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Phase 2 3. Endocrinology > Lab 3 - Thyroid, parathyroid and pituitary glands > Flashcards

Lab 3 - Thyroid, parathyroid and pituitary glands Flashcards

1
Q

What parts make up the pituitary gland?

A
  • adenohypophysis

- neurohypophysis

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2
Q

How does the adenohypophysis develop?

A

from a dorsal outgrowth from the wall of the embryonic pharynx

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3
Q

How does the neurohypophysis develop?

A

as a ventrally orientated down growth from the

diencephalon

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4
Q

How can the adenohypophysis and the neurohypophysis be distinguished histologically

A

H&E stained section

- the adenohypophysis is more darkly stained.

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5
Q

What surrounds the pituitary gland?

A

thin fibro-elastic capsule

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6
Q

What tissue does the capsule of the pituitary gland develop from?

A

meninges - continuous with dura

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7
Q

What makes up the adenopophysis?

A

unequal populations of cells forming irregular cords of secretory cells

Includes:

  • chromophobes
  • chromophils
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8
Q

Describe the staining of the cells within the adenopophysis

A

H& E stained section

chromophobes are palely stained –
phobos =hating

chromophils are strongly stained- chromophil =
colour loving

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9
Q

What is the difference functionally between chromophobes and chromophils?

A

Chromophobes are exhausted secretory cells, chromophils are active
secretory cells.

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10
Q

What are the 5 distinct cell types found in the adenohypophysis

A
  • somatotrophs
  • lactotrophs
  • corticotrophs
  • thyrotrophs
  • gonadotrophs
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11
Q

What do somatotrophs secrete?

A

Growth hormone (GH)

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12
Q

What do lactotrophs secrete

A

prolactin (PL)

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13
Q

What do corticotrophs secrete?

A
  • adenocorticotrophic hormone (ACTH)

- beta-lipotropin (beta-LPH)

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14
Q

What do thyrotrophs secrete

A

thyroid stimulating hormone (TSH)

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15
Q

What do gonadotrophs secrete?

A
  • follicle stimulating hormone (FSH)

- luteinising hormone (LH).

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16
Q

What is the target organ for somatotropin?

A
  • Body tissues

- hepatocytes

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17
Q

What is the target organ for prolactin?

A

Breast

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18
Q

What is the target organ for TSH?

A

Thyroid gland - thyroid follicular cells

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19
Q

What is the target organ for FSH/LH

A

Gonads

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20
Q

What is the target organ for ACTH/lipotropin/melanocyte stimulating hormone

A

Adrenal cortex

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21
Q

What effect does somatotrophin have?

A
  • Metabolic actions - growth
  • Increased protein synthesis
  • Increased growth of cartilage
  • Increased fatty acid production
  • Increased insulin resistance
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22
Q

What effect does prolactin have?

A
  • Lactogenesis
  • renal sodium/water reabsorption
  • steroidogenesis
  • stimulates T cells
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23
Q

What effect does thyroid stimulating hormone have?

A
  • Thyroxine (T4) minimal effect

- Triiodothyronine (T3) – increased metabolism, growth and development, catecholamine effect

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24
Q

What effect does FSH/LH have?

A
  • Early growth of follicle
  • Maturation of follicle
  • oestrogen secretion
  • formation of corpus luteum
  • Stimulates seminiferous epithelium
  • Leydig cells — testosterone
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25
Q

What effect does ACTH/lipotropin/melanocyte stimulating hormone have?

A

Synthesis and release of cortisol principally from zona fasciculata

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26
Q

What is the basic chemistry of somatotrophin

A

protein

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27
Q

What is the basic chemistry of prolactin

A

protein

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28
Q

What is the basic chemistry of thyroid stimulating hormone

A

glycoprotein

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29
Q

What is the basic chemistry of FSH

A

glycoprotein

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30
Q

What is the basic chemistry of LH

A

glycoprotein

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31
Q

What is the basic chemistry of ACTH?

A

a polypeptide

32
Q

What is the basic chemistry of lipotropin?

A

a polypeptide

33
Q

What is the basic chemistry of melanocyte stimulating hormone

A

a polypeptide

34
Q

Which cells in the pituitary gland are acidophils?

A
  • somatotrophs

- lactotrophs

35
Q

Which cells in the pituitary gland are basophils

A
  • thyrotrophs
  • gonadotrophs
  • corticostrophs
36
Q

What is the importance of fenestrated capillaries in the adenohypophysis?

A

facilitates rapid passage of secretory hormones to their target organs

37
Q

How does the thyroid gland develop?

A

as an endodermal downgrowth (the ‘thyroglossal duct’) from the
floor of the developing pharynx

38
Q

What landmark is the site of downgrowth

A

The foramen caecum at the back of the tongue marks the

site of the downgrowth.

39
Q

Are there any remnants of downgrowth?

A

Cyst-like remnants of the original downgrowth may persist in the
adult.

40
Q

Describe the gross structure of the thyroid

A

two lobes connected by a midline isthmus

41
Q

What are the thyroid lobes made of histologically?

