bl213 exam thing 2 ossification

how old does an embryo develop primary ossification?

8 weeks

when does secondary ossifcation happen?

after birth

what is secondary ossification

the area of bone formation that develops in the epiphyses (ends) of long bones. Spongy bone remains in epiphyses.

after secondary ossifcation, where is hyaline cartilage still?

the area of bone formation that develops in the epiphyses (ends) of long bones

first step of primary ossification?

Osteoblasts first make the bone collar, (osteoid outside cartilage.)

second step of primary ossification?

Bone collar cuts off nutrients when it forms around diaphysis. 

third step of primary ossification?

No nutrients, meaning the chondrocytes die off. Swell up with hypertrophy, secrete calcium, and die.

fourth step of primary ossification?

Periosteal bud enters cartilage with nutrients, osteogenic cells, and osteoclasts

fifth step of primary ossification?

Osteogenic cells become osteoclasts, which makes spongy bone, trapped osteoblasts become osteocytes.

sixth step of primary ossification?

Osteoclasts remove spongy bone, making medullary cavity

difference between primary ossification and Intramembranous Ossification?

(the two bone formations)

intramembranous ossification is an entire method of bone formation where connective tissue turns directly into bone,

whereas a primary ossification center is just the specific starting location where bone tissue begins to replace cartilage inside a developing long bone

first step of intramembranous ossification

Ossification center forms (blob of fibrous connective tissue)

second step of intramembranous ossification

Inner mesenchymal cells form clusters inside of fibrous connective tissue, then divide into osteoblasts. 

third step of intramembranous ossification

The osteoblasts secrete osteoid. While trapped osteoblasts become osteocytes (know the process of trapping osteocytes.

fourth step of intramembranous ossification

Bone builds around blood vessels, (the type of bone is spongy)

fifth step of intramembranous ossification

Mesenchymal cells form periosteum

sixth step of intramembranous ossification

Osteoblasts keep forming compact bones outside the bone surface.

obtaining vascularity in intramembranous ossification

To obtain blood vessels, ossification starts with fibrous connective tissue & builds spongy bone around. 

growth plates

epiphyseal plates

during bone growth what two events happen at the same time?

1. Chondrocytes near epiphysis dividing (forcing epiphysis away from diaphysis) 

2. Diaphysis chasing epiphysis (dividing chondrocytes) (ossification) 

summary of growth plates?

cartilaginous portion of long bones where the longitudinal growth of the bone takes place. Its structure comprises chondrocytes suspended in a collagen matrix that go through several stages of maturation until they finally die, and are replaced by osteoblasts, osteoclasts, and lamellar bone.

5 phases of growth plates

In a coordinated stepwise process, the chondrocytes pass through the stages of resting phase, proliferative phase, prehypertrophic phase, hypertrophic phase, and terminal phase.

resting phase / reserve

In the resting phase, the cells are relatively inactive. Anchors the plate and holds inactive cartilage cells.

proliferation zone

Chondrocytes divide rapidly and arrange in stacking columns, lengthening the bone.

Hypertrophic zone

• Lacunae enlarge - connect

Chondrocytes (cartilage cells) swell and mature.

Calcification zone 

Minerals are deposited in the matrix as dying chondrocytes release calcium, creating a temporary calcified scaffold.

ossification zone

Osteoblasts and blood vessels invade this hardened area to lay down permanent new bone. Osteoclasts -> Extend medullary cavity

difference between interstitial growth and appositional growth

interstitial growth increases length from within the tissue, whereas appositional growth increases width by adding layers to the outer surface. Interstitial growth occurs exclusively in flexible cartilage, where internal chondrocytes divide and secrete new matrix to expand the tissue’s internal mass outward, such as within the epiphyseal growth plate. In contrast, appositional growth occurs in both cartilage and rigid bone, relying on cells in the outer layers (the perichondrium or periosteum) to differentiate and deposit new matrix onto existing boundaries. Because calcified bone is too rigid to expand from within, it relies entirely on appositional growth to become thicker and stronger.

growth in long bone width?

appositional

growth in long bone length?

interstitial

cell responsible for appositional?

