integumentary

Includes the skin and its derivatives (Hair nails and glands). Accounts for about 7% of our body weight, and varies in thickness throughout the body

Dermatology

 

Functions of the Skin

  • Protection - provide a physical barrier from bacterial and viral invasion. Also resists physical trauma to the body

    • Provide chemical protection by secreting melanin and natural antibiotics (dermcidin and defensin)

    • Provide biological protection by producing cells (langerhans cells) that are involved in immune responses

  • Thermoregulation - via sweat production or removing blood from the skin to conserve heat

  • Cutaneous sensation - sensory receptors located throughout the skin. Part of the nervous system and function by detecting and responding to stimuli on the surface of skin and external to the skin

  • Vitamin D production - this begins when UV light strikes special molecules in the skin. Travels to kidneys and liver where its converted into the active form of Vit D (calcitrol)

  • Blood Reservoir - skin can store large supplies of blood

  • Immunity

  • Excretion of waste via sweat. Salt and ammonia

  • Water retention - skin prevents the body from losing water to its surroundings, and prevents absorption of excess water by the body

  • Nonverbal communication - facial muscles move the skin to create expression

 

Epidermis - outer layer of the skin. Composed of keratinized stratified squamous epithelium

  • 5 types of cells in Epidermis

    • Melanocytes - synthesize and store melanin. Found in the deepest layers of the skin

      • Melanin is stored in special storage structures called melanosomes

      • Melanosomes accumulate on the sunny side of keratinocytes to protect them from UV light

    • Keratinocytes - produce the protein keratin which forms a protective layer over the skin

      • Most numerous types of cells in the epidermis. Millions rub off daily, fully replaced in 25-45 days

      • Dead at maturity. Store keratohyalin, precursor to keratin

    • Langerhans Cells - arise from bone marrow and migrate to epidermis. Macrophages that help activate our immune system. Easily damaged by UV, Dendritic Cells.

      • Present fragments of a pathogen to other leukocytes, creating an immune response against the invader.

      • Most removal/destruction occurs in lymph nodes

    • Merkel Cells

      • Located deep in the epidermis and are involved in detecting tactile stimuli. These are referred to as tactile cells

        • More common in areas of the skin that do not contain hair

        • Merkel cells are always associated with a nerve ending known as a Merkel (tactile) disc

    • Stem cells - located in the deepest layers of the epidermis. These divide and develop into keratinocytes

  • Layers of the epidermis (deep tosuperficial)

    • Stratum basale - 1 layer thick. Contains stem cells that divide to produce the cells listed above as well as the epidermal deratives (nails hair glands)

    • Stratum spinosum - 8-10 layers thick. Cells in this layer are tightly packed together. Keratinocytes are actively dividing and push upward as they grow and mature

    • Stratum granulosum - 3-5 layers thick. Store keratohyalin, precursor to keratin

    • Stratum lucidum - very thin layer of cells that is only found in thick skin. This layer is dead bc it is too far away from a blood supply. Palms of hands, soles of feet

    • Stratum corneum - 25 cell layers thick. Most superficial layer.

      • Entirely dead cellls. Horny layer

      • Protects body from invaders

      • Dead keratinocytes flake off as dander. Dandruff is dead keratinocytes and sebum (oil)

      • Epidermal regions that contain a stratum corneum are referred to as thick skin

  • Keratinization - process in which cells develop in the Stratum Basale and migrate upwards over time

    • This process allows for the formation of new cells throughout the epidermis.

    • Takes 2-4 weeks for new cells to reach stratum corneum

    • Process regulated by the hormone Epidermal Growth Factor (EGF)

    • In this process, an epidermal water barrier develops between the stratum granulosum and the stratum spinosum. This layer aids in retaining water for the body and prevents dehydration

    • Dander - dead keratinocytes that flake off.

 

Dermis - deeper portion of the skin. Composed of flexible, strong connective tissue which contains abundant collagen fibers

  • Dermis contains an extensive nerve and blood supply

  • Layers of the Dermis:

    • The Papillary Layer - composed of areolar connective tissue with numerous collagen fibers

      • Dermal papillae - projections associated with the papillary region. Extend upward into epidermis. Dermal papillae contain nerve endings and capillaries

        • When capillaries in this layer are damaged by friction or burns, they can leak out of the capillaries to form blisters

        • On the palms and soles, dermal papillae form upward projections known as dermal ridges, which form friction ridges aka fingerprints. They are genetically determined, and help us grip objects

        • Meissners corpuscles - located in dermal papillae. Involved in detecting touch

    • The reticular layer - makes up bulk of dermis. Provides skin with extensibility and elasticity

      • Striae - small tears in this layer, known as stretch marks

      • Pacinian corpuscles-  nerve endings, sensitive to pressure change

    • Subcutaneous layer - composed of areolar and adipose tissue that sits between the dermis and underlying muscles &tissue. Aka Hypodermis

      • Source of stored energy for both skin and muscle cells, insulates the body infants and older adults have less adipose tissue in their subcutaneous layer and are more sensitive to cold

