Lecture 7: Cartilage and Bone Tissue
Reading: M/O 6; E4
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Identify the types of cartilage found in the skeletal system and explain the functions of each.
Compare and contrast appositional and interstitial cartilage growth.
List and describe the cellular and extracellular components of bone tissue.
Identify the internal structural components of compact bone and spongy bone
Compare and contrast intramembranous and endochondral bone formation.
Cartilage: A “special” support CT
Like all CT, cartilage consists of cells, fibers and ground substance.
1. Cells:
A. Mysenchymal cells (undifferentiated precursors of other cells in cartilage; like stem cells)
B. Chondroblasts (build new cartilage)
C. Chondrocytes (mature cartilage cells)
2. Ground substance
A. Chondroitin sulfate (glycosaminoglycogen; very hydrophilic)
B. Other GAG’s and proteoglycans, all of which are very hydrophilic
C. Healthy cartilage is MOIST cartilage
3. Fibers (differ in the different types of cartilage)
A. Hyaline cartilage
i. Appears to be relatively few fibers, but there ARE collagen fibers...they are just too small to see with the microscope.
ii. Locations: most of embryonic skeleton, ends of long bones, and joints
iii. Is a shock absorber
B. Elastic cartilage
i. Mostly elastic fibers
ii. Very flexible; tip of nose, ear pinna
C. Fibrocartilage
i. Lots of collagen fibers
ii. Strong, tough, durable
iii. Found where grinding happens
iv. Ex: Intervertebral disks and other joints that bear weight, like knee meniscus
4. Most cartilage is surrounded by the perichondrium, which is a dense irregular CT covering. Fibrocartilage is the exception.
5. Cartilage is avascular! (This is the exception to the “CT is highly vascular” rule!)
Growth and Formation of Cartilage
Cartilage forms when mesenchymal cells differentiate into chondroblasts, which secrete matrix. When a chondroblast is surrounded
by matrix, it becomes trapped and is now called a chondrocyte.
1. Appositional growth: Takes place when growth occurs “on the surface”
A. Mesenchymal cells found in the perichondrium differentiate into chondroblasts
B. These chondroblasts are found on the surface, and begin secreting matrix.
C. The structure grows, though still surrounded by original perichondrium.
2. Interstitial growth: Takes place when growth occurs in between the chondrocytes...
A. A chondrocyte divides, then differentiates into a chondroblast, which begins secreting matrix.
B. Matrix is pumped into the original space (lacuna) until the original space is divided into two spaces, each with its own cell.
C. This results in the matrix becoming MORE DENSE and COMPRESSED. (Note that bone tissue cannot grow like this,
because bone is not compressible.)
Bio 6: Human Anatomy
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Spring 2014: Riggs
Bone Tissue
Like all CT, bone tissue consists of cells, fibers and ground substance.
1. Cells:
A. Mysenchymal cells (undifferentiated precursors of other cells in cartilage; like stem cells)
B. Osteoblasts (build new bone)
C. Osteocytes (mature bone cells)
D. Osteoclasts (derived from macrophages...and destroy, or CRUSH, bone)
2. Ground substance
A. Osteoid (an organic, gooey substance)
B. Hydroxyapatite (a crystal/mineral made of calcium and phosphate)
3. Fibers
A. Almost exclusively collagen fibers made by the osteoblasts
4. Characteristics of bone (toughness and hardness) are enabled by the combination of the mineral hydroxyapatite and the collagen
fibers.
A. If you dissolve the hydroxyapatite (with acid) you get a bendy bone.
B. If you remove the collagen fibers (with collagenase) you get a brittle bone.
5. Bone tissue has an extensive blood supply...as you will see.
Types of bone tissue
Most bones contain two different types of bone connective tissue.
1. Compact bone (dense, or cortical bone)
A. Functional unit: the osteon with concentric lamellae
2. Spongy bone (cancellous or trabecular bone)
A. No osteons...instead parallel lamellae
3. Bones are surrounded by the periosteum, which is a dense irregular CT covering, like the perichondrium.
Bone formation
Bone can form two different ways. However, ALL bone must arise from PRE-EXISTING connective tissue.
1. Intramembranous ossification- bone formation that takes place in an embryo to form the flat bones of the skull, some facial
bones, the mandible, and parts of the clavicle.
