Integumentary System accuqred imuune system
- 1. Integumentary system Dr. Abdulrahman Muhammed ( MD ) 1
- 2. Introduction • Integumentary system is composed of – Skin – Accessory structures • Hair • Nail • Glands • Receptors 2
- 3. Skin • The largest organ –Surface area of about 1.5–2 m2 –Weighs approximately 4-5 kg • Thickness: vary ( 1-2mm in most body ) • Forms the boundary between our internal and the external environment • It is a pliable but tough organ which is constantly regenerating 3
- 4. Functions 1. Protection • Chemical barrier • Physical or Mechanical barrier • Biological barrier 2. Body Temperature Regulation 3. Cutaneous Sensation 4. Metabolic Functions 5. Blood Reservoir 6. Excretion and absorption 4
- 5. Protection • Chemical barrier – Sweat create an acid environment that retard reproduction of bacteria – Sebum from sebaceous glands is bactericidal – The dark pigment melanin in epidermis protects cells against ultraviolet radiation • Physical or mechanical barrier – Provides a physical barrier against thermal and mechanical insults and against most potential pathogens – Keratinized cells provide a continuous barrier – Skin is also a permeability barrier against excessive loss or uptake of water, which has allowed for terrestrial life 5
- 6. • Biological barrier – Microorganisms that do penetrate skin alert resident lymphocytes and antigen-presenting cells of skin and an immune response is mounted • Langerhans cells present foreign substances ( antigens ) to the lymphocytes which in turn activate immune system • Macrophages of the dermis dispose of viruses and bacteria that have penetrated the skin 6
- 7. Body Temperature Regulation 7 • A constant body temperature is normally maintained by – The skin's insulating components ( eg, the fatty layer and hair on the head ) – Its mechanisms for accelerating heat loss • 2 ways: – Sweat production: Cooling occurs through evaporation of water from the surface of the skin – Adjustment of blood flow in dermis: Cooling occurs through radiation of heat
- 8. Cutaneous Sensation 8 • The skin is richly supplied with cutaneous sensory receptors • Many types of sensory receptors allow skin to constantly monitor the environment and various mechanoreceptors with specific locations in skin are important for the body's interactions with physical objects • Include – Tactile sensations – Thermal sensations – Pain sensation
- 9. Metabolic Functions 9 • Cells of skin synthesize vitamin D3, needed in calcium metabolism and proper bone formation, through the local action of UV light on the vitamin's precursors • Keratinocyte enzymes can “disarm” many carcinogens • Keratinocytes can also activate steroid hormones
- 10. Blood Reservoir 10 • The skin can hold about 8-10% of the body’s entire blood volume • Blood can be diverted from the skin to other organs in need • Blood is diverted to the skin for temperature regulation
- 11. Excretion and absorption 11 • Limited role • Sweat excretes water, heat, electrolytes, salts, CO2 and nitrogen-containing wastes (ammonia, urea, and uric acid)
- 12. Cont… • Certain lipid soluble materials penetrate skin – fat-soluble vitamins (A, D, E, and K), certain drugs, some toxic materials and the gases oxygen and carbon dioxide – that can be absorbed through the skin include organic solvents such as acetone (in some nail polish removers) and carbon tetrachloride (dry-cleaning fluid); salts of heavy metals such as lead, mercury, and arsenic; and the substances in poison ivy and poison oak. – Skin's selective permeability allows some lipophilic drugs to be administered via skin patches 12
- 13. Skin Layers • 2 layers: Epidermis and dermis • Epidermis – Outermost protective shield of the body – Composed of epithelial cells – Avascular • Dermis – A tough leathery layer deep to the epidermis – Making up the bulk of the skin – Composed of fibrous connective tissue – Vascular 13
- 14. 1. Epidermis • The epidermis consists mainly of a stratified squamous keratinized epithelium composed of cells called keratinocytes • Three less abundant epidermal cell types are also present: – pigment-producing melanocytes – antigen-presenting Langerhans cells – tactile epithelial cells or Merkel cells 14
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- 16. • The epidermis forms the major distinction between thick skin, found on the palms and soles, and thin skin found elsewhere on the body • The designations "thick" and "thin" refer to the thickness of the epidermal layer, which varies from 75 to 150 µm for thin skin and from 400 to 1400 µm (1.4 mm) for thick skin • Total skin thickness ( epidermis plus dermis ) also varies according to site – For example, skin on the back is about 4 mm thick, whereas that of the scalp is about 1.5 mm thick 16
