Epithelial and Connective Tissue

• Tissues are groups of cells with similar structure and function

Four Basic Tissue Types

• Epithelial tissue covers surfaces
• Connective tissue provides support
• Muscle tissue facilitates movement
• Nervous tissue controls responses

Epithelial Tissue

• Covers body surfaces
• Lines body cavities
• Forms parts of most glands

Functions of Epithelia

• Protection
• Secretion
• Absorption
• Diffusion
• Filtration
• Sensory reception

Characteristics of Epithelia

• Cells are tightly packed with minimal extracellular material
• Cells are joined by special junctions
• Cells have different apical and basal regions (polarity)
• Supported by connective tissue and nourished from underneath due to a lack of blood vessels
• Rapidly replaced through cell division

Classification of Epithelia (Based on Number of Layers)

• Simple epithelia consist of a single layer attached to the basement membrane
• Stratified epithelia consist of multiple layers, with only the basal layer attached to the basement membrane

Classifications of Epithelia (Based on Cell Shape)

• Squamous cells are wider than tall
• Cuboidal cells are cube-shaped
• Columnar cells are taller than wide

Simple Squamous Epithelium

• Single layer of flat cells with disc-shaped nuclei
• Allows diffusion and filtration and secretes lubricating substances in serosae
• Located in kidney glomeruli, lung air sacs, lining of heart and blood vessels, ventral body cavity lining

Simple Cuboidal Epithelium

• Single layer of cube-shaped cells with spherical nuclei
• Mainly involved in secretion and absorption
• Located in kidney tubules, secretory portions of small glands, ovarian surface

Simple Columnar Epithelium

• Single layer of rectangular cells with round to oval nuclei
• Involved in absorption and secretion of mucus and enzymes
• Cilia assistance helps in moving mucus or cells
• Located in the digestive tract (nonciliated) and small bronchi/uterine tubes/uterus (ciliated)

Pseudostratified Columnar Epithelium

• All cells originate at basement membrane, but only tall cells reach the surface
• May have goblet cells and cilia
• Function: Secretion of mucus and propulsion via cilia
• Locations: Trachea and upper respiratory tract (ciliated) and male reproductive ducts (nonciliated)

Stratified Squamous Epithelium

• Protects against abrasion
• Keratinized version is the epidermis
• Nonkeratinized versions are mucous membranes in esophagus, mouth, anus, vagina, and urethra
• Thickest epithelial type and often regenerative from basal layer

Pathology: Pap Smear Results

• Pap smears can detect infections, inflammation, precancerous cells, and cervical cancer
• Results include: Normal, Atypical Lesion, Pre/Post Menopausal
• Infection categories: Trichomonas and HSV

Stratified Cuboidal Epithelium

• Typically two layers of cube-shaped cells
• Function is protection
• Located in ducts of mammary/salivary glands and larger sweat glands

Stratified Columnar Epithelium

• Several layers, where basal cells are cuboidal and superficial cells are elongated
• Function is protection and secretion
• Rarely found; present in male urethra and large duct glands

Transitional Epithelium

• Mix of stratified cuboidal and squamous cells that appear dome-shaped or squamous based on bladder fullness
• Permits distension of urinary organs
• Locations: Urinary bladder, ureters, and proximal urethra

Glands

• One or more cells that secrete products
• Secretions often contain proteins in an aqueous fluid
• Endocrine glands are ductless and release hormones directly into tissues
• Exocrine glands may be unicellular or multicellular and use ducts to carry secretions

Exocrine Glands

• Mucus-secreting glands
• Sweat and oil glands
• Salivary glands
• Liver and pancreas
• Goblet cells produce mucin which forms mucus when combined with water

Multicellular Exocrine Glands

• Classified by duct structure (simple vs. compound)
• Key components include an epithelium-walled duct and a secretory unit categorized by shape: tubular, alveolar, or tubuloalveolar

Surface Features: Cell Junctions & Supportive Features

• Lateral cell junctions: Tight junctions, adhesive junctions, desmosomes, and gap junctions
• Basal feature: Basal lamina binds epithelial cells
• Apical features: Microvilli increase absorption surface area and cilia assists in substance movement

Lateral Surface Features: Cell Junctions

• Adhesion proteins are linked to adjacent cell membranes
• Membrane contours influence junction types

Lateral Surface Feature: Tight Junctions

• Also known as zona occludens
• Seals off intercellular spaces at apical regions
• Prevents passage of certain molecules

Lateral Surface Features: Adhesive Belt Junctions

• Also called zona adherens
• Anchoring junctions - proteins attach to actin microfilaments
• Binds adjacent cells to maintain tissue integrity

Lateral Surface Features: Desmosomes

• Bind cells together along cell sides
• Linked through plaque systems and intermediate filaments
• Frequent in cardiac muscle and epithelial tissue

Lateral Surface Features: Gap Junctions

• Passageways allowing small molecules to move between adjacent cells
• Facilitates Intercellular communication

Basal Feature: The Basal Lamina

• Located between epithelium and underlying connective tissue
• Acts as a selective filter
• Supports cell migration during regeneration
• Together with the reticular layers, it forms the basement membrane

Apical Surface Features: Microvilli

• Fingerlike extensions of plasma membrane to increase absorption area
• Contain actin filaments
• Common in kidney tubules and small intestines

Apical Surface Features: Cilia

• Whiplike extensions containing microtubules
• Generate movement
• Facilitate movement of substances or perform sensory functions

Connective Tissue

• Most diverse tissue
• Characterized by structural variation
• Types: Connective tissue proper (loose & dense), cartilage, bone tissue, blood
• Supports skeleton, store nutrients, surround nerves, control infections

