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Thursday, April 18, 2024

General anatomy of bone lecture notes for writtern exam and viva

 General anatomy of bone lecture notes for written exam and viva

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Bone

Definition: bone is a highly vascular, hard form of special connective tissue.

 Composition of bone

1.    Cells :

Osteoprogenitor cells: they are stem cells. They can convert to any types of cells

Osteoblast: calcification of bone matrix

Osteoclast: remodeling of bone

Osteocyte : maintenance of calcification

2.Extracellular matrix:

Organic: collagen fibres, chondroitin sulphate  

Inorganic:  Ca, Mg, and PSO4

Function of bone

  1. Structural support,
  2. Protection of vital organs,
  3. Storage of calcium and magnesium 
  4. Bone contain red bone marrow responsible for blood cell formation

Periosteum

It is a thick fibro-vasculo-cellular layer that covers the outer surface of bone except the articular surfaces which are covered by articular cartilage (hyaline cartilage). 

It consists of two layers:

Outer fibro vascular layer –is composed of collagen fibres and fibroblast  and blood vessels

Inner osteogenic layer – Inner cellular layer or osteogenic layer (containing osteoprogenitor cells which form osteoblasts).

It is united to the underlying bone by Sharpey’s fibers (collagen fibers).

It has very rich nerve supply and therefore it is the most pain sensitive part of bone.

Normally this layer responsible for increasing width of bone. By intramembranous ossification, it increase the width of bone  

 

Functions of periosteum

1.     It receives the  attachments of muscles

2.    Gives nutrition to the outer part of the compact bone by the periosteal vessels

3.    It is important in the repair of fractures

4.    During fetal development, this is responsible for appositional growth of bone

 Sharpey's fibers (bone fibers, or perforating fibres):  are a matrix of connective tissue consisting of bundles of strong collagenous fibres connecting periosteum to bone. They are part of the outer fibrous layer of periosteum, entering into the outer circumferential and interstitial lamellae of bone tissue

Macroscopically bones (without microscope) are two types –

1.     Compact (bony tissue without cavity ) and

2.    spongy (bony tissue contain numerous cavities ) 

 

Cross section of long bone, we fine outer compact bone and inner spongy bone 

Cross section of flat bone of skull: we find Inner & outer table (compact bone) and middle diploe spongy bone)

 Microscopically, bone tissue is formed by small cylindrical unit known as haversian system.

Each haversian system contain a haversian canal,

Lamina-thin plate of bone surrounded by haversian canal,

Lacuna (depressed area within the lamina contain osteocyte)

Canaliculi (very tiny canal contain processes of osteocytes

Volkman’s canal connect two separate haversian canal

Classification of bone:

1.    According to the position-

Axial bone : skull bones, vertebrae

Appendicular bone:  bones of upper and lower limb

2.   Classification of bone according to mechanism  of ossification

Membranous ossification:

EX: head and neck: parietal bone, frontal bone, maxilla, zygomatic,

Superior extremity:   clavicle

Cartilaginous ossification:  Ex: all vertebrae, all ribs, sternum, scapula, all bones of upper limb except clavicle, all bones of lower limb

Membrano-cartilaginous ossification:

Occipital: membranous ossification area above the highest nuchal line, rest of the parts arises from cartilaginous ossification 

Sphenoid: membranous ossification above the lateral part of greater wing and pterygoid process except the hamulus, rest of the part arises from cartilage,

Temporal: membranous ossification – squamous part and tympanic part, rest of the parts arises from cartilage,

 Mandible: cartilaginous ossification anterior part of body and part of ramus above mandibular foramen, rest of the body arises from membranous ossification  

3.   According to the shape (Morphological classification of bone)

            Long bone: they are three types

a.    typical long bone: Ex: femur ,

b.   Modify long bone:Ex:  clavicle (because it is the only bone lies horizontally, has no medullary cavity, and ossify in membrane) 

c.    Miniature long bone: Ex: metacarpal bone , shape long but size smaller than the typical long bone

Short bone: cuboid shaped, presents six surfaces, 4 surface form joint and 2 surface for articulation  

Flat bone: this bone form by two plates of compact bone and middle spongy bone. Ex: parietal bone

Irregular bone : irregular in shape. They mostly form by spongy bone and red marrow with thin outer covering of compact bone Ex: vertebrae 

Pneumatic bone : these bone contain air filled cavity, it makes bone lighter, act as an air conditioning chamber and helps in resonance of voice. Ex: Maxilla

Sesamoid bone : it is developed in the tendon of muscle, act as pulley, has no haversian system and periosteum

Parts of an adult long bone

Adult long bone has two ends: upper end and lower end  and an intervening shaft.

