Thyroid Hormones

Question 1

The release of the thyroid hormones starts with the hypothalamus; what does it release?

Answer 1

releases thyrotophin releasing factor straight into the bloodstream

Question 2

Where do the TRH act and what does that cause the release of?

Answer 2

They act on the anterior pituitary which then produces thyroid stimulating hormone (thyrotrophin)

Question 3

What do the TSH act on and what does this cause the release of?

Answer 3

The thyroid gland which releases thyroid hormones (T3 and T4) to target cells throughout the body

Question 4

What kind of glands produce hormones?

Answer 4

Endocrine glands

Question 5

Describe the structure of the thyroid hormones

Answer 5

Two rings linked by an oxygen with a carbon head group and a hydroxyl tail group
The T3 has three I2 groups and the T4 has four

Question 6

The thyroid hormones are zwitterionic; what does this suggest about their hydrophobicity?

Answer 6

They are hydrophillic so will not cross the cell membrane

Question 7

Why would radioactive iodine lead to thyroid cancer and what could be used to treat this?

Answer 7

Since all the iodine you take in from your food is concentrated here to make the T3 and T4 hormones any radioactive iodine would lead to cancer here which can be treated by iodine tablets to compete with the radioactive iodine

Question 8

What does it mean by T3 and T4 have negative feedback?

Answer 8

They control how much TRH and TSH (thyrotropin) are released which ultimately controls the the production of the thyroid horomones

Question 9

What do T3 and T4 act on to cause negative feedback?

Answer 9

The anterior pituitary to inhibit TSH and the hypothaamus to inhibit TRH

Question 10

Describe a follicle of the thyroid and its role in synthesis and storage of thyroid horomes?

Answer 10

The follice contains a layer of cells surrounding a colloid filled with fluid.
The thyroid hormones are synthesised in the cells and then stored in the colloid

Question 11

What form is iodine taken up into the cell in and what does that cause the release of to counteract?

Answer 11

Take up as iodide ions and Na+ is released to balance the charge

Question 12

What is the iodide uptake into the follice cell stimulated by?

Answer 12

TSH

Question 13

Once in the follice cell iodide is oxidised to iodine; what enzyme does this?

Answer 13

Peroxidase enzyme

Question 14

Once iodide has been oxidised what happens?

Answer 14

Active transport of iodine into the colloid from the follice cell

Question 15

Once in the colloid what protein is present and what important residues does it contain?

Answer 15

Thryoglobulin which contains tyrosine residues

Question 16

What happens once the iodine is in the colloid and what does it produce?

Answer 16

It is transferred to tyrosine residues to produce mono-iodinated tyrosine (MIT) and di-iodinated tyrosine (DIT)

Question 17

How do MIT and DIT combine to form the thyroid hormones and where are these stored?

Answer 17

One MIT and DIT combine to make T3 whereas two DITs combine to make T4 - they are linked by enzymes
T3 and T4 are then stored on the thyroglobulin in the colloid

Question 18

How does TSH stimulate the release of the hormone?

Answer 18

When blood levels of T3 and T4 are low it stimulates the uptake of thyroglobulin into the follice cells where T3 and T4 are removed and released into the blood

Question 19

What receptors to T3 and T4 then act on? Which form of thyroid hormone is the ligand?

Answer 19

Nuclear receptors that can associate with DNA - T4 is converted into T3 because T3 is the ligand

Question 20

What effects does the T3 binding the nuclear receptor have?

Answer 20

It stimulates mRNA production and therefore protein synthesis

Question 21

Thyroid hormones act on all the cells of the body but what does this effects produced depend on?

Answer 21

The type of cell the thyroid hormones act on

Question 22

What sort of effects do thyroid hormones produce through regulation of the nuclear receptors they act on?

Answer 22

1. Increased metabolism
2. Increased heat production
3. Increased glucose and amino acid uptake
4. Increased number and size of mitochondria

Question 23

What is hypothyroidism?

Answer 23

An autoimmune disease when you have to little thyroid hormone

Question 24

What is hypothyroidism caused by?

Answer 24

The body making antibodies to attack and breakdown the thyroid gland leading to decreased production of thyroid hormones

Question 25

What sort of complications can hypothyroidism lead to?

Answer 25

Mental retardation and dwarfism in infancy and depressed metabolic rate leads patients being irritable/tired with low appetite

Question 26

How can hypothyroidism be treated?

Answer 26

With T4 tablets (thyroxine) which is converted to T3 after 6-8 weeks

Question 27

What is hyperthyroidism?

Answer 27

An autoimmune disease where you have too much thyroid hormones

Question 28

What is hyperthyroidism caused by?

Answer 28

Antibodies bind to TSH receptors meaning TSH is constantly being produced so therefore thyroid hormones are constantly being produced (not negative feedback)

Question 29

What is hyperthyroidism caused by?

Answer 29

Antibodies bind to TSH receptors meaning TSH is constantly being produced so therefore thyroid hormones are constantly being produced (not negative feedback)

Question 30

95% of thyroid hormones are attached to plasma proteins; what is one reason for this?

Answer 30

The elevated levels of thyroid hormones in the blood plasma is what causes the negative feedback of TSH

Question 31

Thyroid hormones can act on B-adrenoreceptors; what does this cause the release of?

Answer 31

Adrenaline

Question 32

What are the symptoms of hyperthyroidism?

Answer 32

Since there are more thyroid hormones the receptors they act on are more stimulated than normal which causes increased metabolism, cardiac output, appetite, patient is nervous

Question 33

Name 4 ways used to treat hyperthyroidism?

Answer 33

1. Surgery
2. Iradation with iodine 131
3. Iodides
4. Drugs which inhibit iodine synthesis

Question 34

Name three examples of drugs that inhibit iodine syntehsis?

Answer 34

Carbimazole, Methimazole, Propylthiouracil

Question 35

How do drugs that inhibit iodine synthesis work?

Answer 35

1. They inhibit the peroxidase enzyme that convers iodine ions to iodine in the follicle cells
2. they inhibit the tyrosine residues of thyroglobulin becoing iodinated
3. they inhibit mit and dit iodinated tyrosine residues of thyroglobulin coming together to form T3 and T4
4. They inhibit the conversion of T3 to T4 in the follice cell