copyright © 2010 pearson education, inc. appositional growth and bone remodeling normal calcium...

Copyright © 2010 Pearson Education, Inc.

• Appositional Growth and Bone Remodeling

• Normal Calcium Deposition and Removal

• Conditions That Stimulate Bone Remodeling

• Types of Bone Fractures

• Stages of Bone Healing

• Hormone Imbalances and Bone Density Problems

• Developmental Aspects of the Skeleton

• Axial Skeleton: The Skull

• Axial Skeleton: Vertebrae

Bone Growth, Repair, and Axial Skeleton


Postnatal Bone Growth

• Interstitial growth:

• length of long bones

• Appositional growth:

• thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

Figure 6.11

Bone growth(Interstitial growth)

Bone remodeling(Appositional Growth)

Articular cartilage

Epiphyseal plate

Cartilagegrows here.

Cartilageis replacedby bone here.

Cartilagegrows here.

Bone isresorbed here.

Bone isresorbed here.

Bone is addedby appositionalgrowth here. Cartilage

is replacedby bone here.


Bone Growth, Repair, and Axial Skeleton• Appositional Growth and Bone Remodeling








Bone Deposition• Occurs where bone is injured or added

strength is needed

• Requires a diet rich in protein; vitamins C, D, and A; Ca; P; Mg; and Mn

• Sites of new matrix deposit are revealed by the

• Osteoid seam

• Unmineralized band of matrix

• Calcification front

• The abrupt transition zone between the osteoid seam and the older mineralized bone

• Osteoclasts secrete

• Lysosomal enzymes to digest organic matrix

• Acids convert calcium salts into soluble forms

• Dissolved matrix is transcytosed across osteoclast, enters interstitial fluid and then blood

Bone Resorption


Control of Remodeling

• What controls continual remodeling of bone?

1. Hormonal mechanisms that maintain calcium homeostasis in the blood

2. Mechanical and gravitational forces

Ca is necessary for transmission of nerve impulses, muscle contraction, blood coagulation, secretion by glands and nerve cells, & cell division


Hormonal Regulation of Blood Calcium (Ca+2 or Ca2+)

* Leptin (produced by adipocytes) has also been shown to influence bone density by inhibiting osteoblasts


Mechanical and Gravitational Forces

• Wolff’s law: A bone grows or remodels in response to forces or demands placed upon it

• Observations supporting Wolff’s law:

• Handedness (right or left handed) results in bone of one upper limb being thicker and stronger

• Curved bones are thickest where they are most likely to buckle

• Trabeculae form along lines of stress

• Large, bony projections occur where heavy, active muscles attach

• Astronauts who spend months in the absence of gravity have weaker and thinner bones

Figure 6.13

Load here (body weight) Head of

femur

Compressionhere

Point ofno stress (axis or

fulcrum)

Tensionhere


Bone Growth, Repair, and Axial Skeleton• Appositional Growth and Bone

Remodeling










Classification of Bone Fractures Based on Four Aspects

3. Orientation of the break to the long axis of the bone:

• Linear—parallel to long axis of the bone

• Transverse—perpendicular to long axis of the bone

4. Whether or not the bone ends penetrate the skin:

• Compound (open)—bone ends penetrate the skin

• Simple (closed)—bone ends do not penetrate the skin

2. Completeness of the break

• Complete—broken all the way through

• Incomplete—not broken all the way through

1. Position of bone ends after fracture:

• Nondisplaced—ends retain normal position

• Displaced—ends out of normal alignment

Location is also included when describing a particular fracture

Some Types of Fractures

(Splintered or crushed in multiple places)

Bone Growth, Repair, and Axial Skeleton• Appositional Growth and Bone

Remodeling









Hematoma

A hematoma forms.

• Torn blood vessels hemorrhage

• Clot (hematoma) forms

• Site becomes swollen, painful, and inflamed

1

Stages in the Healing of a Bone Fracture

Figure 6.15

Hematoma Externalcallus

Newbloodvessels

Spongybonetrabecula

Internalcallus(fibroustissue andcartilage)

A hematoma forms.




Fibrocartilaginouscallus forms.

- Phagocytic cells clear debris

- Osteoblasts begin forming spongy bone within 1 week

- Fibroblasts secrete collagen fibers to connect bone ends

- Mass of repair tissue now called fibrocartilaginous callus

1 2


Figure 6.15


Bonycallus ofspongybone

Newbloodvessels

Spongybonetrabecula


A hematoma forms.









Bony callus forms.

• New trabeculae form a bony (hard) callus

• Bony callus formation continues until firm union is formed in ~2 months

1 2 3


Figure 6.15


Bonycallus ofspongyboneHealedfracture

Newbloodvessels

Spongybonetrabecula


A hematoma forms.









Bony callus forms.

• New trabeculae form a bony (hard) callus

• Bony callus formation continues until firm union is formed in ~2 months

Bone remodelingoccurs.

• In response to mechanical stressors over several months

• Final structure resembles original

1 2 3 4



Homeostatic Imbalances: Osteomalacia & Rickets

• Osteomalacia: Calcium salts not deposited

• Rickets (childhood osteomalacic disease) causes bowed legs and other bone deformities

• Cause: vitamin D deficiency (lack of sunlight) or insufficient dietary calcium

• Vitamin D deficiency can further cause depression


Homeostatic Imbalances: Osteoporosis

• Loss of bone mass where bone resorption outpaces deposit

• Spongy bone of spine and neck of femur become most susceptible to fracture

• Risk factors

• Lack of estrogen (post-menopause), calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus

• 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 (Osteitis deformans)

• 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 reduced mineralization

• Unknown cause (possibly viral)

• Treatment includes taking calcitonin and biphosphonates


Developmental Aspects of Bones: Embryo and Birth

• Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms

• At birth, most long bones are well ossified (except epiphyses)

Fontanelles are places where skull bones are joined by fibrous membranes

• Completely replaced with bone within two years after birth


Developmental Aspects of Bones: Later Events

• Nearly all bones completely ossified by age 25 (ossification of epiphyseal plates, no more bone growth)

• Bone mass decreases with age beginning in 4th decade (estrogen deficiency in women at menopause may lead to osteoporosis)

• Rate of loss determined by genetics and environmental factors

• In old age, bone resorption predominates. Vertebral collapse may occur, resulting in kyphosis.

Kyphosis

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