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93 Cards in this Set

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  • Back
Bone is a ______ CT. (It is like cartilage but with _____.)
What are the 4 types of bone cells?
Osteoprogenitory cells
Osteoprogenitor cells-
Give rise to?
Appearance and why?
Osteoprogenitor cells are also called preosteoblasts.

They give rise to osteoblasts.

Because they do not make bone matrix, they do not have many organelles and are flat in appearance.
Where are osteoprogenitor cells located?
On bone surfaces. (Like osteoblasts)
These cells produce organic bone matrix (collagen and non-collagenous proteins).
cuboidal cells with an abundance of rER and a prominent Golgi

Their cytoplasm stains eosinophilic, although osteoblasts in general are basophilic because you can see very little of their cytoplasm.
Where are osteoblasts located?
Located on bone surfaces, both inside and outside the bone.
When does an osteoblast become an osteocyte?
Once the osteoblast becomes surrounded by the matrix it has synthesized, it is called an osteocyte.
What type of bone cell is the most prevalent? What type of collagen does it make?

Make Type I and Type V Collagen.
What happens to an osteocytes structure when it becomes an osteocyte?
It loses many of its organelles. There is little rER of Golgi in an osteocyte.
What does an osteocyte look like?
These cells are flat or oval and lie in lacunae in the bone matrix bathed by extracellular fluid.
Are osteocytes involved in the production of bone matrix?
Not to any significant extent but they are involved in the maintenance of bone matrix.
What type of bone cell has thin cytoplasmic processes that extend from the cell body? Why? Where do they go?

Osteocytes have very thin cytoplasmic processes that extend from the cell body and make contact through gap junctions with other osteocytes. The processes run in tiny channels in the matrix called canaliculi. This is how bone cells get nutrition.
What does an osteoblast secrete?
Collagen, ground substance and osteoid.
What is osteoid?
ground substance plus fibers
These bone cells are large and multinucleated.
Formed from?
Reabsorb bone matrix.
Formed from cells of the mononuclear/phagocytic line.
Found on bone surfaces.
How do osteoclasts stain and why?
Aciophilic and have a foamy cytoplasm.
Because they're making lots of lysosomes (which are release into the extracellular space) to actively reabsorb bone.
Where are osteoclasts most active?
Very active around the growth plate. (Seems counter-intuitive but as soon as bone is laid down it is gobbled back up so that you can put more down in its place to elongate the marrow cavity.)
What separates bone from cartilage?
Bone matrix
What is the ground substance of bone?
Osteoid (Organic Matrix)
What is the Osteoid (Organic Matrix) made of?
Proteoglycans and Glycoproteins (osteonectin).
What GAGs are contained in the osteoid?
Chondroitin Sulfate
Keratin Sulfate
What non-collagenous proteins are in the Osteoid (Organic Matrix) and what are their functions?
Osteonectin- anchors collagen to the bone mineral

Osteocalcin- a calcium-binding protein
What is the Inorganic Matrix and how is it usually arranged?
The osteoid when it becomes mineralized by the deposition of crystals of hydroxyapatite on the collagen fibers. The crystals tend to be oriented in the same direction as the collagen fibers.
What type of Collagen Fibers are found in bone?
Type I and Type V.
Vitamin ____ is required for calcification.

