Chapter 6:Skeletal System I

Bernard Siegfried Albinus 1697 – 1770

Famous for his drawings in the work entitled Tables of the Skeleton and Muscles

of the Human Body published in 1747.

An example of Albinus’ drawings of the skeleton.

Figure 6.1 The bones and cartilages of the human skeleton.

Axial skeleton

Appendicular skeleton

Hyaline cartilages

Elastic cartilages

Fibrocartilages

Cartilages

Bones of skeleton

EpiglottisLarynx

TracheaCricoidcartilage Lung

Respiratory tube cartilagesin neck and thorax

ThyroidcartilageCartilage in

external earCartilages innose

ArticularCartilageof a joint

Costalcartilage

Cartilage inIntervertebraldisc

Pubicsymphysis

Articular cartilageof a joint

Meniscus (padlikecartilage inknee joint)

Figure 6.2 Classification of bones on the basis of shape.

(a) Long bone(humerus)

(b) Irregular bone(vertebra), rightlateral view

(d) Short bone(talus)

(c) Flat bone(sternum)

Figure 6.3a The structure of a long bone (humerus of arm).

Proximal epiphysis

(a)

Epiphyseal line

Articularcartilage

Periosteum

Spongy bone

Compact boneMedullarycavity (linedby endosteum)

Diaphysis

Distal epiphysis

(b)

Articularcartilage

Spongy bone

Compact bone

Figure 6.3b The structure of a long bone (humerus of arm).

(c)

Yellowbone marrow

Endosteum

Compact bone

Periosteum

Perforating(Sharpey’s) fibers

Nutrientarteries

Figure 6.3c The structure of a long bone (humerus of arm).

Figure 6.4 Comparison of different types of bone cells.

(a) Osteogenic cell (b) Osteoblast (c) Osteocyte

Stem cell Mature bone cellthat maintains the

bone matrix

Matrix-synthesizingcell responsiblefor bone growth

(d) Osteoclast

Bone-resorbing cell

Figure 6.5 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone.

Compactbone

Trabeculae

Spongy bone(diploë)

Figure 6.9 Endochondral ossification in a long bone.

1 2 3 4 5 Bone collarforms aroundhyaline cartilagemodel.

Cartilage in thecenter of thediaphysis calcifiesand then developscavities.

The periostealbud invades theinternal cavitiesand spongy bonebegins to form.

The diaphysis elongatesand a medullary cavityforms as ossificationcontinues. Secondaryossification centers appearin the epiphyses inpreparation for stage 5.

The epiphysesossify. Whencompleted, hyalinecartilage remains onlyin the epiphysealplates and articularcartilages.

Hyalinecartilage

Area ofdeterioratingcartilage matrix

Epiphysealblood vessel

Spongyboneformation

Epiphysealplatecartilage

Secondaryossificationcenter

Bloodvessel ofperiostealbud

Medullarycavity

Articularcartilage

Childhood toadolescence

BirthWeek 9 Month 3

Spongybone

Bonecollar Primaryossificationcenter

Figure 6.11 Long bone growth and remodeling during youth.

Bone growth Bone remodeling

Articular cartilage

Epiphyseal plate

Cartilagegrows here.

Cartilageis replacedby bone here.

Cartilagegrows here.

Bone isresorbed here.

Bone isresorbed here.

Bone is addedby appositionalgrowth here. Cartilage

is replacedby bone here.

Figure 6.12 Parathyroid hormone (PTH) control of blood calcium levels.

Osteoclastsdegrade bonematrix and release Ca2+

into blood.

Parathyroidglands

Thyroidgland

Parathyroidglands releaseparathyroidhormone (PTH).

StimulusFalling bloodCa2+ levels

PTH

Calcium homeostasis of blood: 9–11 mg/100 mlBALANCEBALANCE

CalcitoninCalcitonin

Figure 6.13 Bone anatomy and bending stress.

Load here (body weight)

Head offemur

Compressionhere

Point ofno stress

Tensionhere

Figure 6.14 Vigorous exercise can lead to large increases in bone strength.

Cross-sectionaldimension of the humerusAddedbone matrixcounteractsadded stress

(b) Serving arm

(a)

Nonserving arm

Steel “Bone Cages” used to lengthen legs. These were originally developed in the Soviet Union in the 1950s to treat dwarfism.

Twelve-year-old boy with pituitary gigantism measuring 6'5" with his mother. Note the coarse facial features and prominent jaw.

An example of untreated acromegaly.

Chelation Therapy – intravenous administration of chemicals designed to absorb toxic substances that have accumulated in the body. Most notably used for exposure to heavy metals such as lead or mercury.

Figure 6.15 Stages in the healing of a bone fracture.

Hematoma Externalcallus

Bonycallus ofspongybone

Healedfracture

Newbloodvessels

Spongybonetrabecula

Internalcallus(fibroustissue andcartilage)

1 A hematoma forms. 2 Fibrocartilaginouscallus forms.

3 Bony callus forms. 4 Boneremodelingoccurs.

Figure 6.16 The contrasting architecture of normal versus osteporotic bone.

Figure UN 6.1

Figure 6.17 Fetal primary ossification centers at 12 weeks.

Parietal bone

Radius

Ulna

Humerus

Femur

Occipital bone

ClavicleScapula

Ribs

Vertebra

Ilium

Tibia

Frontal boneof skull

Mandible

Table 6.2 Common Types of Fractures (1 of 3)

Table 6.2 Common Types of Fractures (2 of 3)

Table 6.2 Common Types of Fractures (3 of 3)