Integument Microanatomy- Pt 1 (Skin).docx

- **Integument: General Info** - Collagen dysplasia is an example of an integumental disease. - Integument is the composition of skin and epidermal derivatives. - Epidermal derivatives include: foot pads, claws, horns, hooves, glands (like anal sacs), uropygial glands,...

- **Integument: General Info** - Collagen dysplasia is an example of an integumental disease. - Integument is the composition of skin and epidermal derivatives. - Epidermal derivatives include: foot pads, claws, horns, hooves, glands (like anal sacs), uropygial glands, wattles, combs, spurs, and feathers. - **Skin: General Info** - Skin is the largest organ in the body, composing 8-16% of body weight. - Skin functions include: protection, prevent water and electrolyte loss, calcium homeostasis, temperature regulation, sensation, energy storage, and immune functions. - The skin is able to act as protection by working as a barrier against physical, chemical, and biological agents. - Skin can be categorized as being thick or thin. - **Thick skin** - Thick skin is hairless and has a thick epidermis layer, and merocrine/eccrine sweat glands. - Examples of thick skin include paw pads and muzzles. - **Thin skin** - Thin skin has hair follicles (often with arrector pili muscles), a thin epidermis layer, sebaceous glands, and apocrine sweat glands. - **Skin: Composition** - The skin is composed of the epidermal layer, dermal layer, and hypodermal layer. - The dermal layer can be further subdivided into the papillary layer and reticular layer. - The **papillary layer** (A) of the dermis is composed of loose connective tissue. - The **reticular layer** (B) of the dermis is composed of dense irregular connective tissue. - **Epidermis** - The epidermis is an avascular, thick barrier of epithelium which is composed of stratified keratinized epithelium. - In embryology, the dermis is derived from the ectoderm layer. - The epidermis is composed of keratinocytes and non-keratinocytes. - Keratinocytes compose 95% of cells in the epidermal layer, making it the most common cell found here. - Non-keratinocytes found in the epidermis include: Langerhans cells, Merkel's cells, and melanocytes. - **Langerhans cells** have an immune function as a tissue macrophage. - **Merkel's cells** act as mechanoreceptors. - **Melanocytes** aid in UV protection. - Melanocytes tend to have a brown pigmentation. - **Dermis** - In embryology, the dermis is derived from the mesoderm layer. - The dermis is composed of blood vessels, connective tissue, and nervous tissue. - The dermis functions to support the epidermis. - Things found in the dermal layer include: blood vessels, collagen fibers, elastic fibers, resident cells, transient cells, nerves, and lymphatics. - **Hypodermis (subcutis)** - The hypodermis contains panniculus adiposus, which is loose connective tissue that's rich in adipocytes. - The hypodermal layer is located beneath the dermis. - **Dermo-Epidermal Junction** - The **dermo-epidermal junction** is the interface between the dermis and epidermis. - Examples of where dermo-epidermal junctions can be found include: - Footpads, nasal planum, scrotum - Areas subjected to traction - The dermo-epidermal junction are NOT typically found in areas of haired skin. - **Epidermal Pegs/Ridges** (A) - The epidermal pegs/ridges are downward projections of the deep epidermis into the dermis. - **Dermal Papilla** (B) - Dermal papillae are upward projections of superficial dermis that bring blood supply closer to the epithelium. - Dermal papilla is used to bind the dermis to the epidermis by increasing the surface area by both layers. - If the dermal papilla are not present, hair follicles can also play a similar role with attaching the dermis to the epidermis. - **Epidermis: Layers** - As cells mature, and progress to the next layer (above them), they move closer to the surface where they eventually die and slough off. - Referring to each layer as being [active], means that specific layers of cells are capable of cell division. - In order from [deep to superficial,] the layers of the epidermis include: Stratum basale, Stratum spinosum, Stratum granulosum, Stratum lucidum, and Stratum corneum. - **Stratum basale** is active and alive. - This layer sits in the basement membrane (via attachment by hemidesmosomes) and is located at the dermo-epidermal junction. - The stratum basale is composed of a single layer of cuboidal to columnar epithelium, as well as keratinocytes, and melanocytes. - This layer is actively dividing (meaning that they have mitotic activity). - Basale keratinocytes are functionally heterogeneous, meaning that some act as stem cells, while others function to anchor the epidermis. - **Stratum spinosum** is active and alive. - This layer can be referred to as the ["spiny cell" layer] because the increased number of tonofilaments (cytokeratin) and desmosomes cause a spiny appearance. - Stratum spinosum is polygonal. - In thin skin, it is 1-2 cells thick. - In thick skin, it has many cell layers. - This layer is cohesive and resistant to abrasion. - This layer is active, in the sense that the cells will divide only if needed. - **Stratum granulosum** is alive but non-active. - This layer of cells contains basophilic keratohyalin granules (which are visible but vary in size). - This layer is typically 3-5celsl thick, and is the location where cells begin to flatten. - Lamellar granules are in this layer, but they are not visible under a light microscope. - **Lamellar granules** are secreted by cells to from a waterproof lipid sheet called "intercellular cement". - Stratum granulosum has no mitotic activity, deeming it to be inactive, however, the cells are still living. - This layer is considered to be [the last living layer], because at this level the cells are beginning to lose their nucleus and organelles, so the next layers above this one will not have any organelles. - **Stratum lucidum** is not always present but is always deceased. - The stratum lucidum is a translucent layer that is only present in thick skin, but not within thin skin. - This layer contains desmosome, many keratin filaments, and cytoplasm with eleidin. - **Eleidin** is a protein that is chemically related to keratin. - At this epidermal layer, all of the cells are fully keratinized, meaning that their cellular organelles are gone. - **Stratum corneum** is very deceased. - Stratum corneum is the outermost epidermal layer, containing up to 20 cell layers (although thickness varies per location), and this layer lacks nuclei and organelles. - This layer is constantly being shed at the surface and consists entirely of keratin. - **Epidermis: Layer Functions** - The functions of the epidermis include: - Generating a constant supply of cells - Facilitate cells adhering - **Desmosomes** are between each cell, and work to adhere neighboring cells to each other. - NOTE: Pic is of arrows pointing to desmosomes - **Hemidesmosomes** are between the basale cells and the basal lamina, where it works to adhere cells to the basement membrane - Bothe desmosomes and hemidesmosomes connect to intermediate filaments. - Replace cytoplasm with keratin - **Keratin** is a water-resistant protein that works to waterproof the epidermis. - This replacement takes place at any layer above the stratum basale layer. - Flatten cells - Provide many layers of a cellular barrier.