456 Chapter 9 Human Body Orientation
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Recall Activity
1. List the fi ve levels of organization in order of complexity from complex to simple. __________________ fi
______________________________________________________________________________________________________________________________________ _
2. Together, all of the __________________________ make up the human organism.
Concept 2: Cell Level
As you have learned, the cell is the basic unit of life. Human body cells are l
specialized to perform specific functions in the body. If you were to look at
the body’s alimentary canal on a cellular level, you would study many types
of cells and their functions. For example, in the stomach, parietal cells release
hydrochloric acid to make the environment acidic. Chief cells in the stomach
secrete pepsinogen, which aids in digestion, and mucous neck cells produce
mucus to protect the cells lining the stomach. Smooth muscle cells move food
through the alimentary canal, and simple columnar epithelial cells with micro-
villi absorb digested macromolecules.
Small S
estines in te
Cell level
Columnar cell
Organ level Organ
Small intestine
Organism
Human
Body system levelv ody system le
m Digestive syst em
Tissue leveleev Tissue lev el el T T
of small intestine ine Tissue u
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© Body Scientific International
Figure 9.16 The body is organized into five different levels.