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TISSUES (cont.) & THE INTEGUMENTARY SYSTEM Hair Skin Nails Sonya Schuh-Huerta, Ph.D. Human Anatomy Glands • Ducts carry products of exocrine glands to epithelial surface • Include the following diverse glands – – – – Mucus-secreting glands Sweat & oil glands Salivary glands Liver & pancreas Unicellular Exocrine Glands: The Goblet Cell • Goblet cells produce mucin – Mucin + water mucus – Protects & lubricates many internal body surfaces – Goblet cells are a unicellular exocrine gland Goblet Cells Microvilli Secretory vesicles containing mucin Rough ER Golgi apparatus Nucleus Multicellular Exocrine Glands • Have 2 basic parts – Epithelium-walled duct – Secretory unit • Classified by structure of duct – Simple – Compound • Categorized by secretory unit – Tubular – Alveolar – Tubuloalveolar Lateral Surface Features: Cell Junctions • Factors binding epithelial cells together – Adhesion proteins link plasma membranes of adjacent cells – Contours of adjacent cell membranes – Special cell junctions Lateral Surface Features: Cell Junctions • Tight junctions – close off intercellular space – Found at apical region of most epithelial tissue types – Some proteins in plasma membrane of adjacent cells are fused – Prevent certain molecules from passing between cells of epithelial tissue Tight Junction Interlocking junctional proteins Intercellular space (a) Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space. Lateral Surface Features: Cell Junctions • Adhesive belt junctions (zonula adherens) = anchoring junction – Transmembrane linker proteins attach to actin microfilaments of the cytoskeleton & bind adjacent cells • With tight junctions, these linker proteins form the tight junctional complex around apical lateral borders of epithelial tissues Lateral Surface Features: Cell Junctions • Desmosomes = main junctions for binding cells together – Scattered along abutting sides of adjacent cells – Cytoplasmic side of each plasma membrane has a plaque • Plaques are joined by linker proteins – Intermediate filaments extend across the cytoplasm and anchor at desmosomes on opposite side of cell – Are common in cardiac muscle & epithelial tissue Desmosome Intercellular space Plaque Intermediate filament (keratin) Linker glycoproteins (cadherins) (b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers. Lateral Surface Features: Cell Junctions • Gap junctions = passageway between 2 adjacent cells – These let small molecules move directly between neighboring cells – Cells are connected by hollow cylinders of protein – Function in intercellular communication! Gap Junction Intercellular space Channel between cells (connexon) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication. Basal Feature: The Basal Lamina • Non-cellular supporting sheet between the epithelial tissue & the connective tissue deep to it • Consists of proteins secreted by epithelial cells Basal Feature: The Basal Lamina • Functions: – Acts as a selective filter, determining which molecules from capillaries enter the epithelium – Acts as scaffolding along which regenerating epithelial cells can migrate • Basal lamina & reticular layers of the underlying CT deep to it form the basement membrane Epithelial Surface Features • Apical surface features – Microvilli = fingerlike extensions of plasma membrane • Abundant in epithelia of small intestine & kidney • Maximize surface area across which small molecules Microvillus enter or leave • Act as stiff knobs Actin that resist abrasion filaments Epithelial Surface Features • Apical surface features – Cilia = whiplike, highly motile extensions of apical surface membranes • The apical surface contains a core of 9 pairs of microtubules encircling one middle pair – Axoneme – a set of microtubules – Each pair of microtubules are arranged in a doublet • Microtubules in cilia – arranged similarly to centrioles • Movement of cilia – in coordinated waves A Cilium Outer microtubule doublet Central microtubule Dynein arms Cross-linking proteins inside outer doublets Radial spoke Plasma membrane Power, or propulsive, stroke