Vitamin ____ is required for the synthesis of collagen.
Vitamin D

Vitamin C
Why is Vitamin D required in bone formation?
Required for calcification.
Why is Vitamin C required in bone formation?
Required for the synthesis of collagen.
What is the Periosteum?
The vascular, noncalcified covering on the outside of a bone.
Where is the Periosteum located?
On the outside of a bone except at articular surfaces.
What are Sharpey's Fibers?
Type I Collagen fibers that anchor the periosteum to the bone as well as the periosteum to dense CT (deep fascia).
How many layers are in the Periosteum and what are they?
Two layers.
1) Outer Fibrous Layer
2) Inner Osteogenic Layer
Outer Fibrous Layer
Outer layer of Periosteum
Made of dense Type I collagen fibers and fibroblasts
Inner Osteogenic Layer
Inner layer of Periosteum
Made of osteoprogenitor cells and osteoblasts
What is the Endosteum?
The bone's cell lining that covers all the interior surfaces of bone (marrow cavity, Haversian canals, etc..)
What types of cells are found in the Endosteum?
The cells of the endosteum include osteoprogenitor cells and osteoblasts but not osteocytes.
This is a thin, specialized CT that lines marrow cavities.
This area of bone is the source of osteoprogenitor cells and osteoblasts for bone growth and repair.
Histologically, how many types of bone are there and what are they?
Two types.
1) Primary (immature, woven) bone
2) Secondary (mature, lamellar) bone
Primary bone-
Collagen organization?
Mineral content?
The collagen fibers run in random directions.
The matrix stains unevenly and may have basophilic regions.
Its mineral content is lower than secondary bone.
It has more cels per unit of calcified bone.
When would you see Primary bone?
You would see it if you were looking at a healing fracture.
Secondary Bone-
Collagen organization?
There is an orderly arrangement of collagen fibers into concentric rings or lamellae.
The matrix stains deeply acidophilic.
Two types- Compact and Spongy
Compact bone
Dense, outer portion of bone
Spongy bone
meshwork of trabeculae in interior of bone
What is an osteon?
Circling of osteocytes around a central vessel
What can connect Haversion canals?
can connect neighboring vessels via Volkmanns Canal
In spongy bone, what is the arrangement of trabeculae? How do these respond to stress?
Trabeculae follow the lines of stress and can realign if the direction of stress changes.
What makes up spongy bone?
Made up of trabeculae which are organized to provide maximum strength.
The long axis of the osteon is ____ to the long axis of the bone.
If trabeculae are sufficiently thick, they can contain _____?
Haversian System aka ?
What is the organization of compact bone?
Outer Circumferential Lamellae- below the periosteum
Inner Circumferential Lamella- adjacent or next to the marrow cavity
The rest of bone is organized as Haversian canal systems.
What is in a Haversian Canal?
What lines it?
What surrounds it?
Contains blood vessels and nerves.
Lined with endosteum.
Surrounded by rings of osteocytes and bone matrix
What connects osteocytes of adjacent lamellae?
What are interstitial lamellae and how are they formed?
Irregularly shaped bits of Haversian systems in between completely formed systems.
Represent Haversian systems that have been destroyed by growth and remodeling.
This completely surrounds the entire circumference of the bone just beneath the periosteum.
Outer circumferential lamellae
What are the two ways that bone forms in the fetus?
Endochondrial Ossification
Intramembranous Ossification
_____ ossification uses a cartilage model. ____ ossification does not.
Endochondrial ossification
Intramembranous ossification
Most bones of the body form by this method.
Endochondrial Ossification (cartilage model)
____ cartilage serves as a scaffold for bone development.
What are the step in endochondral ossification leading the the formation of the primary center of ossification?
1) Mesenchyme condenses and differentiates into hyaline cartilage chondrocytes. These begin to lay down cartilage matrix.
2) The mesenchyme surrounding the cartilage model becomes the Perichondrium.
3) A bony collar forms under the periochondrium of the diaphysis. The perichondrium surrounding the bony collar becomes the Periosteum.
4) The matrix of the diaphysis becomes calcified and is partially reabsorbed.
5) The primary center of ossification is formed.
How does the matrix become calcified in endochondral ossification?
Chondrocytes of the diaphysis become hypertrophic and place alkaline phosphatase into the surrounding matrix. This blocks diffusion of nutrients and causes them to undergo apoptosis. The matrix in this area becomes calcified and is partially reabsorbed.
How is the primary center of ossification formed in endochondral ossification?
A periosteal bud of capillaries invades the degenerating cartilage matrix. Osteoprogenitor cells carried in by the periosteal bud differentiate into osteoblasts which lay down osteoid over degenerating cartilage matrix.
