LECTURE 4- Bone Tissue and its Microscopic Structure
Characteristic of the bone
● Adult skeleton has approx 206 separate bones
● Body system is divided into axial and appendicular skeleton
● Bone has cells and a calcified extracellular matrix- cells, gels, fibers
● Bone responds to external forces we experience, it can remodel and change
shape to reflect how we use them throughout life. Eg. makes area of our body
more robust, build up more muscle attachments.
● Bone also responds to trauma to form and reform/ unite broken parts
Describe the microanatomical structure of bone tissue and explain how this reflects
function.
Bone tissue composition
● Bone is a connective tissue
● Function: support other tissues/ organs and maintain form/ shape
● Two bone extracellular matrix (ECM components (not cells):
● Organic (33%)
● Made up of collagen (protein), ground substance (proteoglycans/proteins)
● Function: resist tension/pull and allow flexibility
● Collagen fibers (bundles of collagen molecules) criss-cross throughout the
matrix allow flexibility for forces to come through and prevent breakage by
weight force.
● Eg. fibula with collagen removed is brittle and breaks easily
● Inorganic (67%)
● Made up of minerals eg. hydroxyapatite (calcium phosphate carbon material)
and other Ca minerals (salts)
● Function of inorganic (mineral) component is to make bone hard and resistant
to compression
● Eg. bone with inorganic components removed makes it too flexible
● Hard but inflexible and brittle/shatters easily
● Cellular component of bone
● Makes up 2% of bone weight
, ● Bone has a calcified matrix that is maintained and altered by osteogenic cells,
osteoblasts, osteoclasts and osteocytes which have specific roles within our
bones.
● Together these cells maintain bone homeostasis which is the stable balance
between bone formation and destruction to maintain bone mass
● Ostegenic (stem) cells (pg 258)
● Location is cellular layer of periosteum and cellular layer of endosteum that
lines medullary cavities
● These stem cells divide to produce daughter cells that differentiate into
osteoblasts
● Function is to maintain osteoblast population
● Osteoblasts (builders)
● Location is
● Function is to produce new bone matrix via ossification/osteogenesis which
involves making and releasing the protein and organic components of the matrix
to convert osteoid to bone
● Osteocytes (maintainers)
● Mature bone cells that develop from osteoblasts that have become completely
surrounded by bone matrix
● Location is
● Function is to monitor and maintain bone matrix by recycling protein and
minerals of surrounding matrix
● Osteocytes make up most of the cell population in bon uhh e.
● Each osteocyte occupies one lacuna (plural=lacunae), fluid filled pocket
sandwiched between layers of matrix/ lamella
● Osteocyte processes extend into canaliculi that penetrate the matrix. Canaliculi
interconnect lacunae and reach vascular passageways to provide route for
nutrient diffusion
● Osteoclasts (destroyers)
● Large cells with 50+ nuclei
● Function is to remove bone matrix via osteolysis, which is secreting acids and
enzymes to dissolve matrix and release stored minerals
Gross structure of two types of bones
,The two types of bones are made of same components but are structured differently:
● Compact bone= osteon structure (like a straw)
● Macroscopically: Periosteum/ outer surface seems dense and impenetrable
and has foramina for blood and nutrient supply, nerves for cell communication.
● Strength and load-bearing
● Longitudinal parallel osteon unit is composed of concentric bone layers called
circumferential lamellae which surround a central canal. Osteocytes are
located in lacunae which are found between these layers.
● Osteon function is to provide a pathway for nutrients and nerves to channel
to cells in the ECM
● Components of Osteon include
● Central canal (bulls eye) are parallel to surface of bone,
● Function is to contain blood vessel and nerves to supply blood to osteons
deeper in the bone and tissues in medullary cavity
● (Concentric) lamellae is a series of cylinders made up of inorganic components
of ECM that surround the central canal.
● Function is to form osteon shape and resist tensile forces (collagen fibers)
○ Interstitial lamellae fill spaces between osteons
○ Circumferential lamellae contribute to bone diameter to give strength
● Lacunae are lakes where osteocytes occupy, and they lie between lamellae.
● Canaliculi are channels that radiate through the lamellae.
● Function is to provide a channel for osteocytes through ECM, interconnect
lacunae between osteon units and lacunae with central canal.
