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Integumentary System, Synovial Joints and Build Your Own Membrane 1/20/15 MDufilho 1 Skin (Integument) • Consists of two distinct regions – Epidermis—superficial region • Epithelial tissue – Dermis—underlies epidermis • Mostly fibrous connective tissue • Hypodermis (superficial fascia) – – – – 1/20/15 Subcutaneous layer deep to skin Not part of skin but shares some functions Mostly adipose tissue that absorbs shock & insulates Anchors skin to underlying structures – mostly muscles MDufilho 2 Figure 5.1 Skin structure. Hair shaft Dermal papillae Epidermis Subpapillary plexus Papillary layer Sweat pore Appendages of skin Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Dermis Reticular layer Hypodermis (subcutaneous tissue; not part of skin) Nervous structures Sensory nerve fiber with free nerve endings Lamellar corpuscle Hair follicle receptor (root hair plexus) 1/20/15 MDufilho Cutaneous plexus Adipose tissue 3 Epidermis • Keratinized stratified squamous epithelium • Four cell types – – – – Keratinocytes Melanocytes Dendritic (langerhans) cells Tactile (merkel) cells - • Four or five distinct layers – – – – – 1/20/15 Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum (only in thick skin) Stratum corneum MDufilho 4 Figure 5.2a The main structural features of the skin epidermis. Stratum corneum Most superficial layer; 20–30 layers of dead cells, essentially flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum Typically five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules. 1/20/15 Dermis 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. MDufilho 5 Layers of the Epidermis: Stratum Basale (Basal Layer) • • • • Deepest epidermal layer Also called stratum germinativum Firmly attached to dermis Single row of stem cells – Actively mitotic – Produces two daughter cells • One cell journeys from basal layer to surface – Takes 25–45 days – Dies as moves toward surface • One cell remains in stratum basale as stem cell • Melanocytes compose 10 – 25% of this layer 1/20/15 MDufilho 6 Layers of the Epidermis: Stratum Spinosum (Prickly Layer) • Several layers thick • Cells contain web-like system of intermediate prekeratin filaments attached to desmosomes • Abundant melanosomes and dendritic cells 1/20/15 MDufilho 7 Layers of the Epidermis: Stratum Granulosum (Granular Layer) • Thin - four to six cell layers • Cell appearance changes – Cells flatten – Nuclei and organelles disintegrate – Keratinization begins • Cells accumulate keratohyaline granules – Help form keratin in upper layers – Cell accumulate lamellar granules • Their water-resistant glycolipid slows water loss • Cells above this layer die – Too far from dermal capillaries 1/20/15 MDufilho 8 Layers of the Epidermis: Stratum Lucidum (Clear Layer) • Only in thick skin • Thin, translucent band superficial to the stratum granulosum • A few rows of flat, dead keratinocytes 1/20/15 MDufilho 9 Layers of the Epidermis: Stratum Corneum (Horny Layer) • 20–30 rows of dead, flat, anucleate keratinized membranous sacs • Three-quarters of epidermal thickness • Though dead, its cells have functions – Protect deeper cells from environment and water loss – Protect from abrasion and penetration – Barrier against biological, chemical, and physical assaults 1/20/15 MDufilho 10 Figure 5.2b The main structural features of the skin epidermis. Keratinocytes Stratum corneum Most superficial layer; 20–30 layers of dead cells, essentially flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum Typically five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules. Stratum spinosum Dendritic Several layers of keratinocytes unified by desmosomes. cell Cells contain thick bundles of intermediate filaments made of pre-keratin. Sensory Stratum basale nerve Dermis Deepest epidermal layer; one row of actively ending mitotic stem cells; some newly formed cells Melanin Tactile become part of the more superficial layers. granule (Merkel) cell See occasional melanocytes and dendritic Melanocyte Desmosomes cells. 