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Lecturer Details

  • Speaker: Dr. R. Ahangari

  • Institution: University of Central Florida, Orlando

Introduction to Tissues

  • Definition of Tissues: Collections of structurally similar cells that perform related functions.

  • Major Types of Tissues: The entire body comprises four primary types of tissues:

    • Muscle Tissue

    • Nervous Tissue

    • Epithelial Tissue

    • Connective Tissue

  • Organ Formation: Groupings of the four primary tissues form organs, which can be organized into systems based on common functions.

Muscle Tissue

  • Muscle Tissue Overview:

    • Contractile tissue derived from the mesodermal layer of embryonic germ cells.

    • Classified into three types: skeletal, cardiac, and smooth muscle.

  • Functions of Muscle Tissue:

    • Produces force and causes motion, including locomotion and internal organ movement.

Types of Muscle Tissue

  1. Skeletal Muscle

    • Description: Striated muscle, typically attached to the skeleton.

    • Function: Creates movement by applying force to bones and joints via contraction.

    • Control: Voluntary control.

  2. Smooth Muscle

    • Description: Long, spindle-shaped cells with a single nucleus.

    • Location: Found in the walls of hollow organs (e.g., esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, and blood vessels).

    • Function: Propulsion of substances along internal passageways.

    • Control: Involuntary control.

  3. Cardiac Muscle

    • Description: Branching, striated cells fused at plasma membranes.

    • Location: Exclusively found in the walls of the heart.

    • Function: Pumps blood in the circulatory system.

    • Control: Involuntary control.

Nervous Tissue

  • Overview: Specialized to react to stimuli and conduct impulses that result in responses throughout the body.

  • Composition: Made up of specialized nerve cells called neurons.

    • Neurons: Easily stimulated and rapidly transmit impulses.

  • Structure of Nerves:

    • Composed of multiple nerve fibers (neurons) bound by connective tissue.

    • Epineurium: Dense connective tissue sheath that surrounds the nerve.

    • Perineurium: Surrounds bundles of nerve fibers, derived from the epineurium.

    • Endoneurium: Thin layer of loose connective tissue surrounding individual nerve fibers.

Epithelial Tissue

  • Functions of Epithelial Tissue:

    1. Protection: Protects underlying tissues against injury, chemicals, bacteria, and water loss.

    2. Sensation: Specialized epithelial cells respond to sensory stimuli, found in the skin, eyes, ears, nose, and tongue.

    3. Secretion: Specialized to secrete substances such as enzymes and hormones in glands.

    4. Absorption: Epithelial cells in the small intestine absorb nutrients from digested food.

    5. Excretion: Excretes waste in kidneys and sweat from sweat glands.

    6. Diffusion: Simple epithelium facilitates the diffusion of gases, liquids, and nutrients due to its thinness.

    7. Cleaning: Ciliated epithelium aids in removing dust and foreign particles from air passages.

    8. Friction Reduction: Smooth, tightly interlocked cells in the circulatory system minimize friction with blood flow.

Classification of Epithelial Cells

  • Shape Classifications:

    1. Squamous: Flat cells.

    2. Cuboidal: Cube-shaped cells.

    3. Columnar: Tall, rod-like cells.

  • Layer Classifications:

    1. Simple: One layer of cells.

    2. Stratified: Multiple layers of cells. Stratified epithelia are named after the shape of the apical cells.

Detailed Types of Epithelia

  1. Simple Squamous Epithelium

    • Description: Flat cells that contact the basement membrane.

    • Function: Facilitates diffusion; smooth surface reduces friction.

    • Locations: Body cavities, capillaries, alveoli for gas exchange.

  2. Simple Cuboidal Epithelium

    • Description: Single layer of cube-like cells with spherical nuclei.

    • Function: Secretion and absorption.

    • Locations: Glands and kidney tubules; also found in ovarian and testicular structures.

  3. Simple Columnar Epithelium

    • Description: Elongated column-shaped cells.

    • Function: Lines stomach and intestines; specialized for sensory reception.

    • Locations: Stomach, intestines, and specialized sensory areas (nose, ears, taste buds).

