Flashcards in Lecture 12: Bone And Cartilage Deck (26)
Describe the three types of cartilage
- There are three major classes of cartilage based on their matrix, especially the predominant types of fibers within the matrix: (Refer to Figure 4-18):
-- Hyaline cartilage
-- Elastic cartilage
- Cartilage may form part or all of the skeletal system in vertebrates.
- Most of the skeletal system in all vertebrates begins as cartilage.
What are the two types of cartilage Cells?
- Chondroblasts (cartilage-forming cells)
- Chondrocytes (cartilagemaintenance cells)
Describe the extracellular matrix of cartilage
- Extracellular matrix:
- Collagen fibers: Mostly type II collagen (type I in fibrocartilage)
- Amorphous ground substance
What are the functions/features of cartilage?
- Resists Distortion
- Absorbs shock in joints
- Reduces friction in movable joints
- Necessary for endochondral bone growth
- Involved in bone fracture repair
Describe the characteristics of cartilage formation
- Chondroblasts: Lay down cartilage matrix and become chondrocytes
- Chondrocytes: Maintain cartilage matrix
- Lacunae: Pockets within the matrix where the chondroblasts and chondrocytes are found
Reminder: Cartilage is avascular: Slow to heal, Nutrients and oxygen are derived from blood vessels that surround the cartilage and must diffuse through the matrix to the cells.
Describe the structure of the perichondrium
- Outer fibrous layer (A): Contains fibroblasts
- Inner chondrogenic layer (B): Gives rise to chondroblasts, which become chondrocytes. The chondrocyte (D) is involved in the production of the collagen and proteoglycans in the matrix. Chondrocytes also secrete chondronectin.
- See slide 7 for diagram picture
Describe isogenous groups
- Groups of 2-8 chondrocytes occupying the same lacunae (C).
- Result of mitotic division.
- Cells will become separated as they begin to lay down matrix of their own.
Describe the matrix of cartilage structure
* Components of the matrix:
- Collagen type II (type I in fibrocartilage)
- Hyaluronan (hyaluronic acid)
- Chondroitin sulfate, keratan sulfate, heparin sulfate
* Territorial matrix:
- Surrounds each chondrocyte
- High glycosaminoglycan content; low collagen content
* Inter-territorial matrix:
- Surrounds territorial matrix
- Low glycosaminoglycan content; high collagen content
Give the characteristics of hyaline cartilage
- Most common type of cartilage:
- Avascular (cells depend on diffusion through matrix for oxygen and nutrients)
- Contains type II collagen fibers
- Surrounded by perichondrium
- Translucent, bluish gray to white
- Solid but flexible
- Chondrocytes are often found in cell groups (resulting from cell division).
- Growth patterns:
Where is hyaline cartilage usually found?
- External auditory meatus
- Tracheal cartilages
- Bronchial cartilages
- Fetal long bones
- Articular ends of bones
Give the characteristics of elastic cartilage, including where it is usually found
- Specialized by the addition of elastic fibers to the matrix
- Surrounded by perichondrium
- Yellow color because of presence of elastic fibers
- More opaque, flexible, and elastic than hyaline cartilage
- Chondrocytes mostly located singly
- Type II collagen plus elastic fibers
- Found in:
-- Auricle (pinna) of the ear
Give the characteristics of fibrocartilage
- Increased collagen in the matrix
- Reduced cellularity compared to hyaline cartilage
- Not surrounded by perichondrium
- Opaque appearance from fibrous texture
- Type I collagen
- Single sparse chondrocytes
- Fibrocartilage location:
-- Intervertebral discs
-- Pubic symphysis
-- Insertion of some tendons and ligaments
-- Closely associated with dense connective tissue or hyaline cartilage
Read through slides 13-15, and go over the photomicrograph cards.
What are the characteristics of bone tissue?
- Bone tissue is based on a canalicular system.
- Bone is highly vascular and is found in close proximity to capillaries.
- Increase in bone length occurs through appositional growth of a hyaline cartilage model.
- Bone tissue is continuously resorbed, reconstructed, and remodeled.
- Bone is formed by osteoblasts which become osteocytes.
