Chapter 4 – Tissue: The Living Fabric

Basic Tissue Types

The human body is composed of four primary tissue types, each with distinct structures and functions. Understanding these tissues is fundamental to the study of anatomy and physiology.

• Epithelial Tissue: Covers body surfaces, lines cavities, and forms glands. Functions include protection, absorption, filtration, excretion, secretion, and sensory reception.

• Connective Tissue: Supports, protects, and binds other tissues. Found throughout the body, including bone, blood, and fat.

• Muscle Tissue: Responsible for movement. Types include skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Initiates and transmits electrical impulses, forming the brain, spinal cord, and nerves.

Structural and Functional Characteristics of Epithelial Tissue

• Cellularity: Composed almost entirely of closely packed cells with minimal extracellular material.

• Polarity: Has an apical (free) surface and a basal (attached) surface.

• Attachment: Supported by a basement membrane.

• Avascularity: Contains no blood vessels; nourished by diffusion.

• Regeneration: High capacity for renewal via mitosis.

Types of Body Membranes

• Mucous Membranes (Mucosae): Line body cavities open to the exterior (e.g., digestive, respiratory tracts).

• Serous Membranes (Serosae): Line closed ventral body cavities; secrete serous fluid (e.g., peritoneum, pleura, pericardium).

• Cutaneous Membrane: The skin; covers the body surface.

Classification of Epithelia

• By Layers: Simple (one layer) or stratified (multiple layers).

• By Shape: Squamous (flat), cuboidal (cube-shaped), columnar (tall).

Chief Functions and Locations:

• Simple squamous: Diffusion/filtration; found in alveoli, blood vessels.

• Simple cuboidal: Secretion/absorption; found in kidney tubules.

• Simple columnar: Absorption/secretion; found in digestive tract lining.

• Stratified squamous: Protection; found in skin, mouth, esophagus.

• Pseudostratified columnar: Secretion; found in respiratory tract.

• Transitional: Stretching; found in urinary bladder.

Glands: Exocrine vs. Endocrine

• Gland: One or more cells that secrete a product.

• Exocrine Glands: Secrete onto body surfaces or into body cavities (e.g., sweat, salivary glands).

• Endocrine Glands: Ductless; secrete hormones into the bloodstream (e.g., thyroid, pituitary).

• Unicellular Glands: Single cells (e.g., goblet cells).

• Multicellular Glands: Composed of many cells; classified by duct structure and secretory units.

Connective Tissue: Characteristics and Types

• Common Characteristics: Mesenchymal origin, varying vascularity, abundant extracellular matrix.

• Structural Elements: Ground substance, fibers, and cells.

Connective Tissue Proper vs. Other Types:

• Connective Tissue Proper: Includes loose (areolar, adipose, reticular) and dense (regular, irregular, elastic) types.

• Other Types: Cartilage, bone, blood.

Loose vs. Dense Connective Tissue:

• Loose: More ground substance, fewer fibers (e.g., areolar tissue under epithelia).

• Dense: More fibers, less ground substance (e.g., tendons, ligaments).

Connective Tissue Fibers:

• Collagen: Strong, provides tensile strength.

• Elastic: Stretch and recoil.

• Reticular: Supportive networks.

Cell Types: Fibroblasts, chondroblasts, osteoblasts, adipocytes, white blood cells, mast cells, macrophages.

Ground Substance: Unstructured material filling space between cells; composed of interstitial fluid, cell adhesion proteins, and proteoglycans.

Chapter 5 – The Integumentary System

Structure of the Skin

• Two Main Layers: Epidermis (superficial, epithelial tissue) and dermis (deeper, connective tissue).

• Subcutaneous Tissue (Hypodermis): Not part of skin; consists mostly of adipose tissue, anchors skin to underlying structures.

Cells of the Epidermis

• Keratinocytes: Produce keratin, a protective protein.

• Melanocytes: Synthesize melanin pigment.

• Epidermal Dendritic (Langerhans) Cells: Immune defense.

• Tactile (Merkel) Cells: Sensory receptors for touch.

Layers of the Epidermis

• Stratum Basale: Deepest, mitotically active layer.

• Stratum Spinosum: Several layers of keratinocytes; some mitosis.

• Stratum Granulosum: Cells flatten, keratinization begins.

• Stratum Lucidum: Only in thick skin (palms, soles); thin, clear layer.

