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Chapter 6 Bone and Skeletal Tissues

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1 Chapter 6 Bone and Skeletal Tissues
Anatomy 32 Chapter 6 Bone and Skeletal Tissues

2 I. Cartilage- A versatile connective tissue that supports body structures. Cartilage also lays down the initial skeletal structure. A. Location and basic structure- found throughout the body, has different functions according to its location. Cartilage contains a great amount of water and low blood vessels and it can reshape easily. Although there are three main types of cartilage there are eight major body locations: 1. external ear 2. nasal 3. articulate cartilage (ends of bones) 4. costal cartilage 5. larynx cartilage 6. tracheal cartilage 7. vertebral discs 8. pubic symphysis

3 B. Classification of cartilage- based on its composition, flexibility, and density.
1. Hyaline cartilage-most abundant, lines joints, bluish, chondrocytes and collagen.

4 2. Elastic cartilage- has chondrocytes, collagen, and elastin fibers
2. Elastic cartilage- has chondrocytes, collagen, and elastin fibers. It is highly elastic, tolerates repeated bending.

5 3. Fibrocartilage-intermediate between hyaline and dense regular connective tissue. Thick collagen fiber rows alternate with chondrocyte rows, embedded in matrix. Support high compression and tension. Found in areas that bear weight, between vertebrates and knees.

6 During lab you will study histology slides of the three types of cartilage. Pay close attention to the structural differences.

7 C. Growth of cartilage- appositional growth stems from the perichondrium towards center while interstitial growth stems from center towards perichondrium. Calcified cartilage occurs when calcium deposits form within the cartilage- this can cause pain or reduce the range of motion of a joint. II. Bones are classified as connective tissue but are also organs. Bones have bone cells embedded in a matrix that has a high concentration collagen and minerals but little water A. Functions of bones- there are five major functions performed by bones: 1. Support- they give shape to the body, hold it up, bare its weight, and contain organs 2. Protection- bones surround soft tissue organs to provide support 3. Movement- bone joints and skeletal muscle work together with bones to make movement possible 4. Storage- the hard matrix the make up bones store minerals like calcium and phosphate, when needed by the body they are released into the blood stream. The bone marrow inside long bone stores fats. 5. Blood Formation- bone marrow is the site of blood cell and immune system cell formation .

8 B. Classification of bones- despite the large array of bones in the body most bones are classified into four types: 1. Long bones-these are bones that more length than width and has a shaft plus two ends. A long bone does not have to be a big bone. 2. Short bones- these are cubed shaped and include sesamoid bones (small short bones) such as the patella. 3. Flat bones- thin, flat, and curved such as the skull or ribs 4. Irregular bones- these are bones that have various shapes within a single bone piece. SESAMOID BONES

9 C. Gross Anatomy of bones-in these sections we study the general characteristics of compact bone and cancellous bone (spongy bone). All bones are innervated with lymphatic vessels, nerves, and blood vessels. They are surrounded on the outside by a membrane called periosteum and the inner cavities are lined with endosteum. The periosteum attaches to the bone surface by sharpey’s fibers. All bones contain the following living cells:

10 Osteoclast- bone destroying cells, help to release minerals into blood stream
Osteoblast- bone generation cells that lay down more matrix Osteocyte- mature bone cell, maintains bone matrix

11 1. Compact and spongy bone- compact bone appears as a dense solid mass as seen on the shaft and edges of long bones. Spongy bone (cancellous) is porous because of the trabeculae structure and is usually surrounded by a layer of compact bone. It is found on the end of long bones. Compact bone may hold yellow bone marrow while spongy bone holds red bone marrow.


13 2. Structure of typical long bone- the shaft is called the diaphysis and the ends are called the epiphysis. Each of these areas has its own blood supply. The nutrient artery and vein serve the diaphysis and enter through the nutrient foramen. There are also epiphyseal arteries and veins. Long bones also have an internal cavity called the medullary cavity filled with bone marrow. The ends of long bones are lined with hyaline cartilage to facilitate joint movement. 2. Structure of typical long bone- the shaft is called the diaphysis and the ends are called the epiphysis. Each of these areas has its own blood supply. The nutrient artery and vein serve the diaphysis and enter through the nutrient foramen. There are also epiphyseal arteries and veins. Long bones also have an internal cavity called the medullary cavity filled with bone marrow. The ends of long bones are lined with hyaline cartilage to facilitate joint movement.


15 3. Structure of short, irregular, and flat bones- although not cylindrical they are like long bones in the compact bone surrounds spongy bone.

16 4. Bone design and stress- as bones bare weight they are compressed and as they bend in one direction they experience tension (stretching) in the other direction. Long bones are designed to withstand this by having compact bones on the external region of the bone. Because these forces do not exists internally the inside of the bone has bone marrow or spongy bone which also reduces bone mass. Trabeculae follow certain stress line to also provide support.

17 D. Microscopic structure of bone- in this section we study the microscopic organization of bone.
1. compact bone- this dense structure is composed of structures called osteon (harvesian system), it is a group of concentric tubes that in cross-section appear as rings. They are made up of lamella (layer if bone matrix with collagen running in one direction). Circular lamella is called concentric and parallel lamella is called interstitial lamella. Within the lamella is a network of osteocytes embedded in lacunae and connected by canaliculi ( little canals). These cells are maintained alive by nutrients and oxygen provided by blood vessels passing through the center of the osteon called the central or harvasian canal and the volkman’s canal (transverse to diaphysis) . Circumferential lamellae follow the circumference of the bone. 2. spongy bone- the trabeculae of spongy bone is made of lamella and ostecytes but not osteons because the trabeculae are so small.


