– Exocytosis is the process by means of cells secrete different kinds of molecules content in a cytoplasmic vesicle from cytoplasm to extracellular (intersticial) space. It occurs in all the eukaryotic cells and it implies the fusion of the vesicular membrane with the cytoplasmic membrane. Exocytosis is very specialized in secreting cells and neurons.
– Pynocytosis is the process by means of cells ingest liquid particles or dissolved particles from extracellular (intersticial) space to cytoplasm. This process is very common in cells with nutritive function (as cells of the intestinal mucose).
Alpha cells produce and secrete glucagon, so the process is exocytosis. At better, in your textbook call them exopynocytosis because alpha cells can carry out the two processes independently. They secrete glucagon by exocytosis, but they can ingest dissolved substances by pynocytosis. Do you understand what I mean?
Question: once a cell secretes substances, can you only call it exocytosis? I mean, would there be sub-categories like secreting more liquid substances e.g. "cell sweating" as the reverse of pinocytosis "cell drinking"?