Bone Histology and Development Flashcards by Jing Ji

What do bone and cartilage have in common histologically?

they both have cells in lacunae

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What are the components of a long bone?

articlar cartilage on epiphysis

a shaft called the diaphysis

compact bone on outside

spongy/cancellous/trabecular bone on the inside (mostly the ends)

marow resides in the middle

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metaphysis

tapering ends of the diaphysis containing the epiphyseal plate

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Why are bones spongy on the inside?

they make the bone lighter

most bones are subject to bending forces, so most of the forces are exerted on the outside rather than the inside

the only force that the inside has to withstand is holding body weight

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What are the important histological features of bone?

osteons

Haversian canals

Volmann’s canals

Lacunae and canaliculi

Lamellae

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lamellae

circumferential, interstitial, and concentric

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osteon

the functional unit of a bone

alsoc alled a haversian system

consists of concentric plates (lamellae) of bone around a Haversian canal containing small blood vessels and nerves

checks microfractures and is often turned over

turned over all the time, old osteons turn into lamellae

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Haversian canal

tunnel in the middle of an osteon that contains nerves and blood vessels

also contains osteoblasts and osteoclasts

cross-connected by Volkmann’s canals

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trabecular (spongy) bone

forms from the interior of most bones

consists of a pathwork of bony spicules or trabeculae surrounded by marrow

trabeculae do not contain osteons unless they are thick, may or may not have lamellae

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layers of the periosteum

outer fibrous layer of dense connective tissue

inner osteogenic layer containing osteoprogenitor cells that become osteoblasts

endosteum that lines the inner surface of compact bone

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What is the function of canaliculi?

used for osteocyte communication and metabolic coupling

no capillaries present here

every osteocyte is touching their neighbros, communication with each other

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What are the three types of bone cells and what are their functions?

osteocytes - maintain bone in lacunae, always embedded in lacunae

osteoblasts - deposit bone on surfaces, always located on bone surfaces

osteoclasts - resorb bone, derived from blood-born monocytes

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What is the difference between an osteoclast and an osteocyte?

often a matter of location

osteocytes are found in lacunae

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What is the difference between active and inactive osteoblasts?

inactive osteoblasts are squamous on the bone surface

active osteoblasts are cuboidal on surfaces active in bone deposition

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What is the composition of bone?

>99% matrix

of that 30% is organic and 70% is mineral

most of the organic part is Type I collagen

cells are only 2%

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What is the role of glycoproteins and sialoproteins in bone?

help bind calcium during mineralization

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hydroxyapatite

a complex of calcium and phosphate, makes up 95% of the the inorganic mineral component of bone

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Describe the process of mineralization.

deposition of osteoid by osteoblasts

vesicle secretion in the matrix, contains alkaline phosphatase and pyrophosphatase, overall effect is to increase matrix calcium and phosphate concentrations, and crystals of CaPO₄ form

mineralization front, crystals bind to neighboring crystals to form hydroxyapatite

formation of true bone matrix

orchestrated by osteoblasts

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What happens when bones lose mineral content?

softe bones

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What happens to bone when it loses collagen?

brittle bones

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What is the process of bone remodeling and development?

involves the apposition and resporption of bone on surfaces

unlike cartilage, there is no interstitial growth

osteoblast deposit both the organic and mineral component of bone

deposit osteoid (the organic matix)

leave small vesicles in the osteoid that initiate mineralization at a mineralization front

Howship’s lacuna

a lacunae that lods osteoclasts, large multi-nucleated osteoclasts that resorb bone on surfaces

How is a new osteon formed?

occurs when osteoclasts lining a Haversian canal resorb bone to carve a tunnel the diameter of the new osteon, the cutting cone

this is followed by a closing cone fromd from osteoblasts depositing lamellae from the outside to the inside

the cutting cone is followed by the closing cone

the remnants of older, adjacent osteons become interstitial lamallae

bone is turned over completely every five years

What are the metabolic roles of the bone?

continual matrx turnover

balance between resorption and deposition

reservoir of calcium

What are the major regulators of bone growth and metablism?

