Exam 2 (6) PDF - Keratinization and Skin Barrier

LO4: Describe the processes of growth and keratinization (cornification) of the epidermis.  The process in which keratinocytes undergo cytodifferentiation as they transition from their initial stage in the stratum basale to become fully differentiated...

LO4: Describe the processes of growth and keratinization (cornification) of the epidermis.  The process in which keratinocytes undergo cytodifferentiation as they transition from their initial stage in the stratum basale to become fully differentiated, hardened cells filled with keratin protein. Desquamation- corneocytes shed into the environment (squames or horny cells) Consists of 20-30 layers of dead cells full of keratin Beneath the plasma membrane: cornified envelope (cross- cornified layer linked proteins+lipids) 3-5 Layers of flattened cells Presence of keratohyalin granules (with keratin filament- granular layer associated proteins) Lipids are stored in lamellar bodies Organelle & nucleus destruction (far from dermal capillaries) spinous layer Keratinocytes detach from the basal mb and start to undergo stoppingvisionen junctg adhesion differentiation formingeatin Keratin expression--Proliferation arrest--Desmosome formation basal layer undifferentiated, mitotic stem cells that are attached to the basement membrane. Continuously provide the stratified 1 single row of Cuboidal cells epithelium with new cells. Shetty, S., & Gokul S (2012). Keratinization and its disorders. Oman medical journal, 27(5), 348–357. https://doi.org/10.5001/omj.2012.90 Epidermis Cross Section Anatomy Skin 3D Model By zames1992 https://llllline.com/epidermis-cross-section-anatomy-skin https://doi.org/10.1038/sj.cdd.4401722  LO5: Explain how extracellular lipids within the stratum corneum contributes to the skin barrier “Brick & mortar” pattern They form the cutaneous permeability barrier They block the movement of water and electrolytes cell-cell junctions the primary fills the spaces between structural units, corneocytes offering strength Lipids are transferred to the extracellular spaces of the stratum corneum by lamellar bodies secreted as cells move from the stratum granulosum to the stratum corneum. (also called lamellar granules) Ref. https://doi.org/10.1038/jid.2012.177 rich in lipid substances  LO6: Discuss the 3 pigments most responsible for producing the various skin colors. Inside keratinocytes, melanosomes are most numerous in areas over the nuclei, creating “dark red+yellow hues umbrellas” that protect the nuclear DNA from the Eumelanin & pheomelanin sun’s harmful ultraviolet (UV) radiation. Brown-black shades Melanin, carotene, and yellow-orange pigment hemoglobin obtained from dietary determine skin Organelles where sources like carrots color melanin is produced. They are transported to neighboring keratinocytes through cytoplasmatic extensions Hemoglobin contributes to a subtle reddish undertone depending on blood flow - noticeable in areas where the skin is thinner (lips) Image credit: "Skin Pigmentation" by Scientific Animations is licensed under Creative Commons “BY-SA 4.0 International".) Fig. Pearson, Inc.  LO7: Identify the dermis layers, including the tissue types making up each dermal layer. The dermis is the underlying connective tissue Epidermal ridges framework that supports the epidermis Well supplied with blood vessels, lymphatic vessels, and nerves. Dermal papillae Contain cutaneous receptors, glands, & The papillary layer forms hair follicles. finger-like projections into the epidermis, known as 2 Layers: dermal papillae Areolar (loose) Dermal ridges and epidermal ridges together form the friction ridges: impressions on the skin's surface, present on our fingers, toes, palms, and soles. They ↑surface area for better grip. Dense irregular Fingerprints are the unique patterns formed by friction ridges on our fingertips and thumbs. Ifig. PEARSON, Inc.mage credit: "Layers of the Dermis @100x" by Jennifer Lange is licensed under CC-BY-NC-SA 4.0  LO8: Describe the general structure and functions of the subcutaneous layer It lies between the dermis and underlying organs. It is composed of a mixture of two main types of connective tissue: loose areolar tissue and adipose tissue--they are interwoven throughout the layer.  