A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structure, function, and chemical composition.

Human anatomy

human anatomy Human anatomy (gr. ἀνατομία, "dissection", from ἀνά, "up", and τέμνειν, "cut") is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross ...

, "cuticle" can refer to several structures, but it is used in general parlance, and even by medical professionals, to refer to the thickened layer of skin surrounding fingernails and toenails (the eponychium), and to refer to the superficial layer of overlapping cells covering the

hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and ...

shaft ( cuticula pili), consisting of dead cells, that locks the hair into its follicle. It can also be used as a synonym for the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...

, the outer layer of skin.

Cuticle of invertebrates

zoology Zoology ( , ) is the scientific study of animals. Its studies include the anatomy, structure, embryology, Biological classification, classification, Ethology, habits, and distribution of all animals, both living and extinction, extinct, and ...

, the

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

cuticle or cuticula is a multi-layered structure outside the

of many invertebrates, notably

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s and roundworms, in which it forms an

exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

(see arthropod exoskeleton). The main structural components of the nematode cuticle are

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s, highly cross-linked

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

s and specialised insoluble proteins known as "cuticlins", together with glycoproteins and

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

s. The main structural component of arthropod cuticle is

chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...

, a

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...

composed of ''N''-acetylglucosamine units, together with proteins and lipids. The proteins and chitin are cross-linked. The rigidity is a function of the types of proteins and the quantity of chitin. It is believed that the epidermal cells produce protein and also monitors the timing and amount of protein to be incorporated into the cuticle. Often, in the cuticle of

arthropods Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

, structural coloration is observed, produced by nanostructures. In the mealworm beetle, '' Tenebrio molitor'', cuticular color may suggest pathogen resistance in that darker individuals are more resistant to pathogens compared to more tan individuals.

Botany

botany Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

, plant cuticles are protective, hydrophobic, waxy coverings produced by the epidermal cells of leaves, young shoots and all other aerial plant organs. Cuticles minimize water loss and effectively reduce pathogen entry due to their waxy secretion. The main structural components of plant cuticles are the unique

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s cutin or cutan, impregnated with wax. Plant cuticles function as permeability barriers for water and water-soluble materials. They prevent plant surfaces from becoming wet and also help to prevent plants from drying out. Xerophytic plants such as cacti have very thick cuticles to help them survive in their arid climates. Plants that live in range of sea's spray also may have thicker cuticles that protect them from the toxic effects of

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

. Some plants, particularly those adapted to life in damp or aquatic environments, have an extreme resistance to wetting. A well-known example is the sacred lotus. This adaptation is not purely the physical and chemical effect of a waxy coating but depends largely on the microscopic shape of the surface. When a hydrophobic surface is sculpted into microscopic, regular, elevated areas, sometimes in

fractal In mathematics, a fractal is a Shape, geometric shape containing detailed structure at arbitrarily small scales, usually having a fractal dimension strictly exceeding the topological dimension. Many fractals appear similar at various scale ...

patterns, too high and too closely spaced for the surface tension of the liquid to permit any flow into the space between the plateaus, then the area of contact between liquid and solid surfaces may be reduced to a small fraction of what a smooth surface might permit. The effect is to reduce wetting of the surface substantially. Structural coloration is also observed in the cuticles of plants (see, as an example, the so-called "marble berry", '' Pollia condensata''.

Mycology

"Cuticle" is one term used for the outer layer of tissue of a

mushroom A mushroom or toadstool is the fleshy, spore-bearing Sporocarp (fungi), fruiting body of a fungus, typically produced above ground on soil or another food source. ''Toadstool'' generally refers to a poisonous mushroom. The standard for the n ...

basidiocarp In fungi, a basidiocarp, basidiome, or basidioma () is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do no ...

, or "fruit body". The alternative term "

pileipellis The pileipellis is the uppermost layer of hyphae in the pileus of a fungal fruit body. It covers the trama, the fleshy tissue of the fruit body. The pileipellis is more or less synonymous with the cuticle, but the cuticle generally describes ...

", Latin for "skin" of a "cap" (meaning "mushroom") might be technically preferable, but is perhaps too cumbersome for popular use. It is the part removed in "peeling" mushrooms. On the other hand, some morphological terminology in mycology makes finer distinctions, such as described in the article on the "

". Be that as it may, the pileipellis (or "peel") is distinct from the trama, the inner fleshy tissue of a mushroom or similar fruiting body, and also from the

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

-bearing tissue layer, the

hymenium The hymenium is the tissue layer on the hymenophore of a fungal fruiting body where the cells develop into basidia or asci, which produce spores. In some species all of the cells of the hymenium develop into basidia or asci, while in oth ...

References

External links

* {{Authority control Animal anatomy Nematode anatomy Plant morphology