A. Ossification center forms within a dense irregular connective tissue “membrane” in an embryo (about 8 weeks along)
B. Osteoblasts (coming from osteoprogenitor cells, which came from mesenchymal cells!) reach out cytoplasmic extensions
and begin laying down new bone tissue.
C. When the osteoblasts become trapped by the new tissue, they become osteocytes.
2. Endochondral ossification- when bone forms from a hyaline cartilage model!
A. Mesenchymal cells in the perichondrium differentiate into osteoblasts, forming a calcified collar around the middle of the
long bone (diaphysis).
B. Chondrocytes start to starve and die...and produce calcified matrix as a result.
C. A periosteal BUD forms (blood vessels plus osteoblasts and osteoclasts!) and bursts into the calcified cartilage matrix!
D. Osteoblasts build new bone!
E. Osteoclasts eat away the old calcified cartilage!
F. All hyaline cartilage is replaced by bone in this way...except for at the epiphyseal plates. Here, you can see 5 distinct zones
where bone growth occurs.
i. Zone of resting cartilage
ii. Zone of proliferation
iii. Zone of hypertrophy
iv. Zone of calcification
v. Zone of ossification
Bio 6: Human Anatomy
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Spring 2014: Riggs
Lab 7: Cartilage and Bone Tissue
M&O Chapter 6; E 4.1 and 4.2
Part 1: Cartilage
Draw each slide and label indicated structures. Examine several different slides, to ensure you can recognize the tissue no matter how
the slide is prepared.
1. Hyaline Cartilage (HB 7-12): hyaline cartilage
A. chondrocytes
B. lacunae
C. intercellular matrix
2. Elastic Cartilage (HB 7-13): elastic cartilage
A. chondrocytes
B. lacunae
C. intercellular matrix
D. elastic fibers (darkly stained)
3. Fibrous Cartilage (HB 7-14 or H 710): fibrocartilage
A. chondrocytes
B. lacunae
C. intercellular matrix
D. collagenous fibers
Part 2: Bone
Draw each slide and label indicated structures. Examine several different slides, to ensure you can recognize the tissue no matter how
the slide is prepared.
1. Human Bone, XS (HB 8-4): compact bone tissue
A. osteon (Haversian system)
B. central canal (Haversian canal)
C. lamellae
D. lacunae
E. canaliculi
2. Developing Intramembranous Bone (HB 8-2) or Cancellous Bone (HB 8-311): spongy bone tissue
A. periosteum
B. trabeculae (spicules)
C. osteoblast
D. osteocyte
E. osteoclast
3. Developing endochondral bone (HB 8-1)
A. perichondrium
B. periosteum
C. zone of proliferation
D. zone of hypertrophy
E. zone of calcification
F. zone of erosion and ossification
G. cartilage matrix
H. chondrocytes (in lacunae)
I. calcified cartilage matrix
J. osteoblasts
K. bone matrix (or osteoid)
L. osteocytes
M. osteoclasts (look along the surfaces of the trabeculae for these)
N. capillaries
Bio 6: Human Anatomy
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Spring 2014: Riggs
External Brain 7: Cartilage and Bone
33.
34.
35.
36.
37.
Identify the types of cartilage found in the skeletal system and explain the functions of each.
Compare and contrast appositional and interstitial cartilage growth.
List and describe the cellular and extracellular components of bone tissue.
Identify the internal structural components of compact bone and spongy bone
Compare and contrast intramembranous and endochondral bone formation.
Your Task
1. Label images or DRAW pictures that include ALL required lab structures.
2. Describe the characteristics you expect to see that will help you distinguish between the 3 types of cartilage.
Hyaline cartilage
Elastic cartilage
Fibrous cartilage
Expected characteristics
Drawing
3. Draw a diagram of all stages of endochondral bone formation. Label all required structures.
4. List several distinguishing characteristics that will make the identification of the different types of cartilage easier for you.
5. Why do the chondrocytes die during endochondral bone formation?
6. Is calcified cartilage matrix the same thing as bone matrix? Why or why not?
7. Which cells are actively secreting bone matrix? Which are reabsorbing bone matrix?
8. Which are mature bone cells?
Bio 6: Human Anatomy
35
Spring 2014: Riggs