Histology Exam 1: Bone Tissue

Front 1

Bones (General)

Back 1

The organs of the skeletal system, composed of bone tissue (a specialized form of connective tissue), cartilage, fibrous CT, adipose tissue, nerves, lymphatics, and blood vessels.

Front 2

Bone Tissue

Back 2

A specialized form of connective tissue containing (like all CT) cells and ECM. Bone is unique in that it contains mineralized ECM that produces extremely hard tissue.

Front 3

Functions of Bone

Back 3

Framework for the body (and support for soft tissues), Protection of internal organs, Locomotion (facilitates movement by providing leverage for muscle contraction), Mineral Storage (calcium and phosphorous are stored and mobilized when needed), Hematapoeisis (Blood cell-producing lines are stored in bone marrow), and Energy storage (in adipose tissue of the marrow).

Front 4

How are osteoblasts derived/what is their origin?

Back 4

Osteoblasts' precursor cells, osteoprogenitor cells, originally arise from mesenchymal stem cells. The first osteoblasts differentiate in the periosteum and form bone collar. They can also potentially originate in bone marrow.

Front 5

Periosteum

Back 5

CT lining the periphery of a bone.

Front 6

Endosteum

Back 6

CT lining the internal surfaces of a bone. In the long bone, it lines the medullary cavity. Like periosteum, it consists of two layers: a protective outer fibrous layer and an osteogenic layer.

Front 7

Where Are Osteoblasts Found?

Back 7

They are found in both the periosteum and endosteum of bone.

Front 8

Functions of Osteoblasts

Back 8

Synthesize and secrete collagen fibers and initiate the process of calcification.

Front 9

How are osteocytes derived/what is their origin?

Back 9

Osteocytes are of mesenchymal origin. They are terminally differentiated osteoblasts that have become trapped by matrix secretion.

Front 10

Functions of Osteocytes

Back 10

Responsible for maintaining the bone tissue, they are found in mature bone cells and no longer secrete matrix.

Front 11

Functions of Osteoclasts

Back 11

Digestion of bone matrix (osteolysis) in a process called bone resorption.

Front 12

Why do osteoclasts have many nuclei?

Back 12

They are derived from the fusion of many monocytes (WBC type).

Front 13

Where are osteoclasts found?

Back 13

They are concentrated in the endosteum.

Front 14

What is the ruffled border of the osteoclast?

Back 14

The ruffled border is folded plasma membrane on the side of the cell that faces the bone surface. Here the osteoclast secretes lysosomal hydrolases and hydrogen ions.

Front 15

Lysosomal Hydrolases (in osteoclasts)

Back 15

Digestive enzymes to digest bone matrix

Front 16

Why are hydrogen ions secreted from the ruffled border of osteoclasts?

Back 16

To create an acidic environment to eat away the ECM.

Front 17

Osteoid

Back 17

Unmineralized bone matrix containing fibers, glycoproteins, and proteoglycans.

Front 18

What are the components of the ECM of bone?

Back 18

Bone ECM is made up of ~1/3 organic and ~2/3 inorganic components. the organic components secreted by osteoblasts include collagen fibers, and non-collagenous matrix proteins

Front 19

What kinds of non-collagenous matrix proteins are found in bone?

Back 19

Proteoglycans, glycoproteins, bone-specific vitamin k-dependent proteins, and growth factors and cytokines.

Front 20

Describe the collagen fibers of the ECM of bone matrix.

Back 20

They are predominately Type 1 (with some of Type 5 and the other types). They function to provide bone with resilience and ability to resist stretching and twisting.

Front 21

What is the role of proteoglycans in the ECM of bone?

Back 21

They contribute to the compressive strength.

Front 22

What is the role of glycoproteins in the ECM of bone? Give two examples.

Back 22

They glue bone cells/fibers to mineralized ground substance. Osteopontin mediates bone cell to matrix attachment and osteonectin links collagen and bone minerals.

Front 23

Name one kind of bone-specific vitamin-K dependent protein in the ECM of bone and describe its function.

Back 23

Osteocalcin captures calcium from circulation for calcification. It attracts and stimulates osteoclasts for remodeling.

Front 24

What is the role of growth factors and cytokines in the ECM of bone? Give some examples of growth factors/cytokines found in the ECM of bone.

Back 24

Growth factors and cytokines in the ECM of bone are regulatory. Examples are insulin-like growth factor (IGF), tumor necrosis factor (TNF-alpha), transforming growth factor beta (TGF-beta), interleukins (IL-1, IL-6), and bone morphogenic proteins (BMP's).

