bodies of the type II alveolar cells, and lytic granules of cytotoxic T cells. Dense granules mainly contain bioactive amines (for example, serotonin and histamine), adenine nucleotides, polyphosphates, and pyrophosphates as well as high concentrations of cations, particularly calcium. These granules derive their name from their electron-dense appearance on whole mount electron microscopy, which results from their high cation concentrations . Dense granule exocytosis is typically evaluated by ADP/ATP release by using luciferase-based luminescence techniques, release of preloaded [ 3H] serotonin, or membrane expression of lysosome-associated membrane protein 2 (LAMP2) or CD63 by flow cytometry. Other platelet granules have been described. Platelets contain about 1–3 lysosomes per platelet and peroxisomes, the platelet-specific function of which remains unclear. Lysosomal exocytosis is typically evaluated by estimation of released lysosomal enzymes such as beta hexosaminidase. An electron-dense granule defined by the presence of Toll-like receptor 9 (TLR9) and protein disulfide isomerase (PDI), termed the T granule, has also been described, although its existence remains controversial. PDI and other platelet-borne thiol isomerases have been reported to be packaged within a non-granular compartment derived from the megakaryocyte endoplasmic reticulum (ER), which may be associated with the dense tubular system. Insulin granules in beta cells A specific type of granule found in the pancreas is an insulin granule. Insulin is a hormone that helps to regulate the amount of glucose in the blood from getting too high, hyperglycemia, or too low, hypoglycemia. Insulin granules are secretory granules, which can release their contents from the cell into the bloodstream. The beta cells in the pancreas are responsible for the storage of insulin and release of it at appropriate times. The beta cells closely control the release, and use unusual mechanisms to do so. Insulin granule maturation process Immature insulin granules function as a sorting chamber during the maturation process listed below. Insulin and other insoluble granule components are kept within the granules. Other soluble proteins and granule parts then bud off from the immature granule in a clathrin-coated transport vesicle. The process of proteolysis, removes the unwanted parts from the secretory granule resulting in mature granules. Insulin granules mature in three steps: (1) the lumen of the granule undergoes acidification, due to the acidic properties of a secretory granule; (2) proinsulin becomes insulin through the process of proteolysis. The endoproteases PC1/3 and PC2 aid in this transformation from proinsulin to insulin; and (3) the clathrin protein coat