Integumentary

• skin - Cutaneous Layer
• Integument - covering
• Functions of the Skin

  1. Protection
  2. Sensory
  3. hermoregulatory
  4. Metabolic
  5. Sexual Signalling
•  TYPES OF SKIN:

  1. Thick Skin
  2. Thin Skin
• A.      Thick Skin – Covers the palms and soles [400 to 1400um (1.4 mm)]
• A.      Thin Skin – Covers the whole body except palms and the soles [varies from 75 to 150 um]
• GENERAL LAYERS OF THE SKIN:

  1. Epidermis
  2. Dermis
  3. Hypodermis
• EPIDERMIS  Primary Tissue Composition: Stratified Squamous Keratinized Epithelium
• EPIDERMIS - Lacks vasculature
• EPIDERMIS - o   Receives nutrients only from the dermis
• CELLS OF THE EPIDERMIS

  ·        Keratinocytes – Primary Cells

  ·        Melanocytes – Pigment producing Cells

  ·        Langerhans Cells – Ag-Presenting Cells

  ·        Merkel Cells – Sensory (Tactile Epithelial Cells)
• KERATINOCYTES - Primary Cells located at Epidermis
• KERATINOCYTES - Originate in the deepest layer of the epidermis, the stratum basale and move up to the final barrier layer of the skin, the stratum corneum
• Melanocytes


  • Located at basal epidermis
  • Neural Crest Derived
  • Pale-staining, rounded cell bodies
  • Synthesize dark melanin pigment in melanosomes
  • Protect nuclear DNA from UV damage
• Eumelanin


  Brown or black pigment; found in hair follicles
• Pheomelanin


  Red hair pigment
• Albinism


  • A condition wherein there are less melanin than usual in the body; condition that leads to having very light skin, hair, and eyes; Due to defect in the enzyme tyrosinase
• Vitiligo


  • A disorder that causes patches of skin to lose pigment or color; happens when melanocytes are attacked and destroyed
• Langerhans Cells


  • APC (Antigen Presenting Cells)
  • 2-8% of cells in epidermis
  • Located at spinous layer [stratum spinosum] of epidermis
  • Bind, process and present antigens to T-lymphocytes
• Merkel Cells


  • Aka Epithelial Tactile Cells
  • Mechanoreceptors for light touch
  • Abundant in fingertips and bases of some hair follicles
  • Characterized by small, Golgi-derived dense-core neurosecretory granules containing peptides
• Layers of the Epidermis

  • Stratum Corneum
  • Stratum Lucidum
  • Stratum Granulosum
  • Stratum Spinosum/Stratum Germinativum
  • Stratum Basale
• Stratum Corneum


  • 15-20 layers of dead, flattened, anucleate, keratin-filled keratinocytes called squames
  • Bound by hydrophobic lipid-rich segment that provides protection against friction and water loss
  • Protects against friction and water loss
  • Superficial
• Stratum Lucidum


  1. 3 layers of anucleate, dead cells; seen only in thick skin
• Stratum Granulosum


  • 3-5 layers of keratinocytes
  • Contains kerato-hyaline Granules
  • Contains lamellar granules
• Stratum Spinosum or Stratum Germinativum


  • THICKEST LAYER
  • Consists of generally polyhedral cells having central nuclei with nucleoli and cytoplasm actively synthesizing keratins
  • Several layers of keratinocytes all joined by desmosomes
  • Contains tonofibrils (keratin filament bundles)
  • Prickle Cells - Keratinocytes in our stratum spinosum
  • Cells may still divide
  • Langerhans cells present
  • Stratum Germinativum – combination of spinosum and basale; layer wherein stratum spinosum and stratum basal meet
• Stratum Basale


  • Single layer of cuboidal to low columnar cells in contact with basement membrane
  • Mitosis occurs here
  • Melanocytes and Merkel cells also present
• Dermis


  • Layer of connective tissue [Fibro-adipose tissue]
  • Supports epidermis and binds it to hypodermis [physically and metabolically]
  • Contains projections called dermal papillae; connects with epidermal ridges
  • Filled with blood vessels, nerves and sensory receptors
  • Basement Membrane - Connects dermis with epidermis
• Layers of the Dermis

  • Papillary Layer
  • Reticular Layer
• Papillary Layer


  • Connects to epidermis
  • More superficial layer of dermis
  • Contains subpapillary vascular plexus
  • Contains: Loose Connective Tissue, Type I and III Collagen, Mast cells, Dendritic cells, Fibrils of Type VII Collagen
• Reticular Layer


  • Thicker than Papillary Layer
  • Deeper layer of dermis
  • Dense irregular connective tissue surrounding hair follicles, skin glands, nerves, and deep plexus of blood vessels extending into subcutaneous layer
  • Contains: Dense connective tissue-mostly type I collagen, Fewer cells than papillary layer, Elastic fibers
• Subcutaneous Layer or Hypodermis


  • Layer beneath the dermis and usually consist of adipose tissue and loose connective tissue
  • Contains the larger vessels which supply and drain the dermal blood vasculature
• Unencapsulated Receptors

  • Merkel Cells - tonic receptors for sustained light touch and for sensing an object's texture
  • Free Nerve Endings - in the papillary dermis; respond primarily to high and low temperatures, pain, and itching
  • Root Hair Plexus - surrounding the bases of hair follicles in the reticular dermis that detects movements of the hairs
• Capsulated Sensory Receptors

  • Meissner Corpuscles - initiate impulses when there is light-touch or low-frequency stimuli against skin
  • Lamellated (Pacinian) Corpuscles - for detection of pressure or firm touch
  • Krause End Bulbs - simpler encapsulated, ovoid structures, with extremely thin, collagenous capsules penetrated by a sensory fiber
  • Ruffini Corpuscles - collagenous, fusiform capsules anchored firmly to the surrounding connective tissue
• Epidermal Appendages

  • Hair
  • Nails
  • Glands (Sweat Glands, Sebaceous Glands)
• Hair


  • Keratinized Structures forming within epidermal evaginations called hair follicles
  • All skin has at least minimal hair except the glabrous skin of the palms, soles, lips, glans penis, clitoris, and labia minora
  • Rapidly undergoing keratinization to form the medulla, cortex, and cuticle of a hair root
• Parts of Hair

  • Hair Bulb
  • Dermal Papilla
  • Hair Root
  • Arrector Pili Muscle
• Nails

  • Hard plates of keratin on the dorsal surface of each distal phalanx
  • Nail Root - Proximal part of the nail
  • Nail Plate - bound to a bed of epidermis, covered by a fold of skin, from which the epidermal stratum corneum extends as the cuticle, or eponychium
  • Nail Bed - contains only the basal and spinous epidermal layers
  • Nail Matrix - cells divide, move distally, and become keratinized in a process somewhat similar to hair formation but without keratohyaline granules
• Skin Glands

  • Sebaceous Glands
  • Sweat Glands (Eccrine, Apocrine)
• Sebaceous Glands


  Produce sebum by terminal differentiation of sebocytes, the classic example of holocrine secretion, secreting this oily substance onto hair in the follicles or pilosebaceous units
• Eccrine Sweat Glands


  In the dermis produce sweat that is mostly water onto the skin surface, where its evaporation provides an important mechanism for cooling the body