Anatomy (L27) - Integumentary System PDF

Integumentary system By Sampath Madhyastha Lecture ID # 7423 Thursday, 28th November 2024, 10.10 to 11 a.m. Learning Objectives 1. Describe different types of skin and corre...

Integumentary system By Sampath Madhyastha Lecture ID # 7423 Thursday, 28th November 2024, 10.10 to 11 a.m. Learning Objectives 1. Describe different types of skin and correlate them with their functions. 2. Describe the microscopic anatomy of epidermis and dermis and relate them to their functions. 3. Describe the arrangement of Langer lines and their clinical importance. 4. Describe cells of epidermis-keratinocytes, melanocytes, Langerhans’ cells and Merkel cells. 5. Describe how the skin acts as a sensory organ. 6. Describe the structure and functions of appendages of skin - hairs, nails, and glands. 7. Describe the clinical importance of skin continuous with oral mucosa - Skin (cutis, integument) forms the external covering of the body, and it is considered as largest organ.  Skin is made up of two distinct layers 1. Epidermis: Stratified squamous keratinized epithelium. epidermis Developmentally it is from surface ectoderm and is avascular (receives its nutrition by diffusion from dermis).↳ outermost layer/ made mostly of cells /can't have a single layer because skin faces abrasions that's - why its stratified 2. Dermis: Connective tissue layer. Developmentally it is mesodermal in origin and is vascular. ↳ mostly (T but few cells are found here fats The hypodermis lies deep to the dermis. It contains variable amount of adipose tissue. It is equivalent to subcutaneous fascia/fat. ↳ not part of skin Lipid-soluble drugs can be absorbed by skin when applied as ointment, spray, or patches The to hypodermic layer ~ - Types: Thick skin (palm and sole) and thin skin (rest of the body) stratified they both have the same squamous Keratinized layer but : at Thick Skin · - has large amounts Keratin ~Thin skin - small amounts of Keratin EPIDERMIS ↳no nucleus is visible Stratified squamous keratinized epithelium with a continuous replacement of cells. only the superficial layer has flat cells < Living cells from the basal layer are transferred to the surface as dead cells with accumulation of ‘Keratin’ in their cytoplasm. Process is Keratinization > - These cells are called “Keratinocytes”. But there are other cell types in epidermis. The cell layers of the epidermis from deep to superficial are as follows—stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. Junction between the epidermis and the dermis presents I are found in stratum basales zigzagging interdigitations between upward projection of dermis (dermal papillae) and downward projections of the epidermis (epidermal ridges). -they form a zigzagging interdigitation that goin the dermis and epidermis Pattern of dermal ridges is unique to each individual & genetically determined. Dermatoglyphics or finger-print patterns form the basis for study of many genetic disorders A The different layers of the epidermis represent process of keratinization (a living cell from stratum basale getting * transformed to a dead cell). > - th cells more upward they start dying as , The entire process takes approximately 47 days. It varies between individuals  here the nucleus of the cells are not visible - cell is dead due tokeratin accumulation I Stratum corneum Epidermis thick only found skin Stratum lucidum > - in Stratum granulosum Stratum spinosum Stratum basale Dermis Layers of the epidermis (thick skin, H & E staining) 1. Stratum basale: Single layer of columnar (mostly) and/or cuboidal cells attached to basement membrane (basal lamina). This Stratum layer is also called as stratum germinatum. Imp corneum Some of the cells in this basal layer contain melanin. Melanocytes A -> Stratum or lucidum - 2. Stratum spinosum (prickle cell layer): Stratum granulosum Contains more mature large sized keratinocytes arranged in several layers. Cells are polygonal in deeper layers while in superficial S layers they are flat.