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Stratum corneum
 
 
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The stratum corneum (or horny layer) is the outermost layer of the epidermis
Epidermis (skin)

The epidermis is the outermost layer of the skin, composed of terminally differentiated stratified squamous epithelium, acting as the body's major barrier against an inhospitable environment....
, composed of large, flat, polyhedral, plate-like envelopes filled with keratin which are the dead cells that have migrated up from the stratum granulosum. From the Latin for "horny layer", this skin layer is composed mainly of dead cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s that lack nuclei
Cell nucleus

In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
. As these dead cells slough off on the surface in the thin air filled stratum disjunctum, they are continuously replaced by new cells from the stratum germinativum
Stratum germinativum

The Stratum germinativum is the deepest layer of the epidermis, a continuous layer of cells often described as one cell thick, though it may be two to three cells thick in glabrous skin and hyperproliferative epidermis....
 (basale).






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The stratum corneum (or horny layer) is the outermost layer of the epidermis
Epidermis (skin)

The epidermis is the outermost layer of the skin, composed of terminally differentiated stratified squamous epithelium, acting as the body's major barrier against an inhospitable environment....
, composed of large, flat, polyhedral, plate-like envelopes filled with keratin which are the dead cells that have migrated up from the stratum granulosum. From the Latin for "horny layer", this skin layer is composed mainly of dead cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s that lack nuclei
Cell nucleus

In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
. As these dead cells slough off on the surface in the thin air filled stratum disjunctum, they are continuously replaced by new cells from the stratum germinativum
Stratum germinativum

The Stratum germinativum is the deepest layer of the epidermis, a continuous layer of cells often described as one cell thick, though it may be two to three cells thick in glabrous skin and hyperproliferative epidermis....
 (basale). In the human forearm, for example, about 1300 cells/cm2/hr are shed and commonly accumulate as house dust. This outer layer that is sloughed off is also known as the stratum dysjunction.

Cells of the stratum corneum contain keratin
Keratin

Keratins are a family of fibrous protein; tough and insoluble, they form the hard but mineral structures found in reptiles, birds, amphibians and mammals....
, a protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
 that helps keep the skin hydrated by preventing water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 evaporation
Evaporation

Evaporation is the slow vaporization of a liquid and the reverse of condensation. A type of phase transition, it is the process by which molecules in a liquid State of matter spontaneously become gaseous ....
. These cells can also absorb
Absorption (chemistry)

File:Absorber.svgAbsorption, in chemistry, is a physical or chemical phenomenon or a Process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material....
 water, further aiding in hydration and explaining why humans and other animals experience wrinkling
Wrinkle

File:Old Bangladeshi drinking tea cropped.jpgA wrinkle is a fold, ridge or crease in the skin. Skin wrinkles typically appear as a result of aging processes such as glycation or, temporarily, as the result of prolonged immersion in water....
 of the skin on the finger
Finger

A finger is a type of digit , an organ of manipulation and sensation found in the hands of humans and other primates.Normally humans have five digits, termed phalanges, on each hand ....
s and toes (colloquially called "pruning") when immersed in water for prolonged periods. In addition, this layer is responsible for the "spring back" or stretchy properties of skin. A weak glutenous protein bond pulls the skin back to its natural shape.

The thickness of the stratum corneum varies according to the amount of protection and/or grip required by a region of the body. For example, the hand
Hand

The hands are the two intricate, prehensile, multi-fingered body parts normally located at the end of each arm of a human or other primate. They are the chief organs for physically manipulating the environment, using anywhere from the roughest motor skills to the finest , and since the fingertips contain some of the densest areas of nerve e...
s are typically used to grasp objects, requiring the palms to be covered with a thick stratum corneum. Similarly, the sole
Sole

Sole may refer to:* Sole , the bottom of the foot* Sole , the bottom supporting member of the shoe* Sole , several species and groups of flatfishes:...
 of the foot
Foot

The foot is an anatomical structure found in many animals. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws or nails....
 is prone to injury, and so it is protected with a thick stratum corneum layer. In general, the stratum corneum contains 15 to 20 layers of dead cells. The stratum corneum has a thickness between 10 and 40 µm.

In reptile
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s, the stratum corneum is permanent, and is replaced only during times of rapid growth, in a process called ecdysis
Ecdysis

Ecdysis is the molting of the cuticula in arthropods and related groups . Since the cuticula of these animals is also the skeletal support of the body and is inelastic, it is shed during growth and a new, larger covering is formed....
 or moulting. The stratum corneum in reptiles contains beta-keratin
Beta-keratin

?-keratin or beta-keratin is in contrast to alpha-keratin, a fibrous protein rich in alpha helices, rich in stacked ? pleated sheets.?-keratin is found in reptiles....
, which provides a much more-rigid skin layer.

Additional images


External links

- "Integument: thick skin"