Histology CT10: Adipose Tissue

Adipose Tissue

• Composed of adipose cells organized into lobules by connective tissue.
• Contains blood vessels, nerves, and lymphatics.
• Functions include energy storage, shock absorption, heat insulation, water source during extreme conditions, and various endocrine and metabolic roles.
• Two types: white (unilocular) and brown (multilocular).

White (Unilocular) Adipose Tissue

• Characterized by a single lipid droplet per cell, giving it a white appearance.
• Contains a thin ring of cytoplasm around a central vacuole (signet ring cell).
• Eccentrically flattened nucleus and surrounded by reticular fibers for structural support.
• Predominantly found in superficial fascia (hypodermis) and between connective tissue.
• Rich in membrane receptors (insulin, growth hormone, etc.) facilitating fatty acid and glycerol metabolism.
• Converts androgens into estrogens and secretes leptin, influencing appetite and energy balance.

Brown (Multilocular) Adipose Tissue

• Cells are smaller with multiple lipid droplets, resulting in a reddish-brown appearance.
• Contains abundant mitochondria, facilitating high rates of fatty acid oxidation and heat production.
• Rich blood supply and uncoupling proteins (thermogenin) for thermoregulation.
• Primarily located in infants around the neck and interscapular regions.

Cartilage General Characteristics

• Specialized connective tissue consisting of cells, fibers, and an extracellular matrix (ECM).
• ECM provides firmness and strength; lacks blood vessels, nerves, and lymphatics.
• Contains high levels of glycosaminoglycans, allowing diffusion between surrounding vessels and chondrocytes.

Development and Growth of Cartilage (Chondrogenesis)

• Mesenchymal cells transform into chondroblasts, which produce the ECM and become chondrocytes within lacunae.
• Perichondrium forms from surrounding mesenchyme.
• Interstitial growth occurs within cartilage during embryogenesis via chondrocyte mitosis and matrix secretion.
• Appositional growth involves the inner layer of the perichondrium adding new cartilage at the surface, primarily in adults.

Types of Cartilage and Their Locations

• Hyaline Cartilage: Most prevalent type; found in synovial joints, tracheal rings, nose, and fetal skeleton. Contains Type II collagen.
• Elastic Cartilage: Provides structure where flexibility is needed; found in the external ear and epiglottis. Contains Type II collagen and elastic fibers.
• Fibrocartilage: Blends dense connective tissue and hyaline cartilage; found in intervertebral discs and pubic symphysis. Contains Type I collagen for tensile strength.

Hyaline Cartilage

• ECM has a smooth, glassy appearance with Type II collagen and a high water content (70%).
• Chondrocytes are oval to round, with basophilic cytoplasm; presence in lacunae and cell nests.
• Perichondrium has an outer fibrous layer and an inner chondrogenic layer; articular cartilage lacks a perichondrium.

Elastic and Fibrocartilage

• Elastic Cartilage: Similar structure to hyaline but includes elastic fibers for flexibility; chondrocytes are similar.
• Fibrocartilage: Contains abundant collagen fibers; lacks perichondrium and has lower proteoglycan and water concentrations.

Cartilage Repair

• Limited regeneration potential primarily via chondrogenic cells in the perichondrium (appositional growth).
• Repair cartilage has mixed matrix compositions of Type I and Type II collagen.

Classification of Joints

• Fibrous Joints: No joint cavity; bones joined by dense connective tissue.

  • Types include sutures (skull), syndesmosis (interosseous membrane), and gomphosis (roots of teeth).

• Cartilaginous Joints: No joint cavity; connected by cartilage.

  • Types include synchondrosis (rib cage and epiphyseal plate) and symphysis (intervertebral discs and pubic symphysis).

Diarthrodial Joints

• Also known as synovial joints, characterized by an articular cavity.
• Articular surfaces are not in direct contact; covered with hyaline cartilage which does not have a perichondrium.