Front 25

What are bone morphogenic proteins (BMP's) and what do they do in the ECM of bone?

Back 25

BMP's in the ECM of bone are unique growth factors that stimulate differentiation of mesenchymal cells into osteoblasts.

Front 26

What are the inorganic components of the ECM of bone?

Back 26

ECM of bone has two primary inorganic constituents, calcium phosphate and calcium hydroxide (together they interact to produce hydroxyapatite that is later crystallized). Bone also contains small amounts of magnesium, fluoride, and sodium. These minerals give bone its characteristic hardness and ability to resist compression.

Front 27

Hydroxyapatite crystals

Back 27

Crystals formed in the ECM of bone by the combination of calcium phosphate and calcium hydroxide. They are hard and resistant

Front 28

What are the two types of mature bone?

Back 28

Compact and cancellous.

Front 29

What is compact bone and what kind of stresses characterize its locations?

Back 29

An outer layer of solid and densely packed bone located where stresses are limited to one direction. It forms the diaphysis and is true Haversian bone. It provides a rigid "wall" to support the bone itself and the tissues of the body.

Front 30

What is cancellous bone and what kind of stresses characterize its locations?

Back 30

(aka Spongy or trabecular bone). An inner layer of bone with a honeycomb pattern located where stresses are weaker or multi-directional. It fills the epiphysis and forms a narrow rim around the medullary cavity.

Front 31

Describe the three important regions of the long bone.

Back 31

The epiphysis (two per bone: one proximal, one distal) are the dilated "ends" of the bone. The diaphysis is the tubular shaft of the bone. The metaphysis (two per bone: one proximal, one distal) is the transition zone between the epiphysis and diaphysis.

Front 32

What is found in the region of the epiphysis in young animals and not mature animals?

Back 32

The epiphyseal growth plate cartilage that consists of actively growing hyaline cartilage. It closes when growth stops.

Front 33

Name the major structures of the long bone.

Back 33

Important structures include the periosteum, articular cartilages, spongy bone, compact bone, medullary cavity, endosteum, nutrient artery, and the nutrient foramen.

Front 34

Describe the periosteum of the long bone.

Back 34

The periosteum is CT that covers the entire surface of the bone except the articular cartilages. It consists of two layers: the outer fibrous layer (for protection and attachment of ligaments/tendons) and the inner cellular layer (comprised of osteoprogenitor cells). The periosteum provides sites for blood vessels to pass into and out of bone.

Front 35

What are articular cartilages of the long bone?

Back 35

Hyaline cartilage pads at the ends of bone which help absorb shock and reduce friction between adjacent articulating bones.

Front 36

Medullary Cavity

Back 36

The space within the diaphysis that contains bone marrow.

Front 37

Nutrient Foramen

Back 37

The nutrient foramen is a hole in the diaphysis through which passes the major nutrient blood vessel. The area surrounding this was the primary ossification center.

Front 38

Describe Haversian systems (osteons) found in compact bone.

Back 38

Haversian systems are composed of numerous cylinders aligned in parallel along the long axis of the bone that increase the bone's resistance to stress.

Front 39

Name some components of Haversian systems (osteons).

Back 39

Components of osteons include central (Haversian) canals, osteocytes, caniculi, bone llamellae, and Volkmann's canals.

Front 40

Central (Haversian) Canals

Back 40

Contain blood vessels, nerves, and lymphatics.

Front 41

What are canaliculi and what processes/functions do have a role in?

Back 41

Narrow passageways that connect lacunae. They play a role in nutrient exchange, communication between bone cells, bone resistance, and shock absorption.

Front 42

Bone Lamellae

Back 42

Concentric layers of bone matrix.

Front 43

Volkmann's Canals

Back 43

Canals running perpendicular to Haversian systems that connect adjacent osteons.

Front 44

How is cancellous bone arranged compared to the arrangement of compact bone? Which is more organized?

Back 44

Cancellous bone is arranged in a 3-D lattice of trabeculae (which are arranged along the lines of greatest force to the bone). It is poorly organized compared to compact bone and contains no osteons (blood vessels run through the trabecular bone but no Haversian or Volkmann's canals).

Front 45

What is meant by the term woven bone? What are some of its characteristics?

