Integumentary System Notes

I. General Information A. Organ system consists of a group of organs working together to perform a specific activity. B. Integumentary System: inte- =whole; gument = body covering = Composed of organs such as skin, hair, and nails. C. Skin (Cutaneous membrane) is the largest organ of the body in surface area and weight. (22 square feet; 10 pounds) D. Functions: Regulate body temperature, protection, detect sensations, excretion, absorption, and synthesis of vitamin D.

II. Structure of the Skin A. Superficial layer – epithelial tissue (epidermis) B. Deep layer – connective tissue makes up the dermis C. Subcutaneous (subQ) layer or (Hypodermis) – Deep to the dermis but not part of the skin. 1. Also called hypodermis 2. This layer consists of areolar and adipose tissues. 3. Anchoring fibers that extend from the dermis attach the skin to the subQ layer. 4. The deep layer of the subQ layer is attached to underlying tissue and organs 5. The subQ and dermis layers contain nerve endings called lamellated (pacinian) corpuscles, which are sensitive to pressure.

III. Epidermis A. Composed of keratinized stratified squamous epithelium B. Contains four types of cells 1. Keratinocytes a). 90% of epidermal cells are keratinocytes b). Arranged in four or five layers c). Produce keratin a tough protein that helps protect skin i. protection from heat, microbes, and chemicals d). Produce lamellar granules, which release a water- repellent sealant.

2. Melanocytes a). 8% of the epidermal cells are melanocytes b). Produce the pigment melanin (melano means black) c). Cytoplasmic extensions of the melanocytes extent between the keratinocytes. d). Melanocytes transfer melanin to the keratinocytes e). Melanin – is a yellow-red or brown-black pigment that gives skin color f). Melanin absorbs damaging ultraviolet (UV) light g). Melanocytes are more susceptible to UV damage than keratinocytes

3. Langerhans cells a). Participate in immune responses against microbes that invade skin b). Langerhans cells, macrophages, and B cells help other immune cells fight microbes. c). Langerhans cells are damaged by UV light. 4. Merkel cells a). Contact the flattened process of a sensory neuron called tactile (Merkel) disc. b). Merkel cells and tactile discs detect touch sensations

C. Five Layers of the Epidermis (Notes are from deep to superficial) 1. Stratum basale a). Single row of cuboidal or columnar keratinocytes b). Some stem cells are found in the stratum basale 2. Stratum spinosum a). Superficial to the stratum basale b). Eight to ten layers many-sided keratinocytes fitted closely together c). More superficial layers become flattened as cell migrate to the surface

3. Stratum granulosum a). Superficial to the stratum spinosum b). Located in the middle of the epidermis c). Three to five layers of keratinocytes that are undergoing apoptosis. i). Apoptosis – Genetically programmed cell death (nucleus fragments before cell dies) d). Nuclei and cell organelles degenerate/dissolve e). Keratinocytes contain mostly keratin and lamellar granules (No organelles) f). Lamellar granules release lipids (oils) as a water-repellent sealant.

4. Stratum lucidum a). Superficial to the stratum granulosum b). Present only in thick skin: fingertips, palms, and soles of foot. c). Three to five layers of flattened clear, dead keratinocytes d). Keratinocytes in this layer contain only keratin.

5. Stratum Corneum a). Superficial to the stratum lucidum b). 25 to 30 layers of flattened dead keratinocytes c). These cells are continuously shed and replaced by migrating keratinocytes from below. d). Multiple layers of cells in the stratum corneum protect deeper layers from injury. f). Constant friction to this layer will cause a callus. i. Callus – abnormal thickening of the stratum corneum

D. Keratinization 1. Newly formed cells in the stratum basale are pushed to the surface 2. As the cells move from one layer to another, keratin increases 3. Keratinized cells slough off when they reach the out layer of the stratum corneum. 4. Cells that are sloughed off are replaced by more keratinocytes from lower layers 5. It takes four weeks for a keratinocytes to form and migrate through the five layers. 6. Dandruff-excessive amount of keratinized cells shed from the skin of the scalp