chapter 6 Flashcards
facts about the bone (4)
- bone is a type of connective tissue; it has cells, fibres and ground substance
- bone come in many shapes and sizes
- the unique shape of each bone fulfills a particular need
- they contains different proportions of the two types of bones -> compact and spongy
structure of a long bone (5)
A bone that is longer than it is wide
Includes all limb bones (except/ ankle/wrist bones).
Long bones are slightly curved for strength
Red bone marrow is found inside the epiphyses
The marrow (medullary) cavity is in the hollow shaft
Endosperm lines marrow cavity
what does the long bone consist of and what does it expand to?
Consists of a shaft (diaphysis) and 2 expanded ends (epiphyses)
metaphysics
is between the diaphysis and epiphysis (contains the epiphyseal plate, in a growing bone)
periosteum
is a touch CT layer that covers the shaft of the bone. it is there for protection
hyaline cartilage
covers the particular surfaces- forming a joint
where is the compact bone found?
on the outer edges of the shaft and epiphyses
where is the spongy bone?
insides the epiphyses
history of bone tissue (4)
Extracellluar matric surrounds the widely separated cells
Its composed of ground substance and fibres
2/3 of it is inorganic matter (crystallized mineral salts); this provides the quality of “hardness” to bone
1/3 of it is organic matter (collagen fibres); this provides the qualities of “flexibilty” and “tensile strength” to bone
what are the four types of cells present in bone tissue?
- osteoprogenitor cells
- osteoblasts
- osteocytes
- osteoclasts
osteoprogenitor cells
Mitotic stem cells found in the periosteum and endosperm
Stem cells are unspecailzed cells, that can divide indefinitely but eventually become a specialized cell.
mesenchyme
embryonic connective tissue from which all other different types of tissues arise
osteocytes
mature bones cells (osteoblasts that are trapped in the matrix)
cytes- mature cells
job is to maintain the nutrients and wastes
osteoblasts
bone building cells that produce the matrix components (collagen. etc)
blasts- younger, immature cells
osteoclasts
cells that break down bone and are found in the endosteum
are really large
compact bone 80%
Forms the outer layer of all bones and most of the diaphysis of long bones.
Arranged into structural units called osteons or Haversian systems
Osteons is long cylinder and run the same way as the long axis of the bone
Each osteon consists of layers (rings) of bone matrix called lamellae
Lamellae encircle a Haversian (central) canal
Volkmann (perforating) canals run horizontally thru bone and join adjacent osteons
Between lamellae are lacunae which contain osteocytes
Osteocytes extend cytoplasmic processes into canaliculi
Canaliculus connect lacunar to each other and to the central canal.
spongy bone 20%
Does not contain osteons
Lamellae are arranged in thin columns of bone called trabecular
Contains osteocytes in lacunar and canaliculi
Between trabeculae there is bone marrow
The trabeculae are arranged in various directions to resist stress
blood supply– nutrient artery
enters the compact bone near the middle of the shaft and branches in the marrow cavity
blood supply
bone is richly supplied with blood
other arteries enter the ends of the bones and also breach to supply the marrow and bony tissues
blood supply – periostea arteries
supply the periosteum and outer part of compact bone
foramen
bone formation (ossification)
is a process by which bone is formed
what are the 3 situations bone formation occurs in?
