Question
Classify connective tissues into their main types and subtypes. Give the location and function of each type with examples.
Solution — Step by Step
Connective tissue connects, supports, and binds other tissues. Its defining feature: cells are scattered in an extracellular matrix made of ground substance + fibres (collagen, elastin, reticular). Unlike epithelial tissue, the cells are not tightly packed.
Loose connective tissue:
- Areolar tissue — found beneath the skin, around organs. Acts as a packing material. Contains fibroblasts, mast cells, and macrophages.
- Adipose tissue — fat storage. Found below the skin, around kidneys. Cells (adipocytes) store fat in large droplets. Insulation + energy reserve.
Dense connective tissue:
- Dense regular — fibres run in one direction. Found in tendons (connect muscle to bone) and ligaments (connect bone to bone).
- Dense irregular — fibres in multiple directions. Found in the dermis of skin.
Cartilage — matrix is solid but flexible (contains chondroitin sulphate). Cells = chondrocytes in lacunae. Found in nose tip, ear pinna, trachea, larynx, between vertebrae (intervertebral discs).
Bone — matrix is hard and mineralised (calcium phosphate, hydroxyapatite). Cells = osteocytes in lacunae, connected by canaliculi. Haversian system = structural unit.
Blood — matrix is liquid (plasma). Contains RBCs, WBCs, and platelets. Transports O₂, nutrients, hormones, and waste.
Lymph — similar to plasma but lacks RBCs and most proteins. Drains from tissues into lymphatic vessels. Contains lymphocytes. Involved in immunity.
flowchart TD
A[Connective Tissue] --> B[CT Proper]
A --> C[Skeletal CT]
A --> D[Fluid CT]
B --> B1[Loose: Areolar, Adipose]
B --> B2[Dense: Tendons, Ligaments, Dermis]
C --> C1[Cartilage: Nose, Ear, Trachea]
C --> C2[Bone: Skeleton]
D --> D1[Blood: Plasma + cells]
D --> D2[Lymph: No RBCs]Why This Works
The classification is based on the nature of the extracellular matrix: soft and flexible (CT proper), solid but pliable (cartilage), hard and rigid (bone), or liquid (blood and lymph). The matrix determines the tissue’s mechanical properties.
Common Mistake
Students confuse tendons and ligaments. Tendons connect muscle to bone (made of dense regular CT with collagen fibres — very strong, not elastic). Ligaments connect bone to bone (also dense regular but contain more elastic fibres — slightly stretchable). Mnemonic: Tendon = muscle-To-bone.
Blood is classified as connective tissue even though it flows — because it connects different organ systems, has cells scattered in a matrix (plasma), and develops from mesoderm like other connective tissues.