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MEH A > Session 7 Lecture 1 > Flashcards

Session 7 Lecture 1 Flashcards

1
Q

Where is the thyroid gland located?

A

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

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2
Q

What nerves are present near the thyroid?

A

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

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3
Q

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

A

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

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4
Q

Describe the structure of the thyroid

A
  • Butterfly shape with the two lobes joined by isthmus
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5
Q

Describe what cartilage surrounds the thyroid

A

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

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6
Q

What is the parathyroid gland?

A
  • Not related to thyroid

- Controls the body’s calcium

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7
Q

What is the first endocrine gland to develop?

A

Thyroid gland

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8
Q

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

A

Follicular cells and parafollicular cells (C-cells)

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9
Q

What is the structure of the follicular cells?

A
  • Arranged in spheres calles thyroid follicles

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

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10
Q

What is colloid?

A

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

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11
Q

What do thyroid parafollicular cells produce?

A

Calcitonin

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12
Q

What are the main cells in the parathyroid?

A

Chief cells

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13
Q

What do the chief cells of the parathyroid gland produce?

A

Parathyroid hormone

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14
Q

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

A

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

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15
Q

What hormones does the thyroid gland produce?

A

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

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16
Q

What is calcitonin?

A

Polypeptide hormones involved in calcium metabolism

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17
Q

What is the basic structure of T3 and T4?

A
  • Small molecules

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

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18
Q

What is a MIT?

A
  • Monoiodotyrosine

- Tyrosine residue with only one iodine attached

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19
Q

What is DIT?

A
  • Diiodotyrosine

- Tyrosine residue with two iodines attached to

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20
Q

What is T3 made of?

A

Coupling of MIT and DIT

21
Q

What is T4 made of?

A

Coupling of DIT and DIT

22
Q

What is thyroglobulin?

A

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

23
Q

What is thyroglobulin rich in?

A

Rich in tyrosine residues

24
Q

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

A
  • Tyrosine residues can be iodinated in the colloid
  • Coupling occurs to form T3 and T4
  • These remain linked to the thyroglobulin protein
25
Q

How are T3 and T4 released from the thyroglobulin protein?

A

Proteolytic cleavage occurs

26
Q

What is na essential in thyroid synthesis?

A

Conversion of iodide ions to the oxidised form of iodine

27
Q

What is thyroid peroxidase?

A

Membrane bound enzyme that regulates 3 separate reactions involving iodide

28
Q

What three reactions does thyroid peroxidase regulate/

A
  • Oxidation
  • Addition of iodine
  • Coupling of MIT or DIT
29
Q

What does the oxidation of iodide ions to iodine require?

A

Enzyme - thyroid peroxidase

Hydrogen peroxide which provides a potent system

30
Q

What happens to dietary iodine before absorption?

A

It is reduced to iodide

31
Q

What thyroid hormone is most secreted?

A

90% of thyroid hormone secreted T4

32
Q

Which thyroid hormone is the most biologically active?

A

T3

33
Q

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

A

Most T4 converted to T3 in the liver & kidneys

34
Q

How are T3 and T4 transposed in the blood?

A

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

35
Q

How is thyroid hormone regulated?

A

Hypothalamus pituitary axis (via negative feedback)

36
Q

What responses to the thyroid hormones have?

A
  • Effects on cellular differentiation and development

- Effects on metabolic pathways

37
Q

What happens when thyroid levels drop too low?

A

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

38
Q

What is TSH?

A

Thyroid stimulating hormone

39
Q

What is the structure of TSH?

A

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

40
Q

What is special about the beta subunits of TSH?

A

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

41
Q

What are the general actions of thyroid hormone?

A
  • Increase in basal metabolic rate and heat production
  • Stimulation of metabolic pathways
  • Sympathomimetic effects
42
Q

How do thyroid hormones stimulate the metabolic rate?

A
  • Increasing number and size of mitochondria

- Stimulating the synthesis of enzymes in the respiratory chain

43
Q

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

A

Catabolic pathways are generally stimulated more than anabolic

44
Q

What sympathomimetic effects does the thyroid hormones have?

A

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

45
Q

What systems can be affected by thyroid hormone?

A

Cardiovascular system and nervous system

46
Q

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

A

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

47
Q

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

A

Thyroid hormone increases myelination of nerves and development of neurones

48
Q

What type of receptors are thyroid hormone receptors?

A

Nuclear receptors

49
Q

What are nuclear receptors?

A

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

MEH A (19 decks)

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