Microanatomy - Integument Spring 2024 PDF

What is the integument? INTEGUMENT = SKIN + EPIDERMAL DERIVATIVES Epidermal Derivatives: Foot pads, claws Hooves Horns Glands, including anal sacs Uropygial gland (birds) Wattles and combs Spurs, feathers ...

What is the integument? INTEGUMENT = SKIN + EPIDERMAL DERIVATIVES Epidermal Derivatives: Foot pads, claws Hooves Horns Glands, including anal sacs Uropygial gland (birds) Wattles and combs Spurs, feathers  Images Skin Prefix/Suffix: Lat. CUTIS, Gr. DÉRMA Largest organ in the body (8-16% of body weight) Functions: Protection: a barrier against physical, chemical and biological agents Prevents water and electrolyte loss Temperature regulation Sensation Calcium homeostasis productionofVitD Energy storage fatdepositsinhypodermis Immune function  Components of Skin Epidermis stratified squamous keratinized epithelium papillary layer Skin Dermis reticular layer loose connective tissue Hypodermis (subcutis) – that may be rich in adipocytes panniculus adiposus  Embryological Origin of Skin farad Epidermis Ectoderm derived Avascular Thick barrier Epithelium Dermis Mesoderm derived Contains blood vessels + nervous tissue Connective tissue Supports the epidermis  Thick vs. Thin Skin Thick skin Thick epidermis directly Hairless foffetht.tn glandgynetes Contains merocrine/eccrine sweat glands Examples: paw pads, muzzle Thin skin Epidermis is thin Contains hair follicles often with arrector pili muscle Sebaceous glands and apocrine sweat glands  basement basicallywhere membranesplits The Dermo-Epidermal Junction Interface between the dermis and Epidermal pegs epidermis EPIDERMAL PEGS/RIDGES Downward projections of the deep epidermis into the dermis DERMAL PAPILLAE Upward projections of the superficial dermis Increased surface area between both layers Brings blood supply closer to the epithelium Examples Footpads, nasal planum and scrotum Areas subjection to traction Not normally seen in haired skin Dermal papillae  TWO ZONES IN THE DERMIS Papillary superficial Papillary = loose connective tissue Reticular = dense irregular connective tissue deepdermis Collagen fibres Elastic fibres Resident cells Transient cells Blood vessels Nerves Lymphatics Reticular From: Junqueira’s Basic Histology, 2010  CELLS OF THE EPIDERMIS 1. KERATINOCYTES: most common cell (95% of the total number of cells) in the epidermis. Keratinizedstratifiedsquamous 2. NON-KERATINOCYTES Langerhans cells –immunity (tissue macrophage) Merkel’s cells-mechanoreception Melanocytes- UV protection  LAYERS OF THE EPIDERMIS Epidermis is composed of several distinct layers. As cells mature and progress to the next layer, they move closer to the surface where they eventually die and slough off. From deep to superficial: 1. Stratum basale: active and alive ofcell capable division 2. Stratum spinosum: active and alive 3. Stratum granulosum: non-active, alive 4. Stratum lucidum (not always present): deceased 5. Stratum corneum: very deceased  Basic plan of the epidermal layers Generate a constant supply of cells Facilitate cells adhering att Desmosomes – between cells att Hemidesmosomes – between basal cells and basal lamina Replace cytoplasm with keratin Waterproof Flatten cells Provide many layers of this cellular barrier LAYERS OF THE EPIDERMIS From: Junqueira’s Basic Histology, 2010  STRATUM BASALE basal layer of the epidermis, located at the epidermal-dermal junction Single layer of cuboidal to columnar epithelium Attached to basal lamina via hemidesmosomes Actively dividing (area of mitotic activity). Basal keratinocytes are functionally heterogenous. Some act as stem cells, whilst some function to anchor the epidermis. Keratinocytes and melanocytes fromUVradiation provideprotectionofDNA  Desmosomes vs. Hemidesmosomes Hemidesmosomes bind cells to basal lamina Desmosomes bind neighbouring cells together Both connect to intermediate filaments  STRATUM SPINOSUM Polygonal Thin skin: 1-2 cells-thick Thick skin: many layers thick Increased number of tonofilaments (cytokeratin) and desmosomes give SPINY appearance Cells are cohesive and they resist abrasion Cells in this layer retain some capacity for division if needed  STRATUM GRANULOSUM Layer that is 3 - 5 cells thick Cells begin to flatten Contain basophilic keratohyalin granules Lamellar granules (not visible via light microscopy)– secreted by cells to form waterproof lipid sheets, “intercellular cement” No mitotic activity, last living layer, nucleus and organelles soon to be lost  STRATUM LUCIDUM Translucent layer Present in thick skin only Many keratin filaments, desmosomes present Cellular organelles are gone – cells are fully keratinized Cytoplasm contains eleidin – protein chemically related to keratin  STRATUM CORNEUM hoovesclawsnails Outermost layer Many (up to 20) layers thick, thickness varies by location Cells consist entirely of KERATIN, a water- resistant protein. No nuclei or organelles Cells continually shed at surface  Keratinization Definition: Process by which keratinocytes differentiate, about 21 days in length in the dog. Cornification Definition: Production of stratum corneum by terminal epidermal differentiation.  