#GrowthHormone

#Biology

#EndocrineSystem

Introduction

• Human growth hormone (HGH) is produced by the pituitary gland and is crucial for growth, metabolism, and maintaining body structure throughout an individual's life.

• HGH is a 191 amino acid single-chain polypeptide produced by somatotropic cells in the anterior pituitary gland, primarily influencing growth during childhood.

• Functions :

• Growth Promotion - Growth hormone (GH) stimulates growth in nearly every tissue and organ, particularly affecting cartilage and bone development.

• Metabolic Regulation - GH plays a significant role in regulating metabolism, which includes how the body converts food into energy and its overall metabolic functions.

• Tissue Repair - It is essential for maintaining, building, and repairing healthy tissue in the brain and other organs, ensuring overall health and functioning.

  
  

Metabolic Reaction

• Growth hormone (GH) significantly enhances lipolysis, leading to elevated free fatty acid (FFA) levels and reduced glucose metabolism. This effect helps in preserving glycogen stores during fasting.

• The release of free fatty acids allows for the preservation of glucose stores for tissues that are unable to use lipid stores such as the brain.

• FFAs activate receptors in pancreatic islet cells, adipocytes, and enteroendocrine cells. This activation regulates the secretion of hormones that influence glucose metabolism.

• GH promotes lipolysis by inhibiting lipoprotein lipase, which is essential for the degradation of triglycerides, thus enhancing fat breakdown.

Tissue Repair

• GH leads to an increased influx of amino acids into the cell, decreasing the flow of these from the same.

• The increase in fatty metabolism that GH produces is also beneficial, since it preserves the amino acids for the synthesis of proteins, instead of being used as an energy resource.

Growth Promotion

• Growth hormone promotes the multiplication of bone cells, particularly in cartilage, facilitating height increase during puberty.

• Growth hormone (GH) binds to specific receptors on target cells, activating the MAPK/ERK pathway, which is crucial for cellular replication and growth.

• The MAPK/ERK pathway is a chain of proteins that transmits signals from a cell's surface to its nucleus.

• The MAPK/ERK pathway, also known as the Ras-Raf-MEK-ERK pathway, is a series of steps that transmit signals from the cell surface to the nucleus: 

  1. Ligand binding: A signaling molecule, such as a hormone, cytokine, or growth factor, binds to the receptor tyrosine kinase (RTK) on the cell surface. 

  2. Dimer formation: The receptor subunits form a dimer, which activates the RTK. 

  3. Adaptor proteins: Cytoplasmic adaptor proteins bind to the RTK. 

  4. Guanine–nucleotide exchange factors (GEFs): GEFs are attracted to the plasma membrane by the adaptor proteins. 

  5. RAS activation: GEFs activate the small GTPase RAS, which is usually inactive and bound to guanosine diphosphate (GDP). 

  6. MAPKKK activation: RAS activates a protein kinase, called mitogen-activated protein kinase kinase kinase (MAPKKK). 

  7. MAPKK activation: BRAF, the MAPKKK, phosphorylates the second protein kinase, MAPKK (MEK). 

  8. ERK activation: MEK activates ERK, the final kinase in the cascade. 

  9. Gene expression: ERK travels to the nucleus and regulates gene expression. 

• Phosphorylating transcription factors: Activated ERK enters the nucleus and phosphorylates transcription factors like Elk-1, c-Myc, STATs, Jun, Fos, ATF2, and Max. This phosphorylation increases DNA binding and transcriptional activity.