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Anatomy Ch. 6
Terms in this set (51)
Basic Structure of Skeletal Cartilages
1. Cells called chondrocytes are found in pockets called lacunae inside the cartilage.
2. Chondrocytes are surrounded by extracellular matrix.
3. Cartilage contains no blood vessels or nerves.
4. Cartilages are surrounded by the perichondrium (dense irregular connective tissue) that resists outward expression and contains blood vessels.
Growth of Skeletal Cartilage
1. Appositional growth: cells in the perichondrium secrete matrix against the external face of existing cartilage.
2. Interstitial growth: chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within.
Functions of Bones
1. Support: bones from the framework that support the body and cradle soft organs.
2. Protection: bones provide a protective case for the brain, spinal cord, and vital organs.
3. Movement: bones provide levers for muscles.
4. Mineral and growth factor storage: bones are a reservoir for minerals, especially calcium and phosphorous. Growth factors such as insulin-like growth factors are also stored in bone matrix.
5. Blood cell formation: hematopiesis occurs within red marrow cavities of bones.
6. Triglyceride (fat) storage: fat (yellow marrow) is stored in bone cavities.
1. Compact bone: a) dense outer layer of bone, and shafts of long bones, b) regular arrangement of lamellae.
2. Spongy bone: honeycomb of trabeculae filled with red bone marrow.
a) Double-layered protective membrane.
b) Outer fibrous layer is dense irregular connective tissue.
c) Inner osteogenic layer is composed mostly of osteoblasts and osteoclasts (also contains osteogenic cells which give rise to osteoblasts).
d) Richly supplied with nerve fibers, blood and lymphatic vessels.
a) Delicate membrane covering all internal surfaces of bone.
b) Also has osteoblasts and osteoclasts.
Chemical Composition of Bone
1. Organic components (cells, osteoid).
2. Inorganic components (hydroxyapatites).
Organic Components of Bone
a) Osteocytes: mature bone cells in bone tissue.
b) Osteoblasts: bone-forming cells.
c) Osteoclasts: large cells that resorb or break down bone matrix.
d) Osteoid: unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen.
Inorganic Compounds of Bone
1. Sixty-five percent of bone by mass.
2. Mainly calcium phosphate.
3. Responsible for bone hardness and its resistance to compression.
4. Serve as a mineral reservoir.
Osteogenesis and ossification: the process of bone tissue formation, which leads to the following:
-The formation of the bony skeleton in embryos.
-Bone growth until early adulthood.
-Bone remodeling, and repair.
Formation of the Bony Skeleton
1. Intramembranous Ossification
2. Stages of Intramembranous Ossification
3. Endochondral Ossification
4. Stages of Endochondral Ossification
a. Bone develops from a fibrous membrane formed by mesenchymal cells.
b. Begins at week 8 of embryo development.
c. Forms the cranial bones of the skull and the clavicles.
Stages of Intramembranous Ossification
a. An ossification center appears in the fibrous connective tissue.
b. Bone matrix is secreted within the fibrous membrane.
c. Woven bone and periosteum form.
d. Bone collar of compact bone forms, and red marrow appears.
a. Bone forms by replacing hyaline cartilage.
b. Begins in the second month of development.
c. Uses hyaline cartilage "bones" as models for bone construction.
d. Forms long bones and other bones of the skeleton.
Stages of Endochondral Ossification
1. Formation of bone collar around a primary ossification center in the diaphysis.
2. Cavitation of the hyaline cartilage.
3. Invasion of internal cavities by the periosteel bud, and spongy bone formation.
4. Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses.
5. Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyeseal plates.
Postnatal Bone Growth
1. Growth in length of long bones.
2. Growth in width (remodeling).
Growth in Length of Long Bones
a. Epiphyseal plate cartilage closest to the epiphysis is relatively inactive.
b. Cells closer to the diaphysis organize into a pattern that allows fast, efficient growth.
c. Four functionally different zones are formed: Proliferation (growth), Hypertrophic, Calcification, and Ossification (osteogenic) zones.
-Proliferation (growth): cartilage cells divide, pushing the epiphysis away from the diaphysis
-Hypertrophic zone: Older cartilage cells enlarge.
-Calcification zone: Matrix becomes calcified; cartilage cells die; matrix begins deteriorating.
-Osteogenic zone: new bone formation occurs as osteoblasts secrete matrix into calcified cartilage spicules
d. Growth of the epyphyses occurs in a similar way to keep pace with the changes in the diaphysis.
Growth in Width (Remodeling)
a. Bone is both formed and resorbed to reshape bone and increase bone width.
b. Osteoblasts deposit bone matrix on the outer surface of the diaphysis (appositional growth).
c. Osteoclasts remove bone from the inner surface to widen the shaft of a bone.
