Endocrinology 6 Flashcards Preview

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Flashcards in Endocrinology 6 Deck (24)
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1
Q

Where is the thyroid located?

A

At the top of the trachea

2
Q

What is the Isthmus?

A

The tissue that joins together the 2 lobes of the thyroid.

3
Q

What is the pyramid?

A

It is a tissue located on the top of the isthmus, which is present in some people. Clinically important as a thyroid tumour may be found here.

4
Q

Describe the basic structure of the thyroid

A

It is bi-lobed and full of follicles.

5
Q

What is the colloid?

A

The proteinaceous substance found inside the follicles.

6
Q

What are Follicular cells?

A

The cells lining the follicle.

7
Q

What are Parafollicular cells?

A

Found between the follicles and they also provide hormones.

8
Q

What are the 5 things that TSH does when it binds to the TSHR?

A
  1. Stimulates the iodine pump to pump iodine into the cell.
  2. Stimulates the synthesis of Thyroglobulin (TG).
  3. Stimulates Thyroid Peroxidase (TPO).
  4. Allows coupling reactions to form T3 and T4.
  5. Stimulates lysosomes to move towards the apical membrane and stimulates uptake of colloid.
9
Q

How is iodine pumped into the colloid from the cell?

A

It’s is pumped through Pendrin pumps.

10
Q

What does TPO do?

A

It converts iodine into a radioactive iodine form (very short lived) in the presence of hydrogen peroxide.

11
Q

What is iodination?

A

It is when iodine is added to TG using TPO to form MIT/DIT in the colloid.

12
Q

What does the coupling reaction involve?

A

It involves combining two TG molecules to form T3 or T4 using TPO.

13
Q

What is the difference between T3 and T4?

A

T3 is formed when a MIT is combined with a DIT whereas T4 involves two DIT’s.

14
Q

What is the difference between MIT and DIT?

A

MIT is when only 1 Iodine is added to tyrosine whereas DIT is when 2 Iodine’s are added.

15
Q

How is T3 and T4 transported in the blood?

A

They are bound to plasma proteins.

16
Q

What are the 3 types of globulins that bind to T3 and T$?

A
  1. TBG - specific to T3 + T4.
  2. Albumin - is not specific, loosely binds to Ts + T4.
  3. Prealbumin - binds to T4 but very little T3.
17
Q

What is the main hormone product of the thyroid?

A

T4.

18
Q

Is T4 or T3 more active?

A

T3 is more active - has a shorter latent period + half life.

19
Q

How is T4 converted to T3?

A

T4 is converted to T3 is a process called Deiodination. This is the removal of one iodine from T4 and occurs in the target tissue.

20
Q

What is reverse T3?

A

It is when T4 is deiodinated at a different position which produces a biologically inactive T3.

21
Q

What are the main actions of Iodothyronines? (7)

A
  1. Increase Basal Metabolism.
  2. Increase protein, lipid and carbohydrate metabolism.
  3. Important for foetal growth + development.
  4. Enhance effects of Catecholamines.
  5. Interact with other endocrine systems.
  6. Effects on CNS.
  7. Increase vitamin C synthesis from retinal.
22
Q

What is a mechanism of action of iodothyronine?

A
  1. Enters target cell readily and binds to intracellular receptors.
  2. Receptor-hormone complex will have effect in nucleus that will lead to new proteins being made.
  3. It can also affect membrane transport pumps.
  4. Has effects on the mitochondria.
23
Q

How is iodothyronine production stimulated?

A
  1. Neurones in hypothalamus release TRH into capillary plexus.
  2. TRH passes down through portal to adenohypophysis.
  3. Stimulates production of TSH.
  4. TSH binds to receptors in thyroid and stimulates T3 + T4 production.
24
Q

How is iodothyronine production decreased?

A
  1. T3 and T4 have negative feedback effects on both the hypothalamus and the pituitary.
  2. Wolff-Chaikoff effect - a large concentration of Iodide inhibits T3 + T4 production.
  3. Somatostatin.