6 - Bones

What are the Five Primary Functions of the Skeletal System

1. Support

2. Storage

3. Blood Cell Production

4. Protection

5. Leverage

The Skeletal System Includes:

Bones and associated Cartilages

Ligaments and other connective tissues

What are Bone (Osseous) Tissue?

Dense, supportive connective tissue

What do Bone (Osseous) Tissue contain?

specialized cells

What do Bone (Osseous) Tissue produce?

solid matrix of calcium salt deposits

What do Bone (Osseous) Tissue form around?

collagen fibers

Organic components of bone (about one-third of bone mass):

Cells

Collagen fibers

Ground substance

Inorganic components of matrix:

Primarily hydroxyapatite

Calcium phosphate and calcium hydroxide (Ca₁₀(PO₄)₆(OH)₂)

Cells of Bone

Osteoprogenitor cells

Osteoblasts

Osteocytes

Osteoclasts

Osteoprogenitor cells

Mesenchymal stem cells in endosteum and periosteum

Osteoblasts

secrete osteoid

Osteocytes

maintain matrix and detect mechanical stress on a bone

Osteoclasts

Large, multinuclear cells that secrete hydrochloric acid and enzymes that dissolve matrix

Compact bone

Solid and relatively dense, and are the external surfaces of long and flat bones

Spongy bone

contain trabeculae and are the internal surface of bones

What is an Osteon?

the basic unit of compact bone

What are Osteocytes are arranged in?

concentric lamellae

Osteocytes arranged around

a central canal containing blood vessels

Circumferential Lamellae

form around long bone and bind osteons together

Periosteum are formed on

the outside of Circumferential Lamellae except joint capsules

Periosteum layers

fibrous and cellular layer

Perforating fibers - collagen

bone

periosteum

joint capsule

tendon/ligament

Endosteum

incomplete cellular layer

What does the endosteum line?

medullary cavity and central canal

Endosteum covers the

trabeculae of spongy bone

Endosteum contain what kind of cells?

Osteoblasts

Osteoprogenitor cells

Osteoclasts

Typical adult has how many bones?

206 (>270 to <200)

What are Bones classified by?

Shape

Internal tissue organization

Bone markings (surface features; marks)

Six Bone Shapes

1. Sutural bones

2. Irregular bones

3. Short bones

4. Flat bones

5. Long bones

6. Sesamoid bones

Structure of a Long Bone

Diaphysis

Epiphysis

Metaphysis

Diaphysis

shaft of the bone

What do Diaphysis contain?

compact bone

medullary cavity

What are Epiphysis?

ends of long bone

Epiphysis

Mostly spongy bone

Surrounded by compact bone

What are Metaphysis?

Where diaphysis and epiphysis meet

Spongy Bone

No osteons

open network of trabeculae

Where is red bone marrow made?

Spongy Bone

Medullary Cavity contain

yellow marrow

Human bones grow until about

age 25

What is Osteogenesis?

Bone formation

What is Calcification?

process of depositing calcium salts

When does calcification occur?

during bone ossification and in other tissues

What is Ossification?

process of replacing other tissues with bone

What are the main forms of ossification?

Endochondral ossification

Intramembranous ossification

Endochondral Ossification

Ossifies bones that originates as cartilage

Intramembranous ossification

makes flat bones

Growth in length at epiphyseal plate: Epiphyseal to Diaphyseal:

1. Zone of resting cartilage

2. Zone of proliferation

3. Zone of hypertrophy

4. Zone of calcification

5. Ossified bone

Summary of bone development

1. Cartilage model forms

2. Bone collar forms

3. 1° ossification center

4. Medullary cavity

5. 2° ossification center

6. Growth continues

What is Appositional Growth?

growth in width

Appositional Growth thickens and strengthens

long bone

Appositional Growth adds more layers of

circumferential lamellae

Bones stop growing around

your early 20’s

Epiphyseal Lines form when

long bone stops growing

When long bone stops growing, after puberty:

Epiphyseal cartilage ossifies which is visible on X-ray as epiphyseal line

Intramembranous Ossification (dermal ossification)

Flat bones of the skull

Mesenchymal tissue model

Three main steps to Intramembranous Ossification (dermal ossification)

Mesenchymal cells differentiate to osteoblasts

Osteoblasts begin ossification

Spongy bone formation – remodeled

Blood Supply of Mature Bones

Nutrient Artery and Vein

Metaphyseal Vessels

Periosteal Vessels

Nutrient Artery and Vein

Supply the epiphyseal cartilage

A single pair of large blood vessels

Enter the diaphysis through the nutrient foramen

Femur has more than one pair

Metaphyseal Vessels

Where bone growth occurs

Where bone growth occurs

Blood to superficial osteons

Secondary ossification centers during development

Process of Bone Remodeling the adult skeleton:

Maintains itself

Replaces mineral reserves

Continually recycles and renews bone matrix

Involves osteocytes, osteoblasts, and osteoclasts

Effects of Exercise on Bone

Remodeling allows bones to acclimate

Stressed bones become stronger/denser

Broken bones, osteoporosis, bedridden

Stressed bones become

stronger/denser

Bone Degeneration affects:

Up to one third of bone mass

Normal Bone Growth and Maintenance

Need good Nutrition and Hormones

Nutrition

Dietary source of Calcium and Phosphate

Drink Milk, Eat Bones!

Hormones – Calcitriol

Synthesized in the kidneys

What does Calcitriol require?

Vitamin D₃

Where is Vitamin D₃ obtained from?

the sun

Other vitamins that are important:

Vitamin C

Vitamin A

Vitamins K and B₁₂

Vitamin C

collagen synthesis/stimulation of osteoblast differentiation

Vitamin A

stimulates osteoblast activity

Vitamins K and B₁₂

help synthesize bone proteins

Other hormones informant for bone development and growth

Growth hormone and thyroxine

Estrogens and androgens

Calcitonin and parathyroid hormone

Growth hormone and thyroxine

determine how large bones grow, secreted by pituitary gland

Hypersecretion of GH leads to

gigantism

Hyposecretion of GH leads to

pituitary dwarfism

Estrogens and androgens

sex differences in height

Estrogens and androgens

Calcium homeostasis; how much calcium is in the blood

Calcium Homeostasis

Bones store calcium and other minerals

Calcium ions are vital to:

Membranes

Neurons

Muscle cells, especially heart cells

Fractures

Cracks or breaks in bones

Fractures are repaired in four steps

1. Formation of clot

2. Formation of callus

3. Ossification of callus

4. Remodeling

Clot formation

Fibrous network

Bone cells in the area die

Calluses stabilize the break

Cells of the endosteum and periosteum

Fibrocartilage callus (soft)

Ossification of

cartilage callus

Remodeled to original look

osteoblasts and osteoclasts

up to a year

little to no evidence

Effects of Aging on the Skeletal System

Reduction in collagen and calcium

Osteopenia begins between ages 30 and 40

The epiphyses, vertebrae, and jaws are most affected

Reduction in collagen and calcium

bones become less dense

Osteopenia begins between ages 30 and 40

Bones become thinner and weaker with age

Women lose 8% of bone mass per decade, men 3%

The epiphyses, vertebrae, and jaws are most affected

fragile limbs

Reduction in height

Tooth loss

Osteoporosis

Severe bone loss

menopause

Osteoporosis Over age 45, occurs in ______ of women

29%

Osteoporosis Over age 45, occurs in ______ of men

18%

Identify 1

Articular cartilage

Identify 2

spongy bone

Identify 3

Medullary cavity

Identify 4

Endosteum

Identify 5

Periosteum