cartilage and bone slides with notes from teacher on bottom... nycpm

1. CARTILAGE AND BONE

2. CARTILAGE & BONE
• Cartilage & bone are examples of specialized
connective tissue
• Both originate from mesoderm and
mesenchyme
• The major difference is that cartilage is
avascular while bone is vascularized
• Cartilage contains an antiangiogenesis factor
that prevents invasion of the tissue by blood
vessels

3. CARTILAGE
• Like all connective tissue, cartilage is composed of
cells, intercellular space called ground substance or
intercellular matrix and fibers – (collagen)
• The cells of cartilage are chondrocytes
• Chondrocytes originate from stellate shaped
mesenchymal cells.
• Mesenchymal cells round up and differentiate into
chondroblasts
• Chondroblasts synthesize the intercellular matrix

4. CARTILAGE
• When chondroblasts surround themselves
with the intercellular matrix, they become less
active and are called chondrocytes
• In fact, when the chondroblasts become
entrapped in small areas of the intercellular
matrix called lacunae – literally small lakes

5. Appearance Of Cartilage
Consists of round cells suspended in an
extracellular matrix
When fixed, round cells shrink and pull away
from matrix
Resultant “empty” space is called a lacuna,
appearing as a halo or crescent around the
remnants of the cell
Avascular

7. Cartilage Types
•Cartilage is classified by the components of the matrix
•Hyaline (very smooth like a lake)
• no apparent fibers in the matrix
•eg. articular cartilages
•Elastic
•presence of elastic fibers in the matrix
•eg. pinna of ear
•Fibrous
presence of an abundance of type I collagen
bundles
eg. intervertebral discs

8. Cartilage Matrix
•Contains:
•hyaluronic acid
•chondroitin sulfate
•keratan sulfate –
•elastin in elastic cartilage
•type II collagen
•type 1 collagen in fibrocartilage

9. CARTILAGE MATRIX
• The extracellular matrix consists of fibers and
an amorphous ground substance
• Fibers are collagen Type II, elastic and reticular
• Ground Substance is composed of GAGs of the
proteoglycans
• Hyaluronic Acid
• Chondroitin sulfate **
• Keratan sulfate

10. Cartilage Growth & Formation
Interstitial
Chondrocytes divide
secrete matrix, and
are pushed apart by the matrix
A positional
catilage surrounded by perichondrium
innermost layer of cells = chondroblasts
secrete matrix materials which are added
on to edge of existent cartilage

13. GROWTH OF CARTILAGE
• Interstitial Growth – literally from within –
chondrocytes undergo mitosis within the
lacunae. There are long rows of chondrocytes
formed called isogenous clusters. Growth in
length of a piece of cartilage is by interstitial
growth
• Appositional Growth – New cartilage cells and
interstitial matrix are added onto the surface
of a piece of cartilage

14. GROWTH OF CARTILAGE
• Appositional Growth continued –
• Cartilage is covered by a connective tissue investment called
the perichondrium
• The perichondrium consists of two layers, a cellular layer
immediately adjacent to the piece of cartilage & a fibrous
layer located more superficially
• The inner cellular layer contains undifferentiated
mesenchymal cells that continue to differentiate into
chondroblasts and slowly add themselves and the matrix that
they produce to the surface of the piece of cartilage
• Blood vessels contained within the perichondruim represent
the source of nutrients that diffuse through the ground
substance to maintain the chondrocytes

15. CARTILAGE MATRIX
• The highest concentration of newly synthesized
GAGs is in the matrix immediately surrounding the
chondroblast or chondrocyte
• Bound Water – Chondroblasts and chondrocytes
receive their nutrients by diffusion through the
water component & if this life line is compromised,
the cells will die
• Because cartilage can do quite well in an avascular
environment, when a piece breaks off, it has no
trouble surviving and can live for years. It has to be
removed surgically

23. BONE

24. CALCIFICATION OF CARTILAGE
• As we shall see in a later lecture, a normal
process called endochondral ossification in
hyaline cartilage models of the long bones in a
fetus and in an area of bone called the
epiphyseal growth plate is a mechanism of
bone formation.
• For now, we shall just look at bone and
compare it to cartilage

25. TERMS
Macroscopic
Compact - solid chunk of bone
Trabecular = Spongy = Cancellous
meshwork of bony spicules
Microscopic
Immature = Woven – all bone starts out as immature
irregular arrangement of fibers in matrix
Mature = Lamellar
layered arrangement of fibers in matrix – tree trunk

29. BONE
• Again like all connective tissue, bone consists
of cells, fibers and intercellular matrix
• Bone like cartilage is invested with a
connective tissue covering called the
periosteum.
• The periosteum contains an outer fibrous
layer and an inner cellular layer

30. BONE
• Within the inner cellular layer, there are small spindle-shaped
cells (mesenchymal cells). These are the osteoprogenitor cells.
• Within the inner aspect of the fibrous layer, there are
osteoprogenitor cells.
• Osteoprogenitor cells and osteoblasts occupy this layer and
it is called the osteogenic layer.
• There are also osteoclasts present in the osteogenic layer.
• Osteoprogenitor cells can undergo malignant transformation.
This disease is osteogenic sarcoma.