• Shaft (diaphysis) The shaft of the long bone is composed of the following from outside to inside

• Cortex (cortical bone):  It is made up of dense compact/cortical bone.

• Marrow cavity: deep to the cortex is the medullary cavity. It is lined by endosteum and is filled with bone marrow (depending upon age of the individual it can be red or    yellow marrow).

 • Ends of long bone (Epiphysis): Are made up of cancellous bone (having bony trabeculae and marrow spaces (filled with red bone marrow)). The articular surfaces at the ends are  covered by articular (hyaline) cartilage).

Parts of growing long bone:

 Epiphysis (E)

Epiphyseal cartilage (EC) ,

Metaphysis (M) (it is the part of diaphysis near the epiphyseal cartilage ) and

Diaphysis(D)

Diaphysis: it is the part of growing long bone which ossify from primary ossification centre and form shaft of bone.

Epiphysis: parts of a growing long bone which ossify from secondary ossification center

Types of epiphysis:

Pressure epiphysis: it transmits body weight. Ex:  head of femur

Traction epiphysis: it is produce by pull of muscles EX:  trochanter of femur 

Atavistic epiphysis: coracoid process of scapula. Coracoids process is independent bone unit with scapula for nutrition.

Aberrant epiphyses: This Epiphysis is not always present. For example: the epiphyses at the head of the first metacarpal bone

Epiphyseal cartilage: it is the plate of hyaline cartilage situated between the epiphysis and diaphysis. The plate is found in children and adolescents; In adults, who have stopped growing, the plate is replaced by an epiphyseal line.

One of the steps of Intracartilaginous ossification occurs in epiphyseal cartilage of growing long bone:

Histologically, there are some zone present in epiphyseal cartilage. These zone explain how a bone grow in length.

Zone of reserve No proliferation of chondrocytes

Zone of proliferation Chondrocytes undergo rapid mitosis under influence of growth hormone

Zone of  hypertrophy Chondrocytes stop mitosis, and begin to hypertrophy by accumulating glycogen, lipids, and alkaline phosphatase

Zone of cellular death Cartilagenous matrix begins to calcify- so chondrocytes do not get nutrition-- death of chondrocytes leaving empty spaces.--  Periosteal bud with Blood vessels begin to grow through the empty spaces

Zone of ossification Periosteal buds contain osteoblast which calcify the bone matrix and blood vessel form red bone marrow. This newly form zone of ossification add as metaphysis of growing long bone and bone increase in length

 When grow of bone complete the zone of reserve begin to proliferate so whole epiphyseal cartilage converted into bone

Metaphysis:it is part of diaphysis near the epiphyseal cartilage

Clinical importance of metaphysis

It is the most actively growing area of long bone

Profuse blood supply, contain hair pin loops like vessels so it is the common sites of infection 

Muscle, ligament and capsule of joint are attached close to it

Metaphysis is common site of osteomyelitis in children

Growing end of the long bone : the epiphysis which appear first and unit last with the diaphysis

The growing end is situated against the direction of the nutrient foramen

 Upper end of humerus and lower end of Radius and ulna is the growing end

Lower end of femus and upper end of tibia and fibula is the growing end

Clinical importance: injury or infection of this end makes the bone stunted in growth

Blood supply of Developing long bone /growing long bone

• Nutrient artery: It enters the shaft through the nutrient foramen, pass obliquely through the cortex of shaft. Then, it enters medullary cavity and divides into ascending and descending branches.

These branches reach the metaphysis and form ‘hair pin loops’ branches which are anastomose with the metaphyseal and epiphyseal arteries.

Supply areas of the nutrient artery  

·       The medullary cavity,

·       Inner 2/3rd of cortical bone of diaphysis,

·       Metaphysis

• Periosteal arteries:

Are branches of neighbouring muscular arteries and therefore they are especially numerous beneath the muscular attachments.

