ANIMAL CELLS AND TISSUES

by Michael J. Farabee, Ph.D., Estrella Mountain Community College, updated 12/06. [edited S. Dillery 4/13]

Animals are multicellularheterotrophs whose cells lack cell walls. Organs are composed of tissues, which are in turn composed of cells.

Animals have four [types of tissue]: epithelial, connective, muscle, and nervous.

Epithelial Tissue

Epithelial tissue covers body surfaces and lines body cavities. Functions include lining, protecting, and forming glands. Three types of epithelium occur:

  • Squamous epithelium is flattened [irregular disk-shaped] cells.
  • Cuboidal epithelium is cube-shaped cells.
  • Columnar epithelium consists of elongated cells.

Functions of epithelial cells include:

  • movement materials in, out, or around the body.
  • protection of the internal environment against the external environment.
  • Secretion of a product.

1.Squamous Epithelial Cells 2. Cuboidal Epithelial Cells 3. Columnar Epithelial Cells

Connective Tissue

Connective tissue serves many purposes in the body:

  • binding
  • supporting
  • protecting
  • forming blood
  • storing fats
  • filling space

Connective cells are separated from one another by a non-cellular matrix. The matrix may be solid (as in bone), soft (as in loose connective tissue), or liquid (as in blood). Two types of connective tissue are Loose Connective Tissue (LCT) and Fibrous Connective Tissue (FCT). Adipose tissue has enlarged fibroblasts storing fats and reduced intracellular matrix. Adipose tissue facilitates energy storage and insulation.

Bone has calcium salts in the matrix, giving it greater rigidity and strength [than cartilage]. Bone also serves as a reservoir (or sink) for calcium. Protein fibers provide elasticity while minerals provide [strength]. [Bone cells have a central canal.]

Blood is a connective tissue of cells separated by a liquid (plasma) matrix. Two types of cells occur. Red blood cells (erythrocytes) carry oxygen. White blood cells (leukocytes) function in the immune system. Plasma transports dissolved glucose, wastes, carbon dioxide and hormones, as well as regulating the water balance for the blood cells. Platelets are cell fragments that function in blood clotting.

4. Red Blood Cells 5. Bone Cells 6. Adipose Cells

Muscle Tissue

Muscle tissue facilitates movement of the animal by contraction of individual muscle cells (referred to as muscle fibers). Three types of muscle fibers occur in animals (the only taxonomic kingdom to have muscle cells):

  • skeletal (striated)
  • smooth
  • cardiac

Muscle fibers are multinucleated, with the nuclei located just under the plasma membrane. Most of the cell is occupied by striated, thread-like myofibrils.

Skeletal (striated) muscle fibers have alternating bands perpendicular to the long axis of the cell. These cells function in conjunction with the skeletal system for voluntary muscle movements.

Smooth muscle fibers lack the banding. These cells function in involuntary movements and/or autonomic responses (such as breathing, secretion, ejaculation, birth, and certain reflexes). Smooth muscle fibers are spindle shaped cells that form masses. These fibers are components of structures in the digestive system, reproductive tract, and blood vessels.

Cardiac muscle fibers are a type of striated muscle found only in the heart. The cell has a bifurcated (or forked) shape, usually with the nucleus near the center of the cell. The cells are usually connected to each other by intercalated disks.

7. Skeletal Muscle Cells 8. Smooth Muscle Cells 9. Cardiac Muscle Cells

Nervous Tissue

Nervous tissue functions in the integration of stimulus and control of response to that stimulus. Nerve cells are called neurons. The neuron is the functional unit of the nervous system. Humans have about 100 billion neurons in their brain alone! While variable in size and shape, all neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body. The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells. The axon conducts messages away from the cell body.

10. Neuron Cell

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