth of the thyroid due to the trophic effects of TSH
    • Enlarged thyroid gland
  • Treatment
    • Iodine supplements
    • Thyroxine to reduced TSH levels
24
Q

what is hashimoto’s disease

A
  • Most common cause of hypothyroidism
  • Autoimmune disease
    • Antibodies against TSH receptor (in the thyroid gland)
    • Prevents TSH binding its receptor
    • Prevents stimulation to T3 & T4
    • Antibodies also against thyroid peroxidase & thyroglobulin
  • Leads to thyroid gland destruction
  • TSH is being produced normally
    • Receptor is attacked so cannot bind
    • Less T3 & T4 production
25
Q

how is critinism - babies with low levels of thyroid hormones - tested for and treated

A
  • Heel prick test - to test levels of plasma proteins, thyroid hormones
  • Supplementation in 3 months can reverse it and benefit
26
Q

what does low levels of thyroid hormones in babies lead to

A

Intellectual disability

Short disproportionate body

Thick tongue and neck

27
Q

common oral findings of hypothyroidism:

A
  • Macroglossia
  • Dysgeusia (abnormal taste)
  • Delayed eruption
  • Poor periodontal health
  • Delay wound healing
28
Q

levels of thyroxine, TSH, TRH in individuals with hypothyroidism :

A

Thyroxine -> Lower

TSH -> Higher

TRH -> Higher

29
Q

symptoms of hyperthyroidism

A
  • Loss of weight
  • Excessive sweating/intolerance to heat
  • Palpitations and an irregular heartbeat
  • Anxiety and nervousness
  • Exopthalamus
30
Q

how could you tell from a clinical examination that someone has hyperthyroidism

A
  • Raised metabolic rate & oxygen consumption
  • Increased heart rate
    • Often high blood pressure also
  • Hypertension
31
Q

what treatments are there for hyperthyroidism

A
  • Surgical removal of all or part of the thyroid
    • Consequences -> permanent hypothyroidism
  • Ingestion of radioactive iodine that selectively destroys the most active thyroid cells
    • Lowers thyroid hormone
  • Drugs that Interfere with the gland’s ability to make T3/T4
32
Q

what causes are there for hyperthyroidism

A

autoimmune diseases.

e.g. Grave’s disease

33
Q

what is Grave’s disease

A

autoimmune disease

  • Autoimmune production of thyroid-stimulating antibody which activates TSH receptor inducing T3/T4 release
    • Antibody mimics TSH
    • Binds to TSH receptor and causes excess release of T3 and T4
    • Not enough feedback to repress release
      • Negative feedback is unable to repress it
  • Characterised by diffuse goitre, exopthalmos and lid retraction
    • Permanent bulging behind the eyes
34
Q

levels of thyroxine, TSH, TRH in individuals with hyperthyroidism :

A

Thyroxine -> Higher

TSH -> Lower

TRH -> Lower

35
Q

common oral findings of hyperthyroidism

A

Particularly radiographic changes

  • Increased susceptibility to caries
  • Periodontal disease
  • Maxillary and Mandibular osteoporosis
  • Accelerated eruption
  • Burning mouth syndrome

z basic sciences (21 decks)

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