Endocrine 1.2: Thyroid et autres

Question 1

What cells release thyroid hormone?

Answer 1

Cellules folliculaires around the substance colloide

Question 2

Calcitonin release point and role?

Answer 2

Cellules C in the thyroid
Has nothing to do with T3/T4 it is a calcium related hormone -> reduces calcium levels

Question 2

True or false,

Iode is a key component of our diet important for multiple physiological roles

Answer 2

FALSE
Seule fonction de l’iode dans le corps = synthèse T4 et T3

Question 3

Explain Iode role in T4/T3 synthesis

Answer 3

1. So first TRH (from hypothalamus) stimulates TSH (anterior pituitary) secretion.
2. TSH stimulates the NIS (Sodium, Iode channel) which allows for Iode ions to enter the thyroid cells.
   note: TSH stimulates everything in the chain!
3. Iode is diffused across the cell and transported into colloide via Pendrins
4. Thyroglobulin (precursor) is produced by the RE and transported to the colloide
5. TPO (key enzyme; thyroperoxidase) will create DIT(T4) and MIT(T3)
6. T3/T4 enter back in the cell (endocytosis)
7. T4 deodinated to T3 and released

Question 4

Why do we say that the T4 hormone doesn’t have an effect although 93% of thyroid hormones are in that form

Answer 4

Thyroid hormones are always conjugated to a protein
(sorta like biliruibin is to albumin)

In this case, principalement à la Thyroxin-binding globulin (TBG)

The reason why T4 is “useless” is because TBG has a high affinity for T4 and thus renders it innactive

Free T3 can act but not T4-> C’est la T3 qui est biologiquement active

As such, T4 can be used as a storage for T3. Remove one iode:
La T4 doit donc être désiodée
Just fun fact: *80% de la T3 provient de la désiodination

Question 5

What kind of hormones are T3/T4?

Answer 5

nuclear receptor hormone

Question 6

TSH and T3/T4 levels:
Lorsque la thyroïde fonctionne trop vite

Answer 6

Low TSH
High T3/T4

Question 7

TSH and T3/T4 levels:
Lorsque la thyroïde fonctionne mal

Answer 7

High TSH (And TRH)
Low T3/T4

Question 8

Why would a damaged thyroid gland be larger?

Answer 8

TSH is inhibited by T3/T4

When T3/T4 is not being released -> +++ TSH
+++TSH = stimulate of thyroid
+++la mitose des cellules folliculaires -> croissance de la thyroïde (effet trophique)

Question 9

Difference between primary or secondary glandular issues in thyroid hormones and associated TSH levels/

Answer 9

When gland is the issue : atteinte glandaire primaire = ++TSH

When it is the hypophyse that is not working: atteinte glandulaire secondaire = –TSH

Question 9

Role of PTH (parahormone)

Answer 9

Regulation of Calcium
Hypercalcimante

Question 10

Describe PTH circuit

Answer 10

1. A decrease in plasmic calcium levels leads to a signaling in the parathyroid hormone
2. PTH is released and acts on 4 organs (bone, skin, intestin, kindey)
3. Major effect is the increase in Calcium from Hypocalcemia to Normal Levels
4. Note that skin effect is the activation of Vitamin D which also helps in Ca+ reabsorption

Question 11

True or False,

The release of PTH in respondance to Ca+ levels follows a sigmoid curve. This means that a gradual decrease in Ca+ is followed byu a gradual PTH release.

Answer 11

FALSE

It does follow sigmoid which means
A decrease in calcium to a set point will lead to RAPID PTH release

Question 12

Why can you say that calcium in a PTH inhibitor?

Answer 12

Calcium can act on CaSR (calcium sensing receptor) and activates it

CaSR leads to inhibition of PTH secretion

Question 13

Effect of phosphore on calcium?

Answer 13

We cannot have both high calcium and phosphor levels at the same time
-> PTH is a phosphoturic hormone -> secretes phosphore in the urine at the kidney level

Counter intuitive however:
PTH ALSO augmente l’absorption du phosphate au
niveau intestinal via 1,25(OH)2D