Connective Tissues Overview

Connective Tissues

• Connect epithelium to the rest of the body
• Provide structural framework and protect organs
• Store energy (fat)
• Transport materials (blood)
• Defend against microorganisms
• Do not contact the outside environment

Cell Types of Connective Tissue

• Fibroblasts: Most abundant cell type in connective tissue proper. Secrete proteins and cellular cement.
• Macrophages: Large immune system cells that consume pathogens and damaged cells.
• Adipocytes: Each cell stores a single, large fat droplet.
• Mesenchymal cells: Stem cells that differentiate into other connective tissue cells.
• Melanocytes: Synthesize and store melanin, the brown pigment.
• Mast cells: Stimulate inflammation after injury or infection. Release histamine and heparin.
• Lymphocytes: Specialized immune cells in the lymphatic system, producing antibodies from plasma cells.
• Microphages: Phagocytic blood cells that respond to signals from macrophages and mast cells.

Fibers in Connective Tissue

• Collagen fibers: Most common fibers in connective tissue proper. Long, straight, and unbranched. Strong and flexible, resisting force in one direction. Found in tendons and ligaments.
• Reticular fibers: Network of interwoven fibers. Strong and flexible, resisting forces in many directions. Stabilize functional cells and structures, like sheaths around organs.
• Elastic fibers: Contain elastin. Branched and wavy, returning to original length after stretching. Found in elastic ligaments of the vertebrae.

Ground Substance

• Found in connective tissue.
• Clear, colorless, and viscous.
• Fills spaces between cells and slows pathogens.

Types of Connective Tissue in Adults

• Areolar (loose)
• Adipose
• Reticular

Areolar Tissue

• Open framework, viscous ground substance
• Holds blood vessels and capillaries

Reticular Tissue

• Provides support
• Complex, 3-dimensional network of supportive fibers, supporting functional cells.
• Found in spleen, liver, lymph nodes, and bone marrow

Adipose Tissue

• Contains many adipocytes (fat cells).
• Stores fat.
• Absorbs shocks.
• Slows heat loss (insulation)

Dense Regular Connective Tissue

• Attachment and stabilization.
• Tightly packed, parallel collagen fibers.
• Tendons attach muscles to bones.

Dense Irregular Connective Tissue

• Strength in many directions.
• Interwoven networks of collagen fibers.
• Layered in skin, around cartilages, etc.

Fluid Connective Tissues

• Blood and lymph
• Watery matrix of dissolved proteins.
• Carry specific cell types (formed elements).

Hemopoietic Tissue

• Red bone marrow connective tissue
• Blood forming
• Found on spongy bone, red bone marrow

Supportive Connective Tissues

• Support soft tissues and body weight
  • Cartilage: Gel-type ground substance; shock absorption and protection.
  • Bone: Calcified (made rigid by calcium salts, minerals); weight support.

Hyaline Cartilage

• Translucent matrix, no prominent fibers.
• Reduces friction in joints and between bones.

Elastic Cartilage

• Flexible support; bends easily
• Found in external ear, epiglottis, auditory canal, cuneiform cartilages of larynx

Fibrocartilage

• Resists compression; limits movement
• Prevents bone-to-bone contact
• Pads knee joints, between pubic bones, and intervertebral discs

Compact Bone

• Hard outer bone, also called osseous tissue.
• Strong (calcium salt deposits).
• Resists forces (due to collagen fibers).

Spongy Bone

• Inner bone; web-like trabeculae.

Membranes

• Physical barriers lining or covering body portions.
• Epithelial layer supported by connective tissue.
  • Types:
    • Mucous
    • Serous
    • Cutaneous
    • Synovial

Mucous Membrane

• Lines passageways that have external connections
• Found in digestive, respiratory, urinary, and reproductive tracts
• Contains mucous secretion.

Serous Membrane

• Lines cavities not open to the outside.
• Thin but strong.
• Contains fluid to reduce friction.

Cutaneous Membrane

• Skin; surface of the body.
• Thick, waterproof, and dry.

Synovial Membrane

• Lines articulating (moving) joint cavities.
• Produces synovial fluid (lubricant).
• Protects the ends of bones.

Fasciae

• Provide strength and stability
• Maintain positions of internal organs.
• Provide routes for blood vessels, lymphatic vessels, and nerves.
• Body's framework of connective tissue.
• Layers/wrappings that support or surround organs.

Types of Fasciae

• Superficial fascia: Between skin and organs; subcutaneous/hypodermis; areolar.
• Deep fascia: Strong fibrous network; dense connective tissue.
• Subserous fascia: Between serous membrane & deep fascia; areolar tissue.

Muscle Tissues

• Skeletal
• Cardiac
• Smooth

Skeletal Muscle

• Striated, voluntary, and multinucleated.
• Moves or stabilizes the position of the skeleton, guards entrances and exits.
• Generates heat.
• Protects internal organs.

Cardiac Muscle Tissue

• Striated, involuntary, branching networks; connected at intercalated disks.
• Single, central nucleus.
• Circulates blood; maintains blood pressure.

Smooth Muscle Tissue

• Nonstriated, involuntary.
• Long, spindle-shaped, single nucleus.
• Moves food, urine, and reproductive tract secretions.
• Controls diameter of respiratory passageways and blood vessels.

Neural Tissue

• Specialized for conducting electrical impulses.
• Rapidly senses internal or external environments.
• Processes information and controls responses.

Neural Cells

• Neurons: Nerve cells; perform electrical communication
• Neuroglia: Support cells; repair, supply nutrients to neurons and anchor neurons.

Neuron Parts

• Dendrites: Short branches extending from the cell body; receive incoming signals.
• Cell body: Contains the nucleus and nucleolus.
• Nucleus: Control center.
• Axon: Long, thin extension of the cell body; carries outgoing electrical signals.
• Synaptic terminals: Send messages to other cells.

Neuroglia

• Maintain physical structure of tissues.
• Repair tissue framework after injury.
• Perform phagocytosis.
• Provide nutrients to neurons.
• Regulate the composition of the interstitial fluid surrounding neurons.

Tissue Injuries and Repair

• Tissues respond to injuries to maintain homeostasis.
• Cells restore homeostasis through:
  • Inflammation (the tissue's first response to injury; characterized by swelling, redness, heat, and pain).
  • Regeneration (occurs when the injury or infection has been cleaned up, leading to healing; fibroblasts lay down collagen fibers creating scar tissue; new cells migrate and regenerate; all tissues do not regenerate equally).

Explore the functions and cell types of connective tissues in this quiz. Understand how these tissues connect, support, and protect various body structures. Test your knowledge on the different cell types and their roles in the immune system and energy storage.