Bone and cartilage Flashcards
what are the functions of the skeleton?
It gives the body its shape and structure
It supports the weight of the body
It provides sites for muscle attachment, allowing movement.
It protects delicate tissues and organs e.g. heart and lungs protected by the ribs and brain encased by cranium.
It makes blood (haemopoiesis), red bone marrow makes blood cells.
The blood making marrow is restricted to bones of axial skeleton.
It stores calcium and phosphorus – low calcium results in osteoclast stimulation to release calcium from skeleton.
what is the skeleton composed of?
The skeleton is composed of specialised connective tissues: Bone & Cartilage (contains both cells and an extracellular matrix)
Skeleton mainly develops as cartilage first… ossifying later (turns to bones)
Cartilage persists at some sites e.g. articular cartilage at joints which reduces friction and the costal cartilages of the ribs
In the diagram below the bones are stained red.
When a baby is born the ends of the bone (epiphyseal plate aka Growth plates) are still made of cartilage.
The epiphyseal plate is the part of a long bone where new bone growth takes place.
what is the difference between the bones in A compared to B?
Cartilage is much better at bone than growing so growth plate of cartilage (epiphyseal plate) are retrained near the ends of long bones when an individual is still growing.
E.g. A = child’s hands and in between the bones is the layer of growing cartilage.
The epiphysial plates close as the bone gets to adult length.
E.g. B = Is an adult where all growth plates have fused.
what are the functions of cartilage?
Supports soft tissues
Provides smooth surface at joints – most synovial joints are lined with hyaline cartilage
Enables long bone growth
what are the characteristics of cartilage?
Stiff, load-bearing
Resists compression, tension and shearing
Structure cells (chondrocytes and chondroblasts) embedded in a matrix of proteoglycans (hang on to water and bulk up cartilage) and collagen
Virtually avascular (no blood vessels running through it), no nerves
If you damage cartilage, it will not hurt (no nerves) and being avascular means, it does not bleed.
However, it does not repair itself so you get fibrous scaring.
what are the 3 types of cartilage?
- Hyaline Cartilage (glassy appearance), e.g: articular cartilage – lines surface of joints and provides low friction sliding surface
- Elastic Cartilage (higher proportion of elastin protein in it), e.g: external ear (can bend it and springs back to shape)
- Fibrocartilage (mixture of fibrous tissue with cartilage cells and matrix), lines few joint surfaces e.g. clavicular joint and it is what makes up intervertebral disc.
what soft tissue lines the cartilage?
Cartilage is covered in a soft tissue called perichondrium.
Perichondrium is made of two layers:
- Outer fibrous layer: A dense membrane of collagenous connective tissue which contains fibroblast cells that produce collagen.
- Inner chondrogenic layer: This layer generates the cartilage. It contains fibroblast cells that differentiate into chondroblasts which produce new cartilage by appositional growth
what is the function of perichondrium?
It functions in growth and repair of cartilage.
It carries the blood vessel of the cartilage.
This blood flow distributes nutrients and oxygen (via diffusion) to the cartilage which are necessary to strengthen and nourish it.
However, the main cartilage tissue is avascular, meaning there are no vessels to carry blood directly to it. This lack of blood supply causes cartilage to heal very slowly compared with bone.
what are the connective tissue components of cartilage?
Cartilage is a form of connective tissue so it is composed of cells, fibres and ground substance.
what cells make up cartilage?
chondroblasts and chondrocytes
Chondroblasts: During cartilage formation it the chondroblasts that synthesise and secrete the ground substance and fibrous extracellular material. As the chondroblasts secrete matrix and fibres, they become trapped inside it, and mature into cells called chondrocytes.
Chondrocytes: these cells maintain tissue homeostasis by synthesizing a very low level of ECM to replace damaged matrix molecules, thereby preserving the structural integrity of the cartilage matrix.
what is ground substance in cartilage composed of?
Ground substance: Proteoglycans make up the ground substance (hang on to water and bulk up cartilage) and account for the semi-ridged nature of cartilage.
what fibres is cartilage composed of?
The different types of cartilage vary in the amount and nature of fibres in the ground substance:
- Hyaline cartilage contains few fibres
- Fibrocartilage contains abundant collagen fibres
- Elastic cartilage contains elastin fibres.
