Identification: Distinctive lacunae (small spaces containing cells) distinguish cartilages from other connective tissues. Lacunae often are paired. Note lack of fibrous appearance, instead an overall glassy appearance. Color varies.
Features to Know: Chondrocyte in lacuna (arrow).
Fibers Present: Collagen fibers (the thin, evenly dispersed fibers do not appear as fibers, but contribute to an overall glassy appearance).
Where Located: Articulating ends of long bones; nose, trachea, larynx; embryonic skeleton; costal cartilages of ribs.
Function: Structural support and reinforcement; cushions joints (resists compressive stress).
Identification: Distinctive large, often paired lacunae (similar to hyaline cartilage), but note extensive dark elastic fibers (2).
Features to Know: Chondrocyte in lacuna (1), elastic fibers (2).
Fibers Present: Elastic fibers (collagen fibers are also present but not visible).
Where Located: Skeleton of pinna (external ear), epiglottis (remember those Es!)
Function: Maintain shape, flexibility.
Identification: Distinct, more or less parallel collagen fibers visible. Distinguished from dense regular connective tissue by the distinct lacunae (arrow). Usually blue in color.
Features to Know: Chondrocytes in lacunae (arrow).
Fibers Present: Collagen.
Where Located: Intervertebral discs, pubic symphysis, menisci of knee joint.
Function: Absorb compressive forces; provide tensile strength.
Osseous Tissue (Compact Bone)
Identification: Concentric rings (like tree rings) are unmistakable.
Features to Know: Lamellae (1), osteocytes in lacunae (2), canaliculi (3), Haversian or central canal (4). An entire set of concentric rings (lamellae) is called a Haversian System or osteon.
Fibers Present: Collagen fibers present but not visible.
Where Located: Bones.
Function: Support, protection; act as levers for muscles; mineral and fat storage; hematopoiesis (blood cell formation).
Identification: The numerous round, red cells in a featureless fluid matrix (plasma) are unmistakable.
Features to Know: The liquid matrix is called plasma. The numerous round, red cells are erythrocytes (red blood cells). Erythrocytes lack nuclei, causing the cell to be biconcave (depressed on both sides), resulting in a center with a lighter color. There are also a small number of larger cells called leukocytes (white blood cells; 1), which have large or multi-lobed nuclei.
Fibers Present: None visible.
Where Located: Heart and vessels of the cardiovascular system.
Function: Transport respiratory gases, nutrients, wastes and other substances.