Ch 7 skeletal system module

Tendon:

A fibrous cord or band of variable which connects the fleshy (contractile) part of muscle with its bony attachment or other structure.

classification of bone fracture slide 56

1. avuision-complete severing of body part ( typically a toe or fingure) 2. colles- fracture of distal end of the lateral forearm bone( radius); produces as dinner fork deformity 3. comminuted- bone is splintered into several small pieces between the main parts 4. complete- bone is broken into two or more pieces 5. compund(open)- broken ends of the bone protrude through the skin 6. compression- bone is squashed ( may occur in a vertebra during a fall) 7. depressed- broken part of the bone forms a concavity ( as in skull fracture)

Osteoblast:

A bone-forming cell that is derived from mesenchymal osteoprognitor cells and forms an osseous matrix in which it becomes enclosed as an osteocyte.

Epiphysis

A part of a long bone developed from a secondary center of ossification, distinct from that of the shaft.

Extension:

A pulling or dragging force exerted on a limb in a distal direction.

Bone Matrix: Its Formation and Resorption

Bone Formation -Bone formation begins with secretion of osteoid. It then proceeds with calcification, when hydroxyapatite crystals are deposited. The process requires vitamin D which enhances calcium absorption from gastrointestinal tract, and vitamin C for collagen formation and calcium and phosphate for calcification. Bone Resorption -Bone matrix is destroyed by substances released from osteoclasts. Proteolytic enzymes released from lysosomes within osteoclasts chemically digest organic matrix components. Calcium and phosphate are dissolved by hydrochloric acid. This may occur when blood calcium levels are low.

Bone Marrow slide 14

Bone marrow is a soft connective tissue. It includes red bone marrow and yellow bone marrow. -Red bone marrow (also known as myeloid tissue) is hemopoietic (blood cell forming). It contains reticular connective tissue, immature blood cells, and fat. In children it is located in the spongy bone and in the medullary cavity of long bones. In adults, it is located in portions of axial skeleton (proximal epiphyses of humerus and femur, skull, vertebrae, ribs, sternum, ossa coxae). -Yellow bone marrow is a product of red bone marrow degeneration. This fatty substance may convert back to red bone marrow during severe anemia and produce additional red blood cells.

Supine:

Denoting the body when lying face upward.

Classification By Shape long, short, flat, irregular bones picture of skeleton slide 6

Let's first look at the way that we classify bones by shape. On the basis of shape, we classify bones into four groups: -Long bones are longer than they are wide. -Short bones are cube shaped and contain large amounts of spongy bone. You find these in the wrists and ankles. -Flat bones are thin and a bit curved . They consist of a layer of spongy bone covered on both sides with a layer of compact bone. The sternum or breast bone and most skull bones are in this group. -Irregular is a category for all bones which do fall into the other groups.

Flexion

Movement decreasing the angle between articulating bones.

Abduction:

Movement of a body part away from the median plane of the body.

Microscopic Structure of Compact Bone slide 24-26

The Haversian system, or osteon is the structural unit of compact bone. You might think of the osteon as a long cylinder which runs longitudinally in the bone. The osteon is made up of lamellae or concentric tubes of matrix containing collagen fibers and small crystals of bone salts. In the middle of the osteon is the Haversian or central canal which is a central channel containing blood vessels and nerves. Volkmann's canals are channels lying at right angles to the central canal. They connect the blood and nerve supply of the periosteum to that of the Haversian canal. At the junctions of the lamellae are cavities called lacunae. These lacunae contain osteocytes or mature bone cells. Canaliculi are thin canals connecting the lacunae to each other and the central canal. These tiny passages allow for exchange of nutrients and waste between the osteocytes and the blood vessels found in the central canal.

Articular cartilage

The cartilage covering the articular surfaces of the bones participating in a synovial joint.

Diaphysis:

The part of a long bone between the epiphyses.

Hematopoiesis:

The process of formation and development of the various types of blood cells and other formed elements.

Periosteum:

The thick, fibrous membrane covering the entire surface of a bone except its articular cartilage and the areas where it attaches to tendons and ligaments.

Rotation:

The turning or movement of a body around its axis.

