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Metabolism, Endocrinology and Haematology > Session 10- The Thyroid Gland > Flashcards

Session 10- The Thyroid Gland Flashcards

1
Q

Where is the thyroid

A

Lies against and around the front larynx and trachea

Below thyroid cartilage

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2
Q

What joins the two lobes of the thyroid

A

Isthmus

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3
Q

When does the thyroid gland appear

A

3-4 gestation it appears as an epithelial proliferation in the floor of pharynx at the base of the tongue

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4
Q

What are follicles filled with

A

Colloid- a deposit of thyroglobulin

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5
Q

How are thyroid hormones formed

A

2 tyrosines linked together with iodine at three or 4 positions on the aromatic rings

3- T3
4- T4

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6
Q

What is T3

A

Triiodothyronine

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7
Q

What is T4

A

Tetraiodothyronine

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8
Q

What is the scaffold on which thyroid hormones are. Formed

A

Thyroglobulin

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9
Q

What is thyroid peroxidase

A

Membrane bound enzyme that regulates 3 separate reactions involving iodide
1) Oxidation of Iodide to Iodine (requires the presence of H2O2)

2) Addition of Iodine to tyrosine acceptor residues
on the protein throglobulin

3) Coupling of MIT or DIT to generate thyroid
hormones within the thyroglobulin protein

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10
Q

How is iodine absorbed

A

It is reduced to iodide before absorption principally in the small intestine by a sodium-iodide symporter

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11
Q

How is thyroid hormone secretion regulated

A

Negative feedback

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12
Q

What are the 2 interconnected responses of thyroid hormone

A
  • effects on cellular differentiation and development

- effects on metabolic pathways

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13
Q

What is Thyroid stimulating hormone

A

Glycoprotein hormone composed of 2 non-covalently bound sub-units

Triggers the release of thyroid hormone

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14
Q

What does TSH stimulate

A
  • Iodine uptake
  • iodide oxidation
  • thyroglobulin iodination
  • Thyroglobulin synthesis
  • Colloid pinocytosis into cell
  • proteolysis of thyroglobulin
  • cell metabolism and growth
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15
Q

General actions of thyroid hormone

A
  • increase in basal metabolic rate and heat production.
  • stimulation of metabolic pathway
  • sympathomimetic effects
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16
Q

How does thyroid hormone increase basal metabolic rate and heat production

A

In most tissues (exceptions include brain, spleen and testis), thyroid hormones stimulate the metabolic rate by:
• Increasing the number and size of mitochondria
• Stimulating the synthesis of enzymes in the respiratory chain

17
Q

How does thyroid hormone stimulate metabolic pathways

A

Catabolic pathways are generally stimulated more than anabolic.
• Lipid metabolism: Stimulates lipolysis and b-oxidation of fatty acids
• Carbohydrate metabolism: Stimulate insulin-dependent entry of glucose
into cells and increase gluconeogenesis and glycogenolysis

18
Q

How does thyroid hormone have sympathomimetic effects

A

Increases target cell response to catecholamines by increasing receptor number in target cells

19
Q

Thyroid hormone on CVS

A

Increase CO
Increase HR
Increase force of contraction
Increase peripheral vasodilation

20
Q

Thyroid hormone on nervous system

A

Increase myelination of nerves and development of neurones

21
Q

What type of receptor is the thyroid receptor

A

Nuclear receptor they bind DNA in the absence of hormone usually leading to transcriptional repression.

22
Q

How do thyroid hormones bind fo intracellular receptor

A

It is lipid soluble and enters cell through thyroid hormone transporters

In the cell the thyroid hormones receptor is pre-bound to specif DNA sequences called hormone response elements- HRE in promoter region

Thyroid hormone enters nucleus and relives repression and now gene is now expressed

Expression of new protein

23
Q

What is goitre

A

Enlargement of thyroid gland develops when thyroid gland is overstimulated

Accompanies hypo/hyper thyroidisme

24
Q

What causes hypothyroidism

A
  • failure of thyroid gland
  • TSH or TRH deficiency
  • Inadequate dietary supply of iodine
  • Radioactive iodine
  • Autoimmunity
  • Post surgery
  • congenital
  • anti-thyroid drugs
25
Q

Symptoms of hypothyroidism

A 
Obesity
Lethargy
Intolerance to cold 
Bradycardia 
Dry skin 
Alopecia
Hoarse voice 
Constipation 
Slow reflexes

LOW T4
LOW T3
ELEVATED TSH

26
Q

Cretinism

A

Hypothyroidms in infants

  • dwarfed structure
  • mental deficiency
  • poor bone dev
  • slow pulse
  • muscle weakness
  • GI disturbance
27
Q

Myedema

A

Hypothyroidms in adults

  • thick puffy skin
  • muscle weakness
  • slow speech
  • mental deterioration
  • intolerance to cold
28
Q

Hashimoto disease

A

Autoimmune disease resulting in destruction of thyroid follicles which leads to hypothyroidism

Plasma

  • low T3
  • low T4
  • Elevated TSH
29
Q

Treatment of hypothyroidms

A

Oral thyroid hormone

t4 used

30
Q

Causes of hyperthyroidism

A
  • Autoimmune graves
  • Toxic multinodulad goitre
  • solitary toxic adenoma
  • Excessive T4 or T3 therapy
  • Drugs Mi
31
Q

Symptoms of hyperthyroidism

A

• Weight loss • Irritability • Heat intolerance, sweating
warm vasodilated hands • Tachycardia (noticeable heart beat)
often irregular • Fatigue, weakness • Increased bowel movements
- increased appetite • Possible tremor of outstretched hands • Hyper-reflexive • Breathlessness • Loss of libido • Sweating and tremor

32
Q

What is graves disease

A

Autoimmune disease resulting in hyperthyroidism

Caused by production of thyroid stimulating immunoglobulin

TSI continuously stimulates thyroid hormone secretion outside normal negative feedback control

33
Q

Signs/ Symptoms of graves

A

Increase T3
Increase T4
Very low TSH

Increase in BMR 
Excessive sweating 
Decrease in body weight 
Muscle weakness 
Heart palpitations 
Bulging eyes
34
Q

Thyroid scintigtaphy

A

Technetium-99m used for isotope scanning of the thyroid with a gamma camera

35
Q

Name an anti thyroid drug

A

Carbimazole which prevents thyroid peroxidase from coupling and iodinating tyrosines on thyroglobulin

Metabolism, Endocrinology and Haematology (20 decks)

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