Levels of Structural Organization in the Human Body

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  • 0:00 Levels of Organization
  • 0:36 Organism Level
  • 0:48 Organ System Level
  • 1:27 Organ Level & Tissue Level
  • 3:22 Cellular Level
  • 4:49 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

Explore the structural organization of the human body, starting at the level of the organism and progressing down in complexity through the organ system, organ, tissue, and cellular levels. Major features of each level are discussed.

Levels Of Organization

The human body is incredibly complex, but it does have an underlying organization. Learning this organizational structure can really help you visualize and understand how the human body is built and how it functions. The levels of organization start at the most complex level and end at the most basic level, from the whole organism to the cellular level. Each step down in level represents a decrease in complexity. The levels include:

  • Organism
  • Organ system
  • Organ
  • Tissue
  • Cell levels

Let's start working our way down through these levels.

Organism Level

The top level is an easy one. This is just the organism, or the life form and all the systems, organs, tissues, cells, and molecules that it contains. An example of an organism: you!

Organ System Level

The first step down starts to break up the body, or the organism, into major systems that are dedicated to specific functions. Organ systems are made up of organs that work together to perform specific and vital functions within the body. You have likely heard of some of these systems, such as the digestive, urinary, muscular, and reproductive systems. You probably even have a pretty good idea of some of the major functions for these systems. In total, there are eleven organ systems in the body. In addition to those listed above, we also have the respiratory, cardiovascular, nervous, endocrine, lymphatic, skeletal, and integumentary systems.

Organ Level

We started with the whole organism, then the organ systems; now we get to the organs that are part of those organ systems. Imagine an airport, a great example of a system, dedicated to getting each passenger from the front entrance onto a plane. Within the system, there are multiple separate units: check-in, security, gates, boarding bridges, etc. These units are like organs: each has a dedicated function and only together do they achieve the overall goal of the system. Within an organ system, an organ is a structure composed of multiple tissue types that carries out a specific function.

There are many organs in the body, so let's just think about the organs that are part of one specific organ system. When you think of the digestive system, you think of processing food and absorbing it. That should bring to mind the stomach and intestines, which are in fact major digestive organs.

Tissue Level

If you could shrink yourself down and take a little stroll through your organs, you would start to notice some similar landscapes. These landscapes are the tissues that make up your organs. A tissue is a group of similar cells working together to perform a function. There are four tissue types within the human body. That means that any individual organ can only be composed of at most four different tissue types; this is why on your stroll through the organs, you would certainly start to notice some similar looking tissues. Let's look at the major features of the four tissue types.

Epithelial tissue- cells are pressed up against one another and can form barriers (think skin).

Connective tissue- cells are embedded in a fluid and protein mixture that varies in consistency from completely liquid (blood) to rigid (bone).

Muscle tissue- collections of cells that are able to contract forcefully in a coordinated way.

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