- In fetus/embryo to form the bony skeleton
- Into early adulthood as growth in length of bones
- Throughout life as remodling of bone and repair of fractures
intermembranous ossification
Bone arises from embryonic mesenchyme tissue
Occurs in the formation of flat bones of the skull, mandible and clavicles
endochondral ossification
Bone develops from an existing hyaline cartilage model
Most bones of the body are formed in this way
intramembranous ossification- step 1- ossification centre forms
Mesenchymal cells differentiate into osteogenic cells, then into osteoblasts
Osteoblasts secrete the organic extracellular matrix
intramembranous ossification- step 2- calcification occurs
Trapped osteoblasts become osteocytes
Mineral salts are deposited and matrix calcifies
intramembranous ossification- step 3 trabecular form
Matric develops into trabecular that fuse with one another to form spongy bone
Red bone marrow forms in the spaces between trabeculae
intramembranous ossification- step 4 periosteum develops
Mesenchyme at periphery of bone condenses to form periosteum
A thin layer of compact bone form sunder periosteum
endochondral ossification step 1 cartilage model develops
Mesenchymal cells crowd together in the shape of future bone
They become chondroblasts and secrete cartilage extracellular matrix
This produces a hyaline cartilage model
A perichondrium develops around the cartilage model
Chemical singles or hormones initiate the process. When gather together they crowd together in the shape of the future bone (from kind of a proto type). Starts in 6th weeks of fetal development and forms all the other bones of the body. They differentiate and become cartilage forming cells. This leads to a bunch of cartilage being produced and replacing the mesenchymal tissue.
interstitial growth
this is how the cartilage model grows in length
endochondral ossification step 2 growth of the cartilage model
The cartilage model grows in length and thickness
Trapped chondroblasts become chondrocytes (no longer producing the matrix but maintaining it).
Chondrocytes in the mid-region enlarge and the matrix becomes calcifies
Chondrocytes die and lacunar form and merge into small cavities
endochondral ossification step 3 primary ossification centre
Nutrient artery penetrates the perichondrium
Osteogenic cells in the perichondrium differentiate into osteoblasts
The perichondrium becomes the periosteum (because you have bone tissue starting to form).
Capillaries grow into the mid-region inducing growth of a primary ossification centre
Osteoblasts deposit bone extracellular matrix over calcifies cartilage remnants
Bony trabeculae form
Ossification spreads to ends of cartilage model
why do the chondrocytes die and the lacunar form?
The model is getting bigger, the cells that are in middle of the model are getting further and further away from the nutrient source (blood vessels). The cells are too far away so not enough things are diffusing through, so they start to die off. When they die off, the cartilage that is around them is not being maintained, you get calcification (hard cartilage).
appositional growth
growing in the thickness of the model in the outer surface.
endochondral ossification step 4 marrow cavity forms
Osteoclasts breakdown some of the newly formed trabecular
Marrow cavity is formed in the shaft
Wall of the shaft is replaced by compact bone
endochondral ossification step 5 secondary ossification centre
Artery grows into epiphysis and secondary ossification centre forms at time of birth
Form spongy bone
endochondral ossification step 5 cartilage remains
Remaining hyaline cartilage at the join surface becomes articular cartilage
Hyaline cartilage remains b/t the diaphysis and epiphysis —> epiphyseal plate (growth plate)- allows our bones to grow in length.
Bone grows in length by adding new chondrocytes on the epiphysis side of the plate
Replace old chondrocytes with bone on the diaphysis side of the plate
At adulthood, the epiphyseal plate becomes ossified are adding one layer of cartilage on one side and removing a later of cartilage and replacing it with bone.
You are adding one layer of cartilage on one side and removing a later of cartilage and replacing it with bone.
bone remodelling
Bone undergoes constant remodelling, replacing old osseous tissue w/ new osseous tissue
Bone repair fractures (any break in a bone)
calcium homeostasis
In order for nerves and muscles to do their job they need a certain amount of calcium
[Ca2+] in blood:
9-11 mg/ 100ml
Outside of this range can cause serious damages and even death!
Bone tissue acts like a “buffer”.
Bone is the body’s major calcium reservoir
About 99% of calcium found in the body is in the bone tissue
what two things regular calcium concentration?
- calcitonin
- parathyroid hormes (PTH)
calcitonin
Calcitonin increase when blood [Ca2+] increases
Calcitonin inhibits bone resorption and more calcium salts are deposited in the bone matrix
parathyroid hormones (PTH)
PTH increase when blood [Ca2+] decreases
PTH stimulus the osteoclast to resorb bone, reales Ca2+ into the blood
PTH cats on the kidneys to decrease loss of Ca2+ in the urine
PTH can act on kidneys to increase the formation of vitamin D.
