A&P CH 6 Cartilage and Bone

Process

Any marked bone prominence

compact vs spongy bone

Compact - solid and relatively dense, forms solid external walls of bone Spongy - porous, forms open lattice of narrow plates of bone called trabeculae In flat bones, spongy bone in sandwiched between two layers of compact bone

osteomalacia

Rickets; disease marked by softening of the bone caused by calcium and vitamin D deficiency

Concentric lamellae

Rings of bone connective tissue that surround the central canal and form the bulk of the osteon. The amount of concentric lamellae in an osteon vary contain Collagen fibers oriented in one direction *Adjacent lamellae contain collagen fibers in perpendicular directions, leading to strength and resilience of bone

Foramen

Rounded passageway through a bone

Intramembranous ossification (dermal ossification)

"bone growth within a membrane" The thin layer of mesenchyme in these areas is sometimes referred to as a membrane, because the mesenchyme that is the source of these bones is in the area of the future dermis Produces the flat bones of the skull, some facial bones like zygomatic bone and maxilla, mandible, and central part of clavicle Begins when mesenchyme becomes thickened and condensed with a dense supply of capillaries, and continues in these steps: 1. Ossification centers form within thickened regions of mesenchyme, beginning in eighth week of development -cells in thick mesenchyme divide, and the committed ones differentiate into osteoprogenitor cells, then osteoblasts, which make osteoid. Multiple ossification centers develop as osteoblast numbers increase. 2. Osteoid undergoes calcification -calcium salts are deposited onto the osteoid and then crystallize. Both organic matrix formation and calcificaiton occur simultaneously at several sites in mesenchyme. Calcification traps osteoblasts in lacunae, and they become osteocytes 3. Woven bone and its surrounding periosteum form. Initially the newly formed bone connective tissue is immature and not well organized. Eventually woven bone is replaced by lamellar bone. Blood vessels begin branching through developed regions. The mesenchyme that surrounds woven bone thickens and organizes into periosteum. 4. Lamellar bone replaces woven bone, as compact bone and spongy bone form. Lamellar bone replaces trabeculae of spongy bone. On internal and external surfaces, the spaces between trabeculae are filled and the bone becomes compact bone. Internally, the trabeculae are modified and produce spongy bone, resulting in structure typical of flatbones, spongy layer sandwiched between compact bone

Chondroblasts

"chondros" - grit/gristle "blastos" - germ Cells that produce the matrix of cartilage.

Skeleton

"skeletos" - dried composed of dynamic living tissues Includes: Bones, cartilage, ligaments, and other connective tissue that stabilizes or connects bones

Zone of resting cartilage

- Layer closest to end of epiphysis - Resting cells -anchors epiphyseal plate to epiphysis - farthest from diaphysis -composed of small chondrocytes distributed throughout cartilage matrix and resembles mature hyaline cartilage

Clinical View 6.5 - Bone Scans

-Tests that can detect bone pathologies sooner than X-rays, and they use much less radiation -patients are injected with radioactive tracer absorbed by bone, then scanned with a camera -dark spots mean high metabolism, light spots mean low metabolism -finds fractures, decalcification, osteomyelitis, degen bone disease, cancer, osteitis deformans

Bone Blood Supply and Innervation

-bone is highly vascularized, especially in regions containing red bone marrow, blood vessels enter bones from periosteum -typical long bone has four major sets of blood vessels -Nerves that supply bones accompany blood vessels through the nutrient foramen and innervate the bone as well as the periosteum, endosteum, and marrow cavity. These are mainly sensory nerves that signal injuries to the skeleton

Clinical View 6.6 - Osteoporosis

-both bone matrix and Ca are lost -prone to fractures -weakened bones -postmenopausal women, elderly age, smoking, Caucasian women

Spongey Bone microanatomy

-contains no osteons -contain trabeculae composed of parallel lamellae -between adjacent lamellae are osteocytes in lacunae -nutrients reach osteocytes via diffusion through canaliculi that open onto the surfaces of the trabeculae

Clinical View 6.4 - Rickets

-disease caused by vitamin D deficiency in childhood -characterized by overproduction and deficient calcification of osteoid -results in bones that are poorly calcified and too flexible -bowlegs -hypocalcemia

