Anatomy and Physiology: Integumentary System, Joints, and Bone Tissue

Comprehensive vocabulary flashcards reviewing the anatomical structures, histological features, physiological functions, and clinical pathologies of the integumentary system, skeletal joints, and bone tissue.

Keratinocytes

The most abundant epidermal cells, comprising approximately $90\%$ of all epidermal cells, that produce keratin to confer mechanical strength, water resistance, and barrier protection.

Melanocytes

Pigment-synthesizing cells located in the stratum basale that produce melanin, packaging it into melanosomes to deliver to adjacent keratinocytes.

Langerhans cells

Specialized dendritic immune cells located primarily within the stratum spinosum that detect foreign pathogens and function as macrophages.

Tactile (Merkel) Discs

Cutaneous sensory receptors in the stratum basale consisting of a Merkel cell connected to a sensory neuron, specialized for sensing light touch, texture, and shape.

Insensible perspiration

The routine, unnoticeable evaporative loss of approximately $500\,\text{mL}$ of sweat per day produced at rest.

Dermcidin

A naturally occurring antimicrobial peptide secreted in sweat that destroys bacteria and contributes to the chemical defense of the skin.

Calcitriol

The biologically active hormonal form of vitamin $D$, converted in the kidneys from calcidiol, that stimulates dietary calcium and phosphorus absorption in the small intestine.

Stratum basale

The deepest epidermal layer, consisting of a single row of cuboidal basal stem cells attached to the basement membrane that constantly divides to produce new keratinocytes.

Stratum spinosum

An epidermal layer consisting of $8\text{--}10$ rows of keratinocytes interconnected by desmosomes, giving cells a spiny appearance under histology.

Stratum granulosum

An epidermal stratum consisting of $3\text{--}5$ layers of flattened, dying keratinocytes actively accumulating keratohyalin granules and releasing glycolipids via lamellar granules.

Eleidin

A clear, translucent intermediate protein transformed from keratohyalin that fills the dead keratinocytes of the stratum lucidum.

Stratum lucidum

A thin, transparent layer of dead, flattened keratinocytes situated between the stratum granulosum and stratum corneum, found solely in the thick skin of palms and soles.

Stratum corneum

The outermost epidermal layer composed of $15\text{--}30$ layers of dead, anucleate, keratin-packed squamous cells that shed and renew completely every $4\text{--}6\,\text{weeks}$.

Papillary layer

The superficial region of the dermis composed of loose areolar connective tissue forming dermal papillae, capillary loops, and free nerve endings.

Reticular layer

The deeper, thicker dermal region composed of dense irregular connective tissue dense with collagen and elastic fibers that houses cutaneous appendages.

Hypodermis

The subcutaneous layer deep to the dermis composed of adipose and areolar connective tissues that provides thermal insulation, shock absorption, and energy storage.

Eumelanin

A subclass of melanin pigment that produces brown to black shades in skin and hair.

Pheomelanin

A subclass of melanin pigment that imparts red to yellow tones to skin and hair.

Carotene

A dietary plant-derived orange-yellow pigment that accumulates in the stratum corneum and subcutaneous fat, capable of being converted into vitamin $A$.

Cyanosis

A bluish discoloration of the skin and mucous membranes caused by low oxygen saturation in hemoglobin.

Acanthosis Nigricans

Hyperpigmented, velvety, dark brown-to-black cutaneous lesions in body folds such as the neck and axillae, commonly indicative of insulin resistance.

Striae

Silvery-white dermal scar lines, commonly termed stretch marks, produced by tearing of dermal collagen fibers under severe skin distension.

Anagen phase

The active growth phase of the hair cycle lasting $2\text{--}7\,\text{years}$, during which hair matrix cells divide rapidly and hair lengthens approximately $0.3\,\text{mm}$ per day.

Catagen phase

The intermediate transitional phase of the hair cycle lasting $2\text{--}3\,\text{weeks}$ characterized by cessation of growth and follicle regression.

Telogen phase

The resting phase of the hair cycle lasting $2\text{--}4\,\text{months}$, concluding when the hair is shed and replaced by a new anagen strand.

Eponychium

The narrow fold of stratum corneum at the proximal margin of the nail plate, commonly referred to as the cuticle.

