BIO 201 Unit 2: Integumentary and Skeletal Systems Study Notes

Chapter 5: Integumentary System

Overview of the Integumentary System

The integumentary system is the body's largest organ system, primarily composed of the skin, hair, nails, and associated glands. It serves as the first line of defense against environmental hazards and plays a vital role in homeostasis.

• Protection: Stratified squamous epithelial cells protect underlying tissues from trauma, pathogens, and dehydration.

• Melanin Production: Melanocytes in the epidermis produce melanin, which protects DNA from ultraviolet (UV) radiation damage.

• Vitamin D Synthesis: The skin converts cholesterol into Vitamin D upon exposure to UV light, which is essential for calcium absorption in the intestines.

• Immune Function: The skin helps prevent illness, autoimmunity, and cancer by acting as a physical and immunological barrier.

• Sensory Reception: Specialized nerve endings and corpuscles in the skin detect touch, pain, temperature, and pressure.

• Thermoregulation: Blood vessels and sweat glands in the skin regulate body temperature through vasoconstriction, vasodilation, and evaporative cooling.

Structure of the Skin

The skin consists of two main layers: the epidermis and the dermis, each with distinct structures and functions.

• Epidermis: The outermost layer, composed of stratified squamous epithelium. It is avascular and relies on diffusion from the dermis for nutrients.

• Dermis: The deeper layer, made of connective tissue, provides strength and elasticity. It contains blood vessels, nerves, and accessory structures.

Layers of the Epidermis (from superficial to deep):

• Stratum Corneum: Dead, keratinized cells that provide a tough, protective barrier. Thickens to form calluses with repeated friction.

• Stratum Lucidum: Clear layer found only in thick skin (palms, soles).

• Stratum Granulosum: Cells contain keratohyalin granules, forming a barrier to water and pathogens.

• Stratum Spinosum: Cells are filled with melanin and connected by desmosomes.

• Stratum Basale: Deepest layer; contains mitotic stem cells and melanocytes. Responsible for continuous cell production.

Accessory Structures

• Hair: Provides protection and sensory input. Types include lanugo (fetal), vellus (fine, body hair), and terminal (thicker, pigmented).

• Nails: Composed of hard keratin, protect the distal tips of fingers and toes.

• Glands:

  • Sebaceous (oil) glands: Secrete sebum to lubricate skin and hair.

  • Sudoriferous (sweat) glands: Eccrine glands are widespread and aid in thermoregulation; apocrine glands are found in specific areas and become active at puberty.

• Arrector Pili Muscles: Smooth muscle fibers attached to hair follicles; contraction causes goosebumps.

Sensory Receptors

• Free Nerve Endings: Detect pain, itch, and temperature.

• Meissner's (Tactile) Corpuscles: Sense light touch and texture, located in the papillary dermis.

• Pacini (Lamellar) Corpuscles: Detect deep pressure and vibration, found deeper in the dermis.

Skin Color and Pigmentation

Skin color is determined by the type and amount of melanin, hemoglobin, and carotene present.

• Melanin: Produced by melanocytes; comes in eumelanin (brown/black) and pheomelanin (red/yellow) forms.

• Hemoglobin: Red pigment in blood; gives skin a pinkish hue when oxygenated.

• Carotene: Yellow-orange pigment from diet; can accumulate in the skin.

Color changes can indicate health conditions:

• Erythema: Redness due to increased blood flow (inflammation, infection, trauma).

• Cyanosis: Bluish tint from deoxygenated hemoglobin.

• Pallor: Pale skin from reduced blood flow or low hemoglobin.

• Jaundice: Yellowing from bilirubin buildup (liver dysfunction).

Skin Pathologies

• Burns: Classified by depth:

  • First-degree: Superficial, only epidermis affected.

  • Second-degree: Involves epidermis and part of dermis; blisters form.

  • Third-degree: Full-thickness; destroys both epidermis and dermis, may damage nerves.

• Rule of 9's: Used to estimate body surface area affected by burns for fluid resuscitation:

  Body Region	% of Total Body Surface Area
  Head	9%
  Each Arm	9% (total 18%)
  Each Leg	18% (total 36%)
  Torso (front and back)	36%
  Genitals	1%

• Skin Cancer:

  • Basal Cell Carcinoma: Originates from stratum basale stem cells; most common, least dangerous.

  • Squamous Cell Carcinoma: From stratum spinosum keratinocytes; can metastasize.