● Cancellous/ Spongy/ Trabecular bone= Trabecular structure
● Cancellous bone are made up of trabeculae, in which, lamella are arranged in
struts and plates.
● Less dense than compact bone, makes up most parts of short, flat, irregular
bones and epiphysis of long bones.
, ● Cancellous bone is found where bones are not heavily stressed or where
stresses come from many directions i.e trabeculae found in epiphysis in criss
cross way
● Osteocytes are housed in lacuna in between lamella or on the surface
● Components of cancellous bone are similar to those in compact EXCEPT
cancellous bone trabecular structure doesn’t have central canal because the
branches are thin and in direct contact with marrow (marrow fills the cavities
between trabeculae) so nutrients can reach osteocytes via diffusion along the
canaliculi that open to the trabeculae surface
● There are no capillaries or venules in the matrix of cancellous bone
● Organisation of cancellous bone in relation to function
● Organization of trabeculae in cancellous bone resists forces from multiple
directions
● This allows it to direct force from body weight in a single direction down the
shaft/ diaphysis, spreading the force distally
● Upper to lower body: trabeculae channel weight around the illia into femora,
trabeculae most focused on primary weight bearing area
Bone tissue remodelling
● Appositional growth
● The growth of bone diameter by addition of bony matrix on the outer surface
● Increases diameter of existing bones but DOESN’T FORM ORIGINAL BONES
1. Osteoblasts communicated by osteocytes to form more bone**
2. Osteogenic cells in inner layer of periosteum produce daughter cells that
differentiate into osteoblast and add bone matrix in lamellae to outer bone
surface, increasing bone diameter since circumferential lamellae deposited
3. Osteoblasts trapped between the lamellae differentiate into osteocytes
4. As bones added to the outer layer by appositional growth, osteoclasts are
removing and recycling lamellae at the inner surface, increasing medullary
cavity diameter at the same time.
Describe how bone maintains homeostasis
● Homeostasis requires balance of osteoblast and osteoclast activity, since
bone is constantly being formed and destroyed to maintain net bone mass
● Bone homeostasis allows body to mobilize trace elements i.e calcium,
phosphate and other minerals stored in the bone matrix (by destroying them)
● Remodeling process allows bone to respond plastically (rejuvenate and
change shape) through lifetime to resist strain
Characteristic of the bone
● Adult skeleton has approx 206 separate bones
● Body system is divided into axial and appendicular skeleton
● Bone has cells and a calcified extracellular matrix- cells, gels, fibers
● Bone responds to external forces we experience, it can remodel and change
shape to reflect how we use them throughout life. Eg. makes area of our body
more robust, build up more muscle attachments.
● Bone also responds to trauma to form and reform/ unite broken parts
Describe the microanatomical structure of bone tissue and explain how this reflects
function.
Bone tissue composition
● Bone is a connective tissue
● Function: support other tissues/ organs and maintain form/ shape
● Two bone extracellular matrix (ECM components (not cells):
● Organic (33%)
● Made up of collagen (protein), ground substance (proteoglycans/proteins)
● Function: resist tension/pull and allow flexibility
● Collagen fibers (bundles of collagen molecules) criss-cross throughout the
matrix allow flexibility for forces to come through and prevent breakage by
weight force.
● Eg. fibula with collagen removed is brittle and breaks easily
● Inorganic (67%)
● Made up of minerals eg. hydroxyapatite (calcium phosphate carbon material)
and other Ca minerals (salts)
● Function of inorganic (mineral) component is to make bone hard and resistant
to compression
● Eg. bone with inorganic components removed makes it too flexible
● Hard but inflexible and brittle/shatters easily
● Cellular component of bone
● Makes up 2% of bone weight
, ● Bone has a calcified matrix that is maintained and altered by osteogenic cells,
osteoblasts, osteoclasts and osteocytes which have specific roles within our
bones.
● Together these cells maintain bone homeostasis which is the stable balance
between bone formation and destruction to maintain bone mass
● Ostegenic (stem) cells (pg 258)
● Location is cellular layer of periosteum and cellular layer of endosteum that
lines medullary cavities
● These stem cells divide to produce daughter cells that differentiate into
osteoblasts
● Function is to maintain osteoblast population
● Osteoblasts (builders)
● Location is
● Function is to produce new bone matrix via ossification/osteogenesis which
involves making and releasing the protein and organic components of the matrix
to convert osteoid to bone
● Osteocytes (maintainers)
● Mature bone cells that develop from osteoblasts that have become completely
surrounded by bone matrix
● Location is
● Function is to monitor and maintain bone matrix by recycling protein and
minerals of surrounding matrix
● Osteocytes make up most of the cell population in bon uhh e.
