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MEH > Session 7 > Flashcards

Session 7 Flashcards

1
Q

Where is the thyroid gland located?

A

Against and around the front larynx and trachea
Below thyroid cartilage
Just above the suprasternal notch

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2
Q

The thyroid gland lies against and around the front __________ and ___________

A

Larynx

Trachea

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3
Q

The thyroid gland is located below the…

A

Thyroid cartilage

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4
Q

The thyroid gland is located just above the…

A

Suprasternal notch

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5
Q

The thyroid gland consists of 2 lobes joined by…

A

Isthmus

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6
Q

The thyroid gland has which rough shape?

A

Bow tie shape

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7
Q

Are the parathyroid and thyroid glands the same?

A

No, two distinct glands

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8
Q

The isthmus extends from which rings of the trachea?

A

From the 2nd to the 3rd rings of the trachea

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9
Q

What is the first endocrine gland to develop?

A

Thyroid gland

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10
Q

When does the thyroid gland first appear during embryological development?

A

3-4 weeks gestation

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11
Q

How does the thyroid gland first appear (at 3-4 weeks gestation)?

A

An epithelial proliferation in the floor of the pharynx at the base of the tongue

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12
Q

How does the thyroid gland develop from being an epithelial proliferation in the floor of the pharynx at the base of the tongue (at 3-4 weeks gestation) to its final position?

A

Descends as diverticulum through the thyroglossal duct and migrates downwards in front of the hyoid bone. Connection to the tongue by the thyroglossal duct degenerates and detached thyroid continues to its final position over the following two weeks.

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13
Q

During embryological development, the thyroid gland descends as _____________ through the __________________ duct and migrates downwards in front of the __________ bone

A

Diverticulum

Thyroglossal

Hyoid

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14
Q

Describe the histology of thyroid tissue

A

Follicular cells arranged in spheres called thyroid follicles

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15
Q

In the thyroid gland, thyroid follicles (formed from follicular cells arranged in spheres) contain…

A

Colloid

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16
Q

What is colloid? Where is it found? Is it extracellular or intracellular?

A

Deposits of thyroglobulin

In thyroid follicles

Extracellular (but within thyroid follicles)

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17
Q

Are the thyroid and parathyroid glands distinct glands?

A

Yes

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18
Q

Describe the cells of the parathyroid gland and the hormone they produce

A

Principal cells produce parathyroid hormone

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19
Q

Which cells produce parathyroid hormone in the parathyroid gland?

A

Principal cells

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20
Q

What hormone is released from the principal cells of the parathyroid gland?

A

Parathyroid hormone

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21
Q

What two types of cells are found in the thyroid gland?

A

Follicular cells

Parafollicular cells

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22
Q

Thyroid follicular cells in the thyroid gland produce…

A

Thyroid hormone

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23
Q

Thyroid parafollicular cells produce…

A

Calcitonin

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24
Q

Colloid in the thyroid gland follicles stores…

A

Thyroglobulin

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25
Q

Describe the general structure of thyroid hormones

A

Two tyrosine linked together + iodine at three (T3) or four (T4) positions on the aromatic rings

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26
Q

T3 is also known as…

A

Triiodothyronine

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27
Q

From which molecules is T3 (triiodothyronine) formed?

A

From MIT + DIT

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28
Q

From which molecules is T4 (thyroxine) formed?

A

DIT + DIT

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29
Q

What is another name for T4?

A

Thyroxine

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30
Q

What is the function of thyroglobulin in the thyroid gland? What does it contain?

A

Acts as a scaffold on which thyroid hormones are formed

Tyrosine residues

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31
Q

What two processes occur on thyroglobulin?

A

Iodination and coupling

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32
Q

What is thyroid peroxidase?

A

Membrane bound enzyme that regulates three separate iodine involving reactions

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33
Q

Which enzyme in the thyroid gland regulates iodine involving reactions?

A

Thyroid peroxidase

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34
Q

Name three functions of thyroid peroxidase

A

Oxidation of iodide to iodine
Addition of iodine to tyrosine acceptor residues on thyroglobulin
Coupling of MIT or DIT to generate thyroid hormones on the thyroglobulin

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35
Q

The oxidation of iodide to iodine by thyroid peroxidase requires…

A

Hydrogen peroxide

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36
Q

Name some common dietary sources of iodine

A

Dairy products
Grains
Meat
Eggs

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37
Q

What happens to dietary iodine consumed in the diet? Where is it absorbed?

A

Reduced to iodide before absorption

Mainly in small intestine

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38
Q

Nearly all the iodine in the body is found in the…

A

Thyroid gland

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39
Q

How is iodide taken up from the blood into the thyroid gland?

