Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

GI Block > Endo: Regul of T3/4 Synthesis > Flashcards

Endo: Regul of T3/4 Synthesis Flashcards

1
Q

Describe the structure of thyroid hormone

A

T3/4 is composed of two tyrosine residues iodinated in 3 or 4 places

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What kind of receptor is used by T3/T4?

A

The receptor for T3/4 exists bound to DNA (intracellular receptor!)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are two major sources of iodine?

A

Water

Salt with added Iodide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does the Iodine get from blood into thyroid colloid? (3 steps)

A
  1. Na/I symporter on basolateral side of follicular cell pumps Iodide into cell
  2. Na then pumped back out by Na/K ATPase
  3. On luminal side, Thyroperoxidase converts I- into I2 and pumps it into follicular lumen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where is Thyroglobulin made?

Where does it go next?

A

Thyroglobulin is synthesized in follicular cell

TG is then pumped into the follicular lumen (colloid)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the overall process of Thyroid hormone synthesis (4)

A
  1. Iodine is taken up by follicular cell and pumped across into follicular lumen (colloid)
  2. Thyroglobulin is made by follicular cell and pumped into lumen
  3. In lumen, TPO adds Iodine to Thyroglobulin
  4. Iodinated Thyroglobulin gets endocytosed by follicular cell and converted to T3/4
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Name the three reactions catalyzed by Thyroid Peroxidase

A

Thyroid Peroxidase…

  • Oxidizes I- into I2
  • Adds Iodide to Tyr residues of thyroglobulin
  • Connects Tyrosine residues (couples MIT and DIT)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens after TPO adds Iodine to thyroglobulin in the lumen?

A
  1. Thyroglobulin-Iodide gets endocytosed by follicular cell
  2. Thyroglobulin-Iodide gets degraded by proteases
  3. This releases T3 and T4
  4. T3, T4 released into blood
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How is thyroid hormone transported in the blood?

A

T3/4 exists in blood bound to TBG

*But remember, only free hormone exerts effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Which is functional: T3 or T4?

A

T3 is functional

(T4 is like a pro-hormone, and gets converted to T3 within cells)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Name the functions of thyroid hormone (6)

A
  1. Brain maturation
  2. Bone growth (permissive effect on GH)
  3. Beta adrenergic stimulation
  4. Basal metabolic rate increases
  5. Blood sugar increases (gluconeogenesis, glycogenolysis)
  6. Break down of fats (lipolysis)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is cretinism?

Name 5 symptoms

A
  • Cretinism = severe growth and mental retardation due to low thyroid hormone (congenital hypothyroidism)
  • Signs: pot-belly, puffy-faced, protruding umbilicus, protruding tongue, poor brain development
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe the hormone axis for thyroid, including negative feedback

A
  1. Hypothalamus releases TRH
  2. TRH stimulates ant pituitary to release TSH
  3. TSH stimulates thyroid to release T3/4

*T3 provides negative feedback on hypothalamus and pituitary

*Somatostatin also inhibits TSH release

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does TSH cause T3/4 release? (3)

A

TSH

  • Stimulates growth of thyroid gland and follicular cells
  • Stimulates protein synthesis (thyroid peroxidase and thyroglobulin)
  • Stimulates iodide uptake
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the TSH and T3/4 levels in

  • Endemic hypothyroidism
  • Hypopituitarism
  • Hashimoto’s thyroiditis
A
  • Endemic hypothyroidism: High TSH, low T3/4
    • Insufficient Iodine in water
  • Hypopituitarism: Low TSH, low T3/4
  • Hashimoto’s thyroiditis: High TSH, low T3/4
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the TSH, T3/4 levels in

  • Thyroid tumor
  • Pituitary tumor
  • Grave’s disease
A
  • Thyroid tumor: low TSH, high T3
  • Pituitary tumor: high TSH and high T3
  • Grave’s disease: low TSH, high T3
    • Autoimmune stimulation of TSH receptors on thyroid
17
Q

What enzyme converts T4 into T3 in peripheral tissues?

Name 3 things that inhibit this enzyme

A
  • 5’ deiodinase converts T4 into T3
    • T3 is active form
  • 5’ deiodinase is inhibited by glucocorticoids, beta blockers, and PTU
18
Q

What is the Wolff-Chaikoff effect?

A

Excess iodine temporarily inhibits thyroid peroxidase, decreasing T3/4 production

19
Q

What is one cause of increased thyroid binding globulin?

One cause of decreased TBG?

A
  • Increased TBG with oral contraceptives
  • Decreased TBG with hepatic failure

GI Block (77 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions