Chapter 6 Notes
Chapter 6 Notes 80887 - BIOL 3150 - 001
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This 23 page Class Notes was uploaded by Abigail Towe on Wednesday September 30, 2015. The Class Notes belongs to 80887 - BIOL 3150 - 001 at Clemson University taught by Tamara L. McNutt-Scott in Fall 2015. Since its upload, it has received 70 views. For similar materials see Functional Human Anatomy in Biological Sciences at Clemson University.
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Date Created: 09/30/15
Chapter 6: Cartilage and Bone Connective Tissue ● Cartilage + bone = Skeleton, which serves to: ○ internal framework that muscles attach to ○ support/protection for organs ○ dynamic structure= meaning that it is constantly rebuilding and remodeling itself ○ interacts with other organ systems ○ made up of: bone + cartilage + ligaments + other connective tissues = all work together to stabilize and connect bones Cartilage Connective Tissue ○ cartilage is a semirigid connective tissue ○ cartilage is weaker than bone, but more flexible and resilient (return to normal shape after compressed) ○ functions: ■ supports soft tissue ● example: trachea supports the soft tissues of the throat ■ provides gliding surfaces for articulations ■ provides a model for bone formation ○ 3 types: ■ hyaline cartilage: ● found in: articular cartilage of joints, costal cartilage, and cartilages in nose ● most abundant ● offers support, flexibility and resilient ● surrounded by perichondrium ● translucent appearance of extracellular matrix ○ there are fine cartilage fibers throughout the entire matrix ○ the translucent appearance doesn't mean there aren’t any fibers, it just means that you need a dye to see them. ■ fibrocartilage: ● found in: cartilage of intervertebral disc and meniscus ● numerous thick collagen fibers for tensile and compressional forces ● lacks perichondrium ■ elastic cartilage: ● found in: ear and epiglottis ● highly branched elastic fibers ● highly flexible form of support ● has perichondrium ○ cells of cartilage: ■ chondroblasts= cells that produce/secrete the matrix of cartilage ● once the cell has become surrounded by matrix through secreting enough, it becomes chondrocytes ■ chondrocytes= the mature cartilage cell that makes sure that the matrix remains healthy and viable ● located within the small spaces = lacunae ■ cells are scattered across the matrix of protein fibers and are embedded in a gellike ground substance ● Growth Patterns of Cartilage: ○ two types of growths: interstitial growth and appositional growth ■ both occur simultaneously during embryonic development ■ interstitial growth = growth from within the cartilage itself ■ appositional growth= growth along the cartilage outside edge (or periphery) ● however, interstitial growth declines rapidly as cartilage matures ● therefore, later growth is mainly appositional growth ● once fully mature, new cartilage growth stops (only resumes when damage occurs) Bone: ● basic functions: ○ support and protection ○ movement ■ skeletal muscles, soft tissues, and organs attach to bones ● skeletal muscles use bones as series of levels by pulling on skeleton ■ big motions= gross ■ small, meticulous motions = precise ○ hematopoiesis ■ blood formation occurs in red bone marrow ■ location varies with age ● also as you get older, you have fewer sites of bone marrow production. ● the red bone marrow degenerates and turns into a fatty tissue called yellow bone marrow ○ storage of mineral and energy reserves within extracellular matrix (this make bone matrix sturdy and rigid) ■ the deposit of minerals in matrix = a process called calcification (mineralization) ■ minerals include: calcium and phosphorous ● calcium is important for muscle contraction, blood clotting and nerve impulse transmission ● phosphate is needed for ATP utilization ■ located within yellow bone marrow ● which is also a storage site for adipose tissue ● composed of osseous tissue (bone connective tissue) ○ also composed of: ■ periosteum = connective tissue proper ■ articular cartilage = cartilage connective tissue ■ forming the walls of blood vessels that supply bone = smooth