BONE

Bone tissue caracteristics and overview

Bone tissue is highly vascular specialized ct with a mineralized matrix.

It is a very metabolically active tissue and dynamic as it is contantly remodeling

It function other then support and movement are hemapoietic ( red bone marrow) of triglycerids storage ( yellow) of mineral homeostasisi of calcium and phopate and also endocrine as it secretes the hormon FGF23 and osteoclacin

What are the functions of bone tissue and what hormons does it secrete?

1. Support and movement skeleton

2. Hemapoietic

3. Trig. Storage in the yellow bone marrow

4. Minerals homeostasis of phophate and calcium

5. Hormons: osteocalcin and fgf23

Which are the bone cells?

Where are the progenitor cells located?

Osteoprogenitors are in the periosteum and endosteum ( non fuori) stem cells

Osteblasts that start the process of mineralization and as they are trapped into lacune mature into osteocytes

Osteocytes ihibit ostoblast produce SCLEROSTIN

Descibe the steps of embryological formation of the bone

Which bone do not deirve from the mesenchyme?

1. DERIVE FROM THE MESENCHYME except for some cranial muscles that derive from NCC

2. From the mesenchynme there are two ways 1. Direct and is INTRAMEMBRANOUS so cells differentiate into osteoprogenitor, blast, cyte

3. Or thorugh cartilage(hylain) and endochondrial ossificifation with intertitial growth and isogenous groups-

Whihc are the 2 factors for bone formation

1. BMP for bone formation

2. RUNX2 osteoblast differentiation

For what doe sthe axial skeleton derive? From what the appendicular? Which are the growth plate zones

Axial is prom the paraxial mesoderm

Appen. From the LATERAL PLATE

Growth plate zones: 1.resiting 2, proliferation 3. Hypertrophy 4. Caclification 4. Ossification-

The bone ecm overview

What is the osteoid? What does it contain?

What is the inorganic?

Inorganic which isa 70% of the matrix from vescicle of the ostoblast we have pHOPHATE AND CALCIUM and also giving the rigidity to the matrix HYRDOXYAPATITE CRYSTALS.

ORGANIC 30% is also called OSTEOID matrix: ground substance of gag and proteoglycans and COLLAGEN I fibers and for glycoproteins: OSTEONECTIN,

OSTEOCALCIN ( PROTEIN) that helps link the collagen to the hyrdoxapataites cristals and it is a hormon produced by bone that also stimulates insulin production, promotes energy use in muscle and supp. Brain development

AND OSTEOPONTIN

Osteocalcin hormon

OSTEOCALCIN ( PROTEIN) that helps link the collagen to the hyrdoxapataites cristals and it is a hormon produced by bone that also stimulates insulin production, promotes energy use in muscle and supp. Brain development

What can i find inside osteoid

Osteoi is the organic matrix 30%

Gag, proetoglycans

Collagn I

Osteocalcin hormon that also links the collagen to the hyrd. Cristals

Osteopontin that link the matrix organic to th e minerals

Osteonectin

Which is the unit of the bone

Thorugh what are they connected

The unit of bone is osteon

The nerves and vessels are in the haversian canal

Osteon are connected thorugh the VOLKMANN canals

In compact bone where are ostocytes and how are they connected

Osteocytes are in LACUNE AND ARE CONNECTED WITH CANALICULES!!!

What are the differences between compact and spongy bones?

Compact: rapresent 80% ofthe sketal mass

STERNGHT AND RESILIENCE

Dense external layer

Osteocytes are in lacune and connected throughcanalicules

Spongy or cancellous

Internal lattice of trabeculae

Inthis internal lattice trabeculae are aligned along stress lines and there are MARROW spaces

The lattice and trabeculae disposition is to allow to distribute the force in more directions

Bone classification

1., long bones for movement and suppoort es. Tiubia

2. Short bones as carpal for stability

3. Flat to protect organs cranium

4. Irregular as vertebres

Microanatomy of a long bones

Which are the 4 parts in a bone?

The longitudinal growth of lond bones is due to?

Lognitudinal growth is due to the EPIPHYSIl growth plate that is a region of hyaline cartilage that allow the longitudinal growth of lonfd bones fro endochondrial ossification

1.epiphysis: spongy bone inside with an outer layer of compoast bone

2. Metaphysis epiphysial growth plane

3. Diahisi: compact bone surrounds the medullary cavity

4. In the outer surface: periosteum excpet in articular surfaces ( come il perichondrium non ce nell aarticular cartilage)

What can i find in the metaphys of a long bone

There the ephyphysial growth plane

Hyaline cartilage

After the longitanal growth is done with endochondrial ossification it reamin only the epihysial line

What can i find in the outer layer of bone

The periosteum which is not present in articular surfaces

Outer fibrous layer with DENSE IRREGULAR CT ( COLLAGEN I, FIBROBLAST AND VESSEL)

Inner osteogenic layer with progenic cells and osteoblasts

( uguale al perichorndry)

What fibers attach the bone to the periosteum

Sharpey fibers

The complete microanatomy of the compact bone

In one direction

1. The unit is osteon: concentric lamallae around the haversian canal

2. The haversial canals are connected through the WOLKKMAN CANAL

   1. In the osteon which are concentric lamellae, between the lamelle there are the LACUNE where osteocyetes are located

   2. Lacune for diffusion and signals communicate with weach other thorigh CANALICULI

MICRO ANATOMY OF A SPONGY BONE

IN EPIPHYSIS

It is for having force in multiple direction

Lattick of TRABECULAE that are aligned along stress lines and marrow spaces.

