Bone Development Histology Flashcards
Process of bone ossification
Osteogensis
What are the two types of ossification?
Intamembranous and Endochondral
- No hyaline cartilage model precursor
- Mesenchyme to Bone
Intanmembranous Ossification
- Hyaline cartilage model precursor
- Mesenchyme to Hyaline to Hyaline cartilage to Bone
Endochondral Ossification
What type of tissue is bone?
Connective
What does bone arise from?
Mesenchyme
When does intramembranous ossification occur?
8th week of gestation
Hyaline cartilage takes on initial shape of bone as well as bones place in the body
Hyaline cartilage model
A- Ossification centers form within thickened regions of mesenchyme
B- Osteoid endergoes calcification
C- Woven bone and surrounding periosteum form
D- Lamellar bone replaces woven bone, as compact and spongy bone form
Intramembranous ossification
Where is spongy bone formed?
Between 2 layers of compact bone
What is one characteristic of all connective tissues?
They arise from embryonic connective tissue called mesenchyme
Leads to the production of flat bones of the skull and the bones of the face
Intramembranous Ossification
Woven or immature bone
Primary
Lamellar or mature bone
Secondary
Eroded and replaced with bone
Hyaline cartilage model
Leads to the production of most short and long bones of the body
Endochondral ossification
When are the first hyaline cartilage models visible?
6th week of gestation
When are ossification centers of long bones of the limns present?
By 12th week of gestation
In intramembranous ossification, Elongated, pale-staining, mesenchymal cells cluster and differentiate to
Osteoprogenitor cells
In intramembranous ossification, What happens when cells differentiate into osteoprogenitor cells?
They become more rounded, while their cytoplasm changes from eosinophilic to basophilic
What is the basophilic cytoplasm change a result of?
More rough ER
What do osteroprogenitor cells differentiate into?
Osteoblasts
What do clusters of osteoblasts create?
The ossification center
Organic extracellular matrix
Osteoid
What secrete osteoid?
Osteoblasts while creating the ossification center
Where are calcium and other mineral salts deposited during calcification?
Around the framework of collagen fibers
Cells that are trapped in the calcifying osteoid
Osteocytes
Where do osteocytes sit?
In lacunae
Produced in small irregularly shaped pieces or spicules that are increased in size by apposition growth
Woven bone in Intramembraous ossification
Growth along the surface
Apposition growth
Small patches of bone production merge together to produce
A labyrinth of woven bone
The spaces between the bone spicules that are infiltrated with embryonic blood vessels differentiate into
Red bone marrow
The mesenchyme at the periphery of the bone condenses and forms the
Periosteum
What is woven bone replaced by?
Lamellar bond
What does lamellar bone form in intramembranous ossification?
Compact and spongy bone
Loosely organized embryonic connective tissue
Mesenchyme
Elongated, pale-staining, undifferentiated cells
Mesenchymal cells
Thin cytoplasmic processes
Mesenchymal cells
- Fetal hyaline cartilage model develops
- Cartilage calcifies and a periosteal bone collar forms around the diaphysis
- Primary ossification center forms in the diaphysis
- Secondary ossification centers form in the epiphysis
- Bone replaces cartilage except the articular cartilage and epiphyseal plates
- Epiphyseal plates ossify and form epiphyseal lines
Endochondral ossification
In endochondral ossification, mesenchymal cells aggregate and differentiate into
Chondroblasts
Secrete matrix, including type II collagen and produce the hyaline cartilage model
Chondroblasts
Formed from the mesenchyme where bone is going to form and in a similar shape
Hyaline cartilage model
How does hyaline cartilage grow?
Interstitial growth and appositional growth
What causes interstitial growth in endochondral ossification?
Activity of chondrocytes located in lacunae
What causes appositional growth in endochondral ossification?
Activity of chondroblasts at the surface
Where does a bone collar form in endochondral ossification?
Around the diaphysis
What does the perichondrium near the nid-region of the cartilage model contain?
Progenitor cells that differentiate into osteoblasts
When does perichondrium become functional periosteum?
When Progenitor cells differentiate into osteoblasts instead of chondroblasts
What creates a bone collar around the mid-section of the hyaline cartilage model?
Osteoblasts that secrete osteoid, that becomes calcified
How does the bone collar effect underlying cartilage?
Impedes the diffusion of oxygen and nutrients
In the mid-region begin to accumulate glycogen, undergo hypertrophy (swell up) and produce alkaline phosphatase
Chondrocytes
Compress the matrix and signal the surrounding matrix to calcify
Changes to chondrocytes in mid-region from formation of bone collar
What is hyaline cartilage primarily made of?
Type II collagen
What is bone primarily made of?
Type I collagen
What color does calcified hyaline cartilage stain with H and E stain?
blue/purple
What color do newly formed bones stain with H and E stain?
pink/red
What cannot take place through calcified cartilage matrix
Diffusion, Chondrocytes can no longer get the nutrients they need
Why does the matrix break down?
No present chondrocytes
Capillaries and osteoprogenitor cells from the new periosteum penetrate the
Bone collar and grow into the disintegrating calcified cartilage location
What does the penetration of the bone collar and growth into calcified cartilage induce?
The creation of the primary ossification center
What is important for the development of the bone marrow for the medullary cavity?
Blood vessels entering open space at the core of the diaphysis
Differentiate into osteoblasts at the opening space at the core of the diaphysis
Osteoprogenitor cells
Deposit bone matrix against the remnants of the calcified cartilage
Osteoblasts
Produced along the side of the remaining spicules of calcified cartilage
Woven bone
Eosinophilic
Primary bone
Basophilic
Calcified cartilage
No chondrocytes present in endochondral ossification
Calcified cartilage
Where is the primary ossification center found?
