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Musculoskeletal System > Bone 1 > Flashcards

Bone 1 Flashcards

1
Q

What are bones?

A
  • specialized connective tissue composed of cells and calcified extracellular matrix (ECM)
  • The cells and calcified ECM form a rigid organ
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2
Q

What is the function of bones?

A
  • Hematopoiesis= the formation of blood cells from hematopoietic stem cells found in the bone marrow
  • Lipid & mineral storage= bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals
  • Support= bone forms scaffolding for skeletal muscle and other soft tissues, it creates a framework that gives the general shape of the body
  • Protection= particularly the axial skeleton which surrounds the major organs of the body
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3
Q

What are components of bone?

A
  1. Extracellular matrix

2. Cells of bone tissues

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4
Q

Describe the extracellular matrix bone

A

Refers to the molecules that provide biochemical and structural support to the cells that populate bone

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5
Q

Describe the organic portion of ECM in bone

A

-Organic portion is predominantly (90% of total weight of matrix proteins) composed of collagen one proteins
-Mainly type 1 collagen (also type V, III, XI, XIII)
-Non-collagenous proteins (about 10%) constitute the ground substance and include proteoglycans, glycoproteins, bone specific proteins, growth factors and cytokines
Essential to bone development, growth, remodel8ng, and repair

Both collagen and ground substance become mineralized to form bone tissue

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6
Q

Describe the inorganic portion of ECM in bone

A

Represents about 50% of the dry weight of the matrix and is composed mainly of calcium phosphate in the form of hydroxyapatite crystals
-Contains trace minerals such as bicarbonate, citrate, magnesium, potassium and sodium

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7
Q

Describe the cells that are components of bone

A

-Osteoprogenitor(osteogenetic): the stem cells of bone, they are derived from primitive mesenchymal cells
Forms a population of stem cells that can differentiate into osteoblasts which secrete the organic unmineralized matrix or osteoid

  • Osteoblasts: synthesize uncalcified/unmineralized extracellular matrix called osteoid. This will later become calcified/mineralized to form bone.
  • Osteocytes: As the osteoid mineralizes, the osteoblasts become entombed between lamellae in lacunae where they mature into osteocytes. They then monitor the minerals and proteins to regulate/maintain bone mass

-Osteoclasts: Multinucleated giant cells derived from monocyte progenitor cells responsible for resorbing and remodeling bone by releasing H+ ions and lysosomalenzymes
The balance of osteoblast to osteoclast activity is crucial in the maintenance of the tissue’s structural integrity. It also plays a role in conditions such as osteoporosis

Bone-lining cells: found on the inner and outer surface of bone; the endosteum & periosteum

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8
Q

What is the function of osteoclasts?

A

Functions in resorption, the breakdown of bone matrix

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9
Q

Describe osteocytes formation

A

Osteoggenic cell develops into an osteoblast

Osteoblast forms bone matrix and develops into osteocytes

Osteocyte maintains bone tissue

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10
Q

What are osteoblasts?

A

Cuboidal cells located on the periphery of bone. Displays euchromatic nuclei with a basophilic cytoplasm

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11
Q

What are osteocytes?

A

Mature osteocytes: mature osteoblasts entrapped in bones matrix

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12
Q

What are osteoclasts?

A

Large, multinucleated macrophages located along the endosteum

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13
Q

What are the shape and location of osteogenic cells?

A
  • Are spindle shaped connective tissue cells (derived from embryonic mesenchyme stem cells) in the periosteum and endosteum that can differentiate into osteoblasts
  • In mature bone in which there is no active new bone formation or remodeling, the osteoprogenitor cells become flattened spindle shaped cells closely applied to the bone surface, when they are sometimes called “inactive osteoblasts”
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14
Q

What are osteoblasts derived from?

A

Osteoprogenator cells; are basophilic

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15
Q

What are the shapes of osteoblasts?

A

Morphologically May appear as a cuboidal layer(high secreting activity) or flattened (declining secretions)

Cytoplasmic processes contact them with other osteoblasts and osteocytes

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16
Q

Describe the significant chemical composition and secretions of osteoblasts

A
  • During synthesis osteoblasts have well developed rER and Golgi apparatus
  • PAS positive granules in the cytoplasm are most likely the precursors of glycosaminoglycans (of the osteoid matrix)
  • Eventually matrix secretion entraps the osteoblast in a lacunae with it’s cytoplasmic processes extending into canaliculi
  • Can secrete osteoclast stimulating factor
    • Osteoclast eventually ceases its secretory function, undergoes changes to its morphology and becomes an osteocyte
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17
Q

Explain the structure-function of osteocytes

A
  • Mature bone cells, derived from osteoblasts
  • Housed in their own lacunae, maintain communication and exchange nutrients and metabolites via gap junctions between their narrow cytoplasmic processes (filopodia) extending through the canaculi
  • Increased amounts of condensed nuclear chromatin, reduced amounts of rER, and a smaller Golgi apparatus vs osteoblasts
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18
Q

Describe ground bone preparations

A
  • Bone samples are ground to near translucency using mechanical attrition
  • No organic components of bone remain after grinding
  • The tissue is then impregnated with Indian ink
19
Q

Describe the structure function of osteoclasts

A

Multinucleated giant cells (up to 50 nuclei) resulting from the fusion of hematopoietic monocyte progenitor cells

  • Howship’s lacunae (resorption bay) are depressions on the bone surface that house osteoclasts
  • These lacunae result from the osteolytic activities of osteoclasts
20
Q

What are the 3 distinct regions of osteoclasts?

A
  1. Ruffled border
  2. Clear zone
  3. Basal region
21
Q

What are the ruffle border for osteoclasts?

A

Finger-like evaginations along Howship’s lacunae depict sites of active bone resorption

22
Q

What is the clear zone of osteoclasts?