The doublets also have attached motor proteins, the dynein arms. The outer microtubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes. 1 2 3 4 Recovery stroke, when cilium is returning to its initial position 5 6 7 (b) Phases of ciliary motion Layer of mucus Cilium Cell surface Basal body (centriole) (a) Structure of a cilium (c) Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces. Connective Tissue • Most diverse & abundant tissue • Main classes: – – – – Connective tissue proper Cartilage Bone tissue Blood • Cells separated by a large amount of extracellular matrix • Extracellular matrix is composed of ground substance & fibers • Common embryonic origin – mesenchyme Mesenchyme (a) Embryonic connective tissue: mesenchyme Description: Embryonic connective tissue; gel-like ground substance containing fibers; star-shaped mesenchymal cells. Function: Gives rise to all other connective tissue types. Mesenchymal cell Ground substance Location: Primarily in embryo. Fibers Photomicrograph: Mesenchymal tissue, an embryonic connective tissue (600); the clear-appearing background is the fluid ground substance of the matrix; notice the fine, sparse fibers. Structural Elements of Connective Tissue • Connective tissues differ in structural properties – Differences in types of cells – Differences in composition of extracellular matrix • However, connective tissues all share structural elements • Loose areolar connective tissue – Will illustrate connective tissue features Structural Elements of Connective Tissue • Cells – primary cell type of connective tissue produces matrix – Fibroblasts • Make protein subunits (protein fibers) • Secrete molecules that form the ground substance – Chondroblasts – secrete matrix in cartilage – Osteoblasts – secrete matrix in bone – Blood cells – an exception • Do not produce matrix Areolar connective tissue: A model connective tissue Cell types Macrophage Extracellular matrix Ground substance Fibers Collagen fiber Elastic fiber Fibroblast Reticular fiber Lymphocyte Fat cell Mast cell Neutrophil Capillary Structural Elements of Connective Tissue • Fibers – function in support – Collagen fibers – strongest; resist tension – Reticular fibers – bundles of special type of collagen • Cover & support structures – Elastic fibers – contain elastin • Recoil after stretching; give resilience Structural Elements of Connective Tissue • Ground substance – – – – – Is produced by primary cell type of the tissue Is usually gel-like Cushions & protects body structures Holds tissue fluid Blood is an exception • Plasma is not produced by blood cells Connective Tissue Proper • Has 2 subclasses: – Loose connective tissue • Areolar, adipose, & reticular – Dense connective tissue • Dense irregular, dense regular, & elastic Areolar Connective Tissue • Areolar connective tissue: – Underlies epithelial tissue – Surrounds small nerves & blood vessels – Has structures & functions shared by other CT – Borders all other tissues in the body Major Functions of Connective Tissue • Structure of areolar connective tissue reflects its functions – – – – Support & binding of other tissues Holding body fluids (interstitial fluid lymph) Defending body against infection Storing nutrients as fat Areolar Connective Tissue • Description: – Gel-like matrix with all 3 fiber types – Cells of areolar CT • Fibroblasts, macrophages, mast cells, & WBCs • Function: – Wraps & cushions organs – Holds & conveys tissue fluid (interstitial fluid) – Important role in inflammation • Locations: – Widely distributed under epithelia – Packages organs – Surrounds capillaries Areolar Connective Tissue (b) Connective tissue proper: loose connective tissue, areolar Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some white blood cells. Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid. Location: Widely distributed under epithelia of body, e.g., forms lamina propria of mucous membranes; packages organs; surrounds capillaries. Epithelium Lamina propria Elastic fibers Collagen fibers Fibroblast nuclei Photomicrograph: Areolar connective tissue, a soft packaging tissue of the body (360). Areolar Connective Tissue • Tissue fluid (interstitial fluid) – Watery fluid occupying extracellular matrix – Tissue fluid derives from blood • Ground substance – Viscous, spongy part of extracellular matrix – Consists of sugar & protein molecules – Made & secreted by fibroblasts Areolar Connective Tissue • Main battlefield in fight against infection • Defenders gather at infection sites – – – – Macrophages Plasma cells Mast cells White blood cells • Neutrophils, lymphocytes, & eosinophils Adipose Tissue • Function: – Provides reserve fuel – Insulates against heat loss – Supports & protects organs • Location: – Under skin – Around organs – Behind eyeballs, within abdomen, & in breasts – Hypodermis Adipose Tissue • Description: – Closely packed adipocytes – Have nucleus pushed to one side by fat droplet – Richly vascularized Adipose Tissue (c) Connective tissue proper: loose connective tissue, adipose Description: Matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet. Function: Provides reserve food fuel; insulates against heat loss; supports and protects organs. Location: Under skin in the hypodermis; around kidneys and eyeballs; within abdomen; in breasts. Adipose tissue Nucleus of fat cell Vacuole containing fat droplet Photomicrograph: Adipose tissue from the subcutaneous layer under the skin (500). Mammary glands Reticular Connective Tissue • Description – network of reticular fibers in loose ground substance • Function – forms a soft, internal skeleton (stroma); supports other cell types • Location – lymphoid organs – Lymph nodes, bone marrow, & spleen Reticular Connective Tissue (d) Connective tissue proper: loose connective tissue, reticular Description: Network of reticular fibers in a typical loose ground substance; reticular cells lie on the network. Function: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages. Location: Lymphoid organs (lymph nodes, bone marrow, and spleen). White blood cell (lymphocyte) Reticular fibers Spleen Photomicrograph: Dark-staining network of reticular connective tissue fibers forming the internal skeleton of the spleen (555). Dense Connective Tissue • Dense irregular connective tissue • Dense regular connective tissue • Elastic connective tissue Dense Irregular Connective Tissue • Description: – Primarily irregularly arranged collagen fibers – Some elastic fibers & fibroblasts • Function: – Withstands tension – Provides structural strength • Location: – Dermis of skin – Submucosa of digestive tract – Fibrous capsules of joints & organs Dense Irregular Connective Tissue (e) Connective tissue proper: dense connective tissue, dense irregular Description: Primarily irregularly arranged collagen fibers; some elastic fibers; major cell type is the fibroblast. Function: Able to withstand tension exerted in many directions; provides structural strength. Location: Fibrous capsules of organs and of joints; dermis of the skin; submucosa of digestive tract. Nuclei of fibroblasts Collagen fibers Fibrous joint capsule Photomicrograph: Dense irregular connective tissue from the dermis of the skin (600). Dense Regular Connective Tissue • Description: – Primarily parallel collagen fibers – Fibroblasts & some elastic fibers – Poorly vascularized – Forms fascia surrounding muscles Dense Regular Connective Tissue • Function: – Attaches muscle to bone – Attaches bone to bone – Withstands great stress in one direction • Location: – Tendons & ligaments – Fascia around muscles – Aponeuroses Dense Regular Connective Tissue (f) Connective tissue proper: dense connective tissue, dense regular Description: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast. Function: Attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction. Collagen fibers Location: Tendons, most ligaments, aponeuroses. Nuclei of fibroblasts Shoulder joint Ligament Photomicrograph: Dense regular connective tissue from a tendon (270). Tendon Elastic Connective Tissue • Description: – Elastic fibers predominate • Function: allows recoil after stretching • Location: – Within walls of arteries, in certain ligaments, & surrounding bronchial tubes Elastic Connective Tissue (g) Connective tissue proper: dense connective tissue, elastic Description: Dense regular connective tissue containing a high proportion of elastic fibers. Function: Allows recoil of tissue following stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration. Elastic fibers Location: Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes. Aorta Heart Photomicrograph: Elastic connective tissue in the wall of the aorta (85). Cartilage • • • • Firm, flexible tissue Contains no blood vessels or nerves Matrix contains up to 80% water Cell type chondrocyte • Types of Cartilage: 1.) Hyaline cartilage 2.) Elastic cartilage 3.) Fibrocartilage Hyaline Cartilage • Description: – Imperceptible collagen fibers (hyaline = glassy) – Chondroblasts produce matrix – Chondrocytes lie in lacunae • Function: – Supports & reinforces – Resilient cushion – Resists repetitive stress Hyaline Cartilage • Location: – Fetal skeleton – Ends of long bones – Costal cartilage of ribs – Cartilages of nose, trachea, & larynx Hyaline Cartilage (h) Cartilage: hyaline Description: Amorphous but firm matrix; collagen fibers form an imperceptible network; chondroblasts produce the matrix and when mature (chondrocytes) lie in lacunae. Function: Supports and reinforces; has resilient cushioning properties; resists compressive stress. Location: Forms most of the embryonic skeleton; covers the ends of long bones in joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx. Chondrocyte in lacuna Matrix Photomicrograph: Hyaline cartilage from the trachea (720). Costal cartilages Elastic Cartilage • Description: – Similar to hyaline cartilage – More elastic fibers in matrix • Function: – Maintains shape of structure – Allows great flexibility • Location: – Supports external ear – Epiglottis Elastic Cartilage (i) Cartilage: elastic Description: Similar to hyaline cartilage, but more elastic fibers in matrix. Function: Maintains the shape of a structure while allowing great flexibility. Location: Supports the external ear (pinna); epiglottis. Chondrocyte in lacuna Matrix Photomicrograph: Elastic cartilage from the human ear pinna; forms the flexible skeleton of the ear (980). Fibrocartilage • Description: – Matrix similar, but less firm than hyaline cartilage – Thick collagen fibers predominate • Function: – Tensile strength & ability to absorb compressive shock • Location: – Intervertebral discs – Pubic symphysis – Discs of knee joint Fibrocartilage (j) Cartilage: fibrocartilage Description: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate. Function: Tensile strength with the ability to absorb compressive shock. Location: Intervertebral discs; pubic symphysis; discs of knee joint. Chondrocytes in lacunae Intervertebral discs Collagen fiber Photomicrograph: Fibrocartilage of an intervertebral disc (180). Special staining produced the blue color seen. Bone Tissue • Function: – Supports & protects organs – Provides levers & attachment sites for muscles – Stores calcium & other minerals – Stores fat – Marrow is site of blood cell formation • Location: – Bones Bone Tissue • Description: – Calcified matrix containing many collagen fibers – Osteoblasts – secrete collagen fibers & matrix – Osteocytes – mature bone cells in lacunae – Well vascularized Bone Tissue (k) Others: bone (osseous tissue) Description: Hard, calcified matrix containing many collagen fibers; osteocytes lie in lacunae. Very well vascularized. Function: Bone supports and protects (by enclosing); provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation (hematopoiesis). Location: Bones Central canal Lacunae Lamella Photomicrograph: Cross-sectional view of bone (190). Blood Tissue • An atypical connective tissue • Develops from mesenchyme • Consists of cells surrounded by nonliving matrix Blood Tissue • Description: – Red & white blood cells in a fluid matrix • Function: – Transport of respiratory gases, nutrients, & wastes; immune system • Location: – Within blood vessels Blood Tissue (l) Others: blood Description: Red and white blood cells in a fluid matrix (plasma). Plasma Function: Transport of respiratory gases, nutrients, wastes, and