Chapter 6
Describe the process of intramembranous ossification and state whether flat or long bones are produced by intrameembenous function.
1.Development of the ossifcation center: At the site of where the bone will develop, specific chemical messages cause the cells in the mesenchyme to cluster together and differentiate,first into osteogenic cells and then into osteoblasts. the site of this cluster is called ossification center.Osteoblasts secrete bone extracellular matrix until they are surrounded by it. 2.Calcification:After secretion of extracellular matrix stops,the cells,now called osteocytes,lie in lacunae and extend their narrow cytoplasmic processes into canaliculi, in all directions. Within a few days,calcium and other mineral salts are deposited and the extracellular matrix hardens as it calcifies.The mesenchyme continues to produce osteogenic cells,which form a peripheral layer of osteoblasts. 3.Formation of trabecular:As the bone extracellular forms, it develops into trabeculae that fuse with one another to form spongy bone tissue.Blood vessels grow into spaces between the trabecular and deposit connective tissue cells that diffrentiate into red bone marrow. 4.Development of the periosteum: At the periphery,the mesenchyme condenses and develops into the periosteum.Within the periosteum,osteoblasts produce a thin layer of compact bone tissue.Much of the newly formed bone is remodeled as the bone is transformed into its adult size and shape.
Describe bone remodeling; define Wolff's Law of bone remodeling.
An osteoclasts reattaches its ruffeled border to the bone surface at the end of the endosteum or periodesteum and releases enzymes and several acids. -the enzymes digest collagen fibers and other organic substances,wile the acids dissolve the bone minerals.Working together,several osteoclasts carve out a small tunnel in the old bone. The degraded bone proteins and extracellular matrix minerals,mainly calcium and phospherous,diffuse into nearby blood capillaries. Osteoblasts follow the osteoclasts to rebuild the bone in the area in that area. -The process of remodeling bone tissues involves bone cells-resorbing or depositing minerals into bone tissue. -During resportion,bone cells break down bone tissue and release calcium and other minerals for use by other cells in the body. -Bone cells also rebuild bone tissue by depositing minerals obtained from the bloodstream.
State the functions of articular cartilage, periosteum, medullary cavity, and endosteum, and the yellow bone marrow location in a long bone.
Articular cartialge : a thin layer of hyaline cartilage covering part of the epihyasis where the bione form articulation joint. With another bone.Artiuclar cartilage reduces friction and absorbs shock at freely moveable joints. Periosteum:is a tough connective tissue that surrounds the bone wherever is not covered by articular cartilage (basically not at the joints).The periosteum contains bone forming cells that enable bone to grow in thickness. The periosteum also helps protects the bone,assists in fracture repair,helps nourish osseous tissue,and serves as an attachement point for ligaments and tendons. The medullar cavity: is a hollow,cylindrical space within the diaphysis that contians yellow bone marrow in adults. Endosteum: is a thin membrane that lines the internal bone surface facing the medulalary cavity,contains bone forming cells. The epiphyasis are the proximal and sital ends of the bone. The metaphyasis are the regions between the diaphysis and the epiphyasis . In a growing bone ,each epiphyasal plate, a layer of hyaline cartilage that allows diaphysis of the bone to grow in length.When a bone ceases t gorw in length (18-21), the cartilage of the epihyasis plate is replaced by osseous tissue and the resulting structure is know as epihyasis line.
Explain how bones grow wider (appositional bone growth) and describe the role and locations of osteoblast and osteoclasts.
Bone widening:The ridges of groove fuse, forming a canal containing the blood vessels, in the canal that formed the periosteum is known as endosteum.Osteoblasts screte bone matrix forms concentrical lamalle to fill in canal. Osteoblasts continue building lamelle inward toward the blood vessels to form a new osteon.All along the outer surface of the shaft, the compact bone thickens.As a bone degrows at the periosteum,osteoclasts degrade the inner surface of bone at the endosteum. The end result is is ab one with greater diameter and a larger medullary cavity
Bone widening
Bones grow in thickness (diameter) by the deposition of osseous tissue on the outer surface of the bone. At the bone surface, cells in the periosteum differentiate into osteoblasts. These osteoblasts secrete the extracellular matrix of osseous tissue, adding lamellae to the surface of the bone, and new osteons of compact bone tissue are formed. As the osteoblasts become surrounded by extracellular matrix, they develop into osteocytes. As new osseous tissue is being deposited on the outer surface of the bone, osseous tissue lining the medullary cavity is destroyed by osteoclasts in the endosteum. In this way, the medullary cavity enlarges as the bone increases in thickness.