-- by desmosomes creating a Stratum spinosum Cells are placed closely, and it gives spiny appearance Stratum basale and is called prickle cell layer. [ Mitosis occurs only in stratum basale, and spinosum and these two layers together called as malpighian layer. Mitosis only occurs here  3. Stratum granulosum: Drastic changes in keratinocyte structure occur. Cells are arranged in three to five layers especially in thick skin. Stratum corneum Cells become flattened and accumulate basophilic granules Important, a called keratohyalin. These keratohyalin granules are rich in Stratum lucidum amino acid histidine (a basic amino acid, hence stain brightly) Stratum which is a precursor of filaggrin. form Keratohyalin granule > - granulosum Pycnotic nuclei begin to disintegrate and other cellular organelles degenerate. Cytoplasm of these cells have lamellar granules which fuse with Stratum plasma membrane and release glycosaminoglycans and spinosum phospholipids into the intercellular spaces. This arrangement Stratum basale prevent water loss from the deeper tissue. 4. Stratum lucidum (Clear layer): The layer is found only in thick skin. Stains strongly than stratum corneum with acidic stain. Appears as translucent band of flattened keratinocytes whose nuclei and intercellular borders are not visible. Mixture of keratohyalin granules and intermediate filaments forms precursor of keratin called eleidin. 5. Stratum corneum (Cornified layer): Consists of closely packed layers of flattened dead cells with keratin filaments in their cytoplasm. Nucleus is absent in these cells, but they have thick plasma membrane.↳ the cell dead so is Cells present the final stage of keratinization and are filled with Stratum corneum mature keratin. usually takes Stratum corneum is very thick in thick skin. -45 days but Stratum lucidum Dead cells are continuously exfoliated from the surface and L Stratum granulosum replaced by cells from the deeper layers. In hyper proliferative L diseases like psoriasis the epidermal turnover is faster (8 to 10 Imp days). Stratum spinosum Stratum basale Cell types in the epidermis Cells Location and function Stem cells Deepest layers of the epidermis. These cells give rise to keratinocytes Keratinocytes All layers of the epidermis. They synthesize keratin Melanocytes In stratum basal of the epidermis. Melanocytes are neural crest in origin. Melanocyte synthesizes melanin and transfer it to melanin nonproducing cells through cell processes. Melanophores are cells that receive melanin from melanocytes Melanocytes are also present in retina, choroid, iris & some neurons of brain. Tyrosine → DOPA → Melanin (MSH from Pituitary). Melanin forms membrane bound granules called melanosomes which acquire > - important supranuclear position in keratinocytes & protect nuclei from UV rays. Albinism is inborn error of metabolism (absence of tyrosinase enzyme) Vitiligo: Occurs on destruction of melanocytes, mostly because of autoimmune reactions. It produces patchy depigmentation of skin Moles: Dark slightly elevated or flat lesion of skin (accumulation of melanocytes) Tactile cells Deepest layers. Merkel cells are mechanoreceptor associated with sensory (Merkel cells) nerve endings. More numerous in fingertips. Dendritic cells In stratum spinosum of the epidermis.-found here but they are formed (Langerhans’s cells) Bone marrow in origin L in They phagocytose bacteria and present bacterial antigens to T- immune cells that migrate lymphocytes. from the bone marrow They contain racket shaped Birbeck's granules in their cytoplasm DERMIS Mechanically dermis provides strength to skin by its collagen fibers and elastin content. Vascular and contains hair follicles, sebaceous and sweat glands. Dermis can be divided into two zones, a narrow superficial papillary layer and deeper reticular layer. 1. Papillary layer superficial layer > - Located immediately deep to epidermis consists of extensive network of capillaries which nourishes superficial epidermis. Allowing diffusion to easily occur > Made up of loose connective tissue and has lot of elastic fibres. Papillary layer contains type I and type II collagen fibers. Collagen fibres are called anchoring fibrils which extend into the basal lamina to reinforce the dermal-epidermal junction. Papillary layer has immunoprotective cells and many free nerve endings which may terminate in dermis or reach epidermis. Junction between epidermis and dermis appears as zigzagging interdigitation between upward projection of the dermis called dermal papillae and downward projection of epidermis called epidermal ridges. Papillae are few and small in thin skin whereas larger and closely aggregated in thick skin. S Dermal papillae contain encapsulated touch receptors called Meissner’s corpuscles.  