They ramify beneath the periosteum and reach the underlying cortical bone through the Volkman’s canals.

Supply area of periosteal arteries

Periosteum

outer 1/3rd of the cortical bone of shaft.

• Epiphyseal arteries:

 They are derived from the peri-articular (around the joint) anastomosis present around the non-articular surface of ends of long bones.

 They enter the epiphyseal ends through the numerous foramina present in the non articular part. The number and size of these foramina gives an idea of the vascularity of the ends of long bones.

• Metaphyseal arteries:

Numerous arteries arise from the anastomosis around the joint and pierce the metaphysis along the attachment of the joint capsule

Ossification

 It  is the process of new bone formation. Two Mechanism of ossification – intra cartilaginous and intramembranous ossification  

How a cartilaginous model of bone converted into adult bone?

Cartilaginous model of a long bone

Bone formation is started at diaphysis of growing long bone. This area is known as primary ossification centre

After formation of diaphysis, bone formation is started at epiphyseal ends. These   areas known as secondary ossification centres

So upper and lower end plus central part of growing long bone converted into bone from cartilage

 but epiphyseal cartilage remain unchanged until the end of growth

 In adult, Epiphyseal cartilages converted into bone and form epiphyseal line,

Adult bone is formed by fusion of epiphysis and diaphysis 

S N: Ossification of long bone: occur by both intracartilaginous and intramembranous ossificatin process

Length of long bone increase by intracartilaginous ossification (location : epiphyseal cartilage of growing long bone )

Width of long bone increase by intra membranous ossification (location : periosteum of growing long bone- osteogenic layer of periosteum is responsible for membranous ossification )

Intra membranous ossification:

1.     Mesenchyme (fetal connective tissue membrane) contain mesenchymal sterm cell , they proliferate and condense to primary ossification centre

2.    The mesenchymal stem cells are converted into osteoblast

3.    Osteoblasts begin to secrete un-calcify bone matrix away from the blood vessel .

4.    Soon matrix become calcify and some of osteoblast tapped   in calcifies matrix become osteocyte.

5.    By this process small bone spicules are form. Bone spicules are unite with each other  and form spongy bone/ trabecular bone

6.    embryonic blood vessels grow within spaces between bone spicules and ultimately form red bone marrow which is formed by  hematopoietic stem cells, reticular cell and fibres and fibroblast and blood vessels

7.    the middle part of spongy bone remain spongy but outer and inner part of spongy bone remodel and form compact bone

8.    Outer and inner vascular mesenchyme do not take part in ossification process are converted into periosteum, endosteum or endosteal dura

Classification of ossification centre

1.     A primary ossification center is the first area of a bone to start ossifying.

 It usually appears during intra-uterine life in the central part of each developing bone.

Exception: carpal bones of hand

 In long bones the primary ossification centers appear in the diaphysis/shaft and in irregular bones the primary centers appear usually in the body of the bone.

All long bones have only one primary center but some irregular bones such as the hip bone and vertebrae have multiple primary centers.

2.    Secondary ossification centre: A secondary ossification center is the area of ossification that appears after the primary ossification center has already appeared - most of which appear during the postnatal and adolescent years. Most bones have more than one secondary ossification center. In long bones, the secondary centers appear in the epiphyses (upper and lower end).

 


Name of bone

Primary ossification center

Secondary ossification center

Clavicle

Two

One for sternal end

Humerus

One for shaft

Three for upper end – head , greater & lesser tubercle & Four for lower end – lateral & medial epicondyle, capitulum, trochlear

Radius

One for shaft

One for upper end & One for lower end

Ulna

One for shaft

One for upper end & One for lower end

Carpal bone

One center which appear after birth

No secondary ossification centre

Metacarpal bone

One center for shaft

One 2nd ossification centre : base of  1st metacarpal bones is ossified from 2nd ossification center& Heads of  2-5 metacarpal bone are ossified from 2nd ossification center

