Connective Tissue

Connective tissue composed of ground substance and protein fibers differs from fibrous connective tissue in that it contains more ground substance. Two main types of this kind of connective tissue are found in the body: cartilage and bone.

Cartilage is composed of cartilage cells, and collagen fibers or a combination of collagen and elastin fibers. An interesting characteristic of cartilage is that when it is compressed it immediately springs back into shape.

Hyaline cartilage is rigid yet flexible, due to evenlyspaced collagen fibers. Hyaline cartilage is found at the ends of the ribs, around the trachea (windpipe), and at the ends of long bones that form joints. Hyaline cartilage forms the entire skeleton of the embryo, which is gradually replaced by bone as the newborn grows.

Fibrocartilage contains densely-packed regularly arranged collagen fibers which impact great strength to this connective tissue. Fibrocartilage is found between the bones of the vertebrae as discs that act as a cushion.

Elastic cartilage contains elastin fibers and is thus more flexible that either hyaline cartilage or fibrocartilage. Elastic cartilage is found in the pinnas of the external ear.

Bone is composed of bone cells (osteocytes), suspended in a matrix consisting of collagen fibers and minerals. The mineral portion imparts great strength and rigidity to bone. Osteocytes are located in depressions called lacunae connected by canals called Haversian canals.

Two types of bone form the mammalian skeleton: cancellous bone and compact bone. Cancellous bone is more lattice-like than compact bone, and does not contain as many collagen fibers in its matrix. Cancellous bone is light-weight, yet strong, and is found in the skull, the sternum and ribs, the pelvis and the growing ends of the long bones. Compact bone is densely packed with fibers, and forms the outer shell of all bones and the shafts of the long bones of the arms and legs. Compact bone is heavier than cancellous bone, and provides great strength and support.