Integumentary System, Skeletal System, and Joints: Study Guide

Integumentary System

Main Layers of the Skin

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

• Dermis: Middle layer; made of connective tissue, contains blood vessels, nerves, and glands.

• Hypodermis (Subcutaneous Layer): Not technically part of the skin; consists of adipose and areolar tissue, anchors skin to underlying structures.

Layers of the Epidermis (from deep to superficial)

• Stratum basale: Single row of stem cells; site of mitosis.

• Stratum spinosum: Several layers of keratinocytes; contains Langerhans cells.

• Stratum granulosum: 3-5 layers; keratinization begins here.

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

• Stratum corneum: 20-30 layers of dead, keratinized cells; provides protection.

Layers of the Dermis

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

• Reticular layer: Dense irregular connective tissue; contains Pacinian corpuscles (pressure receptors), sweat glands, and hair follicles.

Tissue Types in Each Layer

• Epidermis: Keratinized stratified squamous epithelium.

• Dermis: Areolar (papillary) and dense irregular connective tissue (reticular).

• Hypodermis: Adipose and areolar connective tissue.

Functions of the Skin

• Protection (physical, chemical, biological barriers)

• Body temperature regulation

• Cutaneous sensation

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

• Blood reservoir

• Excretion of wastes

Cells and Structures in Each Layer

• Keratinocytes: Produce keratin; found throughout epidermis.

• Melanocytes: Produce melanin; found in stratum basale.

• Langerhans (dendritic) cells: Immune defense; found in stratum spinosum.

• Merkel (tactile) cells: Sensory receptors; found in stratum basale.

• Pacinian corpuscles: Deep pressure receptors; found in reticular dermis.

Skin Surface Features

• Friction ridges: Form fingerprints; enhance grip.

• Cleavage (tension) lines: Orientation of collagen fibers; important for surgical incisions.

• Flexure lines: Dermal folds at joints; allow skin to move easily with joints.

Skin Coloration

• Determined by melanin, carotene, and hemoglobin.

• Melanin: Brown-black pigment; produced by melanocytes.

• Carotene: Yellow-orange pigment; accumulates in stratum corneum.

• Hemoglobin: Red pigment in blood; gives pinkish hue to fair skin.

Sweat Glands

• Eccrine (merocrine) glands: Most numerous; secrete watery sweat for thermoregulation.

• Apocrine glands: Axillary and anogenital areas; secrete milky sweat, function after puberty.

• Ceruminous glands: External ear canal; secrete earwax (cerumen).

• Mammary glands: Modified sweat glands; secrete milk.

Hair: Structure and Function

• Structure: Shaft (above skin), root (within follicle), bulb (base of follicle).

• Function: Protection, sensation, reduces heat loss, shields eyes (eyelashes), filters particles (nose hair).

Tissue Repair and Inflammation

• 4 Cardinal Signs of Inflammation: Redness, heat, swelling, pain.

• Caused by increased blood flow, vessel permeability, and immune cell activity.

• Tissue repair: Involves inflammation, organization (restoring blood supply), and regeneration/fibrosis (replacement of tissue).

Skin Cancer

• Basal cell carcinoma: Cancer of basal cells; most common, least malignant.

• Squamous cell carcinoma: Cancer of keratinocytes in stratum spinosum.

• Melanoma: Cancer of melanocytes; most dangerous.

• ABCD Rule: Asymmetry, Border irregularity, Color variation, Diameter >6mm (used to identify melanoma).

Burns

• First-degree: Epidermal damage only; redness, swelling, pain.

• Second-degree: Epidermal and upper dermal damage; blisters appear.

• Third-degree: Entire thickness of skin; gray-white, cherry red, or blackened; not painful (nerve endings destroyed).

• Critical burn: >25% of body with second-degree burns, >10% with third-degree, or burns on face/hands/feet.

• Rule of nines: Used to estimate body surface area burned.

Degree	Layers Involved	Symptoms
First	Epidermis	Redness, pain
Second	Epidermis + part of dermis	Blisters, pain
Third	Full thickness	No pain (nerves destroyed), risk of infection

Skeletal System

Cartilage

• Perichondrium: Dense connective tissue surrounding cartilage; contains blood vessels for nutrient delivery.

• Types of growth: Appositional (growth from outside), interstitial (growth from within).

Functions of Bone

• Support, protection, movement, mineral storage (Ca2+, PO43-), blood cell formation (hematopoiesis), fat storage, hormone production.

Axial vs. Appendicular Skeleton

• Axial: Skull, vertebral column, rib cage.

• Appendicular: Limbs and girdles (shoulder, pelvic).

Types and Classes of Bone

• Spongy bone: Trabeculae; found in epiphyses, flat bones (diploe).

• Compact bone: Dense outer layer; provides strength.

• Diploe: Spongy bone in flat bones.

• Flat bones: Sternum, skull bones.