- 17. Layers of epidermis 17 • From the dermis outward, the epidermis consists of four layers of keratinocytes, five layers in thick skin:
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- 19. Layers of epidermis in thin skin: epidermal pegs (EP); dermal papillae (DP); dermis (D); stratum basale (B); stratum spinosum (S); stratum granulosum (G); stratum corneum (C) 19
- 20. 1. Basal layer (stratum basale) – Single layer of basophilic columnar or cuboidal cells on the basement membrane at the dermal-epidermal junction – Hemidesmosomes in the basal plasmalemma help bind these cells to the basal lamina and desmosomes bind the cells of this layer together in their lateral and upper surfaces – Characterized by intense mitotic activity and is responsible, in conjunction with the initial portion of the next layer, for constant production of epidermal cells 20
- 21. – The human epidermis is renewed about every 15–30 days, depending on age, the region of the body, and other factors – All keratinocytes in the stratum basale contain intermediate filaments composed of keratins – As the cells progress upward, the amount and types of keratin filaments increase 21
- 22. 2.Spinous layer (stratum spinosum) –The thickest epidermal layer –Consists of polyhedral or slightly flattened cells having central nuclei with nucleoli and cytoplasm actively synthesizing keratin filaments –Just above the basal layer some cells may still divide and this combined zones is sometimes called the stratum germinativum 22
- 23. Cont… –The keratin filaments form microscopically visible bundles called tonofibrils which converge and terminate at the numerous desmosomes –Cytoplasm is drawn into short cellular extensions around the tonofibrils on both sides of each desmosome leading to the appearance of many short spiny projections 23
- 24. Section of skin from the sole of the foot (thick skin), showing only the stratum spinosum, highlights cells with numerous, short cytoplasmic projections (arrow) 24
- 25. 3. Granular layer ( stratum granulosum ) – Consists of 3–5 layers of flattened polygonal cells undergoing terminal differentiation – Cytoplasm is filled with intensely basophilic masses called keratohyaline granules and membrane-coated lamellar granules ( small ovoid structures containing many lamellae composed of various lipids ) • Lamellar granules undergo exocytosis, discharging their contents into the intercellular spaces of the stratum granulosum • this lipid-rich material produces sheets that envelop the cells, which are now little more than flattened sacs filled with keratins and associated proteins • The layer of lipid envelopes is a major component of the epidermal barrier against the loss of water from skin 25
- 26. Cont… • Together, keratinization and production of the lipid-rich layer have a crucial sealing effect in skin, forming the barrier to penetration by most foreign materials 26
- 27. Cont… 27
- 28. 4. Stratum lucidum – Only seen in thick skin – Consists of a thin, translucent layer of extremely flattened eosinophilic cells – The nuclei and organelles have been lost and the cytoplasm consists almost only of densely packed keratin filaments embedded in an electron-dense matrix – Desmosomes are still evident between adjacent cells 28
- 29. Stratum granulosum and stratum lucidum: thick skin: stratum spinosum (S); stratum granulosum (G); stratum lucidum (L); stratum corneum (C) 29
- 30. 5. Stratum corneum – Consists of 15–20 layers of flattened, non- nucleated keratinized cells whose cytoplasm is filled with filamentous keratins – After keratinization, the cells contain only fibrillar and amorphous proteins with thickened plasma membranes and are called squames or horny, cornified cells – These cells are continuously shed at the surface of the stratum corneum 30
- 31. MEDICAL APPLICATION • Psoriasis – An increase in the number of proliferating cells in the stratum basale and the stratum spinosum as well as a decrease in the cycle time of these cells – This results in greater epidermal thickness and more rapid renewal of epidermis, but also can produce abnormal keratinization with a defective skin barrier 31
- 32. Cont… 32
- 33. Keratinocyte 33 • Principal cell • Arise from constant cell mitosis at the deepest layer • Migrate upward through various layers of the epidermis
