Overview
This lecture introduces the main types of connective tissue proper, focusing on their cellular components and fiber types, to support histology lab identification.
General Features of Connective Tissue
- Connective tissue includes diverse types like blood, bone, cartilage, and fat.
- All connective tissues have loosely arranged cells within an extracellular matrix (ECM).
- The ECM contains fibers and ground substance, whose composition defines tissue type.
- Key cells include fibroblasts, mast cells, and sometimes plasma cells.
Loose Connective Tissues
Areolar Connective Tissue
- Areolar CT is a generic, loose, supportive tissue found under epithelia and around organs.
- Contains loosely packed fibroblasts with visible nuclei and nucleoli.
- Mast cells, visible by their large size and granular cytoplasm (contain histamine and heparin), are present.
- Fibers include collagen (thick, wavy), elastic (thin, black, stretchy), and reticular (not seen without special stain).
- Plasma cells (immune cells with a cartwheel-shaped nucleus and Golgi shadow) may be seen in demo slides.
Adipose Connective Tissue (Fat)
- Located in the hypodermis (subcutaneous fat layer) beneath the skin.
- Dominated by adipocytes—large, round cells with a single fat-filled vacuole and nucleus pushed to the edge.
- Fibroblasts, collagen, elastic, and reticular fibers are present but less prominent than adipocytes.
Reticular Connective Tissue
- Defined by a network of reticular fibers (darkly stained with special stains).
- Forms structural framework in soft organs like lymph nodes, spleen, and bone marrow.
- Supports numerous lymphocytes and white blood cells in organs.
Dense Connective Tissues
Dense Regular Connective Tissue
- Composed of densely packed, parallel collagen fibers and prominent fibroblast nuclei.
- Found in tendons, ligaments, and the cornea.
- Provides strong tensile strength in one direction.
Dense Irregular Connective Tissue
- Densely packed collagen fibers arranged irregularly, providing strength in multiple directions.
- Main tissue type in the dermis of the skin.
- Contains fibroblasts and possible other cell types depending on location.
Elastic Connective Tissue
- Characterized by abundant, regularly arranged elastic fibers (wavy, black lines with special stain).
- Located in the wall of the aorta and large arteries, allowing stretch and recoil in response to blood pressure changes.
- Smooth muscle may be present but focus is on elastic fibers.
Key Terms & Definitions
- Extracellular Matrix (ECM) — Non-cellular material outside cells, containing fibers and ground substance.
- Fibroblast — Common cell in connective tissue that produces fibers and ground substance.
- Mast Cell — Immune cell with granules, releases histamine/heparin for inflammation.
- Plasma Cell — Immune cell that produces antibodies; seen by its unique nucleus and Golgi shadow.
- Adipocyte — Fat cell, characterized by a large lipid-filled vacuole.
- Collagen Fiber — Strong, thick fiber providing tensile strength.
- Elastic Fiber — Stretchy fiber allowing flexibility and recoil.
- Reticular Fiber — Thin, branching fiber forming supporting networks in soft tissues.
Action Items / Next Steps
- Prepare for lab by reviewing tissue slides and focusing on identifying key cell and fiber types.
- Attend the lab session to observe actual tissue samples.
- Review demonstration slides for plasma cells and reticular fibers.