Clinical View 6.1 - Osteitis Deformans

-disease that results from imbalance of osteoblast and osteoclast function -characterized by excessive bone resorption followed by excessive bone deposition -osteoclasts are 5 times larger than normal and contain 20+ nuclei (3-5 is normal) -in response to excessive bone resorption, osteoblasts deposit additional bone that is poorly formed and structurally unstable

Bone growth and Sex hormones (estrogen and testosterone)

-dramatically increase bone growth at puberty -increased osteoblast formation of bone within epiph plate

Bones and Mechanical Stress/Exercise

-increases strength of bone by increasing amound of mineral salts deposited and collagen fibers synthesized -also stimulates calcitonin production -most influential forces are repeated muscle contraction and gravitational forces

Bone Remodeling

-ongoing replacement of old bone tissue by new bone tissue -helps maintain Ca and P levels in body fluids -can be stimulated by stress on bone -occurs at both periosteal and endosteal surfaces -either modifies the architecture or the amount of minerals deposited -Bone formation exceeds resorption at a young age, and resorption exceeds formation in older adults -20% of human skeleton is replaced yearly

Growth hormone (somatotropin)

-secreted by the anterior lobe of the pituitary gland -stimulates growth of bones and soft tissues by: stimulating liver to form insulin-like growth factor (IGF), aka somatomedin. Both growth hormone and IGF stimulate growth of cartilage in epiph plate

parathyroid hormone

-stimulates osteoclasts -increases blood calcium via resorption from bone -influences production of calcitriol in kidneys, together increase the release of calcium from bone

Example of endochondral ossification: Long bone development

1. Fetal hyaline cartilage develops -8-12 weeks chondroblasts secrete cartilage matrix and hyaline model forms. Chondrocytes trapped in lacunae, perichondrium surrounds cartilage 2. Cartilage calcifies, and a periosteal bone collar forms - Within center of cartilage model (future diaphysis), chondrocytes start to hypertrophy (enlarge) and resorb (eat away) some of surrounding cartilage matrix, producing larger holes in matrix. These holes allow calcification to occur. Chondrocytes die because nutrients cannot diffuse to them. Overtime, blood vessels grow into cartilage and penetrate perichondrium. Stem cells become osteoblasts, supporting CT becomes really vascularized, and perichondrium becomes periosteum. Osteoblasts within internal layer of periosteum secrete osteoid around calcified cartilage shaft, forming periosteal bone collar around it. 3. Primary ossification center forms in the diaphysis. Periosteal buds invade spaces left by chondrocytes. Remains of calcified cartilage serve as template on which osteoblasts produce osteoid. This region is called the primary ossification center because it is the first major center of bone formation. Most primary ossification centers are formed by 12th week of fetal dev 4. Secondary ossification centers form in epiphyses. Same process as previous step, begins around time of birth. Not all 2ndary ossification centers form at birth, some later in childhood. As 2ndary centers form, osteoclasts resorb some bone matrix in diaphysis, creating medullary cavity. 5. Bone replaces cartilage EXCEPT for articular cartilage and epiphyseal plates. -By late stages of bone development, almost all of hyaline cartilage is replaced by bone. Hyaline cartilage is only found as articular cartilage on articular surfaces of epiphyses, also known as epiphyseal plate, which is sandwiched between diaphyses and epiphyses. 6. Lengthwise growth continues until epiphyseal plates ossify and form epiphyseal lines, indicating bone has reached adult length. -Bone growth continues through puberty until epiphyseal line formation

Epiphyseal Plate Morphology

1. Zone of resting cartilage 2. Zone of proliferating cartilage 3. Zone of hypertrophic cartilage 4. Zone of calcified cartilage 5. Zone of ossification

Compostion of bone matrix

1/3 of bone mass is composed of organic substance called osteoid. Includes cells, collagen fibers, and ground substance

Vitamin Effects on Bones

A - activates osteoblasts C - required for normal synthesis of collagen D - stimulates absorption and transport of Ca and P into the blood. Necessary for calcification of bone. works with calcitonin, which stimulates deposition into bone