● Each osteocyte occupies one lacuna (plural=lacunae), fluid filled pocket
sandwiched between layers of matrix/ lamella
● Osteocyte processes extend into canaliculi that penetrate the matrix. Canaliculi
interconnect lacunae and reach vascular passageways to provide route for
nutrient diffusion
● Osteoclasts (destroyers)
● Large cells with 50+ nuclei
● Function is to remove bone matrix via osteolysis, which is secreting acids and
enzymes to dissolve matrix and release stored minerals
Gross structure of two types of bones
,The two types of bones are made of same components but are structured differently:
● Compact bone= osteon structure (like a straw)
● Macroscopically: Periosteum/ outer surface seems dense and impenetrable
and has foramina for blood and nutrient supply, nerves for cell communication.
● Strength and load-bearing
● Longitudinal parallel osteon unit is composed of concentric bone layers called
circumferential lamellae which surround a central canal. Osteocytes are
located in lacunae which are found between these layers.
● Osteon function is to provide a pathway for nutrients and nerves to channel
to cells in the ECM
● Components of Osteon include
● Central canal (bulls eye) are parallel to surface of bone,
● Function is to contain blood vessel and nerves to supply blood to osteons
deeper in the bone and tissues in medullary cavity
● (Concentric) lamellae is a series of cylinders made up of inorganic components
of ECM that surround the central canal.
● Function is to form osteon shape and resist tensile forces (collagen fibers)
○ Interstitial lamellae fill spaces between osteons
○ Circumferential lamellae contribute to bone diameter to give strength
● Lacunae are lakes where osteocytes occupy, and they lie between lamellae.
● Canaliculi are channels that radiate through the lamellae.
● Function is to provide a channel for osteocytes through ECM, interconnect
lacunae between osteon units and lacunae with central canal.
● Cancellous/ Spongy/ Trabecular bone= Trabecular structure
● Cancellous bone are made up of trabeculae, in which, lamella are arranged in
struts and plates.
● Less dense than compact bone, makes up most parts of short, flat, irregular
bones and epiphysis of long bones.
, ● Cancellous bone is found where bones are not heavily stressed or where
stresses come from many directions i.e trabeculae found in epiphysis in criss
cross way
● Osteocytes are housed in lacuna in between lamella or on the surface
● Components of cancellous bone are similar to those in compact EXCEPT
cancellous bone trabecular structure doesn’t have central canal because the
branches are thin and in direct contact with marrow (marrow fills the cavities
between trabeculae) so nutrients can reach osteocytes via diffusion along the
canaliculi that open to the trabeculae surface
● There are no capillaries or venules in the matrix of cancellous bone
● Organisation of cancellous bone in relation to function
● Organization of trabeculae in cancellous bone resists forces from multiple
directions
● This allows it to direct force from body weight in a single direction down the
shaft/ diaphysis, spreading the force distally
● Upper to lower body: trabeculae channel weight around the illia into femora,
trabeculae most focused on primary weight bearing area
Bone tissue remodelling
● Appositional growth
● The growth of bone diameter by addition of bony matrix on the outer surface
● Increases diameter of existing bones but DOESN’T FORM ORIGINAL BONES
1. Osteoblasts communicated by osteocytes to form more bone**
2. Osteogenic cells in inner layer of periosteum produce daughter cells that
differentiate into osteoblast and add bone matrix in lamellae to outer bone
surface, increasing bone diameter since circumferential lamellae deposited
3. Osteoblasts trapped between the lamellae differentiate into osteocytes
4. As bones added to the outer layer by appositional growth, osteoclasts are
removing and recycling lamellae at the inner surface, increasing medullary
cavity diameter at the same time.
Describe how bone maintains homeostasis
● Homeostasis requires balance of osteoblast and osteoclast activity, since
bone is constantly being formed and destroyed to maintain net bone mass
● Bone homeostasis allows body to mobilize trace elements i.e calcium,
phosphate and other minerals stored in the bone matrix (by destroying them)
● Remodeling process allows bone to respond plastically (rejuvenate and
change shape) through lifetime to resist strain
