Ch. 4 Tissue Level of Organization Part B

Three major types of connective tissue:
- Connective Tissue Proper
- Fluid Connective Tissues
- Supporting Connective Tissues

Connective Tissue Proper
- Contains many types of cells and extracellular fibers in a syrupy ground substance.
- Subtypes:
- Loose Connective Tissue: Fibers create a loose, open framework.
- Dense Connective Tissue: Fibers are densely packed.
- Examples:
- Loose and Dense
  - Areolar tissue
  - Adipose tissue
  - Reticular tissue
  - Dense regular tissue
  - Dense irregular tissue
  - Elastic tissue
Fluid Connective Tissues
- Distinct populations of cells suspended in a watery matrix containing dissolved proteins.
- Examples:
- Blood: Flows within the cardiovascular system.
- Lymph: Flows within the lymphatic system.
Supporting Connective Tissues
- Have a less diverse cell population than connective tissue proper and a matrix with densely packed fibers.
- Examples:
- Cartilage: Solid, rubbery matrix.
- Bone: Solid, crystalline matrix.

Includes:
- Extracellular protein fibers
- A viscous (syrupy) ground substance
Two classes of cells:
- Fixed Cells (stationary):
- Function in maintenance, repair, and energy storage.
- Types include:
  - Fibroblasts: Secrete hyaluronic acid and proteins forming ground substance and fibers.
  - Fibrocytes: Mature from fibroblasts and maintain the extracellular fibers.
  - Adipocytes: Store lipids in large cells.
  - Melanocytes: Synthesize melanin pigment.
  - Fixed Macrophages: Stationary phagocytes agitating debris and pathogens.
  - Mast Cells: Stimulate local inflammation.
- Wandering Cells (mobile):
- Types include:
  - Plasma Cells: Produce antibodies.
  - Free Macrophages: Patrol tissues and engulf debris.
  - Mesenchymal Cells: Mobile stem cells for tissue repair.
  - Neutrophils and Eosinophils: Phagocytic blood cells entering tissues during infection.
  - Lymphocytes: Immune system cells.

Areolar Tissue: Most common, packing material of the body, found deep to the basement membranes of epithelial tissues.
- Contains all types of connective tissue proper cell types.
Adipose Tissue: Found deep to skin in various body areas, primarily made up of adipocytes (fat cells).
Reticular Tissue: Found in liver, kidney, spleen, lymph nodes, and bone marrow; provides support with a complex 3D network of reticular fibers.

Composed mainly of extracellular fibers.
Types of Dense Connective Tissues:
- Dense Regular Connective Tissue: Found in tendons and ligaments with parallel collagen fibers.
- Dense Irregular Connective Tissue: Found covering visceral organs, bones, cartilages, and peripheral nerves; has no consistent pattern of fiber arrangement.
- Elastic Tissue: Contains more elastic fibers than collagen; found in large blood vessel walls.

Blood:
- Contains a watery matrix (plasma) and suspended elements:
- Red blood cells (erythrocytes): Carry oxygen and carbon dioxide.
- White blood cells (leukocytes): Provide body defense.
- Platelets (thrombocytes): Assist in clotting.
Lymph:
- Composed of a watery matrix (lymph) and mainly lymphocytes, collected from interstitial fluid, functions to maintain solute levels, blood volume, and alert the immune system to infections.

Matrix is a firm gel with polysaccharide derivatives (chondroitin sulfates) and secretes proteoglycans.
Utilizes two primary cell types:
- Chondroblasts: Immature cells dividing within the perichondrium.
- Chondrocytes: Mature chondroblasts surrounded by matrix.
Types of Cartilage:
- Hyaline Cartilage: Found between ribs and sternum, provides stiff yet flexible support and reduces friction.
- Elastic Cartilage: Increased flexibility, found in structures such as the external ear.
- Fibrous Cartilage: Resists compression and prevents bone-to-bone contact, found in intervertebral discs.

Composed of cells (osteocytes) in lacunae and a bony matrix.
Matrix Composition:
- 2/3 is calcium salts (strength) including calcium phosphate and calcium carbonate.
- 1/3 is fibers (collagen), providing flexibility.
Comparison of Cartilage and Bone:
- Both support and protect.
- Cartilage is avascular (lacking blood vessels); bone is highly vascular.
- Limited growth and repair in cartilage; extensive remodeling in bone.
Typical Bone Structure:
- Hollow, containing:
- Compact Bone: Well-organized outer layer.
- Spongy Bone: Fine network lining the internal cavity.

These tissue types contribute to various body systems, with muscle tissue contributing the most to body weight and nervous tissue the least.

Skeletal Muscle: Striated and voluntary, moves the body.
Cardiac Muscle: Striated and involuntary, moves blood.
Smooth Muscle: Non-striated and involuntary, moves fluids and solids along digestive tract and regulates the diameters of small arteries.

Specialized for conducting electrical impulses. 98% located in the brain and spinal cord (CNS).
Two main cell types:
- Neurons: Transfer information and perform processing; can be very long (up to 1 meter).
- Neuroglia (or glial cells): Supporting cells performing various functions, including maintenance of tissue structure, repair after injury, and nutrient provision.

Dendrites: Receive information.
Axon: Conducts information to other cells, also known as nerve fibers.
Cell Body: Contains the nucleus and organelles, serves as the control center.