Integumentary system

• General characteristics:

  • Integument/Cutaneous layer
  • Largest single organ of the body
  • 15%-20% of the total body weight
  • For protection, sensory, thermoregulatory, metabolic and sexual signaling
• Types of skin

  1. Thick skin- palms and soles 400 to 1400 um or 1.4 mm
  2. Thin skin- whole body except palm and soles 75 to 150 um
• General layers of the skin

  1. Epidermis
  2. Dermis
  3. Hypodermis
• What is the composition of epidermis?

  Keratinized stratified squamous epithelium

  • Lacks of vasculature
  • Receive nutrients only from dermis
• Primary cells of the epidermis?

  Keratinocytes
• Pigment producing cells of epidermis?

  Melanocytes
• A-g presenting cells of epidermis?

  Langerhan cells
• Sensory (Tactile epithelial cells) of epidermis?

  Merkel cells
• Characteristic of Keratinocytes

  • Primary cells are located at epidermis
  • Originate on the stratum basale moving up to the final barrier layer of the skin, stratum corneum
• Characteristic of Melanocytes

  • Located at basal epidermis
  • Neural crest derived
  • Pale-staining, rounded cell bodies
  • Synthesize dark melanin pigment in melanosomes (organelle where melanin is synthesized)
  • Protect nuclear DNA from UV damage
  • Eumelanin- brown or black; found in hair follicles
  • Pheomelanin- red hair
• Albinism- A condition where there are less melanin than usual in the body; condition that leads to having very light skin, hair and eyes; produce hypopigmentation due to defect of enzyme tyrosinase
• Vitiligo- a disorder that causes patches of skin to lose pigment of color; happens when melanocytes are attacked and destroyed or due to decreased activity of melanocyte
• Characteristic of Langerhan cells:

  • Antigen-Presenting cells
  • 2-8% of cells in epidermis
  • Located at the spinous layer (stratum spinosum) of epidermis
  • Bind, process and present antigen to T-lymphocytes
• Characteristic of 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 skin: according to thickness

  Stratum corneum- Thick and Thin skin

  Stratum lucidum- Thick skin

  Stratum granulosum- Thick and Thin skin

  Stratum spinosum/Stratum Germinativum- Thick and Thin skin

  Stratum Basale- Thick and Thin skin
• 15-20 layers of dead skin?

  Stratum corneum
• It is the dead, flattened, anucleate, keratin-filled keratinocytes?

  Squames
• Squames- Layer of dead keratinocytes bound by hydrophobic lipid-rich segment that provides protection against friction and water loss
• It is the most superficial layer of epidermis?

  Stratum corneum
• 2-3 layers of anucleate, dead cells?

  Stratum lucidum
• Seen only in thick skin?

  Stratum lucidum
• 3-5 layers of keratinocytes?

  Stratum granulosum
• Stratum granulosum

  • Contains kerato-hyaline granules
  • Are intensely basophilic (have intense affinity in basic dyes)
  • Contains lamellar granules
  • (Golgi-derived), produces a lipid-rich impermeable layer around the cells forming major part of the skin's barrier against water loss
• Consider the Thickest layer of the epidermis?

  Stratum spinosum
• Cells may still divide here?

  Stratum spinosum
• Langerhans cells are present here?

  Stratum spinosum
• What is the keratinocytes in our stratum spinosum?

  Prickle cells
• Stratum spinosum

  • consist of generally polyhedral cells having central nuclei with nucleoli and cytoplasm actively synthesizing keratins
  • Several layers of keratinocytes all joined by desmosome
  • Contains tonofibrils (keratin filament bundles)
  • Bind to our desmosomes thus forming spines between keratinocytes in the stratum spinosum
• Stratum germinativum

  • combination of spinosum and basale; layer where stratum spinosum and stratum basale meet
  • provide germinal cells necessary for the regeneration of the layer of the epidermis
• Mitosis occurs here?

  Stratum basale
• Melanocytes and Merkel cells are found here?

  Stratum basale
• Stratum basale

  • Single layer of cuboidal to low columnar cells in contact with basement membrane
• Characteristic of Dermis

  • Layer of connective tissue (Fibro-adipose tissue)
  • Supports epidermis and binds it to hypodermis
  • Contain projection called dermal papillae; which connects with epidermal ridges
  • Filled with blood vessels, nerves and sensory receptors
  • Basement membrane (connects dermis with epidermis)
• What are the 2 layers of the dermis?

  Papillary layer and Reticular layer
• Papillary layer

  • Connects to epidermis
  • More superficial layer of dermis
  • Contains subpapillary vascular plexus
  • Contains the ff:
  • Loose connective tissue
  • Type I and III collagen
  • Mast cells
  • Dendritic cells
  • Fibrils Type VII collagen (inserted in the basal lamina; help in binding the dermis into epidermis)
• Reticular layer

  • Thicker than papillary layer
  • Deeper layer of dermis
  • Made up of dense irregular connective tissue surrounding hair follicles, skin glands (sebaceous glands and sweat 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
• Nutritive vessels form 2 major plexuses

  1. Subpapillary vascular plexus (Superficial Vascular Plexus)

  • Between the papillary and reticular dermal layers
  • Form rich, nutritive capillary network just below the epidermis

  1. Deep plexus

  • With larger blood and lymphatic vessels lie near the interface of the dermis and subcutaneous layer
• Thermoregulatory function of the dermis is done by arteriovenous anastomoses located between the plexuses
• Subcutaneous Layer

  • also called as Hypodermis, Superficial fascia, Panniculus
  • Layer beneath the dermis usually consist of adipose tissue and loose connective tissue
  • Contains large vessels which supply and drain the dermal blood vasculature
• Unencapsulated

  • Simple nerve ending with no schwann cells or collagenous coverings

  Capsulated

  • More complex structures with sensory fibers enclosed by glia and delicate connective tissue capsules