Integumentary System and Skin Pathology Comprehensive Study Guide

Overview of the Integumentary System

  • Definition of an Organ: An organ is defined as two or more kinds of tissues grouped together that work to perform specialized functions.

  • The Skin: The skin is the largest organ in the human body by weight.

  • System Composition: The integumentary system is comprised of the skin and its various accessory structures.

Functions of the Skin and Synthesis of Vitamin D

  • Primary Functions:

    • Maintenance of homeostasis.

    • Protection of internal structures.

    • Prevention of excessive water loss.

    • Regulation of body temperature.

    • Housing of sensory receptors.

    • Synthesis of various chemicals.

    • Excretion of small quantities of waste.

  • Vitamin D Synthesis and Importance:

    • Vitamin D is essential for the effective absorption of calcium.

    • Calcium Utility: Necessary for the health and function of teeth, bones, and nerves.

    • Synthesis Process:

    • Obtained through dietary intake or produced by cells in the digestive system as dehydrocholesterol.

    • Dehydrocholesterol is transported via the bloodstream to the skin.

    • Exposure to ultraviolet (UV) rays from the sun converts dehydrocholesterol into Vitamin D.

The Epidermis

  • General Characteristics:

    • Avascular: It lacks its own blood supply.

    • Tissue Type: Composed of stratified squamous epithelial tissue.

    • Melanocytes: Specialized cells that produce melanin, the pigment responsible for skin color.

    • Keratinization: The process where cells harden and die as they migrate upward toward the surface.

    • Physical Variance: The epidermis is thickest on the palms of the hands and the soles of the feet.

    • Basement Membrane: The layer that anchors the epidermis to the underlying dermis.

  • Layers (Strata) of the Epidermis (Superior to Deep):

    1. Stratum corneum: The outermost layer of dead, keratinized cells.

    2. Stratum lucidum: Found only in thick skin (palms and soles).

    3. Stratum granulosum.

    4. Stratum spinosum.

    5. Stratum basale: The deepest layer where cell division occurs.

  • Clinical Clinical Terms Related to the Epidermis:

    • Callus: Thickened skin due to persistent friction.

    • Corn: A localized thickening of the skin, usually on toes.

    • Decubitus ulcer: Also known as a pressure sore.

Skin Coloration Factors

  • Genetic Factors:

    • Differences in the amount of melanin produced.

    • Variations in the size of melanin granules.

    • Albinism: A genetic condition characterized by a total lack of melanin.

  • Environmental Factors:

    • Exposure to sunlight, UV light from sunlamps, and X-rays can darken existing melanin.

  • Physiological Factors:

    • Oxygenation: High blood oxygen or vessel dilation results in a reddish tint; low oxygen or vessel constriction results in a bluish tint (cyanosis).

    • Diet: Overconsumption of carotene can lead to a yellowish tint in the skin.

    • Health Conditions: Illnesses such as liver malfunction can cause jaundice (yellowing).

The Dermis and Subcutaneous Layer

  • The Dermis:

    • Dermal Papillae: Finger-like projections on the surface that increase surface area for the epidermis and form the basis for fingerprints.

    • Tissue Composition: Contains irregular dense connective tissue.

    • Included Structures: Smooth and skeletal muscle cells, nerve cell processes (such as Pacinian and Meissner's corpuscles), specialized sensory receptors, blood vessels, hair and nail follicles, and glands.

  • Subcutaneous Layer (Hypodermis):

    • Also referred to as the superficial fascia.

    • Located directly beneath the dermis (some definitions exclude it from the "skin" proper).

    • Composition: Contains loose connective tissue (areolar) and adipose (fat) tissue.

    • Functions: Serves primarily as insulation and houses major blood vessels that supply the skin.

Accessory Structures of the Skin

  • General Origin: These structures originate in the epidermis but may extend deep into the dermis.

  • Nails: Protective coverings for the ends of fingers and toes. Parts include:

    • Nail plate.

    • Nail bed.

    • Lunula: The whitish, half-moon-shaped region at the base of the nail.

  • Hair Follicles:

    • Hair is composed of epidermal cells that keratinize and die as they grow.

    • Color is determined by melanin produced in the follicle.

    • Components:

    • Hair Papilla: Contains blood vessels for nourishment.

    • Hair Root: The portion of the hair below the skin surface.

    • Hair Shaft: The visible portion of the hair.

    • Arrector Pili Muscle: A smooth muscle attached to the follicle that causes the hair to stand up (goosebumps).

  • Glands:

    • Sebaceous Glands: Usually associated with hair follicles; classified as holocrine glands (secretions include whole cells). They secrete sebum (oil) to keep skin and hair soft. They are absent on palms and soles and are the primary cause of acne.

