Chapter 4: Histology Vocabulary Flashcards
Overview and Key Characteristics of Epithelial Tissue
Definition: Sheets of cells that cover body surfaces, line body cavities and organs, and form glands.
Core Functions of Epithelial Tissue:
Protection: Forms a continuous surface that shields underlying tissues from mechanical and thermal injury. Epithelial tissues can produce keratin and undergo mitosis rapidly and frequently to repair damaged areas.
Immune Defenses: Cells of the immune system are scattered throughout epithelial tissues to defend against invaders.
Secretion: Forms glands that produce and release essential substances such as sweat, oil, and hormones.
Transport into Other Tissues: Functions as selectively permeable barriers that allow specific substances to pass through via passive or active transport mechanisms.
Sensation: Richly supplied with nerves that detect environmental changes in both internal and external environments; specialized epithelial cells are directly responsible for processing specific sensations.
Key Characteristics:
Found on every internal and external body surface.
Made of tightly packed cells with very little extracellular matrix (ECM) between them.
Cells are tightly linked together by specialized intercellular junctions, specifically tight junctions and desmosomes.
Avascular: Contains no direct blood vessels within the epithelial tissue itself.
Supported and nourished by underlying connective tissue via a non-cellular membrane called the basement membrane.
Structure of the Basement Membrane:
Anchors the epithelial tissue firmly to the underlying connective tissue.
Consists of two distinct structural layers:
Basal lamina: The ECM produced by the epithelial tissue itself, composed primarily of collagen fibers and ground substance.
Reticular lamina: Manufactured by the connective tissue deep to the epithelial tissue, composed of reticular fibers and ground substance.
Cell Surfaces:
Apical surface: The free or exposed boundary in contact with the extracellular space or lumen.
Lateral surfaces: The side boundaries contacting neighboring epithelial cells.
Basal surface: The deep boundary in contact with deeper cells or the basal lamina.
Classification and Structural Types of Epithelia
Structural Significance: The number of cell layers and the specific cell shape dictate the exact functional capabilities of the epithelial tissue.
Simple epithelia: Consists of a single layer of cells suited primarily for efficient diffusion, absorption, and transport.
Stratified epithelia: Consists of more than one layer of cells, making them structurally suited for mechanical protection.
Pseudostratified epithelia: Consists of a single layer of cells that appears multilayered due to varying cell heights and nucleated positions.
Classification by Cell Shape:
Squamous cells: Flattened, thin cells.
Cuboidal cells: Short, cube-like cells.
Columnar cells: Tall, elongated rectangular cells.
Specific Epithelial Tissue Categories (Table 6-1):
Simple Epithelia (Single Cell Layer):
Simple squamous epithelium: Single layer of flattened cells; specialized for rapid diffusion and filtration.
Simple cuboidal epithelium: Single layer of short cube-shaped cells; specialized for secretion and absorption.
Simple columnar epithelium: Single layer of tall cells (e.g., lining surfaces such as the digestive system); specialized for absorption and secretion.
Pseudostratified columnar epithelium: Single layer of elongated cells appearing stratified; often possess cilia to assist in moving mucus across respiratory tract surfaces.
Stratified Epithelia (Multiple Cell Layers):
Stratified squamous epithelium:
Keratinized epithelium: Surface layers contain tough, protective keratin protein; provides high mechanical resistance.
Nonkeratinized epithelium: Surface layers remain moist and lack keratin, lining mucosal cavities subject to abrasion.
Stratified cuboidal epithelium: Multiple layers of cube-shaped cells.
Stratified columnar epithelium: Multiple layers of tall cells.
Transitional epithelium: Specialized stratified tissue capable of stretching and changing shape; lines structures of the urinary tract such as the urinary bladder.
Overview of Connective Tissue and Extracellular Matrix
Definition and Core Concept: Connective tissue consists of specialized cells scattered within an extensive extracellular matrix (ECM). Its main unifying roles are to "support, connect, protect."
Primary Functions:
Connecting and binding structural tissues.
Physical support and structural integrity.
Protection of vulnerable organs.
Transport of nutrients, gases, fluids, and wastes throughout the body.
Components of the Extracellular Matrix (ECM):
Ground Substance: A gel-like material consisting of water, dissolved ions, nutrients, and various solutes. Functions as the primary medium through which substances diffuse between blood capillaries and cells.
