The Integumentary System

1. 1. Resistance to trauma and infection

   Nota:

   • The skin suffers the most physical injuries to the body, but it resists and recovers from trauma better than other organs do.
2. 2. Other barrier Functions

   Nota:

   • 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. 3. Vitamin D synthesis

   Nota:

   • 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. 4. Sensation

   Nota:

   • 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. 5. Thermoregulation

   Nota:

   • 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. 6. Nonverbal communication

   Nota:

   • 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.

Nota:

• Keratinized stratified squamous epithelium.

1. Cell of the Epidermis
   1. 1. Stem Cells

      Nota:

      • 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. 2. Keratinocytes

      Nota:

      • Are the great majority of epidermal cells. They are named for their role in synthesizing keratin.
   3. 3. Melanocytes

      Nota:

      • Also occur only in the stratum basale, amid the stem cells and deepest keratinocytes. They synthesis the brown to black pigment melanin.
   4. 4. Tactile cells

      Nota:

      • 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. 5. Dendritic cells

      Nota:

      • 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.
2. Layers of the Epidermis
   1. 1. Stratum basale

      Nota:

      • 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. 2. Stratum spinosum

      Nota:

      • 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. 3. Stratum Granulosum

      Nota:

      • Two to five layers of cells with dark-staining keratohyalin granules; scanty in thin skin.
   4. 4. Stratum Lucidum

      Nota:

      • Clear, featureless, narrow zone seen only in thick skin.
   5. 5. Stratum corneum

      Nota:

      • Dead, keratinized cells of the skin surface

Nota:

• Fibrous connective tissue, richly endowed with blood vessels and nerve endings. Sweat glands and hair follicles originate here and in hypodermis.

1. Papillary Layer

   Nota:

   • Superficial one-fifth of dermis; composed of areolar tissue; often extends upward as dermal papillae.
2. Reticular Layer

   Nota:

   • Deeper four-fifths of dermis; dense irregular connective tissue.

Nota:

• Areolar or adipose tissue between skin and muscle.

1. Melanin

   Nota:

   • Produced by the melanocytes but accumulates in the keratinocytes of the stratum basale and stratum spinosum.
   1. Eumelanin

      Nota:

      • A brownish black
   2. Pheomelanin

      Nota:

      • A reddish yellow sulfur-containing pigment.
2. Hemoglobin

   Nota:

   •  The red pigment of blood, imparts reddish to pinkish hues as blood vessels show through the skin.
3. Carotene

   Nota:

   • 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.
4. Cyanosis

   Nota:

   • Is blueness of the skin resulting from a deficiency of oxygen in the circulating blood.
5. Erythema

   Nota:

   • Is abnormal redness of the skin.
6. Pallor

   Nota:

   • 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.
7. Albinism

   Nota:

   • Is genetic lack of melanin that usually results in milky white hair and skin, and blue-gray eyes.
8. Jaundice

   Nota:

   • Is yellowing of the skin and whites of the eyes resulting from high levels of bilirubin in the blood.
9. Hematoma

   Nota:

   • aka a bruise, is a mass of clotted blood showing through the skin.

Nota:

• Is also known as a pilus; in the plural, pili.

1. Hair follicle

   Nota:

   • It is a slender filament of keratinized cells that grows from an oblique tube in the skin.
2. Distribution and Types
   1. Lanugo

      Nota:

      • Is fine, downy, unpigmented hair that appears on the fetus in the last 3 months of development.
   2. Vellus

      Nota:

      • Replaced Lanugo at the time of birth, similarly fine, pale hair.
   3. Terminal hair

      Nota:

      • Is longer, coarser, and usually more heavily pigmented.
3. Structure of the Hair and Follicle
   1. Bulb

      Nota:

      • A swelling at the base where the hair originates in the dermis or hypodermis.
   2. Root

      Nota:

      • Is the remainder of the hair within the follicle.
   3. Shaft

      Nota:

      • Is the portion above the skin surface.
   4. Medulla

      Nota:

      • Is a core of loosely arranged cells and air spaces.
   5. Cortex

      Nota:

      • Constitutes most of the bulk of a hair.
   6. Cuticle

      Nota:

      • Is composed of multiple layers of very thin, scaly cells that overlap each other like roof shingles with their free edges directed upward.
   7. Dermal Papilla

1. Nail plate

   Nota:

   • The hard part of the nail
2. Free edge

   Nota:

   • Overhanging the tip of the finger or toe.
3. Nail root

   Nota:

   • Extends proximally under the overlaying skin.
4. Nail body

   Nota:

   • Is the visible attached part of the nail.
5. Nail fold

   Nota:

   • The surrounding skin rises a bit above the nail.

1. Sudoriferous glands

   Nota:

   • Are two kinds: apocrine and merocrine.
   1. Apocrine sweat glands

      Nota:

      • Occur in the groin, anal region, axilla, and areola, and in mature males, in the beard. Respond to stress and sexual stimulation.
   2. Merocrine (eccrine) sweat glands

      Nota:

      • 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.
2. Sebaceous Glands

   Nota:

   • Produce an oily secretion call sebum.
3. Ceruminous Glands

   Nota:

   • Are found only in the external ear canal, where their secretion combines with sebum and dead epidermal cell to form earwax, or cerumen.
4. Mammary Glands

   Nota:

   • Are milk producing glands that develop within the female breast during pregnancy and lactation.

1. Second-degree burns

   Nota:

   • Involve the epidermis and part of the dermis but leave at least some of the dermis intact. Aka partial-thickness burns.
2. Third-degree burns

   Nota:

   • Also known as full-thickness burns because the epidermis, all of the derms, and often some deeper tissues (muscle and bone). are destroyed.
3. First-degree burns

   Nota:

   • Involve only the epidermis and are marked by redness, slight edema, and pain.