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METABOLISM, ENDOCRINOLOGY AND HAEMATOLOGY > Thyroid gland > Flashcards

Thyroid gland Flashcards

1
Q

Where is the thyroid gland found?

A

Neck - front lower larynx and upper trachea

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2
Q

What is the isthmus?

A

Part of the thyroid gland that connects the two lobes

  • Narrower than each lobe which contributes to the bow tie shape
  • Extends from the 2nd to 3rd rings of trachea
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3
Q

What are the 2 nerves near thyroid gland and what are they involved in?

A
  • Recurrent laryngeal
  • External branch of the superior laryngeal

-Speech

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4
Q

Describe the embryological development of the thyroid gland

A

-First endocrine gland to develop

1) Epithelial proliferation in floor of pharynx at the base of tongue
2) Descends as diverticulum through thyroglossal duct and migrates down
3) thyroglossal duct degenerates and detaches, further migrating to final position

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5
Q

What are the two major cell types in the thyroid gland?

A
  • Follicular cells

- Parafollicular (C-cells)

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6
Q

How are follicular cells arranged?

A

functional unit : follicle

-spherical lined with epithelial cells surrounding a central lumen containing colloid

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7
Q

What does colloid mostly consist of?

A

Thyroglobulin

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8
Q

What is the importance of thyroid peroxidase?

A

Membrane bound enzyme that regulates 3 separate reactions for thyroid hormone synthesis

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9
Q

What are the 3 reactions regulated by thyroid peroxidase?

A

1) Oxidation = Iodine to iodide
2) Addition of Iodine = to tyrosine residues
3) Coupling = MIT or DIT to generate thyroid hormone

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10
Q

What does MIT stand for?

A

Monoiodotyrosine

-1 iodide on tyrosine residue

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11
Q

What does DIT stand for?

A

Diiodotyrosine

-2 iodide on tyrosine residue

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12
Q

What is the role of thyroglubilin during thyroid hormone synthesis?

A

Acts as a scaffold for tyrosine residues

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13
Q

What are some sources of dietary iodine?

A
  • Dairy products
  • Grains
  • Vegetables
  • Meat
  • Eggs
  • Iodized salt
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14
Q

Describe how dietary iodine is taken up by the body

A

1) Reduced to iodide
2) Absorbed in small intestine
3) Transported to thyroid epithelial cells through blood
4) Taken up by thyroid epithelial cells via sodium-iodide symporter

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15
Q

Describe the secretion of thyroid hormone from colloid store

A

1) Pinocytosis of thryoglobulin with coupled tyrosine residues(hormone)
2) Lysosymes degrade thyroglobulin
3) Exocytosis of thyroid hormones to blood

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16
Q

Which hormone is secreted more from thyroid glands?

A

T4 (longer half life)

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17
Q

Where is T4 converted to T3 in the body?

A

Liver or kidneys

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18
Q

How is T3 and T4 transported around the body?

A

Thyroxine-binding globulin

not all is bound to it, there are some free

19
Q

By what mechanism is thyroid hormone secretion regulated and name the key players to this

A

Negative feedback

  • TSH acts on hypothalamus (-ve)
  • Thyroid hormone itself acts on anterior and hypothalamus (-ve)
20
Q

What type of receptors are TSH receptors?

A

GPCR
(Alpha s = adenyly cyclase)
(Alpha q = Phospholipase C)

21
Q

What does TSH stimulate?

A
  • Iodide uptake
  • Iodide oxidation
  • Thyroglobulin synthesis
  • Colloid pinocytosis
  • Proteolysis of thyroglobulin
  • Secretion of thyroid hormone

-Has trophic effects (increase size = goitre)

22
Q

What are the general effects of thyroid hormone?

A

1) Increase basal metabolic rate and heat production
2) Stimulation of metabolic pathways
3) Sympathomimetic effects

23
Q

How does thyroid hormone increase basal metabolic rate and heat production?

A

By increasing no. and size of mt and also stimulates synthesis of enzymes in respiratory chain

24
Q

How does thyroid hormone stimulate metabolic pathways?