calcitonin from thyroid parathyroid hormone estrogen vitamin D vitamin C vitamin A

What is the role of calcitonin from thyroid?

decreased serum calcium increased bone calcium secreted by parafollicular cells (C-cells) of thyroid gland

What is the role of parathyroid hormone in bone?

increased serum calcium decreased bone calcium stimulates osteocytes and osteoclasts to resorb bone to release calcium into the blood also reduces calcium excretion by kidneys and increases calcium absorption in the small intestine

What is the role of estrogen in bone development?

inhibits cytokines that promote osteoclast differentiation/activity

What is the role of vitamin D in bone development?

required for intestinal calcium absorption and bone matrix calcification

What is the role of vitamin C in bone development?

required for collagen synthesis and proper colalgen mineralization a deficiency leads to scurvy where the bone matrix cannot be calcified

What is the role of vitamin A in bone development?

promotes mineralization and endochondral bone growth in general a deficiency suppresses endochondral bone growth and results in fragile bones

What does bone develop from?

somite sclerotomes lateral plate mesoderm in somatopleure head mesenchyme from the neural crest

What are the two types of ossification?

endochrondral ossification intramembraneous ossification

endochrondral ossification

bone develops from a cartilage model most of the postcranial skeleton

intramembraneous ossification

bone develops directly from mesenchyme most of the skull (and clavicle)

What are the steps in the cartilage model of bone?

takes about 5 weeks 1) **formation of periosteal bone collar** when the perichondrium differentiates into periosteum, this is the first appearance of bone tissue around what will be the diaphysis 2) **appearance of primary center of ossification for diaphysis** - cartilage is _calcified, then replaced_ with bone tissue and marrow, spreads toward each end of the diaphysis 3) **secondary centers of ossification appear**

What are secondary centers of ossification?

centers that appear in epihyses these also calcify and remove cartilage and replace with trabecular bone this ossification spreads until the only remaining cartilage in the bond is the articular cartilage at the joints and and epiphyseal growth plate of cartilage between epiphysis and diaphysis

epiphyseal cartilage plate

a plate of cartilage between the epihysis and diaphysis called a growth plate because it is the only place where a bone can grow in length once this plate disappears, there will not be any more growth because bone can't grow by interstitial deposition

What is the pathophysiology of dwarfism and gigantism?

problems with proliferation of cartilage

What is the pathophysiology of Rickets?

vitamin D deficiency

What is the pathophysiology of osteomalacia?

decreased calcification

What is the pathophysiology of osteogenesis imperfecta?

brittle bones due to a higher ratio of bone mineral compared to collagen autosomal dominant trait with a rarer autosomal recessive form bones are deformed and fracture very easily ligaments are lax, the sclera of the eye is darker in color

What is the pathophysiology of scurvy?

vitamin C deficiency

Harris Lines

lines of arrested growth densities that mark periods where bones (and the body) stop growing from disease trauma result is a layer of higher density bone matrix

What is the difference between immature and mature bone?

all boen is first deposited as woven bone with collagen distributed randomly - most fetal bone is woven woven bone is replaced by lamellar bone - typically found in adult compact bone

What are the defining features of immature woven bone?

colalgen fibers are arranged in a random orientation in fetal bone

What is the defining feature of mature lamellar bone?

collagen fibers are arranged in concentric or parallel sheets to form lamellae and osteons after birth

Describe the development of cranial bone formation.

most of the neurocranium (brain case) and viscerocranium (facial skeleton) are from intramembraneous ossification the cranial base (bottom of the neurocranium) is from endochondral ossification

yellow vs. red marrow

**yellow marrow** - contains mostly fat and located at the center of the diaphysis **red marrow** - hemopoietic marrow at the epiphyses

components of synovial joints

where bones articulate for movement, contains: **articular (hyaline) cartilage** where the bones meet **fibrous joint capsule**, a continuation of the periosteum from one bone to th eother which tightly surrounds a synovial joint cavity **synovial membrane**, the inner lining of the fibrous joint capsule, produces a thin film of synovial fluid which lubricates the articular surfaces