lesson 9 Flashcards
What are the two types of supportive connective tissue?
Cartilage
Bone
A specialized connective tissue with a few cells embedded in an amorphous gel-like substance.
cartilage
What are the functions of cartilage?
- Supports the body in weight-bearing movement.
- Maintains organ integrity.
- Acts as a primary support tissue in the fetus.
- Functions as a shock absorber.
- Provides a smooth surface for friction-free joint movement.
What encloses the cartilage?
Perichondrium
What are the two layers of the perichondrium?
- Outer fibrous layer (dense white fibrous connective tissue, DWFCT).
- Inner cellular (chondrogenic) layer containing mesenchymal cells that differentiate into chondroblasts.
How does cartilage receive nutrition if it is avascular?
By diffusion of metabolites from the periphery to the center.
What are the two types of cartilage growth?
Appositional growth
Interstitial growth
Addition of new cartilage upon pre-existing cartilage?
Appositional growth
Expansion of pre-existing cartilage by mitosis and production of additional matrix by chondrocytes?
Interstitial growth
What are the three types of cartilage cells?
- Chondrogenic cells
- Chondroblasts
- Chondrocytes
- Found in the inner (chondrogenic) layer of the perichondrium.
- Undifferentiated mesenchymal cells.
chondrogenic cells
Chondogenic cells shape is?
And then with what shape of nucleus and how many nucleoli?
Spindle-shaped with an ovoid nucleus and 1-2 nucleoli.
- Possess small Golgi apparatus, few mitochondria, rough endoplasmic reticulum (RER), and abundant free ribosomes.
- Can differentiate into chondroblasts and osteoprogenitor cells.
chondrogenic cells
- Active, young, differentiated cells that synthesize and secrete cartilage matrix.
- Derived from mesenchymal cells in the center of chondrification and from chondrogenic cells in the perichondrium.
chondroblasts
What are the characteristics of chondroblasts?
Plump, basophilic cells containing:
* Network of RER
* Well-developed Golgi complex
* Numerous mitochondria
* Abundant secretory vesicles
These are Chondroblasts that become isolated in lacunae after secreting matrix.
Chondrocytes
Chondrocytes characteristics?
- Ovoid near the periphery; rounded deeper in the cartilage.
- Large nucleus with a prominent nucleolus.
- Responsible for matrix maintenance and turnover.
- Have reduced synthesizing and secretory activity.
What are the two main components of cartilage matrix?
- Fibers: Collagenous and elastic.
-
Extracellular matrix (amorphous ground substance):
1. Glycosaminoglycans
1. Proteoglycans (e.g., aggrecans)
1. Glycoproteins (e.g., chondronectin)
What are the functions of the extracellular matrix?
Essential for transport of water and electrolytes.
Makes cartilage firm, resilient, pliable, and compressible.
Cartilage classification is based on:
- The amount of amorphous matrix.
- The amount and type of fibers embedded in the amorphous matrix.
What is the Gross appearance of Hyaline cartilage?
- Has a white, glassy appearance (hyas = glass).
- Enclosed by perichondrium, except in the articular surface of bones, which lacks perichondrium.
What is the cell arrangements of Hyaline Cartilage?
Chondrocytes may cluster to form isogenous groups or cell nests.
In Hyaline Cartilage, the predominant fiber type is ____?
fine collagenous fiber (Type II collagen)
In hyaline cartilage matrix composition, it is divided into two types of matrix which are ?
- Territorial Matrix
- Interterritorial Matrix
Location of Hyaline Cartilage?
- Bone-forming sites in embryos.
- Articular cartilages (e.g., ribs and ends of long bones).
- Respiratory organs (e.g., nose, larynx, trachea, bronchi)
What happens to mesenchymal cells in regions where cartilage will develop?
They become rounded, retract their processes, and aggregate into chondrification centers.
What are dense masses of mesenchymal cells called during cartilage formation?
Chondrification centers.
What do mesenchymal cells differentiate into during cartilage formation?
Chondroblasts
What is the function of chondroblasts?
They produce matrix around themselves.
What happens to chondroblasts as matrix formation continues?
They become trapped in their own secretions inside lacunae.
What are chondroblasts called once they are trapped in lacunae?
Chondrocytes
What are groups of 2-4 chondrocytes in a lacuna called?
Isogenous groups
What happens to cells in isogenous groups during interstitial growth?
They continue to produce matrix, pushing each other apart.
How does cartilage enlarge from within?
By the formation of separate lacunae through matrix production by chondrocytes.
What do mesenchymal cells at the periphery of developing cartilage differentiate into?