• Stratum Corneum: Outermost, dead keratinized cells; barrier function.

Dermis Structure and Function

• Papillary Layer: Areolar connective tissue; forms dermal papillae (fingerprints).

• Reticular Layer: Dense irregular connective tissue; provides strength and elasticity.

Skin Color

• Melanin: Brown-black pigment; protects against UV radiation.

• Carotene: Yellow-orange pigment from diet.

• Hemoglobin: Red pigment in blood; visible in fair skin.

Diseases Affecting Skin Color: Cyanosis (blue), jaundice (yellow), erythema (redness), pallor (pale).

Glands of the Skin

• Sudoriferous (Sweat) Glands: Eccrine (thermoregulation, all over body) and apocrine (axillary, anogenital areas; odor).

• Sebaceous (Oil) Glands: Secrete sebum; lubricates skin and hair.

• Modified Glands: Ceruminous (earwax), mammary (milk).

Functions of the Skin

• Protection (chemical, physical, biological barriers)

• Body temperature regulation

• Cutaneous sensation

• Metabolic functions (e.g., vitamin D synthesis)

• Blood reservoir

• Excretion

Skin Cancers and Burns

• Skin Cancers: Basal cell carcinoma, squamous cell carcinoma, melanoma.

• Burns: Classified by depth (first, second, third degree); treatment depends on severity and area affected.

Chapter 6 – Bones and Skeletal Tissue

Cartilage Types: Structure, Function, and Location

• Hyaline Cartilage: Most abundant; provides support, flexibility; found in nose, trachea, articular surfaces.

• Elastic Cartilage: Contains elastic fibers; maintains shape; found in ear, epiglottis.

• Fibrocartilage: Thick collagen fibers; resists compression; found in intervertebral discs, menisci.

Cartilage Growth

• Appositional Growth: Cells in perichondrium secrete new matrix on surface.

• Interstitial Growth: Chondrocytes divide and secrete matrix within cartilage.

Functions of Bone

• Support

• Protection

• Movement

• Mineral storage

• Blood cell formation (hematopoiesis)

• Triglyceride (fat) storage

• Hormone production

Types of Bones

• Long Bones: Longer than wide (e.g., femur).

• Short Bones: Cube-shaped (e.g., carpals).

• Flat Bones: Thin, flat (e.g., sternum, skull).

• Irregular Bones: Complex shapes (e.g., vertebrae).

Gross Anatomy of Bones

• Long Bone: Diaphysis (shaft), epiphyses (ends), membranes (periosteum, endosteum), medullary cavity (contains yellow marrow).

• Flat Bone: Thin plates of spongy bone (diploë) covered by compact bone.

Red Marrow: Hematopoietic tissue; found in trabecular cavities of spongy bone.

Yellow Marrow: Fat storage; found in medullary cavity of adults.

Periosteum: Double-layered membrane covering bone surface; contains osteogenic cells.

Endosteum: Thin membrane lining internal bone surfaces.

Microscopic Structure of Bone

• Osteon (Haversian System): Structural unit of compact bone; concentric lamellae around central canal.

• Cells: Osteogenic cells (stem cells), osteoblasts (bone-forming), osteocytes (mature bone cells), osteoclasts (bone-resorbing).

• Spongy Bone: Trabeculae align along lines of stress; no osteons.

Chemical Composition of Bone

• Organic: Cells and osteoid (collagen fibers, ground substance).

• Inorganic: Hydroxyapatites (mineral salts, mainly calcium phosphate).

Bone Growth and Remodeling

• Epiphyseal Plate: Site of lengthwise growth in children; replaced by epiphyseal line in adults.

• Bone Remodeling: Continuous process of bone deposition and resorption; regulated by hormones (e.g., parathyroid hormone in negative feedback loop).

Negative Feedback Example:

• Low blood calcium stimulates parathyroid hormone (PTH) release, which increases osteoclast activity to release calcium from bone.

Fracture Repair and Bone Diseases

• Fracture Repair: Hematoma formation, fibrocartilaginous callus, bony callus, bone remodeling.

• Diseases: Osteoporosis (bone resorption outpaces deposition), osteomalacia/rickets (soft bones due to vitamin D/calcium deficiency).

Additional info: Students should be able to label diagrams of tissues, skin, and bones as referenced in textbook figures (e.g., Fig 5.1, 6.2, 6.5, 6.8).