The Integumentary System

The Integumentary System

1. Functions of the skins

   • 1. Resistance to trauma and infection
     • The skin suffers the most physical injuries to the body, but it resists and recovers from trauma better than other organs do.
   • 2. Other barrier Functions
     • The skin is important as a barrier to water. It prevents the body from absorbing excess water when you are swimming or bathing, but even more importantly, it prevents the body from losing excess water.
   • 3. Vitamin D synthesis
     • The skin carries out the first step in the synthesis of vitamin D, which is needed for bone development and maintenance. The liver and kidneys complete the process.
   • 4. Sensation
     • The skin is our most extensive sense organ. It is equipped with a variety of nerve endings that react to heat, cold, touch, texture, pressure, vibration, and tissue injury.
   • 5. Thermoregulation
     • Cutaneous nerve endings called thermoreceptors monitor the body surface temperature.
     • In response to chilling, the body retains heat by constricting blood vessels of the dermis (cutaneous vasoconstriction), keeping warm blood deeper in the body.
     • In response to overheating, it loses excess heat by dilating those vessels (cutaneous vasodilation), allowing more blood to flow close to the surface and lose heat through the skin.
   • 6. Nonverbal communication
     • The skin is an important means of nonverbal communication. Complex skeletal muscles insert on dermal collagen fibers and pull on the skin to create subtle and varied facial expressions.

2. Epidermis

   • Keratinized stratified squamous epithelium.
   • Cell of the Epidermis
     • 1. Stem Cells
       • Are undifferentiated cells that divide and give rise to the keratinocytes. They are found only in the deepest layer of the epidermis, called the stratum basale.
     • 2. Keratinocytes
       • Are the great majority of epidermal cells. They are named for their role in synthesizing keratin.
     • 3. Melanocytes
       • Also occur only in the stratum basale, amid the stem cells and deepest keratinocytes. They synthesis the brown to black pigment melanin.
     • 4. Tactile cells
       • Relatively few in number, are receptors for touch. They, too, are found in the basal layer of the epidermis and are associated with an underlying dermal nerve fiber.
     • 5. Dendritic cells
       • Are found in two layers of the epidermis called stratum spinosum and stratum granulosum. They are immune cells that originate in the bone marrow but migrate to the epidemis and epithelia of the oral cavity, esophagus, and vagina.
   • Layers of the Epidermis
     • 1. Stratum basale
       • Single layer of cuboidal to columnar cells resting on basement membrane; site of most mitosis; consists of stem cells, keratinocytes, melanocytes, and tactile cells, but these are difficult to distinguish with routine stains. Melanin is conspicuous in keratinocytes of this layer in black to brown skin.
     • 2. Stratum spinosum
       • Many layers of keratinocytes, typically shrunken in fixed tissues but attached to each by desmosomes, which give them a spiny look; progressively flattened the farther they are from the dermis. Dendritic cells are abundant here but are not distinguishable in routinely stained preparations.
     • 3. Stratum Granulosum
       • Two to five layers of cells with dark-staining keratohyalin granules; scanty in thin skin.
     • 4. Stratum Lucidum
       • Clear, featureless, narrow zone seen only in thick skin.
     • 5. Stratum corneum
       • Dead, keratinized cells of the skin surface

3. Dermis

   • Fibrous connective tissue, richly endowed with blood vessels and nerve endings. Sweat glands and hair follicles originate here and in hypodermis.
   • Papillary Layer
     • Superficial one-fifth of dermis; composed of areolar tissue; often extends upward as dermal papillae.
   • Reticular Layer
     • Deeper four-fifths of dermis; dense irregular connective tissue.

4. Hypodermis

   • Areolar or adipose tissue between skin and muscle.

5. Skin Color

   • Melanin
     • Produced by the melanocytes but accumulates in the keratinocytes of the stratum basale and stratum spinosum.
     • Eumelanin
       • A brownish black
     • Pheomelanin
       • A reddish yellow sulfur-containing pigment.
   • Hemoglobin
     •  The red pigment of blood, imparts reddish to pinkish hues as blood vessels show through the skin.
   • Carotene
     • Is a yellow pigment acquired from egg yolks and yellow and orange vegetables.
     • Depending on the diet, carotene or related compounds can become concentrated to various degrees in the stratum corneum and subcutaneous fat, imparting yellow color.
   • Cyanosis
     • Is blueness of the skin resulting from a deficiency of oxygen in the circulating blood.
   • Erythema
     • Is abnormal redness of the skin.
   • Pallor
     • Is a pale of ashen color that occurs when there is so little blood flow through the skin that the white of the dermal collagen show through.
     • Cause by emotional stress, low blood pressure, circulatory shock, cold temperatures, or severe anemia.
   • Albinism
     • Is genetic lack of melanin that usually results in milky white hair and skin, and blue-gray eyes.
   • Jaundice
     • Is yellowing of the skin and whites of the eyes resulting from high levels of bilirubin in the blood.
   • Hematoma
     • aka a bruise, is a mass of clotted blood showing through the skin.

6. Hair

   • Is also known as a pilus; in the plural, pili.
   • Hair follicle
     • It is a slender filament of keratinized cells that grows from an oblique tube in the skin.
   • Distribution and Types
     • Lanugo
       • Is fine, downy, unpigmented hair that appears on the fetus in the last 3 months of development.
     • Vellus
       • Replaced Lanugo at the time of birth, similarly fine, pale hair.
     • Terminal hair
       • Is longer, coarser, and usually more heavily pigmented.
   • Structure of the Hair and Follicle
     • Bulb
       • A swelling at the base where the hair originates in the dermis or hypodermis.
     • Root
       • Is the remainder of the hair within the follicle.
     • Shaft
       • Is the portion above the skin surface.
     • Medulla
       • Is a core of loosely arranged cells and air spaces.
     • Cortex
       • Constitutes most of the bulk of a hair.
     • Cuticle
       • Is composed of multiple layers of very thin, scaly cells that overlap each other like roof shingles with their free edges directed upward.
     • Dermal Papilla

7. Nails

   • Nail plate
     • The hard part of the nail
   • Free edge
     • Overhanging the tip of the finger or toe.
   • Nail root
     • Extends proximally under the overlaying skin.
   • Nail body
     • Is the visible attached part of the nail.
   • Nail fold
     • The surrounding skin rises a bit above the nail.

8. Cutaneous Glands

   • Sudoriferous glands
     • Are two kinds: apocrine and merocrine.
     • Apocrine sweat glands
       • Occur in the groin, anal region, axilla, and areola, and in mature males, in the beard. Respond to stress and sexual stimulation.
     • Merocrine (eccrine) sweat glands
       • Are widely distributed over the entire body, but are especially abundant on the palms, soles, and forehead. Their primary function is to cool the body.
   • Sebaceous Glands
     • Produce an oily secretion call sebum.
   • Ceruminous Glands
     • Are found only in the external ear canal, where their secretion combines with sebum and dead epidermal cell to form earwax, or cerumen.
   • Mammary Glands
     • Are milk producing glands that develop within the female breast during pregnancy and lactation.

9. Burns

   • Second-degree burns
     • Involve the epidermis and part of the dermis but leave at least some of the dermis intact. Aka partial-thickness burns.
   • Third-degree burns
     • Also known as full-thickness burns because the epidermis, all of the derms, and often some deeper tissues (muscle and bone). are destroyed.
   • First-degree burns
     • Involve only the epidermis and are marked by redness, slight edema, and pain.