Integumentary System, Connective Tissues, and Anatomical Fundamentals

Cutaneous Membrane

The skin that covers the outer surface of the body, composed of an outer superficial epithelium (epidermis) and an inner connective tissue layer (dermis).

Epidermis

The superficial stratified squamous epithelium layer of the cutaneous membrane where nutrients and oxygen diffuse from dermal capillaries.

Dermis

The inner connective tissue layer of the cutaneous membrane located between the epidermis and the hypodermis.

Hypodermis

Also known as the subcutaneous layer or superficial fascia, a loose connective tissue layer primarily composed of adipose tissue deep to the dermis.

Keratinocytes

The most abundant cells in the epidermis, containing large amounts of the protective protein keratin.

Merkel cells

Specialized epidermal cells found in hairless skin that respond to touch and trigger the nervous system.

Melanocytes

Pigment-producing cells scattered throughout the stratum basale that synthesize melanin and store it in melanosomes.

Langerhans cells

Dendritic tissue macrophages in the stratum spinosum that are active in the immune response.

Stratum Basale

The deepest layer of the epidermis attached to the basement membrane by hemidesmosomes, containing germinative cells and forming epidermal ridges.

Stratum Spinosum

The spiny layer of the epidermis, consisting of $8$ to $10$ layers of keratinocytes bound by desmosomes and containing Langerhans cells.

Stratum Granulosum

The grainy layer of the epidermis where cells stop dividing, produce keratohyalin and lamellate granules, dehydrate, and die.

Stratum Lucidum

The clear layer of the epidermis found exclusively in thick skin, covering the stratum granulosum.

Stratum Corneum

The exposed horn layer of the epidermis, consisting of $15$ to $30$ layers of dead, water-resistant keratinized cells shed every $2$ weeks.

Carotene

An orange-yellow pigment found in orange vegetables that accumulates in epidermal cells and dermal fatty tissues.

Melanin

A yellow-brown or black pigment synthesized by melanocytes in the stratum basale and transferred to keratinocytes.

Jaundice

A yellowing of the skin caused by an abnormal buildup of bilirubin.

Vitiligo

A condition characterized by a loss of melanocytes, resulting in localized loss of skin color.

Papillary Layer

The outer layer of the dermis composed of areolar tissue, containing small capillaries, lymphatics, sensory neurons, and dermal papillae.

Reticular Layer

The deep layer of the dermis composed of dense irregular connective tissue containing larger blood vessels, lymphatic vessels, nerve fibers, and collagen/elastic fibers.

Cleavage Lines

Parallel bundles of collagen and elastic fibers in the dermis that establish patterns to resist force in specific directions.

Arrector Pili

Involuntary smooth muscle attached to a hair follicle that contracts to cause the hair to stand up and produce goose bumps.

Sebaceous Glands

Simple branched alveolar holocrine oil glands that secrete sebum to lubricate hair shafts and inhibit bacterial growth.

Sebum

A lipid-rich secretion produced by sebaceous glands that lubricates and protects the epidermis while inhibiting bacteria.

Apocrine Sweat Glands

Coiled sweat glands located in armpits, nipples, and groin that release cloudy secretions into hair follicles that break down and produce odor.

Merocrine Sweat Glands

Widely distributed coiled tubular sweat glands that discharge sensible perspiration directly onto the skin surface to cool the skin and excrete water/electrolytes.

Nail Body

The visible portion of the nail that covers the underlying nail bed.

Lunula

The pale crescent-shaped area located at the base of the nail body.

Hyponychium

The area of skin located beneath the distal free edge of the nail.

Eponychium

Also known as the cuticle, the narrow fold of stratum corneum at the tip of the proximal nail fold where the visible nail emerges.

Rule of Nines

A standardized clinical method used for estimating the percentage of total body surface area affected by burns.

Extracellular Matrix

The non-cellular material of connective tissue consisting of extracellular fibers (collagen, reticular, elastic) and ground substance.

Reticular Tissue

A type of loose connective tissue containing reticular fibers that provides a supportive framework for organs such as the liver, kidney, spleen, lymph nodes, and bone marrow.

Adipose Tissue

A type of loose connective tissue dominated by adipocytes that provides padding, cushions shocks, insulates heat, and stores energy.

Dense Regular Connective Tissue

Connective tissue packed with parallel collagen fibers and fibroblasts, found in tendons, aponeuroses, and ligaments to provide firm attachment.

Dense Irregular Connective Tissue

Connective tissue composed of interwoven collagen fiber bundles that provides strength against forces applied from many directions, found in the dermis and organ capsules.

Elastic Tissue

Dense connective tissue dominated by elastic fibers that permits expansion/contraction and cushions shocks, located between spinal vertebrae and in blood vessel walls.

Hyaline Cartilage

The most common cartilage type, providing stiff but flexible support and reducing friction at synovial joints, rib tips, larynx, and trachea.

Elastic Cartilage

Cartilage containing abundant elastic fibers that tolerates distortion without damage and returns to its original shape, found in the external ear auricle and epiglottis.

Fibrocartilage

Durable cartilage with a dense collagenous matrix that resists compression and limits movement, located in intervertebral discs, pubic symphysis, and knee joint pads.

Osteon

The functional structural unit of compact bone tissue consisting of osteocytes in lacunae arranged around a central blood vessel canal.

Mucous Membranes

Epithelial membranes lining body passageways that connect to the exterior (digestive, respiratory, urinary, reproductive tracts) supported by an areolar lamina propria.

Serous Membranes

Thin, double-layered membranes lining internal ventral body cavities that produce transudate fluid to reduce friction (pleura, peritoneum, pericardium).

Synovial Membranes

Membranes lining articulating joint cavities that lack a true epithelium and produce lubricating synovial fluid.

Anatomy

The study of internal and external body structures and the physical relationships among body parts.

Anatomical Position

The standard reference position for human anatomy: standing erect, feet together, hands at sides, and palms facing forward.

Supine

The anatomical posture of lying down face up.

Prone

The anatomical posture of lying down face down.

Sagittal Plane

A vertical plane that divides the body or an organ into right and left portions.

Frontal Plane

A vertical plane that divides the body into anterior (front) and posterior (back) portions.

Transverse Plane

A horizontal plane that divides the body into superior (upper) and inferior (lower) portions.

Mitochondria

Double-membraned organelles with inner folds called cristae that generate $$950000000000000000000000000000000000