The proportions of these two tissues can vary depending on location in the body Superficial fat layer Hypodermis dense connective tissue sheath (superficial fascia or subcutaneous layer) Deep fat layer envelops all the muscles of the body Deep fascia Thermal Insulator -poor conductor of heat (traps heat generated by internal organs and muscles and prevents its transfer to the surrounding environment through the skin) Stores Energy (TGs). Act as a Shock Absorber--cushion impacts (due to soft, gel- DOI:10.1055/s-0042-1757322 like nature of fat cells) Stecco, C., Macchi, V., Porzionato, A., Duparc, F., & De Caro, R. (2011). The fascia: the forgotten structure. Italian journal of anatomy and embryology = Archivio italiano di anatomia ed embriologia, 116(3), 127–138.  LO9: Indicate the location and function of the sudoriferous glands (sweat glands) Sweat pore Their ducts empty their secretion onto the skin surface via sweat pores Hair follicle Ducts lead to nearby hair follicles Apocrine sweat gland Eccrine (merocrine) sweat gland present in the axilla Distributed over the entire body and pubic area surface (a few exceptions). coiled tubular Simple coiled tubular glands that glands with large secrete a salt solution containing lumen that are small amounts of other solutes. associated with hair follicles Function: thermoregulation. produce milky protein-rich sweat  LO10: Indicate the location and function of the sebaceous glands. They occur all over the body surface except for the palms and soles. They are part of the pilosebaceous unit, including the hair, hair follicle, and arrector pili muscle--- their ducts usually empty into hair follicles (holocrine mode of secretion: cell dies) They are activated (at puberty) and controlled by androgens. Oily substance, a mixture of lipids that forms a thin film on the skin. Sebum lubricates the skin and hair, prevents water loss from the skin, and acts as a bactericidal agent.  LO11: Describe the anatomy of the nails The visible portion, rests on the nail bed. Made up of a dense network of keratin filaments and remnants of cells plus calcium salts. the skin that surrounds Free Edge -the tip of the nail that extends beyond the fingertip the entire nail plate Perionychium White, half-moon shape, located at the base Lunula Lateral fold thick corneal layer (dead cells) of the eponychium that overlaps the thick, hard skin located the base of the nail plate beneath the free edge Nail plate Eponychium the thickened layer of skin at the base of the nails Onychium refers to the entire area where the skin interacts with the nail plate. matrix It's further divided into 3 sections based on their location around the nail. The technical name for the nail is Onyx – used as a prefix to names given to nail disorders.  Anatomy of the basic parts of a human nail is the portion of the matrix that can be seen through the transparent nail plate nail plate lunula sinus root free margin hyponychium nail bed matrix This is the skin beneath the nail plate that is attached to the underlying bone. Responsible for the growth of the nail plate: this is the It is richly supplied with blood vessels, which give live tissue where new nail cells are produced, pushing the nail its pink color. KDS444, CC BY-SA 3.0 , via Wikimedia Commons old cells out distally.  LO12: Describe the general structure of the hair and its associated structures Hair is derived from the epidermis Hair shaft part of the hair above the surface of the skin Hair root Hair follicle part of the hair complex epithelial invagination (sac-shaped) originating in the below the surface epidermis and extending deep into the dermis in which hair grows. Hair bulb Enlarged, hollow portion at the base of the root Contains a matrix -actively divides to extend the hair shaft vertically (Image credit: "Hair Follicles and Hair" by Jennifer Lange is licensed under CC BY-NC-SA 4.0, modification of original by Scientific Animations.) The hair has three layers: central core made of loosely arranged cells and air spaces flat overlapping cells in a scale- like formation thickest, made by several layers of cells that contain hard keratin Types of pigment granules in these cells give hair color Eumelanin (brown/black); pheomelanin (red and blond) Hair consists of dead, keratinized cells  LO7: Name the bones that form each Pectoral component of the appendicular skeleton clavicle scapula Humerus- articulate with clavicle and humerus Radius & -forearm ulna attach the upper limbs to the axial skeleton Hip bone: Thigh--femur. Leg- tibia & fibula A heavy structure specialized for weight bearing, It secures the lower limbs to the axial skeleton. https://www.albert.io/blog/an-overview-of-the-appendicular-skeleton/ https://www.sawanonlinebookstore.com/pelvic-girdle-bony-pelvis/  LO8: Compare and contrast the adult male and female skeletons. The