Body Organization
Cells, Tissues, Organs, Organ Systems
and Organism
Level One: Cells
• A cell is a basic unit of structure and function
in a living thing.
• The human body contains about 100 trillion
cells.
• Cells can not be seen without a microscope.
• Three important structures to recall are cell
membrane, nucleus, and cytoplasm.
• What is the function of the nucleus?
Functions of Cell Structures
• Cell membrane: forms the outside boundary
of the cell; materials move across the cell’s
membranes
• Nucleus: the control center that directs the
cell’s activities and contains information that
determines the cell’s characteristics
• Cytoplasm: a clear, jellylike substance in
which many important cell structures are
found
Level Two: Tissues
• A tissue is a group of similar cells that perform
the same function.
• The human body contains 4 basic types of
tissue:
muscle tissue
nerve tissue
connective tissue
epithelial tissue
Muscle Tissue
• Like the muscle cells that form it, muscle
tissue can contract or shorten.
• One kind of muscle tissue allows the body to
move.
• Other kinds of muscle tissue move:
1. blood through the heart
2. food through the digestive system
Nerve Tissue
• Nerve tissue directs and controls movement.
• Nerve tissue carries messages back and forth
between the brain and every other part of the
body.
• Nerve tissue enables you to see, hear, and think.
• Your brain, spinal cord and nerves consist of
nerve tissue.
• Under a microscope you can see the neurons &
glial cells.
Epithelial Tissue
• Epithelial tissue covers the surfaces of your
body and the outside of your internal organs.
• Under a microscope epithelial tissue looks like
it is packed tight together & in sheets or
layers.
• Your skin is composed of 2 layers of epithelial
tissue, the epidermis and dermis. It is also
composed of connective, nerve & muscle
tissue.
Connective Tissue
• Connective tissue provides support for your body
and connects all its parts.
• Examples of connective tissue are:
bones & tendons-for support
fat-provides insulation from cold & stores
energy
blood-travels to all parts of your body
• Under a microscope connective tissue looks like
fibrous strands of protein collagen
Organs
• An organ is a structure that is composed of
different kinds of tissue. It performs a specific
job.
• For example, the heart pumps blood
throughout the body
• An interesting fact about the heart: it contains
all 4 kinds of tissue! So does the skin!
Organ Systems
• An organ system is a group of organs that work
together to perform a major function.
• 11 systems make up the human body:
1. Circulatory
7. Nervous
2. Digestive
8. Reproductive
3. Endocrine
9. Respiratory
4. Excretory
10. Skeletal
5. Immune
11. Integumentary (Skin)
6. Muscular
Thinking Critically
• Answer the following questions:
1. What systems of the body are involved when
you prepare a sandwich and then eat it?
2. Which 2 systems work together to get oxygen
to your cells?