Integumentary System Pt 1

• Skin is composed of the epidermis and dermis, which sit on top of the hypodermis
• The epidermis is composed of keratinized squamous epithelium, made of 4-5 layers
• Thick skin contains a 5th layer of epithelium called stratum lucidum
• The layers of the epidermis (starting superficially): Stratum corneum, stratum lucidum, stratum grandulosum, stratum spinosum, and stratum basale
• Stratum basale is a single layer of cuboidal mitotic stem cells that become keratinocytes, this layer forms epidermal ridges, for example, fingerprints
• Stratum spinous contains 8-10 layers of keratinocytes and has the greatest amount of melanin granules and dendritic cells
• Stratum granulosum only contains 3-5 layers of flattens cells, also in this layer, cells are undergoing keratinization, causing their organelles to disintegrate
• Keratohyaline granules, found in the stratum granulosum, aid in cell dehydration, cross-linking keratin filaments, and keratinization
• Stratum lucidum consists of 2-3 layer of flat, dead keratinocytes with a clear appearance due to eleidin, and is present only in thick skin
• Stratum corneum is 20-30 layers of horny scales made up of dead keratinocytes and accounts for 3/4 of epidermal thickness, this layer also secretes defensins
• The epidermis is replaced every 25-45 days
• The cells that make up the epidermis are keratinocytes, Merkel cells, langerhans cells, and melanocytes
• Keratinocytes are the most abundant cell type in the epidermis
• Merkel cells are touch receptors whose membranes interact with with free nerve endings
• Langerhans cells are dendritic cells and epidermal macrophages
• Melanocytes are located between cells of stratum basale and produce melanosomes in response to UVB light
• Melanocytes release vesicles called melanosomes that contain melanin, which are phagocytized and donate pigment to keratinocytes
• Albinism is a lack of melanin that leaves an individual defenseless against UV rays
• Vitiligo is when melanocytes dies or are unable to function due to an autoimmune origin
• Cyanosis is caused by disorders of deoxygenated hemoglobin and is characterized by a bluish color
• Jaundice is a condition where the skin and eyes are yellow due to an excess of bilirubin
• Carotenemia is a yellow-orange skin tone due to high carotene levels in the blood
• The dermis contains a papillary layer and a reticular layer
• The papillary level of the dermis is 20% of the dermis and is areolar connective tissue with collagen and elastic fibers, it contains projections called dermal papillae, capillary loops, and nerve endings
• Fingerprints are made by epidermal ridges projecting into dermal papillae, which helps increase surface area and friction
• Cleavage (tension) lines are formed by collagen and elastic fibers in the dermis, and are arranged in parallel bundles, in order to resist force in a specific direction
• In the dermis, the root hair plexus detects hair movement
• In the dermis, the lamellated corpuscle detects deep pressure
• In the dermis, the tactile corpuscle in the papillary layer detect light pressure
• In the dermis, the Ruffini corpuscle detects warmth
• In the epidermis, meissner's corpuscle detects sustained pressure
• The reticular layer of the dermis is 80% of dermis thickness and is made of dense irregular connective tissue, it also contains collagen and elastin
• The hypodermis is made of adipose and areolar tissue and used for shock absorption, insulation, and energy storage, and it is superficial fascia that anchors skin to the underlying structures
• The integumentary system functions as protection as a chemical barrier, physical barrier, and biological barrier
• The integumentary system functions as thermoregulation through dilation/constriction of blood vessels and sweat gland activity
• The integumentary system functions as cutaneous sensory reception in temperature reception, touch, pressure, and pain reception
• The integumentary system has metabolic functions through synthesis of vitamin D precursor and activation of steroid hormones
• The integumentary system functions as a blood reservoir and in excretion of salt and nitrogenous waste