BMI03 - Histology of Bone

What are the major functions of bone?

Bone functions include support, protection, mineral storage, and hemopoiesis.

What is cancellous bone also called?

Cancellous bone is also called spongy bone or medullary bone.

Where is cancellous bone located?

Cancellous bone is located inside the epiphyses (heads) of long bones.

What surrounds cancellous bone?

Cancellous bone is always surrounded by compact bone.

What is the structure of cancellous bone?

Cancellous bone contains large open marrow spaces surrounded by thin plates of bone.

What are marrow spaces?

Marrow spaces are the large open spaces found within cancellous bone.

What are spicules?

Spicules are small thin plates of bone found in cancellous bone.

What are trabeculae?

Trabeculae are larger thin plates of bone found in cancellous bone.

What is compact bone also called?

Compact bone is also called cortical bone.

How does compact bone compare to cancellous bone?

Compact bone is much denser than cancellous bone.

What are the two histological forms of bone tissue?

Bone tissue may be woven (primary, immature) or lamellar (secondary, mature).

What is woven bone?

Woven bone is immature primary bone with less organized collagen fibers.

What is lamellar bone?

Lamellar bone is mature secondary bone with organized collagen fibers.

How are decalcified bone sections prepared?

Bone tissue is soaked in dilute acid or EDTA until hydroxyapatite crystals dissolve.

What do decalcified bone sections show?

Decalcified sections show all soft tissues in and around bone.

Why does decalcified bone stain eosinophilic with H/E?

Decalcified bone stains eosinophilic because of abundant type I collagen fibers.

How are ground bone sections prepared?

A dried chip of bone is attached to a backing and ground into a thin section.

What happens to soft tissues during the grinding process?

Soft tissues do not survive the grinding process.

What remains visible in ground bone sections?

The spaces previously occupied by cells and blood vessels remain visible.

What component of bone remains in ground bone sections?

Hydroxyapatite mineral remains in ground bone sections.

Why are ground bone sections gray, black, or brown?

Ground bone sections are not stained.

What is the composition of calcified bone matrix?

Calcified bone matrix is approximately 50% minerals and 50% organic matter with bound water.

What is the primary mineral in bone matrix?

Calcium hydroxyapatite is the major mineral in bone matrix.

What are the major organic components of bone matrix?

Type I collagen, sulfated GAGs, proteoglycans, and glycoproteins are major organic components.

Why is bone one of the hardest substances in the body?

Bone hardness results from collagen matrix calcified with calcium hydroxyapatite crystals.

What minerals are stored in bone?

Bone stores calcium, phosphate, and other inorganic ions.

Why is bone considered metabolically dynamic?

Bone continuously gains and loses inorganic ions to maintain calcium and phosphate homeostasis.

Which cells produce bone matrix?

Osteoblasts produce bone matrix.

What happens to osteoblasts after they become surrounded by matrix?

Osteoblasts become trapped and differentiate into osteocytes.

What are lacunae?

Lacunae are small cavities in bone matrix that contain osteocytes.

Why are canaliculi necessary in bone?

Canaliculi allow nutrient, hormone, and waste exchange because calcified matrix prevents diffusion.

What are canaliculi?

Canaliculi are tiny channels in bone matrix containing osteocyte processes bathed in interstitial fluid.

What is the shape of osteoblasts?

Osteoblasts are cuboidal in shape.

How many nuclei do osteoblasts have?

Osteoblasts are mononuclear.

How do osteoblasts stain with H/E?

Osteoblasts are basophilic with H/E stain.

Where are osteoblasts located?

Osteoblasts are always located on the surface of bone.

What is the function of osteoblasts?

Osteoblasts secrete both organic and inorganic components of bone matrix.

What organic materials do osteoblasts produce?

Osteoblasts produce type I collagen and bone proteins.

What inorganic material do osteoblasts produce?

Osteoblasts produce hydroxyapatite mineral.

What is osteoid?

Osteoid is unmineralized organic bone matrix.

Where is osteoid located?

Osteoid is located between osteoblasts and mineralized bone matrix.

What is the shape of osteocytes?

Osteocytes are squamous in shape.

How many nuclei do osteocytes have?

Osteocytes are mononuclear.

Where are osteocytes located?

Osteocytes are embedded within mineralized bone matrix.

What space do osteocytes occupy?

Osteocytes occupy spaces called lacunae.

Where are osteocyte cytoplasmic processes located?

Osteocyte processes extend through canaliculi.

What is the function of osteocytes?

Osteocytes maintain bone tissue.

How does immature bone differ from mature bone?

Immature bone contains more numerous, larger, more ovoid osteocytes and less organized collagen fibers.

What is another name for immature bone?

Immature bone is also called primary or woven bone.

What is the shape of osteoclasts?

Osteoclasts are large and round.

How many nuclei do osteoclasts have?

Osteoclasts are multinucleated.

