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The endocrine system physiology

Part 4 (last part)

In this chapter we're going to talk about:

1. Thyroid Hormones.

2. Insulin & Glucagon.

Thyroid Hormones:

T4 or Thyroxine

T3 or Triiodothyronine

Calcitonin.

T4 & T3 :

T4 and T3 are tyrosine based hormones. Produced by the follicular cells (thyrocytes).

Synthesis:

Iodide (I-) is taken from the bloodstream by follicular cells to the colloid where it gets oxidized to iodine (I) then it combines with thyroglobulin to form MIT (monoiodotyrosine) and DIT (diiodotyrosine) .

Two DIT molecules combine to form T4 while MIT & DIT combine to form T3.

Iodinated thyroglobulin is transported back to the follicular cells and is cleaved by lysosomes.

T4 & T3 are then released into the circulation through MCT transporter.

Regulation:

TRH ➡ TSH ➡ THYROID ➡T4 & T3

➡ By:

⏫Iodide pumping

⏫ Iodination

⏫Thyroglobulin synthesis.

⏫ release of thyroid hormone.

T4 & T3 bind in the plasma to plasma proteins such as:

TBG or Thyroxine binding globulin

Albumin

Transthyretin.

The bound form is the inactive form. While free T3 & T4 form the active form that works on cells.

Note that inside the cell T4 is coverted to T3 by 5-Iodinase.

Effects:

⏫ Basal metabolic rate.

⏫Activation of sympathetic nervous system.

⏫long bone growth

⏫Hair follicle growth

Regulation of body temperature & weight.

Brain development.

Insulin:

Is a peptide hormone produced and secreted by Beta cells which are cells in the islets of langerhans

Synthesis:

Single polypeptide (preproinsulin) ➡ proinsulin (which has 3 chains : peptide A, peptide B and peptide C in between.

Proinsulin gets cleaved on two positions leaving the C chain alone (AWW :-( )

Two disulfide bonds connect The B chain and the A chain to form INSULIN

Effects:

⏬⏬ Blood sugar levels.

How :

In the liver:

Activates the formation of glycogen

(glucose ➡ glycogen)

In adipose tissue:

Activates glycolysis

In skeletal muscles :

stimulates amino acids and glucose uptake into muscle cells ➡ protein production and muscle growth.

Inhibites:

▶ Gluconeogenesis

▶ lipolysis.

Glucagon:

A hormone produced by alpha cells which are cells in the islets of langerhans.

Works by ⏫⏫ blood suger ▶ in situations like: fasting.

And it does that by:

▶ activation of gluconeogenesis & glycogenolysis

▶ activation of lipolysis.

Glucagon is a catabolic hormone which means it promotes the breaking down of large storage molecules inside certain tissues into small energy molecules in the blood.

Glucagon stimulators:

▶ low blood suger

▶ adrenaline

▶ cholecystokinin

Glucagon inhibitors:

▶ high blood sugar

▶ somatostatin

▶GH

Part 1

Part 2

Part 3

🌸- 🌸-🌸-🌸-🌸-🌸-🌸-🌸-🌸

Hello 🌸🍃

With this we're done with a good part of endocrine physiology!Next, we're going to start with clinical cases and diseases related to the endocrine system (aka we're gonna get serious SERIOUS xD) I hope you find this helpful in reviewing or studying ☺

Thank you so much🌸🍃

Marie🌸

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