5- Integument Microanatomy- Pt 2.docx

- **Integument: General Info** - **Keratinization** is the process by which keratinocytes differentiate. - Keratinization takes about 21 days in dogs. - **Cornification** involves the production of stratum corneum by terminal epidermal differentiation....

- **Integument: General Info** - **Keratinization** is the process by which keratinocytes differentiate. - Keratinization takes about 21 days in dogs. - **Cornification** involves the production of stratum corneum by terminal epidermal differentiation. - **Nociceptors** are free nerve endings that reach the stratum granulosum epithelium layer, and they detect pain, itch, and temperature. - In contrast, encapsulated nerve endings will detect other skin sensations. - **Meissner's corpuscles** detect light pressure and touch. - **Pacinian corpuscles** detect deep pressure. - **Ruffini corpuscles** sense stretch. - **Non-keratinocytes** - Non-keratinocytes of the epidermis includes: Merkel's cells, melanocytes, and Langerhans cells. - **Merkel's cells** have a protective function. - Merkel's cells are located within the stratum basale epidermal layer of thick skin. - They act as sensory mechanoreceptors for cutaneous sensation, and free nerve endings can be seen at the base of these cells. - **Melanocytes** aid in UV protection via melanin's absorption of UV radiation. - Melanocytes are present in the stratum basale layer and have a neural crest origin. - Melanocytes produce melanin pigmen which is transferred to keratinocytes of the stratum basale and stratum spinosum epidermal layers. - Melanin will transform the absorbed UV radiation into harmless amounts of heat. - **Tyrosinase** is necessary for melanocyte function, as the absence of tyrosinase will result in albinism. - Tyrosinase functions by acting on tyrosine. - Copper is an important co-enzyme for Tyrosinase. - **Langerhans cells** play an immune function via antigen presenting T-cells and acting as mediators of tolerance. - Langerhans cells have an intra-dermal (within the dermis) location. - They are derived from bone marrow monocytes. - These cells are not often seen with H&E staining but can be seen with immunochemistry or electron microscopy. - **Epidermal Derivatives: General Info** - Epidermal derivatives include: hair follicles, compound hair follicles, sinus (tactile) hairs, sebaceous glands, apocrine (sweat)glands, udders and mammary glands, hooves, claws, nails, footpads (which have merocrine/eccrine sweat glands), anal sacs and their glands, and circumanal glands (hepatoid glands). - **Compound follicles** contain clusters of several hair follicles where their follicles merge at the level of the sebaceous gland and emerge through one orifice. - Compound follicles are most common in carnivores. - Compound follicles usually have one primary follicle with an apocrine sweat gland and several secondary hair follicles. - **Arrector pili muscles** are smooth muscles attached to primary hair follicles that play an insulation role. - Their contraction causes hair to stand up (goosebumps). - **Epidermal Derivative: Hair** - Hair/Feather functions include: insulation, camouflage, social display, sense/protection, and sex recognition. - Hair is produced by hair follicles. - Hair follicles are invaginations of the epidermis that contain an internal root sheath, external/outer root sheath, dermal papilla, and hair matrix cells. - The **inner root sheath** is composed of a few layers of squamous cells and a cuticle. - The **external/outer root sheath** is an external glassy membrane due to the thickened basal lamina, while the external root sheath is continuous with the epidermis. - The dermal papilla is composed of connective tissue that carries blood supply to the hair. - Hair matrix cells are comparable to the stratum basale epidermal layer, as it is the layer of cells that are constantly dividing- producing hair via the help of keratinocytes. - Hair is composed of the medulla, cortex, and cuticle. - The **medulla** is composed of loose cuboidal cells with areas of air. - The **cortex** is composed of dense compact keratinized cells. - The **cuticle** is composed of a single layer of flat keratinized cells. - The **hair shaft** is located above the skin surface, while the **hair root** is located within the follicle and ends with a bulb. - The **hair cycle** involves the following stages: anagen, catagen, and telogen. - During the **anagen** period, hair bulb cells are mitotically actives, meaning that the hair is growing. - The **catagen** period is the "regressive stage" where metabolic activity slows down and the base of the follicle migrates towards the surface. - The **telogen** period is the "resting" or "quiescent phase" where hair growth stops, and the base of the bulb is at the level of the sebaceous canal. - New hair grows below the telogen follicle, and the old hair shaft gets shed. - The hair cycle is controlled by daylight, ambient temperature, nutrition, and hormones (estrogen, testosterone, adrenal steroids, and thyroid hormones). - Hair **follicle types** include: primary and secondary hair follicles. - **Primary hair