BMI03 - Histology of Bone

What are the main 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 found?

Cancellous bone is found 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 spicules in bone?

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

What are trabeculae in bone?

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 done to prepare decalcified bone sections?

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

What do decalcified bone sections show?

Decalcified bone sections show soft tissues in and around the bone.

Why is decalcified bone eosinophilic with H/E stain?

Decalcified bone stains eosinophilic because of collagen type I fibers in the matrix.

How are ground bone sections prepared?

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

What happens to soft tissues in ground bone sections?

Soft tissues are destroyed during the grinding process.

What remains visible in ground bone sections?

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

What remains in undecalcified ground bone sections?

Hydroxyapatite mineral remains present in ground bone sections.

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

Ground bone sections are not stained.

What are canaliculi?

Canaliculi are tiny channels in bone matrix that contain osteocyte processes and allow nutrient and waste exchange.

What is the composition of calcified bone matrix?

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

What mineral is most abundant 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 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 trapped in matrix?

Trapped osteoblasts become osteocytes.

What are lacunae?

Lacunae are small cavities in bone matrix that house osteocytes.

Why are canaliculi necessary in bone?

Canaliculi allow transfer of nutrients, hormones, and waste because calcified matrix blocks direct diffusion.

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 organic and inorganic components of bone matrix.

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 surrounded by mineralized bone matrix in lacunae.

What is the function of osteocytes?

Osteocytes maintain bone tissue.

Where are osteocyte cytoplasmic processes located?

Osteocyte processes extend through canaliculi.

How does immature bone differ from mature bone?

Immature bone has 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.

Where are osteoclasts located?

Osteoclasts are located on the surface of bone.

What are Howship’s lacunae?

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

What is the function of osteoclasts?

Osteoclasts resorb and remodel bone.

What are the four regions of an osteoclast?

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

What is found in the basal zone of osteoclasts?

The basal zone contains nuclei and organelles.

What is the ruffled border of osteoclasts?

The ruffled border contains finger-like processes involved in active bone resorption.

What is the subosteoclastic compartment?

The subosteoclastic compartment is the area beneath the ruffled border where bone resorption occurs.

What do proton pumps in osteoclasts do?

Proton pumps secrete hydrogen ions into the subosteoclastic compartment.

What is the role of aquaporins and chloride channels in osteoclasts?

They transport water and chloride ions to form concentrated HCl that decalcifies bone.

What do osteoclast enzymes do?

Osteoclast enzymes degrade organic bone matrix.

How are degradation products handled by osteoclasts?

Degradation products are endocytosed and reused or exocytosed into extracellular space and blood.

What is the function of the vesicular zone of osteoclasts?

The vesicular zone transports materials into and out of the subosteoclastic compartment.

What is the function of the clear zone of osteoclasts?

The clear zone seals the osteoclast to bone and isolates the resorption compartment.

What are osteons also called?

Osteons are also called Haversian systems.

What composes compact bone?

Compact bone is composed of circular lamellae arranged into osteons.

What is the center of an osteon called?

The center of an osteon is the Haversian canal.

What composes spongy bone?

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

Does spongy bone have a regular arrangement?

No, spongy bone has no regular arrangement.

What surrounds bone marrow?

Spongy bone surrounds bone marrow.

What covers the external surface of bone?

The periosteum covers the external surface of bone.

What is the periosteum composed of?

The periosteum has an outer fibrous layer rich in collagen and fibroblasts.

How is the periosteum attached to bone?

The periosteum is attached by Sharpey’s fibers.

What are Sharpey’s fibers?

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

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 lie between compact and spongy bone.

What lines the inner circumferential lamellae?

The endosteum lines the inner circumferential lamellae.

What are outer circumferential lamellae?

Outer circumferential lamellae circle the perimeter of bone.

What are interstitial lamellae?

Interstitial lamellae are irregular pieces of bone located between osteons.

What are lamellae?

Lamellae are circular layers of mineralized bone matrix.

What is found in lacunae of osteons?

Lacunae contain osteocytes.

What do canaliculi contain?

Canaliculi contain osteocyte cytoplasmic extensions.

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 and external blood supply.

How are Volkmann’s canals oriented?

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

What does the periosteum connect bone to?

The periosteum connects bone to tendons and ligaments.

What is the endosteum?

The endosteum is loose connective tissue lining internal bone surfaces.

Which surfaces are lined by endosteum?

Haversian canals, Volkmann’s canals, inner circumferential lamellae, and spongy bone spicules are lined by endosteum.

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?

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?

Maxilla, mandible, alveolar bone, flat bones of the face and skull, and clavicles form this way.

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.

Do cartilage cells become bone cells during endochondral ossification?

No, cartilage is replaced by bone rather than transformed into bone.

What type of tissue is replaced in both ossification methods?

Both methods replace pre-existing connective tissue.

Where does intramembranous ossification occur?

Intramembranous ossification occurs within vascularized mesenchyme.

What initiates intramembranous ossification?

Mesenchymal cells differentiate into osteoblasts.

What do osteoblasts secrete during intramembranous ossification?

Osteoblasts secrete osteoid.

What happens to osteoblasts during intramembranous ossification?

Osteoblasts become trapped and differentiate into osteocytes.

What role do osteoclasts play in intramembranous ossification?

Osteoclasts remodel and shape growing bone.

When does alveolar bone formation begin?

Alveolar bone formation begins during week 8 of development.