Comp vert anatomy Intergument

Integumentary System

The external covering of the body (skin, hair, glands, scales) and the largest organ by weight and surface area.

Mechanical Protection

Function of skin that acts as a physical barrier against abrasion, cuts, and blunt trauma using thick tissue, calluses, or heavy hide.

Infection Barrier

Function where intact skin prevents pathogens (bacteria, viruses, parasites) from entering the body.

Fluid Regulation

Function preventing excessive water loss (desiccation) or unwanted water uptake (swelling in freshwater or shriveling in saltwater).

UV Protection

Skin function and adaptations (e.g., pigments, secretions, melanin) that shield internal tissues from harmful ultraviolet radiation.

Sensory Reception

Function mediated by high concentrations of nerve endings in regions like fingertips, lips, and genitals to detect touch, pressure, and pain.

Excretion

The elimination of excess water, salts/ions, and metabolic waste (urea) via sweat.

Cutaneous Respiration

Gas exchange occurring directly through the skin surface, accounting for ~1% of oxygen uptake in humans and 100% in lungless/gill-less organisms.

Chromatophores

Specialized pigment-containing cells in the skin that give color and allow physiological color changes.

Glandular Secretions

Substances produced by skin glands, including sebum (oils for hair/skin suppleness), mucus, sweat, and protective chemical coatings.

Hippo Skin Secretion

A reddish glandular fluid produced by hippos that acts as a natural sunblock and antimicrobial agent (often mistakenly called "sweat blood").

Parrotfish Mucous Cocoon

A nocturnal mucous envelope secreted by skin glands to mask scent from predators (like sharks) and block parasites.

Pheromones

Chemical communicators secreted externally via skin or bodily fluids to signal territory, reproductive readiness, or food locations.

Thermoregulation

The control of internal body temperature through skin-mediated mechanisms like sweating, radiant heat loss, and blood flow modulation.

Vitamin D Synthesis

The production of vitamin D precursors triggered by UV light exposure on the skin, essential for bone density and strength.

Adipose / Fat Storage

Subcutaneous fat deposits used for high-density energy storage, structural insulation, and hydrodynamic streamlining (blubber).

Amphioxus Integument

A cephalochordate integument consisting of a single layer of columnar epithelial cells covered by a non-cellular, protective cuticle.

Epidermis

The outermost layer of vertebrate skin, derived embryologically from ectoderm.

Glycolipids

Lipid-carbohydrate molecules that act as cellular "glue" to hold epidermal cells tightly together.

Dermis

The thick, fibrous layer beneath the epidermis, derived from mesoderm (with neural crest contributions) and rich in collagen and elastic fibers.

Fish Epidermis

An outer skin layer composed entirely of living cells, containing unicellular mucus glands and covering even bony or placoid scales.

Mucus Glands (Fish)

Unicellular or multicellular epidermal glands that produce a protective, lubricating slime layer.

Stratum Germinativum

The basal, proliferating layer of the epidermis that continuously divides to replace shed superficial cells.

Keratin

A tough, fibrous, structural protein found in the outer dead cell layers of terrestrial vertebrate skin, hair, and nails.

Amphibian Epidermis Transition

The evolutionary shift where the outermost epidermal cells become non-living, keratinized cells to prevent desiccation on land.

Basement Membrane

The acellular boundary layer between epidermis and dermis consisting of the basal lamina (produced by the epidermis) and the reticular lamina (produced by the dermis).

Hypodermis (Superficial Fascia)

The transitional subcutaneous region beneath the dermis composed of loose connective and adipose tissues that overlies deep body musculature.

Periderm

The temporary, single outer layer of embryonic epidermal cells replenished by mitotic division of the underlying stratum basale.

Dermatome

The lateral division of embryonic somites (epimeres) that spreads beneath the ectoderm to form the connective tissue component of the dermis.

Stratum Compactum

A dense, orderly layer of collagen fiber plies arranged in alternating orientations within the dermis of fishes and aquatic vertebrates.

Skin Bias

The biomechanical arrangement where collagen fibers are oriented at 45-degree angles to the body axis, allowing lateral swimming bending while resisting wrinkles and surface drag.