- Matrix of bone consists of two major components:
-- An organic component referred to as osteoid
-- An inorganic component referred to as hydroxyapatite which makes up 35 to 65 percent of the matrix
What is the difference between appositional growth and interstitial growth
- Interstitial Growth is the developmental "lengthening" of cartilage, which is produced by the chondrocytes continuously producing and secreting new matrix...or something.
- Appositional is growth accomplished by adding new layers on top of existing layers. This also increases the thickness of the bone.
What are the 3 types of bone tissue
1. Woven Bone
2. Spongy Bone
3. Compact Bone, also called Lamellar Bone
Describe Woven bone
- Occurs during bone development and bone repair
- Produced rapidly
- Haphazard collagen foundation
- Less structural integrity
Describe spongy bone
- Also called trabecular or cancellous bone
- Has a 3-D lattice of branching, bony spicules intertwined to form trabeculae surrounding the bone marrow spaces in the long bones and flat bones
Describe compact bone
- Lacks cavities and forms a dense plate on the outside of long bones or flat bones.
- Consists of concentric (Haversian) lamellae (D) which encircle a central blood vessel (and associated nerves) forming an osteon, or Haversian system (Refer to Figures 4-20 and 4-21).
- Osteocytes are found between the lamellae located in lacunae (C) and are connected to each other and the Haversian canal (F) via canaliculi (E).
- Volkmann’s canals (G) run perpendicular to the Haversian canals and connect the Haversian canals to each other and to the surface of the bone. (Review Photo Flashcards for diagram pertaining to these letters)
Describe the 3 types of cells involved in bone formation
- Secretes bone matrix
- Secretes collagen and catalyzes mineralization
- Maintains bone matrix
- Help control calcium and phosphate levels in matrix
- Remodels bone through bone resorption
Describe osteoprogenitor cells and osteocytes
- Stem cells which in the adult are described as bone lining cells.
- In the adult they are found in the inner portion of the periosteum, in the endosteum, and lining vascular canals of compact bone.
- These cells are derived from mesenchyme of the embryonic somite (sclerotome) and possess mitotic potential.
- Osteoprogenitor cells give rise to osteoblasts and bone lining cells.
- Derived from osteoblasts and are trapped by the matrix they secrete.
Describe the characteristics of osteoblasts
- Derived from osteoprogenitor cells
- Give rise to osteocytes
- Characterized by:
-- Alkaline phosphatase (Not found in osteocytes)
-- Vitamin D3 (Regulates expression of osteocalcin)
- Major protein products:
-- Type I collagen
--- Osteocalcin (High Binding affinity for hydroxyapatite)
Describe osteoclasts and the ARF cycle
* Osteoclast cells:
- Derived from the monocyte lineage, which, in turn, is derived from the monocyte precursors in bone marrow.
* The ARF (activation-resorption-reversal-formation) cycle occurs at adult remodeling sites and during development.
Describe the parathyroid hormone
- Parathyroid hormone (PTH) is the primary regulator of bone turnover
- At low PTH levels, bone formation by osteoblasts is stimulated.
- At high PTH levels, osteoblasts are stimulated to release osteoclast-differentiation factors.
- PTH stimulates the differentiation of monocyte precursors to form osteoclasts. It also stimulates the formation of ruffled borders on osteoclasts.
- Elevated PTH levels result in eroded bone and fibrosis of the resulting spaces (osteitis fibrosa).
- Some could argue that PTH controls calcium levels in the blood? Maybe?
How do osteoblasts regulate osteoclasts?
- Review slides 42-43
- Parthyroid hormone binds to receptors on the osteoblast.
- The osteoblast is stimulated to synthesize M-CSF and RANKL.
-- M-CSF = Monocyte colony stimulating factor
- The osteoblast releases M-CSF.
- M-CSF binds to the M-CSF receptor on the monocyte that just happened to drop by.
- The monocyte is now a macrophage and expresses RANK.
- RANK binds to RANKL (this couples together the osteoblast and the macrophage).
- The macrophage becomes a multinucleated immature osteoclast
- The osteoblast secretes osteoprotegerin:
-- Osteoprotegerin binds to RANKL with greater affinity than RANK.
-- This inhibits maturation of osteoclasts.
-- Parathyroid hormone blocks the synthesis of osteoprotegerin.
- A non-functional osteoclast uncouples from the osteoblast and becomes a functional osteoclast.
- Calcitonin acts to reduce bone resorption.