Integumentary System Histology PDF

MODULE 6: INTEGUMENTARY SYSTEM Mary Judith S. Rebosa, MD, FPPS Faculty, Biology Department Our Lady of Fatima University  UNIT EXPECTED OUTCOMES Describe the histological structure and functions of the skin and its 2 layers Describe the histological structure and functions of the skin app...

MODULE 6: INTEGUMENTARY SYSTEM Mary Judith S. Rebosa, MD, FPPS Faculty, Biology Department Our Lady of Fatima University  UNIT EXPECTED OUTCOMES Describe the histological structure and functions of the skin and its 2 layers Describe the histological structure and functions of the skin appendages Analyze photomicrographs and histological pictures of the skin and its appendages Correlate histological changes of the skin with some common diseases/disorders  SKIN Largest organ of the body accounting for 15-20% of the body weight Also called the Integument or Cutaneous Layer  SKIN Functions Prevents harmful substances from entering the body Protects the body from mechanical, chemical, and thermal damage Protection from the UV rays of the sun Prevents loss of body fluid Thermoregulation Excretes waste products Receptor for touch, pain, pressure, and temperature Site for production of vitamin D  SKIN Thick Skin Covers the palms and soles Contains numerous sweat glands Lacks hair follicles and sebaceous glands Thin Skin Covers whole body except palms and soles Thinner stratum spinosum Poorly developed stratum granulosum No stratum lucidum Shorter dermal papillae  SKIN Epidermis Superficial Derived from the ectoderm Dermis Corium Derived from the mesoderm Hypodermis Subcutaneous tissue Adipose tissue  EPIDERMIS EPIDERMIS Most superficial layer of the skin Stratified squamous keratinized epithelium Cells flatten as they mature and rise to the surface Renewed every 15-30 days  LAYERS OF THE EPIDERMIS STRATUM BASALE Single layer of tall cuboidal keratinocytes that rest on a basement membrane Consists of keratinocytes connected by desmosomes and hemidesmosomes to neighboring cells Increased mitotic activity Cells include Keratinocytes: produce keratin Melanocytes: produce melanin Merkel cells: “modified keratinocytes” Langerhan’s Cells: contain rod- shaped membrane-bound granules called Birbeck or vermiform granules  LAYERS OF THE EPIDERMIS STRATUM SPINOSUM (PRICKLE CELL LAYER) Several layers of keratinocytes More numerous keratin filaments which form bundles Desmosomes appear like spines protruding out of the cells Intercellular Bridges Limited mitotic activity  LAYERS OF THE EPIDERMIS STRATUM GRANULOSUM 3-5 layers of more flattened dead keratinocytes With numerous keratohyaline granules in the cytoplasm of keratinocytes Lamellar Granules Membrane-bound lipid containing granules in the cytoplasm Consist of closely packed parallel lamellae Barrier against entry and exit of substances to and from the body  LAYERS OF THE EPIDERMIS STRATUM LUCIDUM (CLEAR LAYER) 4-6 layers of flat, dead, anucleated keratinocytes bound to their neighbors by desmosomes Present only in thick skin Translucent appearance due to Eleidin  LAYERS OF THE EPIDERMIS STRATUM CORNEUM Horn-like, 15-20 layers of flattened scale-like anucleated cells filled with filamentous keratin held together by desmosomes Stratum Dysjunction Superficial layer: consists of dehydrated cells which are continuously being desquamated Squames fully keratinized cells continuously shed at the epidermal surface while desmosomes and lipid-rich cell envelope break down LAYERS OF THE EPIDERMIS LAYERS OF THE EPIDERMIS LAYERS OF THE EPIDERMIS LAYERS OF THE EPIDERMIS  CELLS IN THE EPIDERMIS KERATINOCYTES Produce keratin 85-95% of the cell population of the epidermis MELANOCYTES Produce melanin pigments Formed from tyrosine Melanosome produced is transferred to keratinocytes which are the main depot of pigment Present also in the retina and neurons Present in stratum germinativum and spinosum Epidermal Melanin Unit: melanocyte plus the keratinocyte it supplies CELLS IN THE EPIDERMIS CELLS IN THE EPIDERMIS  CELLS IN THE EPIDERMIS LANGERHANS CELLS Antigen-presenting cells Found in Skin Oral cavity Esophagus Vagina Most numerous in the stratum spinosum Contain Birbeck Granules or Vermiform Granules CELLS IN THE EPIDERMIS  CELLS IN THE EPIDERMIS MERKEL CELLS (EPITHELIAL TACTILE CELLS) Most numerous in palms, soles, and bases of some hair follicles Disc-shaped cells with short cytoplasmic processes Cytoplasm is devoid of keratin granules Cytoplasm contains dense granules similar to catecholamines Low-threshold mechanoreceptors for sensing gentle touch Merkel Disc Merkel cell plus an axon termination of a sensory neuron Sensory receptor for pressure and touch CELLS