  • Melanoma: From melanocytes; highly malignant. Use ABCDE rule for identification:

    • Asymmetry

    • Border irregularity

    • Color variation

    • Diameter > 6mm

    • Evolving over time

Chapter 6: Skeletal System

Overview of the Skeletal System

The skeletal system provides structural support, protection for internal organs, facilitates movement, stores minerals, and houses bone marrow for blood cell production.

• Axial Skeleton: Skull, vertebral column, and rib cage.

• Appendicular Skeleton: Limbs and girdles (pectoral and pelvic).

Bone Structure and Types

• Long Bones: Have a shaft (diaphysis) and two ends (epiphyses); e.g., femur, humerus.

• Compact (Cortical) Bone: Dense outer layer; provides strength.

• Spongy (Trabecular) Bone: Less dense, found at bone ends; contains red marrow.

• Hyaline Cartilage: Covers joint surfaces and forms the initial skeleton in development.

Microscopic Structure of Bone

• Osteon: Structural unit of compact bone, consisting of concentric lamellae around a central canal.

• Osteocytes: Mature bone cells residing in lacunae, connected by canaliculi for nutrient exchange.

• Lacunae: Small cavities housing osteocytes.

• Canaliculi: Tiny channels connecting lacunae and central canal.

• Perforating (Volkmann's) Canals: Horizontal channels for blood vessels and nerves.

Bone Cells and Functions

• Osteoblasts: Build bone matrix by secreting collagen and facilitating mineralization.

• Osteocytes: Maintain bone tissue; former osteoblasts trapped in matrix.

• Osteoclasts: Break down bone matrix, releasing calcium into the blood.

Bone Formation and Growth

• Endochondral Ossification: Most bones form from hyaline cartilage templates, which are gradually replaced by bone.

• Intramembranous Ossification: Flat bones (e.g., skull) form directly from connective tissue membranes.

• Epiphyseal Plate: Growth plate of hyaline cartilage where bone lengthening occurs during childhood and adolescence.

• Epiphyseal Line: Remnant of the growth plate after ossification is complete.

Bone Remodeling and Homeostasis

• Calcium Homeostasis: Blood calcium levels are regulated by hormones:

  • Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclasts to resorb bone.

  • Calcitonin: Lowers blood calcium by promoting bone deposition by osteoblasts.

• Equation for Bone Remodeling:

$\text{Bone Mass} = \text{Bone Formation (Osteoblast Activity)} - \text{Bone Resorption (Osteoclast Activity)}$

Bone Disorders

• Osteoporosis: Decreased bone mass and density, increasing fracture risk; common in postmenopausal women due to decreased estrogen.

• Brittle Bone Disease (Osteogenesis Imperfecta): Genetic disorder causing defective collagen production and fragile bones.

Fracture Healing

• Step 1: Hematoma formation (blood clot at fracture site).

• Step 2: Formation of a soft callus by fibroblasts and chondrocytes.

• Step 3: Hard (bony) callus formation as osteoblasts produce new bone.

• Step 4: Bone remodeling restores original shape and structure.

Axial and Appendicular Skeleton

• Axial Skeleton: Skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Limbs and girdles (pectoral and pelvic).

Skull and Facial Bones

• Sinuses: Air-filled cavities in frontal, ethmoid, sphenoid, and maxillae bones; lighten the skull and add resonance to the voice.

• Olfaction: Olfactory receptors in the nasal cavity detect smell; signals travel via the cribriform plate of the ethmoid bone.

• Sphenoid Bone: Articulates with all other cranial bones; contains the sella turcica, which houses the pituitary gland.

• Nasal Septum: Formed by the perpendicular plate of the ethmoid and the vomer; deviation can cause breathing issues.

Vertebral Column

• Cervical Vertebrae: Support the head; atlas (C1) allows nodding "yes," axis (C2) allows rotation "no."

• Thoracic Vertebrae: Articulate with ribs.

• Intervertebral Discs: Composed of fibrocartilage (annulus fibrosus) and a gelatinous core (nucleus pulposus) for shock absorption.

Pectoral and Pelvic Girdles

• Pectoral Girdle: Clavicle and scapula; forms the shoulder joint (glenoid cavity and humerus). Highly mobile but less stable.

• Pelvic Girdle: Hip bones and sacrum; forms the hip joint (acetabulum and femur). More stable, less mobile.

• Sex Differences: Female pelvis is wider and more circular to facilitate childbirth; male pelvis is narrower.

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