Periosteal bud

A growth of capillaries and osteoblasts

Clinical View 6.3 - Achondroblastic Dwarfism

Achondroplasia is characterized by abnormal conversion of hyaline cartilage to bone. Most common form is achondroplastic dwarfism, in which the long bones stop growing in childhood. -often leads to short stature with large head -results from failure of chondrocytes in the second and third zones of the epiphyseal plate to multiply and enlarge. As a result there is inadequate endochondral ossification. -most cases are due to DNA mutation, so normal parents can have dwarf children, or it can be inherited

Endochondral ossification

Begins with hyaline cartilage model Produces majority of bones in the body, including limbs, pelvis, vertebrae, clavicle ends

2. Zone of proliferating cartilage

Chondrocytes undergo rapid mitosis, enlarge slightly, become aligned like a stack of coins into longitudinal columns of flattened lacunae (parallel to diaphysis)

3. Zone of hypertrophic cartilage

Chrondrocytes cease dividing and begin to hypertrophy (enlarge) greatly. The walls of lacunae become thin because the chondrocytes resorb the matrix as they hypertrophy

Bones

Composed of: bone (osseous) connective tissue connective tissue proper (periosteum) cartilage connective tissue (articular cartilage) smooth muscle tissue (vasculature) fluid connective tissue (blood) nervous tissue (nerves that supply bone) Functions: Support and Protection Movement Hemopoeisis Storage of Mineral and Energy Reserves - 90% of calcium and phosphate stores are stored and released by bone. Yellow bone marrow contains lipid energy storage

Red bone marrow

Connective tissue located in spongey bone. Contains stem cells that form all blood cells and platelets. In children: red bone marrow is located in the spongy bone and medullary cavity of most of the bones of the body In adults: A lot of red bone marrow is converted into yellow bone marrow, which is located in the shafts of adult long bones. Adults have red bone marrow in select parts of axial skeleton, like flat skull bones, vertebrae, ribs, sternum, and the ossa coxae (hip bones). Also the proximal epiphyses of each humerus and femur.

Perichondrium

Covering around cartilage, consists of 2 layers Outer layer is fibrous region of dense irregular connective tissue. It provides support, protection, and secures perichondrium to cartilage Inner layer is cellular, contains stem cells for the growth and maintenance of cartilage

Central Canal

Cylindrical channel that lies in the center of the osteon, contains blood vessels and nerves for the bone

Epiphysis

End of a long bone knobby region, strengthens joint, provides added surface area for bone to bone articulation as well as tendon and ligament attachment inner layer of spongy bone

Circumferential lamellae

External circumferential lamellae: -Rings of bone immediately internal to the periosteum of the bone Internal circumferential lamellae: -Internal to the endosteum These distinct regions appear during original formation of the bone Both run the entire circumference of the bone itself

Fibrocartilage

Extremely durable, shock absorber, resists compression No perichondrium because the stress it endures would destroy it Intervertebral discs, pubic symphysis, menisci of knee Numerous coarse, readily visible fibers in the extracellular matrix Densely interwoven collagen fibers Fibers arranged as irregular bundles between large chondrocytes. There is only a sparse amount of ground substance, and often chondrocytes are arranged in parallel rows

Hydroxyapatite

Hardy crystals consisting of calcium and phosphate that form the bone matrix. Also incorporate other salts and ions like CaCO3, Na, Mg, sulfate, F, in calcification

Clinical View 6.2 - Forensic Anthropology: Determining Age at Death

If an epiphyseal plate has not yet ossified (or some have and some haven't), depending on which bone it is on it can be used to help determine age

Growth of Bone

Interstitial: getting longer, occurs within epiphyseal plate (which holds thickness until child gets older and epiphyseal cartilage production slows, then osteoblast activity overcomes it and thins it out) Appositional: getting wider/thicker, think tree rings, occurs within periosteum. Osteoblasts lay down bone matrix internal and parallel to periosteum, leading to widening. Medullary cavity is resorbed along edges by osteoclasts and becomes expanded.

Articulations

Joints; points where two bones meet.

