Study Guide: Tissues – The Living Fabric (Anatomy & Physiology, Chapter 4)

Tissues: The Living Fabric

Introduction to Tissues

Tissues are groups of cells with similar structure and function, forming the fabric of the body. Understanding the types, characteristics, and functions of tissues is fundamental in Anatomy & Physiology.

Special Characteristics of Epithelial Tissue

• Polarity: Epithelial cells have an apical (top) surface and a basal (bottom) surface, each with distinct structures and functions.

• Specialized Contacts: Cells are closely joined by tight junctions and desmosomes to form continuous sheets.

• Supported by Connective Tissue: The basal surface is attached to a basement membrane, which supports and anchors the epithelium.

• Avascular but Innervated: Epithelial tissues lack blood vessels but are supplied by nerve fibers.

• Regeneration: Epithelial cells have a high capacity for renewal, rapidly replacing lost or damaged cells.

Functions of Epithelial Tissue

• Protection: Shields underlying tissues from mechanical and chemical damage, pathogens, and water loss.

• Secretion: Produces and releases substances such as mucus, sweat, enzymes, and hormones.

• Absorption: Specialized cells take in nutrients and other substances, especially in the digestive tract.

• Excretion: Removes waste products from the body.

• Sensation: Contains sensory receptors that detect stimuli such as touch, pressure, temperature, and taste.

Classes of Epithelial Tissue

• Simple Epithelium: Single layer of cells attached to the basement membrane. Example: Simple squamous epithelium in alveoli of lungs.

• Stratified Epithelium: Multiple layers of cells, providing protection. Example: Stratified squamous epithelium in the skin.

• Pseudostratified Epithelium: Appears layered due to varying cell heights, but all cells touch the basement membrane. Example: Pseudostratified ciliated columnar epithelium in the respiratory tract.

Shapes of Epithelial Cells

• Squamous: Flat or irregularly shaped cells, like fried eggs. Function in diffusion and filtration.

• Cuboidal: Cube-shaped cells, as tall as they are wide. Function in secretion and absorption.

• Columnar: Tall, rectangular cells. Function in absorption and secretion; may have cilia or microvilli.

Glandular Epithelium

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

• Exocrine Glands: Secrete products into ducts that open onto surfaces. Examples: Salivary glands (merocrine), sebaceous glands (holocrine), sweat glands.

Functions of Connective Tissue

• Support: Provides structural framework for the body.

• Protection: Cushions and protects organs.

• Binding: Connects tissues and organs together.

• Storage: Stores energy (as fat) and minerals.

• Transportation: Transports substances (e.g., blood transports gases, nutrients, wastes).

Types of Fibrous Connective Tissue

Type	Where it is found in your body	Description, types of cells
Areolar (loose)	Everywhere – binds underlying organs to skin and each other	Very thin, delicate fibers
Reticular (loose)	Lymph nodes, spleen, bone marrow	Network of reticular fibers, support free blood cells
Dense regular	Tendons (muscle to bone), ligaments (bone to bone)	Parallel collagen fibers, very strong in one direction. Fibroblasts between fibers
Dense irregular	Dermis of skin, joint capsules	Thick bundles of collagen fibers arranged irregularly; resists tension from many angles
Dense elastic	Walls of large arteries, certain ligaments, walls of bronchial tubes	Densely packed elastic fibers with fibroblasts, allows stretch and recoil

Types of Cartilage

Type	Where it is found	Description, types of cells
Hyaline cartilage	Covers ends of joints, nose, and respiratory passages; serves as padding	Chondrocytes in lacunae, loose and lots of extracellular matrix (ECM)
Elastic cartilage	External ear and larynx	Chondrocytes in lacunae plus many elastic fibers, flexible and resilient
Fibrocartilage	Between vertebrae, menisci	Tough, shock absorbing, highly packed. Chondrocytes in rows, very tough and shock absorbing

Other Types of Connective Tissue

Type	Where it is found	Description, types of cells
Bone (osseous tissue)	Skeleton	Osteocytes in lacunae, hard matrix of calcium salts, strong from collagen fibers
Blood	Blood vessels, heart chambers	Red blood cells (carry O2), white blood cells (immune defense), platelets (clotting), fluid plasma matrix

Adipose Tissue: White Fat vs. Brown Fat

• White fat: Stores nutrients, found in most adult cells. Contains a single large lipid droplet. Functions as energy storage, insulation, and cushioning.

• Brown fat: Contains abundant mitochondria that use lipids to generate heat instead of ATP. Especially important in infants for thermoregulation.

Muscle Tissue

• Skeletal muscle: Striated, voluntary, multinucleated, long cylindrical cells. Responsible for body movement.

• Cardiac muscle: Striated, involuntary, branched cells with intercalated discs. Found only in the heart; responsible for pumping blood.

• Smooth muscle: Non-striated, involuntary, spindle-shaped cells. Found in walls of hollow organs (digestive tract, blood vessels, uterus).

Nervous Tissue

• Neurons: Transmit electrical signals (nerve impulses). Main functional cells of the nervous system.

• Neuroglia: Support, insulate, and protect neurons. Do not conduct impulses.

Membranes

• Cutaneous membrane: The skin; dry unless sweat, oil, or other secretions are present.

• Mucous membranes: Line body cavities open to the exterior (digestive, respiratory, urinary, reproductive tracts). Kept moist by secretions from goblet cells.

Tissue Repair: Regeneration vs. Fibrosis

• Regeneration: Replacement of destroyed tissue with the same kind of tissue, restoring normal function.

• Fibrosis: Replacement with scar tissue (dense connective tissue), which may impair function.

Clinical Application: Cancer Immunotherapy

• Cancer Immunotherapy: Uses the body's own immune system to attack and kill cancer cells. Represents a promising new therapy in cancer treatment.

Additional info: The study guide references a case study of a child with Epidermolysis bullosa, a genetic disease affecting the skin, to illustrate the importance of tissue structure and function. It also encourages students to reflect on the impact of tissue disorders and advances in therapies.