DERMIS (continued) 2. Reticular layer: Present deep to the papillary layer. Thicker than papillary layer. IMP A Dense irregular connective tissue Reticular layer contains type-I collagen fibers. & limbs In Langer’s lines: These are tension lines corresponds ↳ vertical Intrunamontal to natural orientation of collagen and elastic fibers in reticular layer of skin. Skin incisions made parallel to If thincision the opposite direction of these lines heals with least scaring.collagen - fiber arrangement was in - it will leave a scar Consists of many arterio-venous anastomoses that help to regulate the blood pressure and body temperature. Also contain abundant nerves in both free and encapsulated endings.  the Epidermis is thinner the to and smaller compared Arrector pili thick skin muscle Check the next slide to notice the difference) Blood vessel Sebaceous glands Sweat glands Hair follicles Longitudinal section of thin skin (H & E staining)  Stratum corneum Stratum lucidum Dermal papillae Epidermal papillae Duct of the sweat gland Sweat glands Longitudinal section of thick skin (H & E staining)  Histological difference between thick and thin skin Thick skin Thin skin Location Palms and soles Entire body except palms and soles Average thickness 0.8 to 1.4 mm 0.07 to 1.12 mm One of the most Epidermis obvious visible Stratum corneum Thicker Thinner differences is the lack Stratum lucidum Present Absent of a stratum lucidum Stratum granulosum A few layers Single, often discontinuous layer in the epidermis Stratum basale More Merkel’s cells Few Merkel’s cells in the thin skin and the Dermatoglyphics Present Absent presence of several (fingerprints) glands and hair follicles Dermis in thin skin. Hair follicles Absent Present with few exceptions Sebaceous glands Few More Eccrine sweat glands More Few Meissner’s corpuscles More Few Elastic fibres Few More  Nerve supply to the skin Skin is supplied by cutaneous nerves that carry sensation from free nerve endings, Meissner’s corpuscles, Pacinian corpuscles, & Ruffini end organs. Skin is also supplied by nerves which supply smooth muscles present in the wall of the blood vessels, arrector pili muscles and sweat glands. Nerves ending in the skin (carrying sensation from the skin) can be classified into - free nerve endings and encapsulated nerve endings. Nerves ending in the Skin modified Encapsulated nerve endings Free nerve endings Pacinian corpuscles Meissner’s corpuscles Ruffini’s corpuscles Ends in St. granulosum Located in dermis, Located in the dermal Located in the reticular Serves in functions like fine hypodermis, papillae just beneath the layer of the dermis. touch, heat, cold and pain periosteum, joints and basal lamina of the The nerve terminal is Endings also ends in hair internal organs. epidermis. covered by thin connective follicle by attaching to their Myelinated nerve In H&E section they appear tissue capsule that encloses external root sheath (sense endings are surrounded as a loose, twisted of wool. a fluid filled space. the movement of by capsule. They are touch receptors Surrounding collagen fibres hair/mechanoreceptors) Pacinian corpuscles that sense the low frequency passes through the capsule. detect pressure changes stimuli. They act as and vibrations applied More numerous in papillary mechanoreceptor. on the skin surface layer of hairless skin (lips, fingertips). Pacinian corpuscles Ruffini’s corpuscles Pacinian corpuscles Meissner’s corpuscles (A) Ruffini's corpuscles and bundle with perineurium are observed (H&E, ×100). (B) Nerve bundles with perineurim are seen in the loose and dense connective tissues (H&E, ×400) (black arrow).  Arrector pili muscle Hair follicle Sebaceous glands ↳ clusters of alveoli Arrector pili muscle ↳ smooth Pilosebaceous complex Arrector Pili Muscles ↳ smooth muscles Also called as erector pili muscle or pilomotor muscles. Are non-striated (smooth) muscles which link between hair follicles and papillary layer of the dermis. Originate from the papillary layer of the dermis and extends obliquely towards the hair follicle and inserted into the hair follicle just below the sebaceous glands. Contraction of these muscles tends to pull the hair more vertically and skin in the region of its attachments gets elevated while neighboring region which gives attachment to this muscle is depressed to give rise to ‘goose skin’. occurs during > - sympathetic