Phalanges

One center for shaft & head

One 2nd ossification center for base  of each phalanx

    Lower limb

Name of bone

Primary ossification center

Secondary ossification center

Hip bone

Three – ilium, ischium, pubis

5 secondary ossification center 

Femur

One for shaft

Three for upper end – head , greater & lesser trochanter & One for lower end

Tibia

One primary ossification center for shaft

One for upper end  & One for lower end

Fibula

One primary ossification center for shaft

One for upper end

One for lower end

Tarsal bone (except calcaneus)

One primary ossification center

No secondary ossification centre

Calcaneus

One primary ossification center

One secondary ossification centre

Metatarsal bone

One primary ossification center for shaft

One 2nd ossification centre : base of  1st metatarsal bones is ossified from 2nd ossification center & Heads of  2-5 metatarsal bone are ossified from 2nd ossification center

Phalanges

One  for shaft and head

One center for base  of each phalanx

Bone marrow: It is a soft tissue which fills the medullary cavity of long bone and the trabeculae of spongy bone

Types :   Yellow bone marrow: location: medullary cavity of long bone

Red bone marrow :   Location :

In new bone, it is occupied in whole skeleton

By the 7th year , medullary cavity of long bone contain white bone marrow

By the age of 20, red bone marrow found in  upper and lower end of long, diploe of skull bone, sternum, rib, vertebra

Function : red bone marrow responsible for blood cells formation

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Lumbar vs sacral splanchnic nerve

 

Lumbar vs  sacral splanchnic nerve

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Lumbar  splanchnic nerve

Origin: The lumbar splanchnic nerves go from the abdomen and pelvic areas to the lumbar spinal cord segments (typically L1–L3).
Type: These nerves transmit sympathetic fibers from the spinal cord, as well as occasionally sensory fibers.
Function: The lumbar splanchnic nerves innervate the intestines, bladder, and reproductive organs, among other abdominal and pelvic organs. They are involved in the control of blood vessels, glands, and smooth muscle in these regions.
Ganglia: Within the prevertebral ganglia of the abdominal cavity, these nerves may also synapse in other ganglia, such as the inferior mesenteric ganglion.

 Sacral  splanchnic nerve

Origin: Sacral splanchnic nerves travel to the pelvic area from the sacral spinal cord segments, which are typically S1–S4.
Type: From the spinal cord, these neurons transmit sympathetic fibers as well as occasionally sensory fibers.
Function: Sacral splanchnic nerves serve to govern smooth muscle, glands, and blood vessels via innervating pelvic organs such the bladder, rectum, and reproductive organs.
Ganglia: These nerves may form synapses in the pelvic plexus, also referred to as the inferior hypogastric plexus, and other pelvic ganglia.

 

 

Lumbar splanchnic nerve

Sacral splanchnic nerve

Location of preganglionic neuron

Lateral horn of gray matter of Lumbar 1,2 spinal cord segment

Lateral horn of gray matter of Lumbar 1,2 spinal cord segment

Sympathetic ganglion

Lumbar 1,2

Sacral 1-5

Collateral Ganglion

Inferior mesenteric ganglion

Inferior mesenteric ganglion

Form Autonomic Plexus

Superior hypogastric plexus

Inferior hypogastric plexus

Fibres

 

Preganglionic

Sympathetic

Fibres and

General visceral afferent fiber

Preganglionic and postganglionic fibres

Sympathetic

Fibres and

General visceral afferent fiber

Functions

Innervate pelvic viscera and vasculature

The inferior hypogastric plexus is a plexus of nerves that supplies the viscera of the pelvic cavity. The inferior hypogastric plexus gives rise to the prostatic plexus in males and the uterovaginal plexus in females

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Cartilage lecture notes for written and viva examination

 Cartilage lecture notes for written and viva examination

It is a special form of connective tissue composed of chondrocytes and a highly specialized extracellular matrix which designed to support to regions of body that require rigidity and flexibility.

Functions of Cartilages:

  • Articular cartilage form smooth surface for movement
  • It makes shape of ear, nose
  • Act as shock absorber in spine ( intervertebral discs)
  • It more flexible than the bone, so it breaks less costal cartilage of thoracic cage, ear , nose
  • During development of bone, cartilage forms the initial blueprint of the skeletal system before being replaced by bone (a process called endochondral ossification).
  • It form framework for respiratory passage to prevent their collapse.