Protein Fiber Types:
Collagen fibers: Thick, wavy, eosinophilic fibers under H&E staining; provide extreme tensile strength.
Elastic fibers: Thin, dark, wavy strands; allow tissues to stretch and return to their original shape.
Reticular fibers: Fine, delicate, highly branching meshworks; provide structural supportive frameworks.
Cell Types of Connective Tissue Proper:
Resident Cells (Permanently inhabit the tissue to construct and maintain the ECM):
Fibroblasts: The most common resident cell type; actively synthesizes and secretes ECM components (protein fibers and ground substance).
Adipocytes: Specialized fat cells adapted for lipid storage and energy conservation.
Migrant Cells (Move dynamically into target tissues from the bloodstream to mediate immune responses):
Mast cells: Immune cells that release histamine to mediate inflammatory responses.
Phagocytes (Macrophages): Active defense cells that engulf and ingest foreign pathogens, cellular debris, and dead cells.
Classification of Connective Tissue Proper
A. Loose Connective Tissue:
Areolar (Loose Connective Tissue):
Components: Loose, unorganized arrangement of collagen/elastic fibers and various cells.
Functions: Wraps and cushions delicate body organs; houses blood vessels for nutrient supply.
Locations: Found deep to epithelia (basement membranes) and surrounding internal organs.
Reticular Connective Tissue:
Components: Delicate, interconnected branching network of reticular fibers.
Functions: Forms a soft, supportive internal skeleton or stroma for immune cells.
Locations: Found in lymphoid organs, including lymph nodes and the spleen.
Adipose Connective Tissue:
Components: Dominated by large, clear adipocytes packed with central lipid droplets.
Functions: Long-term energy storage, thermal insulation, mechanical cushioning, and structural support.
Locations: Deep to the skin in subcutaneous tissue and surrounding vital internal organs.
B. Dense Connective Tissue:
Dense Irregular Connective Tissue:
Components: Thick, randomly interwoven bundles of collagen fibers.
Functions: Withstands multidirectional mechanical stress and tension forces.
Locations: Primary structural component of the dermis of the skin and fibrous joint capsules.
Dense Regular Collagenous Connective Tissue:
Components: Densely packed, parallel alignment of thick collagen fibers.
Functions: Provides immense tensile strength, withstanding structural tension in a single direction.
Locations: Form structural tendons (attaching muscle to bone) and ligaments (attaching bone to bone).
Dense Regular Elastic Connective Tissue:
Components: Parallel elastic fibers mixed with randomly oriented collagen fibers.
Functions: Allows extensibility, permitting tissues to stretch under pressure and recoil back to original dimensions.
Locations: Found within the walls of large blood vessels (e.g., arteries) and specialized elastic ligaments.
Specialized Connective Tissues
Cartilage Tissues:
Key Structural Terms:
Chondroblasts: Immature cartilage cells that actively secrete matrix components.
Chondrocytes: Mature cartilage cells that maintain the surrounding extracellular matrix.
Lacunae: Small matrix cavities or pockets housing individual chondrocytes.
Perichondrium: Outer layer of dense irregular connective tissue surrounding most cartilage structures.
Hyaline Cartilage:
Components: Smooth, glassy matrix with fine collagen fibers.
Functions: Resists compressive stress and reduces friction across surfaces.
Locations: Covers articular surfaces of joints, lines the respiratory trachea, and forms costal cartilages of ribs.
Elastic Cartilage:
Components: High density of elastic fibers embedded within the matrix.
Functions: Maintains structural shape and integrity while providing extreme flexibility.
Locations: External ear (pinna) and the epiglottis.
Fibrocartilage:
Components: Densely packed with thick, tough collagen fibers; notably lacks a perichondrium.
Functions: Resists severe compressive forces and tensile strength forces simultaneously.
Locations: Form intervertebral discs between spinal vertebrae and pubic symphysis.
Bone (Osseous Tissue):
Primary Functions: Structural support, visceral protection, lever systems for physical movement, mineral storage (specifically calcium), and blood cell production (hematopoiesis).
ECM Composition:
Organic portion: Mainly collagen fibers, providing flexibility and tensile strength.
Inorganic portion: Calcified matrix made of mineral calcium salts, providing extreme hardness and compression resistance.
