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UWL BIO 312 - Skeletal System 2

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Lecture 4 Outline of Current Lecture I. Connective Tissuesa. Histologyb. Types of connective tissuesII. Cartilagea. Types and developmentIII. Bonea. Types of bone and development Current LectureSkeletal System: all classified as connective tissueConnective Tissue: comprised of connective tissue cells which produce material called matrix which surroundsthe cells- Results in cells being spaced far apart (except adipose)- Matrix allows CT to:o Withstand tensiono Bear weighto Protect- Cell types vary greatly among CT- Matrix composed of ground substance (cement) and fibers (re-bar)- Fibers: major component of matrixo Collagen: thick, bendy and flexible but not elastico Reticular: skinny collagen fibers that form a fishnet like matrixo Elastic: made from elastin, similar to a rubber band- Names and functions of CT cells:o Prefix describes type of CT in which cell is found Osteo: bone Chondro: cartilage Fibro: from CT propero Suffix describes type of CT cell …blast: cells actively secreting matrix into cell …cyte: mature cells that help maintain health of surrounding cells- Cartilage: found in any articulating surface (lubrication) or any surface in need of cushiono Types: Fibrocartilage: lots of fibers, used for cushion Bio 312 1st Edition Elastic cartilage: used for support and protection Hyaline Cartilage: most abundant type- Flexible, rubber like, resilient- Strong and able to support weight- Smooth low friction surface- Forms most of the embryonic skeleton, provides template for skeleton- Provides growth plates (epiphyseal plates) for continued bone growth- Coats parts of bone in joints- Makes up tip of nose, costal (ribs) cartilage, voice box, windpipe, trachea, bronchi- Histology of Hyaline Cartilage:o Consists of widely scattered cells called chondrocytes surrounded by matrix (seeds in a watermelon)o Lacunae: small cavities in matrix that house chondrocyteso Matrix consists of collagen fibers, H2O and proteoglycanso Ground Substance: composed mostly of proteoglycans Negatively charged to hold water molecules for cushion and lubrication Avascular: O2 and waste molecules must diffuse from blood vessels in perichondrium through the matrix (limits thickness of cartilage)o Perichondrium: outer layer of cartilage that houses blood cells and differential cells that can become chondroblasts- Embryonic Development of Cartilage:o Mesenchymal tissue and mesenchyme cells begin to cluster and clump togethero Mesenchymal cells differentiate into chondroblasts and begin to secrete matrixo Chondroblasts now spread out in their lacuna after matrix secretedo Interstitial Growth: chondroblasts divides within lacuna, 2 daughter cells secrete more matrix and push eachother apart (growth from within only possible in young soft cartilage, kids)o Appositional Growth: chondrogenic cells in perichondrium differentiate into chondroblasts which secrete matrix on outer layer of cartilage (requires perichondrium, but is possible in olderpeople)- Calcification of Cartilage: some cartilage is predetermined to calcifyo Chondrocytes hypertrophy (get bigger)o Alkaline phosphatase secreted from chondrocytes Promotes deposition of calcium salts Blocks diffusion of O2 and nutrientso Chondrocytes die, cartilage degenerates, bone leftoverBone: living, dynamic tissue- Composed of cells and matrix (fibers and ground substance)- Matrix becomes calcified by deposition of calcium salts- Functions: support, protect, movement facilitation, mineral storage, storage of energy, hemopoiesis- All bones consists of 2 histologically distinct types of bones:o Outer layer consists of compact dense boneo Inner layer consists of spongy cancellous bone Trabeculae: thin walls of spongy bone- Periosteum: outer fibrous layer of boneo Consists of two layers: Outer fibrous layer Inner cellular layer which consists of three different cell types- Blood supply to bone: vessels enter from periosteum- 4 types of bone based on shape:o Long bone: longer than wide (femur) Found in arms and legs Very vascularo Flat bone: is flat (sternum)o Short bone: cuboidal (wrist, feet)o Irregular bone- Bone Histology: both types (hard and soft) made form same ingredientso Osteogenic Cells: osteoprogenitor cells Found in endosteum and inner periosteum Mitotic stem cells that give rise (differentiate) to osteoblasts Lead to development of new bone tissueo Osteoblasts: bone forming cells Secrete matrix (osteoid)- Collagen fibers and ground substanceo Osteocytes: mature bone cells Former osteoblasts not surrounded living matrix Live in lacunae Maintain bone matrix Act as stress sensorso Osteoclasts: found on bone surfaces Derived from stem cell in bone marrow Responsible for bone resorption Secrete enzymes and acid that breaks down calcified bone matrix Under control of parathyroid hormone (PTH)o Bone matrix: contains organic and inorganic components Organic component (osteoid)- Secreted by osteoblasts- 33% of total matrix- Collagen fibers (90%) give properties of flexibility and great tensile strength- Ground substance (5-10%) made of proteoglycans and glycoproteins Inorganic component: - 67% of total matrix- Compose of hydroxyapatites aka bone saltso Calcium phosphate the most plentiful- Makes the bones hardo Compact Bone: mostly calcified matrix matrix deposited in layers called lamellae Circumferential lamellae: coats outer circumference of entire bone Concentric/Haversian lamellae: layers of bone that coat the individual osteons of the bone Interstitial lamellae: lamellae that do not belong to a specific osteon but fill in the spaces in between the haversian systems Contain evenly spaced lacunae sandwiched between lamellae which each house an individual osteocyte Canaliculi: lead from lacunae to either central canal or periosteum which contain bloodo Spongy Bone: Found at the ends of bones Consists of lots thin bone walls called trebecullae- composed of interstitial lamellae, and lacunae Cavity flooded with blood House hemopoiesis:- Where red and white blood cells are madeo Osteogenesis: process by which bone forms and begins about the 8th week of development Skeletal model in early embryo composed of fibrous membranes and hyaline cartilage Process occurs over long period of time and throughout lifespan 2 types of bone formation-


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UWL BIO 312 - Skeletal System 2

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