One of the metabolic functions of the skin is the production of Vitamin
D3 when ultraviolet light reacts with 7-dehydrocholesterol.
LEARNING OBJECTIVE [ edit ]
Evaluate the integumentary system metabolic function of producing vitamin D
KEY POINTS [ edit ]
Vitamin D3 is made in the skin when 7-dehydrocholesterolreacts with ultraviolet light of UVB
type at wavelengths.Vitamin D is produced in the two innermost strata of the epidermis.
Cholecalciferol (D3) is produced photochemically in the skin from 7-dehydrocholesterol.
The protein keratin stiffens epidermal tissue to form fingernails. Nails grow from thin area called
the nail matrix; growth of nails is 1 mm per week on average.
The integumentary system has multiple roles in homeostasis. The skin has an important job of
protecting the body and acts as the body's first line of defense against infection, temperature
change, and other challenges to homeostasis.
TERM [ edit ]
7-dehydrocholesterol
7-Dehydrocholesterol is a cholesterol precursor that is converted to vitamin D3 in the skin,
therefore functioning as provitamin-D3.
Give us feedback on this content: FULL TEXT [edit ]
The Integumentary System
The integumentary system is the largest of the body's organ systems. In humans, this system
accounts for about 12 to 15 percent of total body weight and covers 1.5-2m2 of surface area. It
distinguishes, separates, and protects the organism from its surroundings. Small-bodied
invertebrates of aquatic or continually
moist habitats respire using the outer
layer (integument). This gas exchange
system, where gases simply diffuse into
and out of the interstitial fluid, is called
integumentary exchange.
The human skin consists of three major
layers: the epidermis;dermis;
and hypodermis. The epidermis forms the
outermost layer, providing the initial
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barrier to the external environment.
Beneath this, the dermis comprises two sections, the papillary and reticular layers, and
contains connective tissues, vessels, glands, follicles, hair roots, sensory nerve endings, and
muscular tissue. The deepest layer is the hypodermis, which is primarily made up of adipose
tissue. Substantial collagenbundles anchor the dermis to the hypodermis in a way that
permits most areas of the skin to move freely over the deeper tissue layers. Vitamin D is
produced in the two innermost strata of the epidermis, the stratum basale and stratum
spinosum.
Vitamin D
Chemical Structure of Vitamin D
The major cell of the epidermis is the keratinocyte, which produces keratin. Keratin is a
fibrous protein that aids in protection. Keratin is also a water-proofing protein. Millions of
dead keratinocytes rub off daily. The majority of the skin on the body is keratinized, meaning
waterproofed. The only skin on the body that is non-keratinized is the lining of skin on the
inside of the mouth. Non-keratinized cells allow water to "stay" atop the structure.
The protein keratin stiffens epidermal tissue to form fingernails. Nails grow from thin area
called the nail matrix; growth of nails is 1 mm per week on average. The lunula is the
crescent-shape area at the base of the nail; this is a lighter color as it mixes with the matrix
cells.
The dermal layer provides a site for the endings of blood vessels and nerves. Many
chromatophores are also stored in this layer, as are the bases of integumental structures such
as hair, feathers, and glands.
Types of cells that are found in the hypodermis are fibroblasts, adipose cells,
and macrophages. It is derived from themesoderm, but unlike the dermis, it is not derived
from thedermatome region of the mesoderm. In arthropods, the hypodermis is an epidermal
layer of cells that secretes the chitinous cuticle.
The integumentary system has multiple roles in homeostasis. All body systems work in an
interconnected manner to maintain the internal conditions essential to the function of the
body. The skin has an important job of protecting the body and acts as the body's first line of
defense against infection, temperature change, and other challenges to homeostasis.
Vitamin D3 is made in the skin when 7-dehydrocholesterol reacts with ultraviolet light of
UVB type at wavelengths between 280 and 315 nm, with peak synthesis occurring between
295 and 297 nm. Depending on the intensity of UVB rays and the minutes of exposure, an
equilibrium can develop in the skin, and vitamin D degrades as fast as it is generated.
Cholecalciferol (D3) is produced photochemically in the skin from 7-dehydrocholesterol ; 7dehydrocholesterol is produced in relatively large quantities in the skin of most vertebrate
animals, including humans.
Metabolism and pathway map for vitamin D
Vitamin D Synthesis Pathway