19 E. Chemical Composition -healthy bone is half as strong as steel in resisting compression and equally strong in resisting tension. Bone is composed of the following: 35% organic components- cells, fibers, and ground substance 65% inorganic components- minerals, mostly calcium phosphate.

20 F. Bone Development- the bone framework is first laid down as cartilage and then changes to bone this process is called osteogenesis or ossification. The skeleton changes throughout the entire life of the individual.

21 1. Intramembranous ossification- this is a process in which bone is not laid out first in cartilage, it happens in membrane bone that form the skull and clavicle. a. –Week 8 of development cells cluster within mesenchyme membranes and become osteoblast. They secrete the osteoid (bone matrix) forming woven bone tissue which thicks into trabeculae. The outer trabeculae thicken to form compact bone. There is no lamella in this type of bone.



24 2. Endochondral ossification- This process begins late into the second month of development and is completed in adulthood. There are four stages: Stage 1- By week 8 the cartilage model has perichondrium that becomes bone forming periosteum and a bone collar forms around the diaphysis Stage 2- The chondrocytes signal calcification at the center of the diaphysis. Calcification of the cartilage deprives the cells of nutrients. Once they die, cartilage disintegrates leaving a cavity at the center that influences elongation and provides a space for the primary ossification center. Stage 3- The primary ossification center forms at the diaphysis by the third month of development. The periosteal bud includes nutrient blood vessels, bone cells, and bone marrow forming cells; it invades the calcification area. Trabeculae is laid out to eventually meet with bone collar in the diaphysis. Osteoclast help to remodel bone and form the medullary cavity. Stage 4- Before birth or shortly after, the epiphyses forms secondary ossification centers and the ends of the bones ossify. Secondary follows the same mechanisms as in primary ossification. At this point hyaline cartilage remains on the surface of joints and at the growth plates.


26 Bone growth Linear growth of long bones takes place at the epiphyseal plates- sex hormones eventually inactivate epilhyseal plates. Epiphysis is the end of a long bone. Diaphysis is the shaft of a long bone. Epiphyseal plate is the site of bone growth. Compact bone Osteoblast Direction of growth Chondrocyte Cartilage owth Newly calcified Bone gr Dividing chondrocytes add length to bone. Chondrocytes produce cartilage. Old disintegrate. Osteoblasts lay down bone on top of cartilage. Figure 23-19

27 G. Anatomy of epiphyseal growth areas- these are areas known as the “growth plates”. The bone continues to elongate. The chondroblasts are organizes as large columns forming four zones 1- Cells divide rapidly pushing the older cells away, thus elongating the bone. 2- In this zone the older chondrocyte enlarge to signal calcification 3 & 4- cells die and disintegrate forming trabeculae at the epiphysis-diaphysis junction

28 H. Bone remodeling- Compact bone is entirely replaced every 10 years and spongy bone every 3-4 years. Not all areas of a single bone are replaced at the same time. Osteoblast perform bone deposition by producing bone matrix and osteoclast re-absorb bone by releasing hydrochloric acid and dissolving the minerals.

29 I. Repair of bone fractures- If the bone does not pierce the skin it is a simple fracture, if it does then it’s a compound fracture. There are six types of fractures (pg 138) : Communited-3+ fragments Depressed- inward depression Compression-crushed Epiphysieal-plate tears Greenstick-partial break Spiral-due to twisting force





34 Ossification steps in a fracture:
1. Hematoma formation-broken blood vessels release blood that form a clot 2. Fibrocartilaginous callus formation-periosteum and endosteum form many bone-forming cells that invade the clot creating a callus containing fibrocartilage and hyaline cartilage.

35 3. Bony callus formation-trabeculae form in callus by enchondrial ossification, it becomes the bony callus. This takes about 2 months. 4. Bone remodeling-the callus is removed by osteoclast removing excess bone mass and compact bone is laid out.

36 III. Disorders of Bones A. Osteoporosis-(bone porous condition) low bone mass due to deterioration and bone reabsorption is faster than bone deposition. Fractures occur easily, especially in the vertebrae, femur, or hip. It happens more in women than in men and more often in Caucasian women. Low estrogen levels, poor diet, and not enough exercise can lead to osteoporosis. Osteomalacia and Rickets- (soft tissue) weakening of the bone resulting from lack of vitamin D or calcium phosphate. Osteomalacia occurs in the adults, the bone does not have a proper amount of minerals and calcification does not occur causing weak bones. Rickets is the childs’ form but is more severe because bones are still developing. May cause bowed legs or malformities in head and ribs. Bones become thick and abnormally long C. Paget’s Disease-( disorder in newly formed bone) bones become soft and weak because new bone is layed out faster than it matures and less mineralization. Bones thicken irregularly happens before age 40 and may result from a viral infection. D. Osteosarcoma-(bone cancer) affects people 10-25, originates in long limb bones. The tumor develops in the regions near growthplates and is of osteoblast origin.

37 Osteoporosis

38 IV. The Skeleton Throughout Life- Mesoderm give rise to embryonic mesenchyme which forms membranes and cartilage Cartilage- grows quickly in youth, stops in adulthood, and calcifies in old age. Bone- ossification begins before birth, after birth movement and tension provided by muscle forms markings, children are more likely to injure bones at the growth plate. --At age 18 women stop growing and men stop at age 21. --During growth bone deposition is faster than bone re-absorption, during adult they happen at equal rates, during old age re-absorption predominates and blood supply drops result in bone death. This can be influence by sex and race.

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