Bio 141: Human Anatomy and Physiology Chapter 5: Integumentary System I. Overview of the Integumentary System a. Organ: b. Organ System: c. Skin Structure: i. Epidermis: ii. Dermis: iii. Hypodermis (also called “Subcutaneous Layer” or “Superficial Fascia”; not actually part of skin): d. Main Functions of Integumentary System i. Protection 1. Mechanical trauma: 2. Pathogens: 3. Environment: ii. Sensation: iii. Thermoregulation: 1. Stimulus: 2. Receptor: 3. Control Center: 4. Effector/Response:
iv. Excretion: v. Vitamin D synthesis: II. The Epidermis a. Superficial layer b. Made of stratified squamous epithelium; 95% of the cells in the epidermis are keratinocytes c. Lacks blood vessels d. Anchored to underlying dermis by a basement membrane e. Functions include i. Protects against mechanical injury, against water loss, against effects of harmful chemicals, and against pathogens f. Five layers in thick skin (from deepest to most superficial) 1. Stratum basale (also known as stratum germinativum) 2. Stratum spinosum 3. Stratum granulosum 4. Stratum lucidum (only found in thick skin—palm of hand and sole of foot) 5. Stratum corneum g. Other cells of epidermis i. Dendritic (Langerhans) cells: located predominantly in the stratum spinosum layer ii. Merkel cells: scattered throughout the stratum basale iii. Melanocytes: located within the stratum basale h. Thick versus Thin Skin i. Thick skin found on palms of hands, soles of feel, palmar surface of fingers, and plantar surface of toes (where mechanical stresses are the greatest); contains stratum lucidum; other strata tend to be thicker as well; lacks hair follicles; contains numerous sweat glands ii. Thin skin is found everywhere else; lacks stratum lucidum and remaining four strata tend to be much thinner than in thick skin; contains abundant hairs, sebaceous glands, and sweat glands III. The Dermis a. Deep to the epidermis; anchors epidermis in place b. Highly vascular c. Contains sensory receptors d. Two distinct layers: i. Papillary Layer 1. Superficial layer of dermis (about 20% of the dermis’ total thickness) 2. Made of loose connective tissue 3. Ground substance contains collagen and elastic fibers 4. Contains phagocytes and fibroblasts
5. Houses dermal papillae , which are where capillaries (thin-walled blood vessels) and tactile (Meissner) corpuscles are usually located. a. Meissner corpuscles are sensory receptors that respond to light touch, light pressure and weak vibration stimuli ii. Reticular Layer 1. Deeper and thicker layer of dermis 2. Composed mostly of dense irregular connective tissue, which contains more collagen and elastic fibers in the ECM compared to papillary layer 3.
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