- 34. Cont… • Keratinocyte cells manufacture keratin during their migration to the skin surface –As cells migrate to the surface their contents become dominated by keratin –The cells will deform to become flattened, dead structures that are keratin filled –Millions of cells on the free surface rub off daily –Cell reproduction is higher in areas subject to friction 34
- 35. Melanocytes • Spider shaped cells found among the cells of the basal layer and in the hair follicles • Specialized epithelial cells that synthesize the pigment melanin –Two types • Eumelanin: brownish black pigment • Pheomelanin:similar pigment found in red hair • One melanocyte accumulates for every five or six basal keratinocytes ( 600–1200/mm2 of skin ) 35
- 36. • They have rounded cell bodies and form hemidesmosomes with the basal lamina, but no desmosomes with adjacent keratinocytes • Long irregular dendritic extensions from each melanocyte branch into the epidermis, running between the cells of the basal and spinous layers and terminating in invaginations of the neighboring five to ten keratinocytes 36
- 37. Cont… • Ultrastructurally, a melanocyte is a pale-staining cell with numerous small mitochondria, short cisternae of RER, and a well- developed Golgi apparatus • Melanin granules are transported to the tips of the melanocyte's dendrites 37
- 38. • The associated keratinocytes phagocytose the tips of these dendrites • These are transported along to the region near the nucleus and accumulate as a supranuclear cap which absorbs and scatters sunlight, protecting nuclear DNA from the deleterious effects of UV radiation • Although melanocytes synthesize melanin, the keratinocytes act as a depot and contain more of this pigment than the cells that make it • One melanocyte plus the keratinocytes into which it transfers melanosomes make up an epidermal-melanin unit • The density of such units is similar in all individuals 38
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- 40. MEDICAL APPLICATION • Albinism –Hereditary inability of the melanocytes to synthesize melanin –As a result, the skin is not protected from solar radiation by melanin, and there is a greater incidence of skin cancers • Vitiligo –The degeneration and disappearance of entire melanocytes causes a patchy loss of pigment in the skin 40
- 41. Cont…. 41
- 42. Langerhans (Dendritic) Cells • Usually seen in the spinous layer • Represent 2–8% of the epidermal cells • Cytoplasmic processes extend from these cells between keratinocytes of all the layers, forming a fairly dense network in the epidermis • Function – Bone marrow–derived, blood-borne cells, capable of binding, processing, and presenting antigens to T lymphocytes 42
- 43. Tactile (Merkel) Cells • Mechanoreceptors • Resemble pale-staining keratinocytes with keratin filaments in their cytoplasm but few if any melanosomes • Located in the basal epidermal layer in areas of high tactile sensitivity and at the bases of hair follicles • Sensitive to light touch 43
- 44. 2. Dermis • Connective tissue that supports the epidermis and binds it to the subcutaneous tissue • The thickness of the dermis varies according to the region of the body, and reaches its maximum of 4 mm on the back • The surface of the dermis is very irregular and has many projections ( dermal papillae ) that interdigitate with projections (epidermal pegs or ridges) of the epidermis – Dermal papillae are more numerous in skin that is subjected to frequent pressure, where they reinforce the dermal- epidermal junction 44
- 45. • A basement membrane is always found between the stratum basale and the papillary layer of the dermis and follows the contour of the interdigitations between these layers • Nutrients for keratinocytes must diffuse into the avascular epidermis from the dermis vasculature through this basement membrane 45
- 46. • The dermis contains two layers with rather indistinct boundaries—the outermost papillary layer and the deeper reticular layer • Papillary layer – Constitutes the major part of the dermal papillae – Thin, composed of loose connective tissue, with fibroblasts and other connective tissue cells – From this layer, anchoring fibrils of type VII collagen insert into the basal lamina and bind the dermis to the epidermis 46
- 47. • Reticular layer – Thicker; accounts for 80% of the dermis – Composed of dense irregular connective tissue (mainly bundles of type I collagen), and has more fibers and fewer cells than the papillary layer – Collagen fibers of the dermis give the skin its strength and resiliency – Collagen binds water, helping to maintain hydration – A network of elastic fibers is also present, providing elasticity to the skin – Spaces between the collagen and elastic fibers are filled with proteoglycans rich in dermatan sulfate 47
