General ---------Biology----------------------------------------------------- ------------------Online--------------------------------------- Ch. 8 Membrane Structure and Function

Endocytosis is the process by which membranes "invaginate" and take substances into the cell. Exocytosis is a reverse of this process, where vesicles (round membrane structures containing chemicals) merge with the plasma membrane and secrete their contents from the cell.

Figure 8.19 Receptor-mediated endocytosis of your text, illustrates three types of endocytosis: phagocytosis, pinocytosis and receptor mediated endocytosis.

Phagocytosis is how amoebae cells ingest food particles and how white blood cells ingest clumps of bacteria.

Pinocytosis is one way cells can pull substances circulating the blood stream into the cell.  Pinocytosis is not selective; it simply  "gulps" in what ever is contained in the blood stream. 

Receptor mediated endocytosis is how cells selectively pull cholesterol out of the blood stream.  If you have hereditary hypercholesteremia, your genetic code produces a defective receptor protein.  This is a selective process that removes specific molecules from the blood stream.