Osteocyte

A cell of osseous tissue that occupies a lacuna and has cytoplasmic processes that extend into canaliculi and make contact by means of gap junctions with the processes of other osteocytes.

Suture:

A form of fibrous joint in which two bones formed in membrane are united by a fibrous membrane continuous with the periosteum.

Articulation

A joining or connecting together loosely to allow movement.

Synovial joint:

A joint in which the opposing bony surfaces are covered with a layer of hyaline cartilage or fibrocartilage within a joint cavity that contains synovial fluid.

Osteoclast:

A large multinucleated cell functioning in the absorption and removal of osseous tissue.

Bone Fracture Repair slide 58

A simple fracture requires about 2 to 3 months to heal while a compound fracture may take longer. Healing generally becomes slower with age Some breaks require surgical intervention to heal correctly. Four steps are involved in of bone fracture repair: 1. A fracture hematoma forms from clotted blood 2. A fibrocartilaginous callus forms Regenerated blood capillaries infiltrate the hematoma. The fracture hematoma is reorganized into a connective tissue procallus. Fibroblasts produce collagen fibers. Chondroblasts form dense regular connective tissue. Eventually the procallus becomes a fibrocartilaginous (soft) callus. 3. Hard (bony) callus forms. The osteoblasts adjacent to callus produce trabeculae The callus is replaced by this bone forming a hard (bony) callus which continues to grow and thicken. 4. The bone is remodeled. In this final phase of fracture repair, osteoclasts remove excess bony material. Compact bone replaces primary bone usually leaving a slight thickening of bone. See next slide.

Function of Bones picture of cartilage slide 3

Besides forming a framework for our body (without it we might look like amoebas!), bone carries out a number of important duties. Our skeleton supports us as we said. In other words, it forms the framework that supports the body and cradles soft organs. It also protects the vital organs of our body such as the brain and spinal cord. As we said earlier, bone is necessary for skeletal movement. It provides a system for muscles to move against producing movement. Bone provides a reservoir for mineral storage, especially calcium and phosphorus. It stores a readily mobilized of calcium to aid in maintaining calcium levels in blood and other body fluids. Hematopoiesis or blood cell formation occurs within the marrow cavities of certain bones. -Bone is dynamic. It is constantly being renewed and reconstructed and will respond to external mechanical stimuli such as weight bearing exercise.

