Integumentary and Skeletal Systems: Study Guide for Anatomy & Physiology

Integumentary System

Functions of the Skin

The skin, also known as the integument, is the largest organ of the body and serves multiple vital functions:

• Protection: Acts as a barrier against mechanical injury, pathogens, and harmful substances.

• Regulation: Maintains body temperature through sweat production and blood flow regulation.

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

• Excretion: Removes waste products through sweat.

• Synthesis: Produces vitamin D when exposed to sunlight.

Layers of the Skin

The skin is composed of two main layers: the epidermis and the dermis. Below these lies the hypodermis (subcutaneous tissue).

• Epidermis: The outermost layer, made of stratified squamous epithelium. It contains several sublayers:

  • Stratum corneum: Outermost, dead keratinized cells.

  • Stratum lucidum: Present only in thick skin (palms, soles).

  • Stratum granulosum: Cells begin to die and keratinize.

  • Stratum spinosum: Provides strength and flexibility.

  • Stratum basale: Deepest layer, site of cell division.

• Dermis: Thicker, connective tissue layer beneath the epidermis. Contains two regions:

  • Papillary layer: Superficial, contains dermal papillae and capillaries.

  • Reticular layer: Deep, dense irregular connective tissue with collagen and elastin fibers.

• Hypodermis: Not technically part of the skin; consists of adipose tissue for insulation and energy storage.

Cells of the Skin

Different cell types are found in the various layers of the skin, each with specialized functions:

• Keratinoctyes: Main cells of the epidermis, produce keratin for protection.

• Melanocytes: Produce melanin pigment, protect against UV radiation.

• Langerhans cells: Immune cells, help defend against pathogens.

• Merkel cells: Sensory cells for touch.

Receptors in the Skin

The skin contains various sensory receptors:

• Meissner's corpuscles: Detect light touch.

• Pacinian corpuscles: Detect deep pressure and vibration.

• Free nerve endings: Sense pain and temperature.

• Merkel discs: Detect sustained touch and pressure.

Skin Color and Disease

Skin color is determined by melanin, hemoglobin, and carotene. Changes in skin color can signal disease:

• Pallor: May indicate anemia.

• Jaundice: Yellowing due to liver dysfunction.

• Cyanosis: Bluish tint from lack of oxygen.

• Erythema: Redness from inflammation or fever.

Appendages of the Skin

Skin appendages include glands, hair, and nails:

• Sudoriferous (sweat) glands: Eccrine (thermoregulation) and apocrine (odor).

• Sebaceous (oil) glands: Secrete sebum for lubrication.

• Hair: Provides protection and sensory input.

• Nails: Protect fingertips and aid in manipulation.

Types of Skin Cancer

Skin cancer types include:

• Basal cell carcinoma: Most common, least dangerous.

• Squamous cell carcinoma: Can metastasize.

• Melanoma: Most concerning, aggressive and likely to spread.

Burns and the Rule of Nines

Burns are classified by depth and extent. The Rule of Nines estimates the percentage of body surface area affected:

• First-degree: Epidermis only.

• Second-degree: Epidermis and part of dermis.

• Third-degree: Full thickness, all skin layers.

Rule of Nines: Divides the body into regions, each representing 9% (or multiples) of total body surface area.

Skeletal System

Types of Cartilage and Locations

Cartilage is a flexible connective tissue found in various locations:

• Hyaline cartilage: Most common; found in nose, trachea, ends of long bones.

• Elastic cartilage: Flexible; found in ear and epiglottis.

• Fibrocartilage: Tough; found in intervertebral discs and menisci.

Classification of Bones

Bones are classified by shape:

• Long bones: Longer than wide (e.g., femur, humerus).

• Short bones: Cube-shaped (e.g., carpals, tarsals).

• Flat bones: Thin, flat (e.g., skull, sternum).

• Irregular bones: Complex shapes (e.g., vertebrae, pelvis).

• Sesamoid bones: Embedded in tendons (e.g., patella).

Functions of Bones

• Support: Framework for the body.

• Protection: Shields vital organs.

• Movement: Acts as levers for muscles.

• Mineral storage: Stores calcium and phosphorus.

• Blood cell formation: Hematopoiesis in marrow.

• Triglyceride storage: In yellow marrow.

Structure of Long and Flat Bones

• Long bones: Consist of diaphysis (shaft), epiphyses (ends), metaphysis, medullary cavity, and periosteum.

• Flat bones: Thin layers of compact bone surrounding spongy bone (diploë).

Microscopic Anatomy of Bone

• Osteon (Haversian system): Structural unit of compact bone.

• Lamellae: Concentric rings of bone matrix.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny channels for nutrient exchange.

Chemical Composition of Bone

• Organic components: Cells (osteocytes, osteoblasts, osteoclasts), collagen fibers.

• Inorganic components: Hydroxyapatite (calcium phosphate crystals).

Bone Development and Remodeling

• Ossification: Process of bone formation (intramembranous and endochondral).

• Remodeling: Continuous renewal by osteoblasts (build bone) and osteoclasts (break down bone).

Hematopoietic Tissue

Red bone marrow is the site of hematopoiesis, the production of blood cells.

Wolff's Law and Parathyroid Hormone

• Wolff's Law: Bone grows and remodels in response to mechanical stress.

• Parathyroid hormone (PTH): Regulates calcium levels by stimulating bone resorption.

Homeostatic Imbalances

• Osteoporosis: Reduced bone mass, increased fracture risk.

• Osteomalacia/Rickets: Softening of bones due to vitamin D deficiency.

• Paget's disease: Abnormal bone remodeling.

Bone Cells: Osteocytes, Osteoblasts, Osteoclasts, Osteogenic Cells

Cell Type	Function
Osteogenic cells	Stem cells that differentiate into osteoblasts
Osteoblasts	Build new bone matrix
Osteocytes	Maintain bone tissue
Osteoclasts	Break down bone matrix

Axial and Appendicular Skeleton

Axial Skeleton

• Includes skull, vertebral column, and rib cage.

• Protects brain, spinal cord, and thoracic organs.

Appendicular Skeleton

• Includes limbs and girdles (pectoral and pelvic).

• Enables movement and interaction with environment.

Bones of the Pelvis

• Pelvic bones include ilium, ischium, and pubis.

• Support body weight and protect pelvic organs.

Key Equations

• Wolff's Law:

$\text{Bone strength} \propto \text{Mechanical stress applied}$

• Calcium Homeostasis (simplified):

$\text{PTH} \uparrow \Rightarrow \text{Bone resorption} \uparrow \Rightarrow \text{Blood Ca}^{2+} \uparrow$

Additional info: Some content was inferred and expanded for completeness and clarity, such as the details of bone cell functions, the Rule of Nines, and the classification of bones.