Bone 1 Flashcards
Functions of bone
Hematopoiesis – the formation of blood cells from hematopoietic stem cells found in
the bone marrow.
•Lipid and mineral storage – bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals.
•Support – bone forms scaffolding for skeletal muscle and other soft tissues, it creates a framework that gives the general shape of the body.
•Protection – particularly the axial skeleton which surrounds the major organs of the body.
Components of bone-The Extracellular matrix
ECM) refers to the molecules that provide biochemical and structural support to the cells that populate bone.
Organic and inorganic portions
Organic portion of of ECM
90 % organic portion - • Mainly type I collagen (also type V, III, XI, XIII) .
Non-collagenous proteins (about 10%) constitute the ground substance and include proteoglycans, glycoproteins, bone specific proteins, growth factors and cytokines
Inorganic portion of ECM
represents about 50% of the dry weight of the matrix and is composed mainly of calcium phosphate in the form of hydroxyapatite crystals
Osteoprogenitor (osteogenic)
the stem cells of bone, they are derived from primitive
mesenchymal cells.
Form a population of stem cells that can differentiate into osteoblasts which secrete
the organic unmineralized matrix or osteoid
Osteoblasts
Synthesize uncalcified/unmineralized extracellular matrix called osteoid.
This will later become calcified/mineralized to form bone.
Osteocytes
As the osteoid mineralizes, the osteoblasts become entombed between lamellae in lacunae where they mature into osteocytes. They then monitor the minerals and proteins to regulate/maintain bone mass.
Osteoclasts
Multinucleated giant cells derived from monocyte progenitor cells responsible for resorbing and remodeling bone by releasing H+ ions and lysosomal enzymes.
The balance of osteoblast to osteoclast activity is crucial in the maintenance of the tissue’s structural integrity. It also plays a role in conditions such as osteoporosis
Bone lining cells
Found on the inner and outer surface of bone; The endosteum and periosteum
Osteogenic cells
Are spindle shaped connective tissue cells (derived from embryonic mesenchyme stem cells) in the periosteum and endosteum that can differentiate into osteoblasts
inactive
osteoblasts
In mature bone in which there is no active new bone formation or remodeling, the osteoprogenitor cells become flattened spindle shaped cells closely applied to the bone surface
how do osteoblasts appear
Morphologically may appear as a cuboidal layer
(high secreting activity) or flattened (declining
secretions
what keeps osteoblasts in contact with other osteoblasts and osteocytes :;
Cytoplasmic processes
what are the precursors of glycosaminoglycans (of the osteoid matrix)
PAS positive granules in the cytoplasm of osteoblasts
osteoclast can secrete the osteoclast stimulating factor , what happens when it ceases the secretory function :
undergoes changes to its morphology
and becomes an osteocyte
mature bonne cells ,derived from osteoblasts
Osteocytes
osteocytes vs osteoblasts mounts of condensed nuclear chromatin, reduced amounts
of RER and a smaller Golgi apparatus ?
osteocytes have increased amounts
The fusion of hematopoietic monocyte progenitor cells
Osteoclasts
Howship’s lacunae
-are depressions on the bone surface that house osteoclasts
-These lacunae result from the osteolytic activities of
osteoclasts
Osteoclasts;Ruffled border
Finger-like evaginations along Howship’s lacunae depict sites of active
bone resorption
Osteoclasts;Clear zone
• Region of cytoplasm that surrounds the ruffled border • Microfilaments, anchor osteoclast to the boney surface and help isolate osteoclastic activity
Osteoclasts- Basal region
• Houses the organelles and
numerous nuclei of the cell
how does bone resorption happen :
-Lysosomal enzymes (from Golgi complex) and hydrogen ions released
into the confined space between bone matrix and the osteoclast’s
peripheral clear zone
-Decalcified bone matrix is then broken down by acid hydrolases, collagenous and proteolytic enzymes and the cell resorbs the organic and inorganic material
Bone lining cells
They are Osteoblast derived flat cells with little cytoplasm and scant
organelles