Characteristics of Connective Tissue

• Few cells; abundant extracellular matrix created by connective tissue cells
• Main functionally different cells: fibroblasts, chondroblasts, and osteoblasts
• Vascularization varies with tissue type

Classification of Connective Tissues

• Connective tissue proper:
  • Loose connective tissue: Areolar, Adipose, Reticular
  • Dense connective tissue: Regular, Irregular, Elastic
• Cartilage Types: Hyaline, Elastic, Fibrocartilage

Structural Elements of ECM

• Fibers: Collagen (strong, resists tension), reticular, and elastic fibers (recoil)
• Gel-like ground substance cushions and protects structures
• Holds tissue fluid (not in blood)

Connective Tissue Proper

• Areolar connective tissue characteristics: Supports tissues, found underlying epithelium, provides a battlefield for infection response

Areolar Connective Tissue

• Widely distributed, packages organs, and surrounds capillaries
• Composition: Gel-like matrix with all fiber types
• Wraps and cushions organs
• Holds tissue fluid
• Plays role in inflammation

Adipose Connective Tissue

• Under the skin, around organs, and in the hypodermis
• Closely packed adipocytes with pushed nuclei
• Stores food energy and insulates against heat loss

Brown Adipose Connective Tissue

• Present in babies for thermoregulation
• Found in adults in specific locations
• Generates heat
• Richly vascularized with numerous mitochondria

Reticular Connective Tissue

• Network of reticular fibers in ground substance
• Provides soft internal skeleton supporting other cell types
• Found in lymph nodes, bone marrow, and spleen

Dense Connective Tissue

• Dense irregular
• Dense regular
• Elastic connective tissue
• Resist strong pulling forces due to high collagen presence

Dense Irregular Connective Tissue

• Thick, irregular collagen fibers with elastic fibers and fibroblasts
• Withstands tension and provides structural strength
• Found in the dermis of the skin, submucosa of the digestive tract, and fibrous capsules surrounding organs

Dense Regular Connective Tissue

• Present in tendons, ligaments, and aponeuroses
• Attaches muscle to bone and withstands stresses in one direction

Elastic Connective Tissue

• Predominantly elastic fibers.
• Allows recoil after stretching.
• Found in the walls of arteries and certain ligaments.

Types of Cartilage

• Hyaline
• Elastic
• Fibrocartilage
• Structural similarity with varying functions

Hyaline Cartilage

• Found in fetal skeleton, end of long bones, costal cartilage of ribs, and trachea
• Provides support and cushioning

Elastic Cartilage

• External ear and epiglottis
• Maintains shape with great flexibility due to elastic fibers

Fibrocartilage

• Intervertebral discs, pubic symphysis, knee joint discs
• Provides tensile strength and shock absorption

Bone Tissue

• Bones have matrix with inorganic calcium and collagen fibers
• Supports organs, stores minerals, and is the site of blood cell formation

Blood Tissue

• Red and white blood cells in fluid matrix
• Transports gases, nutrients, and wastes within blood vessels

The Structure of a Tissue

• Indicates its location and function

Four Types of Membranes

• Cutaneous membrane
• Mucous membranes
• Serous membrane
• Synovial membrane
• Each consists of epithelial layers and underlying connective tissues

Serous Membrane

• Produces serous fluid reducing friction in closed body cavities
• Locations: Pleural, peritoneal, and pericardial cavities

Synovial Membrane

• Lines joint cavities
• Produces synovial fluid for reducing friction

Cutaneous Membrane

• Thick, waterproof membrane forming the outer layer of skin

Mucous Membranes

• Lines hollow organs exposed to the body's surface
• Coated with mucus
• Epithelial layer underlaid with lamina propria

Compare & Contrast Epithelial & Connective Tissue

• Epithelial: Tightly packed, avascular, with nerve supply
• Connective: Widely spaced, vascularized, and supports other tissues

Muscle Tissue

• Muscle fibers containing myofilaments
• Types: Skeletal, Cardiac, and Smooth

Skeletal Muscle Tissue

• Attached to bones
• Long, cylindrical, multinucleate with striations
• Enables voluntary movement and facial expressions

Cardiac Muscle Tissue

• Contracts to propel blood through circulatory system
• Branching, striated, generally uninucleate cells
• Occurs in heart walls

Smooth Muscle Tissue

• Walls of hollow organs
• Spindle-shaped cells with central nuclei, arranged in sheets, no striations
• Moves substances through passageways involuntarily

Nervous Tissue

• Transmits electrical signals from receptors to effectors
• Brain, spinal cord, nerves
• Cell types: Neurons (conduct impulses) and Neuroglia (supporting cells)

Tissue Response to Injury

• Inflammatory response: Local response to injury; includes heat, redness, swelling, and pain
• Immune response: Specific and developed over time to destroy microorganisms

Tissue Repair of a Skin Wound

• Regeneration: Replacement with same type of tissue
• Fibrosis: Formation of scar tissue
• Organization: Clot replaced by granulation tissue

Tissue Capacity for Regeneration

• Good: Epithelial, bone, areolar, blood-forming tissues
• Moderate: Smooth muscle, dense regular connective tissue
• Weak: Skeletal muscle, cartilage
• None: Cardiac muscle, nervous tissue

The Tissues Throughout Life

• Primary tissue types appear by second month; organs develop
• Some tissues have regenerative capacities in adulthood; age-related degeneration observed

Explore the functions and characteristics of epithelial and connective tissues. This includes cell shapes, locations, and primary functions. Questions cover tissue types, components, and their roles in the body.