Describe the process of endochondral ossification, state whether flat or long bones are produced by endochondral ossification, and where hyaline cartilage remains following endochondral ossification.
Development of the cartilage model:At the site of where the bone is specific chemical messages cause the cell in the mesenchyme to crowd together in general shape of the future bone,and then develop into chondroblasts,(immature cells that secrete the extracellular matrix of cartilage_ the chondroblasts secrete the ECM producing hyaline cartilage model,A covering called the perichondrium develops around that hyaline cartilagem odel. 2.Growth of the cartilage model:Once chondroblats beconme deeply buried in the cartilage ECM, they are called chondrocytes,The cartilage model grows by continual cell division accompanied by further secretion of the cartilage ECM,As the cartilage model grows,Chondrocytes in the mid region Hypertophy, and stimulate ECM to calcify.Other chondrycyte die off because not enough nutrient can diffuse quickly enough through the ECM.As these chondro cytes die, the spaces left behind by chondrocytes form into small cavites called lacunae. 3.Development of the primary ossifcation :A nutirent artery penetrates the perichondrium and the calcifying cartilage model through a nutrient foramen. In the mid region of the caritlage model.Stimulating the cells within the perichondrium to differintatie into osteoblasts instead of chondroblasts.The osteoblasts secrete a thin shell of compact of bone tissue deep to the perichondirum.Once osseous tissue forms beneath the perichondrium,the covering is known as the periosteum.Near the middle of the model,periosteal capillaries grow into the disintegrating calcified cartilage,inclduing a growth of primary ossifcation center,a region where osseous tissue will replace cartilage .Osteoblasts then begin to deposit extracellular matrix over the remnants of calcified cartialge.Forming a spongy bone trabaculae.Primary ossifcation spreads toward the ends of the cartialge model. 4.Development of the medullary cavity:As the primary ossfication growts toward the ends of the bone,osteo clasts break down some of the newformed spongy bone trabaculae.This activity leaves a cavity the medullarry or marrow cavity, in the diaphysis . INvading blood vessels fill the medullary cavity with red bone marrow which is progressively replaced by yellow bone marrow.Eventually, most of the wall diaphysis is replaced by compact bone tissue. 5.Development of the secondary ossfication centers:When brances of the epiphyseal artery enter the epiphyases,secondary ossfication center develop.Bone formation in the secondary ossifcation center is similar to that in the primary ossfication centers.One difference, however is that spongy bone tissue remains in the interior of the epiphyassis (no medullary cavity is formed) 6.Formation of articular cartilage and the epipjyseal plate:The hyaline cartilage that covers the epiphyeses becomes the articular cartilage.Pripor to adulthood, hyaline cartilge remains between the diaphysis and epiphyasis which is responsible for the lengthwise of growth of long bones.
Define reduction. Describe the bone healing stages after fracture.
Hematoma formation: Blood vessels in the broken bone tear and hemorrhage, resulting in the formation of clotted blood, or a hematoma, at the site of the break. The severed blood vessels at the broken ends of the bone are sealed by the clotting process. Bone cells deprived of nutrients begin to die. Bone generation: Within days of the fracture, capillaries grow into the hematoma, while phagocytic cells begin to clear away the dead cells. Though fragments of the blood clot may remain, fibroblasts and osteoblasts enter the area and begin to reform bone. Fibroblasts produce collagen fibers that connect the broken bone ends, while osteoblasts start to form spongy bone. The repair tissue between the broken bone ends, the fibrocartilaginous callus, is composed of both hyaline and fibrocartilage. Some bone spicules may also appear at this point. Bony callous formation: The fibrocartilaginous callus is converted into a bony callus of spongy bone. It takes about two months for the broken bone ends to be firmly joined together after the fracture. This is similar to the endochondral formation of bone when cartilage becomes ossified; osteoblasts, osteoclasts, and bone matrix are present. Bone remodeling: The bony callus is then remodelled by osteoclasts and osteoblasts, with excess material on the exterior of the bone and within the medullary cavity being removed. Compact bone is added to create bone tissue that is similar to the original, unbroken bone. This remodeling can take many months; the bone may remain uneven for years.
