Overview
This lecture covers the tissue level of organization, outlining the four basic tissue types, their origins, characteristics, subtypes, and functions in the human body.
Introduction to Tissues
- Tissues are groups of similar cells performing specific functions.
- Four main tissue types: epithelial, connective, muscle, and nervous tissue.
- Histology is the study of tissues.
- All adult tissues originate from three embryonic germ layers: endoderm, mesoderm, and ectoderm.
Cell Junctions
- Tissues use cell junctions for attachment and communication: tight, gap, and anchoring junctions.
Epithelial Tissue
- Epithelial tissue forms coverings and linings, functions in protection, absorption, and secretion.
- Characterized as avascular, regenerative, innervated, and polarized (apical/basal surfaces).
- Can be simple (one layer), stratified (multiple layers), or pseudostratified.
- Cell shapes: squamous (flat), cuboidal (cube-shaped), columnar (tall).
- Stratified epithelium named by the apical cell layer.
- Special types:
- Stratified squamous: protects against abrasion; keratinized (skin) or non-keratinized (mouth, esophagus).
- Stratified cuboidal and columnar: rare, found in glands and ducts.
- Pseudostratified columnar: single layer, nuclei at different levels; ciliated in trachea, non-ciliated in male reproductive tract.
- Transitional: stretches, lines urinary organs.
- Glandular epithelium forms glands (endocrine - ductless; exocrine - ducts).
- Modes of secretion: merocrine (exocytosis), holocrine (cell rupture), apocrine (cytoplasmic loss).
- Glands can be unicellular or multicellular, with simple or compound ducts.
Connective Tissue
- Most abundant tissue, supports, protects, insulates, and transports.
- Composed of cells and extracellular matrix (fibers: collagen, elastic, reticular; ground substance).
- Four classes: connective tissue proper (loose/dense), cartilage, bone, blood.
- Loose connective tissue: areolar (wraps organs), adipose (stores fat), reticular (supports lymphatic organs).
- Dense connective tissue: regular (tendons), irregular (dermis), elastic.
- Cartilage types: hyaline (ends of bones, trachea), elastic (ear, epiglottis), fibrocartilage (intervertebral discs).
- Bone: rigid, supports and protects, stores minerals, site of blood formation.
- Blood: transports gases, nutrients, wastes; matrix is plasma.
Muscle Tissue
- Contains protein filaments (actin, myosin, etc.).
- Skeletal muscle: striated, multinucleated, voluntary movement.
- Smooth muscle: non-striated, involuntary, in walls of hollow organs.
- Cardiac muscle: striated, branched, single nucleus, intercalated discs, involuntary, heart walls.
Nervous Tissue
- Consists of neurons (transmit impulses) and neuroglial cells (support/nourish neurons).
- Found in central and peripheral nervous systems.
Key Terms & Definitions
- Histology — study of tissues.
- Avascular — lacking blood vessels.
- Basement membrane — layer connecting epithelium to connective tissue.
- Striations — striped appearance in muscle tissue.
- Chondrocyte — cartilage cell residing in lacunae.
- Osteocyte — mature bone cell in lacunae.
- Matrix — non-living component in connective tissue consisting of fibers and ground substance.
- Intercalated disc — specialized connection between cardiac muscle cells.
Action Items / Next Steps
- Be able to identify tissue types, cell arrangement, matrix, function, and location.
- Review tissue slides under the microscope during lab.
- Prepare for exam questions covering characteristics and examples of each tissue type.