bone tissue Flashcards
6 functions of skeletal system
- Support
- Protection
- Movement
- Electrolyte balance
- Acid-base balance
- Blood formation
4 major types of bones
- Long bones
- Short bones
- Flat bones
- Irregular bones
spongy bone in the cranium
diploe
2 layers of periosteum
- tough outer fibrous layer of collagen (+perforating, Sharpey fibers)
- Inner osteogenic layer - forming cells
where endosteum can be found
lines internal marrow cavity, surfaces of spongy bone
lines canal systems of compact bone
osteogenic cells
stem cells that develop from mesenchyme
give rise to to most other bone cell types
osteoprogenitor
osteoblasts in mitotic (productive) stage.
osteoblast
bone forming cells (soft organic matter of matrix), non mitotic
single layer on the bone surface under endosteum and periosteum
secrete osteocalcin
osteocytes
- contribute to the homeostasis maintanance of both bone density and Ca/P concentration in blood.
- have strain sensors (regulate bone remodeling)
osteoclasts
- develop from bone marrow cell that give rise to blood cells
- large, multinuclei
- ruffled border to increase the surface for bone resorption
- often reside in pits (resorption bags/Howship lacunae)
organic part of matrix
synthesized by osteoblasts
Collagen+protein+carbohydrate complexes
allows flexibility
osteoid tissue
inorganic part of matrix
85% of hydroxyapatite (crystalized calcium-phosphate salts)
other minerals
allows strength and durabulity
2 main structures of spongy bone
Spicules (rods or spines) and trabeculae (thin plates) align along the lines of stress
no need for central canals
other 2 names for red bone marrow
homopoietic
myeloid tissue
other 2 names for bone formation
ossification or osteogenesis
general characteristic of intramembranous ossification
- in fetus and infants
- produces the flat bones of the skull and clavicle bone
- develop within the fibrous sheet similar to the dermis of skin = dermal bones
4 stages of intramembranous ossification
- mesenchyme condenses, cell enlarge and diff into osteogenic cells. Trabeculae created
- diff into osteoblasts and deposit an organic matrix. Deposition of calcium. Surface mesenchyme remains uncalcified and forms periosteum.
- Minerals deposited. Osteoclast create marrow cavity.
- Surface trabeculae calcify and become a compact bone.
general characteristics of endochondral ossification
the bone is preceded by hyaline cartilage model
most bones of the body
5 stages of endochondral ossification
- Creating a hyaline cartilage model of the future bone with perichondrium from mesenchyme. (chondrocytes)
- diff into osteoblasts = thin bony collar around the middle. Perichondrium becomes periosteum
primary ossification center is created (enlargement, death, merging of lacunae)
3.invasion on primary oss center by blood vessels = primary marrow cavity.
metaphysis - the region of transition form cartilage into bone
Second ossification center is created in epiphysis. - At birth. Secondary marrow cavity is formed and expands outward from the center.
- Infancy and childhood. Cartilage is limited to articular cartilage and epiphyseal plate.
- bone elongation through metaphysis, closing out of epiphyseal plates.
what is metaphysis
transitional zone of epiphyseal plate facing the marrow cavity
zones of metaphysis 4
- Zone of reserved cartilage. typical hyaline, farthest from marrow cavity.
- Zone of cell proliferation. multiplication of chondrocytes and rows of flattened lacunae
- Zone of hypertrophy. Enlargement. thin walls of lacunae
4-5 Zones of temporary calcification and then bone deposition. Chondrocytes die, walls break down, invasion by bone marrow. Concentric lamellae is laid down.
What is interstitial growth
bone elongation as a result of cartilage growth from within by the multiplication of chondrocytes and deposition of new matrix in the interior.
what is appositional growth
growth in diameter and thickness. Deposition of a new tissue on surface (circumferential lamellae). Similar for intramembranous ossification. Widening of marrow cavity
wollff’s law of bone
the architecture of a bone is determined by the mechanical stresses placed upon it. The bone adapts to withstand those stresses.
ectopic ossification
forming of osseous tissue outside of the bone. (calculus)
general functions of Ca
- communication among neurons
- muscle contraction
- blood clotting
- exocytosis
- 2nd and 3rd messengers
- cofactors for many enzymes
General function of P
DNA, RNA, ATP
acid-base balance
Hypocalcemia
exessive excitability of the nervous system
tetany
inability of muscle to relax. Can cause laryngospasm
Hypercalcemia
depression of nervous system, muscle weakness, sluggish reflexes.
calcitriol
hormone, most active form of vit D Raises the blood Ca concentration by 1.incr absorption by small intestine 2.incr Ca resorption by stimulating the production of osteoclasts 3.weakly absorption by kidneys.
also promotes bone depostiong
calcitonin
Thyroid gland secretes when the blood calcium are too high)
- osteoclasts inhibition
- osteoblast stimulation
Parathyroid hormone
secreted when Ca is low, very sensitive
- promotes production of osteoclasts
- Ca resorption by kidneys.
- promotes final step of calcitriol synthesis in kidneys
- inhibits collagen synthesis by osteoblasts
4 stages of fracture healing
- Formation of hematoma and granulation tissue (soft fibrous mass from blood clot)
- formation of soft callus (patches of fibrocartilage)
- Conversion to hard callus. bony collar. 4-6 weeks to form, 3-6 months
- Remodeling
spongy bone and then compact bone (similar to intramembranous ossification)