IN THE EPIDERMIS CELLS IN THE EPIDERMIS  DERMIS DERMIS Deep part of the skin made up of dense connective tissue containing many blood vessels, fibers, lymphatic vessels, and nerves Supports the epidermis and binds it to the subcutaneous tissue (hypodermis)  LAYERS OF THE DERMIS PAPILLARY LAYER Loose connective tissue that makes up 1/5 of the dermis Contains capillary loops and houses pain and touch receptors Forms the base for the friction ridges on the fingers and toes Dermal Papillae Conical projection into the epidermis Numerous in soles Contains capillary bed and nerve endings (Meissner’s Corpuscles)  LAYERS OF THE DERMIS RETICULAR LAYER Dense irregular connective tissue at the deepest layer of the skin Contains blood vessels, sweat and sebaceous glands, and deep pressure receptors (Pacinian Corpuscles) Responsible for toughness and strength of the skin Contains elastic fibers DERMIS  HYPODERMIS HYPODERMIS Loose connective tissue Not a layer of skin Binds the dermis to underlying structures Contains numerous adipose cells except over the Eyelids Penis Scrotum Nipple Areola Panniculus adiposus: layers of adipose tissues HYPODERMIS  SKIN APPENDAGES HAIR Filamentous and keratinized structure Grows out of follicles which are invaginations of the epidermis to the dermis Grows discontinuously with periods of growth followed by periods of rest Growth does not occur synchronously in all regions of the body or even in the same area  SKIN APPENDAGES HAIR Shaft: visible dead part of the hair Hair root: enclosed in the follicles Hair bulb matrix: growth zone of the hair Hair bulb: expanded extremities of the hair follicle Hair papilla: vascular connective tissue occupying the concavity of the hair bulbs  SKIN APPENDAGES HAIR Parts of the body devoid of hair Lips Palms and soles Sides of the fingers and toes Glans penis Clitoris Nipple HAIR FOLLICLE Hair root plus the epithelial sheaths  SKIN APPENDAGES HISTOLOGIC LAYERS OF HAIR MEDULLA Innermost layer Formed by cells of the hair matrix near the dermal papillae Consists of dead and disintegrating vacuolated cells CORTEX Surrounds the medulla Thickest layer Produce numerous trichohyalin granules Consists of packed dead and keratinized cells loaded with plenty of melanosomes  SKIN APPENDAGES HISTOLOGIC LAYERS OF HAIR CUTICLE Thinnest Consists of several layers of dead and flattened cells Heavily keratinized cells  SKIN APPENDAGES HISTOLOGIC LAYERS OF HAIR EPITHELIAL ROOT SHEATH Internal Root Sheath Completely surrounds the initial part of the hair root 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  SKIN APPENDAGES HISTOLOGIC LAYERS OF HAIR GLASSY MEMBRANE Acellular hyaline layer separating the hair follicle from the dermis PHASES OF HAIR GROWTH CYCLE Anagen: long period of mitotic activity Catagen: brief period of arrested growth and regression of the hair bulb Telogen: final long period of inactivity during which the hair may be shed  SKIN APPENDAGES NAIL Keratinized plates of stratum corneum found on the dorsal surface of the fingers and toes Primary function is protection  SKIN APPENDAGES PARTS OF THE NAIL Nail Root: proximal part of the nail Cuticle/Eponychium: covers the nail root Nail bed: stratum spinosum or germinativum beneath the nail plate Nail plate: stratum corneum Nail matrix: responsible for nail growth Hyponychium: distal part of the nail plate which is free of the nail bed Lunula: white crescent-shaped part of the nail  SKIN APPENDAGES SEBACEOUS GLANDS Simple branched alveolar glands embedded in the dermis and occasionally in the hypodermis Holocrine glands Short duct lined by stratified squamous epithelium Continuous with external root sheath of the hair follicle  SKIN APPENDAGES SEBACEOUS GLANDS Produce sebum into the shafts of hair Oily secretion that helps preserve flexibility of the emerging hair Prevents brittleness of hair Keeps skin soft and moist Contains chemicals that kill bacteria SKIN APPENDAGES  SKIN APPENDAGES ECCRINE/MEROCRINE SWEAT GLANDS Simple coiled tubular gland Duct lined by stratified columnar epithelium Secretory portion lined by pseudostratified low columnar epithelium Sweat Pore Opening on the skin surface Functions Help regulate body temperature Excretion of waste products  SKIN APPENDAGES APOCRINE SWEAT GLAND Begins to be active during puberty Coiled tubular gland Mammary Gland Special kind of apocrine gland which secrete milk SWEAT GLANDS SWEAT GLANDS SWEAT GLANDS SWEAT GLANDS SWEAT GLANDS SWEAT GLANDS  SKIN APPENDAGES ARRECTOR PILI MUSCLE Band of smooth muscle connecting the hair follicle to the superficial part of the dermis Contraction causes hair to move into a vertical position producing gooseflesh THANK YOU!