Physiology of the Thyroid Gland Flashcards Preview

Endocrine > Physiology of the Thyroid Gland > Flashcards

Flashcards in Physiology of the Thyroid Gland Deck (36):
1

Describe what colloid is in terms of tructure of the thyroid gland.

colloid = tyrosine containing thyroglobulin filled spheres enclosed by follicular cells

2

What do parafollicular C cells secrete and why is this important?

Secrete cacitonin - involved in cacium metabolism

3

Briefly describe how T3 and T4 are synthesised, stored and released.

Iodine moves into the follicular cell from the blood
This attaches to tyrosine residues on thyroglobulin to form T3 and T4. These can be secreted by pinocytosis or stored in colloid thyroglobuin until required

4

What exactly is T3 made up of?

MIT and DIT

5

If only one iodine joins the tyrosine residue what is created?

Monoiodotyrosine unit (MIT)

6

If 2 iodines join the tyrosine residue, what is the resulting molecule called?

Di-iodotyrosine unit (DIT)

7

If two DIT units join together, what is made?

T4

8

What is the method of action of Carbimazole and Propylthiouracil?

Prevent iodine attaching to tyrsine residues to stop the manufacturing of T3 and T4 - used to treat hyperthyroidism

9

Which thyroid hormone is secreted the most?

T4 = thyroxine - ~90% of thyroid hormones

10

Which thyroid hormone is most potent?

T3 (4x more potent than T4)

11

Can T4 be converted to T3?

yes in the liver and kidney

12

Which thyroid hormone is the major biologically active thyroid hormone?

T3

13

What is the main regulator of thyroid hormone release?

Thyroid stimulating hormone (TSH)

14

Are T3 and T4 hydrophilic or hydrophobic?

Hydrophobic and lipophilic so bind to plasma proteins

15

What is the main plasma protein that T3 and T4 bind to?

Thyroxine binding globulin (TBG)

16

What other plasma proteins can T3 and T4 bind to?

Thyroxine bindding prealbumin (~20%)
Albumin (~5%)

17

The bound/unbound thyroid hormone is biologically active adn therefore available to the tissue?

Unbound

18

What allows the release of T3 and T4 from the colloid?

Thyroid stimulating hormone (TSH)

19

Which thyroid hormone has more rapid onset and offset kinetics?

T3

20

Does the metabolic state correlate more closely with the free hormones or total hormone concentration?

Free

21

Do thyroid hormones increase or decrease basal metabolic rate?

Increase

22

Do thyroid hormones increase or decrease thermogenesis?

Increase

23

What is the effect of thyroid hormones on carbohydrate metabolism?

Increase blood glucose
Increase insulin-dependent glucose uptake into cells

24

What is the effect of thyroid hormones on lipid metabolism?

Mobilise fats from adipose tissue
Incerase fatty acid oxidation in tissues

25

What is the effect of thyroid hormones on protein metabolism?

increase protein synthesis

26

How do thyroid hormones indirectly effect growth?

growth hormone releasing hormone and growth hormone itself required thyroid hormones

27

In the development of foetal and neonatal brain, what exactly requires thyroid hormones?

Myelinogenesis and axonal growth require thyroid hormones

28

What is the effect of thryroid hormones on permissive sympathomimetic action?

Increase responsiveness to adrenaline and NA by increasing number of receptors

29

What class of drugs can be given to treat symptoms in initial stages for hyperthyroidism?

Beta-blockers (e.g. Propanolol)

30

How is the production of thyroid hormones regulated?

- Thyrotrophin releasing hormone (TRH), stimulates thyroid stimulating hormone (TSH) release from anterior pituitary

- TSH = major stimulant to release of T3 and T4 from thyroid gland

- T3 and T4 exert negative feedback control of release of TRH and TSH

31

What are the other 3 minor regulators of thyroid hormone release?

Low temperature
Stress
Circadian rhythm

32

What does the thyroid secrete?

Throxine (T4)
Tri-iodothyronine (T3)
Calcitonin

33

What do the parathyroid glands secrete and what does this act on?

parathyriod hormone (PTH)
Calcium metabolism

34

The Hypothalamus secretes ... that acts on the anterior pituitary to secrete...?
What does this allow the release of

TRH
TSH
T3&T4

35

What are the parathyroid cells composed of?

Chief cells supported by oxyphil cells

36

Describe the cell histology of a normal parathyroid gland.

Round cells with moderate cytoplasm and bland round central nuclei