31. BONE CELLS
• Osteoblasts – differentiate from the mesenchymal
cells but UNLIKE the chondroblasts, osteoblasts
retain their stellate shape and are found on the
surface of a developing spicule of bone
• Osteoblasts make collagen Type I fibers and ground
substance
• Ground Substance contains GAGs, glycoproteins and
osteonectin which anchors mineral components to
collagen fibers & osteocalcin, a calcium-binding
protein

32. BONE CELLS
• Immature bone (before it is calcified) is called osteoid and
consists of collagen fibers and ground substance
• Mineralization involves deposition of many different minerals
to hydroxyapatite crystals Ca 10(PO4) 6(OH) 3
• Vitamin C is necessary for the osteoblast to synthesize
osteoid, i.e. make collagen and is also necessary for fracture
repair
• Vitamin D is necessary for proper intestinal absorption of
calcium, defect results in rickets in children and osteomalacia
in adults. Excess causes bone resorption
• Vitamin A deficiency inhibits bone formation and growth
while excess causes a faster rate of ossification of the
epiphyseal growth plates. Both deficiency and excess cause
small stature

33. Mineralization of bone
Incresed concentrations of Ca and PO ions in the
local matrix are brought about by:
binding of Ca by osteocalcin increases local
concentration
osteoblasts stimulated to secrete alkaline
phosphatase
alkaline phosphatase => increased Ca
accumulation

35. BONE CELLS
Osteocytes – As osteoblasts make and secrete
osteoid around themselves, they get trapped
& surrounded by matrix (like falling into
cement with arms and legs extended). Since
they retain their stellate shape,the matrix
hardens around the cytoplasmic processes
forming tiny tunnels called caniculi where the
cell processes remain

36. BONE CELLS
• Once the cells are trapped in their lacunae, they are called osteocytes
• The cytoplasmic processes of osteocytes communicate with each other
within the caniculi via gap junctions
• The osteocyte is quite metabolically inactive although some activity does
occur
• Osteocytes occupy the most but not the entire lacuna
• They have densely stained small irregular nuclei
• Osteocytes in their lacunae are surrounded by extracellular fluid called
“bone fluid”
• May be different composition from extracellular fluid of other tissues
perhaps due to surface osteocytes & osteoblasts forming some type of
“membrane” or barrier that separated bone fluid from other tissue fluids

37. BONE CELLS – HORMONAL INFLUENCES
• Hormonal control of Calcium Homeostasis
• In times of low plasma Calcium, parathyroid hormone is released from the
parathyroid glands
• Parathyroid hormone interacts with receptors on osteoclasts and
osteocytes to cause calcium to be released from bone – done through
mediation of osteoclast-stimulating factor. Excess PTH resulte in bone
being more susceptible to fracture
• Calcitonin- produced by parafollicular cells of thyroid - when blood levels
of calcium are normal or high, calcitonin is released from the thyroid gland
causing calcium to be absorbed and deposited into bone – does so by
eliminating the ruffled border of the osteoclasts
• Pituitary Growth Hormone – stimulates overall growth – epiphyseal plates.
Overproduction results in gigantism and deficiency in dwarfism

38. BONE CELLS
• Osteoclasts – these are derived from the peripheral blood monocyte and as such
are part of the monocyte phagocyte system
• Large, multinucleated,giant cells formed by the fusion of several monocytes
• Major resorbers of bone matrix
• Found in depressions on the bone surface called Howship’s lacunae
• Contain a ruffled border on the resorptive surface, many mitochindria, Golgi
bodies, vesicles & RER
• Clear Zone surrounds the ruffeled border and contains microfilaments which help
osteoclasts maintain contact with the bony surface and also isolates the
osteoclastic activity
• Vesicular Zone – exocytotic vesicles that transfer the lysosomal enzymes to the
Howship’s Lacula & endocytotic vesicles that transfer degraded bone products
from Howship Lacula to the ingerof the cell
• Basal Area- located on the side of the cell opposite the ruffled border – contains
most of the organelles
Non-dividing but DNA synthesis does occur

39. Cells of bone
Osteoprogenitor cells
derived from stem cells of mesenchyme
triggered to become osteoblast
Osteoblasts
appears as a single layer of cuboidal cells lying
on surface of developing bone
exocytose alkaline phosphatase rich, membrane
bound matrix vesicles that are involved in
mineralization of the matrix

40. Cells of bone (continued)
Osteocytes
mature bone cell trapped in lacunae in matrix
processes contact those of other osteocytes and
osteoblasts, joined by gap junctions
Osteoclasts
large, multinucleated cells found in depressions
on the surface of the bone
cells release hydrolytic enzymes that degrade
the bone matrix

41. BONE RESORPTION
• Osteoclasts secrete acid – decalcifies surface
layer of bone
• Acid hydrolases, collagenases degrade the
organic portion of bone
• Osteoclasts resorb the organic and inorganic
residues of the bone matrix and release them
into connective tissue capillaries.

48. Lamellae
Circumferential
lining or circling the marrow or outer
surface of the bone respectively
Concentric
arranged in concentric circles around the
Haversion canal
Interstitial
short arcs in spaces between Haversion
systems

49. COMPACT BONE
• Outer & Inner circumferential lamellae are produced
by the periosteum and endosteum and encircle the
outer and inner aspects of the bone
• Haversian lamellae are found between the outer and
inner circumferential lamellae
• Haversian lamellae form concentric rings around a
small canal containing blood vessels and nerves – the
canal is called the Haversian Canal and represents
the vascular system of the bone

50. COMPACT BONE
• One Haversian system is also known as an osteon
and is separated from other Haversian systems by a
cement line
• Each lamella is connected to another by the
canaliculi and ultimately with the periosteum and
endosteum
• In this manner the innermost osteocytes maintain a
connection with the circulatory system. If the system
breaks down, the osteocytes die and so does that
portion of bone

52. SPONGY BONE
• This is also mature bone
• Unlike compact bone, spongy bone is merely
spicules covered by endosteum
• Bone marrow is present between spicules
• Found in flat bones of skull

59. Lab 9 Cartilage and Bone

66. BONE FORMATION