Non-Keratinocytes of the Epidermis Langerhan’s cell – immune system Merkel’s cells – sensory Melanocytes – protection  useimmunohistochemistry to identifymacrophages LANGERHANS CELLS Intra-epidermal (within the epidermis) macrophages Derived from bone-marrow monocytes Role in immunity Antigen presenting to T-Cells Mediators of tolerance Not often seen with routine H&E  MERKEL’S CELLS Located in the stratum basale of thick skin Can act as sensory mechanoreceptors for cutaneous sensation Free nerve endings seen at the base of these cells  MELANOCYTES Present in the stratum basale Neural crest origin Produce melanin pigment to keratinocytes of stratum basale and spinosum Protects cells from effects of UV radiation Must have tyrosinase for proper function MELANIN Melanin absorbs harmful UV-radiation Transforms the energy into harmless amounts of heat Must have tyrosinase for proper f x  SENSORY NERVES OF THE DERMIS Nociceptors – free nerve ending that reach the stratum granulosum. Detect: pain, itch and temperature Encapsulated nerve endings: Meissner’s corpuscles: light pressure/touch Pacinian corpuscle: deep pressure Ruffini corpuscle: senses stretch  EPIDERMAL STRUCTURES/DERIVATIVES Hair follicles Compound hair follicles Sinus (tactile) hairs Sebaceous glands Apocrine (sweat) glands Udders, mammary glands Hooves, claws, nails Footpads (have merocrine/eccrine sweat glands) Anal sac glands & anal sacs Circumanal glands (hepatoid glands) LABEL THIS IMAGE thisisthinskin Identify: Epidermis 0 a Dermis Hair shaft Hair follicle Hair bulb Sebaceous gland Apocrine sweat gland Great  Functions of Hair/Feathers Insulation Camouflage Social display Sense/protect Sex recognition  ANATOMY OF HAIR Produced by a hair follicle. Hair shaft is above the surface of the skin Hair root is within in the follicle and ends with bulb. Components of hair: Medulla – loose cuboidal cells ofhair with areas of air In Cortex – dense compact keratinized cells Cuticle – single layer of flat keratinized cells  ANATOMY OF HAIR FOLLICLE Invagination of the epidermis Internal Root Sheath a few layers of squamous cells and cuticle External/Outer Root Sheath sitsonBM external glassy membrane = thickened basal lamina external root sheath = continuous with epidermis Dermal Papilla (DP) HM connective tissue that carries blood supply to the hair Hair Matrix cells (HM) hasactivelydividingcells DP comparable to stratum basale keratinocytes hair  Hair Cycle Anagen: period when hair bulb cells are mitotically active Catagen: Regressive stage when metabolic activity slows down and the base of the follicle migrates towards the surface Telogen: Resting or quiescent phase when growth stops, and the base of the bulb is at the level of the sebaceous canal New hair grows beneath the telogen follicle, and the old hair shaft is shed controlled by daylight, ambient temperature, nutrition, and hormones (estrogen, testosterone, adrenal steroids, and thyroid hormone) needtoknow ejectedlost U  TYPES OF HAIR FOLLICLES gland sweat as soso.nlsebaceous apocrine Primary Hair follicle: Large diameter Rooted deep in dermis Sebaceous glands, arrector pili muscle, sweat glands Primary or Guard Hair Secondary Hair follicle: Smaller diameter Rooted nearer the surface +/-sebaceous gland; no apocrine sweat glands, no arrector pili muscle Secondary or under hairs 2 Follicles can be arranged as individuals or clusters and can vary in the number of hairs per cluster.  COMPOUND FOLLICLES Clusters of several hair follicles The follicles merge at the level of the sebaceous gland (g) and emerge through one external orifice Compound follicles usually have one primary follicle (hf) with an apocrine sweat gland (sg) and several secondary hair follicles (s). Most common in carnivores  ARRECTOR PILI ANScontrolsthis Arrector pili muscle = smooth muscle attached to follicle of primary hairs Contraction causes hair to stand up (goosebumps) Role in insulation  SINUS HAIRS/WHISKERS Tactile hairs Composed of a very large single follicle HB Blood filled sinus between inner and outer RBC dermal root sheath Perfidae Attached to skeletal muscle to allow for voluntary movement Nerve bundles penetrate sheath  SEBACEOUS GLANDS Located in the dermis Produce sebum a mixture of lipid and cell debris Holocrine secretion Antibacterial and waterproofing Ducts empty into a follicle Can be simple, branched or compound glands SPECIALIZED SEBACEOUS GLANDS Supracaudal glands – dog Circumanal / Hepatoid glands Mental organs/glands – cat Horn glands – buck goat Preputial glands – smegma in horse Tarsal (Meibomian) glands – eyelids Uropygial gland (the preen gland) in birds The Uropygial/ Preen Gland Strongly developed in many waterbirds such as ducks The rest of bird skin is aglandular  APOCRINE SWEAT GLANDS Secrete by apical budding/pinches Epithelial cells have apical secretory caps (a) Simple coiled tubular glands opens into the distal hair follicle. Contractile myoepithelial cells (m) help express the product In domestic animals, located throughout most of the skin. Function is mainly communication (attraction, marker). From: Dellmann’s Texbook of Veterinary Histology. 