osteoblasts secreting osteoid on the outside compact bone around medullary cavity. The osteoclasts chew up the bone on the inside at the same rate.

bone functions

1. Supports, 

2. Protection

3. Connecting limbs attachment points (see, axial skeleton) 

4. Movement 

5. Storage (lots of inorganic minerals in the bones, they are reservoirs for calcium and phosphate. 

6. Hematopoiesis (production of all blood cells) hema - blood, poiesis - generating

inorganic bone material facts

65% of Bone Mass

Mineral salts

Hydroxyapatites (Calcium phosphate)

Hardness / Resists compression

-> doesn’t only have inorganic materials, otherwise it’d be too brittle. 

organic bone facts

35% of Bone Mass

Cells <50% 

Osteoid: the scaffolding of inorganic materials to build rigid bone. 

• Ground substance + Collagen 

• Resists tension

high calcium response?

(bone protecting) Osteoprotegrin - [secreted by osteoblasts] successfully protects 

Osteoclasts, by making osteoclasts [decrease levels of calcium in blood]

low calcium response

rank ligand (secreted by Parathyroid hormone) [ PTH secreted by parathyroid gland in osteoblast] successfully protests osteoclasts by making osteoclasts [increase activity of Ca2+ in blood) 

What senses the feedback loop in blood calcium?

Osteoblasts.

What effectors are there in blood calcium feedback loop?

Low calcium response

Parathyroid hormone (PTH) stimulates osteoclasts to break down bone tissue (resorption), releasing stored calcium directly into the bloodstream

High calcium response

 Osteoprotegrin - [secreted by osteoblasts] successfully protects 

Osteoclasts, by making osteoclasts [decrease levels of calcium in blood]

 wolffs law

 bone remodel in response to the demands put on it. 

Evidence: 

1. Where stress is greatest, bone is stronger

2. Least stress on a bone is in the center (hollow cavity) 

3. Right handed folks have bigger bones in the right hand. 

Stress is noticed by osteocytes 

what do osteo clasts secrete?

secrete HCL, a strong acid, and lysosomal enzymes, that chew up enzymes. Osteoclasts walk on the surface with little legs aww how gross. 

purpose of bone remodeling

Fibers need to be exchanged for new ones. -> bone resorption is removing components to recycle (done by osteoclasts)

broken bone treatment steps

1. Reduction (= Realignment)

• Closed – External

• Open – Pins / screws

2. Immobilization

• Keeping those ends in place!

3. Repair (done by the body)

repair steps (gross)

1. Bridge the gap with connective tissue

2. Replace the cartilage with spongy bone

3. Remodel to match original

bone repair in depth step 1 Hematoma formation 

blood clot forms. Occurs with periosteum, (clot is contained by fibrous dense connective tissue) 

remodeling (step 4 of bone repair)

Osteoclasts and osteoblasts (eat away bone to keep it light, clear out medullary cavity and smooth the surface. 

Bony callus forms (step 3 of bone repair

• Osteoblasts ossify the callus (blood vessels bring in bone making vessel) 

• Spongy bone connects 

Soft callus formation (step 2 of bone repair)

• Debridement (pulls out junk, osteoclasts will help)

• Bridge of cartilage! (chondroblasts build cartilage, get trapped into chondrocytes, bridge is formed)

• Vasculature re-enters (chondrocytes are deprived of nutrients, they swell up with calcium, die, and blood vessels can enter. 

what is OSTEOPOROSIS

Bone is porous and brittle

causes of OSTEOPOROSIS

• caused by low estrogen, menopause, lack of vit D or C, smoking and drinking. Happens a lot to women going through menopause (70 & 80) and lack of movement. See CALCIUM USAGE GOES DOWN IN AN INACTIVE PERSON, THEIR BONE DENSITY DECREASES BECAUSES THERES NO USING THE CALCIUM, AND THEREFORE REDUCED PRODUCTION OF CALCIUM.

treatment of OSTEOPOROSIS

•  (exercise,  estrogen (HRT) increases calcium and vitamin D diet.

what reports stress on bones>?

osteocytes!