Cartilage Flashcards
Is cartilage vascular or avascular?
Avascular
What is the name of the cells which lie within cartilage?
Chondrocytes
What do chondrocytes produce and maintain?
Extracellular matrix
What permits the ready diffusion of substances between the chondrocytes and the blood vessels surrounding the cartilage?
The large ratio of GAGs to type II collagen in the cartilage matrix
What are the properties of the extracellular matrix?
Solid and firm, but rather pliable and therefore resilient to the repeated application of pressure
What makes the extracellular matrix resilient to repeated application of pressure?
Large amounts of hyaluronic acid in the matrix.
Discuss the proteoglycan structure in cartilage ground substance
The proteoglycan monomer consists of a core protein to which approximately 100 glycosaminoglycan (GAG) units are joined. Hyaluronic acid molecules form linear aggregates, each with many proteoglycan monomers interwoven with a network of collagen fibrils
Why is cartilage ground substance a hydrated gel?
The high density of negative charges on GAGs attracts water
What are the 3 types of cartilage?
Hyaline, elastic, fibrocartilage
What is the composition of hyaline cartilage
A matrix containing proteoglycans, hyaluronic acid and type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres.
What is the composition of elastic cartilage?
A matrix like that of hyaline cartilage (containing proteoglycans, hyaluronic acid and type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres) but with the
addition of many elastic fibres and elastic lamellae.
What is the composition of fibrocartilage?
Matrix material like hyaline cartilage (containing proteoglycans, hyaluronic acid and type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres) but with abundant type 1 collagen fibres
What cell types are present in hyaline cartilage?
Chondrocytes only
Are chondrocytes present singly?
Yes’m or if recently divided, as small clusters called isogenous groups
When do chondrocytes separate?
The chondrocytes within the isogenous groups separate as they elaborate (lay down) extracellular matrix.
What is hyaline cartilage the precursor for in early fetal development?
Bones which develop by endochondral ossification
Where does hyaline cartilage remain in long bones?
As long bones develop some hyaline cartilage remains at the articulating surface, (and also at the epiphyseal plate until growth ceases).
Where is hyaline cartilage situated?
Hyaline caritlage is sited at articulating surfaces, in parts of the rib cage, nose, and in the trachea, bronchi and larynx.
What is perichondrium and what is its composition?
It covers the margin of hyaline cartilage. It contains many elongate, fibroblast-like cells which can develop into chondroblasts and thereafter into chondrocytes. It is a dense connective tissue.
What is a appositional growth?
The growth from the periphery. The fibroblast-like cells of the perichondrium give rise to flat, newly formed chondroblasts, which secrete matrix components and round up to develop into chondrocytes. (See lecture)
What is interstitial growth?
In addition, chondrocytes deeper in the cartilage may divide and give rise to growth. This is called interstitial growth.
The resultant cells separate as they lay down further matrix.
What makes the matrix resilient to varying pressure loads?
The cartilage extracellular matrix is highly hydrated. This, and the transient movement of water within the matrix.
What is a lacuna?
A small space containing a chondrocyte. There is artificial shrinkage of cells away from lacuna walls.
How do pressure loads affect chondrocytes?
Create chemical, mechanical and electrical signals that direct the synthetic activity of the chondrocytes
In developing tarsal bones is there perichondrium at articulating surfaces?
No
Describe the positioning of cartilage at the end of a long bone
Hyaline cartilage lines the articulating surface of the bone. In this position it is not lined by perichondrium.
Hyaline cartilage also forms the physis, or epiphyseal growth plate (no perichondrium here either). Above it lies the epiphysis.
Describe the epiphyseal edge of a long bone
The articular surface of the bone is very smooth and composed of hyaline cartilage, without a perichondrium. There is an irregular boundary between the articular cartilage and the underlying bone.
Which type of cartilage calcified with age?
Hyaline, but not elastic
Where is elastic cartilage found?
External ear (pinna), external acoustic meatus (in ear), epiglottis, Eustachian tube (in ear)
What appears dark stained in an elastic cartilage slide?
Abundance of elastin fibres lying in the extracellular matrix
What cell types exist in fibrocartilage?
Chondrocytes and fibroblasts
How are cells distributed in fibrocartilage?
In rows
Is there surrounding perichondrium in fibrocartilage?
No
Where is fibrocartilage present?
Intervertebral discs, articular discs of the sternoclavicular and temporomandibular joints, the menisci of the knee joint and in the pubic symphysis.
What is a main property of fibrocartilage?
The fibrocartilage has the resilience to act as a shock absorber and to resist shearing forces.
Does cartilage mend well? Why?
No as it is avascular
What does endochondral ossification involve?
Endochondral ossification involves the replacement of a pre-existing hyaline cartilage template by bone and is the way in which most of the bones of the body develop.
Describe the steps in long bone development by endochondral ossification
1: Embro 6-8 weeks - Collar of periosteal bone appears in the shaft
2: Fetus 8-12 weeks - Central cartilage calcifies. Nutrient artery penetrates, supplying bone-depositing osteopenia cells. Primary ossification centre formed.
3: Postnatal - Medulla becomes cancellous bone. Cartilage forms epiphyseal growth plates. Epiphysis develop secondary centres of ossification.
4: Prepubertal - Epiphyses ossify no growth plates continue to move apart, lengthening the bone
5: Mature adult - Epiphyseal growth plate replaced by bone. Hyaline articulate cartilage persists.
How does the bone increase in length and girth?
Length - endochondral ossification
Girth - periosteal ossification, which is intramembranous ossification.
Describe how the epiphysis grows
Columns of calcified cartilage extend from the growth plate and become mineralised
Name the “zones” of the epiphyseal growth plate
Zone of reserve cartilage Zone of proliferation Zone of hypertrophy Zone of calcified cartilage Zone of resorption
Describe the zone of reserve cartilage
No cellular proliferation of active matrix production
Describe the zone of proliferation
Cells actively dividing to form columns; cells enlarge to secrete matrix
Describe the zone of hypertrophy
Cells enlarge greatly. Matrix compressed into linear bands between cell columns
Describe the zone of calcified cartilage
Enlarged cells begin to degenerate and matrix calcified
Describe the zone of resorption
Calcified matrix is in direct contact with the marrow cavity. Small blood vessels and connective tissue invade the region occupied by the dying chondrocytes
What are spicules?
Calcified cartilage left in the zone of resorption.Bone is laid down on these spicules
Describe a synovial joint
A moveable joint in which the juxtaposed (opposed) bone ends are:
1. covered by hyaline cartilage, and
2. lie within lubricating synovial fluid bounded by an articular
capsule (joint cavity) which is lined by synovial membrane, and reinforced with fibrous tissue and ligaments.
Which cells are found in the synovial membrane?
The synovial membrane consists of macrophages, which remove debris from joint space, and fibroblast- like cells that are thought to secrete the synovial fluid
Name some examples of synovial joints
Shoulder hip and knee joints
Name the commonest joint diseases
Osteoarthritis, rheumatoid arthritis
Describe OA
involves degeneration and subsequent
mechanical failure of the articular cartilage, and a narrowing of the joint space, such that bone rubs against bone. Degradation of cartilage and narrowing of joint space together with the growth of bony spurs (osteophytes), causes inflammation and pain
Describe RA
involves autoimmune inflammation of the synovial membrane such that there is inflammation and thickening of the joint capsule. There can be subsequent damage to underlying bone and cartilage, such that they disintegrate.