Bone Growth After Birth slide 41-44

Bone growth after birth occurs by two processes: (1.) interstitial growth from the epiphyseal plate and (2.) appositional growth. Growth in length of long bones involves the side of the epiphyseal plate facing the epiphysis. This area of the shaft of the bone organizes into a pattern that allows fast, efficient growth. Cells of the epiphyseal plate proximal to the resting cartilage (zone 1) form several different zones: growth or proliferation, hypertrophic, calcification, and ossification. The growth zone contains cartilage cells undergoing mitosis, pushing the epiphysis away from the diaphysis. In the hypertrophic and calcification zones, older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate. In the ossification zone, new bone formation occurs. Growth in length happens as cartilage continually grows in the epiphyseal plate and is replaced by bone. As adolescence ends, cartilage plates divide less often and are replaced by bone at around 18 years of age in females and 21 years in males. -Bone growth after birth occurs by two processes: (1.) interstitial growth from the epiphyseal plate and (2.) appositional growth. Growth in length of long bones involves the side of the epiphyseal plate facing the epiphysis. This area of the shaft of the bone organizes into a pattern that allows fast, efficient growth. Cells of the epiphyseal plate proximal to the resting cartilage (zone 1) form several different zones: growth or proliferation, hypertrophic, calcification, and ossification. The growth zone contains cartilage cells undergoing mitosis, pushing the epiphysis away from the diaphysis. In the hypertrophic and calcification zones, older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate. In the ossification zone, new bone formation occurs. Growth in length happens as cartilage continually grows in the epiphyseal plate and is replaced by bone. As adolescence ends, cartilage plates divide less often and are replaced by bone at around 18 years of age in females and 21 years in males. -Bone growth after birth occurs by two processes: (1.) interstitial growth from the epiphyseal plate and (2.) appositional growth. Growth in length of long bones involves the side of the epiphyseal plate facing the epiphysis. This area of the shaft of the bone organizes into a pattern that allows fast, efficient growth. Cells of the epiphyseal plate proximal to the resting cartilage (zone 1) form several different zones: growth or proliferation, hypertrophic, calcification, and ossification. The growth zone contains cartilage cells undergoing mitosis, pushing the epiphysis away from the diaphysis. In the hypertrophic and calcification zones, older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate. In the ossification zone, new bone formation occurs. Growth in length happens as cartilage continually grows in the epiphyseal plate and is replaced by bone. As adolescence ends, cartilage plates divide less often and are replaced by bone at around 18 years of age in females and 21 years in males. Bone growth after birth occurs by two processes: (1.) interstitial growth from the epiphyseal plate and (2.) appositional growth. Growth in length of long bones involves the side of the epiphyseal plate facing the epiphysis. This area of the shaft of the bone organizes into a pattern that allows fast, efficient growth. Cells of the epiphyseal plate proximal to the resting cartilage (zone 1) form several different zones: growth or proliferation, hypertrophic, calcification, and ossification. The growth zone contains cartilage cells undergoing mitosis, pushing the epiphysis away from the diaphysis. In the hypertrophic and calcification zones, older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate. In the ossification zone, new bone formation occurs. Growth in length happens as cartilage continually grows in the epiphyseal plate and is replaced by bone. As adolescence ends, cartilage plates divide less often and are replaced by bone at around 18 years of age in females and 21 years in males. Appositional Growth Though bone growth in length ceases, bones can still increase in thickness by appositional growth. Basically osteoblasts form new bone on the outside of the bone (in periosteum). These layers are termed external circumferential lamellae. As they increase in number, the structure increases in diameter. Meanwhile. osteoclasts destroy bone next to the endosteum. This process maintains the shape of the bone.

Microscopic Anatomy of Bone Tissue Cells of Bone slide 16- 19

Bone is a connective tissue and thus is composed of cells, a matrix and intracellular fibers. Four types of cells are found in bone connective tissue: 1. Osteoprogenitor cells are stem cells derived from mesenchyme. They produce cells that mature to become osteoblasts. Osteoprogenitor cells are located in periosteum and endosteum. 2. Osteoblasts are often positioned side by side on bone surfaces. They synthesize and secrete osteoid which is the initial semisolid form of bone matrix. Osteoid later calcifies trapping the osteoblasts within the matrix they produced! 3. Osteocytes are mature bone cells derived from osteoblasts. They have lost their bone forming ability and function to maintain bone matrix. 4. Osteoclasts are large, multinuclear, phagocytic cells which are derived from fused bone marrow cells. They have a ruffled border to increase surface area exposed to bone and are often located within or adjacent to a depression or pit on bone surface termed a resorption lacuna (Lacuna of Howship). Osteoclasts are involved in breaking down bone.

Bone Fracture and Repair

Breaks in bone are termed fractures. Such breaks occur as the result of unusual stress or impact. We see an increased incidence with age due to normal thinning and weakening of bone. Types of fractures include 1.stress fractures -which are thin breaks caused by increased physical activity. The bone experiences repetitive loads (e.g., runners). 2. Pathologic fractures- in which bone is weakened by disease. 3.Simple fractures- in which the broken bone does not penetrate the skin. 4. Compound fractures- in which one or both ends of the bone pierce the overlying skin.

Spongy Bone Microscopic Anatomy slide 28-29

Components of spongy bone are trabeculae and parallel lamellae. Trabeculae are an open lattice of narrow rods and plates of bones with bone marrow filling open spaces. This forms an open meshwork of crisscrossing bars providing great resistance to stress. -Parallel lamellae which are composed of bone matrix. In these we see osteocytes resting in lacunae with canaliculi connecting them. -Spongy bone contains trabeculae which align along lines of stress. No osteons are present but it contains irregularly arranged lamellae, osteocytes, and canaliculi. Capillaries in the endosteum supply nutrients

