Chapter 6: Bones and Skeletal Tissue (B)


(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


older chondrocytes in stack that are closer to diaphysis, and lacunae enlarge


surrounding cartilage matrix calcifies and chondrocytes die


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


when blood Ca^2+ levels are too low


high blood levels of Ca^2+, can lead to undesired deposits of calcium in blood vessels, kidneys, and other organs


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


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)


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


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.


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


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;

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