A

By thyroid epithelial cells using a sodium-iodide symporter

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40
Q

Which transporter on thyroid epithelial cells takes up iodide from the blood?

A

Sodium-iodide symporter

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41
Q

Name the three main processes involved in thyroid hormone synthesis

A

Iodide oxidation
Iodination of tyrosine acceptor residues on thyroglobulin
Coupling of DIT with DIT (T4) (or MIT with DIT - T3)

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42
Q

Most of the thyroid hormone secreted is…

A

T4

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43
Q

Does T3 or T4 have greater biological activity?

A

T3 (up to 4x greater)

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44
Q

Most T4 is converted to T3 in the…

A

Liver and kidneys

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45
Q

Both T3 and T4 are transported in the blood bound to…

A

Thyroxine-binding globulin

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46
Q

Regulation of thyroid hormone secretion is via ___________ feedback

A

Negative

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47
Q

Thyroid cells affect which cells in the body?

A

Virtually every cell in the body

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48
Q

What effect do thyroid hormones have on the cells of the body? (2)

A

Effects on cellular differentiation/development

Effects on metabolic pathways

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49
Q

Describe the structure of thyroid stimulating hormone

A

Glycoprotein hormone composed of 2 non-covalently bound subunits (alpha and beta)

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50
Q

Which subunit of thyroid stimulating hormone provides its unique biological activity?

A

Beta subunit

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51
Q

Which hormone is the trigger for thyroid hormone release? Where is it released?

A

Thyroid stimulating hormone

Anterior pituitary

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52
Q

Which hormone triggers the release of thyroid stimulating hormone from the anterior pituitary? Where is this hormone released?

A

Thyrotropin releasing hormone

Hypothalamus

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53
Q

TSH specifically stimulates… (5)

A 
Iodide uptake/oxidation 
Thyroglobulin synthesis/iodination 
Colloid pinocytosis into cell
Cell metabolism and growth 
Proteolysis of thyroglobulin
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54
Q

TSH can couple to which GPCRs?

A

G-alphaQ

G-alphaS

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55
Q

Activation of GalphaQ GPCRs results in increased activity of… and production of…

Activation of GalphaS GPCRs results in increased activity of… and production of…

A

Phospholipase C —> DAG + IP3

Adenylyl cyclase —> cAMP

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56
Q

cAMP activates which late effector?

A

Protein kinase A

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57
Q

Name three general actions of thyroid hormone

A

Increase in basal metabolic rate and heat production

Stimulation of metabolic pathways

Sympathomimetic effects

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58
Q

Thyroid hormone results in an increase in basal metabolic rate and heat production in most parts of the body but excluding the… (3)

A

Brain
Spleen
Testis

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59
Q

How does thyroid hormone result in an increase basal metabolic rate/heat production? (2)

A

Increases number/size of mitochondria

Stimulates the synthesis of enzymes in the respiratory chain

60
Q

Does thyroid hormone generally stimulate catabolic or anabolic metabolic pathways more?

A

More catabolic pathways

61
Q

Give two examples of metabolic pathways that can be affected by thyroid hormone

A 
Lipid metabolism (increased lipolysis/b-oxidation)
Carbohydrate metabolism (increased gluconeogenesis/glycogenolysis
62
Q

Describe the sympathomimetic effects of thyroid hormone

A

Can increase target cell response to catecholamines by increasing receptor number on target cells

63
Q

How can thyroid hormones increase target cell response to catecholamines?

A

By increasing receptor number on target cells

64
Q

Describe the specific effect that thyroid hormone can have on the CVS

A

Increases the heart responsiveness to catecholamines

  • –> Increasing cardiac output (increased HR/force of contraction)
  • –> Increasing peripheral vasodilation
65
Q

What essential function does thyroid hormone have in the nervous system?

A

Increases myelination of nerves and development of neurones

66
Q

What type of receptors does thyroid hormone bind to?

A

Intracellular nuclear receptors

67
Q

TH receptors are effectively hormone activated transcription factors, what is meant by this?

A

They modulate gene expression

68
Q

How do TH receptors affect gene transcription in the absence of thyroid hormone?

A

TH receptors bind DNA and repress transcription

69
Q

What happens to the thyroid hormone receptor and gene transcription upon binding of thyroid hormone?

A

Conformational change of TH receptor

Gene transcription activated

70
Q

Thyroid hormone is _________ soluble and enters the cell through which transporters?

A

Lipid soluble

Thyroid hormone transporters

71
Q

Thyroid hormone receptor is pre-bound to specific DNA sequences on DNA called…

A

Hormone response elements

72
Q

What are hormone response elements? Where are they found?

