The Skeletal System

Chapter 6-8

- 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

The Primary Organs are the BONES:

At birth the bones are made of CARTILAGE – gradually this cartilage will become transformed into bones – calcification makes the bones hard

- 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!!!

How do we get new bone?

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)

Skeletal System contains 2 major types of connective tissue: Bones & Cartilage

- 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

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

Types of Bones:

- 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 Tissue: or Osseous Tissue

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

Bone Cells:

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

- 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

Bone Marrow – myeloid tissue

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

Regulation of Blood Calcium Levels:

- 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

Bone Formation, Growth, & Remodeling:

- 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

Joints (Articulations) –

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