muscle tissue ■ blood = fluid connective tissue ■ lining the inside opening of blood vessels = epithelial tissue ● Classification of Bones: ○ long ■ length > width ■ elongated shaft = diaphysis ■ distinct ends = epiphyses ■ example: femur ○ short ■ length and width similar ● example: sesamoid bone = patella ○ functions to protect/shield knees ● example: tarsal bone ○ flat ■ thin, flattened, usually curved ■ because it’s flattened, there is an increase in available surface area for attachment sites for muscles, and it also means more protection for the soft tissues located under the flat bone. ■ example: frontal bone ○ irregular ■ elaborate, complex shape ■ example: vertebra ● Bone Markings: ○ distinctive surface features that characterize each bone ○ types: ■ projections from the bone surface mark the point where tendons and ligaments attach ● anatomic terms: condyle, facet, head, trochlea ■ sites of articulation between adjacent bones are smooth, flat areas ● anatomic terms: alveolus, fossa, sulcus ■ depressions grooves/tunnels through bones indicate sites where blood vessels and nerves either lie alongside or penetrate the bone ● anatomic terms: crest, epicondyle, line, process, ramus, spine, trochanter, tubercle, tuberosity ■ openings and spaces shows passageways through a bone ● anatomic terms: canal, fissure, foramen, sinus Connective Tissue wraps around bones: ● periosteum: ○ dense irregular connective tissue ■ outer layer of fibrous layer ■ inner layer: cellular layer ○ serves to cover the outer surface of bone (except where there is articular cartilage) ○ anchored to bone by many strong collagen fibers (perforating fibers) ■ these fibers run perpendicular to the diaphysis ○ functions: ■ isolates and protects bone from surrounding structures ■ anchors blood vessels and nerves to surface ■ provides stem cells (osteoprogenitor cells and osteoblasts) for bone growth = appositional (growth around outer edge) ■ fracture repair ● endosteum ○ incomplete layer ○ contains: osteoprogenitor cells, osteoblasts, and osteoclasts ■ all of these cells are important for bone growth, repair and remodeling Bone Cells: ● osteoprogenitor= stem cells derived from mesenchyme ○ when they divide, the produce another stem cell and a “committed cell” that develops into osteoblasts ○ located in both the periosteum and endosteum ● osteoblasts = build bone up by forming bone matrix ○ sometimes they differentiate into osteocytes ● osteoclasts = break bones down ○ they are large, multinuclear, phagocytic cells ○ process of bone breakdown: ■ osteoclasts secrete hydrochloric acid (to dissolve mineral parts of bone matrix) ■ osteolysis= the release of stored calcium and phosphate from bone matrix ● osteocytes= maintains bone matrix ○ also serve as sensor for stress ■ they detect mechanical stress on a bone ■ when there is stress, the information is communicated to osteoblasts so that they can deposit new bone matrix at surface Composition of bone matrix: ● organic components make up ⅓ of the total composition of bone ○ organic components give bone the ability to resist stretching and twisting, and contribute to overall flexibility ○ includes: ■ cells =osteocytes, osteoblasts, osteoclasts ■ osteoid = ground substance and collagen fibers, which are both synthesized by osteoblasts ● inorganic components: ○ inorganic components provide bone its compressional strength ○ includes: ■ hydroxyapatites (mineral salts) = 65% of bone mass ● hydroxyapatite= calcium phosphate + calcium hydroxide ● deposits around collagen fibers in extracellular matrix ● gives bone its hardness Compact vs. Spongy Bone ● compact bone: ○ “dense bone” ○ “cortical bone” ○ solid, relatively dense ○ example of where it is found: outside of bone (along the borders) ○ microscopic anatomy of compact bone: ■ the basic functional and basic structural unit of mature compact bone is osteons. ● osteons= cylindrical units that run parallel to the diaphysis of the long bone ○ components of osteon: ■ centra l canal: the channel located in the center of the osteon that allows blood vessels and nerves to pass through so that it can supply the bone. ● c oncentric lamellae rings of bone