Integumentary, Skeletal, and Joint Systems: Mini-Textbook Study Notes

The Integumentary System

Overview of the Skin

The integumentary system consists of the skin and its derivatives (hair, nails, glands). It serves as the body's first line of defense and performs multiple vital functions.

• Protection: Acts as a barrier against mechanical injury, pathogens, and water loss.

• Thermoregulation: Regulates body temperature via sweat and blood flow.

• Sensation: Contains sensory receptors for touch, pain, and temperature.

• Metabolic Functions: Synthesizes vitamin D.

• Excretion: Eliminates wastes through sweat.

Main Layers of the Skin

• Epidermis: Keratinized stratified squamous epithelium; avascular.

• Dermis: Connective tissue with blood vessels, nerves, and glands.

• Hypodermis (Subcutaneous Layer): Adipose and areolar tissue; anchors skin to underlying structures.

Layers of the Epidermis (from superficial to deep)

• Stratum Corneum: Dead, keratinized cells; provides protection.

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

• Stratum Granulosum: Keratinization begins here; cells flatten and accumulate granules.

• Stratum Spinosum: Several layers of keratinized cells; contains Langerhans cells (immune defense).

• Stratum Basale: Single row of stem cells; site of mitosis and new cell production.

Layers of the Dermis

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

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

Cells and Structures in the Skin

• Keratinocytes: Produce keratin for waterproofing and protection.

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

• Langerhans Cells: Immune defense cells in the stratum spinosum.

• Merkel Cells: Sensory receptors for touch.

• Pacinian Corpuscles: Detect deep pressure; located in the 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 with joints.

Skin Coloration

• Melanin: Brown-black pigment; main determinant of skin color.

• Carotene: Yellow-orange pigment in the stratum corneum.

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

Sweat Glands

Type	Location	Secretion	Function
Eccrine (Merocrine)	All over, especially hands, forehead, feet	Watery sweat	Thermoregulation
Apocrine	Axillary, anogenital areas	Milky sweat	Begin at puberty; scent
Ceruminous	External ear canal	Cerumen (ear wax)	Protects ear
Mammary	Breasts	Milk	Nourishment for infants

Structure and Function of Hair

• Shaft: Visible part above skin.

• Root: Within follicle.

• Bulb: Base of follicle; site of hair growth.

• Functions: Protection, sensation, reduces heat loss, shields eyes, filters particles.

Tissue Repair and Inflammation

• Steps in Tissue Repair: Inflammation, organization (restoring blood supply), regeneration/fibrosis (replacement of tissue).

• Cardinal Signs of Inflammation: Redness, heat (increased blood flow), swelling, pain (increased vessel permeability).

Skin Cancer

Type	Origin Cell	Features
Basal Cell Carcinoma	Basal cells	Most common, least malignant
Squamous Cell Carcinoma	Keratinocytes	Can metastasize
Melanoma	Melanocytes	Most dangerous, highly metastatic

• ABCD Rule for Melanoma: Asymmetry, Border irregularity, Color variation, Diameter > 6 mm.

Burns

Degree	Layers Involved	Symptoms
1st Degree	Epidermis	Pain, swelling, redness
2nd Degree	Epidermis + upper dermis	Pain, redness, blisters
3rd Degree	Full thickness (includes hypodermis)	Gray-white, red, or blackened; no pain (nerve endings destroyed)

• Critical Burn: >25% of body with 2nd degree burns, >10% with 3rd degree burns, or burns on face, hands, feet.

• Rule of Nines: Used to estimate percentage of body surface burned.

The Skeletal System

Cartilage

Cartilage is a resilient, avascular connective tissue found at joints and in various structures throughout the body.

• Functions: Supports, cushions, and absorbs shock between bones.

• Perichondrium: Dense connective tissue surrounding cartilage; supplies nutrients.

• Growth Types:

  • Appositional: Growth from the outside.

  • Interstitial: Growth from within, by chondrocytes.