Fibroblasts
What is the function of fibroblasts in cartilage formation?
They produce the perichondrium, a dense irregular collagenous connective tissue.
What are the two layers of the perichondrium?
Outer Fibrous Layer and Inner Cellular Layer.
What does the Outer Fibrous Layer contain?
Type I collagen, fibroblasts, and blood vessels.
What does the Inner Cellular Layer contain?
Chondrogenic cells
What happens to chondrogenic cells in the perichondrium during appositional growth?
They divide and differentiate into chondroblasts.
What do newly formed chondroblasts do in appositional growth?
They synthesize matrix, adding cartilage at the periphery of the cartilage model.
What type of cartilage growth involves adding new layers on the surface?
Appositional growth.
What is the gross appearance of elastic cartilage?
Yellow
How does elastic cartilage compare to hyaline cartilage in terms of resilience?
It is more resilient.
What types of fibers are found in elastic cartilage?
Collagenous (Type II) and elastic fibers.
How do the chondrocytes in elastic cartilage compare to those in hyaline cartilage?
They are more abundant and larger, with more frequent cell nests.
Where is elastic cartilage found in the body?
- Pinna of the ear
- external auditory meatus
- eustachian tube
- larynx
- epiglottis
How does fibrous cartilage compare to DWFCT and cartilage?
It is intermediate between the two.
What unique feature does fibrous cartilage have in its collagen arrangement?
Large collagenous fascicles (bundles) in an orderly arrangement, separated by isolated portions of cartilage.
What is the herringbone configuration in fibrous cartilage?
A V-shaped arrangement of collagenous bundles
Where is fibrous cartilage usually located?
At transition points between:
1. DWFCT and cartilage
1. DWFCT and bone
What type of collagen is most abundant in fibrous cartilage?
Type I collagen
Where do the chondrocytes of fibrous cartilage originate from?
Fibroblasts
Where can fibrous cartilage be found in the body?
- Intervertebral discs
- attachment of certain tendons and ligaments
- menisci.
What is the function of chondrocytes in cartilage?
Maintenance of cartilage.
How does cartilage repair occur?
By differentiation of chondrogenic cells.
Does cartilage repair occur in adult animals?
No, it only occurs in growing animals.
Which type of cartilage is poorly repaired?
Fibrocartilage.
What happens to damaged articular cartilage in non-weight-bearing surfaces?
It is replaced by fibrocartilage.
Why is the replacement of damaged cartilage problematic?
The replacement tissue lacks the same properties, leading to compromised structure and function.
What type of connective tissue is bone?
A specialized connective tissue.
How does bone differ from other connective tissues?
It has a mineralized matrix.
What mineral components make bone unique?
Amorphous calcium phosphate and hydroxyapatite crystals.
How is bone formation similar to cartilage formation?
Cells secrete matrix and become embedded in it.
What is the primary difference in matrix composition between bone and cartilage?
Bone is mineralized, while cartilage is not.
How do bone cells (osteocytes) interact compared to cartilage cells?
Osteocytes are in contact with each other through canaliculi, while cartilage cells remain isolated.
How does vascularity differ between bone and cartilage?
Bone is highly vascular, whereas cartilage is avascular.
How does growth differ between bone and cartilage?
Cartilage grows by both appositional and interstitial mechanisms, while bone grows only by appositional means due to its rigid mineralized matrix.
What are the two main functions of bone?
Support and locomotion of the body; Dynamic storage of calcium and phosphate
What percentage of the bone matrix is organic and inorganic?
35% organic and 65% inorganic
What is the primary organic component of bone?
Collagen (primarily Type I), making up 80-90% of the organic matrix
What substances are found in the ground substance (osteoid) of bone?
Proteoglycans (with chondroitin sulfate and keratan sulfate side chains); Glycoproteins (osteonectin, osteocalcin, osteopontin, and bone sialoprotein)
What are the primary inorganic components of bone?
Calcium and phosphorus
What other inorganic substances are present in bone?
Bicarbonate, citrate, magnesium, sodium, and potassium
In what form do calcium and phosphorus exist in bone?
Hydroxyapatite crystals (predominant form) and amorphous form
What is the periosteum?
The outer covering of bone, except for articular surfaces
What are the two layers of the periosteum?
Outer fibrous layer (DWFCT); Inner cellular (osteogenic) layer
What is the function of the osteogenic layer of the periosteum?
It is the source of bone cells
What makes the periosteum well-vascularized?
It has a high proliferative activity
What is the endosteum?
