n n n Microscopic structure of the skin Microscopic structure of skin appendages and mammary gland Development of the skin and skin appendages (derivatives) Lecture 10 General Medicine_3rd semester nthe skin (cutis) covers the external surface and is heaviest single organ of the human nbody n - cca 16 % of total body weight n - 1.2- 2.3 m2 in adults n nfunctions: Øprotects body against influence of the external factors, Øcontains tactile, cold, heat and pain receptors, Øparticipates in immune response and processes, Øis involved in regulation of body temperature, Øserves as a complementary excretory organ (sebaceous and sudoriferous glands), Øtakes part in gaseous exchange (to a limited extent) n nthe skin consists of Øepidermis /an epithelial layer of ectodermic origin/ Ødermis /a layer of connective tissue of mesenchymal origin/ n and Øhypodermis or subcutaneous tissue /a layer of loose connective tissue that may contain pads of adipose cells, the panniculus adiposus/ n Øskin appendages - either keratinised (hair and nails) or glandular (sebaceous and sudoriferous glands) nthe mammary gland is regarded as specialized and modified sweat gland (s) 003 nEPIDERMIS n nis stratified squamous keratinized epithelium ncells are called keratinocytes nit contains 3 less abundant cell types: melanocytes, Langerhans cells, and Merkel´s cells n n2 types of the skin are distinguished: n the thick (glabrous) skin - found on palms and soles n the thin (hairy) skin - found elsewhere on the body surface n/„thick“ and „thin“ refer to the nthickness of the epidermis - it nvaries between 75 and n150 µm for the thin skin nand 600-800 µm for the thick skin/ n F18_02 n5. Stratum corneum: lies at the surface, consists of 15-20 layers of flattened non- nnucleated keratinised cells whose cytoplasm is filled with a birefringent filamentous nscleroprotein – keratin n n4. Stratum lucidum : translucent and thin nit lacks regularly in the thin skin; the layer contains dead, nanucleated and eosinophilic cells, desmosomes are still evident n n3. Stratum granulosum: 3 - 5 layers of flattened polygonal cells nwith keratohyalin granules and membrane-coated lamellar ngranules (composed of lamellar discs formed by lipid bilayers) n n2. Stratum spinosum: nconsists of cuboidal, polyhedral, or slightly flattened cells, nthe cytoplasm projects into processes that are filled with bundles of ntonofilaments (under light microscope as tonofibrils) ncells in mitoses n nboth strata are called by common term as stratum germinativum n n1. Stratum basale (stratum cylindricum): na single layer of basophilic columnar or cuboidal cells, ncontain cytokeratin filaments nnumerous desmosomes, intense mitotic activity F18_01 Bez názvu 1 kopie 3. Stratum granulosum 2. Stratum spinosum: 1. Stratum basale F18_03 F18_05 Stratum spinosum: LM TEM F18_08 Melanocytes are specialized cells of the epidermis located beneath or between cells of the stratum basale and in hair follicles cells synthesize and produce eumelanin synthesized melanin granules are then injected in the cytoplasm of keratinocytes After keratinisation, the cells consist of only fibrillar and amorphous proteins and thickened plasma membranes called horny cells F18_06 F18_09 the color of the skin results from the content of melanin supranuclear location of granules nLangerhans cells (dendritic cells) n nare star shaped cells, found mainly in the stratum spinosum of the nepidermis n2 - 8 % of the epidermal cells ncells are supposed for the bone-marrow-derived macrophages and are capable of nbinding and presenting antigens toT lymphocytes n nMerkel´s cells n noccur mostly in the thick skin nthey resemble keratinocytes but contain small dense granules in the cytoplasm nnumerous nerve endings terminate at the base of each Merkel´s cell - nsensory mechanoreceptors n nDERMIS nit supports the epidermis and reaches the thickness about 4 mm n2 layers with rather indistinct boundaries: n nthe outermost papillary layer (stratum papillare corii ) - of loose connective tissue with networks of elastic and reticular fibers n nthe deeper reticular layer (stratum reticulare corii) - of irregular dense connective tissue (collagen I) nthe principal glycosaminoglycan of the dermis is dermatan sulfate Bez názvu 1 kopie the papillary layer the reticular layer * nin the thick (glabrous) skin found on palms and soles dermal papillae run in pairs nthey are suppported with common corial ridges ncorial ridges correspond to the cristae cutis limited by sulci cutis on the surface of the epidermis norientation of cristae cutis is unique for each individual n ndactyloscopy n Kůže - 14 Kůže - 15 nthe dermis has a rich network of blood and lymph vessels nblood may pass through capillaries or directly from arteries to veins via narteriovenous anastomoses or shunts n nthese play a very important role in temperature and blood pressure nregulation 001 F18_13 nerve supply of the skin is very rich SUBCUTANEOUS TISSUE (hypodermis, tela subcutanea) consists of loose connective tissue that binds the skin loosely to the subjacent organs (muscles, perichondrium or periosteum) it may contain fat cells nSkin derivatives of glandular type n nglands of the skin are of 2 types: Øsweat glands Øsebaceous glands n nSweat glands - widely distributed nthroughout the body, are specialized for nproduction of sweat that cools the body nby evaporation, and other complex nsecretions n neccrine sweat glands (gll. sudoriparae, ngll. globiformes) nare found everywhere on the body surface nexcept the free margin of the lip, the nprepuce and glans penis, the clitoris, and nlabia minora n nglands are simple, coiled tubular nconsist of: the secretory portion n the duct F18_17 nthe secretory portion: the thick basement membrane, nmyoepithelial cells and secretory cells: n dark cells (mucoid cells) are npyramidal cells with basophilic ncytoplasm granules contain nglycoproteins n clear cells are devoid secretory ngranules but contain an abundance nof glycogen particles n nthe duct: na) proper duct - in nthe dermis, its wall is composed of ntwo-layered epithelium, myoepithelial ncells and the basement nmembrane n nb) intraepidermal canaliculus - nlocated in the epidermis nit has no proper wall F18_18 Kůže - 15 secretion of eccrine glands is not viscous and contains little protein, components are water, sodium chloride, urea, ammonia, and uric acid napocrine sweat glands nin the axillary and anal regions n nthe secretory part that is much larger than that in eccrine sweat glands and is lined by a cuboidal or columnar eosinophilic secretory cells n nthe duct that opens into hair follicle nglands produce a viscous milky white odorous secretion napocrine glands start secretion after puberty, under influence of sex steroids n n n n n n n n n n n n n n n nmodified apocrine sweat glands: the ceruminous glands in the external auditory nmeatus, glands of Montgomery in the nipple, and glands of Moll in eyelids velkepotni Kůže - 13 mazovazlaza1 Sebaceous glands are holocrine type and are associated with hair follicles they occur practically on all body surfaces except the palms of the hands and soles of the feet consists of several alveoli (acini) and short duct that opens in the upper portion of a hair follicle and is lined by a stratified squamous epithelium mazovazlaza nacini are composed of two types of cells: nan outer layer of stem cells called basal cells and ncentral group of cells that accumulate lipid droplets in their ncytoplasm ncentral cells disintegrate and become a npart of sebum (holocrine secretion) n nsebaceous glands begin to function nat puberty mazovazlaza1 F18_16 nhairs - elongated keratinised fibers derived from invaginations of epidermal nepithelium, occur everywhere on the body nexcept the palms, soles, lips, glans penis, nclitoris, and labia minora n nhair consists of n - free part (scapus pili) and n - hair root (radix pili) - an nextended part of the hair root is nhair bulb n - hair papilla formed nby vascularized loose connective tissue n - hair follicle Skin derivatives of keratinized type hairs, nails Kůže - 13 F18_15 F18_14 nComponents of the hair Øthe hair medulla - central part consisting of 2 to 3 rows (columns) of lightly stained, polyhedral cells, it is discernible only in the hair bulb and in thick hairs, Øthe hair cortex - several layers of spindle-shaped (fusiform), tightly packed cells with melanin granules, Øthe hair cuticle (epidermicule) - is a layer of single keratinised cells that overlap each other and whose the ends are directed towards the scapus pili Ø nHair follicle nenvelopes the hair root nthe internal root sheath - lies close the hair and comprises three layers: Henle's and Huxley's layers, which contain eosinophilic trichohyaline granules, and the cuticle of keratinised cells; the internal root sheath grows from the hair bulb and its cells gradually keratinise towards the neck of the hair follicle (the neck = region of the opening of sebaceous gland) nthe external root sheath - is continuous with the germinal epidermal layer and thins towards the hair bulb; it consists of lightly stained cells and the basement membrane nthe connective tissue sheath - thin leaf of dense collagen tissue that links the hair to its surrounding tissue n nmusculus arrector pili or arrector pili muscle is a bundle of smooth muscle cells stretched between the lower portion of the hair follicle and the superficial layer of dermis at the side where the loose hair end makes a sharp angle with the epidermis ncontraction of the arrector pili muscle causes a depression of the skin where the muscles attach to the dermis. This produces the "gooseflesh" 002 Kůže - 36 cibulkavlasu cibulkavlasu1 nehet_atl NAILS plates of keratinised epithelial cells on dorsal aspect of distal phalanxes (phalanges) nthe proximal part of the nail, hidden in the nail groove, is the nail root nthe nail root is covered with eponychium (or cuticle) nthe nail plate - corresponds to the stratum corneum of the skin nrests on a bed of epidermis termed the nail bed - is composed of stratum basale and the stratum spinosum The cells of the nail bed that are under the root of the nail constitute the matrix. nehetpricne nehetpricne1 nMAMMARY GLANDS nare modified apocrine sweat glands producing milk n neach mammary gland consists of 15-25 lobes which are nseparated each others by dense connective tissue nlobes are drained with excretory lactiferous ducts nthat open in the nipple (15-25 openings) n nhistological structure of mammary glands varies