Components of cartilages:

Cells of cartilage: chondroblasts and chondrocytes

Extracellular matrix:

Fibres : collagen and elastic ( impart tensile strength and elasticity)

Ground substance contain hyaluronic acid , glycosaminoglycans and (chondroitin sulphate, keratan sulphate), glycoproteins (chondronectin).

Types of cartilage: (according to the number of cells and the nature of the matrix)  

  1. Hyaline cartilage 2.Elastic cartilage 3. Fibrocartilage

 

Features

Hyaline cartilage

Elastic cartilage

Fibrocartilage

Distribution

Tracheo-bronchial cartilage, costal cartilage of rib and nasal cartilage, most of the laryngeal cartilage 

Epiglottis, external ear and ear canal, auditory tube, some laryngeal cartilage( corniculate, cuneiform etc.)

Intervertebral discs and pubic symphysis, articular discs of temporo-mandibular, sternoclavicular joint, menisci of the knee joint

Function

Resistant to compression, provides cushioning and low friction surface for joint , structural support in respiratory system

Provides flexible support

Resist deformation under stress

Presence of perichondrium

Yes (except articular cartilage and epiphyseal plates)

Yes

No

Undergoes  calcification

Yes ( during endochondral bone formation )

No

Yes (during bone repair)

Cell types

Chondroblasts, chondrocytes

Chondroblasts, chondrocytes

Chondrocytes, fibroblasts

Chondrocyte in lacunae

Smaller compare to elastic cartilage arranged in isogenous group (2-8)

Larger compare to hyaline  cartilage and closely packed and arranged in isogenous group (2-4)

Small arrange in row parallel to bundles of collagen fibers

Extracellular matrix

Type II collagen fibrils

Homogenous and basophilic

Type II collagen fibrils and elastic fibers

Type II & type I collagen fibers

Eosinophilic

Slide identification

*Cartilaginous matrix: is homogeneous

*Cells: Lacunae (ovoid space within the matrix) contain chondrocyte singly or isogenous groups

*Perichondrium: surround the cartilage (if present within the slide then add this points)

*Cartilage matrix contain elastic fiber so it is not homogenous

Lacunae (ovoid space within the matrix) contain chondrocyte singly or isogenous groups

*Perichondrium surround the cartilage (if present within the slide then add this points)

Cartilaginous matrix: thick collagen fibres located between parallel rows of condrocytes

*Cells: the chondrocytes are smaller than those of hyaline or elastic cartilage and they are arranged in  parallel rows between the bundles of  thick collagen fibers

*Perichondrium: absent

 

Peculiarities of the cartilage:

  1. Cartilages lack blood vessels, lymphatics and nerves.
  2. Cartilage has a limited ability to heal and regenerate, primarily because of its avascular nature.
  3. when matrix calcified the chondrocytes are die
  4. cartilage cells grow by appositional and interstitial methods
  5. Cartilages are supplied by diffusion of oxygen and nutrients through extracellular matrix from blood vessels in perichondrium /surrounding tissues/synovial fluid.
  6. Extracellular matrix of cartilages is highly permeable.
  7. Cartilages are usually surrounded by perichondrium (except articular cartilage and fibrocartilage)

Perichonrium

 it is a connective tissue membrane  that surrounds the hyaline and elastic cartilages.

         It has

(a)  An outer fibrous layer, is composed mostly of fibroblasts and collagen fibers, &

blood vessels  

(b)  A inner cellular or chondrogenic layer, is composed of chondroblast and   chondrogenic cells.

 This   layer helps in growth and repair of cartilage.

Cartilage which are covered by perichondrium:

1.     Hyaline cartilage (except hyaline cartilage of articular surfaces of a  joint, epiphyseal cartilage)

2.     Elastic cartilage

The characteristic features of Chondroblasts and chondrocytes

Chondrocytes and chondroblasts  are derived from mesenchymal cells.

