[#2] INTRODUÇÃO SISTEMA ENDÓCRINO: Síntese, secreção, transporte e mecanismos de ação dos hormônios

Summary

This video provides an in-depth explanation of how hormones are synthesized, secreted, transported, and how they act on target cells. It covers the processes behind the synthesis of peptide, amino acid-derived, and steroid hormones, highlighting the different mechanisms involved. Peptide hormones are synthesized in cells, stored, and secreted via exocytosis in response to specific signals, while steroid hormones are released immediately after synthesis. The video also explores how these hormones travel through the bloodstream—water-soluble ones freely, while lipid-soluble ones bind to transport proteins. Lastly, the video details how hormones bind to receptors on target cells, inducing cellular responses or gene transcription changes.

Takeaways

• 😀 Peptide hormones are synthesized through gene transcription in the cell nucleus and processed through various enzymatic reactions in the endoplasmic reticulum and Golgi apparatus.
• 😀 Amino acid and steroid hormones are synthesized from specific precursors, such as amino acids (for amino acid hormones) or cholesterol (for steroid hormones), and require a set of enzymes to catalyze the reactions.
• 😀 Lipid-soluble hormones, including steroid hormones, cannot be stored in secretory granules and are released immediately upon synthesis, while water-soluble hormones are stored until needed.
• 😀 The secretion of water-soluble hormones involves exocytosis, triggered by specific signals that cause the granules to fuse with the cell membrane.
• 😀 Lipid-soluble hormones diffuse through the cell membrane upon synthesis and are released directly, rather than being stored.
• 😀 The secretion of water-soluble hormones can be triggered by external signals, such as neural input (e.g., insulin secretion in pancreas cells), or by other hormones (e.g., growth hormone secretion in the pituitary gland).
• 😀 Hormones are transported in the bloodstream either freely (water-soluble hormones) or bound to specific carrier proteins (lipid-soluble hormones).
• 😀 To have an effect on a cell, a hormone must bind to a specific receptor present on the target cell. If the receptor is not present, the hormone cannot act on that cell.
• 😀 Water-soluble hormones bind to receptors located on the cell membrane, while lipid-soluble hormones can bind to intracellular receptors, including those in the cytoplasm or nucleus.
• 😀 The action of lipid-soluble hormones is slower, as they typically alter gene transcription, which then influences cell function. However, some lipid-soluble hormones may act faster by using membrane-bound receptors.

Q & A

What is the first step in the synthesis of peptide hormones?

The synthesis of peptide hormones begins with the transcription of the gene encoding the hormone in the nucleus of the endocrine cell.

How are peptide hormones processed after transcription?

After transcription, the mRNA is translated by ribosomes on the rough endoplasmic reticulum, producing a precursor called preprohormone. This precursor undergoes enzymatic modifications to form prohormone, which is then packaged in secretory vesicles in the Golgi apparatus.

Why can't steroid hormones be stored in secretory vesicles?

Steroid hormones are lipophilic (fat-soluble), so they cannot be stored in secretory vesicles. Since these vesicles have lipid membranes, steroid hormones diffuse directly through the cell membrane as soon as they are synthesized.

How are steroid hormones transported in the blood?

Steroid hormones are lipophilic and not soluble in the aqueous plasma of the blood. Therefore, they are transported in the bloodstream by binding to specific plasma carrier proteins.

What triggers the secretion of water-soluble hormones?

The secretion of water-soluble hormones, such as peptide hormones, is triggered when the endocrine cell receives a specific signal, which activates exocytosis of the secretory vesicles containing the hormone.

How do water-soluble hormones act on target cells?

Water-soluble hormones cannot pass through the lipid membranes of cells. Instead, they bind to receptors on the cell membrane, which triggers intracellular signaling pathways that alter the cell’s function.

What is the role of receptors for lipophilic hormones?

Lipophilic hormones, such as steroid hormones, can pass through the cell membrane and bind to intracellular receptors. These receptors can act as transcription factors, influencing the expression of specific genes and thus altering cell function.

How does the action of lipophilic hormones differ from water-soluble hormones?

The action of lipophilic hormones is slower because they alter gene transcription, which requires more time to produce the corresponding proteins. In contrast, water-soluble hormones often initiate faster responses through signaling pathways in the cytoplasm.

Can lipophilic hormones also act through membrane-bound receptors?

Yes, some lipophilic hormones can also bind to membrane-bound receptors, leading to faster cellular responses, similar to how water-soluble hormones act.

What happens when a cell does not have a receptor for a specific hormone?

If a cell does not have a receptor for a specific hormone, it cannot respond to that hormone. Receptors are necessary for the hormone to bind and exert its effects on the cell.