Brainscape's Knowledge GenomeTM

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


See full index

Year 2 - Endocrine System > The Thyroid Gland > Flashcards

The Thyroid Gland Flashcards

1
Q

How much does the thyroid gland weigh?

A
  • 15-20g
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Which thyroid hormones does the thyroid gland synthesise that are physiologically active

A
  • Triiodothyronine (T3)
  • Thyroxine (T4)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Which 2 cell types are found in the thyroid gland

A
  • C (clear) cells
  • Follicular cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

State the funcitons of the 2 cell types found in the thyroid gland

A
  • C (clear) cells: Secretes calcitonin (Ca2+ regulating hormone)
  • Follicular cells: Support thyroid hormone synthesis and surround hollow follicles
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are thyroid follicles?

A
  • Spherical structures whose walls are made of follicular cells
  • Centre of the follicle is filled with colloid which is a sticky glycoprotein matrix which contains 2-3 months supply of thyroid hormone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How to follicular cells support thyroid hormone synthesis?

A

Follicular cells manufacture enzymes that make thyroid hormones

(note: also makes thyroglobulin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Apart from enzymes, what else do follicular cells manufacture?

A

Thyroglobulin: A large protein rich in tyrosine residues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

After follicular cells manufacture enzymes and thyroglobulin, what happens to these products?

A
  • The enzymes and thyroglobulin are packages into vesicles and exported from the follicular cell into the colloid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What substance do the follicular cells actively concentrate from the plasma into the colloid and what does this allow?

A
  • Iodine

This allows the iodine to combine with tyrosine residues to form the thyroid hormones

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

How does Iodine enter follicular cells?

A

Iodine enters follicular cells from the plasma via a Na+/I-transporter (symporter)

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

How does Iodine enter the colloid?

A
  • Pendrin transporter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

After iodine reaches the colloid, what processes occur to form thyroid hormones?

A
  • Enzymes and thyroglobulin are exocytosed into the colloid
  • The enzyme thyroid peroxidase (aka thyroperoxidase) converts I- to I2 by removing an electron
  • This catalyses the addition of iodine to tyrosine residues on the thyroglobulin molecule forming thyroid hormones
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How is triiodothyronine (T3) formed?

A
  • One iodine + tyrosine ➔ MIT
  • Addition of a 2nd iodine ➔ DIT

MIT + DIT ➔ T3

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

How is thyroxine (T4) formed?

A
  • One iodine + tyrosine ➔ MIT
  • Addition of a 2nd iodine ➔ DIT

DIT + DIT ➔ T4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

After thyroid hormone synthesis in the colloid, what happens next?

A
  • In response to TSH, the thyroglobulin T3/T4 complex is taken back into the follicular cells by endocytosis
  • Within the cells, they form vesicles which contain proteolytic enzymes that cut the thyroglobulin to release thyroid hormones (T3/T4)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Both T3 and T4 are water/lipid soluble

A

- Lipid soluble

17
Q

Both T3 and T4 circulate/do not circulate in the plasma

A
  • Circulate
18
Q

Most T3/T4 circulates freely in the plasma.

True/false

A

False

More than 99.8% of T3 and T4 circulates in plasma bound to plasma protein.

(REMEMBER: Thyroid hormones are hydrophobic and so bind to plasma proteins due to their low solubility in water)

19
Q

Why does T4 have a longer half life than T3?

A
  • Thyroxine Binding Globulin (TBG) has a particularly higher affinity for T4 releasing it only slowly into the plasma

(also in the lecture: most TH circulates in the form of protein bound T4)

20
Q

How can T4 be converted into T3?

And what is this process called?

A
  • Remove an iodine
  • Deiodinease enzymes (half deiodinated in plasma, half in target cells)
21
Q

“However 90% of TH binding to TH receptors inside cells is T3.”

(DON’T GET IT!!)

A
22
Q

Descibe the regulation of thyroid hormone release

A
  • A stimulus (i.e cold, exercise, pregnancy) causes the trophic hormone Thyrotropin Releasing Hormone (TRH) in the hypothalamus to act on the anterior pituitary to release Thyroid Stimulating Hormone (TSH)
  • TSH from the anterior pituitary in turn acts on the thyroid gland to promote hormone synthesis (T3/T4)
  • The thyroid hormones normally act as a negative feedback signal to prevent oversecretion
23
Q

Describe how thyroid hormones function affect thier target cells

A
  • Thyroid hormone (TH) binds to nuclear receptors in target cells
  • The complex then binds to specefic sequences of DNA
  • This changes transcription and translation to alter protein synthesis
24
Q

State some functions of thyroid hormones

A
  • Increase metabolic rate (by stimulating the use of cellular O2 to produce ATP)
  • Promotes thermogenesis (production of heat)
  • Increases hepatic gluconeogenesis although has no effect on BG (providing the pancreas is releasing adequete insulin)
  • Net increase in proteolysis
  • Net increase in lipolysis
  • Critical for growth (lack of TH results in retarded growth)
  • Astimulates GH receptor expression
  • Essential for brain development in utero (maternal iodine deficiency = congenital hypothyroidism/cretinism)

Year 2 - Endocrine System (29 decks)

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