Chap5: The Skeletal System Flashcards
Components of skeletal system
Bones
Cartilage
Joints
Ligaments
Living tissues capable of
- growth
- adaptation to stress
- auto repair after injury
Definition of skeletal system
It’s the structural framework that:
- gives the body its shape
- provide protection for internal organs and soft tissues
The skeletal system provides:
Support
Protection
Allows body mvt
Stores minerals and fats
Site of blood cell production
Functions of skeletal system
Support:
- rigid strong bone –> bare weight
- major supporting tissue of body
Protection:
Bone is hard –> protects surrounding organs
Mvt:
Skeletal muscles attach to bones via tendons (strong bands of connective tissues)
Storage:
Minerals in blood are taken into bone and stored
Minerals: calcium, phosphorus, fat (adipose tissue)
Blood cell production:
Cavities filled with red bone marrow (blood cells + platelets)
Number of bones in body
Average adult skeleton: 206 bones
But # decreases as person ages (bones fuse)
Division of bones of skeleton
Axial skeleton
- skull
- vertebral column
- rib cage
Appendicular skeleton
- bones of upper and lower limbs
- girdles/coxal (attach appendicular bones to axial)
Basic types of bone tissue
Compact bone: homogenous
Spongy bone: small needle like structure + has many open spaces
Classification of individual bones
According to shape:
Long (eg femur, humerus)
- longer than wide
- long shaft + 2 ends
- contain mostly compact bone
Short (eg carpals, tarsals)
-cube shaped
Flat (eg skull bones, sternum, scapulae, ribs)
- thin and flattened
- curved
- thin layer of compact bone around layer of spongy
Irregular (vertebrae, coxae)
- complicated shape
- don’t fit in any other class
Components of growing long bone
Diaphysis / shaft
-composed mostly of compact bone –> mostlybone matrix + small few spaces)
Epiphysis (end of bone)
- composed mostly of spongy bone –> mostly small spaces surrounded by bone matrix
- outer surface: layer of compact bone
- joints covered by cartilage
Epiphyseal plate
- hyaline cartilage
- where growth in bone length occurs –> after growth it becomes ossified: epiphyseal line (transformation from cartilage to bone)
From upper to lower:
Proximal epiphysis –> epiphyseal line/plate –> diaphysis –> line/plate –> distal epiphysis
Diaphysis of long bone
Medullary cavity= large space filled with marrow
-red marrow–> site of blood cell formation
(All kid bones filled with red marrow)
-yellow marrow–> adipose tissue
(In adults skull and limbs filled with yellow marrow
EXPT their proximal epiphysis)
Periosteum
Def: connective tissue membrane that covers outer surface of bone
Divided into 2 layers:
Outer fibrous layer
- dense irregular collagenous ct
- contains blood vessels (supply bone with nutrients)
- nerves
Inner layer
-single layer of bone cells (osteoblasts, osteoclasts, osteochondral progenitor)
Sharpey’s fibers
Secure periosteum to underlying bone
Articular cartilage
Covers external surface of epiphysis
Made of hyaline cartilage
Decreases friction at joint surfaces
Hard and flexible bone composition
Osteochondral progenitor cells –> osteoblasts –> osteocytes (bone cells)
Lacunae = cavities in matrix where osteocytes found
Lamellae= concentric circles of lacunae
Harvesian central canal = centers of lamella
Carry blood vessels and nerves
Canaliculi = tiny canals carrying nutrients from central canals to lacunae
Volkmann’s perforating canals = provide communication between layers and center of bone (perpendicular)
Organic components of bone and fct
Comp:
- osteocytes
- osteoclasts
- osteid (ground substance and collagen fibers)
Fct:
Contribute to flexibility and tensile strength of bone
Inorganic components and fct
Comp: make up 65% of bone by mass
-mineral salts –> calcium phosphate
Fct:
Hardness and compression resistance of bone
Bone formation and remodeling
Skeleton formed from strongest and most supportive tissues of body
- cartilage
- bone
In embryos: Skeleton primarily made of hyaline cartilage --> replaced by bone But cartilage remains in isolated areas: -bridge of nose -parts of ribs -joints
Ossification
Def: dev of bones using hyaline cartilage as their model
(Except for flat bones –> form on fibrous membranes)
Steps:
- hyaline cartilage completely covered with bone matrix by osteoblasts
- hyaline cartilage digested away–> medullary cavity
Intramembranous ossification
From week 4 to year 2
In flat bones
Starts with collagen fibers –> connective tissue
-Mesenchymal cells (ct, fibers)
-Osteochondral progenitor
-Osteoblast –> osteocyte
=> ossification center (filling fontanelles)
Endochondral ossification definition
Week 5 to 18-20 years
For the rest of the bones
Starts from cartilage
-Mesenchymal cells
-Chondroblast –> chondrocyte
=> produces hyaline cartilage surrounded by perichondrium (former periosteum)
Endochondral ossification steps
-primary ossification center in diaphysis
Mesenchymal cells –> chondroblasts –> chondrocytes
Chondrocytes produce cartilage surrounded by perichondrium
Perichondrium contains osteoclasts + osteoblasts (produced via osteochondral progenitor)
Blood vessels invasions of perichondrium
Chondrocytes enlarge + accumulate Ca –> forming calcified cartilage
Blood vessels invade cartilage + bring from perichondrium: osteochondral progenitor, osteoblast, osteoblast
Osteoblast: add bone matrix + form bone (start spongy –> compact)
Osteoclast: digest calcified cartilage in the middle –> medullary cavity
+more blood vessels enter
=> primary ossification center in diaphysis
Endochondral ossification steps
-secondary ossification center in epiphysis
- Calcified cartilage
- Invasion of blood vessels
- No transformation to compact + no cavity –> stays spongy
Most hyaline cartilage have been converted to bone except for 2 regions
Articular cartilage
- covers bone ends
- persist for life
- reduce friction at joint surface
Epiphyseal plate
-provide longitudinal growth of long bone during childhood
How do bone widen?
Osteoblast in periosteum
-add bone tissue to external face of diaphysis
Osteoclast in endosteum
-remove bone from inner face of diaphysis wall
Process in which bones increase in diameter = appositional growth