other substances. Location: Contained within blood vessels. Neutrophil Red blood cells Lymphocyte Photomicrograph: Smear of human blood (1785); two white blood cells (neutrophil and lymphocyte) are seen surrounded by red blood cells. Covering & Lining Membranes • Combine epithelial tissues & connective tissues • Cover broad areas within body • Consist of epithelial sheet plus underlying connective tissue 3 Types of Membranes • Cutaneous membrane skin • Mucous membrane – Lines hollow organs that open to surface of body – An epithelial sheet underlain with layer of lamina propria • Serous membrane – Simple squamous epithelium lying on areolar connective tissue – Lines closed cavities • Pleural, peritoneal, & pericardial cavities Covering & Lining Membranes Cutaneous membrane (skin) Mucosa of nasal cavity Mucosa of mouth Esophagus lining Mucosa of lung bronchi (a) Cutaneous membrane (the skin) covers the body surface. (b) Mucous membranes line body cavities open to the exterior. Covering & Lining Membranes Parietal peritoneum Parietal pleura Visceral peritoneum Visceral pleura Parietal pericardium Visceral pericardium (c) Serous membranes line body cavities closed to the exterior. Muscle Tissue • Skeletal muscle tissue • Cardiac muscle tissue • Smooth muscle tissue Skeletal Muscle Tissue • Description: – Long, cylindrical cells – Multi-nucleate – Obvious striations • Function: – Voluntary movement – Manipulation of environment – Facial expression • Location: – Skeletal muscles attached to bones (occasionally to skin) all throughout body Skeletal Muscle Tissue (a) Skeletal muscle Description: Long, cylindrical, multinucleate cells; obvious striations. Striations Function: Voluntary movement; locomotion; manipulation of the environment; facial expression. Nuclei Location: In skeletal muscles attached to bones or occasionally to skin. Part of muscle fiber (cell) Photomicrograph: Skeletal muscle (300). Notice the obvious banding pattern and the fact that these large cells are multinucleate. Cardiac Muscle Tissue • Description: – Branching cells, striated – Generally uninucleate – Cells interdigitate at intercalated discs • Function: – Contracts to propel blood into circulatory system • Location: – In walls of heart Cardiac Muscle Tissue (b) Cardiac muscle Description: Branching, striated, generally uninucleate cells that interdigitate at specialized junctions (intercalated discs). Striations Intercalated discs Function: As it contracts, it propels blood into the circulation; involuntary control. Nucleus Location: The walls of the heart. Photomicrograph: Cardiac muscle (600); notice the striations, branching of cells, and the intercalated discs. Smooth Muscle Tissue • Description: – Spindle-shaped cells with central nuclei – Arranged closely to form sheets – No striations • Function: – Propels substances along internal passageways – Involuntary control • Location: – Mostly walls of hollow organs Smooth Muscle Tissue (c) Smooth muscle Description: Spindle-shaped cells with central nuclei; no striations; cells arranged closely to form sheets. Smooth muscle cell Function: Propels substances or objects (foodstuffs, urine, a baby) along internal passageways; involuntary control. Nuclei Location: Mostly in the walls of hollow organs. Photomicrograph: Sheet of smooth muscle (220). Nervous Tissue • Description: – Main components – brain, spinal cord, & nerves – Contains 2 types of cells • Neurons excitatory cells • Supporting cells neuroglial cells <jeffhurtblog.com> Nervous Tissue • Function: – Transmit electrical signals from sensory receptors to effectors • Location: – Brain, spinal cord, & nerves Nervous Tissue Nervous tissue Description: Neurons are branching cells; cell processes that may be quite long extend from the nucleuscontaining cell body; also contributing to nervous tissue are nonirritable supporting cells (not illustrated). Neuron processes Axon Nuclei of supporting cells Cell body Cell body of a neuron Dendrites Function: Transmit electrical signals from sensory receptors and to effectors (muscles and glands) which control their activity. Neuron processes