connective tissue that surrounds the central canal ○ e ach of the concentric lamellae around the osteon has collagen fibers oriented in opposite directions as the layers increase out from the central canal. ○ t he change in directions gives bone part of its strength and resilience ■ lacuna e: the dark spots that look like spiders located within the rings of each concentric lamellae ■ canali culi tiny, interconnecting channels that extend from lacuna (the legs of the spider) ● t he canaliculus help to connect lacunae to each other and the central canal (where there is blood vessels and nerves) ■ osteoc ytes cells that are located within the lacunae ● spongy bone: ○ “cancellous bone” ○ “trabecular bone” ○ more porous and spongelike ○ forms an open lattice of narrow plates of bone = trabeculae ○ example of where it is found: in the head of the femur and down into the head region ○ microscopic anatomy of spongy bone: ■ does NOT have osteons ■ has trabeculae = the loose material that is only a few layers thick ● assists bone when multidirectional stress is applied ● trabeculae contains irregular lamellae is present = parallel lamellae ○ between the lamellae there are osteocytes resting in lacunae ● trabeculae= meshwork of criss crossing bars and plates of bone pieces ○ the structure of compact bone functions to: ■ reduce stress because of the cross bracing ■ because it’s porous → reduces weight ■ supports and protects marrow (red bone marrow) Ossification: ● osteogenesis= physical process of bone formation ● calcification= deposition of calcium salts ● ossification is the formation and development of bone connective tissue growth (bone replaces other tissues) during development and childhood/adolescence, even into adulthood ○ bony skeleton begins around 8 weeks of development ○ ossification for children/young = bone grows in thickness ○ ossification in adults = used to remodel and repair bones ● intramembranous ossification: “dermal ossification” ○ “bone growth within membrane” ■ the membrane = thin layer of mesenchyme ● mesenchyme= embryonic connective tissue that is characterized by loosely associated cells that lack polarity and surrounded by a large extracellular matrix. these cells have the ability to develop into other tissues ○ process: ■ mesenchyme cells divided into committed cells that form osteoprogenitor cells. some of the osteoprogenitor cells become osteoblasts. the osteoblasts secrete osteoid (semisolid organic component of bone matrix) ■ ossification centers (a group of osteoblasts) form in the thick regions of mesenchyme ■ osteoid (semisolid matter) undergoes calcification (calcium salts are deposited) and then crystallized. as calcification occurs, some osteoblasts are trapped within the lacunaes of the matrix that is solidified. these trapped osteoblasts → osteocytes ■ woven bone and surrounding periosteum forms ● woven bone= immature bone connective tissue “primary bone” ■ eventually lamellar bone (secondary bone) replaces woven bone ● lamellar bone replaces the trabeculae of woven bone ○ compact bone = spaces between trabeculae are filled ○ spongy bone= trabeculae slightly modified ○ intramembranous ossification forms flat bones ● endochondral ossification: ○ endochondral ossification forms long, short, and irregular bones ○ bone formation with help of cartilage template ○ process: ■ fetal hyaline cartilage model develops ● when chondroblasts secrete cartilage matrix, hyaline cartilage model forms. ● chondroblasts → chondrocytes ● perichondrium surrounds cartilage ■ cartilage calcifies, and a periosteal bone collar forms ● chondrocytes start to enlarge (hypertrophy) and resorb (eat) surrounding cartilage matrix → this creates holes in matrix ● while the chondrocytes enlarge, the matrix calcifies ● the calcified matrix ends up killing chondrocytes because they cannot get nutrients ● blood vessels grow toward cartilage through the holes ● perichondrium stem cells divide to form osteoblasts that start secreting osteoid (semisolid matrix) ● through vascularization and osteoblast development, the perichondrium because periosteum ● all the osteoid matrix hardens and forms periosteal bone collar around