Week 1 - Bones Flashcards
What are the diff. tissues working together in the bone
Osseous tissue
Cartilage
Dense connective tissue
Epithelium
Adipose tissue
Nervous tissue
What % of human body weight is bone? And what % of the body’s calcium does it store?
18%
99%
What does red bone marrow consist of?
Developing blood cells
Adipocytes
Fibroblasts
Macrophages w/in a network of reticular fibres.
Where can red bone marrow be found
Developing bones of the foetus + in adult bones:
- Pelvic bones
- Ribs
- Sternum
- Vertebrae
- Skull
- Ends of bones of humerus
- Femur
Bone marrow for newborns
All red + involved in hemopoeisis
What’s in the extracellular matrix?
15% H20
30% collagen fibres
55% crystallised mineral salts
Whats the most abundant crystallised mineral salt in the body?
Calcium phosphate
What does calcium phosphate do in the bones?
Combines w. calcium hydroxide —-> Crystal of hydroxyapatite.
As these form they combine w. other mineral salts i.e calcium carbonate.
Then crystallise when deposited in the framework formed by collagen fibres of the extracellular matrix == Calcification
What is calcification initiated by?
Osteoblasts
External functions of the skeletal system
Protection of internal organs
Movement facilitation
Supports the body
Internal functions of the skeletal system
Prod. of blood cells
Storage of minerals
Storage of TG
Where are TG stored in the skeleton?
Yellow bone marrow
What are the 4 main aspects of a long bone
Epiphysis
Diaphysis
Periosteum membrane
Endosteum membrane
Define the epiphysis
Ends of bones
Joint surface is covered w. articular cartilage
What separates the diaphysis from the epiphysis
Epiphyseal line
At around what ages do long bones stop growing in LENGTH?
18-25
What happens after long bones stop growing in length?
Epiphyseal cartilage disappears
Epiphyseal plate closes
Becomes visible on x-rays as an epiphyseal line
Define metaphyses
Regions between diaphysis + epiphysis
What does a metaphysic contain on a growing bone?
An epiphyseal/growth plate
Hyaline cartilage that allows the diaphysis fo the bone to grow in length
Define the diaphysis
Long, tubular shaft of the bone.
A collar of compact bone surrounds a central medullary/marrow cavity.
Define the medullary cavity
In the diaphysis.
Filled w. yellow bone marrow + in adults contains fat.
Interior of all bones consists largely of spongy bone.
Where is the periosteum
Covers the outer bone surface
What does the periosteum consist of
Dense irregular connective tissue
Osteoblasts
Nerve fibre blood - secured by sharpers fibres
Lymph vessels - secured by sharpeys fibres
Where is the endosteum
Covers the internal bone surfaces
Define the articular cartilage
Thin layer of hyaline cartilage
Covers epiphysis where bone forms an articulation w, another bone = joint.
What is the function of articular cartilage
⬇️ friction + absorbs shock at freely moveable joints.
Why is the repair of damaged articular cartilage limited?
Due to lack of perichondrium + bv.
What are the 2 main types of bones?
Cortical (compact/hard)
Trabecular (cancellous/spongy/soft)
Cortical (compact/hard) bone
Low porosity (5-10%)
Strong + dense (80% of skeleton)
Epiphysis (thin shell)
Diaphysis (shaft, thicker)
Trabecular (cancellous/spongy/soft)
High porosity (30-90%)
Lighter + less dense than cortical
20% of skeleton
Remaining space is filled w. marrow + fat
List the main components of the microscopic structure of compact bone
Osteon
Osteoblasts + clasts
Osteocytes
Osteoid
Osteoprogenitor cells
COMPACT BONE
Osteon
Repeating structural units of compact bone tissue.
COMPACT BONE
Osteoblasts
Make + deposit components of bone extracellular matrix.
Where are osteoclasts often found?
In the endosteum lining the marrow cavity.
What do osteoclasts do
Degrade + resorb bone for remodelling.
Secrete protein-digesting enzymes.
Dissolve bone matrix + release stored minerals (osteolysis).
Define osteocytes
“watcher cells”
Sit in bone + monitor its current status.
Mature bone cells that maintain protein + mineral content of bone matrix.
Also help repair damaged bone.
Where can osteocytes be found
Between lamellae of matrix
What is the osteoid?
Unmineralized bone matrix
What are osteoprogenitor cells?
Mesenchyme stem cells that divide to prod. osteoblasts.
Only bone cells that undergo cell division.
Define concentric lamellae
Circular plates of mineralised extracellular matrix of increasing diameter, surrounding a small network of bv + nerves located in the central canal.
What are lacunae?