A

(generally catabolic)

  • Lipid metabolism
  • Carbohydrate metabolism
25
Q

How does thyroid hormone have sympathomimetic effects?

A

Increases receptor no. for catecholamine target cells

26
Q

What are specific tissue effects of thyroid hormones?

A

1) Increase heart response of heart to catecholamines (inc CO)
2) Development and function of nervous system (myelination of nerves)

27
Q

What type of receptors are thyroid hormone receptors and how does it operate?

A

Nuclear receptors

-usually bound to DNA for transcriptional repression when theres no thyroid hormone

28
Q

Give examples of genes activated by thyroid hormone

A
  • PEPCK
  • Ca2+ ATPase
  • Cytochrome oxidase
  • 6-phosphogluconate dehydrogenase
29
Q

What are normal plasma levels for free T4, T3 and TSH?

A 
T4 = 10-25 pM
T3 = 3-8 pM
TSH = 1-15 pM
30
Q

What is goitre?

A

Enlargement of the thyroid gland when its overstimulated

31
Q

What is hypothyroidism and what are the causes?

A

Low levels of thyroid hormones in the body (T3 and T4)

  • Failure of thyroid gland
  • Anti-thyroid drugs
  • TSH/TRH deficiency
  • Inadequate supply of dietary iodine
  • Autoimmune
  • Congenital
  • Post-surgery
32
Q

What are the general symptoms of hypothyroidism?

A
  • Obesity
  • Lethargy
  • Intolerance to cold
  • Bradycardia
  • Alopecia
  • Dry skin
  • Slow reflexes
33
Q

What is cretinism?

A

Condition from hypothyroidism in infants

  • dwarfed structure
  • mental deficiency
  • poor bone development
  • slow pulse
  • muscle weakness
34
Q

What is myxedema?

A

Condition from hypothyroidism in adults

  • Thick puffy skin
  • Muscle weakness
  • Slow speech
  • Mental deterioration
  • Intolerance to cold
35
Q

What would you see to levels of thyroid hormone and TSH of hypothyroidism?

A

Low T4 and T3

High TSH

36
Q

What is Hashimoto’s disease?

A

Autoimmune destruction of thyroid follicles leading to hypothyroidism
-treated by oral thyroid hormone

37
Q

What is hyperthyroidism and what are the causes?

A

High levels of T4 and T3 in the body

  • Toxic multinodular goitre
  • Solitary toxic adenoma
  • Drugs
  • Excessive T4 therapy
  • Ectopic thyroid tissue
  • Autoimmune
38
Q

What are the general symptoms of hyperthyroidism?

A
  • Increased BMR
  • Irritability
  • Heat intolerance
  • Tachycardia
  • Sweating
  • Bulging eyes
  • Increased appetite
  • Fatigue
39
Q

What would you see to levels of thyroid hormone and TSH of hyperthyroidism?

A

High T4 and T3

Low TSH

40
Q

What is Grave’s disease?

A

Autoimmune disease resulting in hyperthyroidism cause by production of thyroid stimulating immunoglobulin

41
Q

What is thyroid scintigraphy and what chemical do they usually use?

A

A procedure to visualise the thyroid gland

-Technetium-99m

42
Q

What are antithyroid drugs and give an example

A

Treatment for hyperthyroidism that blocks thyroid hormone formation
-Carbimazole (pro-drug that is converted to methimazole in the body) prevents thyroid peroxidase from coupling and iodinating tyrosine residues

43
Q

What causes TRH release?

A
  • Stress
  • Decreased temperature (cold)
  • Low thyroid hormones level in the blood
44
Q

How are thyroid disorders assessed?

A
  • Blood count (Thyroid hormones and TSH levels)
  • Neck examination (palpate)
  • Ultrasound
  • Radio-isotope scan
  • Plain X-ray
  • CT scan

METABOLISM, ENDOCRINOLOGY AND HAEMATOLOGY (19 decks)

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