Integumentary system

• The dermis is the lower layer of skin that provides structure, strength, and elasticity.
• The functions of the Integumentary System include protection, temperature regulation, elimination, synthesis, and sensation.
• The functions of the skin include protection, sensation, and thermoregulation.
• The Integumentary System consists of three major regions: the Epidermis, Dermis, and Hypodermis.
• The Epidermis, the outermost superficial region of the Integumentary System, is composed of keratinized stratified squamous epithelium, consisting of four distinct cell types and four or five layers.
• Cell types in the Epidermis include keratinocytes, melanocytes, Merkel cells, and Langerhans’ cells.
• The outer portion of the skin is exposed to the external environment and functions in protection.
• Keratinocytes in the Epidermis produce the fibrous protein keratin.
• Melanocytes in the Epidermis produce the brown pigment melanin.
• Langerhans’ cells in the Epidermis are epidermal macrophages that help activate the immune system.
• Merkel cells in the Epidermis function as touch receptors in association with sensory nerve endings.
• The deepest epidermal layer is firmly attached to the dermis and consists of a single row of the youngest keratinocytes.
• Cells in the deepest epidermal layer undergo rapid division, hence its alternate name, stratum germinativum.
• The layers of the Epidermis include Stratum Basale (Basal Layer), Stratum Spinosum (Prickly Layer), Stratum Granulosum (Granular Layer), and Stratum Lucidium (Clear Layer).
• The Stratum Basale (Basal Layer) of the Epidermis contains cells with a weblike system of intermediate filaments attached to desmosomes, and melanin granules and Langerhans’ cells are abundant in this layer.
• The Stratum Spinosum (Prickly Layer) of the Epidermis is thin, three to five cell layers in which drastic changes in keratinocyte appearance occurs, and keratohyaline and lamellated granules accumulate in the cells of this layer.
• The Stratum Granulosum (Granular Layer) of the Epidermis is thin, transparent, and superficial to the stratum granulosum, and consists of a few rows of flat, dead keratinocytes.
• Cutaneous sensation is provided by exoreceptors that sense touch and pain.
• The integumentary system serves as a protective barrier against chemical, physical, and mechanical threats.
• Vernix caseosa is a substance produced by sebaceous glands that protects the fetus’s skin in the amnion.
• Body temperature is regulated by dilation (cooling) and constriction (warming) of dermal vessels.
• Sweat glands increase secretions to cool the body.
• Melanoma is treated by wide surgical excision accompanied by immunotherapy.
• Melanoma is a cancer of melanocytes, the most dangerous type of skin cancer, and is characterized by the ABCD rule: asymmetry, border irregularity, color variation, and diameter larger than 6 mm.
• Basal cell carcinoma is the least malignant and most common skin cancer, caused by the proliferation and invasion of stratum basale cells.
• Burns can be classified into first-degree, second-degree, third-degree, and fourth-degree burns, each with different symptoms and severity.
• Lanugo is a downy coat of delicate hairs covering the fetus.
• Skin and hair become oilier and acne may appear after one reaches the 20s and 30s, skin shows the effects of cumulative environmental assaults.
• The integumentary system has excretory functions, limited amounts of nitrogenous wastes are eliminated from the body in sweat.
• The stages of wound healing are developmental aspects of the integument in fetal, adolescent to adult, and old age.
• In the fetal stage of development, the epidermis develops from ectoderm and the dermis and hypodermis develop from mesoderm.
• Squamous cell carcinoma arises from keratinocytes of stratum spinosum and is most often found on the scalp, ears, and lower lip.
• The integumentary system has metabolic functions such as the synthesis of vitamin D in dermal blood vessels.
• Scaling and dermatitis become more common in old age.
• The skin acts as a blood reservoir, storing up to 5% of the body’s blood volume in skin blood vessels.
• The Stratum Lucidium (Clear Layer) of the Epidermis is the outermost layer of keratinized cells, accounts for three quarters of the epidermal thickness, and functions in waterproofing, protection from abrasion and penetration, and renders the body relatively insensitive to biological, chemical, and physical assaults.
• The Dermis, the second major skin region containing strong, flexible connective tissue, includes fibroblasts, macrophages, and occasionally mast cells and white blood cells.
• The Dermis is composed of two layers – papillary and reticular.
• The Papillary Layer of the Dermis is areolar connective tissue with collagen and elastic fibers, and its superior surface contains peglike projections called dermal papillae.
• The Reticular Layer of the Dermis accounts for approximately 80% of the thickness of the skin, and collagen fibers in this layer add strength and resiliency to the skin, while elastin fibers provide stretch-recoil properties.