the diaphysis ○ as this bone collar forms, the cartilage in the center degenerates ■ primary ossification center forms in the diaphysis ● periosteal bud brings in blood vessels into the diaphysis to aid the primary ossification process ■ secondarily ossification centers form in epiphyses ■ bone replaces cartilage (except articular cartilage and the epiphyseal plates) ■ epiphyseal plates ossify and from epiphyseal lines ○ long bones have both primary and secondary ossification centers ○ short bones only have primary ossification centers ○ irregular bones irregular bone ossification all over Growth of Bone: ● interstitial: a long bone’s growth in length ○ occurs: epiphyseal plate (region of hyaline cartilage) ○ there are 5 distinct regions/zones found in the epiphyseal plate ■ zone 1: zone of resting cartilage ● located: farthest out from medullary cavity ● healthy cartilage matrix that helps secure epiphysis to the epiphyseal plate. ■ zone 2: zone of proliferating cartilage ● chondrocytes undergo rapid mitotic cell division, start enlarging, and become arranged in longitudinal columns of flattened lacunae (like a stack of coins) ■ zone 3: zone of hypertrophic cartilage ● chondrocytes do not divide anymore, they just enlarge greatly ● during this enlargement process, the walls of lacunae become thin and absorb matrix ■ zone 4: zone of calcified cartilage ● narrow zone of cartilage that is only a few cells thick ● since the lacunae are absorbing matrix, the “gaps” where it goes missing is filled willed minerals. ● the calcification kills chondrocytes ■ zone 5: zone of ossification: ● walls break down between lacunae in columns ● this forms longitudinal channels ● the channels are filled with capillaries and osteoprogenitor cells (from medullary cavity) ● new matrix is of bone is deposited ○ osteoblasts (new bone) and epiphyseal cartilage grow at same rate. ■ so as long as epiphyseal cartilage can grow, then bone can grow ■ but when you hit puberty, the hormones cause bone growth (osteoblasts) to produce at faster rate than epiphyseal cartilage, so the epiphyseal cartilage gradually disappears ■ closure= when the bone growth overtakes cartilage growth so that cartilage ● appositional growth: long bone’s growth in diameter/thickness ○ increase of width occurs within periosteum and along medullary cavity ○ what happens: ■ osteoblasts in the inner cellular layer of periosteum lays down bone matrix in layer parallel to the surface (the circumferential lamellae increases in layers) ■ the medullary cavity expands to retain proportion. it expands by resorbing bone matrix ■ there is a balance of bone resorption and bone deposition (to keep proportions as bone grows) ● however, during puberty absorption formation is greater. ● but as you age, bone deposition is greater Bone Remodeling: ● the process of continuously depositing new bone and resorption of old bone ● bone continues to grow and renew itself ● bone is a mechanosensitive organ so it alters structure to suite its mechanical environment (to support the weight put on it) ● remodeling is guided by stress ○ stress= mechanical stress and gravity ○ Wolff’s Law: bone grows and remodels itself according to stress/forces ■ McNuttScott said “this is why you need weight bearing exercises” ● occurs at periosteal and endosteal surfaces ● over the course of one year, about 20% of the adult skeleton is replaced ○ age influences rate ○ compact bone replaced slower than spongy bone Blood supply and innervation: ● bones are highly vascularized with blood vessels, but also as nerves and nutrient blood vessels ● blood vessels and nutrient vessels enter from the periosteum ○ nutrient vessels: ■ supplies nutrients to diaphysis and central canals of osteons within compact bone and marrow cavity ○ metaphyseal vessels ■ supplies blood to the diaphyseal side of the epiphyseal plate ○ epiphyseal vessels ■ supplies blood to the epiphyses of bone ○ periosteal vessels: ■ provide blood to external circumferential lamellae and the superficial osteons (in compact bone) at external ends of shaft ● nerves enter through nutrient foramen ○ nerves go through nutrient foramen with blood vessels