- 48. Elastic fibers of dermis: extensive distribution of darkly stained elastic fibers among the eosinophilic collagen bundles 48
- 49. Dermal ridges 49 • On the hands and soles of the feet, the papillae lie atop dermal ridges • The dermal ridges produce conspicuous looped and whorled ridges on the epidermal surface which increase the grip of the fingers and feet • Sweat pores open along the crests of the epidermal ridges leaving a film of sweat we know as fingerprints
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- 51. Lines of cleavage (Tension lines) • In certain regions of the body, collagen fibers tend to orient more in one direction than another • Lines of cleavage (tension lines) in the skin indicate the predominant direction of underlying collagen fibers. • Surgical incision running parallel to the collagen fibers will heal with only a fine scar • A surgical incision made across the rows of fibers disrupts the collagen, and the wound tends to gape open and heal in a broad, thick scar 51
- 52. Dermal stretching and Blisters • During pregnancy dermal tearing may occur indicated by silvery white scars or “stretch marks” • Blisters are the separation of the epidermal and dermal layers with the resulting development of a fluid filled pocket 52
- 53. Flexure lines • Flexure lines are dermal folds that occur at or near joints where the dermis is secured to deeper structures • Folds occur on the surface of the wrists, palms, soles of the feet, fingers and toes 53
- 54. MEDICAL APPLICATION • With age, collagen fibers thicken and collagen synthesis decreases • In old age, extensive cross-linking of collagen fibers, the loss of elastic fibers, and degeneration of these fibers due to excessive exposure to the sun cause the skin to become more fragile, lose its suppleness, and develop wrinkles 54
- 55. Skin Color • The color of the skin is the result of several factors, the most important of which are the keratinocytes' content of melanin and carotene and the number of blood vessels in the dermis • Three pigments contribute to skin color; melanin, carotene, and hemoglobin Melanin • All humans have the same amount of melanocytes • Racial differences in skin coloring is due to the kind and amount of melanin made and retained • Melanocytes of people with ancestral origins near the equator, where the need for protection against the sun is greatest, produce darker melanin granules more rapidly and accumulate them in keratinocytes more abundantly 55
- 56. • UV radiation causes keratinocytes to secrete various paracrine factors that stimulate melanocyte activity • Darkening of the skin ( tanning ) after exposure to solar radiation is the result of a two-step process – First, a physicochemical reaction darkens preexisting melanin – Next, the rates of melanin synthesis in the melanocytes and transfer to keratinocytes accelerate, increasing the amount of this pigment Carotene • Yellow to orange pigment found in certain plant products • It tends to accumulate in the stratum corneum and the fatty tissue of the hypodermis • It is most obvious on the palms and soles of the feet where the stratum corneum is thickest 56
- 57. Hemoglobin • Located in red blood cells circulating in the dermal capillaries • The crimson color of oxygenated hemoglobin gives fair skin its pinkish hue • When hemoglobin is poorly oxygenated the blood and skin of light skinned people appears blue 57
- 58. Subcutaneous Tissue • Consists of loose connective tissue that binds the skin loosely to the subjacent organs, making it possible for the skin to slide over them • Also called the hypodermis or superficial fascia • Contains fat cells that vary in number in different regions of the body and vary in size according to nutritional state • Not considered as part of the skin, but it shares some of the skins protective functions • Functions – Store fat – Anchor the skin to the underlying muscles – Act as insulator against heat loss 58
- 59. Vessels • The connective tissue of the skin contains a rich network of blood and lymphatic vessels • Blood vessels: Form two major plexuses: – Cutaneous plexus • Lies at junction of hypodermis and dermis • Supply hypodermis, deeper dermis, hair follicles and glands – Sub papillary plexus • lies just beneath dermal papilla between the papillary and reticular dermal layers • sends branches into the dermal papillae and supplies a rich, nutritive capillary network just below the epidermis 59
