Ossification
(Osteogenisis) the process of bone formation; formation of the bony skeleton in embryos and bone growth goes in until early adulthood as body continues to increase in size
Membrane Bone
bone developed from fibrous membranes in a process called intramembranous ossification
Endochondral Bone
bone developed by replacing hyaline cartilage in process called Endochondral Ossification
Intremembranous Ossification
results in formation of canial bones of the skull and the clavivles, flat bones mostly formed by this process, begins on fibrous connective tissue membranes formed by mesenchymal cells. 4 Steps
Endochondral Ossification
all bones of the skeleton below base of skull form by this process; begins in 2nd month of development and uses hayaline cartilage as models for bone construction
Primary Ossification Center
region of formation of long bone begins in center of hyaline cartilage shaft
Periosteal Bud
contains a nutrient artery and vein, lymphatic vessels, nerve fibers, red marrow elements, osteoblasts, and osteoclasts
Interstitial Growth
length of long bones
Appositional Growth
thickness and remodeling of all bones by osteoblasrs and osteclasts on bone surfaces
Growth in Length of Long Bones
Epiphyseal plate cartilage organizes into four important functional zones: Proliferation (growth), Hypertrophic, Calcification, Ossification (osteogenic)
Proliferation (growth)
these cells divide quickly, pushing the epihyisis away from the diaphysis, causind entire bone to lengthen
Hypertrophic
older chondrocytes in stack that are closer to diaphysis, and lacunae enlarge
Calcification
surrounding cartilage matrix calcifies and chondrocytes die
Ossification
new bone formation occurs when calcified spicules erode
Growth Hormone
most important stimulus of epiphyseal plate activity released by the anterior pituitary gland
Thyroid Hormone
modulates the activity of growth hormone , ensuring the skeleton has proper proportions as it grows
Testosterone and Estrogen
promote adolescent growth spurts, end growth by inducing epiphyseal plate closure
Bone Remodeling
bone deposit and bone resorption
Bone Deposit
Occurs where bone is injured or added strength is needed; Requires a diet rich in protein; vitamins C, D, and A; calcium; phosphorus; magnesium; and manganese
Osteoid Seam
reveals sites of new matrix deposits: an unmineralized band of matrix
Calcification Front
Abrupt transition zone between the osteid seam and the older mineralized bone
Bone Resorption
(removal) osteoclasts secrete lysosomal enzymes (digest organic matrix) and acids (convert calcium salts into soluble forms). Dissolved Matrix is transcytosed across osteoclast, enters interstitial fluid and then blood
Control of Remodeling
controlled by Hormonal mechanisms that maintain calcium homeostasis in the blood, and Mechanical and gravitational forces
Hormonal Control of Blood Ca2+
Calcium is necessary for
Transmission of nerve impulses, Muscle contraction, Blood coagulation, Secretion by glands and nerve cells, Cell division
Parathyroid Hormone (PTH)
primarily involved in hormonal control; released when blood levels of ionic calcium decline, increased PTH stimulates osteoclasts to reabsorb bone, releasing calcium to blood. Osteoclast break down old and new matrix. As blood concentration of blood rises
Hyperexcitability
when blood Ca^2+ levels are too low
Hypercalcemia
high blood levels of Ca^2+, can lead to undesired deposits of calcium in blood vessels, kidneys, and other organs
Leptin
also been known to influence density by inhibiting osteoblast
Response to Mechanical Stress
second set of controls regulatong bone remodeling; Wolffs Law
Wolff's law
A bone grows or remodels in response to forces or demands placed upon it; Observations supporting Wolff's law:
(1) Handedness (right or left handed) results in bone of one upper limb being thicker and stronger
(2)Curved bones are thickest where they are m
Bone Anatomy and Bending Stress
body weight transmitted to the head of the femur threatens to bend the bone along the indicated arc, compressing it on one side (converging arrows on the right) and stretching it on the other side (diverging arrows on left). Because these two forced cance
Fractures
breaks; excessive intake of vitamin A appears to increase fracture risk in some; Classifications: (1) Position of the bone ends after fracture [nondisplaced fractures - the bone ends retain their normal position, displaced fractures - bone ends are out of
Fractures (2)
all fractures can be describes in terms of location, external appearance, nature of the break
Fractures (3)
Reduction
treatment for bone fracture involving realignment of the broken bone ends
Closed (external) Reduction
bone ends are coaxed into position by the physicians hands
Open (Internal) Reduction
bone ends are secured together surgically with pins or wires
Stages in healing of Fracture
Hematoma Forms, Fibrocartilaginous Callus Forms, Bony Callus Forms, Bone Remodeling Occurs
Hematoma Forms
torn blood vessels tear and hemorrhage, blood, clots called hematoma form, and sites become swollen painful, and inflamed
Fribrocartilaginous Callus Forms
formation of granulation tissue or soft callus, capillaries grow into hematoma and phagocytic cels invade area and clean up debris, Osteoblast and and fibroblast begin to reconstruct bone. Osteoblasts begin forming spongy bone within 1 week, Fibroblasts s
Bony Callus Forms
New trabeculae form a bony (hard) callus, Bony callus formation continues until firm union is formed in ~2 months
Bone Remodeling Occurs
In response to mechanical stressors over several months, Final structure resembles original
Osteomalacia
includes a number of disorders in which the bones are inadequatly mineralized. Osteoid is produced, but calcium salts are not deposited, so bones soften and weaken. caused by insufficient calcium in diet and by vitamin D deficiancy.
Rickets
analogous disease in children. Bowed legs and deformities of the pelvis, skull, and rib cage are common. Because epiphyseal plates cant be calcified they continue to widen and the ends of long bones become visibly enlarged and abnormally long. caused by i
Osteoporosis
refers to a group of diseases in which bone resorption outpaces bone deposit. The bones become so fragile that something like sneezing or stepping off curve can cause a break. Spongy bone of spine and neck of femur become most susceptible to fracture;
Ris
Osteoporosis Treatment
Calcium, vitamin D, and fluoride supplements, Weight-bearing exercise throughout life, Hormone (estrogen) replacement therapy (HRT) slows bone loss , Some drugs (Fosamax, SERMs, statins) increase bone mineral density
Paget's Disease
Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur, or skull; Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur, or skull
Pagetic bone has very high ratio of spongy to compact bone and
Developmental Aspects of Bones
Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms, At birth, most long bones are well ossified (except epiphyses); Nearly all bones completely ossified by age 25, Bone mass decreases with age beginning in 4th