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Skeletal System (Bone Tissue) ☠️ (Structure of bone (Diaphysis (Central…
Skeletal System (Bone Tissue) ☠️
Function of bone
Support
Attachment for soft tissues and organs
Storage
Calcium
Body takes calcium from bone if not in our diet
Nervous system transmission
Phosphate
Cell production
Hematopeiesis- red blood cells, white blood cells, stem cells, & platelets
Protection
Ribs, protect heart
Skull, protects brain
Vertebrae, protects spinal cord
Classifications of bone
Compact
Dense, solid, external layer
Spongy bone (cancellous) (trabecular)
Red and yellow bone marrow
Shapes
Long bones
Longer than they are wide
Limbs (exception of - patella, carpals, and tarsals)
Compact bone
Short bones
Cube like
Spongy bone
Flat bones
Thin, broad, curved (like skull, ribs, scapula)
Irregular bones
Complex shapes
Vertibrae, hip bones
Spongy bone
Sesamoid bone
Embedded within tendon
Structure of bone
Diaphysis
Central shaft of bone (long bone)
Contains collar of compact bone
Metaphysis
Narrow zone
Epiphyseal plate
Epiphysis
Expanded ends
Makes up proximal and distal ends of each bone
Periosteum
Outer membrane
Attached directly to compact bone
Contains immature cells
Osteoblasts
Help bone grow in thickness
Medullary cavity
Within diaphysis
Contains yellow bone marrow
Fat
Endosteum
Thin layer lining internal bone
Helps build bone
Histology of bone tissue
Chemical composition
Organic
Cells
Osteoblasts
Build bone
Osteogenisis - making of bone (No mitosis)
Produce calcified matrix
Osteocytes
Nourish bone
Mature bone cells
Recycle calcium salts in matrix
Help repair (No mitosis)
Osteoclasts
Break down bone
Giant cells (50+ nuclei)
Fusion of 50+ monocytes
Secretes acids that dissolve bone matrix
Release stored material
Calcium & phosphate
Matrix
Glycoproteins & collagen fibers
Made by osteoblasts
Function - gives bone flexibility & strength
Inorganic
Hydroxyapatites
Made of calcium phosphate
Bones hardness
Osteoprogenitor cells
Stem cells
Become osteoblasts through mitosis
Called Osteogenic cells
Compact bone tissue
Made of osteons
Haversian system
Repeating units
Lamellae
Calcified matrix that occurs in rings
Central (haversian) canal
Longitudinal to bone
Canaliculi
Allow communication
Nutriance can travel from blood vessel, to osteocyte, to another osteocyte
Lacunae
Canaliculi runs through
Osteocytes
Spongy bone tissue
No osteons
Made up of trabeculae (struts)
Found around stress areas
Ends of bones
Contains red bone marrow
Found in - ends of long bones, hip bones, & sternum
Bone development
Ossification- the process by which connective tissue is replaced by bone tissue
Two types of bone development
Intramembranous ossification
Bone is developed in an area that had dense connective tissue
Involves cranial bones of skull and clavicles
Simplest of two
Endochondral ossification
Develops in an area that has had hyaline cartilage
Develop bone below base of skull
Second month of development (baby still in womb)
More complex of the two because it has to breakdown hyaline cartilage
Six steps
1) Development of cartilage model
Chondroblasts
Secrete hyaline cartilage
Perichondrium
Where chloroplasts are
2) Growth of cartilage model
Chondrocytes
Have been housed into matrix (calcify) (mature chondroblasts)
Enlargement & calcification
As chondrocytes get larger, they die
Matrix detiriorates, leaving open cavities and bone keeps stable
3) Development of primary ossification center
Nutrient artery, veins, & nerves
Osteoclasts
Erode calcified matrix from chondroblasts
Osteoblasts from spongy bone trabeculae
4) Development of medullary cavity
Osteoclasts forming cavity in center of diaphysis
Break down spongy bone
Growth can move outward
Bone growth chases cartilage formation
5) Development of secondary ossification center
At birth - Bony diaphysis surrounding spongy bone laterally grows medullary cavity & two cartilagenous epiphyses
Starts at ends because we have bone formed at ends
Nutrient artery in ephysis
Osterclasts and osteoblasts
Break down cartilage, build spongy bone
6)Formation of articular cartilage and epiphyseal plate
Each end of bone, from articular cartlage
Where articulate with other bone
Lengthwise growth, lies between ephipysis and diaphysis
structure does not differ between the two
Development does
Postnatal bone growth
Infancy & youth - longbones lengthen by interstitial growth of epiphyseal plates
Zones
Epiphyseal side
Active chrondocytes
Divide quickly
Diaphysical side
Calcification zone
Osteoblasts & osteoblasts
Constant thickness as a bone is growing
Rate of cartilage growth on epiphseal side is balanced by replacement of bony tissue on dialysys side
Adolecence
Nearing end of growth
Female - age 18
Male - age 21
Epiphyseal plate closure
Chondrycytes divide less & plates become thinner, all replaced by bone
Grow in thickness by appositional growth
Osteoblasts, osteocytes, & osteoclasts
Blasts- secrete bone matrix on external surface
Cytes - reside in new osteons
Clasts - remove bone on inside of diaphysis
Most bones stop growing during adolescence
Growth and remodeling
Not lifeless, very dynamic & active
We recycle 5-7% of bone mass weekly
Replace spongy bone 3-4 years
Replace compact bone 10 years
Because calcium crystallizes and bone becomes brittle
Two steps
Bone resorption
Osteoclasts
Bone deposition
Osteoblasts