Small spaces between the conc. lamellae that contain osteocytes
Canaliculi
Radiate from the lacunae in all directions.
Filled w. extracellular fluid.
What can be found in the canaliculi
Slender fingerlike processes of osteocytes
What do the canaliculi connect what with
Lacunae w. each other + w. central canals.
Provide routes for nutrients +O2 to reach osteocytes + for removal of wastes.
How are osteons arranged
In same direction + parallel to the length of the diaphysis.
As a result, the shaft of the long bone resists bending or fracturing even when considerable force is applied from either end.
Interstitial lamellae
Areas between neighbouring osteons
How do bv + nerves from the periosteum penetrate the compact bone?
Through volkmanns/perforating canals
Does spongy bone contain osteons?
NO
Where is spongy bone always located
In the interior of the bone + protected by a covering of compact bone.
What does spongy bone consist of
Lamellae arranged in an irregular pattern of thin columns = trabeculae.
What are the spaces between the trabeculae filled with?
Red bone marrow
What do trabeculae consist of
Concentric lamellae
Osteocytes in the lacunae
Canaliculi that radiate outward from the lacunae.
Where do trabeculae lie?
Along lines of stress - helping bones resist stresses + transfer force w.out it breaking.
Where can spongy bone be found?
Interior bone tissue of short, flat, sesamoid + irregularly shaped bones.
In long bones - Core of epiphysis
Tends to be located where bones aren’t heavily stressed or where stresses are applied from many directions.
How are bones connected to homeostasis?
Bone building, maintenance + bone recycling must balance.
Higher resorption than formation = weaker bones.
Bone Adapt. Through exercise
Wolff’s law holds that a bone grows or remodels in response to the forces which act on it.
Changes in bone density in response to exercise + tension + compression forces must balance.
Where in the bones are BV abundant?
Parts containing red bone marrow, pass into bones from periosteum.
Where do the Periosteal arteries enter the diaphysis through?
What do they do?
Interosteonic canals accompanied by nerves.
Supply periosteum + outer part of compact bone.
What does the large nutrient artery do upon entering the medullary cavity?
Divides into proximal + distal branches that course toward each end of the bone.
What do the Proximal + distal branches do?
Supply inner part of:
- compact bone tissue of diaphysis
- spongy bone tissue
- red bone marrow
as far as the epiphyseal plates.
What type of arteries are the ends of long bones supplied by?
Metaphyseal + epiphyseal arteries
What are the 2 main methods of bone formation?
Intramembranous ossification
Endochondral ossification
= Both seen during embryonic development
Where does intramembranous ossification occurs?
W/in mesenchyme
What type of process is endochondral ossification?
Continuous
How does endochondral ossification begin?
When chemical messages are sent to mesenchyme cells
Endochondral ossification
What happens once chemical messages are sent to the mesenchyme cells
Causes them to crowd together in the shape of the future bone + develop into CHONDROBLASTS
Endochondral ossification
What happens once the chondroblasts have been developed
Secrete extracellular matriculates which prod. a hyaline cartilage model
Endochondral ossification
What happens to the mesenchyme cells surrounding the hyaline cartilage model
Condense to form perichondrium.
Endochondral ossification
What happens as the chondroblasts become encased in the extracellular matrix?
They differentiate into CHONDROCYTES.
Endochondral ossification
What are the 2 methods in which the hyaline cartilage model grows?
Interstitial growth
Appositional growth
Endochondral ossification
Interstitial growth
When chondrocytes undergo continual cell division + more extracellular matrix is secreted.
Occurs from w/in the model + ⬆️ bone length
Endochondral ossification
Appositional growth
Occurs when new chondroblasts continually develop from the outer perichondrium.
They secrete new matrix material + result in ⬆️ bone model WIDTH.
Endochondral ossification
What happens as the hyaline cartilage model grows?
Central chondrocytes hypertrophy
+
Surrounding extracellular matrix calcifies.
Endochondral ossification
What happens once the extracellular matrix has been calcified?
Nutrients can’t diffuse through = encased chondrocytes die = leaving open spaces.
Endochondral ossification
Extracellular matrix has been calcified - nutrients can’t diffuse through.
What happens next?
Nutrient artery passes through:
- perichondrium
- nutrient foramen
then burrows into central region of calcifying cartilage model.
Endochondral ossification
What happens once the nutrient artery passes through the nutrient foramen?
Stimulates new cells in perichondrium to differentiate into osteoblasts – eventually forming the periosteum.
Endochondral ossification
When does the primary ossification centre grow?
When periosteal capillaries grow into the calcified cartilage + chondrocytes hypertrophy + die.