A

The specific DNA sequences where thyroid hormone receptor is pre-bound

In the promoter region of thyroid hormone regulated genes

73
Q

Give two examples of thyroid hormone activated genes

A

PEPCK
Ca ATPase
Na/K ATPase

74
Q

What is RXR and its function?

A

Retinoid X receptor

Forms dimer with thyroid hormone receptor

75
Q

What are the normal plasma levels of…

I) Free T4
II) Free T3
III) TSH

… in SI units

A

10-25 pM

3-8 pM

1-15 pM

76
Q

What is goitre?

A

Enlargement of the thyroid gland

77
Q

Goitre may accompany either _________________ or ______________

A

Hypothyroidism

Hyperthyroidism

78
Q

Is goitre always present in hyper/hypo-thyroidism?

A

Not always present in either

79
Q

When does goitre develop?

A

When the thyroid gland is overstimulated

80
Q

Describe the levels of T3, T4 and TSH seen in hypothyroidism

A

Low T3
Low T4
High TSH

81
Q

State some potential causes of hypothyroidism

A 
Failure of thyroid gland 
TSH/TRH deficiency 
Inadequate dietary supply of iodine 
Autoimmune disease 
Anti-thyroid drugs 
Post surgery
82
Q

Describe some general symptoms seen in hypothyroidism

A 
Obesity 
Lethargy 
Intolerance to cold 
Bradycardia 
Dry skin 
Alopecia
Hoarse voice
Constipation 
Slow reflexes
83
Q

Hypothyroidism can cause _____________ in infants and _____________ in adults

A

Cretinism

Myxedema

84
Q

Describe what happens in cretinism

A

Severely stunted physical/mental growth due to deficiency of thyroid hormone (hypothyroidism)

85
Q

Myxedema is synonymous with which term?

A

Severe hypothyroidism

86
Q

What is Hashimoto’s disease?

A

Autoimmune disease resulting in destruction of thyroid follicles leading to hypothyroidism

87
Q

Describe the levels of T3, T4 and TSH seen in Hashimoto’s disease

A

Low T3
Low T4
High TSH

88
Q

Is Hashimoto’s disease more common in men or women?

A

Women

89
Q

What is the treatment for Hashimoto’s disease?

A

Oral thyroid hormone (T4)

90
Q

What is the most common cause of hyperthyroidism?

A

Autoimmune Graves’ disease

91
Q

Excluding Graves’ disease, name two other potential causes of hyperthyroidism

A

Toxic multinodular goitre

Thyroid carcinoma

92
Q

Bulging eyes may be seen in some cases of hyperthyroidism or hypothyroidism?

A

Hyperthyroidism

93
Q

Describe some general symptoms of hyperthyroidism

A 
Weight loss
Irritability 
Heat intolerance
Sweaty, Warm Hands 
Tachycardia 
Fatigue 
Increased appetite
94
Q

What is Graves’ disease?

A

An autoimmune disease resulting in hyperthyroidism

95
Q

What causes Graves’ disease?

A

The production of thyroid stimulating immunoglobulin

96
Q

TSI is produced in Graves’ disease, how does it result in hyperthyroidism?

A

TSI continually stimulates thyroid hormone secretion outside normal negative feedback control

97
Q

Describe the levels of T3, T4 and TSH seen in Graves’ disease

A

High T3
High T4
Very Low TSH

98
Q

What effect can Graves’ disease have on BMR?

A

Increase in BMR

99
Q

What nuclear medicine procedure is used to show functional thyroid tissue?

A

Thyroid scintigraphy

100
Q

What material is used for the isotope scanning of the thyroid in a thyroid scintigraphy?

A

Technetium-99m

101
Q

Describe the half life of technetium-99m. What are the implications of this?

A

Short half life - ~1/2 day

Low radiation exposure

102
Q

What is more commonly used to scan the thyroid rather than thyroid scintigraphy?

A

Ultrasound

103
Q

What are antithyroid drugs used to treat?

A

Hyperthyroidism

104
Q

How do antithyroid drugs work?

A

Block the formation of thyroid hormone

105
Q

What is the most common antithyroid drug?

A

Carbimazole

106
Q

How does carbimazole work as an antithyroid drug?

A

Converted to methimazole in the body. Prevents thyroid peroxidase action.

107
Q

What is carbimazole converted to in the body?

A

Methimazole

108
Q

How would you carry out a thyroid examination?

A

Stand and feel around the thyroid area from behind the patient

109
Q

What does a normal thyroid gland feel like on examination?

A

Not possible to feel a normal thyroid gland

110
Q

What structure attaches the thyroid gland to the trachea/larynx? What implications does this have on the thyroid during swallowing?

A

Pre-tracheal fascia

Moves upwards on swallowing

111
Q

What is the most common way to examine the thyroid?

