Bone Flashcards
What is cartilage surrounded by?
A membrane called the pericondrium
What causes the strength in cartilage?
Collagen fibres
What causes the resilience in cartilage?
Chondroitin sulfate
What is cartilage nourished by?
Diffusion of gases and nutrients
Are lymphatic vessels or blood vessels present in cartilage?
No
What does cartilage consist of?
- Cells
- Fibers
- Matrix
What type of cells are present in cartilage?
Chondrocytes
Where do cells occur in cartilage?
Within spaces in the matrix called lacunae
What do fibres consist of?
A dense network of collagen and/or elastin fibres
What is the matrix in cartilage composed of?
- Proteoglycans
- Ground substance
What is it called when a structure has no blood vessels?
Avascular
Where is the only place where blood vessels/nerves are present in cartilage?
Perichondrium
What is the function of mesenchymal cells in bone?
Differentiate into chondroblasts
What is the function of chondroblasts?
Synthesise ground & substance & matrix (cartilage)
What are chondrocytes embedded in?
In matrix
What type of cells are chondrocytes
Mature cells
What is the term for the formation of cartilage?
Chondrification
NB!! What are the 5 steps in the formation of cartilage?
- Mesenchymal cells differentiate chondroblast
- Chondroblasts proliferate & synthesise ground substance & fibrous extracellular matrix
- Chondroblasts separate into spaces (lacunae)
- More divisions form clusters (isogenous grps)
- These chondrocytes are embedded in extracellular matrix
What is the term for when cartilage is replaced by bone?
Ossification
In embryogenesis where is the skeletal system derived from?
Mesoderm germ layer
In embryogenesis what is most of the skeleton comprised of?
Cartilage
Name the two methods of growth in cartilage
- Appositional
- Interstitial
What is appositional growth?
An increase in girth or width
What is an interstitial growth?
An increase in length
What happens during appositional growth?
Chondroblasts deposit collagen/matrix on surface of pre-existing cartilage
What is interstitial growth specific for?
For endochondral bone formation
What happens during interstitial growth?
Chondrocytes divide and secrete matrix from within their lacunae
Where do chondrocytes occupy?
Hallow space
What are chondrocytes surrounded by?
By its own secreted matrix
What do chondrocytes synthesise?
- Ground substance
- Fibrous elements
What does elastic cartilage contain?
Many elastic fibres
Where is elastic cartilage present?
In ear and epiglottis
What can elastic cartilage tolerate?
Repeated bending
What is the most abundant cartilage?
Hyaline cartilage
What is the appearance of hyaline cartilage?
Glassy
What does hyaline cartilage provide?
Support through flexibility
Where is hyaline cartilage present (x 5)?
- Articular cartilages
- Costal cartilage
- Larynx
- Trachea
- Nose
Where is fibrocartilage present (x 2)?
- Intervertebral discs
- Pubic symphysis
What can fibrocartilage resist?
Strong compression and strong tension
What is fibrocartilage in comparison to other cartilages?
An intermediate between hyaline and elastic cartilage
Does cartilage have many repair capabilities?
No, limited
Damage of elastic and fibrocartilage
Show less damage or ageing
Damage of hyaline cartilage
Easily damaged & has limited repair
Damage of articular cartilage
Do not repair
What can’t chondrocytes bound in hallow spaces do?
They cannot migrate to damaged areas to make new matrix
What is damaged cartilage replaced by?
By fibrocartilage scar tissue
Are they any issues of rejection in cartilage transplantation?
No
Why are there/ aren’t there any issues of rejection in cartilage transplantation?
no issues of rejection because:
- Antigenic power of cartilage is low
- Immune system cells poorly diffuse cartilage
Give five diseases of cartilage
- Arthritis
- Dwarfism
- Herniated disk
- Tumors
- Scurvy
What happens in arthritis?
Degeneration of cartilage joints (articular cartilage)
What happens in dwarfism?
Reduced proliferation of chondrocytes
What happens in a herniated disk?
Ruptures disk cartilage ring, pushing into spine
What happens in tumours?
Cartilage cells give rise to benign (chondroma) tumours.
Do malignant tumours usually occur in cartilage?
No, in bone
What causes scurvy?
Lack of vitamin c required to process collagen
What does scurvy cause?
Defective cartilage and bone
Why is vitamin c required by cartilage?
