Part 2 - Connective Tissue | BCTC

Areolar (or Loose) Connective Tissue

Identification: Loose arrangement of thin (elastic and reticular) and thick (collagen) fibers that criss-cross haphazardly.

Features to Know: Collagen fibers (1), elastic fibers (2), fibroblasts (3).

Fibers Present: Collagen fibers, elastic fibers, reticular fibers.

Where Located: Surrounding capillaries and most organs; underneath epithelia.

Function: Wraps, cushions, holds defensive cells, holds fluids.


Reticular Connective Tissue

Identification: Dark-staining reticular fibers (2) present, but may be obscured by the numerous nuclei of lymphoblasts and other cells (1). Overall brownish color is also distinctive.

Features to Know: Lymphoblasts (1).

Fibers Present: Reticular fibers (2).

Where Located: Spleen, bone marrow, lymph nodes.

Function: Forms scaffolding/framework to support loose cells (leukocytes, mast cells, macrophages).


Adipose Tissue

Identification: Virtually no extracellular matrix visible due to greatly enlarged cells, nearly the entire volume of which is a fat vacuole (appears empty on slide). Most likely to be confused with simple squamous epithelium: note that the "open" areas are surrounded by narrow bands of cytoplasm, not multiple, nucleated cells. Few nuclei will be visible (arrow).

Features to Know: Adipocyte, nucleus.

Fibers Present: None visible.

Where Located: Underneath skin (subcutaneous tissue), breasts, surrounding eyes and kidneys, within abdomen.

Function: Energy storage; insulation against heat loss; supports and protects (cushions) organs.


Dense Regular Connective Tissue

Identification: Densely packed parallel fibers. Note scattered cells (lack of lacunae distinguish this tissue from cartilages; compare especially to fibrocartilage).

Features to Know: Fibroblast (1).

Fibers Present: Collagen fibers.

Where Located: Tendons, most ligaments, aponeuroses.

Function: Attaches bone to bone; attaches muscle to bone or muscle; resists tensile (pulling) forces in one direction.


Dense Irregular Connective Tissue

Identification: The collagen fibers are in distinct bundles, separated by space, giving an overall patchy or blocky appearance very dissimilar to other tissues.

Features to Know: Fibroblasts, if visible.

Fibers Present: Collagen fibers.

Where Located: Dermis of skin; submucosa (digestive tract); fibrous capsules of some organs and joints.

Function: Provides strength; can withstand tensile forces in many directions.


Elastic Connective Tissue

Identification: Similar to dense regular CT (densely packed collagen fibers), but with distinct dark, usually zigzagging, lines of elastic fibers (arrow). Although it has a similar name to Elastic Cartilage, these two tissues are not that similar (note the more parallel fibers and lack of lacunae here).

Features to Know: Fibroblasts.

Fibers Present: Collagen fibers, elastic fibers.

Where Located: Walls of aorta, arteries, and bronchial tubes; ligaments of vertebral column.

Function: Lets tissue stretch and recoil to original shape; pulsatile blood flow; recoil of lungs after inspiration.