Module 4: The Skeletal System: Histology and Movement Flashcards
What type of tissue is bone classified as?
Connective tissue.
What does the function of connective tissue (whether it is bone, connective tissue proper, cartilage, or blood) depend upon?
It depends on the composition. The bone matrix determines the function.
Blast
Immature cell
Cyte
Mature cell
Osteo
Bone
Osteoblast
A bone-forming cell.
Osteocyte
A mature bone cell surrounded by bone matrix.
What is the function of osteoblasts?
They produce bone matrix.
When is an osteoblast considered an osteocyte?
Once the matrix is fully formed and the cells are surrounded.
Lacuna
The microscopic space within the matrix that houses the osteocytes.
Osteoclast
A large, multinucleated cell that breaks down bone.
Clast
To break.
Why does the body need osteoclasts?
Bones deteriorate on their own, so the body must be able to break down bone in order to build it up again. When the body need minerals that are stored in bone, the osteoclasts break down the bone tissue and release those minerals.
What are the three basic types of bone cells?
Osteoblasts, osteocytes, and osteoclasts.
What is the bone matrix like?
It contains protein in the form of collagen fibers and calcium salts.
What % of bone is collagen?
30%.
Where do the collagen fibers in the bone matrix come from?
They are secreted by the osteoblasts as they build the bone matrix.
What is the function of collagen in bone?
It gives the tissue flexibility and tensile strength.
What are some other names for calcium salts?
Calcium minerals, bone salts, or bone minerals.
Calcium salt
An ionic compound that contain calcium ions.
What does mineral refer to in “calcium mineral”?
Inorganic crystalline compounds.
What are most of the calcium salts in the bone matrix?
Hydroxyapatite.
What is the chemical formula for hydroxyapatite?
Ca10(PO4)6(OH)2
How do calcium salts come to be in the bone matrix?
Unlike other connective tissue matrices, the cells do not produce the calcium salts. Instead, the blood brings the salts into the bone matrix.
What % calcium is bone made of?
40%.
What % phosphorous is bone made of?
20%.
What qualities does hydroxyapatite give bone?
Hardness and compressive strength.
Compressive strength
The kind of strength that holds weight. (Ex. A metal rod.)
Describe the mixture of substances in bone.
Collagen provides tensile strength with flexibility and the calcium salts provide compressive strength so the bones can bear weight.
How does vinegar break down hydroxyapatite?
Vinegar is an acid. The hydroxide ion in hydroxyapatite reacts with the vinegar and destroys the calcium salt, and the Ca2+ ions dissolve into the solution. In the end, the bone matrix loses its calcium salt and loses its compressive strength.
What causes rickets?
Low calcium levels in the body that lead to a lack of hydroxyapatite in the bones, making them rubbery. The bones are made of 30% collagen and that is what mostly remains with rickets.
What is the function of Vitamin D with relation to the bones?
It absorbs calcium out of the intestines and into the blood. Rickets is a lack of Vitamin D.
What would bone be like without collagen fibers?
It would be brittle and hard with no flexibility. Only calcium salts would be left behind.
Trabeculae
The beams that form the latticework of cancellous bone.
What is found in between the trabeculae?
Bone marrow and blood vessels.
Osteons
Tightly-packed cylinders that compact bone tissue is arranged in.
What did osteons used to be called?
Haversian systems.
The central canal
The hollow tube in the middle of an osteon sometimes called the Haversian canal. Blood vessels run through the central canal.
Concentric lamellae
Tubes of bone tissue that surround the blood vessels that run through the central canal that make up the osteon.
Interstitial lamellae
Bony layers of tissue in between the osteons that do not form cylinders. Can be thought of as the “packing material” around the osteons.
How are osteocytes shaped?
They are shaped like spiders because they have microscopic “legs” called processes that extend from the main cell body.
What is the purpose of an osteocyte’s processes?
They allow the cell to communicate with other cells.
How do osteocytes’ processes communicate with one another?
The process of one cell touches another and links the cells together.
Canaliculi
Channels in the bone through which the osteocytes’ processes run. Latin for “tiny canals.”
Describe the process of ossification.
The chondrocytes near the epiphyseal plates (made of hyaline cartilage) undergo mitosis and create new cartilage. The older chondrocytes near the diaphysis enlarge and increase the size of their lacunae. At the same time, calcium salts accumulate in the older cartilage. As they accumulate, the chondrocytes die and leave behind holes. Then blood vessels grow in the lacunae (the holes) and bring in osteoblasts and osteoclasts. The osteoblasts lay bone matrix on top of the calcified cartilage and form new cancellous bone. The process is complete.
Calcified cartilage
The point in ossification in which the chondrocytes have died and left behind holes. Calcium salts are accumulating at this time.
Describe the direction of growth in the ossification of the epiphyseal plate.
The epiphyseal plates stay the same thickness, but the diaphysis forms new bone on its end and increases the length of the bone.
Epiphyseal line
The bony marking that replaces the epiphyseal plate in ossification.
How is the growth of the epiphysis different from the growth of the diaphysis?
In the epiphysis, the articular cartilage never fully ossifies.
Appositional bone growth
The growth of a bone in diameter when osteoblasts lay new bone matrix on the surface of a bone.
Bone remodeling
The process by which osteoclasts break down worn-out bone and rebuild it.
If a person is bed-ridden and does not move much or loses weight, what will happen to their bones?
The bone will gradually be removed by the osteoclasts because of the lack of stress on the bone.
If a person is very active or gains weight, what will happen to their bones?
The bones will be stressed and will respond by increasing their mass to become more firm.
What does an osteoclast do when it experiences excessive stress?
Stress, which is a compressive force, “squashes” the osteoclasts. They do not like to be stressed, so they secrete a protective shell around themselves made of more bone.
What nutrients are necessary to build strong bone?
Protein, calcium, phosphorus, and others.
Describe the general basics of how orthodontics work.
The maxilla and mandible are encouraged to remodel due to the stress of the wire bands. When a tooth is pulled in one direction, its ligaments stress the bone, and more bone is laid. On the opposite side of the tooth, there is compression on the tooth’s ligament, and the bone is gradually removed by osteoclasts. This causes the tooth to move into the newly remodeled socket.
Why must orthodontic patients wear a retainer after their treatment?
The ligaments that hold tooth to bone have long memories. They have been stretched and want to pull back to their original position. Without a retainer, they will remodel the bone toward the original.
How do osteoclasts dissolve bone salts? (Bone minerals, calcium salts)
They secrete an acid that reacts with hydroxyapatite. The hydroxide ion (a base) in hydroxyapatite reacts with the acid and cause the calcium ion to dissolve. Another way they dissolve salts is to secrete proteolytic enzymes that digest protein.
Proteolytic enzymes
Enzymes that digest protein, especially collagen.
Describe the process by which bone heals itself.
When a bone is broken, the blood vessels are broken and blood flows out and forms a hematoma. The hematoma forms a clot and the bone tissue surrounding the break dies. After the clot is formed, a callus forms. As the callus forms, blood vessels grow into the internal callus and fibroblasts start producing collagen. Chondroblasts start producing cartilage. Phagocytic cells break down the blood clot and clean the debris. Osteoclasts break down dead bone tissue and osteoblasts lay down new bone tissue. The cartilage ossifies and forms new bone.
Hematoma
A mass of blood that is confined to a limited space.
Callus
A mass of connective tissue that connects the ends of a broken bone.
Internal callus
The callus that forms between the breaks in the bone.
External callus
The callus that forms around the outside of the bone.
What is the role of the external callus in healing a bone?
It provides stable support for the bone like pieces of tape on the outside of two pieces of wood glued together.