To process collagen
How many bones are in adults?
206
How many bones are in infants?
About 300
Give six functions of bones
- Support, Movement and Protection
- Hematopoiesis
- Mineral storage
- Acid-base balance
- Detoxification
- Sound transduction
What occurs in hematopoiesis?
Red blood cells produced in red bone marrow
What occurs in mineral storage?
A calcium reservoir maintains calcium and phosphorus equilibrium
What occurs in an acid-base balance?
Blood is buffered against excessive pH changes by absorbing or releasing alkaline salts
What does detoxification do?
Stores heavy metals and foreign elements
What aspect of hearing is sound transduction involved in?
Mechanical
Give a physical description of cortical bones
Dense protective shell
Give a physical description of cancellous bones
Rigid lattice designed for strength
What are interstices in cancellous bone filled with?
Marrow
What is the location of cortical bone?
Around all bones, beneath periosteum, primarily in the shafts of long bones
Give location for cancellous bone?
In vertebrae, flat bones (e.g. pelvis) and the ends of long bones
What percentage of skeletal mass does cortical mass make up?
80%
What percentage of skeletal mass does cancellous mass make up?
20%
What is the bone matrix composed of?
- 20% Organic materials
- 70% Inorganic materials salts
- 10% Water
What is the name of the organic material in the bone matrix and where is it from?
Osteoid from osteoblasts
What is osteoid comprised of?
- Type I Collagen fibers (90% of organic osteoid part)
- Glycosaaminoglycans
- Ground substance proteoglycans
What are the inorganic materials in the bone matrix composed of?
Mainly Calcium & Phosphate (in form of hydroxyapatite crystals)
What are the four types of bone cells?
- Osteoprogenitor cells
- Osteoblasts
- Osteocytes
- Osteoclasts
What type of cells are Osteoprogenitor cells?
Bone stem cells
What is the function of Osteoprogenitor cells?
Generate osteoblasts and osteocytes
What type of cells are osteoblasts?
Immature bone forming cells
Where are osteoblasts derived from?
Mesenchymal stem cells
What is the most abundant cell found in bone?
Osteocytes
What is an osteocyte?
An inactive osteoblast
What type of cells are osteoclasts?
Phagocytic cells
What is the function of osteoclasts?
Erode bone, bone resorption and remodelling.
What do osteoblasts contain?
Contain lots of rough ER for collagen synthesis
What do osteoclasts secrete?
Secrete organic acids and lysosomal proteolytic enzymes to erode bone
NB! What are the six types of fixed macrophages?
- Dust/Alveolar type (lungs)
- Histiocytes (connective tissue)
- Kupffer cells (liver)
- Microglial cells (nervous)
- Osteoclasts (bone)
- Sinusoidal lining cells (spleen)
What can osteoclasts clear from the bone?
Dead osteocytes
What are osteoclast capable of with bone collagen
Capable of phagocytosis of bone collagen
What are bones?
Solid network of living cells
What are the four steps in the formation of bone?
- Osteoblasts synthesise & secrete collagen & organic matrix (osteoid)
- Osteoid then becomes calcified (i.e. calcium deposition)
- Osteoblasts secrete vesicles of alkaline phosphatase (AP)
- AP causes matrix mineralisation (gives rigidity & strength)
Mineral issues in rickets and chronic renal failure
Inadequate calcium and phosphate ions in osteiod tissue and mineralisation is slow
Name two types of mature bone
- Compact
- Spongy
How is compact bone arranged?
In Haversian systems
Where is compact bone found?
Found as dense layer on outside of bones
Where is spongy bone found?
In interior of bone
Give the appearance of spongy bone
Trabecular appearance
Immature bone is also known as ….
Woven
What has more cells and ground substance, mature or immature bone?
Immature
What does immature bone stain more intensely with and why?
Hematoxylin as it’s not mineralized
What is the name for the arrangement of immature bone?
Nonlamellar
Describe the arrangement of immature bone
Irregularly arranged collagenous fibers in proteoglycan matrix
Where is immature bone initially deposited?
In skeleton of fetal life or following fracture
Give two types of bone
- Long
- Flat
How does growth occur in long bones
By endochondral ossification
Give two examples of long bones
- Tibia
- Metacarpals
How does growth occur in flat bone?