activity an increase in Their contraction also compresses the sebaceous glands, pushing their secretion into the neck of the follicle and out onto the surface. Supplied by sympathetic nerves. Arrector pili contract and hairs stand erect in response to cold, fear and anger. SEBACEOUS GLANDS Present in dermis of almost whole body except palms and sole. Are associated with hair follicle and arrector pili muscle. Together they forms pilosebaceous complex. Gland secretes an oily substance called sebum to skin surface and hairs. Gland consists of clusters of acini. The duct of the gland opens at the apical portion of hair follicle. Wherever hair follicle is absent, the duct opens directly into skin surface (e.g., lips, corners of mouth, nipple). Entire cell is shed, a type of secretion known as holocrine secretion. and retention of sebum sinflammation Numerous over face, which cause ‘acne’ in adult with retention of secretion. Assists in water proofing of epidermis and contributes to the characteristic body odor. Sebaceous glands produce cathelicidin and β-defensin that improve water barrier function of skin Secretory activity of these glands accelerates during puberty and increased by androgens. SUDORIFIC GLANDS (SWEAT GLANDS) Classified on the basis of their structure and nature of secretion into two types Eccrine sweat glands Are distributed all over body except lips and external genitalia. ~ Gland has duct and body (highly coiled secretory part). Duct is lined by 2 or more layers of cuboidal cells stratified Apocrine sweat glands Located in axilla, mons pubis Duct of the apocrine sweat glands opens just above levels of fubular part sebaceous ducts. secretory part SUDORIFIC GLANDS (SWEAT GLANDS) Eccrine sweat glands Apocrine sweat glands More numerous, abundant in thick skin Less numerous, present only in few parts of the body like axilla, pubic and perineal region Gland has long less coiled duct that opens into the Gland has highly coiled duct that opens into the apical regions skin surface of hair follicles Secretory segment is located deep in the dermis or Secretory segment is located deep in the dermis or hypodermis hypodermis Secretory portion of the gland consists of three Secretory portion of the glands has wide lumen and lined by types-clear cells, dark cells and myoepithelial cells. cuboidal or columnar cells (also have myoepithelial cells). Eccrine secretion is watery and contain NaCl, urea, Secretion is viscous, and once secreted acquires distinctive ammonia and uric acid. odor because of bacterial degradation. Secretion is released by means of exocytosis Secretion is released by means of exocytosis (merocrine (merocrine secretion) secretion). Evaporation of eccrine sweat from the skin surface reduces the body temperature by cooling the blood in the papillary capillaries Eccrine sweat glands are stimulated by heat and stress Apocrine sweat glands are stimulated by emotional and sensory stimuli  Cystic fibrosis: Genetic disorder caused by defect in cystic fibrosis gene in chromosome 7. Cl- concentrations in Cut sections of the eccrine sweat increases because of decreased reabsorption of sweat gland sodium chloride from the lumen of the ducts of sweat glands. Duct passing through the epidermis Appendages of the Skin HAIR Hairs are filamentous, keratinized structures which assist thermoregulation, provide some protection and have sensory function. Present only in thin skin. Length varies from less than a millimeter to a meter. With aging, because of lack of estrogen and estrogen-like hormones, hairline recedes in both male and female Structures that form hairs and maintain their growth are called hair follicle (dermo-epidermal sheath that covers root of the hair) Hair follicle consists of shaft and root. Visible part on the surface is called shaft and embedded part is called root. Root has infundibulum (from surface opening to opening of sebaceous glands) and isthmus (between opening of sebaceous gland to attachment of the arrector pili muscle) Hair follicle extends from dermis. Base of the follicle is broad and is called hair bulb. [ ↳ when a small part of dermis invaginates into the hair Hair papilla: Part of the dermis that invaginates the base of the hair bulb Alopecia areata (spot baldness): In this condition, Germinal matrix is an area of reproducing cells situated around hairs are lost in a small area of the body the