ANAT 261 Lecture Notes - Osteon, Lysosome, Epiphyseal Plate

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Naveen Sooknanan McGill Fall 2011
Cartilage and bone are specialized types of CT which secrete a firmer ECM than normal
This is due to the presence of other minerals which harden the matrix
Cartilage allows the tissue to support mechanical stress without distortion and also provides
support to adjacent soft tissues
This allows for movement and flexibility (such as in the nose and ears)
Cartilage consists of chondrocytes and an extensive ECM contain fibers and ground
These cells are located in spaces within the ECM known as lacunae or “chondroplasts”
o These cells form groups known as isogenic groups
There are three types of cartilage:
Hyaline cartilage (trachea)
o Medium hardness
Elastic cartilage (nose, ear and larynx)
o Flexible, soft
Fibrocartilage (intervertebral discs)
o Hard, won’t be seen in the lab
The ECM for these three types of cartilage differs from one another:
o Collagen type II in hyaline and elastic cartilage
o Elastic fibers in elastic cartilage
o Collagen Type I in fibrocartilage
Ground substance stays the same for them all:
o Proteoglycans including keratin sulfate and chondroitin sulfate
GAGs including hyaluronic acid, which links protein cored together
o Various glycoproteins, including chondronectin
Hyaline cartilage can be found in the trachea. During development, hyaline cartilage also turns
into long bones
The perichondrium is a CT sheath surrounding the
cartilage. It is present everywhere but articulated
surfaces (like the head of a bone), it is made up of 2
o The upper fibrous layer contains fibrocytes,
which no longer produce fibers
o The chondrogenic layer contains chondroblasts
which secrete cartilage ECM
The chondrogenic layer is responsible for
appositional growth, which produces chondroblasts and ECM
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Naveen Sooknanan McGill Fall 2011
As ECM is produces, come chondroblasts will become stuck in the ECM and become
inactive. These are known as
o The ECM contains collagen
type II
o Chondrocytes are bigger than
o Through they do not secrete ECM,
they can still divide
The division of chondrocytes creates isogenic
group within lacunae (spaces) in the ECM
o The isogenic groups within a lacunae
are called chondroplasts
o These chondroplasts are responsible for interstitial growth
Appositional growth is more important because it is capable of making cartilage from
scratch (because it can make chondroblasts)
o Interstitial growth can only expand on an already existing piece of cartilage
Elastic cartilage is the same as hyaline cartilage except that is contains elastic fiber within the
The elastic fibers cannot be seen with HE staining, but we assume they are there
There are special stains which can turn elastic fibers a dark purple, we don’t see these in
the lab, however
Regulation of cartilage growth:
Stimulate protein synthesis:
o Growth hormone
o Thyroid hormone
o Testosterone
Retard protein synthesis:
o Corticosteroids
o Estradiol
o Reitnoids (vitamin A)
In the 60s, people thought it was good to feel babies tons of vitamin A, but
it led to the development of many short people
Bone is one of the hardest tissues in the body. It can withstand a great deal of stress. The EMC of
bone is made of type I collagen (which gives flexibility) and calcified material (which gives bone
its hardness)
Tooth enamel is in fact the hardest material in the body
The cell types are:
o Osteoprogenitor cells, which are stem cells
These are hard to see in the lab, because they are tiny
Fibrous layer
Chondrogenic Layer
Hyaline Cartilage
Elastic Cartilage
Elastic Fibers
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