Flashcards in Bone Deck (42)
What are the three types of bone cells?
What activates osteoclasts? What inhibits them?
What is the name of the inorganic "stuff" of bone? What is it made of?
Ca2+ and Phosphorus
What is the organic stuff that makes up bone? What is it made of?
Type I collagen, proteoglycans, glycoproteins
What is the component of osteoid that promotes hydroxyapatite formation? What is the specific one that is bone-specific?
Glycoproteins promote hydroxyapatite formation
Osteocalcin is the bone specific glycoprotein that is not found in any other tissue.
Why is bone so hard?
Combined hydroxyapatite and collagen type I -- both are needed
Compare bone and cartilage in respect to mineral, water, collagen, neuronal and vascular structures.
Bone: 70% mineral, 25% water, Collage Type I, Neuronal and vascular structures present
Hyaline cartilage: No minerals, 75% water, Collagen Type II, No neuronal and vascular structures
What are osteoblasts? And what are the known osteoblast-specific genes?
Osteoblasts are specialized fibroblasts
Cbfa-1: TF, bone master gene
Growth factors that induce osteoblast differentiation
Bone morphogenetic proteins (BMPs)
What do osteoblasts make?
Osteoid: type I collagen and glycoproteins
How is bone formation completed?
By osteocalcin-mediated deposition of Ca2+ within the osteoid
What happens if you do not have hydroxyapatite?
There is no weight-bearing
Where are osteocytes located?
They occupy the lacunae between layers -- lamellae -- of bone matrix
How many osteocytes per lacuna?
What is the function of osteocytes? How long do they live?
They maintain bone matrix
They live about 25 years
How do osteocytes communicate with one another??
Cytoplasmic processes penetrate the matrix where they join processes of other osteocytes via gap junctions
What do osteoclasts do?
They destroy/remodel bone matrix
How do they develop? Where are they located?
They are multinuclear and develop from macrophages that fuse together
They are located in hollow areas of matrix termed "Howship's lacunae"
What part of the osteoclasts attaches to the ECM to promote bone resorption?
The ruffled border of the osteoclast
What hormones regulate osteoclasts and how?
Calcitonin = inhibits
PTH = activates (lysosomes -- cathepsin K and H+ --> add to the microenvironment)
What are the connective tissues that outline bone called?
Periosteum and Endosteum
Where are each of the three types of bone cells located?
Osteoblasts are located mostly in the periosteum with smaller numbers in the endosteum
Osteocytes are within lacunae of the bony matrix between the periosteum and endosteum
Osteoclasts are mostly found attached to bony matrix on the endosteal side
What are the two types of bone that make up the inside and outside of bone?
Compact/cortical bone: dense, no cavitation, on the outside
Spongy/cancellous/trabecular bone: cavitation, on the inside
What are flat bones and where are they mostly located?
2 plates of compact bone surround diploe of spongy bone
What are the two parts of long bones?
Diaphysis (shaft): compact with spongy bone lining marrow
Epiphysis (ends): caps of compact bone around spongy bone
What is contained within an osteon?
An osteon is a cylinder with concentric lamellae, lamellae have lacunae that harbor osteocytes that inter-communicate by canaliculi
What does the innermost lamella surround?
The Haversian Canal
What are the two ways in which bone develops?
1. intramembranous: osteoblasts deposit osteoid onto mesoderm
2. endochondral: osteoblasts deposit osteoid onto cartilage
How does Endochondral bone develop?
Bone forms on hyaline cartilage
At the diaphysis: osteoblasts invade calcified cartilage, secrete osteoid --> ossification
At the epiphysis: same process but articular cartilage remains at ends of bone and epiphyseal plate cartilage remains for growth in length