Bone markings

Know them bitch

Tuberosity

Large rough projection

Line

Low ridge

Calcitonin

Lowers blood calcium levels by making more calcium be deposited in bone -inhibits osteoclast activity

Lamellar Bone (Secondary bone)

Mature bone in sheets called lamellae. Fibers are oriented in one direction in each layer, but in different directions in different layers for strength.

Chondrocytes

Mature cartilage cells that are encased in the matrix they produced as chondroblasts. The spaces they occupy are called lacunae. These cells maintain the matrix and ensure it remains healthy and viable. Mature cartilage is avascular so nutrients must diffuse through the matrix. Produce a chemical that prevents blood vessel formation and growth within extracellular matrix.

Woven bone (primary bone)

Newly formed bone CT Collagen fibers randomly oriented

Hyaline cartilage

Most common, weakest Rings of trachea Provides support through flexibility and resilience Clear, glassy appearance under microscope Chondrocytes irregularly scattered throughout matrix Collagen is not readily seen with light microscopy. Forms most of fetal skeleton, is a model for future bone growth Hyaline cartilage at the articular ends of long bones allows for joints to move easily and freely.

Compact Bone Structures that are not part of the Osteon Proper

Perforating canals/Volkmann canals Circumferential lamellae Interstitial lamellae

Epicondyle

Projection adjacent to a condyle

Cartilage

Semi-rigid connective tissue that is weaker than bone, but more flexible and resilient Contains a population of cells scattered throughout a matrix of protein fibers embedded within a gel-like ground substance

Ground substance

Semisolid material that suspends and supports the collagen fibers collagen fibers provide flexibility and strength inorganic components provide compressional strength

Tubercle

Small round projection

Bones

Support weight interact with muscles for precise movements Vital reservoirs of calcium and phosphate

Lacunae

The small spaces occupied by chrondrocytes

Flat bones

These bones are thin, flat, and curved. Layer of spongy tissue inside They form the ribs, sternum, scapulae, and skull.

4. Zone of calcified cartilage

This zone is usually composed of 2-3 layers of cartilage. Minerals are deposited in the matrix between columns of lacunae, this calcification kills the chondrocyte and makes the matrix appear opaque

Canaliculi

Tiny, interconnecting channels within the bone connective tissue that extend from each lacuna, travel through the lamellae, and connect to other lacunae and the central canal. House osteocyte cytoplasmic projections that permit intercellular contact/communication. Nutrients, minerals, gases, and wastes can travel through these passageways between the central canal and osteocytes

Periosteum

Tough sheath covers outer surface of bone except areas covered by articular cartilage. Formed by dense irregular connective tissue and consists of outer fibrous layer and inner cellular area Protects bone from surrounding structures, anchors blood vessels and nerves, provides stem cells (osteoprogenitor cells and osteoblasts)

Irregular bones

Unusual bones bones of the vertebrae and face, ossa coxae

Mesenchyme

a loosely organized, mainly mesodermal embryonic tissue that develops into connective and skeletal tissues, including blood and lymph. abundant ground substance

Trochlea

a smooth, grooved articular process shaped like a pulley

nutrient blood vessels

also called the nutrient artery and the nutrient vein supply the diaphysis of a long bone. typically only one nutrient artery enters and one nutrient vein leaves through a nutrient foramen in the bone

Osteoblasts

bone forming cells, secrete the initial semisolid, organic form of bone matrix called osteoid. Osteoid later calcifies and hardens as a result of calcium salt deposition. Produce new bones, become trapped in their secretions, differentiate into osteocytes.

