[5] Integumentary System

• The skin is an integral part of the integumentary system and consists of two types: thick skin which covers the palms of the hand and the soles of the feet, and thin skin which covers every other external surface of the body.
• The layers of the skin include the epidermis, the dermis, and the hypodermis.
• The epidermis is the outermost layer of the skin that is lined by stratified squamous keratinized epithelium.
• The dermis is the underlying layer of dense, irregular connective tissue that contains other structures such as hair follicles and sweat glands.
• The hypodermis is the innermost layer of varying thickness of loose connective and adipose tissue.
• The functions of the epidermis include protecting the body from harmful influences from the environment and protecting the body against water loss.
• The layers of the epidermis from superficial to deep are Stratum Corneum, Stratum Lucidum, Stratum Granulosum, Stratum Spinosum, Stratum Basale, and Mnemonics: Come Let’s Get Sun Burned.
• Stratum Basale is one layer of mitotically active cuboidal cells that is attached to the basement membrane by hemidesmosomes and integrins, and is attached to each other by desmosomes.
• Stratum Spinosum has several layers of polyhedral cells that are attached to each other by desmosomes at the tips of short projections containing bundled keratin, or tonofibrils.
• Stratum Granulosum is a thinner layer of flattened keratinocytes that are densely filled with keratohyalin granules containing flaggrin, and other proteins binding the tonofibrils.
• Stratum Corneum is the most superficial layer that protects against water loss, friction, and microbial invasion, and consists of flat, terminally differentiated cells, or squames, which are slowly lost.
• Stratum Lucidum consists of several layers of flattened dead cells, with faint nuclear outlines visible in only a few cells, and is usually only visible in thick skin; hard to identify in thin skin.
• Merocrine sweat glands are for the regulation of body temperature, while Apocrine sweat glands produce a milky, proteinaceous, and odorless secretion.
• Epidermal appendages include hair follicles of terminal hair that span the entire dermis and usually extend deep into the hypodermis, nails formed in a manner similar to hairs, sebaceous glands that secrete sebum onto hair in the follicles or pilosebaceous units, and have only limited antibacterial, antifungoid activity, and sweat glands distinguished by their secretory mechanism.
• The Dermis is the thick layer of connective tissue to which the epidermis is attached, found immediately below the epidermis, and has two sublayers: the Papillary Layer, a more superficial sublayer composed of areolar connective tissue that forms the dermal papillae, and the Reticular Layer, a thicker layer made up of dense irregular connective tissue.
• Photoreceptors respond to light.
• In mammals other than humans, the odor is important for sexual attraction.
• Free nerve endings, the simplest and most common type of receptor, detect for pain, temperature, and movement (proprioception).
• Mechanoreceptors respond to mechanical stimuli such as compression, bending or stretching.
• Nociceptors, or pain receptors, respond to painful mechanical, chemical, and thermal stimuli.
• The scalp is considered thin skin.
• Thermoreceptors respond to temperature changes.
• Melanocytes within the stratum basale producing melanin are located in brown skin.
• Touch Receptors include Merkel disks, hair follicle receptors, Meissner corpuscle, Ru ffini end organs, Pacini corpuscles.
• Arrector pili, smooth muscles, contracts causing the hair to stand erect, and a "goosebump" forms on the skin.
• Hair Follicle, usually oriented at an angle towards the surface of the scalp, is located in the scalp.
• Sensory receptors, nerve endings or specialized cells capable of responding to stimuli by developing action potentials, are located in the skin.
• Odor produced is due to bacterial decomposition.
• Free nerve endings of nociceptor respond to noxious stimuli, temperature, and are found around the hair roots and under surface of skin.
• Proprioceptors provide awareness of body position and movements.
• Transverse section of hair follicle reveals the following structures: Cuticle, Hair bulb, connective tissue sheath, and several sebaceous glands.
• Reticular Layer, which extends up until the subcutaneous layer, is located lower to the subcutaneous layer are the skeletal muscles.
• Free nerve endings of hair root sense for hair movement and synapse with unmyelinated nerve endings.
• Dermal Papillae, another name for papillary layer, is located in the scalp.
• Fibroblasts are seen as flattened cells around 20 concentric lamellae.
• Variable adaptation is a characteristic of free nerve endings of hair root.
• Meissner Corpuscle are embedded around
• Eccrine Glands exhibit smaller lumens, while Apocrine Glands exhibit larger lumens.
• Meissner Corpuscle are seen in the dermal papillae and are sensitive to light and touch.
• Chemoreceptors respond to chemicals or odor molecules.