EXAM #1: THYROID & PARATHYROID GLANDS Flashcards Preview

Endocrine > EXAM #1: THYROID & PARATHYROID GLANDS > Flashcards

Flashcards in EXAM #1: THYROID & PARATHYROID GLANDS Deck (40):
1

What is the embryological origin of the thyroid gland?

- Endoderm of the primitive pharynx
- Thyroid diverticulum

2

What does the thyroglossal duct connect?

Developing thyroid gland to tongue

3

What does the adult foramen cecum indicate?

Site of the former thyrogossal duct

4

Normally the thyroglossal duct regresses. If it does NOT regress, what may it form?

The adult pyramidal lobe of the thyroid.

5

When does a thyrogossal duct cyst occur?

Occurs when part of the thyroglossal duct fails to obliterate, subsequently forming a cyst.

6

Where are thyrogossal duct cysts commonly located?

Ventral to the hyoid bone and laryngeal cartilage.

7

Where are the parathyroid glands normally located?

Posteriorly in the thyroid capsule

8

What is the function of the thyroid gland i.e. what does the thyroid gland synthesize?

1) T3
2) T4
3) Calcitonin

9

What is the basic structural and functional unit of the thyroid gland

Thyroid follicle

10

What is the embryological origin of the thyroid follicle?

Endoderm

11

What is the normal histological appearance of the thyroid gland?

Simple cuboidal

12

What surround the thyroid follicles?

Basal lamina and a capillary plexus

13

What is contained within the thyroid follicles? How does this substance stain?

Colloid- pink

*This contains thyroglobulin

14

What cells are located adjacent to the thyroid follicular cells?

Parafollicular cells

15

What is the embryological origin of parafollicular cells?

Neural crest cells

16

What is the function of the parafollicular cells?

Secretion of calcitonin

17

What is the stimulus for the secretion of calcitonin?

Elevated blood Ca++

*Think of as an "osteoclast stop sign" i.e. tells the osteoclasts to STOP breaking down bone and releasing Ca++ into the serum

18

What is the effect of calcitonin on osteoclasts and osteoblasts?

Calcitonin
- Inhibits osteoclasts
- Activates osteoblasts

19

Outline the HPA pathway that leads to the secretion of thyroid hormone.

- Hypothalamus= TRH
- Anterior pituitary= TSH
- Thyroid= T3 and T4

20

Outline the synthesis of thyroid hormone.

1) TSH binds TSH receptors on basal membrane of follicular cells
2) RER synthesizes THYROGLOBULIN
3) Golgi apparatus glycosylates and packages into secretory vesicles
4) Released into the colloid of the follicular lumen
5) Iodine is added in the colloid

21

How does iodide get into the thyroid follicular cell?

Na+- I symporter

22

What enzyme is responsible for the oxidation of iodide to iodine in the calloid?

thyroid peroxidase

23

Where does iodination take place?

Adjacent to the apical membrane of the follicular cell

24

What is organification?

Attaching Iodine to thryoglobulin

25

What enzyme couples MIT and DIT?

Thyroid peroxidase

26

How is thyroid hormone released from the thyroid gland?

Lysosomal pathway
- Uptake of colloid by endocytosis
- Lysosome and colloid droplet fuse
- Digestion by proteases in the lysosome releases thyroid hormones
- Hormones diffuse into capillaries near the basal lamina

27

What is the alternative to the lysosomal pathway of thyroid hormone release?

Transepithelial pathway
- Megalin receptor causes uptake of colloid
- T3 and T4 attached to thyroglobulin is released via exocytosis on the basal aspect of the follicular cell

*Note that this bound T3/4 is INACTIVE

28

What is the mnemonic to remember the major functions of the thyroid hormones?

Remember the four B's:
- BMR (increase)
- Bone growth
- Brain maturation
- Beta-adrenergic

29

What is the pathological basis for Grave's Disease?

This is toxic goiter/ hyperthyroidism
- Thyroid-stimulating immunoglobulin i.e. autoantibody to TSH is formed
- Induces hyperthyroid state

30

What causes the exopthalamous seen in Grave's Disease?

- Retro-orbital fibroblasts contain TSH receptors
- TSI stimulates retro-orbital fibroblasts
- Fibroblasts ynthesize hydrophilic glycosaminoglycans

Consequently infiltration of fat and T cells in the retro-orbital space, and edema of the extraocular muscles causes exopthalamous

31

What is the embryological origin of the parathyroid glands?

Derivatives of the pharyngeal pouches:
- Pouch 3= inferior
- Pouch 4= superior

32

Histologically, how does the parathyroid gland differ from the thyroid gland?

Parathyroid gland contains densely packed cells vs. follicular cells

33

What are the major cells of the parathyroid gland?

1) Chief
2) Oxyphil

34

What is the function of chief cells?

Secretion of parathyroid hormone

35

What are the physiological effects of parathyroid hormone?

1) Increase serum [Ca2+]
2) Decrease serum [phosphate]
3) Increase urine [phosphate]

36

Describe the effect of PTH on bone.

PTH increases bone resorption of calcium and phosphate:

PTH binds to receptors on osteoblasts, which secrete macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-kB ligand (RANK-L) in response.
RANK-L binds RANK on osteoclast precursors which promotes their differentiation into mature osteoclasts that are capable of bone resorption and the release of calcium.

37

Describe the effect of PTH on the kidneys.

1) Conserves Ca++
2) Excretes phosphate

38

Describe the effect of PTH on the GI tract.

- PTH regulates the formation of Vitamin D
- Vitamin D stimulates Ca++ absorption in the GI tract

39

Compare the effects of PTH and Calcitonin?

PTH= INCREASES low blood Ca++

Calcitonin= DECREASE high blood Ca++

40

What is the clinical consequence of hypoparathyroidism?

Hypocalcemic tetany

(B/c no PTH to increase low blood Ca++)