Overview
This lecture covers the structure, origin, and classification of connective tissue, emphasizing its components, cell types, and the five main adult connective tissue categories.
Connective vs. Epithelial Tissue
- Epithelial tissue: tightly packed, little extracellular material, avascular, lines structures, generally innervated.
- Connective tissue: lots of extracellular material, scattered cells, embedded fibers, very vascular (except cartilage), generally innervated (not cartilage), does not primarily line structures.
- Main function of connective tissue: support and connect other tissues; highly diverse.
Origin of Connective Tissue
- All connective tissue originates from embryonic mesoderm.
- Mesoderm produces two types of embryonic connective tissue: mucous (Wharton's jelly, found in umbilical cord) and mesenchyme.
- Mucous connective tissue connects mother and child, contains stem cells, and does not differentiate further.
- Mesenchyme is the source of all adult connective tissues and remains throughout life for repair and growth.
Cellular Components of Connective Tissue
- Cells in connective tissue are either transient (come and go) or fixed (remain in tissue).
- Fixed cells:
- Blasts: build tissue (e.g., fibroblasts make fibers).
- Cytes: maintain tissue (e.g., adipocytes maintain fat).
- Clasts: break down tissue.
- Other cells: neutrophils, eosinophils (blood cells), plasma cells (secrete antibodies), mast cells (produce histamines), macrophages (clean debris).
Matrix Components
- Matrix = fibers + ground substance.
- Fibers:
- Collagen: strongest, provides strength.
- Elastic: allow stretch and recoil (extensibility and elasticity).
- Reticular: modified collagen, small, provides extra support/framework.
- Ground substance: made of water, glycosaminoglycans (sugars/proteins), minerals, and fluids; can be solid (bone), liquid (blood), or gel-like.
Adult Connective Tissue Categories
- All adult connective tissues derive from mesenchyme.
- Five main categories (each with subtypes):
- Loose connective tissue (3 types)
- Dense connective tissue (3 types)
- Cartilage (3 types)
- Bone (2 types)
- Liquid (2 types)
Key Terms & Definitions
- Extracellular matrix — non-cellular material between cells, includes fibers and ground substance.
- Blast (e.g., fibroblast) — cell that builds connective tissue.
- Cyte (e.g., adipocyte) — cell that maintains tissue.
- Clast (e.g., osteoclast) — cell that breaks down tissue.
- Mesenchyme — embryonic connective tissue source for all adult connective tissues.
- Mucous connective tissue (Wharton's jelly) — embryonic tissue in umbilical cord, rich in stem cells.
- Collagen fibers — strong fibers providing tissue strength.
- Elastic fibers — fibers allowing stretch and return to shape.
- Reticular fibers — thin fibers providing supportive framework.
- Ground substance — amorphous material in matrix holding cells and fibers together.
Action Items / Next Steps
- Review the five categories and subtypes of adult connective tissue.
- Familiarize yourself with the different connective tissue cell types and their functions.
- Prepare to identify connective tissue types in upcoming practicals or readings.