Membrane Transport Figure [-1-4. Heart Muscle Cell Another example of secondary active transport, the countertransport(molecules move in the opposite direction)of Na* and Ca2+ in heart muscle, is shown in Figure I-1-4. In this case, as in the cotransport of sodium and glucose, transport is dependent on the ATP utilized by the na/k- ATPase pump. VESICULAR TRAFFIC AND THE PLASMA MEMBRANE cytosiN Endocytosis is the movement of macromolecules from outside the cell to the inside of the cell by the active invagination of the plasma membrane Categories Based on State(Solid or in Solution) of the Substance Taken Up Phagocytosis: The process by which solid bits of material, (e.g, bacteria, dead tissue) are engulfed by cells Fluid-phase endocytosis or pinocytosis: The uptake of molecules in solution Categories Based on Uptake Mechanisms Constitutive endocytosis: A noninduced process whereby vesicles are continuously fus- ing with the cell membrane Receptor-mediated endocytosis: The molecule being internalized(the ligand)binds to a receptor on the surface of the cell. These receptor-ligand complexes concentrate at lathrin-coated pits on the plasma membrane. The pit then pinches off, forming a vesicle. In some cases the receptors recycle back to the membrane. This process is more rapid and more specific than constitutive endocytosis edical 7..... Membrane Transport Na+ K+ Ca2+ Na+ Figure 1-1-4.Heart Muscle Cell Another example of secondary active transport, the countertransport (molecules move in the opposite direction) ofNa+ and Ca2+in heart muscle, is shown in Figure 1-1-4.In this case,as in the cotransport of sodium and glucose,transport is dependent on the ATPutilized by the Na/K￾ATPasepump. VESICULARTRAFFICANDTHEPLASMAMEMBRANE Endocytosis Endocytosis is the movement of macromolecules from outside the cell to the inside of the cell by the activeinvagination of the plasma membrane. Categories Based on State (Solid or in Solution) of the SubstanceTaken Up Phagocytosis: The process by which solid bits of material, (e.g., bacteria, dead tissue) are engulfed by cells. Fluid-phase endocytosis or pinocytosis: The uptake of molecules in solution. CategoriesBasedon UptakeMechanisms Constitutive endocytosis: A noninduced process whereby vesicles are continuously fus￾ing with the cell membrane. Receptor-mediated endocytosis: The molecule being internalized (the ligand) binds to a receptor on the surface of the cell. These receptor-ligand complexes concentrate at clathrin-coated pits on the plasma membrane. The pit then pinches off, forming a vesicle.In some cases the receptors recycleback to the membrane. This process is more rapid and more specificthan constitutive endocytosis. \ KAPLA~. meulca I 7