The human body is
organized into various structural levels, beginning with atoms and molecules,
and progressing to more complex levels, including cells, tissues, organs, and
systems that collectively form the complete organism.
Atoms, Molecules,
and Compounds
At its most fundamental level, the body consists of atoms. The primary elements
found in living organisms include carbon, hydrogen, oxygen, nitrogen,
phosphorus, and sulfur.
Atoms → Molecules → Compounds
Cells
Cells are the smallest independent units of life, and all life processes rely
on the numerous chemical activities occurring within them. Basic cellular
functions include growth, metabolism, irritability, and reproduction.
Tissues
Tissues are composed of similar cells that work together to perform specific
functions. There are four primary types of tissue in the body: epithelial,
connective, muscular, and nervous tissue.
- Epithelial Tissue: Found in the outer layer of
the skin, as well as the lining of organs, blood and lymph vessels, and
body cavities.
- Connective Tissue: Provides support and connects
different parts of the body, including the skin, bones, and tendons.
- Muscle Tissue: Responsible for producing
movement through its ability to contract, and is found in skeletal,
smooth, and cardiac muscles.
- Nervous Tissue: Located in the brain, spinal
cord, and nerves, nervous tissue responds to stimuli and transmits nerve
impulses.
Organs
An organ is an integrated collection of two or more types of tissue working
together to perform a specific function. For example, the stomach consists of
all four tissue types.
Systems
A system is a group of organs that work in unison to perform a major function.
For instance, the respiratory system includes several organs working together
for respiration.
Organism Level
The various organs of the body combine to form the entire organism.
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