Back 45

Woven bone refers to primary bone (or immature bone) formed during fetal development and absent in adults (except in pathological conditions). It does not contain lamellae, has a disorganized array of collagen and irregular mineralization pattern, and the lacunae are not arranged in parallel rows as they are in mature lamelar bone.

Front 46

What is meant by the term lamellar bone? What are some of its characteristics?

Back 46

Lamellar bone is mature (secondary) bone composed of collagen fiber bundles arranged in organized sheets (lamellae) in the same direction. It has lacunae in parallel rows. Both compact and cancellous bone types are lamellar bone.

Front 47

What is the function of bone development (osteogenesis or ossification) in the embryo, neonate, and adult?

Back 47

In the embryo it forms the skeleton, n the neonate it occurs as part of bone growth, and in the adult it occurs as part of bone remodeling and repair.

Front 48

What is the difference between ossification and calcification?

Back 48

Ossification is the process of replacing other tissues with bone, while calcification (mineralization) is the deposition of calcium salts in the collagen framework (this occurs in ossification).

Front 49

What are the two mechanisms of bone development? What similarities exist between them?

Back 49

The two mechanisms are intramembranous ossification and endochondral ossification. Both processes begin with proliferation and aggregation of mesenchymal cells at the site of future bone in the embryo. They also both initially produce woven bone that is later remodeled to produce mature lamellar bone.

Front 50

Where do the two mechanisms of bone development take place?

Back 50

Intramembranous ossification occurs in the CT membrane while endochondral ossification occurs in cartilage.

Front 51

Describe intramembranous ossification and give examples of bones formed in this manner.

Back 51

It is the simpler method, forming without a cartilage template and is used by the flat bones of the skull, face, mandible, and clavical. Bones form directly from mesenchyme as mesenchymal cells are converted to osteoblasts, which produce the matrix (osteoid), which eventually becomes mineralized. The osteoblasts are then trapped in the matrix and become osteocytes.

Front 52

Describe endrochondral ossification and give examples of bones formed in this manner.

Back 52

This involves a cartilagenous model and is used by most bones of the body (the long bones and parts of the axial skeleton that bear weight such as vertebrae). Boe forms by differentiation of mesenchymal cells to chondroblasts that migrate to the center of the shaft and produce the cartilage template. Osteoprogenitor cells then differentiate into osteoblasts and make osteoid and bone replaces the cartilage.

Front 53

How does a cartilage model, once formed, grow?

Back 53

A cartilage model grows by appositional and interstitial growth. A primary ossification center develops in the center of the shaft (diaphysis) and secondary ossification centers later arise and form the physis (at/after birth).

Front 54

What types of growth lead to the lengthening/thickening of bone?

Back 54

Lengthening occurs by longitudinal growth, thickening occurs by appositional growth.

Front 55

When might bone modeling or bone remodeling occur? Differentiate between the two.

Back 55

Bone modeling describes changes in bone shape seen during normal growth, altered mechanical use, or disease. It is an adaptive response to changing stresses on the bone. Remodeling is seen in the constant replacement of old bone with new bone (a homeostatic mechanism).

Front 56

Why does bone shape change during bone modeling and not during bone remodeling?

Back 56

In bone modeling, bone resorption and formation both occur at different sites with osteoblasts and osteoclasts act independently so the bone morphology (shape) changes. In bone remodeling, sequential action of osteoblasts and osteoclasts occurs at the same site so there is no change in bone morphology.

Front 57

What are the four zones of the epiphyseal growth plate cartilage?

Back 57

1) Zone of resting cartilage
2) Zone of proliferation
3) Zone of hypertrophy
4) Zone of calcification

Front 58

What allows for the microscopic repair of damaged bone?

Back 58

Bone remodeling.

Front 59

Upon what structure does longitudinal bone growth depend?

Back 59

The lengthening of long bones depends on the presence of epiphyseal cartilage (a growth plate). Activity in this plate is the only means by which the diaphysis can increase in length. Lengthwise growth of the bone stops when the growth place is completely replaced by bone.

Front 60

By what process does longitudinal bone growth occur?

Back 60

Longitudinal bone growth occurs by endochondral ossification.

Front 61

Describe what is happening in the stages of endochondral ossification.

Back 61

Chondrocytes proliferate and proceed through stages of maturation and hypertrophy. Following hypertrophy, the surrounding matrix and vascular tissue calcify. The hypertrophic chondrocytes degenerate and give way to invading osteoblasts. Bone and bone marrow replace calcified cartilage at the metaphysis, pushing the epiphyseal region away from the metaphysis and diaphysis.