11/17 Histo of Bone Flashcards
The function of bone:
Levers for movement. support and protection. hematopoiesis in marrow, store and regulate serum levels of calcium and phosphate.
The two types of bones depending on the density
spongy bone and compact bone….
Describe the outer wall of bones
compact or cortical bone
what type of bone is the interior of bone made of?
trabecular (spongy, cancellous) bone and marrow
I am looking really close at compact and spongy bone samples…how can I distinguish the two? (microscopic scale)
compact and trabecullar bones are identical at the microscopic level…so good luck buddy!
the covering of bone surfaces…
connective tissue: periosteium on the outside and endosteum on the internal surface and long bones have Articular cartilage at the joints
Source of nutrition and progenitor cells for making bone:
periosteum and endosteum
found on the ends of long bones:
articular cartilage (no periosteum
two types of bone cell lineages:
undifferentiated mesenchymal cells and hematopietic stem cells
What is the family lineage of bone cells that come from Undiferentiated mesencymal stem cells?
Messenchymal cells gives rise to Osteoprogenitor cells called an osteoblast that gives rise to osteocyte!
What is teh family lineage of bone cells that come from hematopoietic stem cells.
Hematopoietic stem cells produce monocytes that produce Osteoclasts (they also prodcue macrophages of course so osteoclasts and macrophages are like siblings…:-)
the progenitor cells in periosteum and endosteum:
osteoprogenitor cells (preosteoblast)
what do osteoprogenitor cells produce:
osteoblasts
Can osteoprogenitor cells move or divide?
yes they proliferate and circulate!
how could osteoblasts be connected to calcified vessels
they may circulate in and make cells that make calcium… thus the migration of calcium from the skeleton to the vessels!
what do osteoblasts do?
bone-forming cells that secrete osteoid (ECM) mineralize the matrix and do NOT divide
derived from osteoblasts and surrounded by bone matrix
osteocytes
the opening where the osteocytes sit
lucunae between layers (lamellae) of adult bone.
the principal cell in adult bone 95%
osteocytes
HOw is the ostyocyte like a spider?
they put out little legs from the lacunae, through canaliculi to form gap junctions with other cells around them.
How do ostyocytes communicate, and maintain the matrix of cells in the bone
form continuous system of cells thorghout the bone via gap junctions in canaliculi between cells.
what do the osteocytes do?
maintain the matrix: sense stress, communicate with other cells: THE CELLS THAT MAKE AND MAINTIAN BONE
The cells that take bone apart (resorb bone)
the osteoclasts
multinucleate cells that are derived form macrophages in the bone marrow.
osteoclast
the space that an osteoclast forms on the surface of bone
Howship’s lucunae
what happens in the howship’s lacunae?
Oseoclast excretes acid and lysosomal enzymes that take bone apart and release calcium
what regulates the actions of osteoclasts?
indirectly by parathyroid hormone (up regulate) and perhaps directly by calcitonin
The purpose of osteoclasts
bone turnover and Ca2+ regulation
what is the principle organic components of bone matrix?
collagen type I and GAGs and proteoglycans and a bunch of glycoproteins
what will all of the glycoproteins in the bone matrix do?
promote mineralization, serve as hormones as well!
what is an example of hormone from bone…
osteocalcin released when bone is turned over and is connected to type II diabetes
Inorganic components of bone:
Hydroxyapatite (calcium and phosphate in a molecule) and trace minerals
How do we develop and make bone?
there are two different paths of development and each one will use the same two steps to make the bone and we end up with two different types of bone so…2 by 2 by 2 makes bone! (intramembranous or Endochondral formation makes 1. primary=woven and 2. secondary bone=lamellar, to end up with 1. Compact Cortical bone or 2. Spongy Cancellous Trabecular bone
The two processes of making bone
osteoblasts begin to make bone in : 1. Loose connective tissue in a process called intramembranous bone formation. -or- 2. Hylanine cartilage that makes a matrix and has just died in a process called endochondral bone formation.
what is bone formation on loose connective tissue?
intramembranous bone formation
bone formation on cartilage matrix
endochondral bone formation
the two steps in bone formation
- primary bone = woven bone; 2. Secondary bone = Lamellar bone
what is woven bone
random collagen fiber orientation: temporary bone that is removed or replaced with secondary bone
what is secondary bone
parrallel collagen fibers arranged in layres, can become permanent but will be continuously remodeled.
The two types of mature bone:
compact bone = cortical bone; Spongy bone=cancellous bone=trabecular bone
what is trabecular bone
thin bone that can be nourished form outside
what is compact bone
thick bone that requires internal blood supply: osteons
the microscopic organization of primary (woven bone)
randomly oriented collagen fibers: an orientation called trabecular
when does Primary (woven) bone appear?
appears during development or during repair!
