BIOL 315 1st Edition Lecture 7 Outline of Last Lecture I. Loose areolar connective tissue (continued)II. Dense connective tissuea. Irregularb. Regular III. Cartilage IV. Bone tissue and the bony skeletonOutline of Current LectureI. External gross structure of bonesa. Basic partsb. Bone cellsc. Bone tissueII. Development of Bonea. 2 classes of boneb. Phases of endochondral ossificationc. how bones widenIII. JointsCurrent LectureI. External Gross Structure of Bonesa. Basic Partsi. Diaphysis: shaft, “a growth between”ii. Epiphyseal: growth uponiii. Nutrient Artery: enters at the shaft1. Supply both the bone tissue and the bone marrow and branch to the pariosteum iv. Epiphyseal artery: enters each epiphyseal1. Supply both the bone tissue and the bone marrow and branch to the pariosteum b. Bone Cellsi. 3 Types of bone cells1. Osteocytea. Imbedded in the extracellular matrixb. Shaped like a spiderc. Central cell body (contains the nucleus)d. Occupy the lacunae e. Cell processes occupy tiny canals, canaliculi, which run adjacent to the lacunaeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Connected by gap junctionsf. Nutrients cannot diffuse through the bone matrixi. “bucket brigades” the nutrients between the capillaries through the osteocytes g. Function: maintain the extracellular matrix of bone tissue. Sense stresses placed on the bone matrix and signal bone remodeling in response2. Osteoblastsa. Bone forming cellsb. Not located in the bone matrixc. Located in periosteum, endosteum, and around the blood vessels inside bone tissued. Hemi-sphere shaped cellse. Lay down bone matrix and then transform into osteocytes one the matrix calcifies around them3. Osteoclastsa. Bone destroying cells b. Not located in the bone matrixc. Located in periosteum, endosteum, and around the blood vessels inside bone tissued. Bone-resorbing cellse. Very largef. Ruffled surfaceg. Secrete hydrochloric acid to dissolve mineral of bonei. Releases calcium and phosphate ions into the body fluidh. Activated by a hormone from the parathyroid gland, which is produced whenever the concentration of calcium in body fluid falls to unacceptably low levelsi. Derived from blood-forming cells in the bone marrowc. Bone Tissuei. Woven Bone1. immature and only present during development2. 1st type of bone tissue to be laid down3. Laid down between embryonic blood vessels, giving it a woven appearance4. Extracellular matrix appear uniformii. Lamellar Bone1. Mature bone2. Starts replacing the woven bone during the fetal period3. All bone s in adult are lamellar 4. Lamellae: plate like subdivisions of extracellular matrixa. All collagen fibers run in a single directionb. Adjacent lamellae are oriented in right angles to each other i. Increases strength of the bone tissuec. Not a flat sheet but a sheet bent into a tube, and many concentric lamellae form tubes within tube, like tree ringsd. Resists twisting i. Twisting is the most destructive force5. Osteona. Thousands occur within compact boneb. Form columns/pillars that are parallel to the long axis of the long bonec. Constantly being eaten away and then replaced with other osteonsd. Why remodel??i. Allow constant turnover of calcium and phosphate between the bone and body fluidsii. Allow to realign the osteon pillars along new lines of compressioniii. Remember that bone is DYNAMIC!! ALWAYS REMODELING AND CHANGING6. Central Canala. In the middle of each osteonb. Filled with loose connective tissuec. Artery, vein, and nerve of the osteon run through herei. Supply nutrients to the living bone cells in the wall of the osteonII. Development of the bones (from before birth until the body stops growing)a. 2 classes of bones are:i. Membrane bones1. DO NOT form in cartilage2. develop directly from membranes of mesenchymea. mesenchyme: the embryonic tissue that gives rise to all connective tissues3. form through a process of intramembranous ossification4. the only membrane bone in our skeleton are the skull bones and the clavicles ii. Endochondral bones1. First formed as cartilage2. All bones from base of the skill down, except clavicles 3. Become bony in a process of endochondral ossificationa. Begins at the end of the 8th week of development (late embryo/early fetus)b. Ends 15-20 years laterc. Involves the increase in length of the growing bone d. Hyaline cartilage does all of the growing, because cartilage grows faster than bonei. Bone merely follows along and replaces the cartilage tissue at its own pace e. At week 8 , the “bone model” is not yet a bone, its just hyaline cartilage covered by perichondrium membraneb. The Phases of Endochondral Ossificationi. Periosteum forms1. Perichondrium  periosteum2. Osteoblasts in periosteum lay a collar of bone tissue around the shafta. Needed because the bone will soon be hollow, and would break without the bone collarii. Cartilage calcifies the shaf1. Chrondrocytes in the center of the shaft signal the surrounding matrix to calcify  calcifies cartilage a. Calcified matrix is impermeablei. Chondrocytes are cut off from nutrients supply and dieiii. Artery enters, first spongy bone forms1. the nutrient artery grows into the center of the shaft and begins to sprout branchesa. carries menchyme cells with iti. become osteoblasts which surround the remaining pieces of calcified cartilage and begin to cover with spicules with bone1. earliest form of spongy bone2. with first appearance of bone tissue, the diaphysis is called the primary center of osterificationiv. epiphyses take form1. while bone tissue forming in shaft2. cartilage epiphyses continue to grow fast3. chondrocytes line up in columns to promote efficient growth4. cartilage that lies nearest the diaphysis constantly undergoes: degeneration, calcification, and replacement with spongy bone5. lasts throughout the fetal period until the time of birthv. epiphyses start to ossify (secondary centers of ossification)1. time of birth, cartilage in center of both epiphyses calcifies and degenerates2. an artery enters each epiphysis carrying bone-forming cells3. surround remaining calcified cartilage so spongy bone is laid down4. the cartilage that remains is in the form ofa. articular cartilagesb. epiphyseal platesvi. growth occurs exclusively at the epiphyseal plates1. plate of cartilage continue to grow, being replaced by bone on diaphysis side at about the rate