Depressions

alveolus, fossa, sulcus

Ramus

angular extension of a bone relative to the rest of the structure

Periosteal blood vessels

arteries and vessels -provide blood to the external circumferential lamellae and the superficial osteons within compact bone at the external edge of the bone

chondroma

benign tumor of cartilage

Hemopoeisis

blood cell production occurs in red bone barrow

Osteoprogenitor cell

bone stem cells derived from mesenchyme divide into another stem cell and a cell committed to becoming osteoblast located in periosteum and endosteum

osteoma

bone tumor

Bone Fracture and Repair

breaks in bone are called fractures Types of fractures: -stress fracture -pathologic fracture -simple fracture -compound fracture Bone fracture repair 1. A fracture hematoma forms from clot from broken blood vessels 2. A fibrocartilaginous callus forms - regenerated blood vessels infiltrate the fracture hematoma due to an increase in osteoblasts in the periosteum and endosteum near the fracture site. -Fracture hematoma is reorganized into growing CT called a procallus. -Fibroblasts in procallus produce collagen fibers that help connect broken ends of the bones -Chondroblasts in the new CT for dense regular CT -eventually procallus becomes a fibrocartilaginous callus -lasts 3 weeks 3. A hard (bony) callus forms. -w/in a week, osteoprogenitor cells in areas adjacent to fibrocartilaginous callus become osteoblasts and produce trabeculae of primary bone. The callus is replaced by this bone and becomes a hard callus. Continues to grow and thicken for several months. 4. Bone is remodeled -hard callus persists 3-4 months as osteoclasts remove excess bony material, compact bone replaces primary bone

Openings and spaces

canal, fissure, foramen, meatus, sinus

perforating canals (Volkmann's canals)

canals that run perpendicular to the central canals, provide pathways for blood vessels and nerve fibers to connect central canals with the periosteum (outside the bone)

elastic cartilage

cartilage with abundant elastic fiber more flexible than hyaline cartilage Surrounded by pericardium Found in epiglottis, outer ear chondrocytes are almost indistiguishable from hyaline cartilage, and are closely packed and surrounded by small amount of extracellular matrix Elastic fibers are both denser and more highly branched in the central region of the extracellular matrix, where they form a weblike mesh around chrondrocytes within the lacunae

Sinus

cavity or hollow space in a bone

Medullary cavity

cavity within the shaft of the long bones filled with bone marrow Contains yellow bone marrow in adults

Articulating Surfaces

condyle, facet, head, trochlea

Articular cartilage

covers the surfaces of bones (epiphyses) where they come together to form joints reduces friction and absorbs shock

Projections for tendon and ligament attachment

crest, epicondyle, line, process, ramus, spine, trochanter, tubercle, tuberosity

osteopenia

decreased calcification of bone resulting in insufficient ossification

alveolus

deep pit or socket in the maxillae or mandible

Hyperostosis

excessive formation of bone tissue

fossa

flattened or shallow depression

Ossification (osteogenesis)

formation and development of bone connective tissue begins in embryo and continue as the skeleton grows during childhood and adolescence Ossification continues after adult bones are formed. By 8-12 weeks of fetal development, the skeleton begins forming from condensations of mesenchyme or a hyaline cartilage model of bone. Afterward, these models are replaced by bone.

Interstitial growth of cartilage

growth from within, chondrocytes within cartilage divide into chondroblasts and secrete new matrix, form new lacunae 1. Chondrocytes in lacunae are stimulated to begin mitosis 2. Two cells occupy one lacunae, now called chondroblasts 3. As new matrix is secreted, the cells are pushed apart into separate lacuna 4. Cartilage continues to grow in the internal region as chondrocytes produce more matrix

Metaphysis

growth zone between the epiphysis and the diaphysis during development of a long bone In a growing bone, this region contains epiphyseal plate. In mature bone, the epiphyseal plate is converted into compact bone called the epiphyseal line

Osteomyelitis

infection and inflammation of bone and bone marrow

osteogenesis imperfecta

inherited condition when bone formation is incomplete, leading to fragile, easily broken bones

Osteoclasts

large, multinuclear, phagocytic cells derived from fused bone marrow cells similar to those that produce monocytes Involved in process called bone resorption : 1. Osteoclasts secret HCl acid to dissolve mineral parts of bone matrix (Ca and P) 2. Lysosomes within osteoclasts secrete enzymes that dissolve the organic part of the matrix Ruffled border that increases their surface area exposure to bone Often located in resorption lacunae (depression or pit in a bone)

Condyle

large, smooth, rounded oval structure

Interstitial lamellae

leftover parts of osteons that have been partially reabsorbed They often look like a bite have been taken out of them Incomplete and typically have no central canal