Bone Cell Types:
Osteoblasts: Cells responsible for building organic bone matrix.
Osteocytes: Mature bone cells housed in lacunae that maintain matrix integrity.
Osteoclasts: Specialized multinucleated cells responsible for resorbing and breaking down bone matrix.
Blood (Fluid Connective Tissue):
Plasma: The liquid matrix component, composed mainly of water containing dissolved proteins, inorganic ions, nutrients, cellular wastes, and circulatory hormones.
Formed Elements:
Erythrocytes (Red Blood Cells / RBCs): Biconcave cells specialized for systemic oxygen transport.
Leukocytes (White Blood Cells / WBCs): Diverse group of defense cells responsible for immune responses.
Platelets: Membrane-bound cell fragments specialized for blood clotting and vessel repair.
Muscle and Nervous Tissues
Nervous Tissue:
Primary Function: Specialized for extremely fast cellular communication, electrical signaling, and systemic physiological control throughout the body.
Muscle Tissue:
Primary Function: Specialized for active force generation, contraction, and body movement.
Three Muscle Categories:
Skeletal Muscle Tissue: Voluntarily controlled muscle tissue featuring striated, long, cylindrical multinucleated muscle fibers attached to bones.
Cardiac Muscle Tissue: Involuntarily controlled muscle tissue featuring striated, branching uninucleated cells connected end-to-end by specialized intercalated discs; located exclusively in the heart wall.
Smooth Muscle Tissue: Involuntarily controlled muscle tissue lacking cellular striations; features spindle-shaped uninucleated cells located within the walls of hollow organs and blood vessels.
Recall Check & Comparative Analysis
Epithelial Tissue Review Questions:
Question: Which epithelial tissue type is specialized for diffusion?
Answer: Simple squamous epithelium.
Question: Which epithelial tissue type is found in the urinary bladder?
Answer: Transitional epithelium.
Question: What feature helps move mucus in the respiratory tract?
Answer: Cilia (present on pseudostratified columnar epithelium).
Question: Which epithelial tissue type provides the greatest protection?
Answer: Stratified squamous epithelium (particularly keratinized stratified squamous epithelium).
Epithelial Challenge: Explain why the structure of each epithelial tissue type matches its function.
Explanation: The specific thickness (number of layers) and individual shape of epithelial cells directly determine tissue function; single-layered simple epithelia present minimal physical distance to allow rapid diffusion and cross-membrane transport, whereas multi-layered stratified epithelia provide a thick, resistant barrier to protect underlying structures against mechanical and thermal damage.
Nervous & Muscle Tissue Review Questions:
Question 1: Which muscle tissue type is under voluntary control?
Answer: Skeletal muscle tissue.
Question 2: Which muscle tissue type has intercalated discs?
Answer: Cardiac muscle tissue.
Question 3: Which muscle tissue lacks striations?
Answer: Smooth muscle tissue.
Question 4: What is the main function of nervous tissue?
Answer: Specialized for fast communication and control.
Muscle Tissue Challenge: Compare and contrast the three muscle tissue types with at least three similarities and three differences.
Similarities:
All three muscle tissue types are specialized for generating contractile force and movement.
All three contain contractile protein filaments (actin and myosin).
All three types exhibit cellular excitability in response to specific stimuli.
Differences:
Skeletal muscle is under conscious voluntary control, whereas cardiac and smooth muscle are regulated involuntarily.
Skeletal and cardiac muscle cells feature histological striations, whereas smooth muscle cells completely lack striations.
Cardiac muscle possesses unique intercalated discs and branching fibers, skeletal muscle consists of unbranched multinucleated cylindrical fibers, and smooth muscle consists of unstriated spindle-shaped cells.
Connective Tissue Review Questions:
Question: Which connective tissue type provides the greatest flexibility?
Answer: Elastic connective tissue (and elastic cartilage among specialized connective tissues).
Connective Tissue Challenge: Compare dense regular and dense irregular connective tissue, including their fiber arrangement and function.
Comparison: Dense regular connective tissue consists of parallel collagen fibers that allow the tissue to withstand high tensile stress in a single direction (such as in tendons and ligaments), whereas dense irregular connective tissue consists of thick, randomly interwoven collagen fibers that allow it to withstand mechanical stress from many directions (such as in the dermis of the skin and joint capsules).