Chp 4
Four primary tissue types — general comparison:
Tissue | Key structural feature | General function | Typical locations |
|---|---|---|---|
Epithelial | Cells tightly packed, little ECM, avascular, one free surface, sits on basement membrane | Covering/lining, protection, secretion, absorption, filtration | Skin surface, linings of GI tract, glands, blood vessel linings |
Connective | Sparse cells, abundant extracellular matrix (fibers + ground substance) | Support, binding, protection, transport, energy storage, insulation | Bone, cartilage, tendons/ligaments, blood, adipose tissue, dermis |
Muscle | Elongated, excitable, contractile cells (fibers) | Movement/force generation | Skeletal muscles, heart wall, walls of hollow organs/vessels |
Nervous | Neurons (excitable, long processes) + supporting glial cells | Signal transmission, control/coordination | Brain, spinal cord, nerves |
Epithelial tissue — classification by shape and layers
By cell shape:
Squamous — flat, scale-like
Cuboidal — cube-shaped
Columnar — tall, column-shaped
By number of layers:
Simple — one layer (function: diffusion, secretion, absorption — thin)
Stratified — multiple layers (function: protection — thick, abrasion-resistant)
Pseudostratified — appears layered but is actually one layer of cells of varying height, all touching the basement membrane
Transitional — specialized stratified epithelium capable of stretching (found in urinary bladder)
Common combinations & locations:
Type | Location | Function |
|---|---|---|
Simple squamous | Alveoli, capillary walls, lining of heart/vessels (endothelium) | Diffusion, filtration |
Simple cuboidal | Kidney tubules, gland ducts | Secretion, absorption |
Simple columnar | Lining of GI tract, uterus | Absorption, secretion (often with microvilli/goblet cells) |
Stratified squamous | Epidermis, esophagus, vagina | Protection against abrasion |
Pseudostratified ciliated columnar | Trachea, respiratory tract | Mucus movement (via cilia) |
Transitional | Urinary bladder, ureters | Stretch and recoil |
Connective tissue — cells, fibers, ground substance
Cells: vary by subtype — fibroblasts (produce fibers, most common), chondrocytes (cartilage), osteocytes (bone), adipocytes (fat storage), and resident immune cells (macrophages, mast cells).
Fibers (in the matrix):
Collagen fibers — thick, strong, flexible (tensile strength)
Elastic fibers — stretch and recoil (contain elastin)
Reticular fibers — thin, branching, form supportive networks
Ground substance: gel-like material (water, glycoproteins, proteoglycans) that fills space between cells and fibers; varies from fluid (blood plasma) to firm (cartilage) to solid/mineralized (bone).
Subtypes: loose (areolar, adipose, reticular) connective tissue vs. dense (regular — tendons/ligaments; irregular — dermis) connective tissue vs. supportive connective tissue (cartilage, bone) vs. fluid connective tissue (blood, lymph).
Muscle tissue comparison
Feature | Skeletal | Cardiac | Smooth |
|---|---|---|---|
Appearance | Striated | Striated | Non-striated |
Cell shape | Long, cylindrical, multinucleated | Branched, single central nucleus | Spindle-shaped, single nucleus |
Control | Voluntary | Involuntary | Involuntary |
Special features | — | Intercalated discs (gap junctions for synchronized contraction) | Can sustain prolonged contraction |
Location | Attached to bone | Heart wall only | Walls of hollow organs, blood vessels, airways |
Nervous tissue
Neurons — excitable cells that transmit electrical/chemical signals; structure includes dendrites (receive), cell body/soma (integrates), axon (conducts signal away)
Neuroglia (glial cells) — support, protect, and insulate neurons (e.g., astrocytes, oligodendrocytes/Schwann cells for myelination, microglia for immune defense)