Long bones

longer than they are wide elongated, cylindrical shaft (diaphysis) Arm, forearm, palm, fingers Thigh, leg, sole of foot, toes

Osteoporosis

loss of bone density to the point at which normal function is compromised "porous bone"

Chondrosarcoma

malignant tumor of cartilage

Osteosarcoma

malignant tumor of the bone, most common, mostly affects long bones

Trochanter

massive, rough projection found only on the femur

Osteocytes

mature bone cells derived from osteoblasts Reside in lacunae Maintain the bone matrix and detect mechanical stress on a bone (this is communicated to osteoblasts and may result in new bone matrix at surface)

Endosteum

membrane lining the medullary cavity of a bone covers internal surfaces of bone contains osteoprogenitor cells, osteoblasts, and osteoclasts, and is active during bone growth, repair, and remodeling

Metaphyseal vessels

metaphyseal blood vessels (arteries and veins) provide blood supply to diaphyseal side of epiphyseal plate, which is the region where new bone ossification forms bone CT to replace epiphyseal plate cartilage

sulcus

narrow groove

Crest

narrow, prominent, ridgelike projection

Fissure

narrow, slitlike opening through a bone

Appositional growth of cartilage

new chondrocytes and new matrix are added on the outside of the tissue 1. Undifferentiated stem cells at the internal edge of the perichondrium begin to divide 2. New undifferentiated stem cells and committed cells that differentiate into chondroblasts are formed 3. Chondroblasts push apart because of matrix formation, become chondrocytes in separate lacunae, then cartilage continues to grow at the periphery as chondrocytes continue to produce more matrix.

Canal

passageway through a bone

Meatus

passageway through a bone

spine

pointed, slender process

Glucocorticoids

produced by adrenal cortex -if levels get too high, they stimulate bone resorption and lead to loss of bone mass

Head

prominent, rounded epiphysis

Epiphyseal vessels

provide blood to epiphyses -they are blocked from interacting with metaphyseal vessels by epiphyseal plate, but once epiphyseal line forms, the vessels anastomose through channels in the epiph line

collagen fibers

provides flexibility and tensile strength

Short bones

roughly same length and width interior composed of spongy bone carpals and tarsals Sesamoid bones including patella

perforating fibers (Sharpey's fibers)

secure periosteum to underlying bone

Diaphysis

shaft of a long bone provides for the leverage and major weight support of long bones

Facet

small, flat shallow surface

Thyroid hormone

stimulates bone growth by influencing basal metabolic rate of bone cells -works together with growth hormone to maintain normal activity at epiph plates until puberty.

Osteon (Haversian system)

structural unit of compact bone cylindrical Run parallel to diaphysis of long bone Components: -Central Canal -Concentric lamellae -Osteocytes -Canaliculi -Concentric lamellae: rings of bone connective tissue that surround the central canal and form the bulk of the osteon. The amount of concentric lamellae in an osteon vary. contain Collagen fibers oriented in one direction *Adjacent lamellae contain collagen fibers in perpendicular directions, leading to strength and resilience of bone -Osteocytes: housed in lacunae and occur between adjacent concentric lamellae -Canaliculi: tiny, interconnecting channels within the bone connective tissue that extend from each lacuna, travel through the lamellae, and connect to other lacunae and the central canal. House osteocyte cytoplasmic projections that permit intercellular contact/communication. Nutrients, minerals, gases, and wastes can travel through these passageways between the central canal and osteocytes

Trabeculae

supporting bundles of bony fibers in cancellous (spongy) bone Often form a meshwork of crisscrossing bars and plates of bone pieces, providing great resistance to stresses from any direction by distributing the weight throughout the entire framework

Osteolysis

the release of the stored calcium and phosphate from the bone matrix liberated calcium and phosphate ions enter the tissue fluid and then the blood Osteoblast and osteoclast activity is regulated by hormonal levels, body's need for Ca or P, and gravitational stressors to bone

5. Zone of ossification

walls break down between lacunae in columns, forming longitudinal channels, which are invaded by capillaries and osteoprogenitor cells from the medullary cavity. New bone matrix is deposited on the remaining calcified cartilage matrix