The Integumentary System

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The Integumentary System
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Integumentary System Includes

• Skin (cutaneous membrane)
• Subcutaneous tissue below the skin
• Accessory Structures
• Sweat glands
• Sebaceous or oil glands
• Hair
• Nails

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Layers Of The Skin
Click here to copy and Paste a micrograph of The
layers of the skin.

• Epidermis outer
• composed of stratified squamous epithelium
• Dermis inner
• anchored to a subcutaneous layer

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Epidermis

• Composed of stratified squamous epithelium
• Avascular as it has no blood supply of its own
• Oxygen and nutrients diffuse from the underlying
  dermis
• The epidermis is a keratinized stratified
  squamous epithelium. Oxygen and nutrients diffuse
  from the underlying dermis. Five structurally
  different layers can be identified

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First Layer of the Epidermis

• The stratum basaleis the deepest layer of the
  epidermis (closest to the dermis). It is found
  close to the dermal blood supply. It consists of
  a single layer of columnar or cuboidal cells
  which rest on the basement membrane. Basal cells
  are the stem cells of the epidermis. Their
  mitotic activity replenishes the cells in more
  superficial layers as these are eventually shed
  from the epidermis. The renewal of the epidermis
  takes about 3 to 4 weeks in humans as millions of
  cells are produced daily. Cells die as they are
  pushed away from the source of nourishment.
  Cells undergo keratinization as a tough protein,
  keratin, is deposited within the cell. Keratin
  hardens and flattens the cells as they move
  outward and it waterproofs the skin.

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Optional Epidermal Layers

• In the stratum spinosum,the cells become
  irregularly polygonal. The cells are often
  separated by narrow, translucent clefts. These
  clefts are spanned by spine-like cytoplasmatic
  extensions of the cells (hence the name of the
  layer and of its cells spinous cells), which
  interconnect the cells of this layer.
• The stratum granulosumconsists, in thick skin,
  of a few layers of flattened cells. Only one
  layer may be visible in thin skin.
• The stratum lucidumconsists of several layers of
  flattened dead cells. Nuclei already begin to
  degenerate in the outer part of the stratum
  granulosum. In the stratum lucidum, faint nuclear
  outlines are visible in only a few of the cells.
  The stratum lucidum can usually not be identified
  in thin skin.

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Final Epithelial Layer

• In the stratum corneum,cells are keratinized and
  form a layer that is about 30 cells thick.
  Individual cells are difficult to observe because
  (1) nuclei can no longer be identified, (2) the
  cells are very flat and (3) the space between the
  cells has been filled with lipids, which cement
  the cells together into a continuous membrane.
  Closest to the surface of the epidermis, the
  stratum corneum has a somewhat looser appearance.
  Cells are constantly shed from this part of the
  stratum corneum. This layer makes up three
  fourths of the epidermal thickness. The
  protection of the body by the epidermis is due to
  the functional features of the stratum corneum.

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Click here to copy the picture skin, thick
trichrome And paste it here.
Click here to copy the picture skin, thin
HE And paste it here.
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Dermis or corium

• The dermis, or corium, consists of dense fibrous
  connective tissue with numerous collagenous and
  elastic fibers. The dermis is much thicker than
  the epidermis. In thick skin, dermal papillae
  create a very irregular border between epidermis
  and dermis. Blood vessels, nervous tissue, some
  muscle tissue, certain glands, hair and nails are
  found in the dermis. Nerve endings allow us to
  sense pain, temperature, pressure, and touch.

