Concept 27.1

Structure Fits Functions in theHuman Body

Key Terms anatomy: study of an organism's structure

physiology: study of functions or processes in an organism

tissue: cooperating unit of many similar cells that perform a specific function

organ: unit consisting of several tissues that together perform a specific task

organ system: unit of multiple organs that together perform a vital body function

Anatomy and PhysiologyA close look at a biological structure often provides cluesabout its function. Structures that look alike often havesimilar functions. For example, if you look at your teethin a mirror, you'll see thin-edged, sharp teeth in frontcalled incisors (Figure 27-1).

Their shape may remind you of the sharp blade of acutting tool, such as a knife. Indeed, the function ofincisors is to cut through pieces of food.

Figure 27-1

Incisors and molars have different structures that fit their different functions. Molars have a bumpy surface that mashes food. Incisors

have a sharp, thin edge that cuts food.

Anatomy and PhysiologyThe teeth in the back of your mouth, molars, have manysharp bumps that resemble a meat tenderizer's hard,bumpy surface. Just as a chef pounds a tenderizer againsta tough piece of meat to soften it before cooking, molarsgrind and mash food before it is swallowed.

Anatomy and PhysiologyThe study of the structure of an organism and its parts iscalled anatomy. For example, the anatomy of yourmouth reveals how many teeth you have, their shapes,and their position in your jaw.

Physiology (fiz ee AWL uh jee) is the study of what structuresdo, and how they do it—in other words, their function.Studying how your jaw moves your teeth when you chewand how your teeth cut and mash your food isphysiology.

Levels of Body StructureAs in other multicellular organisms, your body hasseveral levels of organization. Figure 27-2 shows thestructures that make up one system in your body, thecirculatory system.

The first level is the cell, such as a muscle cell in yourheart. Each heart muscle cell is branched, allowing it tointerlock with other surrounding heart muscle cells,much as jigsaw puzzle pieces fit together. Thisinterlocking helps coordinate the actions of neighboringcells. Together, these cells form a muscle tissue.

Levels of Body StructureA tissue is a cooperating unit of many similar cells thatperform a specific function. In this case, the tightorganization of the muscle cells allows the muscle tissueto produce heartbeats that pump blood.

In addition to muscle tissue, the other major types oftissue are epithelial, connective, and nervous tissue.

Figure 27-2

The smallest level of organization shown in this diagram is the cell. Cells working together make up a tissue, which in turn is part of an organ. Organs working together form the different organ systems that make up a whole organism.

Levels of Body StructureAn organ consists of several tissues that togetherperform a specific task. For example, your heart is anorgan composed of muscle and other tissues, such asnervous tissue, that together produce a pumping action.

An organ system consists of multiple organs thattogether perform a vital body function. The organs of thecirculatory system are the heart and blood vessels.Together, they constantly transport blood throughoutthe body.

Levels of Body StructureThe highest level of structure is the whole organism, inthis case a human being.

Different organ systems work together, contributing tothe successful function of the whole organism. Forexample, without oxygen supplied by the respiratorysystem and nutrients provided by the digestive system,the heart cannot pump blood and the circulatory systemcannot function.

Levels of Body StructureAnother example is the coordination of the nervous,muscular, and skeletal systems in moving parts of thebody. Nerves stimulate muscles to contract, and themuscles in turn move the bones of the skeleton to whichthey are attached.

Figure 27-3 introduces the major functions and organsof 12 organ systems in the human body.

Figure 27-3a

This diagram shows 12 organ systems in the human body. Note the major organs that make up each system..

Figure 27-3b

This diagram shows 12 organ systems in the human body. Note the major organs that make up each system..