Integumentary System

• The integumentary system involves the skin and its adnexa.
• Adnexa is the organ or extension of the skin.
• The reason for scar formation is the combination of the first and second intention healings.
• The function of the integumentary system includes acting as a barrier to physical, chemical and biological agents, homeostasis, sensory, secretory, excretory, and communication.
• The skin is the largest organ of the body, firmly attached to the hypodermis or subcutis, and composed of a superficial epidermis and a deeper dermis or corium.
• The functions of the skin include barrier function, thermoregulation, blood pressure regulation, secretion and excretion, species and sex recognition, display and social interaction, and sensory perception.
• Types of skin include thick skin and thin skin.
• Second intention healing involves less epithelial repair but more on invasion of fibroblast.
• The Adnexa include the Feather, the Feather follicle, the Uropygial gland, and the Special Epidermal Structures such as Wattles and combs, Ear lobes, Claws, spurs and beaks, and Toe pads.
• First intention healing is also known as Epithelial healing because of the fast turn over of epithelial cells.
• Connective tissue repair is a part of second intention healing.
• First intention healing occurs when the skin is disrupted by a clean incisional wound and it closes immediately.
• The skin is divided into layers: the superficial St. superficiale, the Stratum profundum, the Compactum (dense layer), the Laxum (loose connective tissue containing large blood vessels, smooth muscle, follicles and fat), and the Lamina Elastica of the dermis.
• The main purpose of studying the skin is to understand its healing process.
• Second intention healing occurs when the skin wound also involves loss of some underlying tissue and is slower than the first intention healing.
• Skin may be repaired by first, second or third intention healing.
• The Hypodermis (Subcutis) is similar to that in mammals except that it has an extensive lymphatic tissue.
• Thick skin is attached to underlying bone or muscle through a thick hypodermis, covers hairless regions of the body like sole or footpad, presents a thick epidermis with thick keratin, has no hair and no hair follicles, and contains more sweat glands than thin skin.
• Thick skin has a layer of thick skin called the epidermis, which is derived from ectoderm, presents folds on the skin surface called epidermal ridges that follow the contour of the underlying dermis, may also invaginate into the dermis to form epidermal pegs, and was discovered by Johannes Purkinje, a Czech anatomist and physiologist, to make the unique pattern of fingerprints.
• The epidermis of thick skin undergoes regular cellular proliferation, death, and renewal, is a thick stratified squamous epithelium with thick keratin that rests on a wavy basal lamina, and has 4 layers: Stratum Basale (inner), Stratum Spinosum, Stratum Granulosum, and Stratum Corneum.
• Stratum Basale is the deepest layer of epidermis that lies over the dermis, is one layer of cuboidal or columnar cells that rests on the basal lamina, and contains stem cells for Keratinocytes, the major cell type.
• Keratinocytes divide rapidly into new keratinocytes which push up toward the surface and become part of the more superficial layers.
• Stratum Spinosum cells are alive and can divide if necessary.
• Stratum Spinosum cells contain thick bundles of tonofilaments made of a tension-resisting protein.
• Stratum Corneum is the hardened and compressed outermost layer of the epidermis, an adaptation to abrasion and high wear and tear areas, and may be traversed by coiled tubular excretory duct of sweat gland.
• Merkel’s cells are associated with a disc-like sensory nerve ending to form structure called Merkel Disc, located in the Stratum Basale of Epidermis, and are connected to neighboring keratinocytes by desmosomes.
• Melanocytes are not part of the keratinizing part of the epidermis and are derived from neural crest.
• Merkel cells, along with a sensory nerve ending, form the Merkel’s disk which is a sensory receptor for touch.
• Stratified Squamous Epithelium consists of 4 types of cell: Keratinocytes, Merkel’s cells, Melanocytes, and Intraepidermal Macrophages.
• Keratinocytes are the most numerous (95%) cell types in the epidermis, produce a protein (keratin) that helps waterproof the skin and protects the skin and the underlying tissues from heat, microbes, abrasion and chemicals, and have a life span of 7 to 10 days from production to sloughing.
• Stratum Corneum consists of several layers of keratinocytes that are flat, completely dead, lifeless bags of Keratin fibers (soft keratin), and its dead keratinocytes are constantly shed in the Stratum Disjunctum.
• The production of Melanosomes needs an enzyme Tyrosinase, which is absent in albino because they can’t produce melanosomes even if they have a sufficient number of melanocytes.
• Stratum Granulosum is the third layer of the epidermis where keratinization process begins, consisting of 2 or 3 layers of Squamous or spindle-shaped dying keratinocytes that contain keratohyalin granules (precursors of keratin) giving the cells a granular appearance, and its cells no longer divide.
• Stratum Basale, along with Stratum Spinosum, constitutes the Stratum Germinativum because the cells they contain undergo mitosis (germinates) to replace those that die into the more superficial layers.
• Melanocytes contain pigments (melanin) of hair and skin, are located in the Basal layer of epidermis, the process extend superficially to the Stratum Spinosum, and have a round or ovoid nucleus and a pale cytoplasm containing ovoid pigment granules called Melanosomes.
• Stratum Lucidum is not typically present in skin of domestic animals, except in canine digital pads, teat, perioplic epidermis and nose epidermis, and consists of several layers of homogenous, translucent, slightly acidophilic keratinocytes.
• Stratum Basale has a wavy outline because it follows the wavy contour of basal lamina.
• Melanocytes are 10 to 25% of Stratum Basale cells and are a stable population of cells with little turnover.
• Melanin pigment is synthesized in packets which are engulf by keratinocytes, carried up to the
• Stratum Spinosum is 2 to 10 cell thick, consists of polyhedral cells joined by intercellular bridges (desmosomes) that give this layer a thorny or spiny “prickle cell” appearance, and its cells can divide if necessary.