The human body has 6 main levels of structural organization. We will begin with the simplest level within the structural hierarchy.
Chemical level– To study the chemical level of organization, scientists consider the simplest building blocks of matter: subatomic particles, atoms and molecules. All matter in the universe is composed of one or more unique pure substances called elements, familiar examples of which are hydrogen, oxygen, carbon, nitrogen, calcium, and iron. The smallest unit of any of these pure substances (elements) is an atom. Atoms are made up of subatomic particles such as the proton, electron and neutron. Two or more atoms combine to form a molecule, such as the water molecules, proteins, and sugars found in living things. Molecules are the chemical building blocks of all body structures.
Cellular level– the cellular level is made up of the smallest unit of living matter, the cell. Individual cells may have some common functions but vary widely in size and shape. Humans are multi-cellular animals. That means we are made of lots of cells, not just one cell. The cells in many multi-cellular animals and plants are specialised, so that they can share out the processes of life. They work together like a team to support the different processes in an organism.
How does the cell works? Look at the video!!
Tissue level– Tissues are groups of similar cells that have a common function. A tissue must contain two different types of cells. The four basic tissue types in humans include epithelium, connective, muscle, and nervous tissue. Each tissue has a characteristic role within the human body which we will discuss later.
Organ level– an organ is a structure composed of at least two different tissue types that perform a specific function within the body. Examples include the brain, stomach, and liver. Complex functions begin to emerge at this level.
Organismal level– The organismal level is the highest level of organization. It is the sum total of all structural levels working together. In short, it is the human being (or organism) as a whole.
Organ system level– One or more organs work in unison to accomplish a common purpose. For instance, the heart and blood vessels work together and circulate blood throughout the body to provide oxygen and nutrients to cells. Besides the cardiovascular system, the other organ systems of the body are the integumentary, skeletal, nervous, muscular, endocrine, respiratory, lymphatic, digestive, urinary, and reproductive systems.
OpenStax College. (2013). Introduction to Anatomy Module 3: Structural Organization of the Human Body. Januray, 22 2015, Creative Commons URL: http://cnx.org/contents/5e1ff6e7-0980-4ae0-bc8a-4b591a7c1760@6/Introduction_to_Anatomy_Module
A&P. (2013). Levels of Structural Organization in the human body. January 22, 2015, Anatomy & Physiology URL: http://anatomyandphysiologyi.com/ap-levels-of-structural-organization/
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