Distinguish between intramembranous ossification and endochondral ossification with regard to the tissue from which each develops.
Intramembenarouns ossifcations develops directly in the mesenchyme. While as endochondrola develops from a cartilage that is dervieded from mesenchyme.
State the functions of osteoblasts, osteocytes, and osteoclasts.
Osteoblasts: secrete the extracellular matrix, they don't divide, they are bone building cells. They make collagenous fibers and other organic ocmponents to build the extracellular matrix. They start calcfication. Once surrouinded by the extracellular matrix,they get struck and mature to become osteocytes. Osteocytes: they are mature bone cells that maintain the daily metabolism such as the exhcange of nutrients and oxygen.Moreover, they regulate the export of wastes both with blood. They do not undergo cell division. Osteoclasts: they are made by the fusion of 50 monocytes (these are types of whiteblood cells). They are concentrated in the endosteum. On the side of the cell that faces the bone surface, they are folded into a ruffeled border. In that broder they secrete a lyosomal enzymes and a digestive acid to break down the underlying extracellular matrix osseous tissue. This break down of extracellular matrix of osseous tissue is called reabsorption and a normal part of maintnence,repair and normal devleopment of bones Osteogenic cells:are unspecicaliezed stem cell that are located in the endosteum,periosteum, and the canals within the blood vessels.
State the locations of red bone marrow.
Red bone marrow is fond in the spongy bone area, it also near the yellow bone marow
Describe how bones are classified and recognize examples of each type.
Short bones,irregular bones,flat bones, and long bones. Short bones are carpal and calcaneal bones. Flat bones: rib cage,cranial bones,sterum, shoudler blades, Long bones:Femur,Tibilia,fibula,Ulna and radius,humerus,and phalanges Sesamoid bones are in places that receive a lot of physical stress,tension, and friction. Which develop in palms and soles.They proctect tendons from excessive wear and they often change the direction of the pull of a tendon. Which improves the mechanical advantage at joint.
Distinguish between spongy and compact bone tissue with regard to location in the bone types, function, and histology.
Spongy bone tissue is located at the end of the boine behind the ephiseyal plate. Compacgt bone tissue is fund along the emedulalary cavity and in general along diaphysist of the bone. Compact bone tissue is the strong type of ossoeus tissue it is found beneath the periosteum and makes uo the bulk of diaphysis of long bones. Compact one tissue provies proteciton,support and resitst the stresses produced by wieght and movement. Compact bone tissue is composed of osteons,each osteon contains rings of the calcified extracellular matrix much like the growth rings of a sliced tree trunk that are arranged around a central canal or haversian canal.Osteons generally form a series of cylinder that tend to run parrlelel axis of the bone. Between lamellae are small spaces called lacunae that contian osteocytes. Compact bone tissue is arranged in a concentric circles around a central canal;spongy bone tissue is arranged in a irregular in trabeculae. Areas between osteons contain intersital lamalle which also have lacunae with osteocytes and canalculi.Interstillar lamellae are fragments of older osteons that have been partially destoryed during bone rebuilding or regrowth. Circumfentail lamellae encile the bone just beneath peristoeum or encirle the medullar cavity Blood vessels ,lymphatic vessels,and nerves of the perisoteum penetrate compact bone tissue through transverse perforating canals.The vessels and nerve of the perforating canals connect those with those of the medullar cavity,periosteum, and central canals. Now spongy bone does not contain osteons.Despite what the name seems to imply,the term "spongy" does not refer to the texture of bone,only its appearance.Spongy bone consists of Lamalle arranged in a irregular lattice of thin columns.Between the trabculae are visible to the unaided eye. They contain red bone marrow, and yellow bone marrow.These spaces are filled with red bone marrow, that produces red blood cells, and is alos filled with yellow bone marrow, which is abone that stgores adipocytes. Spong bone is always located in the interior of the bone where it Is protected by a covering of compact one tissue. It makes up the most of interior of short,flat,irregular,and seasmoid bones. In long bones,spongy bone tissue is always located forms the core of epiphyasis beneath a paper thin layer of compact bone and forms a narrow rim bordering the medullary cavity of the diaphysis The trabculae of spongy bone tissue are precisely oriented along liens of stress,a characteristis of boen that helps bones resist stresses and transfer force without breaking.Spongy bone tends to be located where bones are not stressed or where stress is applied from all directions. Spongy bone tissue is light,which reduces overall weight of the bone and allows the bone to move more readily when pulled by a skeletal muscle. The trabaculae of spongy bone tissue support and protect red bone marrow.Spongy bone tissue are in hip bones,vertebra,ribs,breat bones(sternum), and thneds of long bones
Describe the extracellular matrix of osseous tissue including the definition and function of hydroxyapatites.
