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1
NOITCES
CHAPTER
1
Basic structure and function of cells
Epithelial cells rarely operate independently of each other and com-
CELL STRUCTURE
monly form aggregates by adhesion, often assisted by specialized inter-
cellular junctions. They may also communicate with each other either
GENERAL CHARACTERISTICS OF CELLS by generating and detecting molecular signals that diffuse across inter-
cellular spaces, or more rapidly by generating interactions between
The shapes of mammalian cells vary widely depending on their interac- membrane-bound signalling molecules. Cohesive groups of cells con-
tions with each other, their extracellular environment and internal stitute tissues, and more complex assemblies of tissues form functional
structures. Their surfaces are often highly folded when absorptive or systems or organs.
transport functions take place across their boundaries. Cell size is Most cells are between 5 and 50 µm in diameter: e.g. resting lym-
limited by rates of diffusion, either that of material entering or leaving phocytes are 6 µm across, red blood cells 7.5 µm and columnar epithe-