A

Region of cytoplasm that surrounds the ruffled border

-Microfilaments, anchor osteoclast to the bone surface and help isolate osteoclastic activity

23
Q

What is the. Basal region of the osteoclasts?

A

Houses the organelles and numerous nuclei of the cell

24
Q

How do osteoclasts undertake bone resorption?

A 
Lysosomal enzymes(From Golgi complex) and hydrogen ions released into the confined space betweeen bone matrix and the osteoclast’s peripheral clear zone
   -Acidic environment provides optimal pH for activity of lysosomal hydrolases and facilitates the dissolution of calcium phosphate from bone

Decalcalcified bone matrix is then broken down by acid hydrolases, collagenous and proteolytic enzymes and the cell resorbs the organic and inorganic

25
Q

What are the bone-lining cells?

A
  • Osteoblast derived flat cells with little cytoplasm and scant organelles
  • Found on the outer (periosteal cells) and inner (endosteal cells) surface of non-remodeling bone
  • Function in maintenance and nutritional support of underlying cells
  • Regulate movement of phosphate and calcium into and out of bone
26
Q

What is the significance of the periosteum and endosteum ?

A

-Nom-calcified connective tissue layers covering external & internal surfaces of bone, except over Articular surfaces

27
Q

Where is the periosteum?

A

-Attached to the outer circumferential lamellae by Sharpey’s fibers (type 1 collagen)

28
Q

Describe the layers of the periosteum

A
  • Outer fibrous layers: consists mostly of a dense irregular connective tissue with fibroblasts. Contains blood vessels and nociceptors
  • Inner cellular/ osteogenic layer: contains osteoprogenitor cells and their derivatives (periosteal cells)
  • cells actively secreting matrix increase the width of bone (appositional growth)
29
Q

Where is endosteum contained?

A

-Lines any space or cavity in bone

(Marrow spaces, Haversian canals, volkmann’s canal, lacunae and canaculi)

30
Q

What is contained in the endosteum?

A

-It contains mesenchymal stem cells which have the potential to differentiate into osteogenic progenitor cells and differentiated osteoblasts, fibroblasts, blood vessels, and sympathetic nerves

Contains osteoclasts (bone remodeling occurs from within)

31
Q

Summarize bone growth and remodeling

A

Elongation of bones is a result of interstitial growth of cartilage at epiphyseal growth plate
-Interstitial (internal)growth doesn’t occur in bone

Bone increases in width by apossitional growth (osteprogenitor cells in the periosteum)

  • Remodeling of bone is a coordinated action between osteoblasts and osteoclasts
32
Q

What are the classifications of bones?

A
  1. Immature (primary or woven) bone
  2. Mature (secondary or lamellar) bone

3.

33
Q

Describe immature (primary or woven) bone

A
  • First compact bone elaborated; contains numerous osteocytes and irregular arranged collagen
  • low mineral content
  • remodeled and replaced by mature bone except in certain places such as in tooth sockets, near suture lines in the bones of the skull, and at insertion site of tendons
34
Q

Describe mature bones (secondary or lamellar) bone

A
  • Replaces primary bone and made up to Haversian systems, or osteons
  • Calcified matrix is arranged in regular concentric layers of lamellae (3 to 7 nm thick) surrounding a Haversian canal that transmits blood vessels, nerves and some loose connective tissue
  • Osteocytes in lacunae are located between the lamellae and occasionally within them
35
Q

Contrast gross structure of mature and immature bone

A

Immature- non-lamellar, no Haversian systems

Mature- lamellar, Haversian systems compact outside, spongy inside

36
Q

Contrast collagen fiber arrangement of immature & mature bone

A

Immature- random/disorganized

Mature- parallel, stress oriented (organized)

37
Q

Contrast osteocyte population density of immature and mature bone

A

Immature- high (many)

Mature- relatively low (few)

38
Q

Contrast constitution of immature and mature bone

A

Immature- low mineral density: high water content

Mature- high mineral density: low water content

39
Q

Contrast location of immature and mature bone

A

Immature- embryo, newborn, fracture callus, growth plate

Mature- develops from 1-month post natal

40
Q

What are the types of secondary (mature) bone?

A
  1. Compact bone- very dense and heavy
  2. Spongy (cancellous) bone
  • filled with spaces that are interconnected
    • In long space filled with red (containing hemopoietic cells) or yellow (containing primarily fat) bone marrow
41
Q

What are the characteristics of Haversian canal?

A

Functional unit= Haversian system or osteon
-cylindrical and composed of 4 to 20 concentric lamellae

Because bone is constantly being remodeled, the Haversian systems are NOT all uniform and in parallel array

  • Have numerous canaliculi that permit communication between lacunae and with the Haversian canals
  • Each lamellae consists of multiple parallel arrays of collagen fibers
  • adjacent lamellae, have alternating directions of collagen fibers providing great strength despite its light weight
42
Q

Describe the outer & inner circumferential lamellae of the compact bone

A
  • deep to the periosteum the lamellae are arranged in concentric rings- outer circumferential lamellae
  • Similar arrangement of lamellae can be found next to the endosteum-inner circumferential lamellae
  • interstitial lamellae are remnants of old remodeled osteons between newly laid down osteons
43
Q

Describe volksmann canal of the compact bone

A

Connect adjacent Haversian canals to each other and to endosteum at the marrow cavity on the inside and periosteum on the outside

Allow for passage of neurovascular urel through compact bone

44
Q

Where are inner and outer circumferential lamellae found?

A

These follow the entire inner and outer circumferences of the shaft of long bones

Both perforated by blood vessels and nerves as they access Volkmann’s canals and Haversian canals

OCL lined by periosteum

ICL lined by Endostium

Musculoskeletal System (41 decks)

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