Thyroid Gland

Question 1

How many lobes comprise the thyroid gland?

Answer 1

2

Question 2

What connects the two lobes?

Answer 2

Isthmus

Question 3

What is the pyramidal lobe?

Answer 3

Embryological remnant
Extra lobe
In 20-30% of people

Question 4

What cells make up the thyroid gland?

Answer 4

Follicular cells
Follicles
Parafollicular cells

Question 5

Where are the parathyroid glands?

Answer 5

Embedded in the thyroid

Question 6

Why can surgical procedures on the thyroid be so dangerous?

Answer 6

Near many important structures
e.g. Common Carotid
Internal Jugular

Question 7

Where is the left recurrent laryngeal nerve?

What does it supply?

Answer 7

Runs close to the thyroid
Supplies vocal cords
Damage can interfere with your voice

Question 8

What are the superior and inferior parathyroid glands important in?

Answer 8

Calcium metabolism

Question 9

Describe the embryology of the thyroid gland

Answer 9

Base of the tongue
Thyroglossal duct develops
Divides into 2 lobes
Duct disappears leaving foramen caecum
Final position by week 7 of gestation
Gland then develops

Question 10

What is colloid?

Answer 10

Sticky music found in the middle of the follicle cells

Where thyroid hormone is made

Question 11

How is thyroid hormone made?

Answer 11

TSH secreted from anterior pituitary and binds to TSH Receptor on follicular cell membrane
Arrival of iodide ions, enter follicular cells via Na/I transporter
Iodide enters colloid
Oxidised to make Iodine
TSH activates thyroperoxidase enzyme catalyses (with H2o2) the iodination reactions in colloid
Thyroglobulin (prohormone) produced, has tyrosine residues within its structure
Iodine sticks to tyrosine residues
Produces mono/di iodotyrosine
Couple to give T3 + T4
Bound to thyroglobulin move to follicular cell
Released from thyroglobulin
Released into capillaries

Question 12

What is the chemical name for T3?

Answer 12

3,5,3’-Tri-IodoThyronine

Question 13

What is the chemical name for T4?

Answer 13

3,5,3’,5’-Tetra-IodoThyronine

Question 14

What is T4 more commonly known as?

Answer 14

Thyroxine

Question 15

What is T3?

Answer 15

Bioactive form
Provides almost all activity in target cells
Half life 2 days

Question 16

What are the main features of T4?

Answer 16

Prohormone converted by deiodinase enzyme into the more active metabolite T3
Half life 7-9 days

Question 17

What are the percentages of organ for T3?

Answer 17

80% from deionisation of T4

20% from direct thyroidal secretion

Question 18

How is thyroid transported?

Answer 18

Mostly bound to plasma proteins
1. TBG (Thyroid binding globulin)
2. Albumin
3. Prealbumin
Less than 1% is unbound and active

Question 19

What are their effects on gene expression?

Answer 19

Enter nucleus and binds to THR receptor

Question 20

What are the action of Thyroid hormone?

Answer 20

Foetal growth and development (in particular the CNS)
Increases basal metabolic rate
Protein, carbohydrate and fat metabolism
Potentiate actions of catecholamines (e.g. tachycardia, lipolysis)
Effects on the GI, CNS and Reproductive systems

Question 21

What is cretinism?

Answer 21

Untreated congenital hypothyroidism

Born with no thyroid hormone

Question 22

Why is cretinism not seen much anymore?

Answer 22

Tested for in the heel prick test
Measure TSH levels
If high, baby is not producing enough thyroid hormone

Question 23

What controls thyroid hormone production?

Answer 23

Hypothalamus produces TRH (Thyrotropin releasing hormone)
Enters anterior pituitary
Stimulates thyrotroph cells to release TSH
Enters systemic circulation and arrives at the thyroid
Negative feedback loop

Question 24

What can thyrotropin also be known as?

Answer 24

TSH

Thyroid Stimulating Hormone

Question 25

What can patients with an overactive thyroid be given?

Answer 25

Potassium iodide | Switches of thyroid hormone production

Question 26

What is more common hyper/hypothyroidism?

Answer 26

The same

Question 27

Are men or women more commonly affected?

Answer 27

Women | 4:1

Question 28

What results from hypothyroidism?

Answer 28

Thyroxine levels decline | TSH levels climb- want to stimulate production of T3 and T4

Question 29

What can cause hypothyroidism?

Answer 29

No thyroid gland Autoimmune disorders Hashimoto's and Graves' disease The presence of one autoimmune disease increase the chance of contracting another

Question 30

What are the symptoms/ signs of hypothyroidism?

Answer 30

``` Fatigue Depression Deepening voice Cold intolerance Weight gain with reduced appetite Constipation Bradycardia Eventual myxoedema coma Low libido Period issues ```

Question 31

What is the treatment methods for hypothyroidism?

Answer 31

Levothyroxine | If taken completely restores normal function

Question 32

What is the treatment method for hyperthyroidism?

Answer 32

A blocker is given | Levothyroxine got give normal levels

Question 33

What's the deal with dosing?

Answer 33

Adjusted to TSH (aim to get in normal range) Common does 100 micrograms Most commonly administered orally

Question 34

Potential complications?

Answer 34

Weight loss Headaches Tachycardia Heart Attack

Question 35

What's the deal with combine thyroid hormone replacement?

Answer 35

You do not need T4 | Some reports showing that psychologically people fell better

Question 36

What results from hyperthyroidism?

Answer 36

Thyroxine levels rise | TSH levels drop

Question 37

What can cause hyperthyroidism?

Answer 37

Graves' disease Toxic multi nodular goitre Solitary toxic nodule

Question 38

What are the main features of Graves' disease?

Answer 38

Autoimmune disease Antibodies bind to an stimulate TSH receptor in the thyroid Completely disrupts negative feedback loop - Smooth goitre (diffuse enlargement and engorgement of the thyroid gland) Other antibodies bind to muscle behind the eye can causes bulging (Exopthalmos) Others stimulate growth of soft tissues of shins (Pretibial myxoedma)

Question 39

What are the symptoms and signs of Hyperthyroidism?

Answer 39

``` Heat intolerance Weight loss with increase appetite Myopathy Mood swings Diarrhoea Tremor of hands Palpitations Sore eyes, goitre Tachycardia and arrhythmia High blood pressure ```