What we’ll cover:1.Tissues of the skeletal system2.Functions of the skeletal system3.Cartilages of the skeletal system4.Bone development5.Ossification6.Cells of the skeletal system7.Types of bone8.Gross anatomy of bones9.Classification of bones10.Bone features11.Bone injuries12.Aging bones

Skeletal Tissues

JACKI HOUGHTON, DC

Contains cartilages, ligaments, blood vessels, nerves and connective tissues

Provides support/framework for the body

Stores mineral, lipids (in yellow bone marrow)

Blood cell production

Provides levers for muscles to produce actions

Contains calcium and phosphate ions

Define Cartilage – remember your connective tissues?

What should I know about cartilage?

1. What are the types of cartilages?

2. Where would I find each of these types of cartilages?

3. What are the functional properties of cartilage as a tissue?

Cartilage• Embryo

– More prevalent in the embryo than in adult

– Skeleton is initially mostly cartilage

– Bone replaces cartilage in fetal and childhood periods

– 3 types: hyaline, elastic and fibrocartilage

So what is cartilage? It is a connective tissue which has differing properties, depending on it’s function. Hyaline cartilage lines the ends of bones and cushions them. The hyaline wears better than bone.

Elastic cartilage is still but will bend and return to it’s original shape.

Fibrocartilage has great tensile strength and can absorb shock.

Cartilages

• 3 types– Fibrocartilage– Elastic cartilage– Hyaline cartilage

Location of cartilage in adults

• External ear - elastic• Nose - hyaline• “Articular” – covering the

ends of most bones and movable joints - hyaline

• “Costal” – connecting ribs to sternum - hyaline

• Larynx - voice box -elastic

• Epiglottis – flap keeping food out of lungs - elastic

• Cartilaginous rings holding open the air tubes of the respiratory system (trachea and bronchi) hyaline

• Intervertebral discs - fibrocartilage

• Pubic symphysis - fibrocartilage

• Articular discs such as meniscus in knee joint - fibrocartilage

• Functions of the Skeletal System– Support against gravity

– Protection of soft internal organs

– Movement (Leverage)

– Storage• Minerals (calcium, phosphorous) – within the

matrix of bone tissue• Energy reserve (adipose) – within the yellow

marrow of long bones

– Blood cell production – within red marrow of spongy bone tissue

Chemical composition of bones

• Cells, matrix of collagen fibers and ground substance (organic: 35%)– Contribute to the flexibility and tensile strength

• Mineral crystals (inorganic: 65%)– Primarily calcium phosphate – Lie in and around the collagen fibrils in

extracellular matrix– Contribute to bone hardness

• Small amount of water

Bone development

• Osteogenesis: “formation of bone” – From osteoblasts– Bone tissue first appears in week 8 (embryo)

• Ossification: “to turn into bone”– Intramembranous ossification (also called “dermal”

since occurs deep in dermis): forms directly from mesenchyme (not modeled first in cartilage)

• Most skull bones except a few at base• Clavicles (collar bones)• Sesamoid bones (like the patella)

– Endochondral ossification: modeled in hyaline cartilage then replaced by bone tissue

• All the rest of the bones

Remember the three germ tissues…1. Ectoderm - epithelial

2. Endoderm - epithelial

3. Mesoderm is a mesenchyme tissue– Mesenchyme cells are star shaped and do

not attach to one another, therefore migrate freely

– From the last slide:

Intramembranous ossification: forms directly from mesenchyme (not modeled first in cartilage)

• Most skull bones except a few at base

• Clavicles (collar bones)

• Sesamoid bones (like the patella)

Intramembranous ossification1. ossification centers appear in the

fibrous connective tissue membrane. Certain mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center.

2. Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies. Osteoblasts begin to secrete osteoid which is calcified within a few days. Trapped osteoblasts become osteocytes.

3. Woven bone and periosteum form. Blood vessels perforate the growing bone in a random manner resulting in a network instead of lamellae and forms trabeculae called woven bone.

4. Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. Eventually a plate of compact bone forms on the cortex of the flat bones.

