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Lecture Slides-Animal Structure and Function

5 x 1013 why are cells so small and why do we have so

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Unformatted text preview: 75 trillion cells (7.5 x 1013) Why are Cells So Small and Why Do We Have So Many? • There are ~ 1 billion cells per gram of tissue (109 cells/g) assuming nominal human male weight of 70 kg • Small cells maximize surface area to volume ratio • Variability between cells is minimized by having very large numbers • Statistical variability (s.d.) approx. by √N • For 1 g of tissue: √N = √109 = 3.2 x 104 Relative error = √N/N = .003% Relative Tissues, Organs, and Organ Systems • Epithelial tissues are sheets of tightly connected cells that cover body surfaces and line hollow organs. • Connective tissues support and reinforce other tissues. They generally consist of dispersed cells in an extracellular matrix. • Muscle tissues contract. There are three types: skeletal, cardiac, and smooth. • There are two types of cells in nervous tissues: Neurons generate and transmit electrochemical signals, and glial cells provide supporting functions for neurons. Epithelial Tissues • EPITHELIAL TISSUES are sheets of interconnected cells that cover the body surfaces and line hollow internal b...
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