Читать книгу Essential Endocrinology and Diabetes - Richard I. G. Holt - Страница 42

Newly synthesized peptide hormone is stored within the cell in small vesicles or secretory granules. Movement of these vesicles to a position near the cell membrane is influenced by two types of filamentous structure: microtubules and microfilaments (Figure 2.3a). Consequently, the secretion of stored hormone tends to be rapid but only occurs after appropriate stimulation of the cell. Whether this is hormonal, neuronal or nutritional, it usually involves a change in cell membrane permeability to calcium ions. These divalent metal ions are required for interaction between the vesicle and plasma membrane, and for the activation of enzymes, microfilaments and microtubules. The secretory process is called ‘exocytosis’ (Figure 2.3a). The membrane of the storage granule fuses with the cell membrane at the same time as vesicular endopeptidases are activated. The active hormone is expelled into the extracellular space from where it enters the bloodstream. The vesicle membrane is then recycled within the cell.