Bone Development, Strength, & Repair

Osetogenesis (ossification):

• in embryos this leads to the formation of ____ ___

• in children and young adults, ossification occurs as part of ____ ___

• In adults, it occurs as part of bone ___ and bone ____

the process of bone tissue formation

• bony skeleton

• bone growth

• remodeling,repair

Intramembranous ossification:

• what does it exist as prior to this

• examples?

• how long does this growth take place?

• Fontenella:

• describe

Replacement of sheet-like connective tissue membranes with bony tissue

• mesenchyme

• bones of skull, facial bones, clavicles

• 8 weeks - 2 years

• soft spot on baby

• osteoblasts invade CT membrane by laying down spongy bone → spongy bone remodel edges with compact bone

Endochondral ossification:

• explain the process

replacement of hyaline cartilage with bony tissue (most bones of skeleton)

1. Cartilage model forms (9 weeks)

2. Cartilage grows and osteoblasts invade center of cartilage and lay down a bony collar to help stabilize it

3. Blood vessels enter middle of bone (diaphysis) and compact bone replaces cartilage in the shaft (primary ossification center)

4. medullary cavity forms, and osteoblasts invade epiphyses to help preserve epiphyseal discs (after birth) (secondary ossification center)

5. cartilage at joints becomes articular cartilage and bone begins growing lengthwise (adolescence & mid 20s)

When growth hormone declines, it causes the …..

bone stop growing length wise

• men→

• women→

complete ossficatiom of epiphyseal plates

27-28

23-24

How is growth in bones influenced?

Growth in Width a.k.a

• Osetoblasts beneath the _____ secrete _____ on external surface

• Osteoclasts on the _____ surface of ______ remove bone

• the break down of bone happens at a slower rate than new bone =

• continuation to increase thickness throughout life because of…

GH from anterior pituitary gland and sex hormones from ovaries and testes

appositional growth

• periosteum,bonematrix

• endosteal,diaphysis

• thicker,stronger bone

• stress, increased muscle activity, excess weight

Gigantism:

Growth Hormone deficiency:

What is essential for homeostasis?

we recycle ____ of our bone mass each week

Explain how our bone architecture is changing and recycles differently

hypersecretion of GH

early ossification of growth plates

bone remodeling

5-7%

changes based on different stress and areas with more stress would remodel quicker than those with lower stress

What the two process of bone remodeling?

Remodeling Unit:

Bone Deposit and Resorption

coordinated by osteoblasts/osteoclasts while being helped by stress sensing osteocytes

Process of bone remodeling

1. Orgination: microdamage, kicks of process

2. Osteoclast recruitment: osteocytes sense stress & calls for bone remodeling unit

3. Resorption: where osteoclast come in and eat away at damaged bone matrix to clear all of it

4. Osteoblast recruitment: recruited and secrete new bone matrix

5. Osteoid formation: section of bone matrix that has yet to be mineralized (soft)

6. Mineralization: osetoblast do this if there is proper diet/nurtiention

7. Mineral Matruration: cavity filled by bone matrix, compact and allow more minerals to get a stronger bone than before

8. Quiescence: returning to function as normal until microdamage occurs again

Bone deposit occurs where?

• can only occur if?

• Osteocytes:

Remodeling is controlled by two control loops?

bone is injured or where added bone strength is needed

• healthy diet in proteins, Vitamin C<D<A and minerals

• tells us where bone deposit is needed

Negative feedback hormone mechanism to control Calcium ( tells us if bone remodeling can occur properly

Response to mechanical stress and gravitational forces (tells us where we should remodel first)

What is Ca responsible for?

How much Ca is present in blood?

What is normal level of Ca?

Daily requirement of Ca?

transmision of nerve impulses, muscle contraction, blood coagulation, secretion of glands and cell division

less than 1.5g

9-11mg per dl of blood

400-800 mg until 10 years. 1200-1500 mg from 11-24 years

What is released when blood levels of calcium DECLINES?

• when this is released what happens?

• why isn’t the osteoid touched?

• As calcium levels rise, the stimulus PTH ends→

PTH

• stimulates osteoclasts to resorb bone, releasing calcium to blood

• has no calcium salts

• causes blood calcium levels to decrease

Where is the greatest stress?

where is no stress?

on the exterior of bone

center of bone (medullary)

Wolff’s Law:

• Long bones are the thickest where?

• Where are curved bones the thickest?

• Trabeculae of spongy bone form what to help add intergity

• What type of projection occur where heavy,active muscles attach?

A bone grows or remodels in response to the demands placed on it

• midway along the diaphysis(shaft)

• where they are most likely to buckle

• trusses or struts along lines of compression

• large and bony