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The Integumentary System: Skin Structure and Function

Learn about the complex integumentary system, including the skin layers, cells, and functions. Dive into the epidermis and dermis, understanding keratinocytes, melanocytes, Merkel cells, and Langerhans cells.

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The Integumentary System: Skin Structure and Function

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  1. THE INTEGUMENTARY SYSTEM • Complex set of organs that includes the skin and its derivatives (sweat and oil glands, hairs, and nails) • Includes: • Nerves • Blood vessels • Muscles • Major function: protection

  2. THE SKIN • Also called the integument, which simply means: covering • Epidermis: • The epidermis is a keratinized stratified squamous epithelium (epi=upon) • Outer most protective shield of the body • Dermis: • Underlying epidermis • Makes up bulk of skin • Composed of: • Fibrous connective tissue • Blood vessels: • Nutrients reach the epidermis by diffusion

  3. SKIN

  4. THE SKIN • Hypodermis: also called superficial fascia • Subcutaneous tissue: • Deep to the skin • Not really part of the skin but it shares some of the skin’s protective functions • Superficial to the tough connective tissue wrapping (fascia) of the skeletal muscles • Consists mostly of adipose tissue: • Stores fat: • Shock absorber • insulation • Anchors the skin to the underlying structures (muscles) • Thickens as one gains weight: • Thighs • Breast • Beer belly

  5. SKIN

  6. Epidermis • A keratinized stratified squamous epithelium consisting of four distinct cell types and four or five distinct layers: • Stratum Corneum • Stratum Lucidum (thick skin) • Stratum Granulosum • Stratum Spinosum • Stratum Basale

  7. Cells of the Epidermis • Include: • Keratinocytes • Melanocytes • Merkel cells • Langerhan’s cells

  8. EPIDERMIS

  9. Cells of the EpidermisKeratinocytes • Produce keratin • Fibrous protein that helps give the epidermis its protective properties • Tightly connected to one another by desmosomes (cell junction composed of thickened plasma membranes joined by filaments) • Arise in the deepest part of the epidermis from a layer of cells (stratum basale) that undergo almost continuous mitosis • Cells pushed upward by the production of new cells beneath them • By the time they reach the free surface of the skin, they are dead, scalelike structures that are little more than keratin-filled plasma membranes • Millions rub off everyday giving us a totally new epidermis every 25 to 45 days • Friction rubs them off (hands, etc) • Persistent friction causes a thickening of the epidermis called a callus

  10. EPIDERMIS

  11. Cells of the EpidermisMelanocytes • Spider shaped cells • Found in the deepest layer of the epidermis • Synthesize the pigment melanin (melan=black) • Made and accumulated in membrane-bound granules (small. grainlike mass) called melanosomes • Moved along actin filaments by motor proteins to the ends of the melanocyte’s processes (spider arms) • From here they are taken up by the keratinocytes • Accumulate on the superficial (sunny side) of the keratinocyte nucleus, forming a pigment shield that protects the nucleus from the damaging effects of ultraviolet (UV) radiation in sunlight

  12. EPIDERMIS

  13. Cells of the EpidermisLangerhan’s Cells • Star-shaped • Arise from bone marrow and migrate to the epidermis • Also called epidermal dendritic cells • Are macrophages (WBC) that help activate our immune system • Their slender processes extend among the surrounding keratinocytes, forming a more or less continuous network

  14. EPIDERMIS

  15. Cells of the EpidermisMerkel Cells • Present at the epidermal-dermal junction • Saped like a spiky hemisphere • Intimately associated with a disclike sensory nerve ending: • This combination is called a Merkel disc • Functions as a sensory receptor for touch

  16. EPIDERMIS

  17. Layers of the Epidermis • Variation in epidermal thickness determines if skin is thick or thin • Thick skin covers: palms, fingertips, and soles of the feet • Five layers: strata (bed sheets) • Deep to superficial: • Stratum basale • Stratum spinosum • Stratum granulosum • Stratum lucidum • Stratum corneum • Thin skin covers the rest of the body • Stratum lucidum is absent and the other layers are thinner

  18. EPIDERMIS

  19. Layers of the EpidermisStratum Basale • Deepest epidermal layer • Attached to the underlying dermis along a wavy borderline • Consists (mostly) of a single row of cells representing the youngest keratinocytes • Many mitotic nuclei • Reflects rapid cell division • Alternate name: stratum germinativum

  20. EPIDERMIS

  21. Layers of the EpidermisStratum Spinosum • Spinosum (prickly) • Several cell layers thick • Cells contain a weblike system of intermediate filaments, which span their cytosol to attach to desmosomes • These intermediate filaments consist mainly of tension-resisting bundles of prekeratin filaments • Keratinocytes appear irregular (spiny) in shape, causing them to be called prickle cells • Spines do not exist in the living cells • They arise during tissue preparation when these cells shrink but their numerous desmosomes hold tight • Scattered among the keratinocytes are: • Melanin granules • Langerhan’s cells (highest concentration)

  22. EPIDERMIS

  23. Layers of the EpidermisStratum Granulosum • Consist of 3-5 layers in which keratinocyte appearance changes drastically • Cells flatten • Nuclei and organelles begin to disintegrate • They accumulate: • Keratohyaline granules: • Help to form keratin in the upper layers • Lamellated granules: • Contain a waterproofing glycolipid that is spewed into the extracellular space and is a major factor in slowing water loss across the epidermis • Cell membranes thicken • Lipids coat the external membrane • Above this layer the epidermal cells are too far from the dermal capillaries, so they die

  24. EPIDERMIS

  25. Layers of the EpidermisStratum Lucidum • Thin translucent band • Few rows of clear, flat, dead keratinocytes with indistinct boundaries • Gummy substance of the keratohyaline granules clings to the keratin filaments in the cells, causing them to aggregate in parallel arrays (regular arrangement) • Visible ONLY in THICK SKIN

