University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2024
Views:

116

Pages:

72
Author:

Lamghari6kx

Skin Histology Integumentary system The skin is considered the largest organ of the body Basic Skin Histology The skin is composed of two layers: the outer epidermis and the deeper dermis Rests on the hypodermis. Epidermis Dermis Hypodermis Major Skin Functions Protection Sensory Perception Temperature Regulation Excretion Formation of Vitamin D Epidermis Dermis Hypodermis Superficial fascia Subcutanous tissue Subdermal fat The dermal papillae are nipple-like extensions of the dermis into the epidermis The epidermis conforms to the contours of the underlying dermal papillae forming epidermal ridges Note: the basement membrane follows the contour of the interdigitations between epidermis and dermis Epidermal-dermal junction Prevents the two layers of skin from separating Epidermal-dermal junction More prominent in palms and soles Blisters Epidermal ridge Dermal papilla Epidermis  Is the outermost layer of the skin  It is composed of four or five layers, depending on the type of skin.  It is rich in a tough protein called keratin Contains four different cell types: Keratinocytes Melanocytes Langerhans cells Merkel cells  Avascular  The epidermis forms a waterproof barrier between the body and the external environment, which resists friction and microbial invasion and prevents water loss Is derived from ectoderm Keratinized stratified squamous epithelium (1) Stratum basale  Is the deepest layer in the epidermis.  Consists of a single layer of basophilic columnar to cuboidal cells that rest on a basement membrane  The cells are attached to one another by desmosomes, and to the underlying basement membrane by hemidesmosomes.  Cells are characterized by intense mitotic activity (2)Stratum spinosum  Is the layer above the stratum basale  Consists of 8-10 rows of cells  Cells synthesize keratin filaments that become assembled into tonofilaments  During histologic preparation, cells shrink and intercellular spaces appear as spines  Spines represent sites of desmosome attachments to keratin tonofibrils Stratum basale along with the deepest part of stratum spinosum is called Stratum germinativum (3)Stratum granulosum  Cells above the stratum spinosum  Consists of 3-5 cell layers of flattened cells  Cells filled with dense basophilic keratohyalin granules and membrane- bound lamellar granules Keratohyalin granules are intensely basophilic, non membranous bound masses of filaggrin cross-links with keratin tonofibrils Tonofibrils Intermediate filaments= keratin Tonofilaments Lamellar granules discharge lipid material between cells and waterproof the skin (4)Stratum Lucidum  In thick skin only  Is translucent and barely visible  The tightly packed cells (desmosomes) lack nuclei or organelles and are dead. (5)Stratum corneum  Most superficial layer of the skin.  Consists of dead, flattened cells with no nuclei and cell organelles  The dead cells contain much keratin filaments with plasma membranes surrounded by lipid-rich layer  The cells from this layer are continually shed, or desquamated, and are replaced by new cells arising from the deep stratum basale.  During the keratinization process, the hydrolytic enzymes disrupt the nucleus and all cytoplasmic organelles, which disappear as the cells fill with keratin. Calluses and corns By the end of keratinization, the cells contain only keratin with plasma membranes surrounded by lipid rich layer Psoriasis is a common skin condition that speeds up the life cycle of skin cells. It causes cells to build up rapidly on the surface of the skin. The extra skin cells form scales and red patches that are itchy and sometimes painful. Types of skin Thin skin * Dominant and lines most of the body surface Thick skin * Palms of the hands and soles of the feet Note: that the thin and thick refer to the thickness of epidermal layer Thick skin Thin skin Types of skin Thin skin Thick skin *4 layers *5 layers *less Prominent stratum corneum * Less developed stratum granulosum * Dominant and lines most of the body surface * Thicker dermis * hair and sebaceous glands * Prominent stratum corneum * Well developed stratum granulosum * Palms of the hands and soles of the feet * Thinner dermis * No hair and sebaceous glands TYPES OF EPIDERMAL CELLS (1)-keratinocytes:  Approximately 90% of epidermal cells are keratinocytes.  Produce keratin  Produce lamellar granules that helps waterproof the skin (2)-Melanocytes: Melanocytes are our natural SPF  Are derived from the neural crest cells.  Have protrusions that transfer melanin granules to the keratinocytes  Are located in the stratum basale  Synthesize the dark brown pigment melanin  Melanin protects the skin from the damaging effects of ultraviolet radiation Melanin imparts a dark color to the skin, and exposure of the skin to sunlight promotes increased synthesis of melanin 1 melanocyte for every 10 basal keratinocytes Albinism (3)- Langerhans cells:  Originate from bone marrow (monocytes)  Mainly in the stratum spinosum  Langerhans cells recognize, phagocytose, and process foreign antigens  Represent 2-8% of epidermal Cells (4)- Merkel cells:  Are found in the stratum basale  Are most abundant in the fingertips  Are closely associated with afferent (sensory) unmyelinated Axons  Function as light touch receptors (mechanoreceptors) NOTE: Sensory neurons form terminal disk under Merkels cells Dermis  The dermis lies immediately beneath the epidermis and is much thicker.  