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Skin or cutaneous membrane
Functions: maintain a constant body temperature, protects the body and provides sensory information about the surrounding environment
Description: skin, hair, oil, sweat glands, nails and sensory receptors.
-Has three principal layers: Epidermis, Dermis and the subcutaneous layer
- the superficial thinner portion which is composed of the epithelial tissue.
- -It is composed of keratinized stratified squamous epithelium.
- -It contains four major cells: Keratinocytes, langerhans, Melanocytes, and Merkel cells.
Epidermis cells: Keratinocytes
- -found in all layers of the epidermis
- -Produces Keratin and Lamellar grandules
- a tough fiborous protein that helps protect the skin and underlying tissue from heat, microbes and chemicals.
- -produced by keratinocytes
- -produced by keratinocytes
- -they release a water repellent sealant that decreases water entry and loss and inhibits the entry of foreign materials
Epidermis cells: Melanocyte
- -produce the pigment melanin
- -their long slender projections extend to the keratinocytes and transfer melanin grandules to them
is a yellow-red or brown-black pigment that contributes to skin colour and absorbs harmful ultraviolet light.
-once they enter the keratinocyte the form a protective veil over the nucleus on the side of the side toward the skins surface to protect the DNA from being damaged by the sun
Epidermis cells: Langerhans cells
- -arise from red bone marrow and migrate to the epidermis
- -they participate in immune responses mounted against microbes
Epidermis cells: Merkel cells
- -found in the deepest layer of the epidermis where they are in contact with a sensory neuron.
- - they detect touch and sensations
Epidermis Layers or Strata: Stratum basale
- -deepest layer of the epidermis
- -contains one row of cubial keratinocytes that contain scattered tonafilaments(intermediate filaments)
- -melanocytes and merkel cells are scattered among the keratinocytes
- -where most of the stem cells are that aid in new cell development
Epidermis Layers or Strata: Spinosum stratum
- eight to ten rows of many-sided keratinocytes with bundles of tonafilaments; includes armlike processes of melanocytes and langerhans cells.
Epidermis Layers or Strata: Granulosum stratum
three to five rows of flattened keratinocytes, in which organelles are beginning to degenerate (apoptosis), cells contain the protein keratohyalin which converts the tonofilaments into keratin and lamellar grandules which release a lipid-rich, water-repellent secretion
Epidermis Layers or Strata: lucidium
-Present only in finger tips, palems and soles; consists of three to five rows of clear, flat, dead keratinocytes with large amounts of keratin
Epidermis Layers or Strata: Corneum
twenty-five to thirty rows of dead, flat, keratinocytes that contain mostly keratin
- -as the cells move from one epidermal layer to the next, they accumulate more and more keratin a process called keratinization.
- -then they undergo apoptosis
- -is composed of strond connective tissue containing collagen and elastic fibres giving it the ability to stretch and recoil easily
- -the few cells present are fibroblasts, macrophages, adipose cells.
- -blood vessels, nerves, hair follicles and glands are embedded in the dermis
- -two regions: papillary region and reticular region
Dermis layers: Papillary
- the superficial portion of the dermis (about one-fifth) consists of areolar connective tissue with thin collagen and fine elastic fibers; contains dermal ridges that house capillaries, meissner corpuscles and free nerve endings
- -greatly increase the surface area of the papillary region
- -small fingerlike structures that project into the undersurface of the epidermis.
Papillary Region: Meissner corpuscles or corpuscles of touch
- -tactile receptors found in some dermal papillae.
- -nerve endings that are sensitive to touch.
Papillary region: Free nerve endings
- -found in some dermal papillae
- -dendrites that lack any apparent structural specialization.
- -different nerve endings intiate signals that give rise to sensations of warmth, coolness, pain, tickling and itchiness
Dermis layers: Reticular
- the deeper portion of the dermis (about four-fifths)
- consist of dense irregular connective tissue with bundles of thick collagen and some coarse elastic fibers.
- -The space between fibers contain some adipose cells, hair follicles, nerves, sebaceous glands, and sudoriferous glands.
Recticular region of Dermis: Epidermal ridges
the surface of palms, fingers, soles, and toes have a series of ridges and grooves. They appear as either straight lines or as a pattern of loops and whorls, as on the tips of the digits.
Structural basis of skin color
Melanin, hemoglobin and carotene are the three pigments that impart a wide variety of colors to the skin
Skin color: Melanin
- -the amount of melanin causes the skin's colour to vary from pale yellow to reddish brown to black.
- -two types of melanin: Pheomelanin (yellow to red) and eumelanin (brown to black)
- -difference in skin colour is due to the amount of pigment the melanocytes produce and transfer to keratinocytes as well as the amount of melanin present
Skin Colour: carotene
- -a yellow-orange pigment that gives egg yolk and carrotes their colour
- -this pigment is stored in the stratum corneum and fatty areas of the dermis and subcutaneous layers in response to excessive dietary intake. So much may be deposited that the skin can actually look orange
Skin color: Albinism
- is the inherited inability of an individual to produce melanin
- -they have melanocytes that are unable to synthesis tyrosinase.