Endochondral ossification
Where does the primary ossification centre grow?
W/in the shaft of the bone
Endochondral ossification
When is the spongy trabecular bone formed?
When osteoblasts replace the calcified cartilage + secrete bone extracellular matrix = osteoid.
Endochondral ossification
What do the invading osteoclasts do?
Break down some of the central trabecular bone to form a medullary cavity in the diaphysis (shaft) of the bone.
Surrounding bone is replaced by compact bone.
Endochondral ossification
What happens when the surrounding bone is being replaced by compact bone?
Branches of the epiphyseal artery invade the epiphyses.
== Induces a 2ndary ossification centre.
Endochondral ossification
What happens at the 2ndary ossification centre?
Cartilage is replaced by bone
but
No medullary cavity is formed.
Endochondral ossification
Lastly, what happens to the hyaline cartilage covering the epiphysis?
+ then what happens to the hyaline cartilage between the epiphysis + diaphysis?
Covering epiphysis - Develops into articular cartilage
Between ep. + diaphysis - Remains + forms epiphyseal growth plate.
Where does bone develop from in intramembranous ossification?
A fibrous membrane
What is intramembranous ossification responsible for?
Prod. flat bones in skull + clavicle
What 4 steps are in intramembranous ossification?
Ossification centre
Calcification of matrix
Formation of trabeculae
Development of periosteum
Intramembranous ossification
- Ossification centre
What happens?
Chemical messages cause mesenchyme cells to crowd together to form ossification centre.
Intramembranous ossification
- Ossification centre
What happens to the mesenchyme cells once they’ve formed the ossification centre?
Differentiate into osteogenic cells
Later osteoblasts – which secrete extracellular matrix.
Intramembranous ossification
- Calcification of matrix
What do the osteoblasts do?
Secrete a mix of collagen fibres + osteoid.
What does osteoid do over time?
Calcifies
Intramembranous ossification
- Calcification of matrix
What happens as the layers of calcified matrix are continuously laid down?
The trapped osteoblasts, now osteocytes, lie w/in lacunae of an osteon + project their cytoplasmic processes into the radiating canaliculi.
Intramembranous ossification
- Formation of trabeculae
Trabeculae bone - Formed by the accumulating layers of calcified matrix
Intramembranous ossification
- Development of the periosteum
Mesenchyme cells condense around the outside of bone to form periosteum.
Thin layer of compact bone is deposited over surface layers of spongy bone while the rest remains in centre to form DIPLOE.
Intramembranous ossification
- Development of the periosteum
What does the vascular tissue in the diploe differentiate into?
Red bone marrow.
Growth in length of long bones
What part of the cartilage grows by interstitial growth?
Cartilage on side of the epiphyseal plate closest to the epiphysis.
What are the 4 zones of which the epiphyseal growth plate is divided up into?
Zone of resting cartilage
Zone of proliferating cartilage
Zone of hypertrophic cartilage
Zone of calcified cartilage
EPIPHYSEAL GROWTH PLATE
Zone of resting cartilage
- Small scattered chondrocytes on side of epiphyseal plate facing epiphysis.
- Chondrocytes don’t participate in bone growth
- Instead, they attach epiphyseal plate to epiphysis of bone.
EPIPHYSEAL GROWTH PLATE
Zone of proliferating cartilage
- Larger chondrocytes in tall columns.
- Undergo interstitial growth as they divide quickly + secrete extracellular matrix.
== Causing epiphysis to move away from diaphysis == lengthening bone.
EPIPHYSEAL GROWTH PLATE
Zone of hypertrophic cartilage
- Mature chondrocytes
- Enlarge as cells hypertrophy
- Lacunae surrounding cells erode, leaving large spaces.
EPIPHYSEAL GROWTH PLATE
Zone of calcified cartilage
- Thin layer of epiphyseal plate
- Surrounding matrix calcifies + chondrocytes die off.
- Where endochondral bone formation occurs
Where are osteoclasts derived from?
Stem cells that produce macrophages.
Huge cells derived from the fusion of 50 monocytes + are conc. In the endosteum.
Do osteocytes divide?
NO
Are osteoprogenitor cells specialised?
NO
Where are osteoprogenitor cells located?
Inner cellular layer of periosteum
What do osteoprogenitor cells assist with?
Fracture repair
What does each osteon consist of?
Osteocytes arranged in a conc. lamellae around a central canal containing bv.
Osteoblasts are IMMATURE bone cells that secrete matrix compounds, what do they become after this when surrounded by CALCIFIED BONE?
Osteocytes
What is cartilage on the diaphysial side of the bone replaced with?
Bone from endochondral ossification.
