Glossary of Bone Histology

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Created by optom

bone is a specialized connective tissue. What makes up bone and what is its distinguishing feature?
cells, fibres & ground substand

distinguishing feature: mineralized matrix (ECM)of calcium and phosphate. Produces extremely hard tissue

What are the functions of bone?
(1) support and attachment of muscles
(2) protection of soft organs
(3) storage and mobilization of calcium and phosphate
(4) marrow produces blood cells

What is the major type of collagen in bone matrix?

Which other types are present?

major = Type I collagen (some type V)

minor = III, XI and XIII

By weight, what % of bone matrix is ground substance?

What is the function of ECM?

Name 4 things bound in bone matrix

10% of ECM is ground substance (ie. not collagen fibres)
By weight, what % of bone matrix is ground substance?

What is the function of the ground substance?

10% of ECM is ground substance (ie. not collagen fibres)

Function = bone growth, development, remodelling and repair

Name 4 structures bound in bone matrix

(1) PG and GAG
(2) MAGs (osteonectin and osteopontin)
(3) Bone-specific vitamin-K dependent proteins
(4) Growth factors and cytokines

What are lacunae?
holes in the matrix inside which an osteocyte (bone cell) is found
What are canaliculi?
canals that run through the matrix and connect adjacent lacunae. Osteocyte cell processes extend through these channels so that they can communicate with other cell processes (via gap junctions)
What is an osteocyte?
bone cell surrounded by its own matrix
What are osteoprogenitor cells?
precursors to osteoblasts; arise from mesenchymal cells
What are osteoblasts?
cells responsible for bone formation
--> actively secrete bone matrix
What are
a) periosteal cells?
b) endosteal cells?

a) periosteal cells line the external bone surface

b) endosteal cells line the internal bone surface

What are osteoclasts?
bone resorbing cells (break down bone)
What are the two types of bone on a gross morphological level?
compact and spongy
What are 3 characteristics of spongy bone?

Where in long bones is it usually found?

(1) trabeculae
(2) spaces continuous
(3) contain bone marrow

The epiphysis (ends) of long bone are mostly spongy bone

What are the 4 classifications of bone shape?

..give an example of each

(1) long bones (eg. tibia)
(2) short bones (eg. carpals)
(3) flat bones (thin, plate-like --> eg. sternum.. also skull cap, calavarium, displays how flat bones have 1 layer of spongy bone between 2 layers of compact
(4) irregular bones (complex shape, or air spaces.. eg. vertebrae or ethmoid)

what are the 5 parts of a long bone?
(1) diaphysis - shaft
(2) epiphysis - ends
(3) metaphysis - from diaphysis to epiphyseal line
(4) marrow cavity
(5) periosteum - covers surface

In a long bone, what type of bone is in the diaphysis
almost all compact

(small amount of spongy faces marrow cavity)

What type of bone is found in the epiphysis of a long bone
mostly spongy

.. except articular cartilage, which is covered with hyaline cartilage

where is the metaphysis
from diaphysis to epiphyseal line
most of the shaft is ______ bone.

The _______ _________ forms the inner portion of the bone


marrow / medullary cavity

Short bones resemble the ______ of long bones. Why?
ends (epiphysis)

because they are mostly spongy bone [and bone marrow], have thing compact bone, and have articular surfaces with hyaline cartilage and non-articular surfaces with periosteum

Periosteum covers NON-articulating areas. Describe the periosteum of NON-GROWING bone.
If bone is NOT growing, the fibrous layer is the main component of the periosteum. The cellular layers is less prominant, but the few periosteal cells that are present will give rise to osteoblasts.
The endosteum is usually _____ cell layer thick.

What 2 areas does it line?

(1) marrow cavity
Endosteum contains ___________ cells (aka ________ cells) that differentiate into ___________ and bone lining cells

Endosteum has osteoprogenitor cells (aka endosteal cells) that differentiate into osteoblasts and bone lining cells

Note that the endosteum contains some collagen

What are the two types of bone marrow? Distinguish between them.
(1) Red bone marrow
- developing blood cells
- network of fibres and vessels (support developing cells)
- does NOT increase in proportion with bone growth

(2) Yellow marrow
- When marrow growth dimishes (ie. rate of blood cell formation has dropped)
- Fat cells occupy space
- can convert to red marrow when needed

Where is red marrow found in an adult?
iliac crest and sternum
What are osteons?
The osteon, or Haversian system is the functional unit of mature [compact] bone. It is a cylindrical structure that consists of concentric lamella (layers) surrounding a central canal (Haversian canal)
What are lamellae?
Concentric layers of the bone matrix that surround the central Haversian canal of the osteon
What is the function of the Haversion canal of the osteon?

what lines the central canal?

vascular and nerve supply

lined by osteonal endosteum

what are interstitial lamellae?
osteon remnants (remains of older osteons which are being overlapped and covered over by new osteons)
what is another name for mature bone?
Lamellar bone
What are volkmann canals and what is a key feature in identifying them histologically?
canals running perpendicular to the axis of the Haversian canal, that connect Haversian canals. They connect periosteal and endosteal surfaces

Key feature: the Volkmann canals are NOT surrounded by lamellae

What are the differences between immature and mature bone?
Immature bone:
(1) nonlamellar or "woven bone"
(2) more cells, randomly arranged
(3) not heavily mineralized, more ground substance

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