The inner lining of bone, covering the marrow canals (Haversian and Volkmann’s canals)
What type of cells are found in the endosteum?
Osteoprogenitor cells and osteoblasts
How is the endosteum connected to the periosteum?
Through the Volkmann’s canal
What are osteoprogenitor cells, and what is their function?
Mesenchymal cells that actively divide and give rise to other bone cells
Where are osteoprogenitor cells located?
Inner cellular layer of the periosteum, lining Haversian canals, and the endosteum
What are osteoblasts, and what is their function?
Bone-forming cells responsible for secreting fibers and ground substance
What are the two phases of osteoblast activity?
Secretion of organic material (fibers and amorphous ground substance); Deposition of mineral substance on the osteoid
What cellular structures are abundant in osteoblasts under electron microscopy (EM)?
Rough Endoplasmic Reticulum (RER), well-developed Golgi complex, and numerous secretory vesicles
How do osteoblasts communicate with each other?
Through short processes with neighboring osteoblasts and long processes with osteocytes via gap junctions
What receptors are found on osteoblast cell membranes?
Integrins and parathyroid hormone (PTH) receptors
What happens when PTH binds to osteoblast receptors?
Osteoblasts secrete osteoprotegerin ligand and osteoclast-stimulating factor, which promote osteoclast activity
What are osteocytes?
Osteoblasts that have become embedded in their own secretions
Where are osteocytes located?
Inside spaces called lacunae
What structures do osteocytes use for communication?
Cytoplasmic (osteocytic) processes within canaliculi
What do osteocytic processes allow?
Formation of gap junctions between osteocytes
What is the function of extracellular fluid in canaliculi?
Carries nutrients and metabolites to nourish osteocytes
What are the functions of osteocytes?
Maintain the bone matrix; Perform osteolysis (removal of bone matrix); Secrete new matrix material (but less than osteoblasts); Contribute to osteoblast formation by fusing with them
What are osteoclasts?
Multinucleated giant cells responsible for bone resorption (osteoclasia)
Where do osteoclasts reside?
In concavities called Howship’s lacunae (erosion lacunae)
What is the origin of osteoclasts?
They originate from blood monocytes
What are the four functional regions of active osteoclasts?
Basal zone (houses most organelles) Ruffled border (directly involved in bone resorption)
Clear zone (surrounds ruffled border, contains actin filaments, organelle-free)
Vesicular zone (contains numerous endocytotic and exocytotic vesicles)
What are the two main types of bone?
Woven bone (cancellous or immature bone) and Lamellar bone (compact or mature bone)
Where does woven bone first form?
In ossification centers of the fetus, in the primary spongiosa of developing adolescent bone, and at the site of fractures
Where else can woven bone be found?
In alveolar bone (associated with teeth) and at points where ligaments and tendons attach to bone
What happens to woven bone over time?
It is always replaced by lamellar bone
What are the characteristics of woven bone?
Arranged in spicules or trabeculae, has more interosseous space and less bone substance
What is lamellar bone also called?
Compact bone or mature bone
What percentage of the adult skeleton is made of lamellar bone?
It comprises the bulk of the adult skeleton
What structures make up lamellar bone?
Lamellae or osteons (Haversian system)
What are the characteristics of lamellar bone?
More bone substance and less interosseous space
What are the two organizational structures of bone?
Lamellated bone and Osteonal bone
Where is lamellated bone found?
In the periosteum and parts of the endosteum
What are circumferential lamellae?
Outer circumferential lamellae (periosteal lamellae) – found in the periosteum and Inner circumferential lamellae – found in the endosteum surrounding the marrow cavity
What is osteonal bone?
Lamellar bone that contains osteons or Haversian systems
How are osteons organized?
Arranged in concentric lamellae or sheets around a central Haversian canal
What marks the peripheral limits of osteonal bone?
A reversal line or cement line
What does the Haversian canal contain?
Blood vessels and cells of the osteonal endosteum
What are interstitial lamellae?
Bone lamellae located between concentric osteonal bone
What are osteons, and what do they contain?
Basic units of bone, long cylinders with a hollow cavity (Haversian canal) in the center
How do the Haversian canals connect?
They connect with the transversely located Volkmann’s canals
How are the blood vessels of the Haversian canal connected?
Through the Volkmann’s canal, which links to vessels in the periosteal and endosteal surface
What is internal remodeling?
A process where bones change internally without altering their gross morphology
What does internal remodeling involve?
Removal of old lamellar bone and replacement with new lamellar bone
Which part of the bone is responsible for internal remodeling?
The endosteum
