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mareroa mareroa
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9 years ago
using body temperature as a example explain the importance of homeostasis

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9 years ago
https://biology-forums.com/index.php?topic=77440.0

The epidermis, where keratinization occurs, is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface and is made up of stratified squamous epithelium with an underlying basal lamina.

The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis. The main type of cells which make up the epidermis are Merkel cells and keratinocytes. Melanocytes and Langerhans cells are also present.

This overall process of keratinization, which takes approximately 27 days, proceeds as follows:

The epidermis can be subdivided into the following strata (beginning with the outermost layer):

(1) Stratum corneum,
(2) Stratum lucidum (only in palms of hands and bottoms of feet),
(3) Stratum granulosum,
(4) Stratum spinosum, and
(5) Stratum basale.

Cells are formed through mitosis at the basale layer. The daughter cells resulting from cell division move up the strata, from basale to corneum, changing shape and composition as they die due to isolation from their blood source. Their cytoplasm is released and the protein keratin is inserted. After they reach the corneum, they are eventually slough off in a process called desquamation. Most of the dust found in homes is desquamated skin. This keratinized layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and pathogens out, making skin a natural barrier to infection.

The process of keratinization produces an outermost layer of the epidermis consisting of 25 to 30 layers of dead cells. These dead cells are what is seen when we look at our own skin, or at the bodies of other people.

Keratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but nonmineralized structures found in reptiles, birds, amphibians and mammals. They are rivaled as biological materials in toughness only by chitin, found on the outer surface of invertebrates.

Keratins are the main constituent of structures that grow from the skin:

α-keratins are found in the hair and nails. Nails also contain the harder β-keratins.

Keratin proteins, like all intermediate filaments, form filamentous polymers in a series of assembly steps beginning with dimerization; dimers assemble into tetramers and octamers and eventually, the current hypothesis holds, into unit-length-filaments (ULF) capable of annealing end-to-end into long filaments. During the process of epithelial differentiation, cells become cornified as keratin protein is incorporated into longer keratin intermediate filaments. Eventually the nucleus and cytoplasmic organelles disappear, metabolism ceases, and cells undergo a programmed death as they become fully keratinized. In many other cells types, such as dermis, keratin functions in the cytoplasm to mechanically stabilize the cell against physical stress. It does this through connections to desmosomes, cell-cell junctional plaques, and hemidesmosomes, cell-basement membrane adhesive structures.

Cells in the epidermis contain a structural matrix of keratin which makes this outermost layer of the skin almost waterproof, and along with collagen and elastin, gives skin its strength. Rubbing and pressure cause keratin to proliferate with the formation of protective calluses — useful for athletes and on the fingertips of musicians who play stringed instruments. Keratinized epidermal cells are constantly shed and replaced (see dandruff).

These hard, integumentary structures of keratinization are formed by intercellular cementing of fibers formed from the dead, cornified cells generated by specialized beds deep within the skin. Hair, which grows continuously, is primarily composed of keratin.

In conclusion, keratin affects our appearance in many ways:

(1) As the primary constituent of hair, it generates our many beautiful hair styles.

(2) As the primary constituent of the outer 30 layers of our skin, it provides the beautiful glow that we see when we gaze at the bodies of other human beings.

(3) As a flexible stabilizer of our dermis and epidermis, it gives to skin its many curvaceous features, and enables skin to move when touched by another person, such as a lover.
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