A

By ultrasound

112
Q

What is a lingual thyroid? Where is it found? What causes it?

A

A type of ectopic thyroid

Mainly in the tongue

Lack of normal caudal migration of the thyroid gland

113
Q

What happens in a thyroglossal duct cyst?

A

Remnants of the thyroglossal duct that connects the tongue to the thyroid during embryonic development remain and form a cyst near/within the body of the hyoid

114
Q

Where is a thyroglossal duct cyst normally found? What swelling does it cause?

A

Near/within the body of the hyoid

Swelling in the anterior of the neck - ON THE MIDLINE

115
Q

Thyroglossal duct cysts can form a swelling in the anterior of the neck which is always…

A

ON THE MIDLINE OF THE NECK

116
Q

What can cause upwards movement of a thyroglossal duct cyst?

A

Tongue protrusion

117
Q

Is it common for a pituitary adenoma to produce TSH and lead to thyrotoxicosis?

A

No - extremely rare

118
Q

What is an adenoma?

A

A benign tumour of glandular epithelial tissue

119
Q

What is hyperthyroidism?

What is thyrotoxicosis?

A

Over-activity of the thyroid gland (source is thyroid)

Too much thyroid-like activity (e.g. Hyperthyroidism, Thyroxine Tablets)

120
Q

The vast majority of hypo- and hyperthyroidism is due to a primary abnormality of the ______________ __________ itself

A

Thyroid gland

121
Q

Describe the free T4 and TSH levels seen in…

I) hyperthyroidism
II) hypothyroidism

A

High T4, Low TSH

Low T4, High TSH

122
Q

Autoimmune endocrine diseases are generally more common in…

A

Women

123
Q

Name an autoimmune condition of the Islets of Langerhans of the pancreas

A

Type 1 Diabetes

124
Q

What is the name given to the autoimmune disease causing…

I) hyperthyroidism
II) hypothyroidism

A

Graves’ disease

Hashimoto’s disease

125
Q

What is the name given to autoimmune disease of the adrenal glands?

A

Addison’s disease

126
Q

Describe three different types of goitre

A

Diffuse
Multinodular
Single nodule

127
Q

When can goitre occur with normal thyroid function?

A

In women during pregnancy/menopause/menarche

128
Q

What are the two most commonest causes of goitre? Which is the most common cause globally and in the UK?

A 
Iodine deficiency (Global)
Multinodular goitre (UK)
129
Q

How can iodine deficiency lead to goitre?

A

Reduced thyroxine levels —> Increased TSH —> Generalised thyroid enlargement (Goitre)

130
Q

Describe the thyroid function status usually seen in multinodular goitre

A

Normal thyroid function

131
Q

Iodine deficiency is particularly concerning during…

A

Pregnancy

132
Q

An iodine deficient mother in pregnancy will result in an iodine deficient foetus. What can this result in?

A

Cretinism in the child.

Mental retardation
Abnormal gait
Deaf mutism
Short stature

133
Q

What is a retrosternal multinodular goitre? What can it cause?

A

A multinodular goitre that enlarges inferiorly into the superior mediastinum

Tracheal compression

134
Q

Describe the specific hair loss that may be seen in hypothyroidism

A

Loss of the hair on the outer third of the eyebrows

135
Q

State three potential causes of hypothyroidism

A

Autoimmune destruction of thyroid follicles (Hashimoto’s disease)
Severe iodine deficiency
Post surgical removal of thyroid (with inadequate T4 replacement)

136
Q

What is the normal treatment for hypothyroidism?

A

Oral thyroxine (T4)

137
Q

State three potential causes of hyperthyroidism/thyrotoxicosis

A

Graves’ disease
Toxic multinodular goitre
Toxic adenoma

138
Q

State two unique symptoms/features of hyperthyroidism due to Graves’ disease

A

Exophthalmos

Pre-tibial myxoedema

139
Q

What is exophthalmos?

A

Bulging eyes

140
Q

What is the usual treatment for hypothyroidism/thyrotoxicosis?

A

Carbimazole (anti-thyroid drug)

141
Q

How does carbimazole work as an anti-thyroid drug?

A

Converted to methimazole in the body and blocks action of thyroid peroxidase reducing the production of thyroxine

142
Q

Other than anti-thyroid drugs (e.g. Carbimazole) what other treatments are there for hyperthyroidism/thyrotoxicosis?

A

Surgical excision of thyroid - thyroidectomy

143
Q

How does thyroid cancer present? Are they usually malignant?

A

As a thyroid nodule

No very rarely malignant

144
Q

Do thyroid cancers cause hypo/hyper-thyroidism?

A

No

145
Q

Describe the prognosis for thyroid cancer

A

Excellent prognosis - very high cure rate

MEH (9 decks)

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