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Click here to copy and paste the picture skin,
thick van Gieson elastin
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Melanin
Click here to copy and paste a picture of The
integument showing melanocytes stained blue
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Red and Yellow, Black and White

• The red and yellow hues of the skin are due to
  hemoglobin in the red blood cells, which pass
  through the capillaries beneath the epidermis,
  and carotene (yellowish pigment), which
  accumulates in fat cells found in the dermis and
  hypodermis (subcutaneous layer beneath dermis).
• Melanocytes
• The brown in skin color is due to melanin, which
  is produced in the skin itself in cells called
  melanocytes. These cells are located in the
  epidermis. In the melanocytes, the melanin is
  located in membrane-bound organelles called
  melanosomes. Melanocytes can transfer melanin to
  keratinocytes - mainly to the basal cells.
  Melanin protects the chromosomes of mitotically
  active basal cells against light-induced damage.
• Pigmentation is not just under the control of
  light. Hormones produced by the pituitary and the
  adrenal glands also affect pigmentation. Diseases
  of these two endocrine organs often result in
  changes of pigmentation of the skin.

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Malfunctioning Melanocytes

• Albinism melanocytes completely fail to secrete
  melanin. Hair, skin, and iris are white.
• Vitiligo loss of pigment in certain areas of
  the skin producing white patches.
• Freckles and moles are formed when melanin
  becomes concentrated in local areas.
• Malignant melanoma a cancerous change in a mole
  that may metastasize (spread) rapidly and is most
  difficult to treat. Exposure to sunlight
  increases risk.

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Other Pigments in Skin

• Carotene a yellow pigment in skin usually
  hidden by the effects of melanin. Asians have
  little melanin which allows the yellow to show
  more than other nationalities.
• Pinkish color seen in fair-skinned persons
  because the vascular dermis is visible.
• Cyanosis blue look to skin due to poorly
  oxygenated blood
• Blushing caused by dilation of blood vessels
• Pale by fright caused by restriction of vessels

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Response to Disease

• Jaundice caused when bilirubin is deposited in
  skin because a diseased liver is unable to
  excrete this pigment
• Skin may appear bronzed due to the deposit of
  excess melanin when a persons adrenal gland is
  functioning poorly.
• A bruise indicates that blood has escaped from
  the blood vessels and has clotted under the skin.
• Over eating carotene-rich vegetables such as
  carrots may cause skin to have a yellow tint.

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Accessory Structures of the Skin

• Hair
• A characteristic feature of the human skin is the
  apparent lack of hair on most of the body
  surface. This is actually not quite true. Most of
  the skin is haired although the hair in most
  areas is short, fine and only lightly pigmented.
• Truly hairless are only the palms of hands and
  soles of feet, the distal phalanges and sides of
  fingers and toes and parts of the external
  genitalia.

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Accessory Structures of the Skin

• In those parts of the skin which we perceive as
  "hairy" we find terminal hairs. The free part of
  each hair is called the shaft.
• The root of each hair is anchored in a tubular
  invagination of the epidermis, the hair follicle,
  which extends down into the dermis and, usually,
  a short distance into the hypodermis.
• The hair that you groom daily is actually dead
  keratinized cells.
• Each hair follicle has an associated bundle of
  smooth muscle, the arrector pili muscle. This
  muscle inserts with one end to the papillary
  layer of the dermis and with the other end to the
  dermal sheath of the hair follicle. This makes
  your hair stand up on its end.

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Accessory Structures of the Skin
Click here and copy and paste the Picture of a
hair follicle here.
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Hair Color and Texture

• Hair color is determined by the amount and type
  of melanin present.
• Melanocytes become less active with age. Gray
  hair is a mixture of pigmented and non-pigmented
  hairs.
• Red hair results from a a modified type of
  melanin that contains iron.
• The shape of the hair shaft determines texture.
• Round shaft straight hair
• Oval shaft wavy hair
• Flat shafts curly or kinky hair
• Perms use chemicals to flatten shafts and makes
  hair curly.
• Alopecia is the term for hair loss.

