Histology
→ The study of tissues and their microscopic structure and function.
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| Term | Definition |
|---|---|
| Histology | → The study of tissues and their microscopic structure and function. |
| Tissue | → A group of similar cells that perform a common or related function to maintain homeostasis. |
| Epithelial tissue | → Covers body surfaces, lines cavities, forms most glands. |
| Connective tissue | → Supports, binds, protects, transports, stores energy, and defends the body. |
| Muscle tissue | → Contracts to produce movement. |
| Nervous tissue | → Conducts electrical signals for communication and control. |
| Epithelial tissue | ~Tightly packed cells ~Little to no extracellular matrix ~Avascular ~Has apical and basal surfaces ~Forms barriers and glands |
| Connective tissue | ~Cells scattered within the extracellular matrix ~Matrix = ground substance + fibers ~Usually vascular ~Supports and connects tissues |
| Cartilage | ~A type of connective tissue ~Chondrocytes in lacunae ~Firm but flexible matrix ~Avascular ~Receives nutrients from perichondrium |
| Apical surface | ~Free, exposed surface ~Faces the external environment or lumen ~May have microvilli or cilia |
| Basal surface | |
| May have microvilli or cilia | |
| Anchored to basement membrane | |
| Basement membrane attaches epithelium to connective tissue | |
| 5. Naming/classifying epithelial tissues | |
| Two criteria | |
| Number of layers | |
| Simple = one layer | |
| Stratified = two or more layers | |
| Cell shape | |
| Squamous | |
| Cuboidal | |
| Columnar | |
| Transitional | |
| 5a. Six characteristics of epithelial tissue | |
| 1. Polarity | |
| → Apical and basal surfaces allow directional absorption and secretion. | |
| 2. Cellularity | |
| → Tightly packed cells create protective barriers. | |
| 3. Innervation | |
| → Nerve supply allows sensation and detection of environmental changes. | |
| 4. Regeneration | |
| → Rapid replacement due to frequent damage. | |
| 5. Basement membrane attachment | |
| → Anchors tissue and forms barrier between epithelium and connective tissue. | |
| 6. Avascularity | |
| → No blood vessels; nutrients diffuse from connective tissue. | |
| 5b. Basement membrane | |
| Function | |
| Anchors epithelium | |
| Reinforces epithelial sheet | |
| Acts as barrier | |
| Layers | |
| Basal lamina | |
| Reticular lamina | |
| 6. Types of epithelial tissue (description, function, location) | |
| Simple squamous epithelium | |
| Description | |
| One layer of flat cells | |
| Function | |
| Diffusion, filtration, secretion | |
| Location | |
| Lungs, kidney glomeruli, capillaries, visceral pleura | |
| Simple cuboidal epithelium | |
| Description | |
| Single layer of cube-shaped cells with spherical nuclei | |
| Function | |
| Secretion and absorption | |
| Location | |
| Kidney tubules, ducts of glands, thyroid gland | |
| Simple columnar epithelium | |
| Description | |
| Single layer of tall cells | |
| May have microvilli, cilia, goblet cells | |
| Function | |
| Absorption | |
| Secretion of mucus and enzymes | |
| Cilia move substances | |
| Location | |
| Digestive tract, gallbladder, uterine tubes | |
| Pseudostratified columnar epithelium | |
| Description | |
| Appears stratified but is one layer | |
| Nuclei at different heights | |
| Often ciliated | |
| Function | |
| Secretion and movement of mucus | |
| Location | |
| Upper respiratory tract | |
| Ducts of large glands | |
| Testes tubules | |
| Stratified squamous epithelium | |
| Description | |
| Multiple layers | |
| Apical cells flattened | |
| Function | |
| Protection against abrasion | |
| Keratinized | |
| Dead cells with keratin | |
| Tough, water-resistant | |
| Skin, hair, nails | |
| Non-keratinized | |
| Living cells | |