How do osteoclasts stain with H/E?

Osteoclasts are acidophilic with H/E stain.

Where are osteoclasts located?

Osteoclasts are always located on the surface of bone.

What is the function of osteoclasts?

Osteoclasts resorb and remodel bone.

What are Howship’s lacunae?

Howship’s lacunae are depressions in bone where osteoclasts actively resorb bone.

What are the four regions of an osteoclast?

The four regions are the basal zone, ruffled border, vesicular zone, and clear zone.

What is compact bone composed of?

Compact bone is composed of circular lamellae organized into osteons or Haversian systems.

What is an osteon?

An osteon is a circular arrangement of lamellae surrounding a central Haversian canal.

What are lamellae?

Lamellae are circular layers of mineralized bone matrix.

What is found between lamellae?

Lacunae containing osteocytes are found between lamellae.

What do canaliculi contain?

Canaliculi contain cytoplasmic extensions of osteocytes.

What is located at the center of each osteon?

The Haversian canal is located at the center of each osteon.

What structures are found in Haversian canals?

Haversian canals contain blood vessels, lymphatic vessels, and nerves.

How are Haversian canals oriented?

Haversian canals run parallel to the long axis of the osteon and bone.

What are Volkmann’s canals?

Volkmann’s canals are vascular channels connecting osteons to each other and to the external blood supply.

How are Volkmann’s canals oriented?

Volkmann’s canals run perpendicular to the long axis of bone.

What is spongy bone also called?

Spongy bone is also called cancellous, trabecular, or medullary bone.

What is spongy bone composed of?

Spongy bone is composed of thin plates called bone spicules or trabeculae.

Does spongy bone have a regular arrangement?

No, spongy bone does not have a regular arrangement.

What does spongy bone surround?

Spongy bone surrounds bone marrow.

What covers the external surface of bone?

The periosteum covers the external surface of bone.

What type of connective tissue is the periosteum?

The periosteum is dense irregular connective tissue.

What composes the outer fibrous layer of the periosteum?

The outer fibrous layer contains mainly collagen fibers and fibroblasts.

How is the periosteum attached to bone?

The periosteum is attached to bone by Sharpey’s fibers.

What are Sharpey’s fibers?

Sharpey’s fibers are collagen bundles trapped in calcified bone during ossification.

What structures does the periosteum connect bone to?

The periosteum connects bone to tendons and ligaments.

How do blood vessels enter bone from the periosteum?

Blood vessels enter through nutrient canals and Volkmann’s canals.

What are inner circumferential lamellae?

Inner circumferential lamellae are lamellae located between compact and spongy bone.

What are outer circumferential lamellae?

Outer circumferential lamellae circle the outer perimeter of bone.

What are interstitial lamellae?

Interstitial lamellae are irregular bone fragments located between osteons.

What is the endosteum?

The endosteum is loose connective tissue lining the internal surfaces of bone.

Which surfaces are lined by endosteum?

The endosteum lines Haversian canals, Volkmann’s canals, inner circumferential lamellae, and spongy bone spicules.

Where are osteoprogenitor cells found?

Osteoprogenitor cells are found in the endosteum as bone lining cells.

What is osteogenesis?

Osteogenesis is the process of bone formation or ossification.

What are the two methods of bone formation?

Bone forms by intramembranous ossification and endochondral ossification.

What is intramembranous ossification?

Intramembranous ossification is bone formation directly from mesenchyme.

What is mesenchyme?

Mesenchyme is embryonic connective tissue containing pluripotent mesenchymal cells.

Which bones form by intramembranous ossification?

The maxilla, mandible, alveolar bone, flat bones of the face and skull, and clavicles form by intramembranous ossification.

What is endochondral ossification?

Endochondral ossification is bone formation from a hyaline cartilage model.

Which bones form by endochondral ossification?

Long bones and the base of the skull form by endochondral ossification.

What tissue is replaced during intramembranous ossification?

Bone replaces mesenchyme during intramembranous ossification.

What tissue is replaced during endochondral ossification?

Bone replaces hyaline cartilage during endochondral ossification.

Do both ossification methods produce the same type of bone tissue?

Yes, both methods produce bone with the same histological structure.

Where does intramembranous ossification occur?

Intramembranous ossification occurs within vascularized mesenchyme.

What initiates intramembranous ossification?

Mesenchymal cells differentiate into osteoblasts.

What do osteoblasts produce during intramembranous ossification?

Osteoblasts secrete osteoid and form spicules and trabeculae.

What happens to osteoblasts after secreting matrix in intramembranous ossification?

Osteoblasts become trapped and differentiate into osteocytes.

What role do osteoclasts play during intramembranous ossification?

Osteoclasts remodel and shape growing bone.

How do trabeculae change during intramembranous ossification?

Trabeculae enlarge and interconnect as more bone forms.

When does alveolar bone formation begin?

Alveolar bone formation begins during week 8 of development.