SÍNTESIS DE T3 Y T4 | GuiaMed

Introduction and Overview

The speaker introduces themselves as Cristian Púlsar and begins discussing the topic of thyroid hormone synthesis. They outline the content that will be covered, including the anatomy, histology, physiology, and synthesis of T3 and T4 hormones.

Anatomy of the Thyroid Gland

• The thyroid gland is located in the neck region.

• It consists of a right thyroid lobe, left thyroid lobe, and an isthmus that connects them.

• The superior boundary is mainly formed by the larynx (thyroid cartilage), while the inferior and lateral boundaries are formed by the trachea.

Delimitations and Parts of the Thyroid Gland

• The thyroid gland has three important parts: right thyroid lobe, left thyroid lobe, and isthmus.

• It resembles a shield or butterfly shape.

• The delimitation of the gland is mainly determined by surrounding structures such as the larynx (superiorly), trachea (inferiorly), and other neighboring tissues.

Histology of the Thyroid Gland

• Microscopically, the functional unit of the thyroid gland is called follicles.

• Follicles are composed of follicular cells that secrete colloid internally.

• Other cell types present in histology include parafollicular cells responsible for calcitonin secretion.

Function of the Thyroid Gland

• The main function of the thyroid gland is to produce and release T3 (triiodothyronine) and T4 (thyroxine) hormones.

• These hormones are involved in growth, maintenance of bodily activities, and regulation of metabolism.

Synthesis of Thyroid Hormones

• The synthesis of T3 and T4 hormones requires iodine as a raw material.

• Iodine is obtained through dietary intake, mainly from iodized salt.

• After ingestion, iodide is absorbed into the bloodstream and transported to the thyroid gland.

• Approximately one-fifth of the ingested iodide accumulates in the thyroid gland.

Uptake of Iodide by Follicular Cells

• Iodide is taken up by follicular cells (thyrocytes) from the bloodstream.

• Follicular cells have an important ATPase pump that facilitates this uptake process.

Control of Thyroid Hormone Synthesis

• The synthesis of T3 and T4 hormones is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus and thyroid-stimulating hormone (TSH) produced by the pituitary gland.

• TSH controls proper synthesis and release of thyroid hormones.

These notes provide a clear overview of the transcript, summarizing key points related to the anatomy, histology, physiology, and synthesis of thyroid hormones. Each section is organized with concise bullet points linked to relevant timestamps for easy reference during study.

Sodium Transport into the Cell

This section explains how a pump removes sodium from the cell, creating a decrease in sodium concentration. As a result, the cell tries to bring in more sodium, which is facilitated by an importer called anis. The anis molecule allows the entry of iodide along with two sodium molecules.

• The pump removes large amounts of sodium from the cell, causing a decrease in intracellular sodium concentration.

• The cell responds by trying to bring in more sodium.

• An importer molecule called anis facilitates the entry of iodide along with two sodium molecules.

• This process is known as trapping iodide inside the follicular cell.

Iodide Transport into the Colloid

Once iodide is trapped inside the follicular cell, it needs to be transported into the colloid. This transport is facilitated by a molecule called endrina, which acts as a transporter for chloride and iodide ions.

• Endrina helps transport iodide into the colloid by exchanging it with chloride ions.

• Chloride ions exit while iodide ions enter the colloid.

• This process is known as iodine transport to the colloid.

Formation of Thyroglobulin and Thyroid Hormones

Thyroglobulin is formed within thyroid cells and plays a crucial role in hormone synthesis. It is composed of tyrosine amino acids that bind with iodine molecules to form thyroid hormones T1 and T2. These hormones can further combine to form T3 and T4.

• Thyroglobulin is synthesized within thyroid cells using tyrosine amino acids derived from rough endoplasmic reticulum.

• Tyrosine amino acids bind with iodine molecules to form thyroid hormones T1 and T2.

• T1 (monoiodotyrosine) and T2 (diiodotyrosine) are the initial products of this process.

• T1 and T2 can combine to form T3 (triiodothyronine) or T4 (thyroxine).

• The majority of synthesis results in the production of T4.

Oxidation of Iodide to Iodine

Before iodide can bind with tyrosine within thyroglobulin, it needs to be oxidized to iodine. This oxidation process is facilitated by an enzyme called peroxidase.

• Peroxidase enzyme oxidizes iodide ions, converting them into iodine.

• This process is known as the oxidation of iodide ions.

• Oxidized iodine is necessary for binding with tyrosine within thyroglobulin.

Coupling of Iodotyrosines and Formation of Thyroid Hormones

Once iodide has been oxidized to iodine, it can couple with tyrosine amino acids within thyroglobulin to form thyroid hormones. The coupling can result in the formation of either T3 or T4, depending on the specific combination.

• Coupling refers to the joining of iodotyrosines (T1 and T2) with each other or with other forms of tyrosines within thyroglobulin.

• Different combinations can lead to the formation of either T3 or T4.

• If two diiodotyrosines combine, they form tetraiodothyronine (T4), also known as thyroxine.

• If a monoiodotyrosine combines with a diiodotyrosine, they form triiodothyronine (T3).

Synthesis Ratio and Coupling Efficiency

The synthesis of thyroid hormones results in a higher production of T4 compared to T3. Approximately 93% of the synthesized hormones are T4, while only around 7% are T3.

• The synthesis ratio between T4 and T3 is approximately 93:7.

• The majority of synthesized hormones are in the form of T4.

• Coupling efficiency determines the proportion of T3 formed from iodotyrosine coupling.

Timestamps have been associated with relevant bullet points as requested.

Storage and Release of Thyroid Hormones

This section explains how thyroid hormones are stored and released in the body.

Storage of Thyroid Hormones

• Thyroid hormones T4 and T3 are stored in the thyroglobulin within the thyroid gland.

• These hormones are bound to thyroglobulin until they are needed by the body.

• The storage can last for two to three months before the hormones are released.

Release of Thyroid Hormones

• When the body requires thyroid hormones, they are released from the thyroglobulin.

• The hormones are transported as vesicles from the thyroid cells to follicular cells through a process called pinocytosis.

• Enzymes break down thyroglobulin, releasing T1 and T2.

• T1 and T2 do not play a significant role in regulating metabolism, so an enzyme called deiodinase removes iodine from them for recycling.

• T3 and T4, on the other hand, pass through the follicular cell membrane into circulation.

• In circulation, they bind to proteins like globulin and albumin before traveling to peripheral tissues.

Synthesis of Thyroid Hormones

This section discusses the synthesis of thyroid hormones.

Trapping Iodide

• Iodide is trapped by sodium iodide symporter (NIS) in thyroid cells.

Iodination of Tyrosine

• Iodine is added to tyrosine residues within thyroglobulin through a process called tyrosine iodination.

• Multiple iodinated tyrosines combine to form T3 or T4.

Storage in Thyroglobulin

• Newly synthesized T3 and T4 molecules bind with thyroglobulin for storage.

Release of Thyroid Hormones

• T3 and T4 are released from thyroglobulin through enzymatic breakdown.

• The hormones then enter circulation for distribution to peripheral tissues.

Conclusion and Call to Action

This section concludes the video and encourages viewers to engage with the content.

• Understanding thyroid hormone synthesis and storage is crucial for comprehending related pathologies.

• Viewers are encouraged to like, comment, share, and subscribe to the channel for more informative videos on thyroid-related topics.