Physiology of the Thyroid Gland Flashcards Preview

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Flashcards in Physiology of the Thyroid Gland Deck (30):
1

Where is the thyroid gland located?

- anterior to the trachea and below the larynx (midline of the neck).
*can feel an increase in size when the gland hypertrophies (normal weight= 15-20 grams).

2

Does the thyroid gland of a good blood supply?

YES, bc it releases hormones to the blood.

3

What is one of the largest endocrine organs?

- thyroid gland

4

What does the thyroid gland secrete?

- triiodothyronine (T3)= 7%
- thyroxine (T4)= 93%
- calcitonin

5

**** Is T3 or T4 more potent?

- T3 (4x more potent)
*however, it's presence is much lower than T4

6

Into what is T4 converted in the blood?

- T4 is converted to T3 in the blood

7

**** What stimulates the thyroid gland to secrete T3/T4?

- thyroid stimulating hormone (TSH)

8

** What gland modulates the metabolic rate?

- thyroid gland

9

What will you see on histology of the thyroid?

- follicles (contains T3/T4) and colloid/thyroglobulin

10

*** How much IODINE does the thyroid gland require per week to make thyroxine?

- 1 mg
*iodized salt, fish and seafood are good sources

11

How is iodine metabolized?

- oral route (PO) absorbed like chloride and excreted by the kidneys.

12

*** How is T4 synthesized? (see diagram)

- thyroid cells synthesize and secrete thyroglobulin into the follicle (tyrosine amino acids).
- oxidation of iodide ion by PEROXIDASE and HYDROGEN PEROXIDE.
- iodination of tyrosine (organofication) via IODINASE
- mono- di- triiotyrosine progression.

13

How is iodide added to thyroid hormones?

- Iodide is taken into the thyroid cells (iodide trapping) and secreted into the lumen of the follicle (colloid), where it iodinates thyroid hormones.

14

How much thyroid hormone is stored in the thyroid gland?

- 2-3 month supply

15

How is thyroid hormone released into the blood?

- taken from the colloid, cleaved by the lysosomes, and released into the blood.

16

What happens to thyroxine (T4) in the blood?

- binds to thyroxine-binding globulin (TBG)
*T3 has lower affinity for TBG

17

What is the mechanism by which T3/T4 work?

- cAMP second messenger system (bind to cell surface)

18

**** What are the effects of thyroid hormones?

- increased PROTEIN SYNTHESIS
- increased PROTEIN CATABOLISM
- increased GROWTH
- increased MENTAL EXCITEMENT
- increase in SYSTEMIC ENDOCRINE ACTIVITY (menses, sweating...)
- increased NUMBER OF MITOCHONDRIA (increases body temp; HEAT)
- increased Na+/K+ ATPase at cellular membranes
- increased FETAL BRAIN DEVELOPMENT
- increased CARBS, FAT, and PROTEIN METABOLISM
- increased NEED for VITAMINS
- increased basal metabolic rate (BMR)
- increased HEART RATE
- increased IONOTROPY (contractility) of the MYOCARDIUM
- increased GI MOTILITY
- increased TREMORS
- increased FREE FATTY ACIDS in PLASMA

- decreased CHOLESTEROL levels in the PLASMA
- decreased PHOSPHOLIPIDS
- decreased TRIGLYCERIDES
- decreased BODY WEIGHT
- decreased sleep
*remember T3 does this better than T4

19

Is thyroid hormone needed for normal sexual function?

YES

20

Does hyper or hypothyroidism lead to menstrual defects?

- HYPOthyroidism

21

What are the effects of TSH?

increased:
- proteolysis of thyroglobulin.
- iodide pump activity.
- increased iodination of tyrosine.
- increased size and activity of thyroid cells.
*modulated by cAMP

22

**** How do we REGULATE/SUPPRESS thyroid hormone production? (TEGRITY)

- thiocyante/perchlorate= decreased iodide trapping, not thyroglobulin synthesis
- PTU (propylthiouracil)= decrases thyroid hormone formation.
- iodide in high concentrations= decreases thyroid activity and size.

23

What are some diseases of the thyroid?

- HYPERthyroidism: Grave's disease, thyrotoxicosis...
- HYPOthyroidism:
- toxic goiter= continues stimulation of the thyroid due to hormone synthesis breakdown.
- myxedema= deficient hormone production.

24

What are some diseases of the thyroid?

- HYPERthyroidism: Grave's disease, thyrotoxicosis (thyroid storm)
- HYPOthyroidism (treat with hormone replacement).
- toxic goiter= continuous stimulation of the thyroid due to hormone synthesis breakdown.
- myxedema= deficient hormone production.
- cretinism

25

What is important to know about calcitonin?

- secreted by parafollicular cells of the thyroid causing blood calcium to decrease.
*remember calitonin TONES THE BONES

26

Can thyroid dysfunction cause exophthalmos (bulging eyes)?

- YES

27

What causes TRH, and thus TSH to be released?

- cold
- emotional stress

28

What causes termination of TSH release?

- increased levels of thyroid hormones in the blood (negative feedback).

29

**** Should you use PTU (propylthiouracil) before or after iodide, when attempting to suppress the thyroid gland? (TEST QUESTION)

- BEFORE

30

What should you check when evaluating a pt for HYPERthyroidism?

- BMR/TSH and thyroid stimulating initiator levels.
*remember to prescribe PTU before Iodine to suppress it.