Chapter 4 – Histology

Basic Components of Tissues

• All tissues are composed of two main components: cells and extracellular matrix (ECM).

• The ECM consists of ground substance and protein fibers, providing structural and biochemical support to cells.

Major Tissue Types

• There are four major tissue types in the human body:

  1. Epithelial tissue

  2. Connective tissue

  3. Muscular tissue

  4. Nervous tissue

Ground Substance and Macromolecules

• Ground substance is the amorphous, gel-like material in the ECM that fills the space between cells and fibers.

• Key macromolecules in ground substance:

  • Glycosaminoglycans (GAGs): Long, unbranched polysaccharides that attract water, providing resistance to compression.

  • Glycoproteins: Proteins with carbohydrate groups that help cells adhere to the ECM and guide cell migration.

Protein Fibers in the ECM

• Three main types of protein fibers:

  • Collagen fibers: Provide tensile strength and resist stretching.

  • Elastic fibers: Allow tissues to stretch and recoil.

  • Reticular fibers: Form supportive networks in soft tissues like the spleen and lymph nodes.

Cell Junctions

• Tight (occluding) junctions: Seal adjacent cells together, preventing passage of substances between them.

• Desmosomes: Anchor cells together, providing mechanical stability.

• Gap junctions: Allow direct communication between cells via small channels.

Epithelial Tissue

• General functions: Protection, absorption, secretion, and sensation.

• Types of epithelial tissue:

  • Simple squamous epithelium: Single layer of flat cells; allows for rapid diffusion and filtration. Location: alveoli of lungs, lining of blood vessels.

  • Simple columnar epithelium: Single layer of tall, column-shaped cells; absorption and secretion. Location: lining of digestive tract.

  • Pseudostratified columnar epithelium: Appears layered but all cells touch the basement membrane; secretion and movement of mucus. Location: respiratory tract.

  • Stratified squamous epithelium: Multiple layers of flat cells; protection against abrasion. Location: skin, mouth, esophagus.

• Structures within epithelial tissue:

  • Microvilli: Increase surface area for absorption.

  • Cilia: Move substances across the cell surface.

  • Goblet cells: Unicellular glands that secrete mucus.

Glands

• Exocrine glands: Secrete products into ducts (e.g., sweat, saliva).

• Endocrine glands: Release hormones directly into the bloodstream.

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

• Multicellular exocrine glands: Composed of many cells, often with ducts.

• Modes of secretion:

  • Merocrine: Secrete by exocytosis (e.g., sweat glands).

  • Apocrine: Part of the cell pinches off with the secretion (e.g., mammary glands).

  • Holocrine: Entire cell ruptures to release product (e.g., sebaceous glands).

Connective Tissue

• General functions: Support, protection, binding, insulation, and transport.

• Types of connective tissue:

  • Adipose tissue: Stores fat, insulates, and cushions organs. Location: under skin, around organs.

  • Hyaline cartilage: Provides support with flexibility. Location: nose, trachea, ends of long bones.

  • Fibrocartilage: Resists compression and tension. Location: intervertebral discs, pubic symphysis.

  • Elastic cartilage: Maintains shape with flexibility. Location: external ear, epiglottis.

  • Bone: Rigid support, protection, mineral storage.

  • Blood: Transports gases, nutrients, wastes, and cells.

Muscle Tissue

• Skeletal muscle: Long, striated, multinucleated cells; voluntary movement. Location: attached to bones.

• Cardiac muscle: Striated, branched cells with intercalated discs; involuntary movement. Location: heart.

• Smooth muscle: Non-striated, spindle-shaped cells; involuntary movement. Location: walls of hollow organs.

Membranes

• True membranes: Composed of epithelial and connective tissue layers (e.g., serous, synovial, cutaneous, mucous membranes).

• Membrane-like structures: Similar in function but may lack one of the layers.

• Locations:

  • Serous membrane: Lines body cavities not open to the exterior (e.g., peritoneum).

  • Synovial membrane: Lines joint cavities.

  • Cutaneous membrane: The skin.

  • Mucous membrane: Lines cavities open to the exterior (e.g., digestive tract).

Tissue Repair

• Regeneration: Replacement of damaged cells with the same cell type; restores normal function.

• Fibrosis: Replacement with scar tissue (dense connective tissue); function may be lost.

• Tissues that regenerate: Epithelial, most connective, smooth muscle.

• Tissues that undergo fibrosis: Cardiac muscle, nervous tissue.

Chapter 5 – Integumentary System

Structure of the Skin

• The skin consists of two main layers:

  • Epidermis: Superficial layer; composed of keratinized stratified squamous epithelium.