What is the fate of primary bone?
to be replaced by mature lamellar bone or removed to make marrow cavity.
Describe the microscopic organization of secondary bone
Lamellar bone is composed of layers of matrix that are parallel to each other, oriented 90 degrees from fibers in adjacent lamellae. (like a sheet of plywood, or a skateboard deck!)
Where are the osteocytes in lamellar bones?
they are in lacunae between the lamellae layers! (stuck in the glue between layers of the skateboard deck!)
The Microscopic orientation of all mature adult bone:
Lamellar.
The composition of most compact bones:
they consists of osteons, or haversian systems in long lines around canals of nerves blood and lymph called haversian canals.
lamellae of bone surrounding individual haversian canals
Osteons
the contents of osteons
Layers of mature secodary bone wrapped around haversian canals that contain nerves, blood vessels and lymphatics
the vertical connections between seperate lines of haversian canals
volkmanns canals
if it is thick enough, trabecular spongy bone bone can also have..
osteons
Enclose osteons, and are close to blood vessels in connective tissue coverings
circumferential lamellae
The canals in the middle of Osteons
haversian canals
the canals that connect haversian canal
volkmann canal
the space between osteons (triangular space)
intersitial lamella
the tissue between two osteons that are a little darker staining
Cement lines
The type of bone development that is responsible for the development of flat bones of skull and mandible
intramembranous ossification
How do long bones grow in diameter?
in the pericardium of the cartilage, the osteoblasts invade and begin to calcify the tissue and kill the cartilage and the osteoclasts then chew up the bones in the middle and the osteoblasts build it on the outside. This is called: INTRAMEMBRANOUS OSSIFICATION
how can you make a bone wider and not make it heavier?
add on the outside and chew up on the inside (osteoblasts and osteoclasts) or INTRAMEMBRANOUS OSSIFICATION
How do long bones grow longer?
they grow through endochondral ossification: replacement of cartilage model with bone! the cartilage continues to grow and is alive under the developing bone, creating a secondary center of ossification above the living cartilage model now called the epiphyseal growth plate.
The layers of the epiphyseal growth plate
the resting cartilage, the proliferation zone, the maturation/hypertrophy zone, the calcification zone, and the ossification zone! (transition from cartilage to ossified bone!)
Does the bone in the epiphyseal growth plate get remodeled?
yes deffinetly! it is being deposited and removed simultaneously in the growth plate! (osteoclasts / osteoblasts at work)
Why do we every stop growin?
Systemic growth hormone production stops and chondroblast produced factors are lost as chondroblast proliferation stops leading to the closure of the epiphyseal growth plate when all of the cartilage becomes bone!
bone growth will continue until closure of…
the epiphyseal growth plate
how can the movement and stress on a bone affect growth?
the physical forces influence bone modeling that is constantly taking place with osteoclast/blasts
how much bone is replaced in an adult?
about 10% of total bone is replaced yearly.
the way that bone is replaced
osteoclasts degrade old osteons and osteoblasts generate newe osteons
how is fracture repaired?
blood clot soon invaded by myofibroblasts, chondroblasts, osteoblasts; soft callus formed (loose CT and hyaline cartilage) then intramembranous and endochondral bone formation happens initially; then hard callus of primary woven bone and then remodeled to lamellar bone
what is the overriding factor that balances bone resorption in the body?
calcium mobilization
what is the condition where the bone formation balance doesn’t match resorption?
osteoporosis
what is the cause of osteoporsis
activity of osteoclasts outpaces the now much lazy osteoblasts
what happens in osteoporosis in bone?
decrease in bone mass with composistion of bone matrix is normal.
factors associated with osteoporosis?
aging, decreased estrogen in postmenopausal women, inactivity (space flight)
decreased bone resorption due to defective osteoclasts:
osteopetrosis
the results of osteopetrosis
reduced marrow cavity, decreased blood formation, anemia and infection.
what is the deffect in osteoclasts in osteopetrosis?
no ruffled border so can’t make the little cacoon
disease with loss of articular cartilage
osteoarthritis (OA)
what happens in osteoarthritis?
erosion of articular cartilage that reduces joint function: leads to bone remodeling, pain, and loss of activity.
Describe the change in the joints that may lead to osteoarthritis?
the stable chondrocytes in the articular surface change and start acting more like transient growth cartilage, they proliferate and become Hypertrophic-like, turning over matrix more quickly. this leads to worse damage.
