3.8 Cellular Extensions

Microvilli

-Minute, fingerlike extensions of plasma membrane that project from surface of select cells (example: intestinal and kidney tubule cells) -Used to increase surface area for absorption -Have a core of actin microfilaments that is used for stiffening of projections

Cilia

-are whiplike, motile extensions on surfaces of certain cells (such as respiratory cells) -Thousands of cilia work together in sweeping motion to move substances (example: mucus) across cell surfaces in one direction

Cilia and Flagella

-have "9 + 2" pattern of microtubules (9 sets of double tubes surrounding a central pair of doublets). -Slightly different from 9 + 0 pattern of centriole (9 triplets with no tubules in center) -Cilia movements alternate between power stroke and recovery stroke; this alteration produces a current at cell surface that moves substances forward

Cellular extension

Certain cells have structures extending from the cell surface

Flagella

longer extensions that propel the whole cell (example: tail of sperm) Both structures are made up of microtubules synthesized by centrioles that are called basal bodies because they form the base of each cilium and flagellum