Integumentary System, Skeletal System, Joints, and Muscle Tissue: Study Notes

Skin Color and the Integumentary System

Skin Color

The color of human skin is determined by several pigments and physiological factors. These contribute to individual variation and can indicate health status.

• Melanin: Reddish yellow to brownish black pigment. Protects DNA from UV radiation.

• Carotene: Yellow to orange pigment. Found in stratum corneum and converted to vitamin A.

• Hemoglobin: Oxygenated hemoglobin imparts a pinkish color to fair skin.

Abnormal Skin Color

• Cyanosis: Bluish color, poorly oxygenated hemoglobin.

• Pallor: Pale skin; may indicate anemia or low blood pressure.

• Erythema: Redness; fever, inflammation, allergy, blushing.

• Jaundice: Yellow skin; liver disorder, excess bilirubin.

• Bronzing: Addison's disease; low hormone production by adrenal cortex.

• Hematoma: Bruising; blood clotted under skin.

Additional info: Skin color can be a diagnostic tool for underlying health conditions.

Accessory Organs of the Skin

• Pili (Hair): Flexible strands of dead keratinized cells. Functions include protection, sensory input, and thermoregulation.

• Hair Structure:

  • Shaft: Part above the skin (determines appearance).

  • Root: Embedded in skin; extends into dermis or lower.

  • Hair follicle: Surrounds root; contains hair bulb and papilla.

• Types of Hair:

  • Terminal hair: Coarse, long hair (scalp, eyebrows).

  • Vellus hair: Fine, pale hair (children, adult females).

Nails

• Nail Plate: Hard keratinized cells.

• Nail Bed: Epidermis under nail plate.

• Cuticle (Eponychium): Proximal nail fold.

Glands of the Skin

• Sudoriferous (Sweat) Glands:

  • Eccrine: Most numerous; secrete watery sweat for thermoregulation.

  • Apocrine: Axillary and anogenital areas; secrete milky sweat, begin functioning at puberty.

• Modified Sweat Glands:

  • Ceruminous: Ear canal; secrete earwax.

  • Mammary: Secrete milk.

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

Skeletal System

Functions of Bones

Bones serve multiple functions essential for movement, protection, and homeostasis.

• Support: Framework for the body.

• Protection: Protects vital organs (e.g., skull, rib cage).

• Movement: Leverage for muscles.

• Mineral Storage: Reservoir for calcium and phosphorus.

• Blood Cell Formation: Hematopoiesis in red marrow.

• Triglyceride Storage: Yellow marrow stores fat.

• Hormone Production: Osteocalcin regulates bone formation and energy metabolism.

Bone Structure

• Long Bones: Limbs; shaft (diaphysis) and ends (epiphyses).

• Short Bones: Wrist, ankle.

• Flat Bones: Skull, ribs, sternum.

• Irregular Bones: Vertebrae, hip bones.

Bone Tissue Types

• Compact Bone: Dense, outer layer; provides strength.

• Spongy Bone: Honeycomb of trabeculae; contains red marrow.

Microscopic Structure of Bone

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

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny canals connecting lacunae; allow nutrient/waste exchange.

Bone Membranes

• Periosteum: Outer covering; contains nerves, blood vessels, osteogenic cells.

• Endosteum: Lines internal bone surfaces; contains osteogenic cells.

Bone Development and Growth

• Ossification (Osteogenesis): Process of bone formation.

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

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

Bone Remodeling and Repair

• Bone Homeostasis: Bone is continuously remodeled by osteoblasts (build bone) and osteoclasts (break down bone).

• Hormonal Regulation: Parathyroid hormone (PTH) and calcitonin regulate blood calcium levels.

Equation:

$\text{Ca}^{2+} \text{ homeostasis:} \quad \text{PTH increases blood Ca}^{2+}, \text{calcitonin decreases blood Ca}^{2+}$

Bone Fractures

• Types: Simple (closed), compound (open), comminuted, greenstick, spiral, etc.

• Stages of Healing:

  1. Hematoma formation

  2. Fibrocartilaginous callus formation

  3. Bony callus formation

  4. Bone remodeling

Common Bone Disorders

• Osteoporosis: Reduced bone mass; increased fracture risk.

• Osteomalacia/Rickets: Soft bones due to vitamin D/calcium deficiency.

• Paget's Disease: Excessive bone remodeling; thick, weak bones.

Joints (Articulations)

Classification of Joints

• Fibrous Joints: Bones joined by dense connective tissue; little/no movement (e.g., sutures, syndesmoses, gomphoses).

• Cartilaginous Joints: Bones joined by cartilage; limited movement (e.g., synchondroses, symphyses).

• Synovial Joints: Bones separated by fluid-filled cavity; freely movable.

Types of Synovial Joints

• Plane: Nonaxial, gliding movements.

• Hinge: Uniaxial, flexion/extension (elbow).

• Pivot: Uniaxial, rotation (radioulnar joint).

• Condyloid: Biaxial, flexion/extension, abduction/adduction (wrist).

• Saddle: Biaxial (thumb).

• Ball-and-Socket: Multiaxial (shoulder, hip).

Movements at Synovial Joints

• Angular Movements: Flexion, extension, hyperextension, abduction, adduction, circumduction.

• Rotation: Medial/lateral rotation.

• Special Movements: Supination, pronation, elevation, depression, inversion, eversion, protraction, retraction.

Muscle Tissue

Structure of Skeletal Muscle

Skeletal muscle fibers are long, cylindrical cells containing multiple nuclei and specialized organelles for contraction.

• Sarcolemma: Muscle cell membrane.

• Sarcoplasm: Cytoplasm; contains myofibrils, mitochondria, glycogen.

• Myofibrils: Contractile elements; composed of sarcomeres.

• Sarcomere: Functional unit; contains thick (myosin) and thin (actin) filaments.

Sliding Filament Model of Contraction

• During contraction, actin and myosin filaments slide past each other, shortening the sarcomere.

• Equation:

$\text{Force} \propto \text{Number of cross-bridges formed}$

Neuromuscular Junction and Muscle Contraction

• Acetylcholine (ACh): Neurotransmitter released from motor neuron; binds to receptors on sarcolemma.

• Action Potential: Electrical signal triggers Ca2+ release from sarcoplasmic reticulum.

• Cross-Bridge Cycling: Myosin heads bind to actin, pull, release, and repeat.

Muscle Relaxation

• Ca2+ is pumped back into sarcoplasmic reticulum by ATP-dependent pumps.

• Tropomyosin blocks myosin binding sites on actin; relaxation occurs.

Additional info: Muscle contraction and relaxation are tightly regulated by ion channels, ATP availability, and regulatory proteins.