It is responsible for the elasticity and strength of skin  Contains blood vessels and nerve supply It supplies the epidermis with nutrients, and plays an important role in thermoregulation Is derived from mesoderm The dermis can be divided into two sub-layers: (1) Papillary layer of dermis Loose connective tissue (2)Reticular layer of dermis Dense irregular connective tissue The blood vessels form two major plexuses: Subpapillary plexus Thermoregulation Subdermal plexus Hemorrhage from the cutaneous blood vessels is called ecchymosis (bruise) The acid mantle is a very fine, slightly acidic film on the surface of human skin Is made up of natural oils, sweat, and dead skin cells, and is slightly more acidic in nature to prevent harmful (naturally alkaline) contaminants from penetrating and damaging the skin Ph: 5.5 Sensory receptors Unencapsulated receptors Encapsulated receptors 1- Merkel disc  for light touch and sensing an object texture  expanded nerve endings associated with merkel cell 2- Free nerve endings  In papillary dermis  Temperature, pain, itching, tactile sensation 3- Root hair plexuses  Surround the bases of hair follicles in reticular dermis Detect movements of hair Root hair plexuses Unencapsulated nerve receptors Merkel disc Free nerve endings Meissner corpuscles:  Encapsulated  In the dermal papilla  Light touch  Are numerous in fingertips, palms and soles  Decline in number with aging Pacinian corpuscles Encapsulated Found deep in reticular dermis and hypodermis Coarse touch, pressure (sustained touch) and vibrations Ruffini corpuscles: Encapsulated Stretch (tension) and twisting (torque) Skin Appendages Hair Follicles and hair Sweat glands Sebaceous glands Nails Hairs are elongated keratinized structures that form within epidermal invaginations (hair follicles) Types of hair: 1- Lanugo: fetal hair 2- Down hair: light colored hair of child 3- Terminal (adult) hair: thicker, darker hair that begins to grow at puberty Hair shaft: The part of a hair extending beyond the skin surface (visible part) Hair root: The part of a hair below the skin surface (embedded part) Hair follicle is a tube of stratified squamous epithelium, invaginated into the dermis INNER ROOT SHEATH Disintegrates at the level of the sebaceous gland OUTER ROOT SHEATH  Is continuous with the epidermis  It does not take part in hair formation Surrounded by a glassy basement membrane Basement membrane is surrounded by a connective tissue sheath. Inner root sheath Hair matrix  Contains the proliferating cells that generate the hair and the internal root sheath  Located just above the dermal papilla Melanocytes located in the matrix produce hair color. Sebaceous glands  secrete an oily or waxy matter, called sebum, to lubricate and waterproof the skin and hair Secrete by holocrine mode of secretion Acne Comedo (blackheads) A comedo is a clogged hair follicle (pore) in the skin. Keratin combines with oil to block the follicle Arrector pili muscles are small muscles extend from hair follicles to the dermal papilla  Contraction of these muscles causes the hairs to stand on end (goose bumps)  Innervated by the autonomic nervous system (sympathetic ) Depilatory Pulls hairs upright when cold or frightened Structure of the hair shaft Medulla: large vacuolated and moderately keratinized cells Cortex: heavily keratinized and densely packed cells Cuticle: thin layer heavily keratinized squamous cells covering the cortex 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 Dermal papilla Cuticle Cortex Medulla Outer root sheath Inner root sheath Epidermis of skin Dermal papilla Matrix cells Melanocytes Sweat glands 59 Sweat Glands Eccrine sweat gland  Merocrine secretion  Empty directly onto skin surface  Location: most all over body (esp. abundant on palms & soles: ~ 500/cm2)  Clear, watery secretion (99% H2O; rest NaCl + some waste products Apocrine sweat gland      Empty into hair follicle Location: armpits, groin, nipples Viscous, cloudy secretion  good nutrient source for bacteria (odor !!) Secretion may contain Pheromones Secretion begins at puberty and is stimulated during emotional distress Scent glands Apocrine sweat glands Eccrine (merocrine) sweat glands 62 Nails Hard plates of keratin on the dorsal surface of each distal phalanx Lack of pigment makes them colorless Nail parts 1. Free edge: the part you cut 2. Body: pink part 3. Lunula: white semicircle area 4. Eponychium: proximal nail fold (cuticle) 5. Hyponychium: under the free edge where dirt accumulates 6. Nail bed: directly under the pink part 7. Nail matrix: growth Nail matrix Practical sections for the exam Epidermal ridge Dermal papilla Sebaceous gland Hair follicle Arrector pili Pacinian corpuscle Sweat gland Hair shaft/root Dermal papilla Hair matrix Meissner corpuscle Pacinian corpuscles Sebaceous gland Hair follicle Arrector pili THICK OR THIN SKIN ????

Skin Histology

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