- 60. • Arteriovenous anastomoses – Shunts located between the two major plexuses – Has a thermoregulatory function – The shunts decrease blood flow in the papillary layer to minimize heat loss in cold conditions and increase this flow to facilitate heat loss when it is hot, thus helping maintain a constant body temperature • Lymphatic vessels – Begin as closed sacs in the dermal papillae and converge to form two plexuses located with the blood vessels 60
- 61. Sensory Receptors 61 • With its large surface and external location, the skin functions as an extensive receiver for certain stimuli from the environment • A variety of sensory receptors are present in skin, including both simple nerve endings with no covering and more complex structures with sensory fibers enclosed by glia and delicate connective tissue capsules
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- 63. • Unencapsulated receptors – Tactile discs • associated with the epidermal tactile cells • receptors for light touch – Free nerve endings • in the papillary dermis • respond primarily to high and low temperatures, pain, and itching, but also function as tactile receptors – Root hair plexuses • a web of sensory fibers surrounding the bases of hair follicles in the reticular dermis • detects movements of the hairs 63
- 64. • Encapsulated receptors ( are tactile mechanoreceptors ) – Tactile corpuscles ( Meissner corpuscles ) • elliptical structures • perpendicular to the epidermis in the dermal papillae and papillary layer of the fingertips, palms and soles • detect light touch • few spiraling dendrites are surrounded by Schwann cells, which in turn are surrounded by an egg-shaped capsule of connective tissue 64
- 65. Tactile (Meissner) corpuscle (TC): dermal papillae (DP); epidermis (E) 65
- 66. – Lamellated ( Pacinian ) corpuscles • large oval structures • found deep in the reticular dermis or hypodermis • with an outer capsule and 15 to 50 thin, concentric lamellae of flat Schwann-type cells and collagen surrounding a highly branched, unmyelinated axon • specialized for sensing coarse touch, pressure (sustained touch), and vibrations – Krause corpuscles and Ruffini corpuscles • encapsulated, pressure-sensing mechanoreceptors in dermis, but are more poorly characterized structurally 66
- 68. Hair • Hairs are elongated keratinized structures derived from invaginations of the epidermal epithelium called hair follicles • Two parts 1. Hair shaft: the part that projects from the skin 2. Hair root: the part embedded in the skin • The color, size, shape and texture of hairs vary according to age, genetic background, and region of the body • All skin has at least minimal hair except that of the palms, soles, lips, glans penis, clitoris, and labia minora • The face has about 600 hairs/cm2 and the remainder of the body has about 60/cm2 68
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- 70. • The hair follicle has a terminal dilatation called a hair bulb • A dermal papilla inserts into the base of the hair bulb and contains a capillary network required to sustain the hair follicle • The epidermal cells covering this dermal papilla form the hair root matrix that produces and is continuous with the hair shaft protruding beyond the skin surface 70
- 71. • Papilla (a) protrudes into a hair bulb and supplies nutrients • The wall of the follicle is made of an outer connective tissue sheath (b) and inner epithelial root sheath (c) • A single layer of stratum basale cells (d) divide to form hair 71 a c d b
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- 73. The base of a hair follicle: dermal papilla (DP); connective tissue sheath (CTS); internal root sheath (IRS) and external root sheath (ERS); glassy membrane (G); cortex (CO) 73
- 74. • The epithelial cells (keratinocytes) that make up the hair bulb are similar to those in the basal and spinous layers of epidermis • They divide constantly and then undergo keratinization, differentiating into specific cell types • In certain types of thick hairs, the cells of the central region of the root at the apex of the dermal papilla produce large, vacuolated, and moderately keratinized cells that form the medulla of the hair 74
