Chapter 6 (1)

• The Integumentary system consists of the skin and accessory organs; hair, nails, and cutaneous glands. Inspection of the skin, hair, and nails is a significant part of a physical exam and the skin is the most vulnerable organ as it is exposed to radiation, trauma, infection, and injurious chemicals.
• The integumentary system receives more medical treatment than any other organ system. Dermatology is the scientific study and medical treatment of the integumentary system.
• With the skin and subcutaneous tissue, the skin is the body’s largest and heaviest organ. It composes 15% of body weight.
• The layers of the skin are the epidermis (stratified squamous epithelium), dermis (deeper connective tissue layer), and hypodermis (connective tissue layer below the dermis. It is NOT part of the skin but associated with it).
• Skin thickness ranges from 0.5 to 6 mm. Thick skin covers the front of the hands, and bottoms of the feet. Thick skin has sweat glands, but no hair follicles or sebaceous (oil) glands. The epidermis here in thick skin is 0.5 mm thick. Thick skin has 5 layers (strata) the fifth one being Stratum lucidum.
• Thin skin covers the rest of the body. It possesses hair follicles, sebaceous glands, and sweat glands. The epidermis is about 0.1 mm thick. Thin skin has four layers (strata) meaning NO Stratum lucidum.
• The functions of the Skin: Resistance to trauma andinfection (Keratin, Dermacidin and defensins, Acid mantle), Vitamin D synthesis, Sensation, Thermoregulation (Thermoreceptors, Vasoconstriction/vasodilation, Perspiration), Nonverbal communication (Facial expression, Importance in social acceptance and self-image), and Other barrier functions (Water, UV radiation, Harmful chemicals)
• The skin carries out the first step of vitamin D synthesis and the liver and kidneys complete the process. The skin is an extensive sense organ. They (skin) is/are receptors for temperature, touch, pain, and more.
• The Epidermis is keratinized stratified squamous epithelium. It includes dead cells at the skin surface and is packed with tough keratin protein. It lacks blood vessels and depends on the diffusion of nutrients from underlying connective tissue. The epidermis also contains sparse nerve endings for touch and pain.
• There are five epidermal cell types: Stem cells, Keratinocytes, Melanocytes, Tactile cells, and Dendritic cells.
• Stem cells are undifferentiated cells that give rise to keratinocytes and are found in the deepest layer of the epidermis (stratum basale). Keratinocytes are a great majority of epidermal cells and they synthesize keratin. Melanocytes make melanin that shields DNA fromultraviolet radiation and while they occur only in stratum basale they have branched processes that spread among keratinocytes and distribute melanin.
• Tactile cells are touch receptor cells associated with dermal nerve fibers. They are found in the basal layer of the epidermis. Dendritic cells are macrophages originating in the bone marrow that guardagainst pathogens. They are found in the stratum spinosum and granulosum.
• Layers of the Epidermis: Stratum basale (deepest epidermal layer), Stratum spinosum, Stratum granulosum, Stratum corneum (surface layer), and Stratum lucidum.
• The stratum basale is the deepest epidermal layer. It is a single layer of stem cells and keratinocytes resting on the basement membrane. Stem cells divide and give rise to keratinocytes that migrate toward the skin surface to replace lost cells. It also contains a few melanocytes and tactile cells.
• Stratum spinosum has several layers of keratinocytes joined together by desmosomes and tight junctions. It is named for the appearance of cells after histological preparation (hence it being called spiny). It also contains some dendritic cells.
• Stratum granulosum has three to five layers of flat keratinocytes. Its cells contain dark-staining keratohyalin granules.
• Stratum corneum is the surface layer and it has several layers (up to 30) of dead, scaly, keratinized cells. It resists abrasion, penetration, and water loss.
• Stratum lucidum is a thin, pale layer found only in thick skin. It is keratinocytes packed with clear protein eleidin.