Overview
This lecture covered the major types and characteristics of connective and epithelial tissues, including their structure, function, classification, and tissue repair processes.
Connective Tissue Overview
- Connective tissues originate from mesenchyme, mostly derived from mesoderm.
- Four main types: connective tissue proper (loose and dense), cartilage, osseous (bone), and blood.
- All connective tissue consists of living cells within a non-living extracellular matrix.
- Extracellular matrix includes protein fibers (collagen, elastic, reticular) and ground substance (fluid and proteoglycans).
- Functions: protect, support, bind tissues/organs, and repair (scar tissue formation).
Connective Tissue Types & Functions
- Loose connective tissue: includes areolar, adipose (fat), and reticular tissues.
- Dense connective tissue: regular (tendons), irregular (joint capsules).
- Cartilage: chondrocytes reside in lacunae; types are hyaline (joints, fetal skeleton), fibrocartilage (intervertebral discs), and elastic (ear, epiglottis).
- Osseous tissue: rigid matrix with osteocytes in lacunae; forms compact bone.
- Blood: living cells (RBCs, WBCs, platelets); plasma is the non-living matrix; fibrinogen forms fibers during clotting.
Epithelial Tissue Overview
- Epithelial tissues cover surfaces, line cavities, and form glands.
- Functions: protection, absorption, secretion, filtration, and sensory reception.
- Polarity: apical (free) surface and basal (attached) surface; always anchored to connective tissue via basement membrane.
- Avascular (no blood supply) but innervated (has nerves); regenerates rapidly.
Epithelial Tissue Classification
- Classified by layers: simple (one layer), stratified (multiple layers).
- Cell shapes: squamous (flat), cuboidal (cube-shaped), columnar (tall).
- Special types: pseudostratified columnar (appears layered, but all cells touch basement membrane; found in trachea), transitional (urinary bladder; stretches).
- Goblet cells are specialized for mucus secretion.
Glands & Membranes
- Endocrine glands: release hormones into interstitial fluid/blood.
- Exocrine glands: secrete products via ducts to surfaces (e.g., sweat, digestive enzymes).
- Membranes: cutaneous (skin - dry), serous/mucous (wet).
Tissue Repair & Scar Formation
- Tissue damage triggers coagulation, fibroblast activity, and scar (collagen) formation.
- Collagen is piezoelectric—generates electric current under stress, affecting scar maturation.
- Adhesions: abnormal binding between tissues due to scar tissue.
- Keloid/hypertrophic scars: excessive collagen deposition during healing.
Key Terms & Definitions
- Mesenchyme — embryonic connective tissue from which all connective tissues develop.
- Extracellular matrix — non-living material surrounding cells in connective tissue.
- Lacuna (lacunae) — small cavity within matrix where a cell resides (e.g., chondrocyte in cartilage).
- Fibroblast — cell that produces fibers in connective tissue.
- Chondrocyte — mature cartilage cell.
- Osteocyte — mature bone cell.
- Apical surface — the free, exposed surface of epithelial tissue.
- Basement membrane — protein layer anchoring epithelium to connective tissue.
- Goblet cell — mucus-secreting columnar epithelial cell.
- Endocrine gland — gland secreting hormones without ducts.
- Exocrine gland — gland secreting through ducts.
Action Items / Next Steps
- Review table on connective tissue (page 34 in lab manual).
- Read end-of-chapter section on tissue repair processes.
- Study images of tissue types for lab identification.
- Prepare for lab/practical questions on tissue type function, location, and characteristics.