Hyponychium

The thickened epidermal region beneath the distal free edge of the nail body that seals the nail bed against pathogens.

Sebaceous glands

Holocrine exocrine glands associated with hair follicles that release an oily mixture of lipids called sebum to lubricate and waterproof the skin.

Eccrine Sweat Gland

Abundant, coiled tubular sweat glands that open directly onto skin surface pores to secrete a watery, hypotonic fluid essential for thermoregulation.

Apocrine Sweat Glands

Specialized sweat glands concentrated in the axillary and anogenital regions that secrete a viscous, milky fluid into hair follicles that skin bacteria break down into body odor.

Basal cell carcinoma

The most common and least malignant skin cancer, arising from the uncontrolled proliferation of stratum basale cells that invade the dermis and hypodermis.

Squamous cell carcinoma

The second most common skin cancer, originating from keratinocytes of the stratum spinosum, presenting as a scaly, reddened papule capable of metastasis.

Melanoma

The most dangerous and malignant form of skin cancer, originating from melanocytes, characterized by high metastatic capacity and resistance to chemotherapy.

Rule of Nines

A clinical estimation method dividing adult body surface area into sections of $9\%$ (with the perineum at $1\%$) to gauge burn extent and compute fluid resuscitation needs.

Articulation

The structural junction where two or more bones meet, also termed a joint.

Synarthrosis

An immovable joint category defined by functional classification, such as a cranial suture or dental gomphosis.

Amphiarthrosis

A slightly movable functional joint classification, exemplified by intervertebral symphyses and the pubic symphysis.

Diarthrosis

A freely movable functional joint classification, representing all synovial joints.

Suture

A fibrous synarthrosis joint composed of dense fibrous connective tissue uniting adjacent flat bones of the skull.

Fontanels

Unossified, membranous fibrous regions in fetal and infant skulls that allow compression during birth and complete ossification by age $2$.

Syndesmosis

A fibrous joint in which opposing bones are united by an interosseous ligament or membrane, allowing a slight give or shifting movement.

Gomphosis

A specialized peg-in-socket fibrous joint securing a tooth within its alveolar socket via periodontal ligaments.

Synchondrosis

A rigid cartilaginous joint joined entirely by hyaline cartilage, exemplified by the temporary epiphyseal plate.

Symphysis

A cartilaginous amphiarthrosis joint where articulating surfaces are capped by hyaline cartilage and fused to an intervening fibrocartilage pad.

Synovial fluid

A viscous, egg-white-like fluid rich in hyaluronic acid that lubricates articular cartilage, absorbs shock, and distributes nutrients within a synovial joint.

Bursa

A flattened fibrous sac lined by a synovial membrane and filled with synovial fluid, situated to reduce friction where tendons, ligaments, or skin slide over bone.

Tendon sheath

An elongated, tubular bursa wrapped completely around a tendon subjected to repeated friction across a joint.

Bursitis

Inflammation of a bursa, typically provoked by traumatic injury or physical overuse, common at the knee and elbow.

Hinge joint

A uniaxial synovial joint in which a cylindrical bone fits into a trough-like surface, permitting flexion and extension along a single plane.

Pivot joint

A uniaxial synovial joint in which a rounded bone process rotates within an osteoligamentous ring, such as the proximal radioulnar joint.

Condyloid joint

A biaxial synovial joint featuring an oval convex condyle articulating with an elliptical cavity, allowing flexion, extension, abduction, and adduction.

Saddle joint

A biaxial synovial joint where complementary concave and convex surfaces articulate, found at the first carpometacarpal joint of the thumb.

Ball-and-socket joint

A multiaxial synovial joint featuring a spherical head fitted into a cup-shaped cavity, allowing movements across three axes of rotation.

Acetabular labrum

A circular lip of fibrocartilage that deepens the acetabular socket to enhance the stability of the hip joint.

Osteoarthritis

A chronic, non-inflammatory, degenerative joint disorder characterized by the progressive wear and breakdown of articular cartilage.

Rheumatoid arthritis

A chronic systemic autoimmune disease in which the immune system attacks synovial membranes, producing an erosive inflammatory pannus.

Gout

A painful metabolic arthritic disorder caused by hyperuricemia and the deposition of needle-like monosodium urate crystals in joint tissues.