    • Components: Goblet cells secrete mucus.

  4. Pseudostratified Columnar Epithelium

    • Function: Secretes mucus.

    • Locations: Ducts of large glands, trachea, and upper respiratory tract.

  5. Stratified Cuboidal Epithelium

    • Description: Multi-layered; primarily protective.

    • Function: Protects areas like sweat gland ducts and male urethra.

  6. Stratified Columnar Epithelium

    • Description: Several layers of cells.

    • Function: Protection and secretion.

    • Locations: Found in small amounts in male urethra and large ducts of some glands.

  7. Stratified Squamous Epithelium

    • Location: Found in areas such as the vagina.

  8. Transitional Epithelium

    • Description: Appears as stratified squamous and cuboidal; basal cells are cuboidal/columnar, surface cells can be dome-shaped or squamous-like depending on organ stretch.

    • Function: Allows stretching and distension due to contained urine.

    • Locations: Lines ureters, bladder, and part of the urethra.

Glands

  • Classification of Glands: Glands can be classified into:

    • Exocrine Glands: Retain ducts that lead to body surfaces.

    • Endocrine Glands: Ductless glands that secrete hormones directly into the bloodstream.

Exocrine Glands

  • Function: Secrete products onto body surfaces or cavities.

  • Structure: Can be categorized as simple or compound; secretory units can be tubular, alveolar (acinar), or tubuloalveolar.

    • Examples: Goblet cells (mucus-secreting unicellular exocrine glands).

Endocrine Glands

  • Function: Secretes hormones that enter circulation.

  • Examples: Pancreas has both endocrine (insulin, glucagon) and exocrine (digestive enzymes) functions.

Modes of Secretion of Exocrine Glands

  • Types of Secretion:

    1. Merocrine Secretion:

    • Secretory cells release products via membrane-bound vesicles that fuse with the apical membrane.

    • Common mechanism of secretion in most glands.

    1. Apocrine Secretion:

    • Pinches off apical portions of cells during secretion, resulting in secretion containing portions of the cell membrane.

    • Example: Mammary glands.

    1. Holocrine Secretion:

    • Entire secretory cells rupture and release their contents as the secretory product.

    • Example: Sweat glands in specific areas (axillae, pubic region) and sebaceous glands.

Features of Epithelial Tissue

Lateral Cell Surfaces

  • Adhesion Mechanisms:

    1. Adhesion proteins connecting adjacent cell membranes.

    2. Contours of adjacent cell membranes facilitate contact.

    3. Types of Cell Junctions:

    • Tight Junctions (Zona Occludens): Formed by proteins (claudin and occludin) to prevent passage of materials between cells and maintaining transcellular transport.

    • Desmosomes: Connect cells with disc-like plaques; cadherin proteins connect plaques, interdigitating into extracellular space.

    • Gap Junctions: Hollow protein cylinders allowing molecule passage between adjacent cells.

Basal Surface

  • Basal Layer Details:

    1. Lies on a protein sheet called the basal lamina, which acts as a filter and allows regeneration of epithelial cells.

    2. Basal lamina and reticular fibers create the thicker basement membrane.

Connective Tissue

  • Function of Connective Tissue: Serves as a supporting and binding function to other tissues; typically has cells dispersed in an extracellular matrix.

  • Origin: Derived from mesoderm.

Types of Connective Tissue

  1. Loose Connective Tissue: Contains collagenous, elastic, and reticular fibers.

  2. Fibrous Connective Tissue.

  3. Specialized Connective Tissues:

    • Adipose Tissue

    • Cartilage

    • Bone

Genetical Disorders Related to Connective Tissue

  1. Marfan Syndrome

    • Type: Autosomal dominant genetic disorder.

    • Characteristics: Disproportionately long limbs and fingers, tall stature, cardiovascular abnormalities affecting heart valves and aorta.

    • Pathogenesis: Linked to a defect on chromosome 15 for the fibrillin-1 gene, crucial for elastic fiber formation.

  2. Ehlers-Danlos Syndrome

    • Type: Rare genetic disorders caused by defects in collagen synthesis (Collagen I and III).