Anatomy & Physiology Study Guide: Skin, Cartilage, and Bone

Skin (Integumentary System)

Functions of the Skin

The skin 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 and blood flow.

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

• Excretion: Removes waste products via sweat.

• Synthesis: Produces vitamin D when exposed to sunlight.

Layers of the Skin

The skin consists of two main layers: the epidermis and the dermis, with a subcutaneous layer beneath.

• Epidermis: Outermost layer, composed of stratified squamous epithelium.

• Dermis: Middle layer, contains connective tissue, blood vessels, nerves, and appendages.

• Hypodermis (Subcutaneous layer): Deepest layer, mainly adipose tissue for insulation and cushioning.

Layers of the Epidermis (from superficial to deep)

• Stratum corneum: Dead, keratinized cells providing protection.

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

• Stratum granulosum: Cells begin to die and accumulate keratin.

• Stratum spinosum: Provides strength and flexibility.

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

Areas and Functions of the Dermis

The dermis is divided into two regions:

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

• Reticular layer: Deeper, dense irregular connective tissue, provides strength and elasticity.

Types of Cells in the Skin

• Keratinoctyes: Produce keratin, main cell type in epidermis.

• Melanocytes: Produce melanin, responsible for skin color.

• Langerhans cells: Immune defense.

• Merkel cells: Sensory receptors for touch.

Receptors in the Skin

• Meissner's corpuscles: Light touch.

• Pacinian corpuscles: Deep pressure and vibration.

• Free nerve endings: Pain and temperature.

• Merkel discs: Sustained touch.

Skin Color and Disease

Changes in skin color can indicate 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

• Glands: Sweat (eccrine/apocrine) and sebaceous glands.

• Hair: Provides protection and sensory input.

• Nails: Protects fingertips and aids in manipulation.

Types of Skin Cancer

• 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, destroys both layers.

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

Cartilage and Bone (Skeletal System)

Types of Cartilage and Locations

• Hyaline cartilage: Most common; found in nose, trachea, articular surfaces.

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

• Fibrocartilage: Strong; found in intervertebral discs, pubic symphysis.

Classification of Bones

• 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).

• 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.

Structure of Long Bone vs. Flat Bone

• Long bone: Diaphysis (shaft), epiphyses (ends), medullary cavity, periosteum.

• Flat bone: Thin layers of compact bone enclosing 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/waste exchange.

Chemical Composition of Bone

• Organic: Collagen fibers, cells (osteoblasts, osteocytes, osteoclasts).

• Inorganic: Hydroxyapatite (calcium phosphate crystals).

Bone Development and Remodeling

• Ossification: Formation of bone tissue (intramembranous and endochondral).

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

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

Parathyroid hormone: Regulates blood calcium by stimulating bone resorption.

Hematopoietic Tissue in Bone

• Red marrow: Site of blood cell formation, found in spongy bone of flat bones and epiphyses of long bones.

• Yellow marrow: Fat storage, found in medullary cavity of long bones.

Homeostatic Imbalances of Bone

• Osteoporosis: Decreased bone density, 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

• Osteoblasts: Build new bone matrix.

• Osteocytes: Mature bone cells, maintain bone tissue.

• Osteoclasts: Break down bone matrix.

• Osteogenic cells: Stem cells that differentiate into osteoblasts.

Axial vs. Appendicular Skeleton

• Axial skeleton: Skull, vertebral column, rib cage.

• Appendicular skeleton: Limbs, pelvic and pectoral girdles.

Bones of the Pelvis

• Ilium

• Ischium

• Pubis

Table: Types of Cartilage and Locations

Type	Main Locations	Properties
Hyaline	Nose, trachea, articular surfaces	Flexible, smooth
Elastic	Ear, epiglottis	Flexible, resilient
Fibrocartilage	Intervertebral discs, pubic symphysis	Strong, shock-absorbing

Table: Bone Cells and Functions

Cell Type	Function
Osteoblast	Builds bone matrix
Osteocyte	Maintains bone tissue
Osteoclast	Resorbs bone matrix
Osteogenic cell	Bone stem cell

Key Equations

• Hydroxyapatite formula:

$Ca_{10}(PO_4)_6(OH)_2$

• Wolff's Law (conceptual):

$\text{Bone adapts to the loads under which it is placed}$

Additional info: Some content was inferred and expanded for completeness and clarity.