Homeostatic Imbalances picture of normal bone and osteoporectic slide 52-54

Diseases of the adult skeleton are usually due to imbalances between bone deposition and bone resorption. We will now examine some of these diseases. -Osteopenia occurs slightly in all people with age and begins as early as ages 35-40. Osteoblast activity is declining; osteoclast activity remains at previous levels. Vertebrae, jaw bones, and epiphyses lose a large amount of mass. Women lose more of their skeletal mass every decade than men. -In osteomalacia, bones are inadequately mineralized causing softened, weakened bones. The main symptom is pain when weight is put on the affected bone. This condition is caused usually caused by insufficient calcium in the diet, or by vitamin D deficiency. Rickets is the analogous disease in children. Bones of children are inadequately mineralized causing softened, weakened bones. Bowed legs and deformities of the pelvis, skull, and rib cage are common. Rickets is caused by insufficient calcium in the diet or by vitamin D deficiency -Osteoporosis involves a group of diseases in which bone reabsorption outpaces bone deposit. The spongy bone of the spine is most vulnerable. This condition occurs most often in postmenopausal women. Bones become so fragile that sneezing or stepping off a curb can cause fractures!! -Paget's disease is characterized by excessive bone formation and breakdown forming "Pagetic" bone with an excessively high ratio of woven to compact bone. The presence of Pagetic bone, along with reduced mineralization, causes spotty weakening of bone. Osteoclast activity slows, but osteoblast activity continues to work resulting in abnormal bone remodeling. The disease is usually localized in the spine, pelvis, femur, and skull. The causes are unknown but could possibly be viral.

Endochondral Ossification slide 38-39

Endochondral ossification begins with a hyaline cartilage model. It produces most bones of the skeleton, including the bones of the upper and lower limbs, the pelvis, the vertebrae and the ends of the clavicle. Let's study the six steps of long bone development in a limb. 1. The fetal hyaline cartilage model develops. Chondroblasts begin to secrete cartilage matrix during eighth to twelfth week of development. 2. Cartilage calcifies, and a periosteal bone collar forms around diaphysis. Chondrocytes in the cartilage model produce holes in the matrix. The matrix begins to calcify, and chondrocytes die producing a calcified cartilage shaft with large holes. Blood vessels grow toward cartilage. Osteoblasts develop and begin secreting osteoid forming a layer of osteoid around calcified cartilage shaft. This layer is termed the periosteal bone collar. 3. A primary ossification center forms in the diaphysis. The periosteal bud (a growth of capillaries and osteoblasts) extends from periosteum into cartilage shaft. Osteoblasts produce osteoid on a calcified cartilage template. This region is termed the primary ossification center and is the first major center of bone formation. Most of these centers are formed by twelfth week of development. Bone development extends in both directions toward the epiphyses. Bone connective tissue displaces calcified, degenerating cartilage. 4. Secondary ossification centers form in the epiphyses. Hyaline cartilage in the epiphysis calcifies and degenerates. Blood vessels and osteoprogenitor cells enter. Secondary ossification center formation occurs as bone displaces cartilage. Osteoclasts resorb some bone matrix creating a hollow medullary cavity. 5. Bone replaces cartilage, except in articular cartilage and epiphyseal plates. 6. Epiphyseal plates ossify and form epiphyseal lines. Lengthwise bone growth continues into puberty. Growth continues until epiphyseal plate is converted to the epiphyseal line indicating that the bone has reached adult length. This occurs between the ages of 10 and 25.

Hormonal Regulation of Bone Growth gigantism slide 46 dwarfism slide 47

Hormones are molecules released from one cell into the blood. They travel through the body to affect other cells. Some altering rates of chondrocyte, osteoblast, and osteoclast activity affecting bone composition and growth patterns. -During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone. Thyroid hormones work with growth hormone to keep the skeleton in proper proportion as it grows. During puberty, testosterone and estrogens initially promote the adolescent growth spurt. This causes masculinization and feminization of specific parts of the skeleton and later epiphyseal plate closure, ending longitudinal bone growth. Abnormally low or high production of growth hormones may lead to homeostatic imbalances. Gigantism results from hypersecretion of growth during childhood. Dwarfism may result from a deficiency of growth hormone. (See next slides) -High amounts of glucocorticoids may increase bone loss and can impair growth of the epiphyseal plate in children. Serotonin plays a role in rate and regulation of normal bone remodeling. If levels are too high, osteoprogenitor cells are prevented from becoming osteoblasts.

