Integumentary

• Integumentary System


  Skin + Accessory organs/derivatives (including hair, glands, hooves, horns, scales and claws)
• Healthy Skin
• Skin Pathology (Skin Diseases)

  • Lumpy skin disease in cattle
  • Ringworm in cattle
  • Demodex Mite Bites in cattle
  • Ringworm in Dogs
  • Diamond Lesions in pig
  • Skin tumor/cancer in Dog
• Skin/Integument


  Largest organ in the vertebrate body, comprised of an epithelial covering and its associated connective tissue
• The skin has a basic structure in all vertebrates (including fish, reptiles birds, Amphibian & mammals) with a few differences to suite their environment/habitat & function
• Functions of the integument

  • Protection
  • Regulation of body temperature/Thermoregulation
  • Secretion
  • Sensory Organ
  • Communication
  • Reflects the physiological condition of the animal
• Protection


  The most important function of the skin is its effectiveness as a barrier between the internal and external environments (guards against injury, bacterial invasion, UV damage and desiccation)
• Regulation of body temperature/Thermoregulation

  Mediated by the hair coat, cutaneous blood supply and in some animals, sweat glands
• Secretion


  From sweat, sebaceous and mammary glands
• Sensory Organ


  Innervation of the skin provides pain, touch, pressure and temperature sensation
• Communication


  The skin is an important organ in the social life of animals because it gives off odors that govern sexual behavior and helps animals identify each other and their territories
• Reflects the physiological condition of the animal


  Skin and coat condition are good indicators of overall health and alterations may reflect a variety of external and internal disease processes (endocrine disorders, nutritional problems; i.e. Vitamin A deficiency is characterized by very dry, hardened skin, dry lack-luster hair and hair loss)
• Epidermis


  Outermost layer of the skin, composed mostly of keratinized stratified squamous epithelium
• Dermis


  Connective tissue layer that supports the epidermis and binds it to the subcutaneous tissue (hypodermis)
• Hypodermis


  Tissue that connects the dermis to underlying muscles, stabilizes the skin, and allows separate movement
• Cell types of the epidermis

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


  Represent the majority of cells, produce keratin, a fibrous protein that gives the epidermis its protective properties
• Melanocytes


  Located at the stratum basale, derivatives of the neural crest, produce melanin to protect against UV damage
• Langerhans' cells


  Dendritic cells located in the stratum spinosum that arise from the bone marrow, play a pivotal role in induction of cutaneous immune responses
• Merkel cells


  Present at the junction of the epidermis and dermis in thick skin, couple with axon terminals to form mechanoreceptors
• Layers of the epidermis (thin skin)

  • Stratum Basale
  • Stratum Spinosum
  • Stratum Granulosum
  • Stratum Corneum
• Layers of the epidermis (thick skin)

  • Stratum Basale
  • Stratum Spinosum
  • Stratum Granulosum
  • Stratum Lucidum
  • Stratum Corneum
• Stratum Basale


  Deepest layer that rests on basal lamina, mitosis occurs here to produce new keratinocytes
• Stratum Spinosum


  Several layers thick, composed of polyhedral cells with undulations on their plasma membranes, melanin granules and Langerhans cells are abundant
• Stratum Granulosum


  1. 5 cell layers thick, keratinocytes become more flattened and contain more keratin, electron-dense keratohyalin granules and lamellated granules
• Stratum Lucidum


  Consists of several layers of fully keratinized, closely compacted dense cells devoid of nuclei and cytoplasmic organelles, contains translucent droplets of eleidin
• Stratum Corneum


  The migrating cells terminally differentiate to form the cornified layer of the epidermis, consists of several layers of flattened, completely keratinized dead cells (corneocytes)
• Keratinization and strata differentiation

  1. Synthesis of keratin filaments begins in stratum basale

  2. Aggregation of filaments occurs in superficial cells of stratum spinosum

  3. Membrane coating granules release lipid-rich contents in stratum spinosum

  4. Keratohyalin granules appear in stratum granulosum

  5. Degradation of nucleus and organelles occurs in stratum granulosum and stratum lucidum

  6. Formation of keratin filament matrix complex occurs in stratum corneum
• Keratin


  Structural protein that forms the cytoskeleton of all keratinocytes, there are "soft" keratins and "hard" keratins
• Papillary layer

  Outer layer of the dermis, consists of loose connective tissue, fibroblasts, macrophages, mast cells, smaller capillaries, lymphatics, and sensory neurons
• Reticular layer


  Deeper layer of the dermis, composed of dense irregular connective tissue containing collagen and elastic fibers, has a rich network of larger blood and lymph vessels
• Hypodermis


  Tissue that connects the dermis to underlying muscles, stabilizes the skin, and allows separate movement, made of elastic, areolar and adipose tissues
• Skin appendages/accessory structures


  • Hair
  • Sweat glands
  • Sebaceous glands
  • Ceruminous gland
  • Anal sac glands
  • Mammary glands
• Hair


  Elongated keratinized structures derived from invaginations (hair follicles) of epidermal epithelium, produced by living keratinocytes at the base of the hair follicle
• Structure of the hair and hair follicle

  • Hair shaft (cuticle, cortex, medulla)
  • Hair root
  • Internal root sheath
  • External root sheath
  • Hair bulb (germinal matrix)
  • Dermal papilla
• Hair follicle


  The structure from which the hair grows, contains the internal root sheath, external root sheath, hair bulb, and dermal papilla
• Types of hair follicles

  • Single (simple) follicle
  • Compound follicle
• Parts of the hair follicle

  • Internal Root Sheath
  • External Root Sheath
  • Dermal Papilla
  • Hair bulb (Germinal matrix)
• Internal Root Sheath


  Part that completely surrounds the initial part of the hair shaft, a transient structure whose cells degenerate and disappear above the level of sebaceous glands
• External Root Sheath


  Continuous with the epidermal cells and, near the surface, shows all the layers of the epidermis. Near the dermal papilla, it is thinner and is composed of cells corresponding to stratum basale of the epidermis