  • Dermis: Deep layer; composed of connective tissue (areolar and dense irregular).

• Hypodermis (subcutaneous layer): Not a true skin layer; consists of adipose and areolar tissue, anchors skin to underlying structures.

Functions of the Integumentary System

• Protection against mechanical, chemical, and biological damage

• Prevention of water loss

• Thermoregulation

• Sensory reception

• Vitamin D synthesis

Layers of the Epidermis

• From deep to superficial:

  1. Stratum basale

  2. Stratum spinosum

  3. Stratum granulosum

  4. Stratum lucidum (only in thick skin)

  5. Stratum corneum

Thick vs Thin Skin

• Thick skin: Found on palms and soles; contains all five strata, including stratum lucidum; lacks hair follicles and sebaceous glands.

• Thin skin: Covers most of the body; lacks stratum lucidum; contains hair follicles and sebaceous glands.

Cells of the Epidermis

• Dendritic cells (Langerhans cells): Immune defense.

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

• Melanocytes: Produce melanin, which protects against UV radiation.

Dermis Structure

• Two layers:

  • Papillary layer: Superficial; areolar connective tissue; contains dermal papillae, capillaries, and sensory receptors.

  • Reticular layer: Deep; dense irregular connective tissue; contains blood vessels, nerves, hair follicles, and glands.

Diagnostic Skin Color Terms

• Erythema: Redness; indicates increased blood flow (e.g., inflammation).

• Pallor: Paleness; may indicate anemia or shock.

• Cyanosis: Bluish color; indicates low oxygen levels.

• Bilirubin: Yellow pigment; high levels cause jaundice, indicating liver dysfunction.

Accessory Structures of the Integument

• Hair, nails, sweat glands, sebaceous glands, and ceruminous glands.

Hair

• Growth stages: Growth (anagen) and resting (telogen) stages.

• Types of hair:

  • Lanugo: Fetal hair.

  • Vellus: Fine body hair in children and adults.

  • Terminal: Coarse, pigmented hair (scalp, eyebrows, etc.).

Nails

• Actively dividing cells: Found in the nail matrix.

• Nail plate parts: Nail body and nail root.

Sweat and Sebaceous Glands

• Merocrine (eccrine) sweat glands: Most common; secrete watery sweat for thermoregulation; found throughout the body.

• Apocrine sweat glands: Secrete thicker, odoriferous sweat; found in axillary and genital regions.

• Ceruminous glands: Produce earwax (cerumen); found in the external ear canal.

• Sebaceous glands: Produce sebum (oil); found throughout the skin except palms and soles.

Burns

• 1st degree: Damages epidermis only.

• 2nd degree: Damages epidermis and part of dermis.

• 3rd degree: Destroys epidermis, dermis, and may affect deeper tissues; major concern is fluid loss and infection.

Chapter 6 – Skeletal System

Functions of the Skeletal System

• Support, protection, movement, mineral storage, blood cell production (hematopoiesis), and fat storage.

Bone Classification

• Long bones: e.g., femur, humerus

• Short bones: e.g., carpals, tarsals

• Flat bones: e.g., sternum, skull bones

• Irregular bones: e.g., vertebrae, pelvis

Structure of a Long Bone

• Diaphysis: Shaft of the bone.

• Medullary cavity: Central cavity containing bone marrow.

• Epiphysis: Ends of the bone.

• Epiphyseal line/plate: Site of bone growth in length.

• Periosteum: Dense connective tissue covering the bone.

Bone Marrow

• Children: Medullary cavity contains red marrow (hematopoietic).

• Adults: Medullary cavity contains yellow marrow (fat storage).

Bone Matrix

• Organic matrix (osteoid): Collagen fibers and ground substance; provides flexibility and tensile strength.

• Inorganic matrix: Hydroxyapatite (calcium phosphate crystals); provides hardness and resistance to compression.

Bone Cells

• Osteoblasts: Build bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Break down bone matrix; secrete acids and enzymes to dissolve organic and inorganic components.

Compact Bone Structures

• Canaliculi: Small channels connecting osteocytes.

• Central canal: Contains blood vessels and nerves.

• Lacunae: Small spaces housing osteocytes.

Bone Formation (Ossification)

• Intramembranous ossification: Bone develops from a fibrous membrane; forms flat bones (e.g., skull, clavicle).

• Endochondral ossification: Bone develops from hyaline cartilage; forms most bones.

• Spongy bone forms before outer compact bone.

Bone Growth

• Longitudinal growth: Increase in bone length at the epiphyseal plate.

