signalling systems

• signalling system needed 


  co-ordinate activities in multi-cellular organism
• signalling systems

  • neurotransmission
  • developmental processes
  • homeostasis (maintain internal environment)
• signalling by free diffusion

  • autocrine - signalling and reception by same cell
  • paracrine -nearby cells
  • endocrine- distant cells
• autocrine signalling 


  chemicals secreted, modify its own behaviour

  e.g. growth regulation (-/+)
• paracrine signalling

  • neighbouring cells
  • effects are local, short-lived
  • e.g. coordinate actions of neighbouring cells in embryonic development
• synaptic signalling is example of _ signalling

  paracrine
• endocrine signalling

  • ductless glands secrete hormones into extracellular spaces
  • diffuse into circulatory signal
• endocrine signalling example glands 


  pituitary, adrenal and thyroid
• signalling via cytoplasmic connections

  • pores in membrane
  • fastest mode to communicate
  • e.g. muscle cells in heart via gap junctions
• signalling by cell to cell contact

  • cell cell recognition in animals
  • important in embryonic development and immune system
• local regulators and hormones are examples of signalling molecules
• local regulators such as growth factors

  • stimulate cell proliferation
  • more than 1 target cell, so more than 1 function
• local regulators such as gases

  • nitric oxide (paracrine signal molecule)
  • synthesized from arginine by nitric oxide synthase
  • induces vasodilation in cardiovascular system
• local regulators such as prostaglandins

  • modified fatty acids
  • excitation of uterine wall during childbirth
  • induction of fever and inflammation in immune system (pain-alleviation)
• local regulators such as neurotransmitters

  • Acetylcholine
  • Amino acids
  • inhibitory or excitatory
  • in CNS and PNS
• hormones are secreted by endocrine glands, transported in blood
• homeostasis 


  maintenance of relatively state internal environment
• blood pH is around

  7.4
• arterial blood pressure 


  120/80 mmHg
• 2 classes of hormones

  • peptides and proteins
  • steroids
• peptide and protein hormones

  • bind to receptors on cell surface
  • trigger events in cell cytoplasm through second messenger
• steroid hormones

  • manufactured from cholesterol
  • pass through membrane, and bind to receptors in cell
• signal transduction

  • conversion of signal to response in cell
• 3 steps of signal transduction

  1. reception of signal at cell surface
  2. transduction of signal
  3. cellular response
• reception of signal

  • binding of signal molecule, changing conformation of receptor
• transduction of signal

  • convert signal into response
  • multi-step
• cellular response

  • output response
  • in cytoplasm, action of nucleus, enzyme regulation, transcription factors
• signal transduction can cause more than one response from reception of single ligand
• signal specificity

  • single response
  • 2 responses
  • cross talk between 2 pathways
  • different receptor leads to different response