HISTO

• Functions of the Integumentary System

  • Body temperature regulation
  • Protection from external environment
  • Cutaneous sensations
  • Excretion and absorption
  • Vitamin D synthesis
• Vitamin D


  A group of soluble secosteroids responsible for enhancing intestinal absorption of calcium and phosphate
• Vitamin D synthesis


  Body can synthesize vitamin D in the skin from cholesterol when exposed to the sun
• Skin


  The largest organ of the body
• Principal parts of the skin

  • Epidermis
  • Dermis
• Epidermis


  • A keratinized stratified squamous epithelium
  • Forms the major distinction between thick and thin skin (refer to the thickness of epidermal layer)
• Principal cell types in the epidermis

  • Keratinocytes
  • Melanocytes
  • Langerhans cells
  • Merkel cells
• Keratinocytes


  90% of epidermal cells, produce the protein keratin, produce lamellar granules
• Melanocytes


  8% of epidermal cells, located at the basal layer, produce the pigments eumelanin and pheomelanin
• Langerhans cells


  Arise from red bone marrow and migrate to the epidermis, participate in immune responses as antigen presenting cells
• Merkel cells


  The least numerous of the epidermal cells, located in the deepest layer of epidermis where they contact the sensory neuron known as Merkel or tactile disc, essential for light touch sensation
• Layers of the epidermis

  • Stratum corneum
  • Stratum lucidum
  • Stratum granulosum
  • Stratum spinosum
  • Stratum basale
• Stratum corneum


  Consists of 20-30 layers of dead flat keratinocytes, contains keratohyalin and lamellar granules, effective water repellent barrier and protects against injury and microbes
• Stratum lucidum


  Present only in thick skin, consists of 2-3 layers of clear, flat dead keratinocytes that contain densely packed intermediate filaments and thickened plasma membranes
• Stratum granulosum


  Consists of 3-5 layers of flattened keratinocytes, contains basophilic granules of keratohyalin and lamellar keratohyalin, forms a lipid rich impermeable layer around the cell
• Stratum spinosum


  Superficial to the stratum basale, thickest layer especially in epidermal ridges, where 8-10 layers of polyhedral keratinocytes fit closely together, bundles of intermediate filament tightly join the cells
• Stratum basale


  The deepest layer of the epidermis, characterized by intense mitotic activity, single row of basophilic cuboidal or columnar keratinocytes, melanocytes and merkel cells scattered among the keratinocytes
• Dermis


  • Second deeper part of the skin, composed of connective tissue containing collagen and elastic fibers, includes cells such as fibroblasts, macrophages, and some adipocytes, blood vessels, nerves, glands, and hair follicles are embedded in dermal tissue
• Regions of the dermis

  • Papillary region
  • Reticular region
• Papillary region


  The superficial portion of the dermis, consist of areolar connective tissue with elastic fibers & small fine type I & III collagen fibers, fibroblasts, macrophages and other WBCs, contain dermal papillae and mechanoreceptors like Meissner's corpuscle and free nerve endings
• Reticular region


  Deeper portion of dermis, consists of dense irregular connective tissue containing more coarsely textured bundles of collagen and some elastic fibers, combination of collagen and elastic fibers provides the skin with extensibility and elasticity
• Functions of the connective tissue of the dermis

  • Provide mechanical strength for skin
  • Serve as substrate for diffusion of nutrients and wastes
  • Carry out immune surveillance
  • Capable of active response to injury
• Types of skin


  • Thin skin
  • Thick skin
• Thin skin


  • Covers all parts of the body except palms, palmar surfaces of the digits, and soles, epidermis is thin, lacks stratum lucidum, has fewer dermal papillae and epidermal ridges, has hair follicles, arrector pili muscle and oil glands but fewer sweat glands, sparser distribution of sensory receptors
• Thick skin


  • Covers palms, palmar surfaces of digits and soles, thick epidermis with stratum lucidum and thicker stratum spinosum and corneum, more numerous dermal papillae thus has epidermal ridges, lacks hair follicles, arrector pili, sebaceous glands, has more sweat glands, displays blood vessels and adipose tissues, sensory receptors are more densely clustered
• Types of mechanoreceptors


  • Unencapsulated
  • Encapsulated
• Unencapsulated mechanoreceptors


  • Tactile / Merkel disc
  • Free nerve endings
  • Root hair plexus
• Tactile / Merkel disc


  Type 1 cutaneous mechanoreceptor, for tonic receptors: for light touch and for sensing an object's texture
• Free nerve endings


  In papillary dermis, respond to high and low temperature, pain & itching, also function as tactile receptors
• Root hair plexus


  Surrounds bases of hair follicles in reticular dermis, detects movement of hair
• Encapsulated mechanoreceptors


  • Meissner's corpuscle
  • Pacinian corpuscle
  • Krause end bulbs
  • Ruffini corpuscles
• Meissner's corpuscle


  Encapsulated endings in dermal papillae, most common in palmar and plantar skin, especially in fingertips
• Pacinian corpuscle


  Located deeper in dermis, also found in tissue organs deep in the body including wall of rectum and urinary bladder, ovoid structures resembling small onions, respond to deep pressure, vibration and coarse touch
• Krause end bulbs


  Found in skin of penis and clitoris where they sense low frequency vibration
• Ruffini corpuscles


  Have collagenous, fusiform capsules, with sensors
• Mechanoreceptors


  • Unencapsulated
  • Encapsulated
• Unencapsulated mechanoreceptors


  • Tactile / Merkel disc
  • Free nerve endings
  • Root hair plexus
• Tactile / Merkel disc


  Type 1 cutaneous mechanoreceptor, for tonic receptors, for light touch and for sensing an objects texture
• Free nerve endings


  In papillary dermis, respond to high and low temperature, pain & itching, function also as tactile receptors
• Encapsulated mechanoreceptors


  • Meissner's corpuscle
  • Pacinian corpuscle
  • Krause end bulbs
  • Ruffini corpuscles