Diaphysis
Where it hylaine cartilage found when primary ossification center is present
Epiphyses
When do secondary ossification centers develop?
After birth
Where do secondary ossification centers form?
Epiphyses
Chondrocytes in epiphyses undergo
Hypertrophy
The cartilage matrix is compressed, the cartilage matrix calcifies, and the chondrocytes subsequently die: Which leads to
Opening up of spaces between spicules of calcified cartilage
Enter the spaces that have been opened up in the epiphyses and secondary ossification centers develop.
Blood vessels and osteoprogenitor cells
Hyaline cartilage is retained on the ends of the model and becomes
Articular cartilage
Used for cushioning of bone ends participating in joints
Articular cartilage
The remnant of hyaline cartilage between the epiphysis and the flared portion of the diaphysis is retained as the epiphyseal plate, which will be responsible for
Lengthwise growth of long bones
Flared portion of the diaphysis
Metaphysis
Epiphyseal cartilage is replaced with bone forming the
Epiphyseal line
What causes the formation of the epiphyseal line?
Hormone changes
Marks the end of growth in terms of height
End of puberty
The remnant of the last location of the epiphyseal plate.
Epiphyseal line
Long bones increase in ______ during infancy and youth
Length
What process allows bone to increase in length during infancy and youth?
Endochondral ossification at epiphyseal plate
Found between the epiphysis and the metaphysis
Epiphyseal plate
Composed of hyaline cartilage that can be divided into different zones
Epiphyseal plate
Zone 1
Zone of resting cartilage
Zone 2
Zone of proliferating cartilage
Zone 3
Zone of hypertrophic cartilage
Zone 4
Zone of calcified cartilage
Zone 5
Zone of ossification
Zone closest to the epiphysis
Zone of resting cartilage
Chondrocytes singularly or in very small groups
Zone of resting cartilage
Cartilage cells are undergoing mitosis and are stacking up like coins in line with the long axis of the bone
Zone of proliferation
Stacks of cartilage cells that look like coins
Isogenous groups
What do isogenous groups produce?
Matrix
Epiphysis is pushed away from the diaphysis causing the bone to lengthen in what zone?
Zone of proliferation
Chondrocytes increase in size.
Zone of Hypertrophy
- The cytoplasm of the chondrocytes accumulates glycogen.
- The matrix is compressed/thinned due to the expansion of the cells.
Zone of Hypertrophy
The cartilage matrix begins to calcify through the formation of hydroxyapatite crystals.
Zone of Calcified Cartilage
Calcified cartilage matrix stains
Basophilic
The chondrocytes can no longer receive the nutrients they need via diffusion and they die because of
Calcified cartilage
This zone is in direct contact with marrow tissue, as it right next to the diaphysis.
Zone of ossification
Small blood vessels, blood cells, osteoprogenitor cells, and osteoclasts enter into the spaces previously occupied by the chondrocytes.
Zone of ossification
Bone (specifically primary/woven bone) is laid down by osteoblasts onto the calcified cartilage spicules that were left behind.
Zone of ossification
What does bone stain?
Eosinophilic
Eventually, much of this new bone and calcified cartilage will be eroded by the osteoclasts, so that secondary bone can be developed or to add space to the already existing medullary cavity.
Zone of ossification
The epiphyseal plate remains the same _____ during growth
Width
Cartilage growth must equal
Bone tissue replacement
At epiphyseal plate closure - hormones signal for the end of chondrocyte division and bone replaces all of the cartilage. Producing..
Epiphyseal line
Zone is composed of quiescent hyaline cartilage
Zone of resting cartilage
Chondrocytes have the characteristic appearance of stacking like coins along the long axis of the bone. Chondrocytes in this region are actively undergoing mitosis and matrix production. This causes the lengthening of the long bone
Zone of proliferation
Where chondrocytes undergo hypertrophy and compress the matrix.
Zone of hypertrophy
Where the cartilage matrix calcifies, the chondrocytes die, and spaces open up.
Zone of calcified cartilage
In this region, items such as blood vessels and osteoprogenitor cells enter into the now open spaces and osteoblasts start to produce primary (woven) bone.
Zone of ossification
Chondrocytes looklike they are being chased by
Bone cells
Appears that bone cells have caught up with chondrocytes
Epiphyseal plate closure
What happens to bone with appositional growth?
Increases in diameter and width
What happens at periosteal surface of bone in appositional growth?
Osteoblasts secrete bone matrix
What happens at endosteal surface of bone in appositional growth?
Osteoclasts breakdown bone matrix
Two controls impacting bone remodeling
- Negative feedback loop for maintenance of Calcium homeostasis
- Bone’s response to mechanical stress and gravity
Impacts when remodeling occurs
Negative Feedback Loop of Maintenance of Calcium Homeostasis
Impacts where remodeling occurs
Bone’s response to mechanical stress and gravity
Deposit and removal of bone
Bone remodeling
How much of your bone do you remodel every year?
5-10%
Controls for remodeling
Negative feedback loop, mechanical stresses and gravity
Maintains the homeostasis of a certain amount of Ca2+ in the blood through the release of the hormones calcitonin and parathyroid hormone
Negative feedback loop
Important in the blood as it is needed for many physiological processes.
Ca 2 +
What secretes calcitonin?
Parafollicular cells
Inhibits osteoclasts, and therefore bone resorption
Calcitonin
What secretes parathyroid hormone?
Parathyroid glands
Stimulates osteoclasts to resorb bone
Parathyroid hormone