Nursemaid’s elbow

A subluxation of the radial head past the annular ligament occurring in young children following sudden pulling traction on an extended arm.

Lyme disease

An infectious disease caused by the spirochete Borrelia burgdorferi transmitted via blacklegged tick bites, often presenting with an erythema migrans rash and joint pain.

Red bone marrow

Vascularized connective tissue within spongy bone cavities containing hematopoietic stem cells that generate red blood cells, platelets, and leukocytes.

Yellow bone marrow

Medullary bone tissue composed primarily of adipocytes and blood vessels, functioning as a lipid energy reserve.

Osteon

The structural and functional repeating unit of compact bone, composed of concentric lamellae arranged around a central neurovascular canal.

Central canal

The longitudinal conduit at the center of an osteon containing blood vessels, lymphatic vessels, and nerve fibers.

Perforating canals

Transverse or oblique channels in compact bone that connect the periosteal blood and nerve supply to the central canals and medullary cavity.

Canaliculi

Microscopic hair-like canals radiating between lacunae that allow osteocyte cytoplasmic extensions to communicate and exchange nutrients.

Trabeculae

A network of interconnected struts and plates of bone tissue lacking true osteons that constitutes spongy bone.

Osteogenic cells

Mitotically active, unspecialized stem cells situated in the periosteum and endosteum that differentiate into osteoblasts.

Osteoblasts

Bone-forming cells that synthesize and secrete unmineralized bone matrix (osteoid) and become entombed as osteocytes.

Osteoid

The unmineralized organic component of bone matrix secreted by osteoblasts, composed of $90\%$ collagen fibers and calcium-binding proteins.

Osteocytes

Mature, non-dividing bone cells residing within lacunae that maintain the bone matrix and act as mechanical stress sensors.

Bone-lining cells

Flattened cells situated on periosteal and endosteal bone surfaces that help maintain matrix integrity and regulate calcium exchange.

Osteoclasts

Giant, multinucleated bone-resorbing cells derived from macrophage precursors that enzymatically degrade bone matrix.

Resorption bays

Enzymatically excavated depressions or grooves in the bone matrix, also known as Howship lacunae, occupied by active osteoclasts.

Ruffled border

The deeply folded apical membrane of an active osteoclast that expands surface area for hydrochloric acid and protease secretion.

Hydroxyapatite

Inorganic mineral salts, predominantly calcium phosphate crystals, comprising $65\%$ of dry bone mass and imparting exceptional hardness.

Sacrificial bonds

Reversibly breakable chemical bonds within and between collagen molecules that dissipate applied mechanical energy to prevent bone fractures.

Calcitonin

A peptide hormone produced by the thyroid gland in response to high plasma calcium levels that inhibits osteoclast activity and stimulates bone mineral deposition.

Parathyroid hormone (PTH)

A hormone released by the parathyroid glands during hypocalcemia that stimulates osteoclast resorption and renal/intestinal calcium retention.

Endochondral ossification

The embryonic bone development pathway in which a pre-existing hyaline cartilage model is broken down and replaced by bone tissue.

Intramembranous ossification

The embryonic process whereby bone forms directly from fibrous mesenchymal connective tissue without a prior cartilaginous model.

Appositional growth

The process of bone remodeling that increases bone diameter via osteoblast matrix secretion beneath the periosteum coordinated with endosteal osteoclast resorption.

Wolff's law

The physiological law stating that bones remodel and adapt structurally to resist the specific mechanical loads and compressive stresses placed upon them.

Greenstick fracture

An incomplete pediatric bone break where one side of the bone shaft bends while the opposite cortex cracks, resulting from pliable, softer bone.

Comminuted fracture

A high-impact bone fracture where the bone shatters or fragments into three or more pieces.

Rickets

A pediatric bone disorder resulting from vitamin $D$ or dietary calcium deficiency, causing unmineralized osteoid buildup, epiphyseal enlargement, and bowed legs.

Osteomalacia

An adult skeletal disorder characterized by inadequate mineralization of osteoid matrix, producing soft, weak bones and pain upon bearing weight.

Osteoporosis

A systemic metabolic bone disease where osteoclastic resorption outpaces osteoblastic deposition, leading to diminished bone mass, fragility, and kyphosis.