Anatomy and Physiology of the Skin and Nail
From cell to system
Cells → tissues → organs → systems. The skin has three layers: epidermis (stratum corneum, granulosum, spinosum, basale), dermis (nerves, vessels, glands, follicles), and subcutaneous tissue (fat). The nail is a specialized epidermal structure; the plate is compacted keratinocytes produced by the matrix.
Functions to memorize
Skin: protection, sensation, heat regulation, excretion, secretion, absorption. Nails: protect the fingertip, assist grasping and fine manipulation, and provide sensation. The acid mantle (about pH 4.5–5.5) helps suppress bacteria, which is why harsh soaps and over-soaking matter.
Structures you work around
Sebaceous glands (oil), sudoriferous glands (eccrine sweat; apocrine in axillae), hair follicles, and arrector pili muscles. Hand and arm bones: carpals, metacarpals, phalanges (three per finger, two in the thumb). Muscles attach by tendons; the origin is the fixed attachment, the insertion is the movable one. Flexors bend, extensors straighten.
Directional and movement terms
Superior/inferior, anterior/posterior, medial/lateral, proximal/distal. Abduction moves away from the midline, adduction toward it; pronation turns the palm down, supination turns it up.
Trap watch: the nail plate is produced by the matrix, not the bed; the cuticle is the eponychium, not the lunula; the hyponychium is the seal under the free edge.
Rule of thumb: proximal is toward the body, distal is toward the fingertip - once that pair is automatic, most nail and hand terms decode themselves.