What is cartilage?
Cartilage is an AVASCULAR form of CONNECTIVE TISSUE. It is composed of COLLAGEN AND ELASTIC FIBRES embedded in a gel-like MATRIX, containing localised CELLS in cavities
Cartilage is enveloped in PERICHONDRIUM which is a type of connective tissue
What is perichondrium?
It is a layer of dense, irregular CONNECTIVE TISSUE that envelopes cartilage.
What are the complications associated with cartilage being avascular?
Because cartilage is avascular, all nutrients need to DIFFUSE through the matrix to reach chondrocytes (cartilage cells)
This contributes to WEAKED DEGENERATIVE PROPERTIES of cartilage and thus they have very slow healing
What are the functions of cartilage?
- support and protection of soft tissues
- provide a gliding surface at articulations (joints)
- basis for some joints
- provide a model for the FORMATION OF BONES (precursor)
What is a chondroblast?
Chondroblasts are cartilage cells located between the perichondrium and gel matrix, whose role is to MAKE CARTILAGE by secreting cartilaginous matrix. In doing this, the matrix surrounds and isolates chondroblasts, embedding them in the cartilage
What is a chondrocyte?
When a chondroblast becomes embedded in the cartilage, it is called a chondrocyte and their role is to maintain cartilage. Chondrocytes are found in lacunae which are spaces in the matrix
appositional growth of cartilage
- growth in diameter
- chondroblasts secrete new matrix at the periphery of cartilage
What is interstitial growth of cartilage?
- growth in length
- through mitosis
- two daughter cells occupy one lacuna (they do not like this)
- they secrete new matrix in order to separate
What are the different types of cartilage?
- hyaline cartilage
- elastic cartilage
- fibrocartilage
What is hyaline cartilage?
Hyaline cartilage covers bony articular surfaces (joints)
- most common in the body
- matrix contains a moderate amount of collagen fibres - not visible
what is articular hyaline cartilage?
- hyaline cartilage found at bone ends
- the key thing to note is that it does not contain perichondrium
- this is ensure smooth gliding of joints of which perichondrium is too rough. Furthermore, perichondrium would be broken down and wasted if located at joints
- this is why cartilage wears down over time leading to joint problems
What is elastic cartilage?
Elastic cartilage contains bundles of elastic fibres arranged in irregular patterns, providing flexibility
- highly flexible
- least abundant in the body
- the branhed, irregular fibres allow for the cartilage to be very mobile and to experience force from multiple directions
- found in the external ear, auditory tube and parts of the larynx
what is fibrocartilage?
fibrocartilage is tough, containing thick, regular patterns of collagen fibre
- prevents stretching and compression
- acts as a shock absorber
- lacks perichondrium (don’t want damage)
- found in the intervertebral disk (weight), public symphysis (prevents stretching and healing during child birth) and found in the meniscus (knee)
What are the functions of bone?
- support and protection of soft tissue
- movement (muscle does not push or pull, it only shortens. Therefore when a muscle is anchored on two bones, it will cause movement)
- hormonal component - regulate blood sugar, kidney function, suppress appetite
- hemopoiesis - blood cell production
- maintaining homeostasis
What is the difference between red and yellow bone marrow?
yellow bone marrow contains adipose tissue and can act as a source of energy
- in adults, much of red bone marrow degenerates into yellow bone marrow
red bone marrow is where hematopoiesis - the production of blood cells (red blood cells, white blood cells and platelets are all produced in red bone marrow)
- in children, red bone marrow is found in spongy bone throughout the body
- in adults, red bone marrow is found in spongy bone of some bones
- during trauma events, the body has the ability to convert yellow bone marrow to red bone marrow to assist in replenishing red blood cell’s lost
How do bones assist in maintaining homeostasis?
storage of mineral and energy reserves
- more than 90% of body’s calcium and phosphate reserves are found in bone
- phosphate is needed for ATP
- calcium needed for blood clotting, movement, nerve impulse transmission
- lipids are stored in yellow bone marrow
- the body will go to bones to retrieve this minerals if it is deficient in the body (this is why those who are anorexic are at much greater risk of osteoperosis)
pWhat are osteoblasts?
The osteoblast is the bone cell responsible for forming new bone and is found in the growing portions of bone including the periosteum and endosteum
- they produce osteoid (protein matrix)
what are osteocytes?
As the secreted matrix surrounding the osteoblast calcifies, the osteoblast becomes trapped within it and becomes an osteocyte
- osteocytes maintain bone including the mineral concentration
- each osteocyte is located in a space called a lacunae
- osteocytes can communicate with each other and recieve nutrients via canaliculi which are channels within the bone matrix
What are osteoclasts?
Bone is dynamic, meaning that new bone tissue is constantly formed and old, injured or unecessary bone is dissolved for repair or for calcium release
- osteoclasts are responsible for the destruction or resorption of bone
- helps with remodelling of bone during growth, remodelling and repair
What is compact/cortical bone?
Compact bone is the denser, stronger of the two types of bone tissue. It can be found in the outer layers and offers protection and support. Compact bone is dense so that it can withstand compressive forces
What is spongy/trabecular/cancellous bone?
Spongy bone is the inner structure of bone and is honeycombed and lightweight. It houses bone marrow and is directed to stress lines
- spongy bone has open spaces and supports the shift in weight distribution
