cartilage and bone Flashcards
What is cartilage
Cartilage is a robust and viscoelastic connective tissue that can be found in joints between bones, the rib cage, intervertebral discs, the ear, and the nose. While more rigid and less flexible than muscle, cartilage is not as stiff as bone. These properties allow cartilage to serve as a support structure for holding tubes open or for proper locomotion.
👉It has a firm extracellular matrix.
👉It contains chondrocytes embedded in matrix
What are some examples of where cartilage can be found
👉cricoid cartilage and carina of the trachea,
👉the torus tubarius at the opening of the auditory tube, and
👉the auricle/pinna of the ear.
What are some functions of cartilage
👉A supporting framework for the walls of airways in the nose,
trachea, larynx and bronchi, preventing airway collapse.
👉Forms the articulating surfaces of bones.
👉Forms the template for the growth and development of most of
the fetal skeleton including long bones.
👉It contributes to the expansion of the thoracic cage during respiration
What can you say about the cells in cartilag
👉The cells in cartilage are chondroblasts and chondrocytes.
👉Chondroblasts are found in the outer covering layer of cartilage.
👉They secrete the extracellular matrix and fibers and, as they do so, they become trapped inside it and mature into chondrocytes.
👉In growing cartilage , the chondrocytes can divide, and the daughter cells remain close together in groups, forming a ‘ nest ’ of
2 – 4 cells.
👉These trapped cells sit together in clear areas called lacunae ( lacunae means ‘ little lakes ’ ).
👉Active chondrocytes are large secretory cells with a basophilic
(purple staining) cytoplasm, which arises from a high content of
rough endoplasmic reticulum (ER).
👉Older chondrocytes contain fat droplets.
Older chondrocytes contain:
Fat droplets
Discuss how chondrocytes are formed
👉The cells in cartilage are chondroblasts and chondrocytes.
👉Chondroblasts are found in the outer covering layer of cartilage.
👉They secrete the extracellular matrix and fibers and, as they do so, they become trapped inside it and mature into chondrocytes.
Discuss the formation of the lacunae
👉In growing cartilage , the chondrocytes can divide, and the daughter cells remain close together in groups, forming a ‘ nest ’ of
2 – 4 cells.
👉These trapped cells sit together in clear areas called lacunae ( lacunae means ‘ little lakes ’ ).
👉Active chondrocytes are large secretory cells with a basophilic
(purple staining) cytoplasm, which arises from a high content of
rough endoplasmic reticulum (ER).
👉Older chondrocytes contain fat droplets.
Why are active chondrocytes basophilic (purple staining)
a high content of
rough endoplasmic reticulum (ER).
comment on the extracellular matrix of the cartilage
👉The extracellular matrix (ECM) of cartilage is made up of aggrecan (10%), water (75%) and fibers.
👉Aggrecan is formed of aggregates of up to 100 molecules of the GAG, chondroitin sulfate, bound to hyaluronic acid.
👉Chondroitin sulfate is rubbery, provides cartilage with resilience, and this type of GAG is only found in cartilage.
comment on the extracellular matrix of the cartilage
👉The extracellular matrix (ECM) of cartilage is made up of aggrecan (10%), water (75%) and fibers.
👉Aggrecan is formed of aggregates of up to 100 molecules of the GAG, chondroitin sulfate, bound to hyaluronic acid.
👉Chondroitin sulfate is rubbery, provides cartilage with resilience, and this type of GAG is only found in cartilage.
what is the % composition of aggrecan in cartilage
10%
what is the %comp. of water in cartilage
75%
what is aggrecan composed of
Aggregates of up to a 100 the Glycosaminoglycan(GAG), chondroitin sulphate, bound to hyaluronic acid
comment on the fibres in cartilage
👉Fibers in cartilage are either collagen (Type I or Type II), or a mixture of collagen and elastin fibers.
👉A network of collagen fibers generates a very high tensile strength.
👉Elastic fibers provide elasticity.
comment on perichondrium
👉The perichondrium is a layer of dense, irregular connective tissue that surrounds hyaline cartilage and elastic cartilage.
👉It consists of an outer fibrous layer containing type I collagen, fibroblasts, and blood vessels and
👉an inner cellular layer containing chondrogenic cells and chondroblasts.
👉It provides the nearest blood supply to the avascular cartilaginous tissue
why cant cartilage not become very thick
👉Unlike other connective tissue, cartilage is AVASCULAR (like epithelium). 👉Cartilage is nourished by long-range diffusion from nearby capillaries in the perichondrium.
👉Therefore, cartilage can never become very thick, as diffusion would not be sufficient to supply the cartilage with nutrients and oxygen.