(osteoid is the organic part)

Endochondral ossification• Modeled in hyaline cartilage, called cartilage

model• Gradually replaced by bone: begins late in second

month of development• Perichondrium is invaded by vessels and

becomes periosteum• Osteoblasts in periosteum lay down collar of bone

around diaphysis• Calcification in center of diaphysis• Primary ossification centers• Secondary ossification in epiphyses• Epiphyseal growth plates close at end of

adolescence– Diaphysis and epiphysis fuse– No more bone lengthening See next slide

Endochondral ossification

Stages 1-3 during fetal week 9 through 9th month

Stage 4 is just before birth

Stage 5 is process of long bone growth during childhood & adolescence

Epiphyseal growth plates in child, left, and lines in adult, right (see arrows)

Factors regulating bone growth

• Vitamin D: increases calcium from gut • Parathyroid hormone (PTH): increases

blood calcium (some of this comes out of bone)

• Calcitonin: decreases blood calcium (opposes PTH)

• Growth hormone & thyroid hormone: modulate bone growth

• Sex hormones: growth spurt at adolescense and closure of epiphyses

Bone Composition

• Cells and matrix• Matrix

– Calcium phosphate 2/3, collagen fibers 1/3– Collagen forms a lattice frame to hold saltsCells

Osteocytes – mature bone cells which create and maintain a structure ”osteon”Osteoblast – produces new osteocytesOsteoclasts – destroy worn out bone cells – are actually derived from blood cells (ref:http://edrv.endojournals.org/content/32/1/31.full)Osteoprogenitor Cells from mesenchyme for bone repair

Compact bone

• Osteons: pillars (functional unit)

• Lamellae: concentric tubes

• Haversian canals

• Osteocytes

Spongy boneNo osteons

• Layers of lamellae and osteocytes

• Seem to align along stress lines - traebeculae

•Nutrients diffuse from vessels in central canal•Alternating direction of collagen fibers increases resistance to twisting forces

Isolated osteon:

canaliculi

Long bones

• Tubular diaphysis or shaft

• Epiphyses at the ends: covered with “articular” (=joint) cartilage

• Epiphyseal line in adults – the epiphyseal plate usually closes at 20 years old– Kids: epiphyseal growth plate (disc of hyaline

cartilage that grows to lengthen the bone)• Blood vessels

– Nutrient arteries and veins through nutrient foramen

Classification of bones by shape

• Long bones

• Short bones

• Flat bones

• Irregular bones

• Pneumatized bones

• Sesamoid bones

(Short bones include sesmoid bones)

Gross anatomy of bones

• Compact bone• Spongy

(trabecular) bone

• Blood vessels• Medullary

cavity• Membranes

– Periosteum– Endosteum

Know these!

Flat bones

• Spongy bone is called diploe when its in flat bones– Have bone

marrow but no marrow cavity

Bone markings reflect the stresses

Periosteum • Periosteal Bud - A vascular connective tissue bud from the 

perichondrium that enters the cartilage of a developing long bone and contributes to the formation of a center for ossification.

• Connective tissue membrane• Covers entire outer surface of bone except at epiphyses• Two sublayers

– 1. Outer fibrous layer of dense irregular connective tissue– 2. Inner (deep) cellular osteogenic layer on the compact bone containing

osteoprogenitor cells (stem cells that give rise to osteoblasts) • Osteoblasts: bone depositing cells• Also osteoclasts: bone destroying cells (from the white blood cell line)

• Secured to bone by perforating fibers (Sharpey’s fibers)

Endosteum• Covers the internal bone surfaces• Is also osteogenic

Bone markings

• *Bone pain is called ostealgia*• Projections that are the attachments sites for muscles and

ligaments• Surfaces that form joints• Depressions and openings

Learn them using:Marieb lab book p 101, Table 8.1, Bone MarkingsorMartini p 128, Table 5.1, Common Bone Marking Terminology (next slide)

Bone remodeling

• Osteoclasts– Bone resorption

• Osteoblasts– Bone deposition

• Triggers– Hormonal: parathyroid hormone– Mechanical stress

• Osteocytes are transformed osteoblasts

Terms (examples)• chondro refers to cartilage

– chondrocyte– endochondral– perichondrium

• osteo refers to bone– osteogenesis– osteocyte– periostium

• blast refers to precursor cell or one that produces something– osteoblast

• cyte refers to cell– osteocyte

Repair of bone fractures (breaks)

• Simple and compound fractures

• Closed and open reduction