Thyroid and Parathyroid Glands

Question 1

What are some of the primary functions of thyroid hormone?

Answer 1

Produces 2 iodine-containing amine hormones DERIVED FROM THE a.a. TYROSINE:

T3 & T4

• acts on almost every cell in body
• ↑ base metabolic rate (boosts energy metabolism in mitochondria)

• triggers rapid protein synth.
(influences gene transcription)

• permissive action on catecholamines
• enhances effect of GH (synergy)
• development and differentiation of cells
• involved in fuel metabolism
• regulates body temp.

Question 2

T or F:

T4 is x10 more potent than T3?

Answer 2

FALSE

Question 3

What do C cells secrete?

Answer 3

Calcitonin

Question 4

What is happening @ each step?

Answer 4

1. Synthesis & secretion of thyroglobulin
2. Uptake & concentration of iodide from blood, oxidation to iodine, release into the colloid
3. Iodination of thyroglobulin – one or two iodine atoms are added to tyrosine residue in thyroglobulin to form monoiodotyrosine (MIT) or diiodotyrosine (DIT)
4. Thyroid hormones, triiodothyronine (T3) & thyroxine (T4) are formed by interactions between MIT or DIT with another DIT. T3 & T4 remain bound to thyroglobulin in the colloid
5. Endocytosis of colloid & lysosomal breakdown of colloid to form T3 & T4
6. Release of T3 & T4 into blood

Question 5

Answer 5

Question 6

….. more active than …..

….. and ….. are inactive

….. has a longer duration than …..

Answer 6

T3, T4

T2 (DIT), rT3

T4, T3

Question 7

What initiates thyroglobulin secretion?

Answer 7

TSH

Question 8

How is T3 & T4 synth. regulated?

Answer 8

TRH stim. release of TSH {aka thyrotropin}

Neg (-) f.b maintains relatively constant supply of thyroid hormones!

Question 9

How is the thyroid stimulated?

Answer 9

TSH binds to TSH R’s (plasma mem. of thyroid epith. cells)

THUS, stimulating:

–iodine uptake

–iodination & coupling

–thyroglobulin production

–retrieval from thyroglobulin

–glucose oxidation, protein synth. & growth of these cells (mediated by IGFs)

THUS, INCREASED PRODUCTION OF T3 & T4!

Question 10

Answer 10

Question 11

Answer 11

Question 12

Answer 12

Question 13

Answer 13

Question 14

What is the primary function of parathyroid hormone (PTH)?

Answer 14

Ca METABOLISM

–maintenace of body’s Ca lvlwithin a narrow range so nervous & muscular systems can function properly

–Ca2+ is absorbed (intestines) or excreted (kidneys) under slow regulation

–Ca2+ is exchanged between bone & plasma rapidly

–Activates osteoclast activity on bones

–Increases Ca2+ absorption in intestines

Question 15

What stimulates the release of PTH?

Answer 15

When Ca lvls DECREASE!

THUS, Ca-sensing R’s in parathyroid hormone stimulate release of PTH

Question 16

What is the function of calcitonin?

Answer 16

• Inhibits osteoclast activity in bones
• Ihibits Ca2+ absorption by intestines
• Inhibits reabsorption of Ca2+ AND phosphate in kidney tubules

Question 17

What is the main function of Vitamin D (Calcitrol)

Answer 17

INCREASES Ca2+ ABSORPTION IN INTESTINES!

Question 18

How does Vit. D increase Ca2+ absorption in intestines?

Answer 18

1. Increasing expression of Ca channels on apical mem.
2. Increasing expression of calbindin which ferries Ca across cell
3. Increasing expression of Ca-ATPase pumps of basolateral mem.