pelvis is the deep, basin-like structure formed by the hip bones, sacrum, and coccyx. larger, heavier bones forms the birth canal Quadriceps angle the angle formed between the quadriceps muscles and the patella tendon. https://doi.org/10.1371/journal.pone.0218387  LO9: Relate the shapes of bones to their functions. Protection sternum ribs skulls Support weight; movement Protect organs Reinforce tendons Stability, movement (kneecap) © 2018 Pearson Education, Inc. tarsals  LO10: State the components of a flat bone Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone. dense connective tissue membrane Compact bone enveloping most bones Outer table diploë Inner table Compact bone Trabeculae thin plates or rods of bone that form a honeycomb-like network compact bone Spongy bone Short and irregular bones resemble flat bones structurally.  LO11: Identify the structural components of a long bone makes up the outer layer of the bone =shaft The bone's articulating segment, usually at the Spongy bone bone's proximal and distal poles. =Cancellous tissue =trabecular bone the remnant of a growth plate (physis) in a mature bone BONE Soft, gelatinous tissue. Fills the cavities of long bones and occupies the spaces of spongy bone. 2 Types: red and yellow. https://www.visiblebody.com/blog/3d-skeletal-system-compact-bone-spongy-bone-and-osteons https://www.cancer.gov/publications/dictionaries/cancer-terms/def/bone-marrow  Made mostly of fat. Contains stem cells that can become cartilage, fat, or bone cells. Found in the central cavities of long bones. (membrane that covers entire bone) thin vascular membrane that lines the inner surfaces of bones Contains blood stem cells. Found in articular ends of long bones (also in medullary cavities of flat and short bones, vertebral bodies, spongy bone of the cranium, sternum, ribs, and scapulae). https://www.visiblebody.com/ https://www.cancer.gov/publications/dictionaries/cancer-terms/def/bone-marrow  LO12: Identify bone Fovea capitis markings in long bones Small pit head * Tubercle =Small, rounded process Examples of processes formed where tendons or ligaments attach: sulcus (Groove) Head= rounded, prominent, bony extension that forms part of a joint. It is usually covered in hyaline cartilage and a synovial capsule. Rough surface * Examples of processes formed to Fossa A shallow depression on the bone surface articulate with adjacent bones: Condyle = large rounded prominence that articulates with a complementary Facet condyle on another bone. Flat surface It provides structural support to the overlying hyaline cartilage. https://open.oregonstate.education/aandp/chapter/7-2-bone-markings/ https://www.ncbi.nlm.nih.gov/books/NBK513259/  LO13: Identify the internal structural components of compact and spongy bones. 2 Types of bone tissue: compact (dense or cortical) and spongy (cancellous)-names imply that the two types differ in density Compact bone consists of closely packed osteons or haversian systems. mature bone cells Extracellular Matrix Calcium & phosphate These crystals associate with the collagen fibers, making bone hard and strong. The osteon consists of a central canal called the osteonic The structural unit houses blood vessels (haversian) canal, which is surrounded by concentric rings (lamellae) of matrix. Fan, Jingzhi & Abedi Dorcheh, Keyvan & Vaziri, Asma & Kazemi-Aghdam, Fereshteh & Rafieyan, Saeed & Sohrabinejad, Masoume & Ghorbani, Mina & Rastegar Adib, Fatemeh & Ghasemi, Zahra & Klavins, Kristaps & Jahed, Vahid. (2022). A Review of Recent Advances in Natural Polymer-Based Scaffolds for Musculoskeletal Tissue Engineering. Polymers. 14. 10.3390/polym14102097. https://training.seer.cancer.gov/anatomy/skeletal/tissue.html  Between the rings of matrix (lamellae), the bone cells (osteocytes) are located in spaces called lacunae (singular: lacuna) Small channels (canaliculi) radiate from the lacunae to the haversian canal to provide passageways through the hard matrix. Sketchfab https://training.seer.cancer.gov/anatomy/skeletal/tissue.html  Spongy (cancellous) bone Spongy bone doesn't have osteons or Haversian canals. Instead, the lamellae are organized into thin plates or rods called trabeculae. These trabeculae form a branching network throughout the spongy bone. ↓weight of skeleton housed in lacunae--not arranged in a specific pattern STEVE GSCHMEISSNER / Science Photo Library / Getty Images connect to the adjacent cavities filled with red bone marrow instead of a central canal.  