IHP Lecture 3 - Histology of Bone and Cartilage

What are the possible bone shapes

• flat

• tubular: long or short

• sesamoid

• irregular

What are the possible bone textures, and what maturity alligns with what kind of matrix?

textures: spongey or compact

matrix: Lamellar= mature. Woven= immature

What are the possible developmental origins?

1. Intramembranous ossification= Bone forms directly from embryonic connective tissue. (CT—> bone)

2. Endochondral ossification= bone replacing a cartilage template

What are the layers of bone

outside —> inside

periosteum, compact bone, endosteum, spongy bone, bone marrow

Label

Fill in the blanks

order them from smallest to biggest: canaliculi, lamellae, lucunae, osteon

lacunae, lamellae, canaliculi, osteon

The volksmann canal is the same as the ___ canal

perforating: parallel to osteon (vertical)

the haversian is the same as the ___ canal

Central: through center of osteon (horizontal)

What is bone

Specialized connective tissue

90% of bone is made up of this

Type I collagen (major)

Type V collagen (minor)

Type III, XI, XIII collagen (trace)

What is the inorganic part of the matrix made of

• calcium and phosphorous

• crystals of calcium hydroxyapatite

• 65% dry weight

• provides strength and ridgity

• trace elements influence crystal structure and bone quality

What is osteocalcin (organic)

binds calcium, marker of bone turnover

What is osteonecitin (organic)

Links collagen and hydroxyapatite

What is bone sialoprotein (organic)

Promotes mineral nucleation by binding hydroxyapatite

What is matrix Gla Protein (organic)

• inhibits (stops) calcification

• in soft tissues and cartilage

What is matrix fibronectin, thrombospondin, decorin (organic)

modulates

modulate cell attachment and organization

What is the path to osteoblast

primitive mesenchymal cell —> preosteoblast —> mature osteoblast

What is the function of an osteoblast and how does it do its function

• build bone by proteolysis and polymerization of collagen in EC space

• alkaline phosphatase involved in mineralization

When an osteoblast is trapped in bone matrix what does it become

osteocyte (maintains bone)

What is an osteoclast

breaks down bone

What is the passage to an osteoclast

heatopeitic stem cell —> preosteoclast —> osteoclast

Where is the osteoblast located and what percent does it occupy of cells in the bone

• bone surface, closing cone of resorption canals

• 5%

Where is the osteocyte located and what percent does it occupy of cells in the bone

• lacunae and canaliculi of bone matrix

• 95%

Where is the osteoclast located and what percent does it occupy of cells in the bone

• bone surface, cutting cone of resorption canals

• 1%

What is intramembranous ossification

process of producing flat bones

intramembranous ossification steps

1. Blood supply increases

2. Mesenchymal cells become osteoblasts

3. Osteoblasts secrete osteoid

4. Osteoid calcifies/mineralizes

5. Trapped osteoblasts become osteocytes

6. Bone spicules join to form trabeculae

7. Periosteum and outer compact bone form

What is Endochondral Ossification

Hyaline cartilage forming

Endochondral Ossification steps

1. early cartilage model formation of

   primary

2. ossification center, bony collar, and periosteum formation

3. vascular invastion, formation of primary marrow cavity

4. enlarged appearance of primary marrow cavity

5. epiphyseal plate at distal end

6. closed epiphyseal plate at adult age

label each region on the far right (colors)

What factors influence mineralization?

• Collagen

• tumor necrosis factor

  • acute: promotes preosteoblast activity and collagen synthesis

  • chronic: inhibits mineralization and promotes bone resorption

• IGF1

• BMP’s

• parathyroid horomone ( intermitten = growth, too high= resorption)

• vitamin D3 (calcium and phosphate absorption)

What factors influence mineralization

• insulin

• estrogen (inhibits osteoclast, promotes osteoblast)

• alkaline phosphatase (marker of osteoblast activity, breaks down pyrophosphate permitting hydroxyapatite crystal growth)

which is the cutting cone and which is the closing cone

Cartilage is what

• solid, pliable connective tissue

• proteoglycans

• 60-80 water weight

What is the histogenesis (steps) to make cartilage

Mesenchymal cell → prechondrocyte → chondroblast → cartilage matrix → chondrocyte

What are the cartilage types

• hyaline

• elastic (pinnea of external ear)

• fibrocartilage

What is hyaline cartilage

• most abundant

• fetal skeletons, joints

• matrix is homogenous

What is hyaline cartilage and where are they located

• the matrix has elastic fibers

• larynx, epiglottis

What is fibrocartilage, where is it located

• resists compression

intervertebral disks articular discs of the TMJ

• No perichondrium (dense layer around most other cartilage)

What are the cartilage cell types and what are their functions/ purpose

• chondroblasts: secrete matrix that becomes cartilage

• chondrocytes: in cartilaginous matrix, found in lacunae

What type of collagen fibers are I, II, III, IV

What is the arrangement of collagen

What is Condylar Cartilage

• secondary cartilage

• part of TMJ (google)

• responsive to mechanical stimuli

*not part of epiphyseal growth plate, articular cartilage, Meckel’s cartilage (embryo)

What is osteoperosis

More osteoclasts than osteoblasts

What are the stages of healing in bone fractures

1. fracture then hematoma forms and inflammation

2. angiogenesis (blood vessels form in existing ones) + granulation tissue formation

3. soft callus forms - fibrocartilage

4. hard callus - woven bone

5. remodeling - lamellar bone

What are rickets

vitamin D deficiency in kids = poor mineralization

What are osteomalacia

adult version of rickets, linked to vitamin d deficiency

What is scurvy

vitamin C deficiency so bleeding gums, wound healing issues, collagen deficiency

What is arthritis

disease that affects joints, causes inflammation of articular cartilage, synovium, or surrounding bone