Location: Brain, spinal cord, and nerves. Photomicrograph: Neurons (200) Tissue Response to Injury • Inflammatory response – Nonspecific, local response – Limits damage to injury site • Immune response – Takes longer to develop & very specific – Destroys particular microorganisms at site of infection Inflammation • Acute inflammation – Heat – Redness – Swelling – Pain – Chemicals signal nearby blood vessels to dilate • Histamine increases permeability of capillaries Inflammation • Edema – accumulation of fluid – Helps dilute toxins secreted by bacteria – Brings oxygen & nutrients from blood – Brings antibodies from blood to fight infection Repair • Organization – Clot is replaced by granulation tissue • Regeneration – Replacement of destroyed tissue with same type of tissue • Fibrosis – Proliferation of scar tissue Tissue Repair of a Skin Wound Scab Blood clot in incised wound Epidermis Regenerating epithelium Regenerated epithelium Area of granulation tissue ingrowth Vein Fibroblast Macrophage Inflammatory Migrating Artery chemicals white blood cell 1 Inflammation sets the stage: • Severed blood vessels bleed. • Inflammatory chemicals are released. • Local blood vessels become more permeable, allowing white blood cells, fluid, clotting proteins, and other plasma proteins to seep into the injured area. • Clotting occurs; surface dries and forms a scab. Fibrosed area 2 Organization restores the blood supply: • The clot is replaced by granulation tissue, which restores the vascular supply. • Fibroblasts produce collagen fibers that bridge the gap. • Macrophages phagocytize cell debris. • Surface epithelial cells multiply and migrate over the granulation tissue. 3 Regeneration and fibrosis effect permanent repair: • The fibrosed area matures and contracts; the epithelium thickens. • A fully regenerated epithelium with an underlying area of scar tissue results. Capacity for Regeneration – Good to excellent: • ET, bone CT, areolar CT, dense irregular CT, & blood forming CT – Moderate: • Smooth muscle, dense regular CT – Weak: • Skeletal MT, cartilage – None or almost none: • Cardiac MT, Nervous Tissue The Tissues Throughout Life • At the end of 2nd month of development: – Primary tissue types – Major organs in place • Adulthood <newsbusters.org> – A few tissues regenerate – Many tissues still retain populations of stem cells The Tissues Throughout Life • With increasing age: – Epithelia thin – Collagen decreases – Bones, muscles, & nervous tissue begin to atrophy – Poor nutrition & poor circulation lead to poor tissue health Part II: The Integumentary System The Skin & The Hypodermis • Skin our largest organ – Accounts for 7% of body weight – Varies in thickness from 1.5–4.4 mm – Divided into 2 distinct layers: • Epidermis • Dermis – Hypodermis lies deep to the dermis (covered in skin chapter, but not really part of skin) Skin Structure Hair shaft Dermal papillae Subpapillary vascular plexus Epidermis Papillary layer Dermis Pore Appendages of skin Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Reticular layer Hypodermis (superficial fascia) Nervous structures Sensory nerve fiber Lamellar (Pacinian) corpuscle Hair follicle receptor (root hair plexus) Dermal vascular plexus Adipose tissue The Skin & Hypodermis • Functions: 1. Protection cushions organs and protects from bumps, chemicals, water loss, UV radiation 2. Regulation of body temperature 3. Excretion urea, salts, and water lost through sweat 4. Production of vitamin D 5. Sensory reception keeps us aware of conditions at body’s surface Epidermis • Contains 4 main cell types: – Keratinocytes • Location: stratum spinosum; produce keratin (a fibrous protein) – Melanocytes • Location: basal layer; manufacture & secrete pigment Epidermis • 4 main cell types (cont.) – Tactile epithelial cells • Location: basal layer; attached to sensory nerve endings – Dendritic cells • Location: stratum spinosum; part of immune system; macrophage-like Epidermis • Keratinocytes – most abundant cell type in epidermis – – – – Arise from deepest layer of epidermis Produce keratin, a tough fibrous protein Produce antibodies & enzymes