  26. EPIDERMIS

  27. Layers of the EpidermisStratum Corneum • Horny (hard, callous) layer • 23-30 cell layers thick (3/4 of epidermis) • Keratin and the thickened plasma membranes of cells protect the skin against abrasion and penetration • Glycolipid between cells waterproofs this layer • The stratum corneum (horny layer) is the outermost protective layer of the epidermis composed of a thick layer of dead keratinocytes

  28. EPIDERMIS

  29. SKIN

  30. EPIDERMIS

  31. Dermis • Composed of strong, flexible connective tissue • Its cells are typical of those found in any connective tissue proper: • Fibroblasts: cells that form the fibers of connective tissue • Macrophages: protective cell capable of phagocytosis • Mast cells: immune cell that initiates inflammation • White blood cells: protection • Its semifluid matrix is heavily embedded with: • Collagen: strong, fibrous (threadlike) insoluble protein • Elastin: extracellular connective tissue protein • Reticular fibers: supporting framework tissue • The dermis binds the entire body together like a body stocking • It is your hide and corresponds exactly to animal hides used to make leather products • Richly supplied with nerve fibers, blood vessels, and lymphatic vessels • Major portions of hair follicles, as well as oil and sweat glands, are derived from epidermal tissue but reside in the dermis

  32. DermisTwo Layers • 1.The thin, superficial papillary layer is highly vascularized areolar connective tissue containing a woven mat of collagen and elastin fibers • Its superior surface is thrown into peglike projections called dermal papillae (papill=nipple) that indent the overlaying epidermis • Many contain: • Capillary loops • Meissner’s corpuscles: touch receptors • Pain receptors

  33. SKIN

  34. DermisTwo Layers • On the palms of the hands and soles of the feet, these papillae lie atop larger mounds called dermal ridges • Which in turn cause the overlying epidermis to form epidermal ridges that increase friction and enhance the gripping ability of the fingers and feet • Epidermal ridge patterns are genetically determined and unique to each of us • Because sweat pores open along their crest, our fingerprints leave identifying films of sweat called fingerprints on almost anything they touch

  35. SKIN

  36. DermisTwo Layers • Three types of skin markings: • Finger prints • Cleavage lines • Flexure lines

  37. DermisTwo Layers • 2.The reticular layer: • Deeper • Account for 80% of the thickness of the dermis • Extracellular matrix contains thick bundles of interlacing fibers that run in various planes • Most run parallel to the skin surface • Less dense regions, between these bundles form cleavage, or tension lines: • Important to a surgeon: • Incision made parallel to these lines, the skin gapes less and heals more readily than when the incision is made across cleavage lines • Collagen fibers give skin strength and resiliency • Binds water, helping keep the skin hydrated • Elastin fibers provide the stretch-recoil properties of skin

  38. SKIN

  39. DermisTwo Layers • Flexure lines: • Dermal folds that occur at or near joints, where the dermis is tightly secured to deeper structures (notice the deep creases on your palms) • Since the skin cannot slide easily to accommodate joint movement in such regions, the dermis folds and deep skin creases form • Visible on wrists, fingers, soles, and toes

  40. HOMEOSTATIC IMBALANCE • Dermal tearing: • Stretching of the skin during pregnancy • Stretch marks • Blister: • Separation of the epidermal and dermal layers by a fluid-filled pocket

  41. Skin Color • Determined by three pigments: • Melanin • Hemoglobin • Carotene

  42. Melanin • Only pigment made in the skin • Polymer of tyrosine amino acid • Ranges in color from yellow to reddish-brown to black • Synthesis depends on an enzyme in melaocytes called tyrosinase • Passes from melanocytes to the basal keratinocytes

  43. Melanin • All humans have the same relative number of melanocytes • Individual and racial differences in skin coloring reflect the relative kind and amount of melanin made and retained • Melanocytes of black and brown skinned people produce many and darker melanosomes than those of fair-skinned individuals, and their keratinocytes retain it longer • Freckles and pigmented moles are local accumulations of melanin

  44. Melanin • Melanocytes are stimulated by sunlight • Causes substantial melanin buildup, which helps protect the DNA of viable skin cells from UV radiation by absorbing the light and dissipating the energy as heat

  45. HOMEOSTATIC IMBALANCE • Excessive sunlight damages the skin: • Clumping of elastin fibers: results in leathery skin • Depresses the immune system • Alters DNA

  46. Carotene • Yellow to orange pigment found in certain plant products such as carrots • Tends to accumulate in the stratum corneum and in the tissue of the hypodermis • Color most obvious in the palms and soles, where the stratum corneum is thickest (example: the skin of the heel) • Most intense when large amounts of carotene-rich foods are eaten

  47. Hemoglobin • Pinkish hue of fair skin people

  48. Redness: erythema Embarrassment Fever Hypertension Inflammation Allergy Pallor: blanching Fear Anger Emotional stress Anemia Low blood pressure Jaundice: yellow cast Liver disorder (yellow bile pigment accumulates in the blood and deposited in body tissues) Bile normally secreted in the bile pigments (bilirubin) as part of bile Bronzing: Metallic appearance of skin Addison’s disease Hyperfunction of adrenal cortex Black and blue: bruises Blood escaping from the blood vessels and clotting under the skin Skin Color Variations

  49. APPENDAGES OF THE SKIN • Derivatives of the epidermis: • Sweat Glands • Sebaceous Glands • Nails • Hair • Hair Follicles

  50. Sweat (Sudoriferous) Glands • Distributed over the entire skin surface except the nipples and parts of the external genitalia • Two types of sweat glands: • Eccrine • Apocrine

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