Lecture 9: Skeletal System II Bone composition (LO1-2) Physiology of embryonic bone formation (ossification) (LO3) Physiology of bone growth, remodeling (LO4-8) Physiology of fracture healing (LO9-10) Hormonal regulation (LO11-12) FPPT.com Other references: Chagin, A. S., & Newton, P. T. (2020). Postnatal skeletal growth is driven by the epiphyseal stem cell niche: potential implications to pediatrics. Pediatric research, 87(6), 986–990. https://doi.org/10.1038/s41390-019-0722-z Bartl, R., Bartl, C. (2019). Modelling and Remodelling of Bone. In: The Osteoporosis Manual. Springer, Cham. https://doi.org/10.1007/978-3-030-00731-7_3  BONE COMPOSITION Extracellular Cellular matter component Osteoblasts Organic Matrix Inorganic Matrix (Osteoid Tissue) (Bone Mineral) Osteoclasts Osteocytes Endosteal lining cells Collagen I fibrins bound Calcium by amorphous ground phosphate substance (+other proteins) (hydroxyapatite)  LO1: List and describe the cellular components of bone tissue. “bone builders” matrix-synthesizing cells Endosteal lining cells Line internal bone surfaces “bone breakers” where no bone activity is bone destruction ongoing cells (resorption) bone “housekeepers” Presumed to develop from bone matrix inactive osteoblasts maintenance cells “bone maintainers” former osteoblasts that have become trapped in the Lose their ability to secrete bone matrix (↓Synthetic activity). matrix they deposited Transport of organic and inorganic materials within the bones.  LO2: List and describe the extracellular components of bone tissue (bone matrix). main organic component of the bone matrix osteocyte matrix metalloproteinases (MMPs), degraders of the bone matrix. lysyl oxidase (LOX), a crosslinker of collagen osteoclast osteoblast Osteoid is the unmineralized organic part of the bone matrix, consisting of interwoven type I collagen and bone matrix proteins. Over time, the osteoid is mineralized with calcium phosphate (hydroxyapatite) to form layers in the bone matrix (lamellae), creating hard, mineralized bone. Cancers 2019, 11(7), 1020; https://doi.org/10.3390/cancers11071020 / KenHub  LO3: Compare and contrast intramembranous and endochondral (intracartilaginous) bone formation (osteogenesis or ossification). Explain the sequence of events in each process. This process involves the = a hyaline cartilage direct model conversion of mesenchyme to This process bone involves the replacement of hyaline cartilage with bone. Mesenchyme: A loose embryonic connective tissue containing undifferentiated mesenchymal cells that develop into most of the body's connective tissues. @bytesizemed  Intramembranous Bone Formation (3) Osteoid mineralization (Ca2+) →matrix hardening →entrapment of osteoblasts → conversion to osteocytes (1) Mesenchymal cells differentiate into osteoblasts. (2) Osteoblasts begin They group into ossification centers secreting osteoid (4) Osteoid surrounds blood (5) vessels, forming spongy bone. Cells on the inner surface of the periosteum differentiate into periosteum  Formed by mesenchymal osteoblasts. cells on the surface of the They secrete osteoid parallel to that bone of the existing matrix, thus forming layers forming the compact bone DOI: 10.1615/critreveukargeneexpr.v21.i2.10. https://www.ncbi.nlm.nih.gov/books/NBK539718/  Endochondral (Intracartilaginous) Bone Formation (1) Cartilage Model Formation Mesenchymal cells condense & differentiate into chondrocytes that multiply and secrete ECM. This matrix forms hyaline cartilage, resembling the future bone's shape. A surrounding membrane called the perichondrium develops. (2) Matrix Calcification Chondrocytes near the bone center enlarge (hypertrophy). Their matrix changes, containing more collagen X and fibronectin, allowing calcification. Calcification blocks nutrient supply to chondrocytes, leading to their death (apoptosis). (3) Vascularization and Bone Formation Cell death creates voids in the cartilage, allowing blood vessel invasion. Blood vessels expand these spaces, forming the medullary cavity. They carry osteogenic cells and trigger the perichondrium to become the periosteum. Osteoblasts in the periosteum create a thickened bone collar in the diaphysis. This region becomes the primary ossification center, where cartilage is replaced by bone. While diaphysis undergoes ossification, cartilage continues to proliferate at the bone ends. DOI:10.1016/j.bioactmat.2021.03.043 https://www.ncbi.nlm.nih.gov/books/NBK539718/ https://www.kenhub.com/en/library/anatomy/bone-tissue-formation  (4) Secondary Ossification Center formation (5) Articular cartilage and epiphyseal line formation Shortly after birth a large proportion of chondrocytes