Is all hyaline cartilage in endochondral ossification turned to bone?
All hyaline cartilage in this model is eventually turned into bone EXCEPT at the epiphysis where it is now called articular cartilage.
This is the main site of endochondral ossification.
What condition is caused by a deformity of cartilage at the growth plate?
Where is the secondary center of ossification formed?
In the epiphyses.
What persists between the epiphysis and diaphysis? What is it made of?
Epiphyseal plate
Hyaline cartilage
What are the five zones in the epiphyseal plate (from epiphysis to diaphysis)?
1. Zone of resting (reserve) cartilage
2. Zone of Proliferation
3. Zone of hypertrophy
4. Zone of calcification
5. Zone of ossification
Zone of resting cartilage
Cells waiting to be called into action
Zone of Proliferation
Cells on active duty that are starting to divide.
Zone of hypertrophy
Chondrocytes in this zone make alkaline phosphatase which calcifies the cartilage matrix. The cartilage matrix is also reabsorbed, increasing the size of the lacunae.
This Zone is where the most critical changes occur in the development of bones.
Zone of Hypertrophy
This is the zone where chondrocytes enlarge and begin to make alkaline phosphatase.
Zone of Hypertrophy
Zone of calcification
Chondrocytes die and leave behind empty lacunae.
Bone is layed down in these zones by osteoblasts.
Zone of ossification
Osteoblasts lay down bone matrix over the spicules of calcified cartilage matrix
What is the effect of growth hormone on the growth plate?
Growth hormone has an anabolic effect on the cartilage of the growth plate. At puberty, increased amounts of sex hormones cause the growth plate to calcify. This is referred to as closure of the epiphyseal plate.
What would result in excessive height/ short stature?
Excess production of growth hormone before closure of the growth plate results in excessive growth in height. Growth hormone deficiency in children results in short stature.
What bones are formed by Intramembranous Ossification?
Frontal, Parietal and Occipital Bones.
Parts of the mandible and maxilla.
What is responsible for producing the bony collar surrounding the cartilage model?
Intramembranous ossification
What are the five steps in Intramembranous Ossification?
1) Mesenchyme condenses and mesenchymal cells differentiate into osteoblasts.
2) Osteoblasts produce osteoid, which becomes calcified. Spicules of bone are formed which grow and fuse together to form spongy bone.
3) Blood vessels invade the spaces of the spongy bone. The mesenchyme in the spaces gives rise to the bone marrow.
4)The mesenchyme that does not undergo ossification develops into the periosteum and the endosteum.
5) Over time, this primary bone is reabsorbed by osteoclasts and replaced with secondary bone.
What is a BMU?
Bone Multicellular Unit
Microscopic Unit on all bony surfaces where bone remodeling occurs throughout life. Couple resorption of osteoclasts with formation by osteoblasts in time and space.
What kind of stimuli activate BMUs?
Mechanical Usage
What is the current theory on what signals the reabsorption of bone?
It is thought that the signal to reabsorb bone is received and processed by osteoblasts, which then secrete a molecule that stimulates the osteoclasts.
What happens in the process of fracture repair?
1) Hemorrhage due to broken blood vessels in the fracture area and clot formation. Loss of blood supply leads to death of bone cells and destruction of bone matrix.
2) The periosteum and endosteum grow due to proliferation of osteogenic cells, forming a callus.
3) The osteogenic cells develop into bone cells that lay down primary bone, or cartilage cells that lay down hyaline cartilage.
4) The cartilage in the callus is replaced by primary bone in a manner similar to endochondral ossification.
5) The bony callus is eventually remodelled.
In repairing a fracture, where do osteogenic cells develop into bone cells? Cartilage cells?
Bone cells- deep in the callus where the blood supply is good.
Cartilage cells- near the surface of the callus where the blood supply is scarce.
Characterized by?
Caused by?
Characterized by deficient calcification of newly formed bone and decalcification of calcified bone. Caused by a calcium or vitamin D deficiency in adults.
Decrease in bone mass and quantity associated with a normal ratio of mineral to matrix. Due to decreased bone formation, increased bone resorption, or both.
Why does osteoporosis occur in old age? immobile patients? post-menopausal women?
Old age- diminished secretion of growth hormone
Immobile patients- lack of physical stress on bone
Post-menopausal women- diminished estrogen secretion
excess pituitary growth hormone in adults characterized by very thick bones in the extremities and in parts of the facial skeleton.
metastatic tumor of the bone
extreme bending of long bones