Alpha-Keratin

A flexible, soft structural protein found in the skin of synapsids and in extensible epidermal regions of sauropsids.

Beta-Keratin

A hard, rigid structural protein found exclusively in sauropsids that forms hard scales, claws, beaks, and feathers.

Mucous Cuticle

A protective surface coat secreted by fish epidermal and unicellular glands that ensures laminar water flow, provides slipperiness, and resists infection.

Club Cell

An elongate, often binucleate unicellular epidermal gland in fishes that contributes to the mucous cuticle and releases fear- or alarm-inducing chemicals.

Granular Cell

A unicellular epidermal gland found in lampreys and other fishes that secretes components into the surface mucous cuticle.

Goblet Cell

A cup-shaped unicellular gland found in cartilaginous and bony fishes (absent in lampreys) that secretes mucus directly onto the skin.

Sacciform Cell

A specialized unicellular epidermal gland containing a large, membrane-bound secretory product that functions as a chemical repellent or toxin.

Thread Cell

A specialized epidermal cell in hagfishes that discharges thick, coiled cords of mucus when the animal is irritated.

Dermal Armor

Large bony plates formed via intramembranous ossification within the dermis, characteristic of ostracoderms and placoderms.

Placoid Scale

A shark scale (denticle) that develops in the dermis and projects through the epidermis, consisting of a pulp cavity, dentin, and an enamel cap.

Scale Riblets

Microscopic, aligned surface ridges on shark placoid scales that reduce turbulent skin friction drag during swimming.

Cosmoid Scale

A primitive sarcopterygian scale composed of a double basal layer of bone (vascular and lamellar), a thick middle layer of dentin (cosmine), and a thin outer coat of enamel.

Ganoid Scale

A shiny, interlocking scale (found in gars and polypteriforms) composed of a basal bony foundation topped directly by a thick enamel layer (ganoin) without dentin.

Teleost Scale

A thin, flexible scale (cycloid or ctenoid) lacking enamel, dentin, and vascular bone, composed exclusively of noncalcified, acellular lamellar bone.

Circuli

Concentric growth rings laid down on teleost scales that can be used to determine the annual age of a fish.

Leydig Cells

Large unicellular epidermal glands present in larval salamanders (absent in adults) that secrete antiviral and antibacterial compounds.

Nuptial Pads

Raised calluses of cornified epidermis that develop seasonally on the limbs or digits of male amphibians to assist in gripping the female during mating.

Poison (Granular) Glands

Large, multicellular dermal glands in amphibians that store distasteful or toxic chemical defenses.

Epidermal Scale

A prominent fold of the surface epidermis containing a thickened, keratinized outer layer, characteristic of reptiles and distinct from bony dermal scales.

Hinge (Scale)

The thin, flexible region of epidermis situated between adjacent epidermal scales in reptiles.

Osteoderm

A bony plate formed directly within the dermis that provides structural support beneath epidermal scales in crocodilians, certain lizards, and turtles.

Ecdysis (Molting)

The periodic shedding of extensive outer cornified skin sheets in squamates, mediated by white blood cell infiltration into the stratum intermedium.

Femoral Glands

A row of specialized integumental glands found along the ventral thigh of many lizards used for social or reproductive signaling.

Brood Patch

A featherless, heavily vascularized dermal region on the breast of brooding birds that facilitates heat transfer to incubating eggs.

Uropygial Gland

A prominent lipid-secreting gland at the base of a bird's tail used during preening to condition keratin and waterproof feathers.

Salt Gland

A specialized cephalic gland found in marine birds and reptiles that excretes excess metabolic salt.

Pterylae

Distinct, patterned tracts on the avian body surface from which feathers originate.

Feather Rachis

The stiff, central tubular shaft of a pennaceous feather that supports the lateral vanes.

Feather Barbules

Microscopic, hooked processes that extend from feather barbs and interlock with neighboring barbules to maintain vane integrity.

Calamus (Quill)

The hollow, barbless proximal base of a feather shaft anchored inside the dermal feather follicle.