according to sex, age, and nphysiologic status n nNonlactating mammary glands n nglandular tissue is reduced on only duct system, e.g. lactiferous ducts, nterminal interlobular ducts and intralobular ducts n nan area of one interlobular duct is a lobule nthe lobules are separated by a denser, less cellular interlobular connective tissue n nspaces within lobules are filled with loose intralobular tissue abundant in cells. Gl. mammae mamma non lactans mammanonlact1 kopie mammanonlact kopie nLactating mammary glands n nglandular tissue is fully differentiated nby thin connective tissue septa, the glandular parenchyma is ndivided into the lobules n nlobules contains spherical to elongated acini (alveoli) ndiffer in size nthe wall of acini consist of n- the basement membrane n- cuboidal or columnar secretory cells and n- myoepithelial cells located between the basement membrane and bases of nsecretory cells n nducts na) intralobular ducts lined by a simple cuboidal to columnar epithelium nb) lactiferous ducts lined by two layers of columnar cells which, in the lactiferous sinus, changes into stratified squamous epithelium n nthe first secretion appearing after birth is called the colostrum nit contains less fat and more protein than regular milk and is rich in antibodies mammalact kopie Gl. mammae mamma lactans DEVELOPMENT OF SKIN AND SKIN APPENDAGES Epidermis initially, a single layer of ectodermal cells covers the embryo starting from the 2nd month, the ectodermal cells divide and form a superficial protective layer of flattened cells, the periderm or epitrichium at the end of 4th month, the epidermis acquires its definitive arrangement and 4 layers are distinguished: basal, spinous, granular and horny layer Kůže - 45 cells that have been exfoliated during fetal life form part of the vernix caseosa, a white, cheese-like, protective substance that covers the fetal skin during the early fetal period, melanoblasts migrate from the neural crest to the dermoepidermal junction, where they differentiate into melanocytes Kůže - 3 nDermis n nthe dermis is derived from the mesenchyme underlying the surface nectoderm n nthe mesenchyme arises from 2 sources: nfrom the somatic layer of lateral mesoderm (most of the mesenchyme), nfrom the dermomyotome regions of the somites (in lesser extent) n nby 11 weeks, the mesenchymal cells have begun to produce ncollagenous and elastic connective tissue fibers n nas the epidermal ridges form, the dermis project upward into nthe epidermis and forms dermal papillae Eccrine sweat glands develop as solid epidermal downgrowths that extend into the underlying dermis as buds elongate, their ends become coiled, forming the primordia of future secretory portions of glands Kůže - 6 Kůže - 7 Kůže - 5 nDevelopment of hairs n nthey develop early in the fetal period, but they do not become readily visible until about n20th week nfirst recognizable hairs occur on the eyebrows, upper lip, and chin n na hair follicle begins to develop nas a solid downgrowth of the stratum ngerminativun of the nepidermis called the hair bud nit extends into the underlying dermis n Kůže - 9 Kůže - 10 the deepest part of the hair bud soon becomes club-shaped, forming a hair bulb the epithelial cells of the centre of the hair bulb constitute the germinal matrix - it gives rise to proper hair the hair bulb is then invaginated by a small mesenchymal hair papilla n nthe peripheral cells of the developing hair bud (follicle) form the epithelial root sheath n nthe surrounding mesenchymal cells differentiate into the dermal (connective tissue) root nsheath n nthe first hairs are called lanugo, are fine and colourless n nlanugo is replaced during the perinatal period by coarser hairs, called vellus n nthese hairs persist over most of the body, except in the axillary and pubic regions n nhairs of those regions are replaced during puberty Kůže - 46 apocrine sweat glands (axilla, pubic region, anal region, areolae) develop from the hair follicle as sebaceous glands Kůže - 47 Development of mammary gland mammary glands develop during the 6th week as a solid downgrowth of the epidermis that grow against the underlying mesenchyma downgrowths occur along the mammary ridges - two thickened strips of ectoderm that run from the axillary to the inguinal regions in human embryos, mammary ridges occur during the 4th week, but except the pectoral area rapidly disappear each primary mammary bud soon gives rise to several secondary buds that develop into lactiferous ducts and their branches the fibrous connective tissue and fat develop from the surrounding mesenchyme nNails n ntoenails and fingernails begin to develop at the distal ends of digits at about n10 weeks, development of fingernails precedes that of the toenails n nthe nails first appear as thickened areas of the developing epidermis on the ndorsal aspect of each digit n nthe nail fields are surrounded laterally and proximally by folds - nail folds ncells from the proximal nail fold grow over the nail field and become nkeratinised to form the nail, or nail plate n nat first, superficial layers of epidermis called the eponychium cover the ndeveloping nail, this later degenerates, except at the base of the nail, nwhere it persists 001 002 F18_04 Kůže - 14