Chemical messengers

• Classic Endocrine


  Hormones produced by specific glands or cells and released into the bloodstream, travel throughout the body to reach distant target cells, crucial for regulating long-term processes like growth, reproduction, and metabolism
• Paracrines


  Signals secreted by cells and act on nearby target cells, don't travel through the bloodstream but instead diffuse through the extracellular fluid to nearby cells, regulate processes such as cell growth, division, and tissue repair
• Paracrine signals


  • Histamine
  • Nerve growth factor (NGF)
  • Epidermal growth factor (EGF)
  • Vascular endothelial growth factor (VEGF)
• Autocrines


  Molecules produced by a cell and act on receptors located on the same cell that released them, can also function as paracrines or other types of messengers
• Autocrines


  • Growth factors
• Cytokines


  Signaling molecules secreted by various cells, including immune cells, can act locally on nearby cells, diffuse to neighboring cells, or be transported through the bloodstream to affect distant cells, play crucial roles in regulating immune responses, inflammation, and other cellular processes
• Cytokines


  • Interleukins
  • Interferons
• Neurotransmitters


  Molecules released by neurons at specialized junctions called synapses, travel a short distance across the synaptic gap and bind to receptors on the surface of target cells
• Neurohormones


  Hormones secreted by specialized neurons, known as neurosecretory cells, but instead of acting locally like neurotransmitters, they are released into the bloodstream for transport to distant target cells