Functions of Bone

• Support

• Protection

• Movement

• Mineral storage (especially calcium and phosphate)

• Blood cell formation (hematopoiesis)

• Fat storage

• Hormone production

Classification of Bones

Type	Example
Flat	Sternum, skull bones
Short	Carpals, tarsals
Long	Femur, humerus
Irregular	Vertebrae, hip bones

• Spongy Bone: Trabeculae; found in epiphyses and flat bones (as diploe).

• Compact Bone: Dense outer layer; provides strength.

• Diploe: Spongy bone in flat bones.

Axial vs. Appendicular Skeleton

• Axial: Skull, vertebral column, rib cage.

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

Structure of a Typical Long Bone

• Diaphysis: Shaft; compact bone surrounding medullary cavity.

• Epiphysis: Ends; spongy bone inside compact bone.

• Periosteum: Outer membrane; contains osteoblasts and osteocytes.

• Endosteum: Lines internal bone surfaces.

Microscopic Structure: Osteon

• Lamella: Concentric rings for support.

• Central (Haversian) Canal: Contains blood vessels and nerves.

• Perforating (Volkmann's) Canal: Connects blood and nerve supply of periosteum to central canal.

• Lacunae: Spaces for osteocytes.

• Canaliculi: Small canals connecting lacunae.

Bone Cells

Cell Type	Function
Osteoblasts	Bone-forming cells
Osteocytes	Mature bone cells; maintain matrix
Osteoclasts	Bone-resorbing cells
Osteogenic Cells	Stem cells

• Calcium phosphates: 65% of bone mass; provide hardness.

Bone Formation (Ossification)

• Intramembranous Ossification: Forms flat bones (skull, clavicle).

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

1. Ossification center forms.

2. Osteoid is secreted.

3. Woven bone and periosteum form.

4. Lamellar bone replaces woven bone.

• 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 in hands, feet, face.

• Achondroplasia: Inability to convert cartilage to bone; causes 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: Provides rigidity; serves as a reservoir for plasma calcium.

• 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 the demands placed on them.

Types of Bone Fractures

Type	Description
Depressed	Bone pressed inward
Greenstick	Incomplete break (common in children)
Spiral	Ragged break from twisting forces
Epiphyseal	Separation at growth plate

Bone Fracture Healing

1. Hematoma formation

2. Fibrocartilaginous callus formation

3. Bony callus formation

4. Bone remodeling

Bone Disorders

• Osteomalacia: Soft bones due to poor mineralization.

• Rickets: Osteomalacia in children; bowlegs, deformities.

• Osteoporosis: Bone resorption outpaces deposition; fragile bones.

Joints (Articulations)

Definition and Function

A joint (articulation) is the site where two or more bones meet. Joints allow movement and provide support to the skeleton.

Classification of Joints

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

  • Fibrous: Dense fibrous connective tissue; no cavity. Example: Sutures (skull).

  • Cartilaginous: Cartilage; no cavity. Example: Intervertebral discs.

  • Synovial: Joint cavity with synovial fluid. Example: Knee, elbow.

• Functional Classification: Based on movement allowed.

  • Synarthroses: Immovable

  • Amphiarthroses: Slightly movable

  • Diarthroses: Freely movable

Synovial Joints

• All are diarthroses (freely movable).

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

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
Condylar	Biaxial	Flexion/extension, abduction/adduction	Wrist
Saddle	Biaxial	Flexion/extension, abduction/adduction	Thumb carpometacarpal joint
Ball and Socket	Multiaxial	All movements	Shoulder, hip

• Elbow: Hinge joint

• Shoulder: Ball and socket

• Hip: Ball and socket

• Temporomandibular joint: Modified hinge

Movements at Synovial Joints

• Gliding: Flat surfaces slide past each other.

• Angular: Flexion, extension, abduction, adduction.

• Rotation: Bone turns around its own long axis.

• Special Movements: Supination, pronation, etc.

Joint Injuries and Disorders

• Cartilage Tears: Due to compression and shear stress.

• Sprain: 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.