Keratinocytes are dead at skin's surface Layers of the Epidermis • • • • • Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum (only in thick skin) Stratum corneum Epidermal Cells & Layers of the Epidermis Stratum corneum Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules. Stratum spinosum Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin. (a) Stratum basale Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells. Dermis Epidermal Cells & Layers of the Epidermis Keratinocytes Stratum corneum Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules. Stratum spinosum Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin. Stratum basale Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells. Dendritic cell Dermis Melanin granule Desmosomes Melanocyte Tactile epithelial cell Sensory nerve ending Layers of the Epidermis • Stratum basale – Deepest layer of epidermis – Attached to underlying dermis – Cells actively divide – Stratum basale contains: • Merkel cells – associated with sensory nerve ending • Melanocytes – secrete the pigment melanin -gives skin its color! Layers of the Epidermis • Stratum spinosum (spiny layer) – “Spiny” appearance caused by: • Artifacts of histological preparation – Contains thick bundles of intermediate filaments (tonofilaments) • Resist tension • Contain protein prekeratin – Contains star-shaped dendritic cells • A type of macrophage • Function in immune system Layers of the Epidermis • Stratum corneum (“horny” outer layer) – Thick layer of dead keratinocytes & thickened plasma membranes – Protects skin against abrasion & penetration Thick Skin Epidermis Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum basale Dermis Papillary layer Reticular layer Dermis • • • • 2nd major layer of the skin Strong, flexible connective tissue Richly supplied with blood vessels & nerves Has 2 layers: – Papillary layer – includes dermal papillae – Reticular layer • Deeper layer – 80% of thickness of dermis • Flexure lines – Creases on palms 2 Regions of the Dermis Dermis (b) Papillary layer of dermis, SEM (570) (a) Light micrograph of thick skin identifying the extent of the dermis, (100) (c) Reticular layer of dermis, SEM (430) Dermal Modifications Friction ridges Openings of sweat gland ducts Flexion creases on digit (a) Friction ridges of finger tip (SEM 20) Flexion creases on the palm (b) Cleavage lines in the reticular dermis (c) Flexure lines of the hand Hypodermis • • • • Deep to the skin – also called superficial fascia Contains areolar & adipose CT Anchors skin to underlying structures Helps insulate the body Skin Color • 3 pigments contribute to skin color: – Melanin • Most important pigment – made from tyrosine – Carotene • Yellowish pigment from carrots & tomatoes – Hemoglobin • Caucasian skin contains little melanin • Allows crimson color of blood to show through • Do light-skinned people have fewer melanocytes or what?... Nails • Nails = scale-like modification of epidermis – Made of hard keratin – Parts of the nail • • • • • Free edge Body Root Nail folds Eponychium (cuticle) Structure of a Nail Lunule Free edge of nail Lateral nail fold Body Eponychium Root of nail of nail (cuticle) Proximal Nail nail fold matrix Nail bed Phalanx (bone of fingertip) Appendages of the Skin: Hair • Hair – Flexible strand of dead, keratinized cells – Hard keratin – tough & durable – Chief parts of a hair • Root imbedded in the skin • Shaft projects above skin Hair • Hair has 3 concentric layers of keratinized cells – Medulla central core – Cortex surrounds medulla – Cuticle outermost layer Cross Section of a Hair Follicle wall Connective tissue root sheath Glassy membrane External epithelial root sheath Internal epithelial root sheath Hair shaft Hair Cuticle Cortex Medulla Arrector pili Sebaceous gland Hair root Follicle wall Connective tissue root sheath Glassy membrane Hair bulb External epithelial root sheath Internal epithelial root sheath Hair Cuticle Cortex Medulla (b) Photomicrograph of a cross section of a hair and hair follicle (185) Hair • Hair follicles – Extend from epidermis into dermis • Hair bulb – Deep, expanded end of the