Microscopic Anatomy of Hyaline Cartilage

Hyaline cartilage consists of a population of cells scattered through a matrix of protein fibers. These cells are embedded in a gel-like ground substance that contains proteoglycans but not calcium. Hyaline cartilage is resilient and flexible. It contains a high percentage of water and is highly compressible and a good shock absorber. This cartilage is avascular and contains no nerves. -Cells found in hyaline cartilage include chondroblasts which produce cartilage matrix. These become encased within the matrix and occupy small spaces called lacunae. As they are encased, they develop into chondrocytes which are mature cells that maintain the matrix. Hyaline cartilage is surrounded by the perichondrium which is dense irregular connective tissue which covers cartilage and helps maintain its shape. Hyaline cartilage of trachea

Hyaline Cartilage

Hyaline cartilage is the most abundant skeletal cartilage. It provides support, flexibility, and resilience. We find it in these cartilages: 1.Articular - covering the ends of long bones 2.Costal - connecting the ribs to the sternum 3.Respiratory - making up the larynx and reinforces air passages 4.Nasal - supporting the nose

Structure of Long Bones picture slide 8-12

Long bones such as the femur or humerus consist of diaphysis and an epiphysis. The diaphysis or shaft is basically a thick walled tube of compact bone. The middle of the tube which is filled with yellow bone marrow is called a medullary cavity. The expanded ends of long bones are referred to as the epiphyses. The exterior of the epiphyses is compact bone and the interior is spongy bone. At the ends of the epiphyses the joint surfaces are covered with articular (hyaline) cartilage. An epiphyseal line which marks the point where growth occurred in the bone separates the diaphysis from the epiphysis. -The outer surface or periosteum of the bone is double-layered protective membrane. The outer fibrous layer is dense regular connective tissue. The inner osteogenic layer is composed of the bone cells osteoblasts which deposit matrix and osteoclasts which dissolve matrix. The periosteum is richly supplied with nerve fibers, blood, and lymphatic vessels and is secured to underlying bone by Sharpey's fibers. A less developed endosteum lines the marrow cavity. This consists of just one layer and contains osteoclasts and osteoblasts. -Bone is highly vascularized, especially spongy bone. Blood vessels enter from the periosteum and pass into the bone through nutrient foramina which are small openings or holes in the bone. Arteries, veins, and nerves enter an exit here.

Adduction:

Movement of a body part toward the median plane of the body.

Circumduction:

Movement of a part or an extremity in a circular direction.

Composition of the Bone Matrix

Organic components include osteoid which is produced by osteoblasts. This material makes up about 1/3 of the matrix and contains proteoglycans, glycoproteins, and collagen fibers. All of these substances are secreted by osteoblasts. This organic material gives the bone flexibility and tensile strength. During bone growth and development, the amount of organic material stays relatively constant while the amount of water decreases. The amount of inorganic material increases, however. Inorganics may make up 50% to 65% of the dry weight of bone but may drop to 35% if the bone is poorly calcified. -The inorganic component of the matrix contains submicroscopic crystals of a material called hydroxyapatite (Ca10(PO4)6(OH)2 and significant amounts of citrate ion and carbonate ion. The crystals of hydroxyapatite form slender needles located alongside the collagen fibers but are surrounded by ground substance. The surface of the crystal is surrounded by a layer of water called an hydration shell. The hydration shell allow for rapid exchange of ions between the crystals and body fluids. Bone also serves as a storage depot for magnesium and sodium. Both of these substances are normal constituents of body fluid and are responsible for hardness and resistance to compression of bone. The correct proportion of organic and inorganic substances allows optimal functioning of bone. Loss of protein results in brittle bones and insufficient calcium results in soft bones