in Articular cartilage the center of each epiphysis are consumed to form the secondary ossification center Epiphyseal line (SOC). Epiphyseal plate ossifies SOC develops into a mature and becomes epiphyseal bone tissue (forming the bony line; cartilage remains only epiphysis). at joint surface as articular Cartilage remains at cartilage. epiphyseal (growth) plate. Mature structure of long bone has formed EPIPHYSEAL DISK (growth plate or physis) is a band of cartilage between the epiphysis and diaphysis Epiphyseal lines are the remnants of  Long bones increase in length by epiphyseal plates in a mature bone. interstitial growth of the epiphyseal plate cartilage and its replacement by bone. https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Human_Anatomy_%28Lange_et_al.%29/05%3A_Bone_Tissue_and_Skeletal_System/5.04%3A_Bone_Formation_and_Development  (children) LO4: Explain postnatal longitudinal growth & epiphyseal cartilage organization The growth plate or physis, is made of layers- Think of each layer as a stage in the life of a bone cell Resting Zone (=Zone of reserve cartilage) Bone cells start out as cartilage cells (chondrocytes), here they are in the least differentiated stage (chondro-progenitors), which divide rarely. Proliferative Zone: When the cells gets the signal, they multiples (mitosis) they arrange into columns that align parallel to the direction of growth. Hypertrophic Zone: These cartilage cells get bigger Calcification Zone: These cells calcify the cartilage surrounding them They undergo apoptosis which leaves empty lacunae surrounded by calcified cartilage. Lacunae are invaded by blood vessels accompanied by osteo-progenitors, which produce bone matrix. (“Ossification Zone”) DOI:10.1186/s40634-015-0022-4 https://www.bonetalks.com/pedsgrowthplate https://doi.org/10.1038/s41390-019-0722-z  LO5: Explain the mechanism responsible for increasing the diameter/thickness of a growing bone (appositional growth) (on the inside, enlarging the medullary cavity) In the outer surface ©Fig. Pearson, Inc.  LO6: Distinguish between the concepts of bone modeling and bone remodeling. The amount of bone tissue and the structure of bones are determined by two processes: Bone Modeling Bone Remodeling Continuous renewal of bone tissue: Shaping and repair microfractures, release reshaping minerals into blood… existing bone The adult skeleton is renewed by remodeling every 10 years Credit: N. Smith/Springer Nature Limited (10%/year) Independent action of Involves sequential osteoclast-mediated bone resorption and osteoblasts and osteoclasts. bone formation at the same location. It occurs predominantly during By removing old and damaged bone targeted remodeling plays a skeletal growth (can also be key role in maintaining the mechanical strength of bone. observed in pathological conditions) Bone remodeling replaces old and damaged bone with new bone through a sequence of cellular events occurring on the same surface without any change in bone shape. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5322859/  LO7: Define Bone Remodeling Unit (BRU) or Basic Multicellular Unit (BMU)  By definition, bone remodeling is a process where osteoclasts and osteoblasts work sequentially in the same BRU  a microscopic location within bone tissue where remodeling takes place. (Produce osteoblasts) progenitor cells They are essentially temporary "work crews" made up of different types of cells working together to remove old bone and create new bone. BMUs are present simultaneously at very many different sites at surfaces of trabecular and cortical bones FYI: ~1 million BRUs are actively engaged in bone turnover at any time https://link.springer.com/chapter/10.1007/978-3-030-00731-7_3  LO8: Sequence the process of bone remodeling 2 Resorption: during which osteoclasts digest old bone. Cell membrane consists of numerous “folds”—the “ruffled border” which faces the surface of the bone lysosomal enzymes Their secretions dissolve the minerals and some of the bone matrix. The dissolved products are released to blood “bone breakers” multinucleated giant cells; derived from 1 monocytes of the bone marrow Quiescence: By covering the bone surface, they protect it from any osteoclast resorptive activity. 3 Function as mechanosensory Reversal: when Osteocytes cells: detect the need for bone mononuclear cells appear ↑or ↓ or for repairing on the bone surface microfractures (transmit the removal of the debris left by signals to other cells) the osteoclasts © Biomedical Tissue Research, University of York DOI: 10.1196/annals.1365.035