• Short bones: Carpals, tarsals.

• Long bones: Femur, humerus.

• Irregular bones: Vertebrae, hip bones.

Parts of a Bone

• Diaphysis: Shaft; compact bone surrounding medullary cavity.

• Epiphysis: Ends; spongy bone inside compact bone.

• Periosteum: Outer membrane; contains osteoblasts and osteoclasts.

• Endosteum: Lines internal bone surfaces.

Osteon Structure

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

• Lacunae: Spaces for osteocytes.

• Canaliculi: Small canals connecting lacunae.

Bone Cells

• Osteoblasts: Bone-forming cells.

• Osteocytes: Mature bone cells; maintain matrix.

• Osteoclasts: Bone-resorbing cells.

• Osteogenic cells: Stem cells.

Bone Formation (Ossification)

• Intramembranous ossification: Forms flat bones (skull, clavicle); 4 steps: (1) Ossification center forms, (2) Osteoid secreted, (3) Woven bone and periosteum form, (4) Lamellar bone replaces woven bone.

• Endochondral ossification: Forms most bones; bone replaces hyaline cartilage model.

• Growth plates (epiphyseal plates): Remnants of cartilage; site of longitudinal growth.

Disorders of Bone Growth

• Gigantism: Excess growth hormone in children; abnormally tall stature.

• Acromegaly: Excess growth hormone in adults; enlarged bones of hands, feet, face.

• Achondroplasia: Genetic disorder; affects cartilage growth, leading to dwarfism.

Bone Remodeling

• Bone deposition: Osteoblasts lay down new bone matrix.

• Bone resorption: Osteoclasts break down bone matrix.

• Osteoid seam: Unmineralized band of bone matrix.

• Calcification front: Area between osteoid seam and mineralized bone.

Calcium Homeostasis

• Role of calcium: Nerve impulse transmission, muscle contraction, blood clotting.

• Homeostatic control: If plasma Ca2+ drops, parathyroid hormone (PTH) stimulates osteoclasts to release Ca2+ from bone.

• Healthy range: 9-11 mg/dL.

Wolff’s Law

• Bones grow or remodel in response to demands placed on them (e.g., dominant arm bones are thicker).

Types of Bone Fractures

Type	Description
Depressed	Bone pressed inward (e.g., skull)
Greenstick	Incomplete break; common in children
Spiral	Ragged break from twisting forces
Epiphyseal	Epiphysis separates from diaphysis at growth plate

Bone Fracture Healing Steps

1. Hematoma formation

2. Fibrocartilaginous callus formation

3. Bony callus formation

4. Bone remodeling

Bone Disorders

• Osteomalacia: Soft bones due to poor mineralization (adults).

• Rickets: Osteomalacia in children; bowed legs, deformities.

• Osteoporosis: Bone resorption outpaces deposition; fragile bones.

Joints (Articulations)

Definition and Function

• Joint (articulation): Site where two or more bones meet; allows movement and provides support.

Classification of Joints

• Structural: Based on material binding bones and presence of joint cavity.

• Functional: Based on movement allowed (synarthroses—immovable, amphiarthroses—slightly movable, diarthroses—freely movable).

Structural Type	Characteristics	Example
Fibrous	Joined by dense fibrous connective tissue; no cavity	Sutures (skull)
Cartilaginous	Joined by cartilage; no cavity	Intervertebral discs
Synovial	Joint cavity with synovial fluid	Knee, elbow

Synovial Joints

• All are diarthroses (freely movable).

• Common features: Articular cartilage, joint (synovial) cavity, articular capsule, synovial fluid, reinforcing ligaments, nerves, and blood vessels.

Movements at Synovial Joints

• Gliding, angular movements (flexion, extension, abduction, adduction), rotation, special movements (supination, pronation, etc.).

Types of Synovial Joints

Type	Range of Motion	Movement	Example
Plane	Nonaxial	Gliding	Intercarpal joints
Hinge	Uniaxial	Flexion/extension	Elbow
Pivot	Uniaxial	Rotation	Proximal radioulnar joint
Biaxial	Flexion/extension, abduction/adduction	Wrist
Saddle	Biaxial	Flexion/extension, abduction/adduction	Thumb (carpometacarpal joint)
Ball-and-socket	Multiaxial	All movements	Shoulder, hip

Examples of Specific Joints

• Elbow: Hinge joint

• Shoulder: Ball-and-socket joint

• Hip: Ball-and-socket joint

• Temporomandibular joint (TMJ): Modified hinge joint

Joint Injuries and Disorders

• Cartilage tears: Due to compression and shear stress; may require surgery.

• Sprains: Ligaments stretched or torn.

• Osteoarthritis: Degenerative; wear and tear of articular cartilage.

• Rheumatoid arthritis: Autoimmune; inflammation of synovial membrane.

• Gouty arthritis: Uric acid crystals in joints; causes inflammation and pain.