Ossification slide 36

Ossification also known as osteogenesis is the formation and development of bone. It begins in the embryo and continues through childhood and adolescence. It begins by the eighth through twelfth weeks of embryonic development. It occurs either through intramenbrous ossification or endochondral ossification. Let's examine intramembranous ossification first. -Intramembranous ossification also known as dermal ossification produces the flat bones of the skull, some of the facial bones, the mandible, and the central part of the clavicle. It begins when the mesenchyme becomes thickened with capillaries. Let's look at the steps of intramembranous ossification. 1. Ossification centers form within thickened regions of mesenchyme. Some cells becoming osteoprogenitor cells and some cells becoming osteoblasts secreting osteoid. 2. Osteoid undergoes calcification. Calcium salts are deposited onto osteoid and crystallize. The trapped cells become osteocytes. 3. Woven bone and the surrounding periosteum form. At first, the bone is immature and poorly organized. We call this woven bone (primary bone). Mesenchyme surrounding woven bone begins to form the periosteum. 4)Lamellar bone (secondary bone) replaces woven bone. Compact and spongy bone are formed from the trabeculae. This process forms the typical structure of a flat cranial bone (two external layers of compact bone with a layer of spongy bone in between).

Regulating Blood Calcium Levels hormone mechanism slide 49 -50

Regulating calcium concentration in blood is essential since it is required for many body processes such a muscle contraction and blood clotting. Two primary hormones regulate blood calcium: calcitriol and parathyroid hormone. Calcitriol stimulates absorption of calcium ions from the small intestine into the blood. Parathyroid hormone (PTH) is secreted and released by parathyroid glands in response to reduced blood calcium levels. Calcitriol is formed more readily in the presence of PTH. -Hormonal Mechanism: -Rising blood Ca2+ levels trigger the thyroid to release calcitonin. -Calcitonin stimulates calcium salt deposit in bone. -Falling blood Ca2+ levels signal the parathyroid glands to release PTH. -PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood. See next 2slides

Bone Remodeling

The continual process of bone deposition and resorption is termed bone remodeling. This continues throughout adulthood. Remodeling occurs at the periosteal and endosteal surfaces of a bone. It is dependent on the coordinated activities of osteoblasts, osteocytes, and osteoclasts. Remodeling occurs at different rates. The distal part of femur is replaced every 4 to 6 months. The diaphysis of femur is not completely replaced over a lifetime. Twenty per cent of the skeleton is replaced yearly. Two control loops regulate bone remodeling: Hormonal mechanisms that maintain calcium homeostasis in the blood and Mechanical and gravitational forces acting on the skeleton. -Mechanical stress occurs in weight-bearing movement and exercise. This is required for normal bone remodeling. This stress is detected by osteocytes and communicated to osteoblasts. This results in an increase in synthesis of osteoid causing an increase in bone strength.

Bone Structure and Function

The skeleton is more than a supporting framework. It is composed of dynamic living tissues and interacts with all other organ systems. The skeleton continually changes in response to the needs of the body. Components of the skeletal system include bones , cartilage, ligaments and other connective tissues. -Bones form a rigid framework and perform other functions. Types of bone include compact bone which is also called dense or cortical bone. This relatively dense bone tissue appears white, smooth, and solid and makes up 80% of bone mass. The second types is spongy bone which is also called cancellous or trabecular bone. This porous bone is located internal to compact bone and makes up about 20% of bone mass. -Cartilage is a semi-rigid connective tissue which is more flexible than bone. Types of cartilage include: 1. Hyaline cartilage which attaches ribs to the sternum, covers the ends of some bones. This cartilage is found within growth plates and is often serves a model for bone formation. 2. Fibrocartilage is a weight bearing cartilage that forms intervertebral discs, the pubic symphysis and the cartilage pads of knees. -Other skeletal structures include ligaments which anchor bone to bone and tendons which anchor muscle to bone.

Matrix components

bone matrix: organic-strength and resilience inorganic- responsible for hardness

comparison of bone tissue and hyaline cartilage connective tissue slide 32-34

characteristics---> bone connective tissues--> hyaline cartilage connective tissue 1.cells that form matrix--> osteoblasts---> chondroblast 2. mature cells---> osteocytes--->chondrocytes 3. calcium present in matrix---> yes ---> no 4. blood supply in mature tissue---> extensive--> avascular the process of cartilage growth begins during embryologic development. Growth in length through interstitial growth occurs within the internal regions of cartilage.

Prone:

the body when lying face downward.