CM

Integument and Related Structures

Skin Functions

  • Prevent Desiccation and Infection: Skin acts as a barrier to prevent moisture loss and entry of pathogens.
  • Protection: Covers and protects underlying tissues and organs from physical damage.
  • Temperature Regulation: Helps maintain normal body temperature through sweat and blood flow.
  • Excretion: Excretes water, salts, and organic wastes.
  • Sensory Reception: Contains receptors for touch and pressure, sending signals to the nervous system.
  • Vitamin D Synthesis: Engages in the synthesis of Vitamin D and stores nutrients.

Structure of the Epidermis

  • Keratinocytes: Majority of epidermal cells; responsible for forming the protective outer layer of skin.
    • Keratinization Process: New keratinocytes push older cells outward; older cells become lifeless and filled with keratin, aiding in skin resilience.

Layers of the Epidermis

  1. Stratum Germinativum (Basale):

    • Single row of actively dividing keratinocytes.
    • Contains Merkel cells (touch receptors) and melanocytes (pigment cells).

  2. Stratum Spinosum:

    • Known as the spiny layer due to cell shape when fixed for examination.
    • Contains several cellular layers joined by desmosomes.

  3. Stratum Granulosum:

    • Composed of 2-4 layers of flattened keratinocytes.
    • Cells fill with keratohyalin and lamellated granules, leading to cell death and waterproofing of the skin.

  4. Stratum Lucidum (Clear Layer):

    • Present only in thick skin; appears as translucent layer of dead cells.

  5. Stratum Corneum (Horny Layer):

    • Outermost layer with 20-30 layers of dead keratinized cells; provides a tough protective barrier.

Dermis Structure

  • Composed of dense, irregular connective tissue, containing collagen, elastic, and reticular fibers.
  • Houses hair follicles, nerves, blood vessels, and glands, along with fibroblasts, adipocytes, and macrophages.
  • Connects the epidermis to underlying tissues; referred to as the "hide" of the animal.

Skin Specializations

  • Pigmentation: Result from melanin distribution; more granules in cellular arms lead to darker coloration.

  • Digital Pads:

    • Thick layers of fat and connective tissues; toughest skin for weight-bearing.
    • Composed of all five epidermal layers, with a thicker stratum corneum.

  • Planum Nasale:

    • Thick but contains only three epidermal layers; lacks stratum lucidum and stratum granulosum.

Hair Structure

  • Hair Anatomy:

    • Shaft: Visible part above skin.
    • Root: Buried within the skin; contains sensory nerve endings (root hair plexus).
    • Follicle: Invagination of epidermis; contains hair bulb and papilla for nourishment.
    • Layers: Hair constructed from dead epithelial cells, with medulla (central), cortex (thickest), and cuticle (outer).

  • Hair Growth Phases:

    1. Anagen: Growth phase.
    2. Telogen: Resting phase when hair is at its maximum length.
    3. Catagen: Transitional phase between growth and resting.

Sweat Glands

  • Eccrine Glands:

    • Coiled tubes connected to skin surface; primarily found in footpads of dogs.

  • Apocrine Glands:

    • Located deeper; empty into hair follicles rather than skin surface.

  • Anal Sacs:

    • In dogs and cats, found near the anus; involved in marking territory through secretions during defecation.