Trabacules are still osteocytes in lacune but they are coveted with ENDOSTEUM

The nutrients directly diffuse from the bone marrow

What are trabaculea

Trabeculae in spongy bone are osteocytes in lacune covered by ENDOSTEUM which is a aocnnective tissue with osteoporosis progenitor cells and osteoblasts and osteoclast!!!

How are the different shapes of the bone cells and where are they found

1. Osteoprogenitor cells are found in the PERIOSTEUM AND ENDOSTEUM they are spindle shaped ( STEM CELLS FROM THE MESENCHYME)

2. Differentiate into OSTEOBLAST

Osteoblast start mineralization process and procduce collagen and other ecm components as tehya re trapped into lacune thery diff. In ostocytes with RUNx2

Ostobelast appear: ABBUNDANT RED ( BASOPHILIC) AND CUBOIDAL

3. Ostocytes are in lacune between lacune they communicate thorugh canaliculi

4. Osteocytes MNATIN THE MATRIX and produce SCELROSTIN

Osteocytes appear FLAT ( SCHIACCIATI TRA LE LACUNE)

Which cell are cuboidal, which cells are flat

FLAT as they are in lacune: ostoecytes

CUBOIDAL: OSTEOBLAST

Describe osteoclast

Structure

Lineage

Function

Where in the cells are most common to be found

Osteoclast are very LARGE CELLS ( infatti sono prsaticamente die macrophagy)

They derive from the MONOCYTES

They are more in the surface of the bone as they have to reasborbed t

They are found in HOLLOSHIP lacunae!!!!

They degaradate collage, degaradate hyrdoxyapatattite cristals

Where are ostoclast located

In HOLLOWSHIP LACUANES

BASED ON COLLAGEN organization how can you differentate bones?

Based on collagen: LAMELLAR BONES WHERE COLLAGEN ARE IN PARALLEL LINES VERY ORGANIZED BUT WITH LOW CELLULARITY from higher resistance

Non lamellar: embryo bone with many osteocytes so high cellularity but not organized collagen which is more fragile

Describe the osteoid in detail

The osteoid is the PLAE UNMINERALIZED PART OF BONES

It is the organic part made of collage I in the majority

And with glycoprotein, gag and proteoglicans

Glycoprotein presents are 1. Ostopontin

2. Osteonectin which connects collagen to hydrox. Cristals

3. And osteocalcin osteocalcin inthe bone serves to connect the organic matrix to the minerals but outside it acts as an organ stimulating insulin, energy use in muscle and also brain develoopmenet! It is vtamin K dependednt

How does the minearliazation of the inorganic matrix work?

From osteoblast ALKALINE PHOPATASES is released from vescile increasing local phophate concentrations

This leads to cristal formation that are deposited around the colagen for stifess

Osteogenesis which are the tree options

1. Intermembraneous so directly from mesenchyme aas FLAT BONE OF SKULL, MANDIBLE AND CLAVICLE

2. From ncc other boned of the skull

3. All the rest especially long bones from endocondrial oss.

How does interm. Ossification appear?

What are spicules and what do they form by fusion

This is directly from the mesenchyme as for the flat bone of skull the mandible and the clavicle

Differentiation from osteo prog. Cell intoostobats and osteocyte with BMP and RUNx2

As the ecm is secreted by osteoblast a. Some remain trapped and become ostocytes in lacune

2. Other from the spicules fusion form trabeuculae and the blood vessels trapped inside the trabeculae then lead to bone marrow formation

3. Intermembraneous so appears highly cellular, irregular due to spicules of bones around the osteoblast

4. The spicules arond the osteoblast when fuse form trabeculeae

Describe in detail the endochondrial ossification

1. First hyaline cartilage surround by perichrondrium there is intertitial growth of hyaline cartialge

2. Condrocytes enarlge and become HYPERTROPHIC they start secreting alkaline phophates

3. The phophate concentration leads to CALCIFICATION of cartilage and the condroycites die

4. BLOOD VESSELS INVADE THE CALACIFIED MATRIX WITH HEMAPOIETIC AND OSTOPROG. CELS

5. The center of the dipahisis becomes the first ossification center

6. The medullary cavity enlarges execpt for the epiphesis and this is the second oss. Center

After ossification what remains of the cartialge?

1. Articular ( this is why it does not have perichornrium)

2. Epipheyisal growth plate that then in tthe complete bone remains the epihysisial line

Which are the 5 histological zones of the epiphysial growth plane

This allow sthe long. Growth of the lond bones

5 zone

1. RESTSITING ( INACTIVE CONDORCYTES)

2. PROLIFERATIVE ( confdrocyte proliferate )

3. 3. Hyperptrophyic ENELARGE AND SECRETE ALKALAINE PHOPHATES

4. CALCIFICATION

Increase in phophate leads to the calcification of the matix so condrocytes die and the matrix calcifies

5. OSFFICATION ZONE

BLOOD VESSELS, HEMAPOITEIC AND OSTEOPROG, CELLS invade there is there ossification

Bone remodeling and calcium homoestasis

Osteoclast when they reabsorb bone they activate also osteocblast

Ostoebalst so deposit new organic matrix and also

Produce RANKL bind to RANK which activates OSTOECLAST

Osteoblast also produce OPG WHICH INHIBITS OSTECLAST S

THERE HAS TO BE A ABALCNE BWTEEN RTKL AND OPC

Why does osteoporosis is more common in menapause

There is a decrease in calcium cabsorbtion and in estrogen estrogens normally inhibit ostoclasts

Which hormon promotes osteoclast

Paratyroid it promotoes osteoclast in oder to increase calcemia ( calcium in blood not in bone)

Osteoblast produec… to activate osteoclast and….. to inhibit them

RANKL THAT BIND TO RANK TO ACTIVATE THM

OPG TO INHIBIT THEM