- 75. • Other cells differentiate into heavily keratinized, compactly grouped fusiform cells that form the hair cortex • The most peripheral cells produce the hair cuticle, a thin layer of heavily keratinized cells covering the cortex • Melanocytes in the hair bulb transfer melanin granules into the epithelial cells that will later differentiate to form the hair 75
- 76. Hair root: medulla (M), cortex (CO), and cuticle (CU) 76
- 77. • The three concentric layers of hair – Medulla: central core of large cells separated by air spaces – Cortex: bulky layer surrounding the medulla – Cuticle: a thin layer of overlapping cells 77
- 78. • Epithelial root sheath – Surrounds the hair bulb with the outermost cells of hair bulb are continuous with it – Form two layers • Internal root sheath –completely surrounds the initial part of the hair but degenerates above the level of the attached sebaceous glands • External root sheath –covers the internal sheath and extends all the way to the epidermis, where it is continuous with the basal and spinous layers 78
- 79. • Separating the hair follicle from the dermis is an acellular hyaline layer, the thickened basement membrane called the glassy membrane • The surrounding dermis forms a connective tissue sheath • Running from a midpoint on this sheath and to the dermal papillary layer is a small bundle of smooth muscle cells, the arrector pili muscle 79
- 80. – Contraction of these muscles pulls the hair shafts to a more erect position, usually when it is cold in an effort to trap a layer of warm air near the skin – In regions where hair is fine, contraction of arrector pili muscles is seen to produce tiny bumps on the skin surface ("goose bumps") where each contracting muscle distorts the attached dermis – Contraction of These muscles Bring the Sebaceous glands to secrete Sebum 80
- 81. • Hair color is produced by the activity of melanocytes located between the papilla and the epithelial cells of the hair root • The melanocytes produce and transfer melanin granules to these keratinocytes by a mechanism that is generally similar to that for the epidermis • However, keratinization to produce hair does differ in some respects 81
- 82. – Unlike epidermal keratinization where terminal differentiation of all cells gives rise to the stratum corneum, cells in the hair root differentiate into the cell types of the hair medulla, cortex, and cuticle – Keratin of hair has a harder and more compact nature than that of stratum corneum, maintaining its structure much longer – Keratinization in the epidermis occurs continuously and over the entire surface, it is intermittent in the hair and occurs only in the hair root 82
- 83. Hair Type • Vellus and terminal –The body hair of children and women is the fine vellus variety –Hair of the eyebrows and scalp is called terminal hair –At puberty terminal hair appears in the axillary and pubic regions of both sexes 83
- 84. Hair Growth 84 • Hairs grow discontinuously, with periods of growth followed by periods of rest, and this growth does not occur synchronously in all regions of the body or even in the same area • The duration of the growth and rest periods also varies according to the region of the body • In the scalp, growth periods may last for several years, whereas the periods of follicle regression and inactivity may together last only 3 to 4 months • Hair growth on the face and pubis is strongly influenced by sex hormones • The rate of hair growth varies from region to region and with sex and age, but averages 2 mm a week
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- 86. Growing hair Resting hair 86
- 87. Nails • Hard, flexible plates of keratin on the dorsal surface of each distal phalanx • Produced by a similar process of keratinization • The proximal part of the nail is the nail root and is covered by the proximal skin fold which is thin and lacks both hair and glands • The epidermal stratum corneum extending from the proximal nail fold forms the cuticle, or eponychium • The keratinized nail plate is bound to a bed of epidermis called the nail bed, which contains only the basal and spinous layers 87
- 88. • The nail plate arises from the nail matrix, which extends from the nail root • Cells of the matrix divide, move distally, and become keratinized, forming the nail root • This matures as the nail plate, with continuous growth in the matrix pushes forward over the nail bed (which makes no contribution to the plate) at about 3 mm/month for fingernails and 1 mm/month for toenails 88
- 89. Cont… • The distal end of the plate becomes free of the nail bed at the epidermal fold called the hyponychium and is worn away or cut off • The nearly transparent nail plate and the thin epithelium of the nail bed provide a useful window on the amount of oxygen in the blood by showing the color of blood in the dermal vessels 89
