Connective tissue comprises a diverse group of cells embedded in a tissue-specific extracellular matrix. Different type of connective tissue are responsible for a variety of functions. Classification of connective tissue is based on the composition and organization of its cellular and extracellular components and on its functions. Tissue cells are widely separated by extracellular matrix. Can be solid, semisolid, or liquid. Matrix of connective tissue determine its properties:
- Binds structures together
- Provides support and protection
- Fills spaces
- Produces blood cells
- Defensive functions
- Barrier
- Engulf bacteria
- Antibodies
- Stores fat for;
- Energy
- Insulation
- Organ protection
Cells
- Inter/extra-cellular substance or matrix
- Fibres
- Ground substance
Cells of Connective Tissue
- Fixed/Resident cells
- Fibroblasts
- Myofibroblasts
- Macrophages (Histiocytes)
- Adipose cells
- Mast cells
- Undifferentiated mesenchymal cells
- Wandering cells
- Lymphocytes
- Plasma cells
- Neutrophils
- Eosinophils
- Basophils
- Monocytes
Connective Tissue Matrix: Fibres
Collagen Fibres
Large fibres made of the protein collagen. Typically the most abundant fibres. Promote tissue flexibility.
Elastic Fibres
Intermediate fibres made of the protein elastin. Branching fibres that allow for stretch and recoil.
Reticular Fibres/ Lymphatic Tissue
Small delicate, branched fibres that have same chemical composition of collagen. Forms structural framework for organs such as spleen and lymph nodes. Store and produce white blood cells (part of immune system).
Connective Tissue Matrix Ground: Substance
Hyaluronic Acid
Complex combination of polysaccharides and proteins found in "true" or proper connective tissue.
Chondroitin Sulfate
Jellylike ground substance of cartilage, bone, skin and blood vessels.
Other Ground Substance
Dermatin sulfate, keratin sulfate, and adhesion proteins.
Adult connective tissues
- Loose connective tissue
- Areolar
- Adipose
- Reticular (lymphatic)
- Dense connective tissue
- Dense regular
- Dense irregular
- Elastic
- Embryonic connective tissue
- Mesenchyme
- Mucous tissue (Wharton’s jelly)
- Specialized connective tissue
- Cartilage
- Hyaline
- Elastic
- Fibrocartilage
- Bone
- Compact
- Spongy
- Blood
Loose Connective Tissue
Areolar
Description: Gel-like matrix with all three fibre types. Cells: fibroblast, macrophages, mast cells, and some white blood cells.
Location: Widely distributed under epithelia of body, e.g., form lamina propria of mucous membranes. Packages organs. Surrounds capillaries.
Function: Wraps and cushions organs. Its macrophages phagocytize bacteria. Plays important role in inflammation. Holds and conveys tissue fluid.
Adipose
Description: Matrix as in areolar but very sparse. Closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet. Types: white, brown.
Location: Under skin in the hypodermis. Around kidneys. Around eyeballs. Within abdomen. In breasts.
Function: Provides reserve food fuel. Insulates against heat loss. Supports and protects organs.
Reticular (Lymphatic)
Description: Network of reticular fibres in a typical loose ground substance. Reticular cells lie on the network.
Location: Lymphoid organs; Lymph nodes. Bone marrow. Spleen.
Function: Fibres form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages.
Dense Connective Tissue
Dense Regular
Description: Primarily parallel collagen fibres. A few elastic fibres. Major cell type is the fibroblast.
Location: Tendons. Most ligaments. Aponeuroses.
Function: Attaches muscles to bones or to muscles. Attaches bones to bones. Withstands great tensile stress when pulling force is applied in one direction.
Dense Irregular
Description: Primarily irregularly arranged collagen fibres. Some elastic fibres. Major cell type is the fibroblast.
Location: Fibrous capsules of organs (e.g., heart valves) and of joints. Dermis of the skin. Submucosa of digestive tract.
Function: Able to withstand tension exerted in many directions. Provides structural strength.
Elastic
Description: Dense regular connective tissue containing a high proportion of elastic fibres.
Location: Walls of large arteries. Within certain ligaments associated with the vertebral column. With the walls of the bronchial tubes.
Function: Allows recoil of tissue following stretching. Maintains pulsatile flow of blood through arteries. Aids passive recoil of lungs following inspiration.
Cartilage
Jelly-like matrix (chondroitin sulfate) containing collagen and elastic fibres and chondrocytes surrounded by a membrane called perichondrium. Unlike other CT, cartilage has NO blood vessels or nerves except in the perichondrium. The strength of cartilage is due to collagen fibres and the resilience is due to the presence of chondroitin sulfate. Chondrocytes occur within spaces in the matrix called lacunae.
Types
- Hyaline cartilage
- Fibrocartilage
- Elastic cartilage
Hyaline Cartilage
Description: Amorphous (gel-like) but firm matrix. Collagen fibres form an imperceptible network. Chondroblasts produce the matrix and when mature (chondrocytes) lie in lacunae.
Location: Forms most of the embryonic skeleton. Covers the ends of long bones in joint cavities. Forms costal cartilages of the ribs. Cartilages of the nose, trachea, and larynx.
Function: Supports and reinforces. Has resilient cushioning properties; resists compressive stress.
Elastic Cartilage
Description: Similar to hyaline cartilage, but more elastic fibres in matrix. Threadlike network of elastic fibres within the matrix.
Location: Supports; The external ear (pinna). Auditory tubes epiglottis.
Function: Maintains the shape of a structure while allowing great flexibility.
Fibrocartilage
Description: Matrix similar to but less firm than that in hyaline cartilage. Thick collagen fibres predominate.
Location: Intervertebral discs. Pubic symphysis. Discs of knee joint.
Function: Tensile strength with the ability to absorb compressive shock.
Bone
Description: Hard, calcified matrix containing many collagen fibres. Osteocytes lie in lacunae. Very well vascularized.
Location: Bones.
Function: Bone supports and protects (by enclosing). Provides levers for the muscles to act on. Stores calcium and other minerals and fat. Marrow inside bones is the site for blood cell formation (haematopoiesis).
Compact Bone
Found in the outer portion of long bones. Consists of many cylindrical-shaped units called osteon.
Spongy Bone
Found on ends of long bone. Contains bony bars and plates called trabeculae separated by irregular spaces. Blood cells are made within the red marrow found in the spongy bone.
Blood
Description: Connective tissue composed of cells suspended in liquid matrix called plasma. Red blood cells (erythrocytes) – carries oxygen. White blood cells (leukocytes) – fights infection. Platelets – fragment of giant cells found in bone marrow.
Location: Contained within blood vessels.
Function: Transport of respiratory gases, nutrients, wastes and other substances.
Disorders Of Connective Tissue
- Actinic keratosis or solar elastosis
- Hypertrophic scars and keloids
- Tendinosis
- Whipple disease
- Scurvy
- Ehlers-danlos syndrome
- Osteogenesis imperfect (brittle bone disease)
- Spontaneous pneumothorax
- Obesity – hypertrophic obesity
- Cirrhosis
- Marfan syndrome (cystic medial degeneration)