| Moist surfaces | |
| Mouth, esophagus, vagina, anus | |
| Stratified cuboidal epithelium | |
| Description | |
| Multiple layers of cuboidal cells | |
| Function | |
| Protection and secretion | |
| Location | |
| Sweat and mammary gland ducts | |
| Stratified columnar epithelium | |
| Description | |
| Rare | |
| Multiple layers, columnar surface cells | |
| Function | |
| Protection and secretion | |
| Location | |
| Salivary glands, pancreas | |
| Transitional epithelium | |
| Description | |
| Cells change shape when stretched | |
| Function | |
| Allows stretching and recoil | |
| Location | |
| Urinary bladder, ureters, urethra | |
| 7. Endothelium and mesothelium | |
| Endothelium | |
| Simple squamous epithelium lining blood vessels, lymphatic vessels, and heart chambers | |
| Mesothelium | |
| Simple squamous epithelium lining serous membranes of ventral body cavities | |
| 8. Microvilli vs cilia | |
| Microvilli | |
| Increase surface area | |
| Found in intestines | |
| Function: absorption | |
| Cilia | |
| Longer, motile structures | |
| Move substances across surface | |
| Found in respiratory tract and uterine tubes | |
| 9. Glands | |
| Glands | |
| One or more cells that produce secretions | |
| Endocrine glands | |
| Ductless | |
| Secrete hormones into bloodstream | |
| Example: pituitary, pancreas | |
| Exocrine glands | |
| Use ducts | |
| Secrete onto surfaces or into cavities | |
| Example: sweat, salivary glands | |
| 10. Connective tissue components | |
| Cells | |
| Fibroblasts, adipocytes, macrophages, mast cells, lymphocytes | |
| Extracellular matrix | |
| Ground substance | |
| Fibers (collagen, elastic, reticular) | |
| 10a. Matrix and cell types | |
| Matrix varies from fluid (blood) to solid (bone) | |
| Cells produce and maintain matrix | |
| 10b. Connective tissue proper | |
| Loose connective tissue | |
| Areolar | |
| Packing material | |
| Under epithelia, around organs | |
| Adipose | |
| Energy storage, insulation | |
| Under skin, around organs | |
| Reticular | |
| Support framework for lymph nodes, spleen, bone marrow | |
| Dense connective tissue | |
| Dense regular | |
| Parallel collagen fibers | |
| Tendons and ligaments | |
| Dense irregular | |
| Irregular collagen | |
| Dermis, organ capsules | |
| Elastic | |
| Elastic fibers | |
| Arteries, vertebral ligaments | |
| 10c. Connective tissue cells | |
| Fibroblast – produces fibers and ground substance | |
| Macrophage – phagocytosis, immune defense | |
| Lymphocyte – immune response | |
| Mast cell – inflammation (histamine) | |
| Adipocyte – fat storage | |
| 10d. Fibers | |
| Collagen | |
| Strong, resists tension | |
| Reticular | |
| Thin, branching support network | |
| Elastic | |
| Stretch and recoil | |
| 10e. Cartilage | |
| Chondrocytes | |
| Mature cartilage cells | |
| Lacunae | |
| Spaces housing chondrocytes | |
| Types | |
| Hyaline | |
| Collagen fibers | |
| Trachea, ribs, joints | |
| Elastic | |
| Elastic fibers | |
| Ear, epiglottis | |
| Fibrocartilage | |
| Thick collagen | |
| Intervertebral discs, knee | |
| 17. Cell junctions | |
| Tight junctions | |
| Seal cells | |
| Prevent leakage | |
| Desmosomes | |
| Strong attachments | |
| Resist stretching | |
| Gap junctions | |
| Communication channels | |
| Ion and molecule passage | |
| 18. Body membranes | |
| Mucous | |
| Lines cavities open to exterior | |
| Digestive, respiratory tracts | |
| Serous | |
| Lines closed cavities | |
| Reduces friction | |
| Cutaneous | |
| Skin | |
| Protection and waterproofing | |
| Synovial | |
| Lines joints | |
| Reduces friction, nourishes cartilage | |
| Optional | |
| Parenchyma | |
| Functional tissue of an organ | |
| Stroma | |
| Supporting connective tissue | |
| Tissue repair | |
| Regeneration or fibrosis (scar tissue) |