Cartilage is classified into the following types based on its composition:
- Hyaline cartilage: is composed of type II collagen and an abundance of ground substance, which gives it a glossy appearance. It is the most abundant type of cartilage found in joints (articular cartilage)
- Elastic cartilage is similar to hyaline cartilage but contains more elastic fibres
- Fibrocartilage is composed of plenty of collagen fibres type I and a smaller amount of ground substance. Examples of fibrocartilage include intervertebral discs, pubic and other symphyses.
explain the growth and repair of cartilage
Cartilage develops from embryonic mesenchyme (loose connective tissue)
It is capable of Interstitial and appositional growth
Interstitial Growth: chondrocytes grow and divide and lay down more matrix inside the existing cartilage.
Appositional Growth: new surface layers of matrix are added to the pre-existing matrix by new chondroblasts.
Poor repair - replaced by fibrous tissue.
Many cartilages ossify (turn to bone) with age.
what are the characteristics of bone?
- Hard, resilient tissue
- Cells (osteoblasts (bone making cells), osteocytes, osteoclasts (large multinucleate cells that resorb bone – release calcium) embedded in a mineralised matrix
- Highly vascular – full of blood vessels –> o when you break a bone you get a lot of swelling (blood pouring out)
- Periosteum very well innervated – breaking bone is very painful
Extremely strong
what is bone composed of breifly
Bone is also a form of connective tissue so it is composed of cells, and an extracellular matrix (fibres and ground substance).
what is the gross structure of periosteum?
It consists of two layers of tissues:
- Outer Fibrous Layer (or Outer Layer) – A dense membrane of collagenous connective tissue which contains fibroblast cells that produce collagen. It is contact with bone, tendons and ligament and the joint capsule.
- Inner Cellular Layer – has osteoblasts cells
what are the 2 types of bone?
Cortical (compact) and Cancellous bone
- Compact Bone: Solid Mass of dense connective tissue
- Cancellous Bone (spongy bone/trabecular bone): A branching Network of dense connective tissue
Cortical bone forms the extremely hard exterior of bones while cancellous bone fills the interior.
The tissues are biologically identical but differ in the arrangement of their microstructure.
what can you see in a cross section of cortical bone?
You can see systems with blood vessels in the centre and layers of the mineralised matrix built up (onion rings).
The Black specs are osteocytes which are in lacuna between layers. Osteocytes are connected to vessels and send spindles out through tunnels in the bone to communicate with each other.
This communication is important as it allows bones to respond to the mechanical environment signalling to either add or remove tissue.
what is a trabecular bone?
found in the body of the vertebrae with cortical bone found on the outside.
what are flat bones?
Flat bones are considered to be strong and to be protective
In a cross-section, flat bones are structurally tri-laminar:
Compact Bone (Outer Table)
Spongey Bone (middle)
Compact Bone (Inner Table)
The inner and outer tables of flat bones are lined with Periosteum
Flat bones are used for bone marrow samples e.g., sternum
what is the structure of a long bone?
The external surface of the bone is covered by periosteum.
Compact bone forms the dense walls of the diaphysis (shaft)
Cancellous bone occupies part of the large central medullary cavity.
The medullary cavity (medulla, innermost part) is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow
The endosteum (plural endostea) is a thin vascular membrane that lines the inner surface of the bony tissue that forms the medullary cavity.
The articular (joint) surfaces of the epiphyses, of long bones are protected by a layer of specialised hyaline cartilage called articular cartilage.
The long bones grow in length by the process of endochondral ossification which occurs at a growth or epiphysial plate situated at each end of the bone at the junction of the diaphysis (shaft) and epiphysis .s
This is interstitial growth
explain the process of endochondral ossification
- Starts with condensation of mesenchyme (loose embryonic connective tissue).
- These cells then turn into cartilage cells - formation of cartilage.
- Blood vessels then arrive and bring osteoblasts which lay down bone tissue.
- Final image shows how ossification has spread along the shaft of the bones towards the ends but the ends are made of cartilage and ossification centres starting to appear.
- A wedge of cartilage is retained below ossification centre (growth plate) whilst bone is still growing.
- Both processes however result in the same bone tissue; however, they are distinguished by the presence or absence of a cartilage model.
what age do major growth plates close?
Most close at the late teens which makes sense as this is when most of us stop growing.
Clavicular growth plates are some of the last to grow.
When bone reaches adult length, the epiphyseal plate ossifies & closes