• Five zones of the epiphyseal plate (from epiphysis to diaphysis):

  1. Zone of reserve cartilage

  2. Zone of proliferation

  3. Zone of hypertrophy

  4. Zone of calcification

  5. Zone of ossification

• Proliferation and hypertrophy zones actively participate in growth.

• Steps: Chondrocytes divide, enlarge, die, matrix calcifies, bone replaces cartilage.

• Appositional growth: Increase in bone diameter by adding new bone to the surface.

Hormonal Regulation of Bone Growth

• Growth hormone: Stimulates bone growth at epiphyseal plate.

• Testosterone and estrogen: Promote growth and later closure of epiphyseal plate.

Bone Remodeling

• Continuous process of bone resorption and deposition.

• Compression: Stimulates bone formation.

Calcium Homeostasis

• Parathyroid hormone (PTH): Increases blood calcium by stimulating osteoclasts.

• Calcitonin: Decreases blood calcium by inhibiting osteoclasts and stimulating osteoblasts.

Fracture Healing

• Steps: Hematoma formation → fibrocartilaginous callus → bony callus → bone remodeling.

• Simple fracture: Bone does not penetrate skin.

• Compound fracture: Bone penetrates skin.

Chapter 8 – Articulations

Functional Classification of Joints

• Synarthrosis: Immovable joints (e.g., sutures of the skull); highest stability.

• Amphiarthrosis: Slightly movable joints (e.g., intervertebral discs).

• Diarthrosis: Freely movable joints (e.g., shoulder, knee); least stable.

• As range of motion increases, stability decreases.

Structural Classification of Joints

• Fibrous joints: Bones joined by dense connective tissue; no joint cavity (e.g., sutures, gomphoses).

• Cartilaginous joints: Bones joined by cartilage; no joint cavity (e.g., synchondroses, symphyses).

• Synovial joints: Bones separated by a fluid-filled joint cavity; most movable type.

Definitions

• Suture: Immovable joint between skull bones.

• Gomphosis: Peg-in-socket joint (e.g., teeth in alveolar sockets).

Cartilaginous Joints

• Synchondroses: Bones joined by hyaline cartilage; functionally synarthroses (e.g., epiphyseal plates).

• Symphyses: Bones joined by fibrocartilage; functionally amphiarthroses (e.g., pubic symphysis).

Synovial Joint Structures

• Fibrous layer of articular capsule: Strengthens joint and prevents excessive movement.

• Synovial membrane: Produces synovial fluid for lubrication.

• Synovial fluid: Reduces friction, nourishes cartilage.

• Articular cartilage: Hyaline cartilage covering bone ends; absorbs shock.

• Ligaments: Connect bone to bone; stabilize joints.

• Tendons: Connect muscle to bone; aid movement.

• Tendon sheaths: Tubular bursae that surround tendons; reduce friction.

Range of Motion in Synovial Joints

• Monoaxial: Movement in one plane (e.g., hinge joint).

• Biaxial: Movement in two planes (e.g., saddle joint).

• Multiaxial: Movement in multiple planes (e.g., ball-and-socket joint).

Joint Movements

• Flexion/Extension: Decrease/increase angle between bones.

• Abduction/Adduction: Movement away/toward midline.

• Depression/Elevation: Lowering/raising a body part.

• Dorsiflexion/Plantar flexion: Upward/downward movement of foot at ankle.

• Supination/Pronation: Rotation of forearm (palm up/palm down).

Types of Synovial Joints

• Hinge joint: Monoaxial; e.g., elbow, knee.

• Pivot joint: Monoaxial; e.g., atlantoaxial joint (neck).

• Ball-and-socket joint: Multiaxial; e.g., shoulder, hip.

• Plane joint: Nonaxial; e.g., intercarpal joints.

Elbow Joint Structures

• Radial collateral ligament: Stabilizes lateral aspect of elbow.

• Ulnar collateral ligament: Stabilizes medial aspect of elbow.

Knee Joint Structures

• Medial and lateral menisci: C-shaped fibrocartilage pads; absorb shock and improve fit.

• Anterior cruciate ligament (ACL): Prevents anterior displacement of tibia.

• Posterior cruciate ligament (PCL): Prevents posterior displacement of tibia.

Hip Joint Structures

• Ligament of the head of the femur: Provides blood supply to femoral head.

• Acetabular labrum: Deepens socket, increases stability.

Hip Replacements

• Total hip replacement: Both acetabulum and femoral head are replaced.

• Partial hip replacement: Only femoral head is replaced.