ch 04 Tissues

Human Tissues Study Guide

Introduction to Tissues

• Tissue: A group of similar cells working together as a unit.

• Histology: The study of tissues.

Major Types of Tissues

1. Epithelial

2. Connective

3. Muscle

4. Nervous

Epithelial Tissue

Definition

• Sheets of cells covering body surfaces, cavities, and lining tubes.

Main Forms

1. Covering and Lining Epithelia: e.g., skin, digestive tract.

2. Glandular Epithelia: e.g., salivary glands.

Main Functions

• Protection

• Absorption

• Filtration

• Excretion

• Secretion

• Sensory reception

Characteristics

• Polarity: Apical (top) and basal (bottom) surfaces.

• Specialized Contacts: Tight junctions and desmosomes.

• Support by Connective Tissue: Basement membrane.

• Avascular but Innervated: No blood vessels; has nerve endings.

• High Regenerative Ability: Quick to regenerate.

Cell Shapes

• Squamous: Flat, thin cells.

• Cuboidal: Cube-shaped cells.

• Columnar: Tall, cylindrical cells.

Tissue Layering

• Simple Epithelium: One layer.

• Stratified Epithelium: Multiple layers.

Types of Epithelial Tissue

• Simple Squamous: Flat, used for diffusion; locations: alveoli, blood vessels.

• Simple Cuboidal: For secretion/absorption; locations: kidney tubules.

• Simple Columnar: May have microvilli/cilia; locations: lining of stomach/intestines.

• Stratified Squamous: Protection; locations: skin (keratinized), mouth (non-keratinized).

• Pseudostratified Columnar: Often ciliated; locations: respiratory tract.

• Rare Types: Stratified Cuboidal (sweat, mammary glands) & Stratified Columnar (pharynx, male urethra).

Glandular Epithelia

Definition

• Gland: Secretes aqueous fluids (secretions).

Classification

1. By Product Release Location:

   • Endocrine: Internally secreting (e.g., hormones).

   • Exocrine: Externally secreting (e.g., sweat, saliva).

2. By Cell Number:

   • Unicellular: e.g., goblet cells.

   • Multicellular: e.g., salivary glands.

Types of Exocrine Secretion

• Merocrine: Exocytosis (e.g., sweat).

• Holocrine: Ruptured cell during secretion (e.g., sebaceous glands).

• Apocrine: Apical part ruptures (e.g., mammary glands, debated in humans).

Connective Tissue

Definition

• Most abundant and widely distributed tissue type.

Major Functions

• Binding/supporting, protecting, insulating, storing nutrients, and transporting substances (e.g., blood).

Types of Connective Tissues

1. Connective Tissue Proper

2. Cartilage

3. Bone

4. Blood

Common Characteristics

• Embryonic Origin: All arise from mesenchyme.

• Vascularity: Ranges from avascular (cartilage) to highly vascularized (bone).

• Extracellular Matrix: Helps provide support and allows for tension.

Structural Elements

• Ground Substance: Gel-like material between cells (contains fluids and proteins).

• Fibers:

  • Collagen: Provides tensile strength.

  • Elastic: Allows stretch and recoil.

  • Reticular: Form networks for support.

• Cells:

  • Blast cells: Immature and secreting (e.g., fibroblasts, chondroblasts).

  • Cyte cells: Mature and maintain the matrix (e.g., chondrocytes).

Types of Connective Tissue Proper

• Loose Connective Tissues: Areolar, Adipose, Reticular.

• Dense Connective Tissues: Dense regular, Dense irregular, Elastic.

Cartilage

Definition

• Supportive but flexible, avascular tissue.

Types of Cartilage

• Hyaline Cartilage: Most abundant; in joints, ribcage.

• Elastic Cartilage: More elastic fibers; in ears.

• Fibrocartilage: Strong; in intervertebral discs.

Bone

Definition

• Osseous tissue that supports and protects structures.

Composition

• Matrix with collagen and inorganic calcium salts; contains osteocytes in lacunae.

Blood

Definition

• Fluid connective tissue composed of cells in liquid matrix (plasma).

Functions

• Transports gases, nutrients, wastes.

Muscle Tissue

Types

1. Skeletal Muscle: Attached to bones; voluntary, striated, multinucleated.

2. Cardiac Muscle: Found in heart; involuntary, striated, branched.

3. Smooth Muscle: Involuntary, non-striated, spindle-shaped.

Nervous Tissue

Composition

• Main component of the nervous system; includes neurons and supporting cells.

Functions

• Conducts electrical signals throughout the body.

Covering and Lining Membranes

• Composed of epithelium attached to connective tissue.

Types

• Cutaneous Membranes: Skin, dry.

• Mucous Membranes: Line cavities open to exterior, secrete mucus.

• Serous Membranes: Line closed cavities, produce serous fluid.

Tissue Repair

Mechanisms

• Regeneration: Same type replaces lost tissue.

• Fibrosis: Connective tissue replaces lost tissue; may lose function.

Steps in Tissue Repair

1. Inflammation: Blood vessel dilation and increased permeability.

2. Organization: Blood clot replaced with granulation tissue.

3. Regeneration and Fibrosis: Scar tissue formed, thickening epithelium.

Regenerative Capacity of Tissues

• Well-regenerating: epithelial, bone, blood-forming.

• Moderate: smooth muscle, dense regular connective.

• Poor: cardiac muscle, nervous tissue.

Scars

Types

• Hypertrophic: Raised scars due to excessive collagen.

• Keloid: Excessive scarring, benign neoplasms.

• Atrophic: Sunken scars due to loss of support.

Clinical Implications

• Scar tissue can impair organ function and normal movement.