Integumentary System

• Integumentary System


  The largest single organ of the body, comprising 15%-20% of total body weight
• Dexter Giovanni Arellano Andales, RMT, MD, MBA, FPCP is from the University of Cebu, College of Medical Technology and College of Psychology
• Skin / integument / cutaneous layer


  • The largest single organ of the body
  • 15%-20% of total body weight

  
• Skin structures


  • Epidermis
  • Dermis
  • Dermal papillae

  
• Epidermal derivatives


  • Hairs
  • Nails
  • Sebaceous glands
  • Sweat glands
• Hypodermis / subcutaneous tissue


  Loose connective tissue layer containing pads of adipocytes, binds the skin loosely to the underlying tissues

  
• Functions of the Skin


  • Protective
  • Sensory
  • Thermoregulatory
  • Metabolic
  • Sexual signaling
• Dermal-epidermal interdigitations


  • Peg-and socket
  • Well-formed ridges and grooves in the thick skin of the palms and soles
  • Form distinctive patterns unique for each individual (dermatoglyph)

  
• Epidermis


  Stratified squamous epithelium, keratinizing type, avascular, nourished by diffusion of substances from the connective tissue
• Cell types in the Epidermis


  • Keratinocytes
  • Melanocytes
• Keratinocytes


  Cells that make up the bulk of the epidermis, undergo a series of transformation into dead scales
• Melanocytes


  Responsible for production of melanin, found in the stratum basale, melanin protects the cells of the skin from ultraviolet radiation from the sun
• Layers of Epidermis (Thick Skin)


  • Stratum basale (stratum germinativum)
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum

  
• Stratum basale


  Basal layer, single layer of basophilic cuboidal or columnar cells on the basement membrane, intense mitotic activity, contains progenitor cells for all the epidermal layers
• Stratum germinativum


  Stratum basale and stratum spinosum, cells may still divide in this combined zone
• Stratum spinosum


  Spinous layer, the thickest layer, polyhedral cells having central nuclei with nucleoli and cytoplasm actively synthesizing keratins
• Stratum granulosum


  Granular layer, three to five layers of flattened cells undergoing keratinization, cytoplasm filled with intensely basophilic keratohyaline granules

  
• Stratum lucidum


  Found only in thick skin, thin, translucent layer of flattened eosinophilic keratinocytes with nuclei and organelles lost

  
• Stratum corneum


  15-20 layers of squamous, keratinized cells filled with birefringent filamentous keratins, continuously shed at the epidermal surface

  
• Melanocytes


  Specialized cells of the epidermis found among the cells of the basal layer and in hair follicles, produce eumelanins (brown or black pigments) and pheomelanin (similar pigment found in red hair)
• Langerhans Cells


  Antigen-presenting cells derived from monocytes, 2%-8% of the cells in epidermis, bind, process, and present antigens to T lymphocytes
• Merkel Cells


  Epithelial tactile cells, low-threshold mechanoreceptors sensing gentle touch, found in the basal epidermal layer
• Dermis


  Layer of connective tissue that supports the epidermis and binds it to the subcutaneous tissue (hypodermis), surface has many projections (dermal papillae) that interdigitate with the epidermis

  
• Sublayers of the dermis


  • Papillary layer
  • Reticular layer

  
• Papillary layer


  Thin layer including the dermal papillae, consists of loose connective tissue with fibroblasts, mast cells, dendritic cells, and leukocytes

  
• Reticular layer


  Thicker layer consisting of dense irregular connective tissue (type I collagen), more fibers and fewer cells than the papillary layer, also contains elastic fibers and abundant proteoglycans

  
• Hypodermis (subcutaneous tissue)


  Adipose tissue layer, not part of the skin, provides looseness and mobility of the skin, insulates the deeper tissues from extreme temperature

  
• Unencapsulated sensory receptors


  • Merkel cells
  • Free nerve endings
  • Root hair plexuses
• Meissner corpuscles


  Elliptical structures in the dermal papillae, sensory axons winding among flattened Schwann cells, detect light-touch or low-frequency stimuli, numerous in the fingertips, palms, and soles
• Unencapsulated sensory receptors


  • Merkel cells
  • Free nerve endings
  • Root hair plexuses
• Merkel cells


  • Associated with expanded nerve endings
  • Sustained light touch and for sensing an object's texture
• Free nerve endings


  • In papillary dermis and lower epidermal layers
  • Detect high and low temperatures, pain, and itching
  • Tactile receptors
• Root hair plexuses


  • Surrounding the bases of hair follicles in the reticular dermis
  • Detects movements of the hairs
• Meissner corpuscles


  • Elliptical structures
  • 30-75 μm by 50-150 μm
  • Sensory axons winding among flattened Schwann cells arranged perpendicular to the epidermis in the dermal papillae
  • Detect light-touch or low-frequency stimuli
  • Numerous in the fingertips, palms, and soles
  • Decline slowly in number during aging after puberty
• Pacinian / lamellated corpuscles


  • Large oval structures (0.5 mm by 1 mm)
  • In reticular dermis and hypodermis
  • Outer capsule and 15-50 thin, concentric lamellae of flattened Schwann cells and collagen surrounding a highly branched, unmyelinated axon
  • Sensing coarse touch, pressure (sustained touch), and vibrations
  • Found in the wall of the rectum and urinary bladder
• Krause end bulbs


  • Encapsulated, ovoid structures
  • Thin, collagenous capsules penetrated by a sensory fiber
  • Found in the skin of the penis and clitoris where they sense low-frequency vibrations
• Ruffini corpuscles


  • Collagenous, fusiform capsules
  • Stimulated by stretch (tension) or twisting (torque) in the skin
• Hairs


  • Elongated keratinized structures that form within epidermal invaginations (hair follicles)
  • Hairless areas: palms, soles, lips, glans penis, clitoris, labia minora
  • Grow discontinuously, with periods of growth followed by periods of rest
• Hair bulb


  • Terminal dilation of the hair follicle
  • Dermal papilla inserts into the base and contains a capillary network
  • Keratinocytes cover the dermal papilla and form the matrix of the elongating hair root
• Hair shaft


  Part of a hair extending beyond the skin surface