The Skeletal System
The Primary Organs are the BONES:
- buried w/in the muscles
- functions are:
a.) provide a rigid framework for protection
b.) support structure for the body
c.) movement
d.) storage
e.) blood cell formation
- living organs bec they change & help the body
respond to a changing envir – allows us to grow
At birth the bones are made
of CARTILAGE – gradually
this cartilage will become
transformed into bones –
calcification makes the bones
hard
How do we get new bone?
-
Osteoblasts (bone cells) form new bones
- Osteoclasts reabsorb bone
- The combined action of these two sculpt
the bone into its adult shape
- This allows the bones to respond to
stress, or injury by changing size, shape, &
density - EXERCISE MAKES BONES
DENSER!!!
Skeletal System contains 2 major types
of connective tissue: Bones & Cartilage
I. Bones – 2 basic types of osseous (bone) tissue
A. Compact Bone – outer layer, hard & dense also has
different appearance & texture according to the location
of the bone – looks smooth & homogeneous
- compact bone doesn’t contain a network of open spaces
– instead their structural unit is the Haversian System or
osteon (composed of multiple layers of calcified matrix
arranged in 3 types of rings)
- osteocytes are found in the lacunae which are
arranged in concentric circles called lamella
around the central (Haversian) canals
- canaliculi – tiny canals that radiate outward
from central canals to all lacunae – these canals
provide the transportation system that connects
all bone cells to the nutrient supply
- blood vessels & nerves run lengthwise
through the bony matrix
- perforating (Volkmann’s) canals –
provides routes from the outside of the
bone to the interior
- all of the rings are covered by
periosteum (double-layered connective
tissue that covers & nourishes bone)
B.
Spongy Bone – porous with small needle-like
pieces
- contains many spaces that may be filled with red
marrow
- the needle-like threads of spongy bone that surround a
network of spaces are called trabeculae
II. Cartilage – resembles & differs from bone
- fibers are embedded in a firm gel instead of calcified to
allow for flexibility
- cartilage cells - Chondrocytes
- no blood vessels in cartilage
Types of Bones:
1.) Long – longer than wide – have a shaft w/ a head at
both ends - ex. humerus, femur
2.) Short – generally cube shaped & contain mostly
spongy bone – ex. carpals, tarsals
3.) Flat –thin, flatted & usually curved – have 2 thin layers
of compact bone sandwiching a layer of spongy bone – ex.
frontal bone of skull, ribs, sternum
4.) Irregular – don’t fit any of the other 3 – ex. Vertebrae
Bone Tissue: or Osseous Tissue
- contains cells, fibers & calcified extracellular matrix
- the matrix is more abundant in bone – divided into 2
chemical components
1.) Inorganic salts – Ca2+, PO42-,Mg, Na, SO42-, F 2.) Organic Matrix –collagenous fibers & ground
substances (proteins & polysaccharrides)
- chondroitin sulfate – along with glucosamine are
req for repair & maintenance of bone & cartilage
Bone Cells:
1. Osteoblasts – small cells that synthesize & secrete
osteoid
- collagen fibrils line up in the osteoid where Ca
& PO4 are deposited
- results in accumulation of mineralized bone
- made from osteogenic stem cells found in the
endosteum & Haversian canal lining that
undergo cell division
2. Osteoclasts – large multinucleated cells
that are responsible for the erosion of bone
minerals
- formed from fusion of precursor cells
- contain lots of mitochondria &
lysosomes
3. Osteocytes – mature, non-dividing
osteoblasts that are surrounded by matrix
& now lie w/in lucunae
Bone Marrow – myeloid tissue
- functions in blood cell production (Hematopoiesis)
- found in medullary cavities of long bones, & in spaces of
spongy bone
- 2 types of marrow:
A.) Red Marrow – produces RBCs
B.) Yellow Marrow – marrow cells are saturated w/ fat – no
blood cell production- found in older people – is inactive
adipose (fatty) tissue that is converted from Red Bone
Marrow
*****During anemic conditions, yellow marrow
can alter to become red marrow
Regulation of Blood Calcium Levels:
2 Hormones are responsible:
1.)
Parathyroid Hormone – produced by parathyroid gland
- when Ca levels dec, it stimulates osteoclasts to break
down bone matrix
- also increases renal absorption of Ca from urine
- stimulates vitamin D synthesis, helps intestinal
absorption of Ca
2.)
Calcitonin – produced by thyroid gland
- when Ca levels inc, it stimulates osteoblasts to deposit bone
Bone Formation, Growth, & Remodeling:
- in embryos the skeleton is made mostly of hyaline cartilage
- as the child grows ossification (bone forming) occurs in 2 steps:
1.) hyaline cartilage is completely covered w/ bone matrix by
osteoblasts
2.) then the hyaline cartilage is digested away opening up a
medullary cavity
- by birth or shortly after most of the hyaline cartilage is
converted to bone
- bone remodeling retains the bones normal proportions &
strength as the body increases in weight & size
Joints (Articulations) –
- every bone in the body connects to at least 1 other except the hyoid bone
- Purpose - hold bones together & allow for movement
-classified in 2 ways:
1.) structurally – based on the material that separates the bony regions
a.) fibrous joints – united by fibrous tissue -usually immovable - ex.) sutures in skull
b.) cartilaginous joints – united by cartilage - slightly movable - ex.) intervertebral
joints
c.) synovial joints – bone ends are separated by a joint cavity containing synovial
fluid
- very movable but flexibility varies
- nonaxial joints only allow slipping movement – wrist joints
- uniaxial joints only allow movement in 1 plane – elbow joint
- biaxial joints allow movement in 2 planes – knuckles & thumb
- multiaxial joints move in all planes – shoulder joint
2.) functionally – based on the amount of movement allowed – 3 types:
a.) synarthroses - no movement – ex.) skull sutures
b.) amphiarthroses – slight movement – ex.) intervertebral disc
c.) diarthroses – free movement – most joints are this type
- types of diarthroses:
a.)
ball & socket – ex.) shoulder & hip
b.)
hinge – flexing & extending – ex.) elbows & knees
c.)
pivot – atlas & axis – neck & head
d.)
saddle – only 1 pair in the body located between the
thumb & wrist – extreme range of motion
e.)
gliding – least movable – ex.) vertebrae
f.)
condyloid – ones in which a condyle fits into an elliptical
socket – ex.) knuckles
Osteomalacia
Paget Disease
OSTEOMYELITIS
Osteoarthritis
Gout