Chapter 6- Bones

What do bones do for you other than make up 18% of your weight?

• 1. Support- muscles• 2. Protection- organs• 3. Movement- with muscles• 4. Mineral storage- calcium (99% of body's),

phosphorus, • 45% of bone weight• 5. Hemopoiesis- Blood cell production, in the Red

bone marrow• 6. Fat storage- Yellow bone marrow

Figure 6-1 A Classification of Bones by Shape

Sutures

Suturalbone

Vertebra

Carpalbones

Parietal bone External table

Internaltable

Diploë(spongy

bone)

Humerus

Patella

Sutural Bones Flat Bones

Long Bones

Sesamoid Bones

Irregular Bones

Short Bones

Structure of Bone(pg 173)

• 1. Diaphysis- shaft• 2. Epiphyses- ends• 3. Metaphyses- b/w 1 & 2, includes the

epiphyseal plate (cartilage)- cartilage replaced by bone when

done growing = epiphyseal line• 4. Articular cartilage- reduces friction• 5. Periosteum-covering for protection &

nourishment• 6. Medullary cavity/ Marrow cavity-

yellow marrow• 7. Endosteum- lines the marrow cavity

6-3 Bone (Osseous) Tissue

• Matrix composed of:– Minerals:

• Hydroxyapatite (Calcium)• Function: Hard, brittle and can withstand

compression

– Protein Fibers:• Collagen• Function: Tensile strength, tolerates

twisting/bending

Bone Cells

Maintain matrix, help repair damage bone

Secrete new matrix (osteoid), become osteocytes

Produce osteoblasts, repair fractures

Remove/recycle matrix by dissolving with acids/enzymes (osteolysis)

Resorption- breakdown of bone *every 7 years you make a new skeleton

Bone Tissue

• 1. Compact- 80% of bone, few spaces– Haversian canals (bld vessels), Lamellae (layers),

Lacunae(pockets with osteocytes)

* All bone tissue has a rich supply of blood

2. Spongy- 20% of bone, found in the epiphyses

• No osteons

• Matrix = trabeculae

(lattice structures), appears to have holes

stores red marrow– Open network of fibers w/

no blood vessels

6-4 Compact Bone and Spongy Bone

• Periosteum:– Outer membrane

covering compact bone

– fibrous and cellular layer

– Functions:

– Isolates bone

– Route for blood vessels/nerves

– Bone growth/repair

6-4 Compact Bone and Spongy Bone

• Endosteum– incomplete cellular

layer lining the medullary cavity

– Contains osteoblasts, osteoprogenitor cells and osteoclasts

– Functions:– Covers trabeculae – Lines central canals– bone growth and repair

6-5 Bone Formation and Growth

• Ossification

• The process of replacing other tissues with bone

• Includes calcification: deposition of Ca salts

• Two Main forms of ossification:

• Endochondral Ossification and Intramembranous

Ossification

Endochondral Ossification

• Ossifies bones that originated as hyaline

cartilage

• Step 1:

• Chondrocytes increase in size

• Matrix begins to calcify

• Enlarged chondrocytes die

Endochondral Ossification

• Step 2:

• BVs grow into perichondrium

• Cells of perichondrium

convert to osteoblasts and

produce thin layer of

superficial bone

Endochondral Ossification

• Step 3:

• BVs penetrate cartilage

• Fibroblasts migrate and

differentiate into osteoblasts

• Form primary ossification

center, cartilage replaced with

spongy bone

Endochondral Ossification

• Step 4:

• Remodeling occurs

• Osseous tissue becomes thicker

• Cartilage near epiphysis

replaced by bone

• Osteoclasts erode spongy bone

and form medullary cavity

• Step 5:

• Capillaries and osteoblasts

migrate into epiphyses

• Secondary ossification

centers form

Endochondral Ossification

Endochondral Ossification• Step 6:

• Epiphyses fill with spongy bone

• Articular cartilage remains

• Metaphysis: epiphyseal cartilage

separates epiphysis from

diaphysis

• Epiphyseal cartilage lost after

puberty complete females 23, males 25when complete-no epiphyseal disks

Figure 6-11a Bone Growth at an Epiphyseal Cartilage

An x-ray of growing epiphysealcartilages (arrows) Epiphyseal lines in an

adult (arrows)

Intramembranous (Dermal) Ossification

Bone Formation Video

6-6 Bone Remodeling• The adult skeleton:

• Maintains itself

• Replaces mineral reserves

• Recycles and renews bone matrix

6-7 Exercise, Hormones, and Nutrition

• Exercise

– Mineral recycling allows bones to adapt to stress

– Heavily stressed bones become thicker and

stronger

• Bone Degeneration

– Bone degenerates quickly

– Up to one third of bone mass can be lost in a few

weeks of inactivity

6-7 Exercise, Hormones, and Nutrition• Nutrition

– Diet must include calcium and phosphate salts,

plus small amounts of magnesium, fluoride, iron,

and manganese

– Calcitriol

• Vitamin C required for collagen synthesis and stimulation of osteoblast differentiation