Remiges and Rectrices

Specialized asymmetric flight feathers found on the wings (remiges) and the tail (rectrices).

Pulp Caps

Sequential protective caps derived from the stratum cylindricum that protect the delicate dermal core of a developing feather.

Patterning Zone

The signaling region at the base of the feather follicle that dictates cell fates, barbs, barbules, and the spacing slits between feather parts.

Langerhans Cells

Stellate, dendritic epidermal cells residing in the stratum spinosum that function in cell-mediated immune responses.

Merkel Cells

Tactile mechanoreceptors of neural crest origin located in the stratum basale associated with sensory nerve fibers.

Hair Cuticle, Cortex, and Medulla

The structural layers of a hair shaft, progressing from the outer scaly cuticle through the intermediate pigmented cortex to the central core medulla.

Hair Follicle Cycle

The cyclic mammalian hair growth pattern consisting of three phases: active proliferation (growth), cell death (degeneration), and dormancy (rest).

Arrector Pili Muscle

A dermal band of smooth muscle attached to a hair follicle that pulls the hair erect during cold, fear, or sympathetic activation.

Guard Hairs and Underfur

The two main layers of mammalian pelage, where coarse outer guard hairs protect against wear while dense inner underfur provides thermal insulation.

Vibrissae

Specialized sensory tactile hairs ("whiskers") innervated by complex nerve networks at the base of the follicle.

Sebaceous Glands

Globular, exocrine glands that secrete an oily substance (sebum) into hair follicles to waterproof and lubricate skin and hair.

Eccrine Glands

Coiled, duct-bearing sweat glands innervated by cholinergic nerves that produce watery fluids for friction enhancement and evaporative cooling.

Apocrine Glands

Coiled epidermal glands associated with hair follicles, innervated by adrenergic nerves, that secrete viscous, lipid-rich fluids primarily for chemical communication.

Alveoli (Mammary)

Microscopic, bulb-like secretory clusters within mammary lobules where milk synthesis occurs.

Teat and Cistern

A mammalian nipple specialization featuring an expanded internal holding chamber (cistern) connected to a tubular secondary duct.

Oxytocin (Lactation)

The neurohypophysial hormone released during suckling that stimulates the contraction of myoepithelial cells to trigger milk letdown.

Unguis and Subunguis

The hard, dense outer dorsal plate of a claw, nail, or hoof (unguis) and the softer ventral keratinized supporting layer beneath it (subunguis).

Horse Hoof Wall

A U-shaped cornified structure consisting of three layers: outer stratum externa, thick stratum medium, and heavily folded stratum internum.

Frog (Equine)

A wedge-shaped, shock-absorbing keratinized pad of integument that fills the opening at the heel of a horse hoof.

True Horn

A permanent, unbranched cranial projection found in Bovidae consisting of a vascular bony skull core encased in a non-deciduous keratin sheath.

Antler

A deciduous, branched cranial structure found in Cervidae made entirely of bone, initially nourished by vascular skin ("velvet") that is later shed.

Pronghorn Horn

A specialized horn featuring an unbranched permanent bony core topped by a branched, deciduous keratin sheath that is shed annually.

Giraffe Horns (Ossicones)

Permanent, unbranched bony knobs on the skull derived from separate cartilaginous centers that remain covered in noncornified, living skin.

Rhinoceros Horn

A solid cranial weapon formed entirely from compacted, agglutinated keratin fibers without any inner bony core.

Baleen Plates

Frilled, keratinized epidermal sheets hanging from the palate of mysticete whales used as a sieve to strain krill and plankton.

Carapace and Plastron

The dorsal shell (carapace) and ventral shell (plastron) of a turtle formed by the fusion of dermal bone with axial skeleton elements, covered by epidermal scutes.

Dehydrocholesterol

The cutaneous chemical precursor converted by ultraviolet radiation in the skin into active vitamin D.

Batrachotoxin

A deadly neurotoxin found in the skin/feathers of hooded pitohui birds and poison dart frogs, sequestered from their dietary arthropod pre