1/20/15 MDufilho 11 Dermis • Strong, flexible connective tissue • Cells – Fibroblasts, macrophages, and occasionally mast cells and white blood cells • Fibers in matrix bind body together – "Hide" used to make leather • Contains nerve fibers; blood and lymphatic vessels • Contains epidermal hair follicles; oil and sweat glands • Two layers – Papillary – Reticular 1/20/15 MDufilho 12 Figure 5.1 Skin structure. Hair shaft Dermal papillae Epidermis Subpapillary plexus Papillary layer Sweat pore Appendages of skin Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Dermis Reticular layer Hypodermis (subcutaneous tissue; not part of skin) Cutaneous plexus Nervous structures Sensory nerve fiber with free nerve endings Lamellar corpuscle Hair follicle receptor (root hair plexus) 1/20/15 Adipose tissue MDufilho 13 Figure 5.4a Dermal modifications result in characteristic skin markings. Openings of Friction sweat gland ducts ridges 1/20/15 Friction ridges of fingertipMDufilho (SEM 12x) 14 Figure 5.4b Dermal modifications result in characteristic skin markings. Cleavage lines in the reticular dermis 1/20/15 MDufilho 15 Chapter 8 – Joints 1/20/15 MDufilho 16 Joints (Articulations) • Articulation – Site where two or more bones meet • Functions of joints – Give skeleton mobility – Hold skeleton together • Two classifications – Functional – Structural 1/20/15 MDufilho 17 Functional Classification of Joints • Based on – Amount of movement joint allows • Three functional classifications: – Synarthroses—immovable joints – Amphiarthroses—slightly movable joints – Diarthroses—freely movable joints 1/20/15 MDufilho 18 Structural Classification of Joints • Based on – Material binding bones together – Presence/absence of joint cavity • Three structural classifications: – Fibrous joints – Cartilaginous joints – Synovial joints 1/20/15 MDufilho 19 Synovial Joints: Six Distinguishing Features 1. Articular cartilage: hyaline cartilage 2. Joint (synovial) cavity 3. Articular (joint) capsule 4. Synovial fluid 5. Different types of reinforcing ligaments 6. Nerves and blood vessels 1/20/15 MDufilho 20 Figure 8.3 General structure of a synovial joint. Ligament Joint cavity (contains synovial fluid) Articular (hyaline) cartilage Fibrous layer Synovial membrane (secretes synovial fluid) Articular capsule Periosteum MDufilho 1/20/15 21 Other Features of Some Synovial Joints • Fatty pads – For cushioning between fibrous layer and synovial membrane or bone • Articular discs (menisci) – Fibrocartilage separates articular surfaces to improve "fit" of bone ends, stabilize joint, and reduce wear and tear 1/20/15 MDufilho 22 Structures Associated with Synovial Joints • Bursae – Sacs lined with synovial membrane • Contain synovial fluid – Reduce friction where ligaments, muscles, skin, tendons, or bones rub together • Tendon Sheaths – Elongated bursa wrapped completely around tendon subjected to friction 1/20/15 MDufilho 23 Figure 8.4a Bursae and tendon sheaths. Acromion of scapula Subacromial bursa Joint cavity containing synovial fluid Fibrous layer of articular capsule Articular cartilage Tendon sheath Synovial membrane Tendon of long head of biceps brachii muscle MDufilho 1/20/15 Fibrous layer Humerus Frontal section through the right shoulder joint 24 Figure 8.4b Bursae and tendon sheaths. Bursa rolls and lessens friction. Humerus head rolls medially as arm abducts. MDufilho 1/20/15 Humerus moving Enlargement of (a), showing how a bursa eliminates friction where a ligament (or other structure) would rub against a bone 25 Three Stabilizing Factors at Synovial Joints • Shapes of articular surfaces (minor role) • Ligament number and location (limited role) • Muscle tendons that cross joint (most important) – Muscle tone keeps tendons taut • Extremely important in reinforcing shoulder and knee joints and arches of the foot 1/20/15 MDufilho 26