Session 7 Lecture 1

Question 1

Where is the thyroid gland located?

Answer 1

In the neck in front of the lower larynx and upper trachea.

Question 2

What nerves are present near the thyroid?

Answer 2

Two nerve near the thyroid - recurrent laryngeal and external branch of the superior laryngeal nerves

Question 3

Is the thyroid highly vascularised, and if so what arteries/veins are there?

Answer 3

Yes - three arteries supplying it and three veins draining it. Superior, middle and inferior thyroid arteries and veins.

Question 4

Describe the structure of the thyroid

Answer 4

• Butterfly shape with the two lobes joined by isthmus

Question 5

Describe what cartilage surrounds the thyroid

Answer 5

Cricoid cartilage goes all the way round however the thyroid cartilage is just at the front.

Question 6

What is the parathyroid gland?

Answer 6

• Not related to thyroid

- Controls the body’s calcium

Question 7

What is the first endocrine gland to develop?

Answer 7

Thyroid gland

Question 8

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

Answer 8

Follicular cells and parafollicular cells (C-cells)

Question 9

What is the structure of the follicular cells?

Answer 9

• Arranged in spheres calles thyroid follicles

- Lined with cuboidal epithelial cells that surround a central space (lumen) containing colloid

Question 10

What is colloid?

Answer 10

It is rich in protein thyroglobulin. It is ‘extracellular’ even though it is inside the follicle

Question 11

What do thyroid parafollicular cells produce?

Answer 11

Calcitonin

Question 12

What are the main cells in the parathyroid?

Answer 12

Chief cells

Question 13

What do the chief cells of the parathyroid gland produce?

Answer 13

Parathyroid hormone

Question 14

How can we get cells from both parathyroid gland and thyroid gland in the same histological section?

Answer 14

Take a section through the thyroid gland in the location of one of the parathyroid glands

Question 15

What hormones does the thyroid gland produce?

Answer 15

Thyroxine (T4) and triiodothyronine (T3) produced in follicular cells and calcitonin produced by parafollicular cells.

Question 16

What is calcitonin?

Answer 16

Polypeptide hormones involved in calcium metabolism

Question 17

What is the basic structure of T3 and T4?

Answer 17

• Small molecules

- Derived from the amino acid tyrosine with the addition of atoms of iodine

Question 18

What is a MIT?

Answer 18

• Monoiodotyrosine

- Tyrosine residue with only one iodine attached

Question 19

What is DIT?

Answer 19

• Diiodotyrosine

- Tyrosine residue with two iodines attached to

Question 20

What is T3 made of?

Answer 20

Coupling of MIT and DIT

Question 21

What is T4 made of?

Answer 21

Coupling of DIT and DIT

Question 22

What is thyroglobulin?

Answer 22

It is a protein that acts as a scaffold on which thyroid hormones are formed.

Question 23

What is thyroglobulin rich in?

Answer 23

Rich in tyrosine residues

Question 24

Why is it important that thyroglobulin is rich in tyrosine residues?

Answer 24

• Tyrosine residues can be iodinated in the colloid
• Coupling occurs to form T3 and T4
• These remain linked to the thyroglobulin protein

Question 25

How are T3 and T4 released from the thyroglobulin protein?

Answer 25

Proteolytic cleavage occurs

Question 26

What is na essential in thyroid synthesis?

Answer 26

Conversion of iodide ions to the oxidised form of iodine

Question 27

What is thyroid peroxidase?

Answer 27

Membrane bound enzyme that regulates 3 separate reactions involving iodide

Question 28

What three reactions does thyroid peroxidase regulate/

Answer 28

- Oxidation - Addition of iodine - Coupling of MIT or DIT

Question 29

What does the oxidation of iodide ions to iodine require?

Answer 29

Enzyme - thyroid peroxidase | Hydrogen peroxide which provides a potent system

Question 30

What happens to dietary iodine before absorption?

Answer 30

It is reduced to iodide

Question 31

What thyroid hormone is most secreted?

Answer 31

90% of thyroid hormone secreted T4

Question 32

Which thyroid hormone is the most biologically active?

Answer 32

T3

Question 33

What happens to most of the T4 and where does this happen?

Answer 33

Most T4 converted to T3 in the liver & kidneys

Question 34

How are T3 and T4 transposed in the blood?

Answer 34

Whilst being bound to the protein thyroxine-binding globulin - when bound, not biologically active

Question 35

How is thyroid hormone regulated?

Answer 35

Hypothalamus pituitary axis (via negative feedback)

Question 36

What responses to the thyroid hormones have?

Answer 36

- Effects on cellular differentiation and development | - Effects on metabolic pathways

Question 37

What happens when thyroid levels drop too low?

Answer 37

Hypothalamus secretes TRH which stimulates TSH secretion. This causes the thyroid gland to secrete more thyroid hormone

Question 38

What is TSH?

Answer 38

Thyroid stimulating hormone

Question 39

What is the structure of TSH?

Answer 39

Glycoprotein hormone composed of 2 non covalently bound subunits (a and b)

Question 40

What is special about the beta subunits of TSH?

Answer 40

They are unique to the TSH whilst the same alpha subunit is present in FSH and LH.

Question 41

What are the general actions of thyroid hormone?

Answer 41

- Increase in basal metabolic rate and heat production - Stimulation of metabolic pathways - Sympathomimetic effects

Question 42

How do thyroid hormones stimulate the metabolic rate?

Answer 42

- Increasing number and size of mitochondria | - Stimulating the synthesis of enzymes in the respiratory chain

Question 43

What type of metabolic pathway is stimulated more by the thyroid hormone?

Answer 43

Catabolic pathways are generally stimulated more than anabolic

Question 44

What sympathomimetic effects does the thyroid hormones have?

Answer 44

Increases target cell response to catecholamines by increasing receptor number on target cells.

Question 45

What systems can be affected by thyroid hormone?

Answer 45

Cardiovascular system and nervous system

Question 46

What tissue specific effect does the thyroid hormone have in the cardiovascular system?

Answer 46

Increased heart's responsiveness to catecholamines which inc CO and inc peripheral vasodilation to carry extra heat to body surface

Question 47

What tissue specific effect doe thyroid hormone have in the nervous system?

Answer 47

Thyroid hormone increases myelination of nerves and development of neurones

Question 48

What type of receptors are thyroid hormone receptors?

Answer 48

Nuclear receptors

Question 49

What are nuclear receptors?

Answer 49

Class of proteins found within the cells and not on the cell surface membrane.