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Hyponychium: Acts as a barrier to prevent dirt and debris from getting underneath the nail plate.
Free Edge: The visible part of the nail that extends beyond the fingertip.
Nail Body: Main part of the nail that is hardened and visible.
Lunula: The crescent-shaped area at the base of the nail.
Eponychium: Also known as the cuticle, protects the nail base.

Nail Root: Part of the nail where cells undergo mitosis to grow the nail.
Growth occurs from the nail root towards the free edge.
Nails are composed of keratinized epithelial cells, making them harder than hair due to higher keratin content.

Two types of sweat glands:
- Apocrine Glands: Function begins around puberty; associated with hair, such as in the armpits. Produce pheromones that may influence social interactions.
- Eccrine Glands: More common and distributed throughout the body, responsible for temperature regulation by evaporating sweat.

Thin Skin: Contains hair; covers most body regions except palms and soles of feet.
Functions: Temperature regulation, protection, vitamin D synthesis, sensation.

Rule of Nines: Method to assess the percentage of body surface burned.
First Degree Burns: Affect only the epidermis, painful but do not blister.
Second Degree Burns: Affect epidermis and part of dermis, cause blistering and are painful.
Third Degree Burns: Affect all layers (epidermis, dermis, and fat), typically do not hurt due to nerve damage; may require skin grafting.
Fourth Degree Burns: Extend into muscle and bone, often necessitating amputation.

Damage to collagen and elastin fibers leads to potential scarring and contractures as skin heals.

Basal Cell Carcinoma: Most common and slow-growing; appears as a pimple-like lesion that does not heal.
Squamous Cell Carcinoma: Malignant, grows faster than basal cell; often shows scabs and is commonly found in sun-exposed areas.
Melanoma: Dangerous form of skin cancer; can occur at any age and may spread rapidly. Characteristics include asymmetrical moles with uneven borders and varied coloration.

Skin loses elasticity and thickness, leading to wrinkles and susceptibility to injury.
Decreased oil and sweat production results in dryness and cracking of skin.
Loss of melanocytes leads to graying hair and hyperpigmented spots.
Subcutaneous fat diminishes, leading to sagging skin and altered facial contour.

Protection: Bones shield internal organs; e.g., cranium protects the brain, ribs protect thoracic organs.
Calcium Storage: Bones store calcium and release it as needed for bodily functions.
Bone Structure:
- Diaphysis: Shaft of long bones.
- Epiphysis: Ends of long bones; varies in shape according to joint function.
- Metaphysis: Area between the diaphysis and epiphysis; growth plate during development.

Hyaline Cartilage: Covers ends of bones for shock absorption and friction reduction in joints.
Periosteum: Dense irregular connective tissue covering the bone, contains bone-forming cells.

Osteoblasts: Bone-forming cells that create the mineralized matrix of bone.
Osteocytes: Mature bone cells trapped within the matrix.
Osteoclasts: Cells that break down bone tissue.
Calcification Process: Bone formation through osteoblast activity; important for achieving bone hardness.

Compact Bone: Dense and strong; forms the outer layer of bones.
Spongy Bone: Lighter and less dense; located inside bones, helps with weight reduction.
Bone Marrow: Located in the medullary cavity; involved in blood cell formation.

Bone healing involves complex processes that include remodeling after fractures, influenced by various factors including nutrition and blood supply.
Types of Fractures: Discussed later in detail.