2006  SPECIALIZED APOCRINE SWEAT GLANDS Mammary glands mostimpo Ciliary glands (of Moll) in eyelid, make tear film Apocrine glands of the anal sac Ceruminous glands (ear wax) Mental organ and planum rostrale of pigs Anal sacs – are supplied by perianal glands (sebaceous) and apocrine glands, that should be empty or be manually emptied. We will cover the histology of these in depth during lab! Source: Bacha & Bacha  MEROCRINE/ECCRINE SWEAT GLANDS noloss Hai Merocrine – excrete via exocytosis Open directly on to skin surface vs hair follicle Minor in domestic animals except for footpad of dog Thermoregulation and electrolyte balance; Secrete fluid onto skin surface when body temperature rises  Mammary Glands Ishtar basketeens nave a Tubuloalveolar glands connected by ducts and separated into lobules by connective tissue septae and interstitium Mammary Glands Clusters of alveoli form lobules Ducts drain into sinuses Smooth muscle in teat (sphincter) Lactiferous ducts (cuboidal) Height of epithelium = activity Lactiferous sinus (cuboidal) someofmilk store of gland Teat sinus (cuboidal) Teat canal (stratified squamous epithelium) need duetosucking moreprotection Alhussien MN, Dang AK (2018) Milk somatic cells, factors influencing their release, future prospects, and practical utility in dairy animals: An overview, Veterinary World, 11(5): 562-577. HOOVES AND CLAWS Modification of skin Variation of the STRATUM CORNEUM Supported by highly vascular dermis Lack stratum granulosum & stratum lucidum  he ismost 9 tk EQUINE HOOF Distal phalanx encased in heavily keratinized epidermis (‘horn’) growth bity Skin angles internally at coronary band/groove distal growth of stratum corneum White line joins sole with wall sensitivelaminaemeet i nsensitivelaminae Dermiscoreumusedinterchangeably Al-Agele R, Paul E, Kubale Dvojmoc V, et al. (2019) The Anatomy, Histology and Physiology of the Healthy and Lame Equine Hoof. Veterinary Anatomy and Physiology. IntechOpen. DOI: 10.5772/intechopen.84514.  CORIUM (DERMIS) OF THE EQUINE HOOF Coronary Terminal corium Highly vascular and innervated papillae Perioplic connective tissue (dermis) corium Laminar corium- primary dermal Corium laminae (500-600) interdigitate of frog with primary epidermal laminae Papillae at coronary corium, sole corium and distal laminae Corium of sole (terminal papillae)  Insensitive laminae Coronary corium (epidermis) (dermis) Laminar corium (dermis) Sensitive laminae Epidermis is avascular Corium contains nerves and massive network of blood vessels  dying'tn wait grow KERATINISED HOOF WALL HAS 3 LAYERS normally Horn – keratin arranged in parallel Laminar corium with microscopic tubules (like hair shaft) and primary dermal laminae intertubular horn = SENSITIVE LAMINAE Stratum externum (tectorium) Continuation of perioplic epidermis tubular and intertubular “Glaze” horn Stratum medium mostimpoperValentine Majority of wall Produced from coronary epidermis Stratum internum (lamellatum) blueinsensitivelaminae Primary epidermal laminae (~600) INSENSITIVE LAMINAE interdigitate with primary dermal laminae Stratum medium  m= stratum medium i= stratum internum t= tubular horn ih=intertubular horn Sensitive lc= primary dermal laminae (of the laminar corium) (sensitive laminae) pe= primary epidermal laminae (insensitive laminae) se= secondary epidermal laminae sd= secondary dermal laminae From: Dellmann’s Texbook of Veterinary Histology. 2006  ifpInitied pe= primary epidermal lamina se= secondary epidermal laminae sd= secondary dermal laminae lc= primary dermal laminae (of the laminar corium) From: Dellmann’s Texbook of Veterinary Histology. 2006 GLOSSARY Epidermis, dermis (papillary vs reticular), subcutis (hypodermis), dermoepidermal junction Epidermal pegs vs dermal papillae Keratinocyte, Langerhan’s cell, melanocyte, Merkel cell Desmosome, hemidesmosome Keratohyaline granules Uropygial gland Hair cycle (anagen, catagen, telogen) White line Panniculus Arrector pili Apocrine Sweat gland (merocrine) vs sebaceous gland Layers of the epidermis (s. basale, s. spinosum, s. lucidum, s. corneum) Nociceptors Components of hair (cortex, medulla, root sheaths, bulb) Hoof wall (laminae; s. lamellatum, laminar corium, s. externum, s. medium)