By intramembranous ossification
Give the four parts of long bones
- Diaphysis
- Epiphysis
- Metaphysis
- Epiphyseal plate
What is the diaphysis of long bone?
A shaft consisting of marrow cavity surrounded by compact bone (little spongy bone between compact bone & marrow)
What is the epiphysis of long bone?
The expanded end; mainly spongy bone surrounded by thin outer shell of compact bone
What is the metaphysis of long bone?
The flared portion between diaphysis & epiphysis
What is the epiphyseal plate of long bone?
Cartilage that separates epiphyseal & diaphyseal cavities which maintains growth process
Give two examples of flat bone
Skull and sternum
Describe flat bone
Thin and plate-like
Name the two bone forms
- Woven (immatute)
- Lamellar (adult)
What do osteoblasts produce?
Osteoid (rapidly)
What do osteoblasts form?
Forms random collagen fibres in osteoid
What does lamellar do and why? (development)
Replaces woven bone as it’s stronger
Describe lamellar bone
Regular parallel collagen sheets
What does woven bone have a role in?
- Fetal bone development
- Healing fracture
- Paget’s disease
What are the 6 zones where the transition between cartilage and new bone occurs?
- Reserve cartilage
- Proliferation
- Maturation
- Hypertrophy / calcification
- Cartilage degeneration
- Osteogenic
What does the reserve cartilage zone consist of?
Chondrocytes
Does proliferation occur in the reserve cartilage zone?
No
What happens in the proliferation zone?
Chondrocytes undergo mitotic divisions
What happens in the maturation zone?
Chondrocytes increase in size
What happens in the hypertrophy / calcification zone?
Chondrocytes and lacunae are enlarged & matrix calcified
What happens in the cartilage degeneration zone?
Chondrocytes degenerate
What happens in the osteogenic zone?
Osteoblasts commence bone formation – deposit osteoid on exposed cartilage
What are the five types of fractures
- Simple
- Compound/impacted
- Comminuted
- Greenstick
- Stress
Give the 5 steps in a bone fracture
- Blood clot forms at fracture site (6-8h)
- Replaced by collagen tissue
- Chondroblasts lay down cartilage (provisional callus) (2-3 weeks)
- Osteoblasts lay down woven bone (bony callus) (3-4 months)
- Bony callus then remodelled to mature lamellar bone
What are the two types of ossification / osteogenesis
- Intramembranous ossification
- Endochondral ossification
What occurs in intramembranous ossification?
Direct chondrocytes lay down bone
What is endochondral ossification most common in?
In fracture healing
What are fractures of long bones treated by?
Plaster of Paris
What does endochondral ossification involve as a precursor?
Involves cartilage as a precursor
What can fractiures be treated with in intramembranous ossification?
With internal fixation with screws/pins
What percentage of the bodies calcium is in bone?
99%
What are the two calcium compartments called?
- Bone fluid
- Mineralised bone
What type of exchange occurs in bone fluid?
Fast exchange by pumps
What type of exchange occurs in mineralised bone?
Slow exchange by bone resorption
What happens in mineralised bone?
The osteoclasts phagocytic activity is increased and Ca2+ is released during low Ca2+ levels
What is the function of vitamin D in bone growth?
To promote osteoblast differentiation
What is the function of growth hormone in bone growth?
To promote osteoblast function
What is the function of oestrogen in bone growth?
To inhibit osteoclast
What is the function of calcitonin in bone growth?
To inhibit osteoclast
What is the function of cortisol in bone loss?
To promote osteoblast death (apoptosis)
What is the function of parathyroid hormone (PTH) in bone loss?
To activate osteoclast
What is the function of the thyroid in bone loss?
To activate osteoclast
What is the function of vitamin A in bone loss?
To activate osteoclast
What happens in bone growth?
Osteoblast is activated and osteoclast is inhibited
What happens in bone loss?
Osteoblast is inhibited and osteoclast is activated
What are the three cartilage cells?
- Mesenchymal cells
- Chondroblasts
- Chondrocytes
What are the four bone cells?
- Osteoprogenitor cells
- Osteoblasts
- Osteocytes
- Osteoclasts
What are the three different parts of development and growth of cartilage?
- Chondrification (development)
- Interstitial Growth (mass)
- Appositional Growth (thickness)
What are the two parts in development and growth of bone?
- Intramembranous Ossification
2. Endochondral Ossification