A major challenge in physiology and pathology is an understanding of the link between the function of a cell population within its tissue environment and its interactions with other organs. The pituitary gland, regulating a diverse range of essential physiological functions, exemplifies this challenge: stimulation from the brain is relayed as variable hormone pulses (the hypothalamicpituitary (HP) system), which are decoded by peripheral organs into differential effects. The stimulatory inputs and intermediary/final secretory output of the HP system have impressive differences in time-scale and the number of cells involved: a few thousand hypothalamic neurons with signalling frequencies in the millisecond range drive hundreds of thousands of pituitary cells to secrete hormone pulses over a period of hours. These features of the HP system are conserved across a diverse range of mammals. However, how distinct populations of pituitary endocrine cells which are organized in 3D as intermingled cell networks transform hypothalamic inputs into hormone pulses in vivo was unknown. The inaccessibility of the pituitary gland, hypothalamus and target organs has led us to develop and adapt a range of methodologies to allow imaging and manipulation of their function with different experimental time-scales and level of control. Using newly-developed techniques for imaging and manipulating cells in vivo, namely in freely-behaving mouse models, we unveiled how the pituitary somatotroph network translates its hypothalamic inputs into GH pulses in the bloodstream.