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Accessory Structures of the Skin

• Nails
• Plates of stratified squamous epithelial cells
  with hard keratin
• Protect distal ends of phalanges
• Cells are keratinized in the nail root
• Nail growth occurs in the lunula
• Cuticle is a fold of stratum corneum on the
  proximal end of nail

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Click here to copy and paste a Picture of the
skin and nail here.
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Exocrine Glands

• Sebaceous glands or oil glands are simple
  branched areolar glands. They secrete the sebum
  (seb oil) an oily product. Sebum is usually
  secreted into a hair follicle. Sebum is a natural
  skin cream it helps hair from becoming brittle,
  prevents excessive evaporation of water from the
  skin, keeps the skin soft and contains a
  bactericidal agent that inhibits the growth of
  certain bacteria.
• Sebaceous glands are scattered all over the
  surface of the skin except in the palms, soles
  and the side of the feet.
• Vernix caseosa - white covering on fetus.
• Blackhead
• Pimple

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Exocrine Glands

• Sweat glands or sudoriferous glands are simple
  coiled tubular glands. They are divided into two
  principal types eccrine and apocrine.
• Apocrine glands are found mainly in the skin of
  the armpits, of the anogenital areas and of the
  areola of the breasts. Their secretory portion
  can be located in the dermis or in the
  hypodermis. Their excretory ducts open into hair
  follicles. Their secretion is more viscous than
  that of the eccrine glands. They start secreting
  at puberty and may be analogous to the sexual
  scent glands of other animals.
• Eccrine glands are the most common. Their
  secretory portion can be located in the dermis or
  in the hypodermis. They produce sweat, a watery
  mixture of salts, antibodies and metabolic
  wastes. Sweat prevents overheating of the body
  and thus helps regulate body temperature.
• Ceruminous glands (or ear wax glands) and mammary
  glands are modified apocrine sweat glands.

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Click here to copy and paste a picture Of a sweat
gland here.
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Physiology of the Skin

• Protection - the epidermis provides a barrier to
  fluid loss from the body (this protective
  function is impaired in patients with burns).
• barrier function - intact skin prevents the entry
  of micro-organisms into the body. Antimicrobial
  proteins are produced by the epidermis - they act
  by piercing holes in the outer membranes of
  micro-organisms.
• Resistance to wear and tear - continuous
  replacement of the outer epidermal cells that
  wear off - new cells are produced in the deepest
  layer of the epidermis and gradually migrate
  towards the surface

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• Skin can excrete water, salt, and small amounts
  of waste products such as urea.
• Vitamin D can be synthesized in skin exposed to
  sunlight (vitamin D can also be obtained from the
  diet)
• The skin provides a barrier to ultraviolet light.
  The melanocytes contain melanin, which absorbs UV
  radiation, and also distribute the pigment to
  neighboring cells. Skin exposed to sunlight
  becomes wrinkled and creased. Changes seem to be
  due to disruption of collagen and elastin in
  dermis, and loss of fibroblasts which make new
  proteins.

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• Three types of skin cancer corresponding to three
  major types of skin cells basal cells, squamous
  cells, and melanocytes.
• Cancer of melanocytes - malignant melanoma - is
  the most lethal variety, but also the least
  common.
• If caught early, most cases of non-melanoma skin
  cancer are easily treated under local anaesthetic
• Whites in Australia have the highest rates of
  skin cancer of all types in the world.
• The damaging effects of sunlight can occur many
  years before tumors appear.
• ultraviolet light causes mutations at points on a
  DNA strand.

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• The integumentary system is well-supplied with
  receptors for touch, pain, temperature, vibration
  and pressure
• Sensory information is relayed to the central
  nervous system via sensory nerves
• Social interactions are influenced by facial
  expressions, blushing, touching, etc.

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Fun Facts

• House dust is mainly skin flakes!
• If you laid out all your skin on a flat surface,
  it would have an area of about 2 square meters.
• Skin weighs about 2.5 kilograms - the largest
  organ in the body.
• What hurts if you pull it, but doesn't hurt if
  you cut it? Your hair, of course!
• Skin is elastic - it springs back into shape when
  stretched. Some medicines (estrogen, nicotine)
  can pass through the skin, but others cannot
  (insulin). Why is that? Because only fat-soluble
  substances can enter the skin, not water-soluble
  ones.
• Your hair stands on end and you develop 'goose
  bumps' because there are tiny muscles attached to
  the hair follicles and they contract when you are
  frightened or cold.

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