- 90. Surface view of a finger shows the nail's major parts 90
- 91. Sagittal section of finger tip 91
- 92. sagittal section from a fetal finger: proximal nail fold (PNF); eponychium (E) or cuticle; nail root (NR), the most proximal region of the nail plate (NP); dorsal nail matrix (DNM); ventral nail matrix (VNM); nail bed (NB); dermis (D) 92
- 93. Glands of the Skin • Sebaceous Glands – Embedded in the dermis over most of the body surface, except the palms and soles – There is an average of about 100 such glands per square centimeter of skin, but the frequency increases to 400–900/cm2 in the face and scalp – Sebaceous glands are branched acinar glands with several acini converging at a short duct which usually empties into the upper portion of a hair follicle 93
- 94. – In certain hairless regions, such as the genitals, eyelids, and nipples, sebaceous ducts open directly onto the epidermal surface – The acini consist of a basal layer of undifferentiated flattened epithelial cells on the basal lamina – Their cytoplasm is filled with small fat droplets – Their nuclei shrink and undergo autophagy along with other organelles and near the duct the cells disintegrate and release the lipids via holocrine secretion 94
- 95. – The product of this process is sebum, which is gradually moved to the surface of the skin along the hair follicle or duct – Sebum is a complex mixture of lipids which are hydrolyzed by bacterial enzymes after secretion – Secretion from sebaceous glands greatly increases at puberty, stimulated by hormones – Functions of sebum • coats the surface of hairs and helps keep them from drying and becoming brittle • prevents excessive evaporation of water from the skin • keeps the skin soft and pliable • inhibits the growth of some bacteria 95
- 96. Small cells near the connective tissue capsule which proliferate and give rise to an acinus composed of large sebocytes (S), which undergo terminal differentiation by filling with small lipid droplets and then disintegrating at the ducts (D) near the hair (H) shaft 96
- 97. capsule and differentiating sebocytes 97
- 98. MEDICAL APPLICATION • Acne – The flow of sebum is continuous, and a disturbance in the normal secretion and flow of sebum is one of the reasons for the development of acne, a chronic inflammation of obstructed sebaceous glands common during and after puberty 98
- 99. Sweat Glands • Sweat glands are epithelial derivatives embedded in the dermis which open to the skin surface or into hair follicles • Two types – Eccrine sweat glands – Apocrine sweat glands • The two have different distributions, functions, and structural details • Eccrine sweat glands – Widely distributed in the skin and are most numerous on the soles of the feet (620/cm2 ) – Both the secretory portions and ducts of eccrine sweat glands are coiled and have small lumens 99
- 100. – The secretory part lies coiled in the dermis and the duct extends to open in a funnel shaped pore – The secretory part is generally more pale- staining than the ducts and has stratified cuboidal epithelium 100
- 101. • Apocrine sweat glands – confined to skin of axillary and perineal regions – development depends on sex hormones and is not complete until puberty – has much larger lumen than eccrine glands – their ducts open into hair follicles rather than to the epidermal surface – secretion contain the same basic components as sweat plus some fatty substances and protein – the slightly viscous secretion is initially odorless but may acquire a distinctive odor as a result of bacterial activity 101
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- 103. Eccrine sweat gland: small lumens in the secretory portions (S) and the ducts (D), both of which have an irregular stratified cuboidal appearance 103
- 104. The secretory portions of eccrine sweat glands have a stratified cuboidal epithelium, containing cell types with different staining properties. Cells closest to the lumen contain eosinophilic granules. 104
- 105. Apocrine sweat glands: lumens of secretory portion (S) are much larger than those of eccrine glands and their ducts open into hair follicles (H) rather than to the epidermal surface 105
- 106. Ceruminous glands • Modified apocrine glands found in the lining of the external ear • Secrete cerumen ( earwax ) which because of its sticky texture deters insects and foreign material from entering the ear 106