Features of Chondroblasts

  1. Immature and young cells of cartilage
  2. Shape : oval shape with few processes
  3. Location : Chondroblasts are typically found in the perichondrium, a layer of connective tissue surrounding most types of cartilage (excluding articular cartilage, fibrocartilage)
  4. Chondroblasts are responsible for producing the extracellular matrix (ECM) of cartilage, which includes collagen fibers and proteoglycans
  5. Chondroblasts are precursor cells that can differentiate into chondrocytes, the mature cells of cartilage
  6. Chondroblasts contain a high density of organelles, such as the rough endoplasmic reticulum and Golgi apparatus, which are essential for the synthesis and secretion of proteins and other components of the extracellular matrix.
  7. Chondroblasts play a central role in both appositional growth (growth in width) and interstitial growth (growth in length) of cartilage.

 

Features of chondrocytes

  1. older and mature cells
  2. Shape : rounded or spherical shape in the center part of cartilage and oval at the periphery
  3. Location : Chondrocytes are found within small cavities called lacunae in the extracellular matrix (ECM) of cartilage singly or in isogenous groups..
  4. Chondrocytes generally have a low rate of cell division and mitotic activity, contributing to the limited regenerative capacity of cartilage tissue.
  5. Chondrocytes can sense changes in mechanical stress and respond by altering their production of extracellular matrix components.
  6. Chondrocytes typically function in a low-oxygen environment because cartilage is avascular (lacks blood vessels).
  7. Chondrocytes have some rough endoplasmic reticulum,golgi Apparatus, Lysosome which are involved in the degradation of cellular waste and  mitochondria, which provide energy for cellular activities, primarily through anaerobic metabolism due to the low oxygen environment of cartilage.

Growth of  cartilage

      Cartilage grows by two methods:

 

Interstitial growth: In this type of growth, newly generated chondrocytes deposit extracellular matrix while existing chondrocytes divide mitotically to produce new cartilage.

Appositional growth: The inner layer of perichondrium cells, also known as chondrogenic cells, divide and develop into chondroblasts during a process known as apogephalic growth. The matrix and freshly produced cells are introduced at the surface and periphery.

 

Appositional growth:  In this type of growth,  the inner layer of perichondrium cells ( chondrogenic cells) divide and differentiate into chondroblasts. The newly formed cells and matrix are added at the periphery/surface

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Confusing terminology trabeculae of bone , trabeculae of gland , trabecular sinuses , trabecular artery or vein

 Confusing terminology trabeculae of bone , trabeculae of gland , trabecular sinuses , trabecular artery or vein 

Trabeculae of glands

glands are surrounded by a strong connective tissue capsule, which has fibrous extensions within the gland which is known as trabeculae

Trabeculae or trabeculae of bone

they are the thin columns and plates of bone that create a spongy structure in a cancellous bone, which is located at the ends of long bones and in the pelvis, ribs, skull, and vertebrae.

Trabecular sinus

The trabecular sinuses are those sinuses that surrounding the trabeculae of the lymph node.

Trabecular arteries or vein

They are the name of the branches of the splenic artery after it passes into the trabeculae of the spleen

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Tuesday, April 16, 2024

periosteum vs endosteum

 periosteum vs endosteum 

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Periosteum

Endosteum

Location : external surface of bone except articular surface

 

Location :

medullary cavity

Compact bone facing marrow cavity

Lined the trabeculae of spongy bone

Haversian canal

Volkmann’s canal

 

Formation : it is a connective tissue membrane formed by dense irregular connective tissue

Formation : it is formed by only one cell layer thick osteoprogenitor cells and little connective tissue 

 

Histology:  it consists of an outer fibrous layer, and an inner cambium layer (or osteogenic layer). The fibrous layer is of dense irregular connective tissue, containing fibroblasts, while the cambium layer is highly cellular containing progenitor cells that develop into osteoblasts

Histology : Osteoprogenitor cells and bone-lining cells are difficult to distinguish at the microscopic level. They are both flattened in shape with elongated nuclei and indistinguishable cytoplasmic features. Because of their location within the bone cavities they are frequently called endosteal cells.

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Osteon vs osteoid : confusing term in skeletal system

 

Osteon vs  osteoid

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Osteon

Osteoid

An osteon, it is also known as a Haversian system which is a cylindrical structure found in compact bone tissue. It provides strength and support to the bone, and it also helps in the repair and remodeling of bone tissue.

It is  typically develop in preexisting compact bone

Osteoid, it’s another meaning is ‘like bone’. it is defined as un-mineralized bone tissue and is a key structure in the development of mature mineralized bone