Lecture 10: Bone Histology Flashcards
What is another name for Mature or Secondary bone?
Lamellar Bone
What exists between the inner and outer circumferential lamellae, outside of the individual osteons?
Interstitial lamellae
What can be found in the inner layer of the periosteum?
What is this layer called?
Osteoprogenitor cells
Osteogenic layer
Where do osteoprogenitor cells come from?
Mesenchyme
What can be found in the endosteum?
Osteoprogenitor cells
What are the four steps of intramembranous ossification?
1: Mesenchyme condenses due to signaling molecules
2: Osteoblasts differentiate and begin forming osteoid around the blood vessels inside the condensed mesenchyme
3: Osteoblasts begin calcifying that osteoid forming a honeycomb around the blood vessels
4: Bone develops outward until the spongy bone is covered
What can be found in the outer layer of periosteum?
What is this layer called?
Blood Vessels and Nerves
Fibroblasts and Collagen
Sharpey’s Fibers
Fibrous layer
What cells activity is associated with high Alkaline Phosphatase activity?
Osteoblast activity
(specifically as they are becoming osteocytes, they give off “AlkPhos”)
Where is red bone marrow primarily found in adults and children?
In the flat bones in adults, and in all bones in young children
What do osteoprogenitor cells differentiate into?
Osteoblasts
What lamellae are adjacent to the endosteum?
The Inner Circumferential Lamellae
Actions of which zone of endochondral ossification cause lengthining of the bone?
Zone of hypertrophy
What are the four steps of bone fracture repair?
1: Hematoma Formation
2: Soft (Fibrocartillagenous) callus formation
3: Hard (bony) callus formation
4: Bone remodeling
Where are osteoprogenitor cells found?
Inner layer of the periostium
Endosteum
What is the normal function of FGFR3?
What changes to cause Achondroplasia?
FGFR3 stops growth during adulthood
It activates prematurely
What is the heredity of Achondroplasia?
Autosomal Dominant
What are Sharpey’s fibers, and what is their function?
They are collagen fibers that penatrate the outer circumferential lamellae.
They anchor they periosteum to the bone itself
Where would you find the endosteum?
Covering the spongey walls.
(Said another way, on the walls of the medullary cavity)
What lamellae lie just deep to the periosteum in bone?
The Outer Circumferential Lamellae
How do osteoclasts resorb bone? (Two enzymes)
They create a localized secluded acidic environment using H+-ATPase, then degrade the organic matrix via Cathepsin K Protease
Where do osteoclasts come from?
The Monocyte Lineage
In what zone of endochondral ossification is the medullary cavity produced by osteoclasts?
Zone of resorption
(Osteoclasts eat the dead chondrocytes)
What might be a more primary disease that could cause Osteomalacia?
GI disease (Calcium / Vitamin malabsorption)
What causes Rickets?
Calcium or Vitamin D deficiency during growth, causing deficient mineralization of cartilage in the growth plate
What do we call Vitamin D or Calcium deficiency in adults?
Osteomalacia
When might osteoprogenitor cells be the most active?
During times of bone repair
In endochondral ossification, what surrounds the cartilagenous blueprint?
Perichondrium
What separates the interstitial circumferential lamellae from the osteon?
The cement line
What lies at the center of the osteon?
The Haversian Canal
What are the symptoms of Rickets?
Delayed closure of the fontanelles
Bowed lower limbs
Bossing of the skull
Bowing of distal radius and ulna
What gene is involved in achondroplasia?
FGFR3 gene
(Fibroblast Growth Factor Receptor)
What cell deposits and mineralizes the osteoid?
Osteoblasts
In endochondral ossification, what is the bone’s blueprint made of?
Hyaline Cartilage
When might we see woven bone?
During fracture repair
During Remodeling
During initial bone formation
What population is more likely to get osteoporosis?
Elderly and postmenopausal females
What connects Haversian Canals?
Volkman’s Canals
In which zone of endochondral ossification do the chondrocytes begin to die?
Zone of calcified cartilage
Osteocytes create a complex network of branches to communicate with each other and with the nutrient supply - what is this network made of?
Canaliculi
Why do you feel pain when you’ve broken a bone?
Because of the nerve endings in the fibrous outer layer of the periosteum
On what part of the bone is there no periosteum?
The articular surfaces (joints)
When does an Osteoblast become an Osteocyte?
When it entraps itself in its lacuna.
What is the mechanism of osteoporosis?
Imbalance in Osteoblast and Osteoclast action leading to demineralization of the bone.
What forms the soft callus in bone repair?
Chondroblasts
What is another name for immature or primary bone?
Woven bone
In endochondral ossification, what forms the primary ossification center?
Hypertrophy and subsequent death and phagocytosis (by osteoclasts) of chondrocytes in the middle of the diaphysis. This creates an opening known as the primary ossification center.