hair follicle • Root plexus – Knot of sensory nerves around hair bulb Longitudinal Section of Base of Follicle Hair shaft Arrector pili Sebaceous gland Hair root Follicle wall Connective tissue root sheath Glassy membrane External epithelial root sheath Internal epithelial root sheath Hair root Cuticle Cortex Medulla Hair bulb Hair matrix Hair papilla Melanocyte Subcutaneous adipose tissue (c) Diagram of a longitudinal view of the expanded hair bulb of the follicle, which encloses the matrix Follicle wall Connective tissue root sheath Glassy membrane External epithelial root sheath Internal epithelial root sheath Hair root Cuticle Cortex Medulla Hair matrix Hair papilla Subcutaneous adipose tissue (d) Photomicrograph of longitudinal view of the hair bulb in the follicle (130) Hair Follicle • Wall of hair follicle – CT root sheath – Epithelial root sheath • Arrector pili muscle – Bundle of smooth muscle – Hair stands erect when arrector pili contracts Types & Growth of Hair • Vellus hairs – Body hairs of women & children • Terminal hairs – Hair of scalp – Axillary & pubic area (at puberty) • Hair thinning & baldness – Due to aging – loss of follicle stem cells – Male pattern baldness – genetics Sebaceous Glands • Occur over entire body – Except palms & soles • Secrete sebum an oily substance – Simple alveolar glands – Holocrine secretion – entire cell breaks up to form secretion – Most are associated with a hair follicle • Functions of sebum – Collects dirt; softens & lubricates hair & skin Sebaceous Glands Sweat pore Dermal connective tissue Sebaceous gland duct Sebaceous gland Hair in hair follicle Eccrine gland Secretory cells (a) Photomicrograph of a sectioned sebaceous gland (140) Sweat Glands • Sweat glands (sudoriferous glands) widely distributed on body • Sweat is a blood filtrate – 99% water with some salts – Contains traces of metabolic wastes • About 2% urea Sweat Glands Sweat pore Eccrine Gland (sweat gland) Sebaceous gland Duct Dermal connective tissue Secretory cells (b) Photomicrograph of a sectioned eccrine gland (140) Sweat Glands • 2 types of sweat gland – Eccrine gland • Most numerous – these produce true sweat – Apocrine gland • Confined to axillary, anal, & genital areas • Produce a special kind of sweat – Musky odor attracts a mate? – Signal information about a person’s immune system, MHC • Ceruminous glands & mammary glands – Are modified apocrine glands Burns • Classified by severity – First-degree burn – only upper epidermis is damaged – Second-degree burn – upper part of dermis is also damaged • Blisters appear • Skin heals with little scarring – Third-degree burn • Consumes thickness of skin • Burned area appears white, red, or blackened Estimating Burns Using the Rule of 9s Anterior values 1st degree burn Totals 41⁄2% Anterior and posterior head and neck, 9% Anterior and posterior upper limbs, 18% 2nd degree burn 41⁄2% Anterior 41⁄2% (a) Skin bearing partial thickness burn (first- and second-degree burns) 3rd degree burn trunk, 18% Anterior and posterior trunk, 36% 9% (Perineum, 1%) 9% Anterior and posterior lower limbs, 36% 100% (b) Skin bearing full thickness burn (third-degree burn) (c) Rule of nines; used to estimate extent of burns Skin Cancer • Basal cell carcinoma – Least malignant & most common • Squamous cell carcinoma – Arises from keratinocytes of stratum spinosum • Melanoma – A cancer of melanocytes – The most dangerous type of skin cancer • The ABCDE rule of skin cancer… Skin Cancer The Skin Throughout Life: Embryo • Epidermis – Develops from embryonic ectoderm • Dermis & hypodermis – Develop from mesoderm • Melanocytes – Develop from neural crest cells The Skin Throughout Life: Fetus • Fetal skin – Well-formed after the 4th month – At 5–6 months, the fetus is covered with lanugo (downy hairs) – Fetal sebaceous glands produce vernix caseosa The Skin Throughout Life: Adult • Middle to old age – Skin thins & becomes less elastic – Shows harmful effects of environmental damage – Skin inflammations become more common Questions…? What’s Next? Lab: Tissues & Skin Wed Lecture: Review Wed Lab: Lab Exam 1 Mon Lecture: Lecture Exam 1