Hormonal Regulation Bone Growth During Youth
1. During infancy and childhood the epiphyseal plate activity is stimulated by growth hormone.
2. During puberty, testosterone and estrogens.
-Initially promote adolescent growth spurts.
-Cause masculinization or feminzation of specific parts of the skeleton.
-Later induce epiphyseal plate closure, ending longitudinal bone growth.
Bone is both resorbed and deposited at the endosteum and periosteum.
-Remodeling units: collections of osteoblasts and osteoclasts that deposit and resorb bone.
a. Occurs where bone is injured or added strength is needed.
b. Requires a diet rich in protein, vitamins, calcium, phosphorus and other minerals.
c. The enzyme alkaline phosphatase is essential for mineralization of bone.
a. Accomplished by osteoclasts .
b. Resorption involves osteoclast secretion of:
-Lysosomal enzymes that digest organic matrix.
-HCL that dissolves calcium salts.
c. Calcium is necessary for:
-Transmission of nerve impulses.
-Secretion by glands and nerve cells.
Control of Bone Remodeling
a) Hormonal Mechanism
b) Mechanical Stress (Wolff's Law)
Maintains calcium homeostasis in the blood.
1. Rising blood Ca2+ levels trigger the thyroid gland to release calcitonin.
2. Calcitonin stimulates calcium salt deposit in bone.
3. Falling blood Ca2+ levels signal the parathyroid glands to
release parathyroid hormone.
4. PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood.
Mechanical Stress (Wolff's Law)
Mechanical and gravitational forces acting on the skeleton affect bone structure.
1. Observations supporting Wolff's law include the following:
a. Curved bones are thickest where they are most likely to buckle .
b. Long bones are thickest midway along the shaft (where bending stress is greatest).
c. Trabeculae in spongy bone form along lines of stress.
d. Large, bony projections occur where heavy, active muscles attach.
Classification of Fractures
Based on: the position of the bone ends after fracture, the completeness of the break, the orientation of the fracture to the long axis of the bone; Whether or not the bone ends penetrate the skin.
Bone ends retain their normal position.
Bone ends are out of normal alignment.
Bone is broken all the way through.
Bone is not broken all the way through.
The fracture is parallel to the long axis of the bone.
The fracture is perpendicular to the long axis of the bone.
Open (compound) Fracture
Bone ends penetrate the skin.
Closed (simple) Fracture
Bone ends do not penetrate skin.
Bone fragments into three or more pieces; common in the elderly.
Bone is crushed; common in porous bones.
Broken bone portion pressed inward; typical skull fracture.
Incomplete fracture where one side of the bone breaks and the other side bends; common in children.
Ragged break when bone is excessively twisted; common sports injury.
Epiphysis separates from diaphysis along epiphyseal line.
Phases of Fracture Repair
1. Hematoma Formation
2. Fibrocartilagenous Callus Formation
3. Bone Callus Formation
4. Bone Remodeling
1. A mass of clotted blood (hematoma) forms at the fracture.
2. Site becomes swollen, painful, and inflamed.
Fibrocartilagenous Callus Formation
1. Granulation tissue (soft callus) forms a few days after the fracture.
2. Capillaries grow into the tissue and phagocytic cells begin cleaning debris.
3. Osteoblasts and fibroblasts begin reconstructing the bone.
4. Osteoblasts begin forming spongy bone.
5. Fibroblasts secrete collagen fibers and cartilage matrix.
6. A bulging external callus of cartilaginous matrix is formed that later calcifies.
7. The Fibrocartilagenous callus formed temporarily splints the bone.
Bony Callus Formation
1. New spongy bone appears forming a bony (hard) callus.
2. Bony callus formation continues until firm union is formed about 2 months later.
Bone Remodeling Formation
1. Excess material from the bony callus is removed.
2. Compact bone is laid down to reconstruct shaft walls.
Homeostatic Imbalances of Bone
3. Paget's Disease
1. Bones are inadequately mineralized causing softened, weakened bones.
2. Caused by insufficient calcium in the diet, or by vitamin D deficiency.
3. Rickets- Osteomalacia in children; Bowed legs and deformities of the pelvis, skull, and rib cage are common.
1. Group of diseases in which bone resorption outpaces bone deposit.
2. Occurs most often in postmenopausal women.
3. Bones become extremely fragile with loss of bone mass.
1. Characterized by excessive bone formation and breakdown.
2. Results in irregular growths of Pagetic bone with a high ratio of woven to compact bone.
3. Usually localized in the spine, pelvis, femur, and skull.
Developmental Aspects of Bone
A. The embryonic skeleton ossifies along a predictable timetable that allows fetal age to be determined from sonograms.
-At birth, most long bones are well formed or ossified.
-By age 25, nearly all bones are completely ossified.
B. In old age, bone resorption dominates.
-Rate of bone loss in old age differs with race and gender.
-Bone loss is greater in caucasians.
-Bone loss is greater in females than in males.
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