    • Sudoriferous (Sweat) Glands: Widespread glands that originate deep in the dermis.

    • Eccrine Glands: Most common, found all over the body; not associated with hair follicles; function in temperature regulation.

    • Apocrine Glands: Found in axillary (armpit) and groin regions; associated with hair follicles; active during emotional stress.

    • Ceruminous Glands: Specialized glands producing earwax.

    • Mammary Glands: Specialized glands producing milk.

Temperature Regulation and Heat Balance

  • Basic Mechanics:

    • Normal Body Temperature: Approximately 37 ∘C37\,^\circ\text{C} (98.6 ∘F98.6\,^\circ\text{F}).

    • Control Center: The hypothalamus in the brain detects deviations and signals effectors.

  • Hyperthermia (Rise in Temperature):

    • Stimulus: Body temperature rises above normal.

    • Receptors: Thermoreceptors send signals to the hypothalamus.

    • Effectors: Skin blood vessels dilate (vasodilation) and sweat glands secrete.

    • Response: Heat is lost to surroundings; temperature returns to normal.

  • Hypothermia (Drop in Temperature):

    • Stimulus: Body temperature drops below normal.

    • Effectors: Skin blood vessels constrict (vasoconstriction) and sweat glands remain inactive.

    • Muscle Activity: If temperature continues to drop, the hypothalamus signals muscles to contract involuntarily (shivering) to generate heat.

    • Response: Heat is conserved and generated; temperature rises toward normal.

  • Heat Production and Loss:

    • Production: Heat is a byproduct of cellular metabolism. Most active producers include skeletal muscle, cardiac muscle, and the liver.

    • Loss Mechanisms:

    • Radiation: Heat loss to cooler surroundings.

    • Conduction: Heat loss via direct contact with cooler objects.

    • Convection: Heat loss to moving air currents.

    • Evaporation: Heat loss as water (sweat) changes from liquid to gas.

Wounds, Burns, and the Rule of Nines

  • Inflammation: The normal response to injury or stress.

    • Physiology: Blood vessels dilate and become more permeable, allowing fluids to leak into tissues.

    • Signs of Inflammation: Redness, Heat, Pain, Swelling.

  • Classification of Burns:

    • First-degree Burn: Superficial; involves only shallow layers of the epidermis.

    • Second-degree Burn: Involves the epidermis and some of the dermis; characterized by blisters and fluid escape; appearance is dark red to waxy white. Stem cells in the deep dermis survive to rebuild the skin.

    • Third-degree Burn: Destruction of the epidermis, dermis, and accessory structures. Skin appears dry and leathery (red, black, or white). Often requires skin grafts.

    • Autograft: Tissue from the same individual.

    • Allograft: Tissue from a different person (donor).

    • Skin Substitutes: Includes amniotic membrane, nylon, or other synthetic materials.

  • Rule of Nines (Body Surface Area Percentages):

    • Anterior and Posterior Head and Neck: 9%9\% (divided into 4.5%4.5\% anterior/4.5%4.5\% posterior).

    • Anterior and Posterior Trunk: 36%36\% (divided into 18%18\% anterior/18%18\% posterior).

    • Anterior and Posterior Upper Extremities: 18%18\% (divided into 9%9\% anterior/9%9\% posterior).

    • Anterior and Posterior Lower Extremities: 36%36\% (divided into 18%18\% anterior/18%18\% posterior).

    • Perineum: 1%1\%

    • Total: 100%100\%

Common Symptoms and Skin Carcinomas

  • Common Symptoms:

    • Pruritis: Itching.

    • Edema: Swelling.

    • Erythema: Redness.

  • Decubitus Ulcers: Localized areas of dead skin (necrosis) caused by a lack of blood supply due to pressure. They are difficult to heal. Prevention involves skin care, position changes every 2 hours2\,\text{hours}, special padding, and early ambulation.

  • Skin Carcinomas (Cancer):

    • Basal Cell Carcinoma (BCC): Most common type; arises from the deepest layer of the epidermis (stratum basale).

    • Squamous Cell Carcinoma (SCC): Arises from outer layers of the epidermis; serious form that may ulcerate, crust, and metastasize if advanced.

    • Malignant Melanoma: The most serious type of skin cancer. Usually manifests as a change in a new or existing mole.

  • ABCDEs of Malignant Melanoma:

    • A: Asymmetry.

    • B: Border irregularity.

    • C: Color (variations or multiple colors).

    • D: Diameter (greater than 1/4 inch1/4\,\text{inch} or 6 mm6\,mm).

    • E: Elevation (or Evolution).