Explain the purpose of each of the following modes of cellular communication in multicellular organisms, and give an example of each from human physiology. For each, identify the ligand, and the response:
a. Cell-Cell contact - allow for cytoplasm movements between cells for ions, sugars, amino acids and other small molecules; Heart tissue use this to move stimulation for heart contraction through the muscle; Ligand stimulation of SA node in back of atrium chambers that releases calcium for muscle contraction throughout the heart
b. Paracrine signaling - between local cells where the signals elicit quick responses and last only a short amount of time due to the degradation of the paracrine ligands. Growth hormone between cells or the release of calcium from one nerve cell to stimulate the membrane of muscle tissue for contraction
c. Endocrine signaling - long distance communication that is slow starting and long lasting; you can have both protein and lipid (steroid) based ligands; For milk let down for a suckling child both prolactin and oxytocin are released to act on the mammary glands to release milk for the child until the child is removed from the breast
d. Nervous system signaling - to transfer nervous stimulation across synaptic gap for further integration in the brain for production of appropriate neural response; neurotransmitter release from presynaptic nerve to postsynaptic nerve carries signal to brain or to muscles for decision making or movement needed for stimulus