follicles** are large in diameter, rooted deep in the dermis, and contain sebaceous glands, arrector pili muscles, and sweat glands. - Examples of primary hair follicles include: primary or guard hairs. - **Secondary hair follicles** are small in diameter, rooted near the surface, may or may not contain sebaceous glands, and lack both apocrine sweat glands and arrector pili muscles. - Examples of secondary hair follicles include: secondary or under hairs. - Hair follicles can be arranged as individuals or clusters, varying in number of hairs per cluster. - **Whiskers** are also referred to as "sinus hairs" which as tactile hairs composed of a very large single follicle. - A blood-filled sinus is located between the inner and outer dermal root sheath. - Whiskers contain nerve bundles penetrating the sheath. - Whiskers are attached to skeletal muscle which allows for voluntary movement. - **Epidermal Derivative: Sebaceous Glands** - Sebaceous glands are located in the dermis, where they produce sebum. - Sebum is a mixture of lipid and cell debris. - Sebaceous glands partake in holocrine secretion, and aid in antibacterial and waterproofing. - Their ducts empty into a follicle. - They can be simple, branched, or compound glands. - **Specialized sebaceous glands** include: - **Supracaudal glands** are in dogs - **Circumanal/hepatoid glands** - **Mental organs/glands** are in cats - **Horn glands** are in buck goats - **Preputial glands** are in the smegma of horses - **[Tarsal (meibomian) glands]** are in eyelids - **[Uropygial lands (preen glands)]** are in birds - Uropygial glands are strongly developed within water birds like ducks. - Aside from this gland, the skin of birds are aglandular. - **Epidermal Derivative: Apocrine Sweat Glands** - Apocrine sweat glands are secreted by apical bidding/pinches. - Epithelial cells have apical secretory caps. - Simple coiled tubular glands open into distal hair follicles. - Contractile myoepithelial cells help express product. - In domestic animals, the apocrine sweat gland is located throughout most of the skin, where they function to communicate via attraction or markers. - **Specialized apocrine sweat** **glands** can be found in: - Mammary glands - Ciliary glands (of Moll) in eyelid, making tears form - Apocrine glands of anal sacs - Anal sacs are supplied by perianal glands (sebaceous) and apocrine glands, that should empty or be manually empty. - Ceruminous glands (ear wax) - Mental organs and planum rostrale of pigs - **Epidermal Derivative: Merocrine/Eccrine Sweat Glands** - Merocrine means that the method of secretion involves excretion via exocytosis. - These glands open directly onto the skin surface rather than the hair follicle. - Merocrine/eccrine sweat glands are minor in domestic animals except for the footpad of dogs, where they aid in thermoregulation and electrolyte balance. - This function is completed via the secreted fluid onto the skin's surface whenever body temperature rises. - **Epidermal Derivative: Mammary Gland** - Mammary glands contain tubuloalveolar glands that are connected by ducts, and are separated into lobules by connective tissue septae and interstitium. - Mammary glands are composed of clusters of alveoli forming lobules, and ducts that drain into sinuses. - Mammary glands have smooth muscle in the teat (sphincter). - The height of the epithelium relates to the activity of the gland. - **Epidermal Derivative: Hooves and Claws** - Hooves and claws are skin modifications composed of a variation of stratum corneum, and is supported by a highly vascularized dermis. - Hooves and claws lack stratum granulosum and stratum lucidum. - The **equine hoof** is their distal phalanx encased in heavily keratinized epidermis (horn). - In the equine hoof, the skin angles internally at the coronary band/groove causing distal growth of the stratum corneum epidermal layer. - The equine hoof has a white line that joins the sole with wall. - The corium (dermis) of the equine hoof is a highly vascular and innervated connective tissue (dermis). - The laminar corium-primary dermal laminae (500-600) interdigitates with the primary epidermal laminae. - There is papillae at the coronary corium, sole corium, and distal laminae (terminal papillae). - The epidermis of the equine hoof (insensitive laminae) is avascular. - The epidermis in the equine hoof is the insensitive laminae. - The dermis in the equine hoof is the coronary corium, and laminar corium. - The keratinized hoof wall has 3 layers: stratum externum (tectorium), stratum medium, and stratum Internum (lamellatum). - **Stratum externum (tectorium)** is a continuation of perioplic epidermis, referred to as a "glaze". - **Stratum medium** is composed majority of the wall and is produced from the coronary epidermis. - **Stratum Internum (lamellatum)** is the primary epidermal laminae (\~600), and is the **[insensitive laminae]** that interdigitates with the primary dermal laminae. - **Sensitive laminae** is composed of laminar corium with primary dermal laminae. - The horn is composed of keratin arranged into parallel microscopic tubules (like hair shafts) and intertubular horn.