A

follicles – flask-shaped structural units that are epithelial structures

42
Q

Describe the epithelium of inactive follicles in the thyroid gland

A

simple low cuboidal or squamous

epithelium

43
Q

Describe the epithelium of active follicles in the thyroid gland

A

the cells become columnar when they are actively

secreting.

44
Q

What is the function of thyroid epithelium?

A

concentrate iodide from the blood and synthesize two hormones: thyroxine (T4) and tri-iodothyronine (T3).

45
Q

What hormone regulates the activity of the thyroid gland and where is it produced?

A

THYROID STIMULATING HORMONE FROM ADENOHYPOPHYSIS

46
Q

What stages are required for thyroid hormone synthesis?

A

exocrine and an endocrine stage

47
Q

What is the exocrine stage of thyroid hormone synthesis?

A

Firstly, colloid is produced. This iodinated glycoprotein, rich in thyroglobulin, is a storage form of thyroxine and is secreted by exocrine secretion to the follicle lumen.

48
Q

Which cell organelle produces the protein part of thyroglobulin?

A

Rough endoplasmic reticulum

49
Q

Where is the sugar component of thyroglobulin added?

A

Golgi apparatus

50
Q

Which enzyme enables iodide to be converted to iodine?

A

Thyroid peroxidase

51
Q

Which cell synthesises thyroid peroxidase?

A

the follicle cell

52
Q

How is thyroglobulin re-uptaken by the follicle epithelium?

A

involves pseudopodial extensions of cytoplasm which can enclose droplets of thyroglobulin and bring them into the cell when
thyroxine and tri-iodothyronine are required.

53
Q

Describe the endocrine stage of thyroid hormone synthesis

A

storage form is broken down by lysosomes;
T4 and T3 are released across the basal lamina of the epithelium and enter capillaries – i.e.
by endocrine secretion.

54
Q

What antibodies are produced in Hashimoto’s?

A

because antibodies to thyroid

peroxidase (antimicrosomal antibodies) are produced

55
Q

What connective tissue changes occur in Hashimoto’s?

A

prominent fibrosis

56
Q

What are the follicle changes in Hashimoto’s?

A

few normal follicles

57
Q

What is the colloid and where is it found?

A

The colloid within the follicles is an inactive, storage form of the thyroid hormones T3 and T4.

58
Q

What is the major component of the colloid

A

thyroglobulin, an iodinated glycoprotein

59
Q

Define glycoprotein

A

any of a class of proteins which have carbohydrate groups attached to the polypeptide chain.

60
Q

What is the epithelium lining the follicles called?

A

the follicular epithelium.

61
Q

What are the three hormones produced and secreted by the follicular epithelium, and which cells are they secreted by?

A

triiodothyronine (T3),
tetraiodothyronine (T4) (thyroxine) released by follicular cells and calcitonin released by C
cells.

62
Q

Describe the structure of T3 and T4

A

T3 and T4 hormones are iodinated derivatives of tyrosine.

63
Q

What controls the synthesis and breakdown of thyroglobulin

A

controlled by the hypothalamus and

adenohypophysis through the action of TSH (thyrotropinin).

64
Q

How does TSH work?

A

TSH reaching the thyroid gland via the circulation binds to its receptor (Thyrotropin receptor (TSHr), a glycoprotein hormone
receptor) stimulates the cAMP pathway and results in hormone synthesis, differentiation and enhanced growth.

65
Q

What happens when there is low levels of thyroxine in the blood?

A

stimulate the hypothalamus to produce TRH

thyrotopin-releasing hormone

66
Q

How does TRH work?

A

TRH stimulates the adenohypophysis to produce thyroid stimulating hormone (TSH).

67
Q

What happens when TSH receptor is activated?

A

Activation of TSHr stimulates thyroid follicular cells to synthesise and breakdown thyroglobulin from thyroid follicles and result in an increased release of thyroxine into the thyroid capillaries.

68
Q

What are the functions of T3 and T4?

A

regulate cell and tissue basal metabolism, may stimulate production of heat and influence body growth and development.

69
Q

What is a sign of low calcium levels in the blood?

A

twitching of muscles of face and arms and results in an

increased level of phosphate in the blood (normal range 0.8-1.4 mmol/L).

70
Q

What are signs of hyperphosphataemia?

A

severe itching of the skin and weakening of bones.

71
Q

What can result from hypophosphataemia?

A

linked to increased insulin

resistance.

72
Q

What hormone do C cells synthesise and release?

A

Calcitonin

73
Q

What is the function of calcitonin

A

lowers serum calcium levels - inhibits osteoclast activity and reduces renal calcium reabsorption

74
Q

What is the functional significance of the close packing of the small tubes and the secretory
epithelium of the follicles?

A

facilitates endocrine secretion of hormone directly into the blood stream

75
Q

What produces parathyroid hormone?

A

the four parathyroid glands which are located

posterior to the thyroid gland or sometimes embedded within the thyroid gland

76
Q

What kind of cells are found in the parathyroid glands?

A
  • chief cells (basophilic)

- oxyphil cells (acidophilic)

77
Q

Does a parathyroid gland possess a CT capsule?

A

variable - it is often within the thyroid capsule. If it is found at a separate site, a fine fibrous capsule is usually seen

Phase 2 3. Endocrinology (25 decks)

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