WHAT ARE THE 2 WAYS CARTILAGE GROW
👉Interstitial growth: chondrocytes grow and divide and lay down
more matrix inside the existing cartilage. This mainly occurs
during childhood and adolescence (In the epiphyseal plates of long bones)
👉Appositional growth: new surface layers of matrix are added to
the pre - existing matrix by new chondroblasts from the
perichondrium. i.e the differentiation of chondrogenic cells in the perichondrium.
explain interstitial growth of cartilage
👉Interstitial growth: chondrocytes grow and divide and lay down
more matrix inside the existing cartilage. This mainly occurs
during childhood and adolescence (In the epiphyseal plates of long bones)
explain appositional growth of cartilage
👉Appositional growth: new surface layers of matrix are added to
the pre - existing matrix by new chondroblasts from the
perichondrium. i.e the differentiation of chondrogenic cells in the perichondrium.
what are the types of cartilage
👉hyaline cartilage
👉fibrocartilage
👉elastic cartilage
comment on hyaline cartilage
👉This is the most common, and the weakest type of cartilage in the body
* It stains light purple (basophilic) in H & E.
* It contains dispersed fine type II collagen fibers, which provide
strength.
* It has an outer layer called the perichondrium, except at articular surfaces
* Hyaline cartilage is a precursor of bone
* Hyaline cartilage is found in epiphyseal growth plates, ribs, nose, larynx, and trachea
* Chondrocytes are arranged in groups
comment on elastic cartilage
- It is found in the external ear (pinna), auditory canal, larynx, and epiglottis where it helps to maintain their shapes.
- It is flexible and resilient and contains elastic as well as collagen fibers (type II).
- The chondrocytes are found in a threadlike network of elastic fibers within the matrix.
- It has a perichondrium.
comment on fibrocartilage
- Fibro-cartilage is found in joint capsules, ligaments, tendon insertions, and intervertebral discs
- It is made up of alternating layers of hyaline cartilage matrix
and thick layers of dense parallel bundles of collagen fibers (type I and type II), oriented in the direction of applied stresses, to reinforce this cartilage. - This is the strongest kind of cartilage.
- It does not have a perichondrium as it is usually sandwiched
between hyaline cartilage and tendons or ligaments. - Chondrocytes are arranged in parallel rows between bundles of collagen
where is hyaline cartilage found
👉epiphyseal growth plates
👉ribs (ventral ends)
👉nose,
👉larynx,and
👉trachea
where is elastic cartilage found
👉external ear,
👉larynx, and
👉epiglottis
where is fibrocartilage found
👉joint capsules,
👉ligaments,
👉tendon insertions, and
👉intervertebral discs
what is bone
Bone is the primary constituent of the adult skeleton. It is a specialized type of connective tissue with a calcified extracellular matrix in which characteristic cells are embedded
applied pressure to bone does what
bone resorbtion
applied tension to bone does what
bone formation
what are the functions of bone
👉Support: Bones provide a structural framework for the body.
👉Protection: Bones in the skull and the ribs protect internal organs such as the brain, heart and lungs, respectively.
👉Assisting movement: Bones provide the major attachment sites
for muscles, and joints between bones allow movement to take place.
👉Mineral homeostasis: Bone stores calcium and phosphorus.
👉Blood cell production: Cells are produced in the bone marrow.
what are the types of bone formation
👉Endochondral bone formation
👉Intramembranous bone formation
which bone formation is the most common
endochondral
which bone formation is the rare one
intramembranous
comment on endochondral bone formation
Endochondral (most common): bone forms on a temporary cartilage model.
👉As the cartilage grows (zone of proliferation), and the chondrocytes
mature (zone of maturation) and start to hypertrophy (zone of
hypertrophy).
👉The matrix starts to calcify, and the chondrocytes die (zone
of cartilage degeneration).
👉The fragmented calcified matrix left behind acts as a structural
framework for bony material.
👉Osteoprogenitor cells and blood vessels from the periosteum invade this area, proliferate, and differentiate into osteoblasts, which start to lay down bone matrix (osteogenic zone).
comment on intramembranous bone formation
👉Intramembranous ossification occurs in a few specialized places such as the flat bones of skull (i.e. parietal bone), mandible, maxilla, and clavicle.
👉Mesenchymal cells, in the presence of a vascular zone, condense into primary ossification centers, differentiate into osteoblasts, and begin secreting osteoid.
👉As calcification occurs, osteoblasts become trapped in their own matrix and become osteocytes. These centers of developing bone are called trabeculae.
👉Fusion of the bony trabeculae produces spongy bone as blood vessels invade the area and other undifferentiated mesenchymal cells give rise to the bone marrow.
👉The periosteum and endosteum develop from portions of the mesenchymal layer that do not undergo ossification.
👉Mitotic activity of the mesenchymal cells gives rise to osteoprogenitor cells, which undergo cell division and form more osteoprogenitor cells or differentiate into osteoblasts within the inner layer of the developing periosteum.
In endochondral bone formation, what is the first step?
👉As the cartilage grows (zone of proliferation), and the chondrocytes
mature (zone of maturation) and start to hypertrophy (zone of
hypertrophy).
after the cartilage grows (zone of proliferation), and the chondrocytes
mature (zone of maturation) and start to hypertrophy (zone of
hypertrophy) in endochondral bone formation, the second step is:
👉The matrix starts to calcify, and the chondrocytes die (zone
of cartilage degeneration).
After the matrix starts to calcify, and the chondrocytes die (zone
of cartilage degeneration) in endochondral bone formation, the third step is:
The fragmented calcified matrix left behind acts as a structural
framework for bony material.
