ENDOCYTOSIS ::
May be of two types pinocytosis and phagocytosis pinocytosis (cell drinking) is the movement of fluids and whole macromolecules into the cell whereas phagocytosis (cell eating )is the movement of particles into into the cells absorption of intact proteins and vitamin B12 by the digestive system occurs through
the process of pinocytosis phagocytosis is an important mechanism by which the body removes foreign or abnormal cells from circulation it is a defense mechanism carried out by leucocytes and macrophages
The interaction of strong salt solution and proteins with molecules in cell membrane leads to its infolding as a result extracellular fluid and its contents become surrounded by the membrane changes in surface tension cause the fluids components of cell membrane to make deeper folds fuse and form a spherical sac called pinocytic vessicle lysosomes within the cytoplasm because become attached to the pinocytic vesicle and release hydrolytic enzymes into it the enzymes break up large molecules such as proteins etc and the subsatances are diffused out into the cytoplasm
EXOCYTOSIS is essentially the reverse of endocytosis molecules synthesized within the cell are surrounded by membranous components forming secretory vesicles which seem to originate from the golgi apparatus each vesicle fuses with the plasma membrane and makes opening in it the molecules compressing the outer limiting vesicle membrane separate out and the contents pass out into the extracellular fluid exocytosis is reponsible for secretion of proteins including neurotranasmitters some enzymes hormones and other molecules
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