The extracellular matrix of osseous tissue includes 15% water,30% collagenous fibers, and 55% percent crystallized mineral salts. In the ECM their it contains calcium and phosphate. It them combines with hydroxide to create a crystal form of hydroxapetite. It then is dpeoisted in the collageouns fibers of the Extracellular matrix.. It then beigins toh arden causing the ossoeus tissue to harden. This process is called calcifcation and is initated by osteoblasts.
Describe the functions of the skeletal system, red bone marrow, and yellow bone marrow.
The skeletal system function consist of support,protection,movement, producing blood, suppling minerals into the blood stream, and storing trigylcerides.
Explain how bones grow longer at the epiphyseal plate (interstitial bone growth) and describe the fate of the epiphyseal plate.
one of resting cartilage:This layer meets the epiphyesis and consist of small,scattered chondrocytes.The cells do not function in bone growth.Instead,they anchor the epiphyseal plate to the epiphyesis of bone. Zone of proliferating cartilage:Slightly larger chondrocytes in this zone are arranged like stacks of coin.These chondorcytes secrete cartilage extracellular matrix and divide to replace chondorycytes that die at the dipahyseal side of the epiyseal plate. Zone of hypertrophic cartilage: This layer consist of large,maturing chondrocytes arragned in columns. Zone of calcified cartilage:The final zone of the epiphyseal plate is only a few cells thick and consist mostly of dead chondrocytes because the extracellular matrix around them has calicified.Osteoclasts dissolve the calcified cartilage , and osteoblasts and capilaries from the diaphysis invade the area.Osteoblasts lay down bone extracellular matrix,replacing the calcifed cartilage by endochondral ossification. As a result, the zone calcified cartilage become "new diaphysis" that is firmly cemented to rest of the diaphysis of bone.
Describe bone fractures in terms of open (compound) or closed. Distinguish between various fracture types: Compression, Spiral, Comminuted, Epiphyseal, and Greenstick
ransverse fracture. A transverse fracture occurs when a bone breaks at a 90-degree angle to the long axis of the bone. This typically occurs when a blow transmits a large amount of force directly perpendicular to the bone. Transverse fractures require an orthopedic trauma surgeon Oblique fracture. An oblique fracture is characterized by a break that is curved or at an angle to the bone. A sharp blow that comes from an angle (i.e., above or below) may cause oblique fractures. Comminuted fracture. A comminuted fracture can be very serious. In this type of fracture, a bone actually breaks into several fragments. Small bones, such as the bones in the hands or feet, are highly susceptible to comminuted fracture. Comminuted fractures often occur following a car accident or another serious event. Greenstick fracture. A Greenstick fracture is most often observed in children, whose bones have yet to fully develop. A child's soft bones may not break when dealt a significant force, causing the bone to bend. Sometimes, the outer side of the bend breaks while the rest of the bone remains unbroken. Stress fracture. Athletes sometimes complain of stress fractures, which can seriously impede athletic performance. A stress fracture is a hairline fracture in the bone that may lead to significant discomfort. Pathologic fracture. When a disease weakens bones so much that they fracture easily, orthopedic doctors sometimes refer to the break as a pathologic fracture. Osteoporosis is a leading cause of pathologic fracture. People with osteoporosis have bones that have become brittle or weak, causing them to break easier than healthy bones.
Define osteoporosis, briefly describe osteoporotic bones, state common causes of osteoporosis, the gender/ethnic/physical characteristics that predisposes one to the disease and how the onset of osteoporosis can be prevented or delayed.
which literally means porous bone, is a disease in which the density and quality of bone are reduced. As bones become more porous and fragile, the risk of fracture is greatly increased. The loss of bone occurs silently and progressively. Often there are no symptoms until the first fracture occurs.