papilla at the base of the hair bulb. 1. Germinal matrix: Cluster of epithelial cells capping the dermal papilla. The zone closest to the papilla resembles stratum basale in structure and function. It has columnar cells and also melanocytes Internal root sheath which gives colour to the hair. Around the bulb of the hair this layer continuous with external root sheath and near the surface it continuous External root with stratum basale. sheath Cuticle 2. Hair shaft: Made of keratin filaments. Shows three concentric zones from outside to inside, the cuticle, cortex and medulla. Cuticle is the outermost layer. It consists of single layer of highly keratinized cells. It forms a hard, shingle like outer covering of the hair. These three layers can be better identified in transverse section through the skin. # Cuticle A Cortex & Medulla  Hair root (root sheaths) 1. Connective tissue sheath 2. Glassy membrane Internal root sheath 3. External root sheath 4. Internal root sheath External root sheath Internal root sheath: This is the layer closest to Glassy membrane the hair shaft. It extends from the level of bulb to the level of the sebaceous gland ducts. There are three layers Connective tissue i). Outermost Henle’s layer: It consists of flattened layer or cuboidal cells resembling epidermal stratum lucidum. Medulla ii). Middle Huxley’s layer: Which is made up of Hair bulb one to three layers of low cuboidal cells iii). Cuticle of the internal root sheath (a layer of Hair papilla flat cells). Longitudinal section through hair bulb  Connective tissue layer Glassy membrane External root sheath Internal root sheath Henle’s layer Huxley’s layer Cuticle Cortex Medulla Transverse section through hair follicle  Nails This Slide is NOTin the EXAM Nails are plates of keratinized cells containing hard keratin. These fingernails or toenails rests on nail beds. The nail bed consists of epithelial cells that are continuous with stratum basale and stratum spinosum of the epidermis. The nail (or nail plates) has two parts: the nail body (the visible part of the nail) and the nail root (the part hidden in the nail groove). Nail matrix is a thickened portion of epidermis that contains dividing cells in the layer directly contacting the dermis and many keratinizing cells (between this basal layer and nail plate). Eponychium (or cuticle) is a thick keratinized layer extending from the upper surface of the nail groove over the most proximal part of the nail body. Hyponychium is local thickening of the stratum corneum underlying the free (distal) end of the nail. The lunula is whitish opaque region of the proximal nail body, adjacent to the nail groove Take Home Messages Skin → outer epidermis (cellular) + inner dermis (connective tissue). Epidermis → Stratified squamous keratinized epithelium. Cell layers of the epidermis from deep to superficial are — stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. Cells of the epidermis → Keratinocytes (majority of the cells) + Melanocytes (pigment forming cells) + Langerhans’ cells (phagocytic cells) + Markel cells (nerve endings). Dermis → superficial papillary layer + deeper reticular layer. Skin of the human body is of two types – thin skin and thick skin. Free nerve endings terminate in stratum granulosum, and they serve in many functions like fine touch, heat, cold and pain. Pacinian corpuscles detect pressure changes and vibrations. Meissner’s corpuscles are touch receptor that sense the low frequency stimuli. Ruffini’s corpuscles act as mechanoreceptor. Hairs are keratin filaments having three concentric zones from outside to inside, the cuticle, cortex and medulla. Arrector pili muscles are non-striated (smooth) muscles which link between hair follicles and papillary layer of the dermis. Contraction of these muscles tends to pull the hair more vertically and compresses the sebaceous glands, pushing their secretion into the neck of the follicle and out onto the surface. The muscle is supplied by sympathetic nerves. Sebaceous glands are present in dermis of almost whole body except palms and sole. They secrete an oily substance called sebum to skin surface and hairs. The entire cell is shed, a type of secretion known as holocrine secretion. Sweat glands are of two types and are present in dermis - Eccrine sweat glands (typical) + Apocrine sweat glands. They pour their secretion to skin surface through duct.