to innervate the bone, periosteum, endosteum, and marrow cavity ○ mainly sensory nerves that signal injuries to the skeleton Homeostasis and Bone Growth through hormones and vitamins: ● Effects of hormones – control growth patterns, they do so by altering activity of osteoblasts & osteoclasts. ● increase in osteoclasts activity ends up increases bone. ○ GH (growth)– stimulate liver somatomedins that directly stimulate cartilage growth at EP ○ TH (thyroid)– influences the BMR of bone cells ○ CT (calcitonin) is your friend = encourage Ca deposition bone resorption sses osteoclast activity so we are slowing down/retarding ○ PTH (parathyroid)– stimulates osteoclast activity to resorb bone. PTH always wins even if it’s negative effects to skeleton/bone. ○ Sex hormones – dramatically accelerate bone growth, stimulate osteoblasts at epiphysis, HOWEVER, at puberty signal EP closure ○ Glucocorticoids (stress hormones)– normal levels no effect but if chronically high, increase bone resorptionloss of bone mass ● Effects of vitamins – impt for normal growth ○ Vitamin A ■ accelerates osteoblasts ○ Vitamin C ■ required for normal cartilage synthesis ○ Vitamin D ■ stimulates absorption & transport of Ca and P ions into blood ● exercise is required for normal bone remodeling because when bones encounter mechanical stress it gains strength. ○ there is an increase in amount of mineral salt deposition and collagen fibers synthesized. Fracture Repair: 1. fracture hematoma forms a. because there are blood vessels within the bone, when a fracture occurs it disrupts vessels and causes a bleeding. When the blood clots, there is a hematoma that formed. 2. fibro cartilaginous (soft) callus forms a. first a procallus forms of actively growing connective tissue. the fibroblasts within this procallus aid in connecting broken ends of bones. b. leads to formation of dense irregular connective tissue to form a fibrocartilaginous callus (soft callus) c. lasts 3 weeks 3. a hard (bony) callus forms a. the osteoprogenitor cells around the fibrocartilaginous callus become osteoblasts and produce trabeculae of primary bone to form a hard callus (bony callus) b. this occurs within a week 4. bone is remodeled a. hard calllus lasts 34 months b. osteoclasts remove excess bony material c. compact bone replaces primary bone Aging of Skeletal System: 1. tensile strength decreases because less protein synthesis a. this leads to reduced production of organic portion of bone matrix and an increase in the inorganic portion, causing bone to become brittle 2. demineralization: losing calcium and other minerals a. when ossification is insufficient (osteopenia), then the bones become thinner and weaker i. osteopenia weakening bones 1. lower than noral bone mineral density (BMD) but not low enough to be osteoporosis ii. osteoporosis less bone 1. such a reduction in bone mass that it compromises normal function ● Paget’s Disease: ○ old bone is broken down faster than new bone is made ○ to counteract the bone being broken down so fast, body tries to make bones faster but the new bones are weaker and softer. ○ this diseases leads to bone pain, deformities, and fractures ○ more common in Europe and Australia. and more common in men than women. Review Cartilage: hyaline fibrocartilage elastic compare intramembranous and endochondral ossification intramembranous endochondral starting tissue mesenchyme hyaline cartilage initial development 8 weeks 812 weeks ossification centers multiple diaphysis first, then epiphyses examples of bones: flat bones of skull, some upper and lower limb facial bones, mandible, bones, pelvic, vertebrae, and central clavicle ends of clavicle, ribs Epiphyseal plate zones zone 1 secures epiphysis to epiphyseal plate zone 2 rapidly growing, enlarge, and arrangement of chondrocytes in longitudinal columns zone 3 chondrocytes stop dividing, enlarge greatly zone 4 narrow layer where minerals are deposited in matrix between columns of lacunae chondrocytes die zone 5 longitudinal channels form. the spaces between are filled with capillaries and osteoprogenitor cells. new bone matrix is deposited.
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