  • Skin Markings

    • Friction ridges - dermal papillae. Fingerprints

    • Flexion lines - lines on the flexor surfaces on digits, palms, wrists, and elbows. Mark where the skin folds during flexion of joints

 

Pigments that provide us with our skin color patterns

  • Melanin - brown/black pigment. Stored in melanocytes

    • All individuals have the same number of melanocytes, but differences in color are caused by differences in the amount of melanin in the melanocytes. Primary pigment in humans

    • Protects skin and body from high levels of UV

    • Freckles - form when melanin accumulates in patches

    • Albinism - inherited inability of a person to produce melanin

    • Vitiligo - partial loss of melanocytes from a small portion of skin

    • A mole - elevated patch of melanized skin, often with hair

  • Carotene - yellow/orange pigment. Can be converted to vitamin A which aids in vision, skin growth and development

  • Hemoglobin - red pigment in blood

  • Skin color clues:

    • Cyanosis, jaundice

    • Erythema, pallor/blanching

    • Bronzing and bruises

  • Hemangiomas - red clusters on the skin. Color is the result of accumulation of numerous BV in a particular area

 

Epidermal Derivatives - all develop from the embryonic epidermis, and all play a role in maintaining body homeostasis

  • Glands - 2 types associated with the skin

    • Sudoriferous (sweat) glands - 2.5 million of these over the entire human body

    • 2 types of sudoriferous glands

      • Eccrine sweat glands - most numerous type of sweat gland, more numerous on palms, soles, and forehead

      • Apocrine sweat glands - located in the axillary region and open directly into hair follicles. Activated by nerves during pain and stress. Exact function is unclear

    • Perspiration - cools the body and removes nitrogenous wastes

      • 99% water but also includes salt, urea, uric acid

      • Sweat production and release is regulated by the hypothalamus

    • Specialized sweat glands

      • Ceruminous glands - modified apocrine sweat glands that line the external ear canal. These produce cerumen (earwax) which serves as a protective barrier in the ear

      • Mammary glands secrete milk after childbirth

  • Sebaceous (oil) glands - located all over the body except for on the palms and soles. Glands open into hair follicles

    • Sebum is oil that is secreted by sebaceous glands. Functions of sebum include softening and lubricating the hair and skin, reducing water loss from the skin, and preventing bacterial growth on the surface of the skin

    • The secretion of sebum is stimulated by hormones (esp sex hormones)

    • Acne - inflammation of sebaceous glands that leads to the formation of pimples

    • Blackheads - occur when some bacteria begin feeding on sebum

    • Seborrhea - overactive sebaceous glands on the skull of an infant. Known as cradle cap

  • Nails - located at the ends of fingers and toes

    • The major parts of nails include the body, root, lunula, cuticule, and free edge

  • Hair (pili - mostly composed of dead, keratinized cells

    • Hair anatomy:

      • Shaft, hair root, hair follicle

      • Bulb - enlarged region at the base of the hair follicle. This contains the Papilla of the Hair which houses blood vessels and oil glands

    • Arrector pili muscle - smooth muscle fibers that connect the follicle to the underside of the epidermis. Muscle pulls the hair upright to form dimples on the skin

    • Hair growth is most influenced by nutrition and hormone (esp testosterone)

    • Alopecia - hair thinning or balding

    • Male pattern baldness

 

Skin Wound Healing - 2 types

  • Epidermal wound healing - involves abrasion of the epidermis. In this process, stem cells in the Stratum Basale enlarge and migrate across the wound, thus covering the site of injury

  • Deep wound healing - involves damage to the dermis. Phases in this type of healing include:

    • Inflammatory phase - inflammation occurs to kill microbes, blood clots form here as well

    • Migratory phase - a scab forms and cells begin to fill in under the scab

    • Proliferative phase - epithelial cells grow under the scab

    • Maturation phase - scab falls off

 

Skin Cancer

  • Basal cell carcinoma - least malignant and most common type of skin cancer. Most common in areas exposed to direct sunlight, easily treated

  • Squamous cell carcinoma - arises from keratinocytes in the stratum spinosum. Can grow and spread quickly. Early detection, surgical removal and radiation are all effective ways to cure

  • Melanoma - cancer of melanocytes. Rare but incidence is increasing. Early detection is critical in treating melanoma.

  • ABCD rule - asymmetrical, border, color, diameter

 

Burns

  • First, second, third degree

 

Clinical Terms/Disorders

  • Albinism - genetic inability to produce melanin

  • Boils and Carbuncles - bacterial infection of the skin that extends into the subcutaneous layer

  • Cold sores - herpes infection that accumulates around moist or mucus regions of the body

  • Contact dermatitis - redness and itching f the skin due to chemicals that come in contact with the skin

  • Decubitis (bed sores) - reduced blood flow to regions over a bony prominence. Often leads to tissue death (gangrene)

  • Impetigo - light red rash that is bacterial in nature

  • Eczema - itchy, weeping skin lesions. Eczema is typically the result f an allergic reaction