• Vitamin A stimulates osteoblast activity

• Vitamins K and B12 help synthesize bone proteins

6-7 Exercise, Hormones, and Nutrition

• Hormones

– Growth hormone and thyroxine stimulate

bone growth

– Estrogens and androgens stimulate

osteoblasts

– Calcitonin and parathyroid hormone regulate

calcium levels

Figure 6-16b Factors That Alter the Concentration of Calcium Ions in Body Fluids

Bone Response Intestinal Response Kidney Response

Thyroid Gland Response

Factors That Decrease Blood Calcium Levels

These responses aretriggered when plasmacalcium ion concentrationsrise above 11 mg/dL.

HIgh Calcium Ion Levels in Plasma(above 11 mg/dL)

Parafollicular cells (C cells) in thethryoid gland secrete calcitonin.

Osteoclasts inhibited whileosteoblasts continue to lockcalcium ions in bone matrix

Bone

Rate of intestinalabsorptiondecreases

Kidneys allowcalcium loss

Calcitonin

less

calcitriol

Calcium stored

Calcium absorbed slowly Calcium excreted

Increased calciumloss in urine↓Ca2+

levels inbloodstream

Figure 6-16a Factors That Alter the Concentration of Calcium Ions in Body Fluids

Bone Response Intestinal Response Kidney Response

Parathyroid Gland Response

Factors That Increase Blood Calcium Levels

These responses aretriggered when plasmacalcium ion concentrationsfall below 8.5 mg/dL.

Low Calcium Ion Levels in Plasma(below 8.5 mg/dL)

Low calcium plasma levels causethe parathyroid glands to secreteparathyroid hormone (PTH).

Osteoclasts stimulated torelease stored calcium ionsfrom bone

Osteoclast

Bone

Rate ofintestinalabsorptionincreases

Kidneys retaincalcium ions

PTH

more

calcitriol

Calcium released Calcium absorbed quickly Calcium conserved

Decreased calciumloss in urine↑Ca2+

levels inbloodstream

Cracks/breaks in bones

Caused by physical

stress

Repaired in four steps

Figure 6-17 Types of Fractures and Steps in Repair

Immediately after the fracture, extensivebleeding occurs. Over aperiod of several hours, alarge blood clot, or fracturehematoma, develops.

An internal callus forms as a network of spongy boneunites the inner edges, and anexternal callus of cartilage and bonestabilizes the outer edges.

PeriosteumSpongy bone ofexternal callus

Fracturehematoma

Bonefragments

Deadbone

REPAIR OF A FRACTURE

Figure 6-17 Types of Fractures and Steps in Repair

The cartilage of the external callus has been replaced bybone, and struts of spongy bone nowunited the broken ends. Fragments ofdead bone and the areas of boneclosest to the break have beenremoved and replaced.

A swelling initially marks the location ofthe fracture. Over time, thisregion will be remodeled,and little evidence of the fracture will remain.

Externalcallus

Externalcallus

Internalcallus

Fractures• 1. Open/Compound- through the skin• 2. Closed/ Simple- not through the skin• 3. Comminuted- smaller fragments• 4. Greenstick- only children, 1 side broken, 1 side

bends• 5. Impacted- bone through bone• Stress fracture- microscopic , repeated stress

• can withstand 24,000 lbs/sq in, 4x greater than steel

Transverse- break along shaft Spiral- from twistingDisplaced- produces abnormal bone alignment

6-10 Effects of Aging on the Skeletal System

• Bones become thinner and weaker with age

• Osteopenia begins between 30 - 40

• Inadequate ossification/osteoblast activity declines = loss of bone mass

• Women lose 8% of bone mass/decade, men 3%

• The epiphyses, vertebrae, jaws most affected

• Result = fragile limbs, reduction in height, tooth loss

SEM 25Normal spongy bone

Spongy bone in osteoporosis SEM 21

• Osteoporosis

• Severe bone loss

• Affects normal

function/increases possibility of

fracture

Causes:• inadequate intake of calcium and

vitamin D• lack of weight-bearing exercise• lack of certain hormones, particularly

estrogen in women (menopausal women are at higher risk)

• Cigarette smoking• eating disorders such as anorexia

nervosa or bulimia

Abnormal Development of Bone

Pituitary dwarfism =inadequate production of growth hormone resulting in short bones

Gigantism= overproduction of HGHRobert Wadlow (Alton) 8ft, 11in

Marfan’s syndrome =excess cartilage at epiphyseal plates