Connective Tissue Notes
Connective Tissue
Characteristics
- Most abundant tissue in the body.
- Characterized by abundant intercellular material.
- Highly vascular (contains blood vessels).
- Has a nerve supply.
- Typically located underneath epithelial tissue.
- Composed of three basic elements:
- Cells
- Fibers
- Ground substance (matrix)
Functions
- Support
- Protection
- Attachment
- Maintains strength
- Insulates and stores energy
- Transportation of substances
Cells
- Vary according to the type of connective tissue.
- Fibroblasts: Produce fibers and ground substance.
- Adipose cells (Adipocytes): Store fat.
- Macrophages: Phagocytic cells involved in immune response.
- Reticular cells: Produce reticular fibers.
- Osteocytes: Mature bone cells.
- Chondrocytes: Mature cartilage cells.
- Plasma cells: Produce antibodies.
- Blood cells: Various types including red and white blood cells.
Types of Fibers
- Collagen (white fibers):
- Broadest and most widespread type.
- Provide high tensile strength.
- Elastic (yellow fibers):
- Can be stretched and return to their original shape.
- Provide elasticity.
- Reticular fibers:
- Form a network or mesh-like structure.
- Provide support.
Intercellular Material: Matrix
- Also known as ground substance.
- Varies in consistency:
Embryonic Connective Tissue
Mesenchyme
- Structure:
- Mesenchymal cells are stellate or spindle-shaped.
- Ground substance is a viscous fluid with some immature protein fibers.
- Function: Common origin for all other connective tissue types.
- Location: Throughout the body of the embryo and fetus.
Mucous Connective Tissue
- Structure:
- Mesenchymal cells scattered within a viscous ground substance.
- Immature protein fibers are more abundant here than in mesenchyme.
- Function: Support of structures in the umbilical cord.
- Location: Umbilical cord of the fetus.
Connective Tissue Proper
- Loose Connective Tissue
- Dense Connective Tissue
- Dense Regular (white fibrous)
- Dense Irregular
Loose Connective Tissue
Areolar Connective Tissue
- Structure:
- Abundant, viscous ground substance.
- Few collagen and elastic fibers.
- Scattered fibroblasts.
- Many blood vessels.
- Function:
- Protects tissues and organs.
- Binds skin and some epithelia to deeper tissues.
- Location:
- Papillary layer of the dermis (skin).
- Subcutaneous layer (deep to skin).
- Surrounds organs, nerve cells, some muscle cells, and blood vessels.
Adipose Connective Tissue
- Structure:
- Closely packed adipocytes.
- Nucleus pushed to the edge of the cell by a large fat droplet.
- Contains many blood vessels.
- Function:
- Stores energy.
- Insulates.
- Cushions and protects.
- Location:
- Subcutaneous layer.
- Surrounds and covers some organs.
Reticular Connective Tissue
- Structure:
- Viscous ground substance.
- Meshwork of reticular fibers, leukocytes, and some fibroblasts.
- Function:
- Provides stroma (supportive framework) to lymphatic organs.
- Location:
- Spleen.
- Lymph nodes.
- Red bone marrow.
Dense Connective Tissue
Dense Regular Connective Tissue
- Structure:
- Densely packed, parallel arrays of collagen fibers.
- Fibroblasts squeezed between layers of fibers.
- Scarce ground substance.
- Limited blood supply.
- Function:
- Attaches bone to bone (most ligaments) as well as muscle to bone (tendons).
- Resists stress applied in one direction.
- Location:
- Tendons (attach muscle to bone).
- Ligaments (typically attach bone to bone).
Dense Irregular Connective Tissue
- Structure:
- Collagen fibers randomly arranged and clumped together.
- Fibroblasts in spaces among fibers.
- More ground substance than in dense regular connective tissue.
- Extensive blood supply.
- Function:
- Withstands stresses applied in all directions.
- Durable
- Location:
- Most of the dermis of skin.
- Periosteum covering bone.
- Perichondrium covering cartilage.
- Epineurium covering nerves.
- Epimysium covering skeletal muscle.
- Some organ capsules.
Elastic Connective Tissue
- Structure:
- Predominantly composed of elastic fibers.
- Fibroblasts occupy some spaces between fibers.
- Function:
- Allows for stretching and recoil.
- Location:
- Walls of elastic arteries (such as the aorta).
- Trachea.
- Vocal cords.
Supporting Connective Tissue: Cartilage
Hyaline Cartilage
- Structure:
- Glassy-appearing matrix.
- Irregularly arranged chondrocytes in lacunae.
- Function:
- Provides support.
- Forms most of the fetal skeleton.
- Location:
- Tip of nose.
- Trachea.
- Most of larynx.
- Costal cartilage.
- Epiphyseal (growth) plates and articular ends of long bones.
- Most of fetal skeleton.
Fibrocartilage
- Structure:
- Readily visible, numerous, parallel collagen fibers with limited ground substance.
- Large chondrocytes in lacunae.
- Function:
- Resists compression.
- Acts as a shock absorber in some joints.
- Location:
- Intervertebral discs.
- Pubic symphysis.
- Menisci of knee joints.
Elastic Cartilage
- Structure:
- Abundant elastic fibers that form weblike mesh.
- Closely packed chondrocytes in lacunae.
- Function:
- Maintains shape while permitting extensive flexibility.
- Location:
- External ear.
- Epiglottis of larynx.
Supporting Connective Tissue: Bone (Osseous Tissue)
- Structure:
- Calcified extracellular matrix containing osteocytes trapped in lacunae.
- Compact bone organized in osteons (concentric lamellae arranged around a central canal).
- Spongy bone is a meshwork with a different organization from compact bone.
- Well vascularized.
- Function:
- Provides levers for body movement.
- Supports soft structures.
- Protects organs.
- Stores calcium and phosphorus.
- Spongy bone contains hemopoietic tissue and is the site for hemopoiesis.
- Location: Bones of the body.
Fluid Connective Tissue: Blood
- Location: Within blood vessels and the heart.
- Main function: Transport of nutrients, gases, and wastes through the body.