The skeletal system consists of bones, cartilage, and ligaments that provide structure, support, protection, movement, and blood cell formation. There are two main types of bones - long bones which have a shaft and ends, and flat/irregular bones. Bones develop through intramembranous ossification which forms flat bones of the skull, or endochondral ossification where cartilage models are replaced by bone. Bones continuously remodel through the actions of osteoblasts which build bone and osteoclasts which break it down. The skeletal system is divided into the axial skeleton which includes the skull, vertebral column, ribs, and sternum, and the appendicular skeleton which includes the limbs and their attachments.

1. English
Skeletal System
Falsely colored radiograph of the human skull.

2. You are responsible for the following figures and tables:
Part I. Characterization of the CT, bone.
Tab. 1.2 - Functions of the Skeletal System.
Fig. 7.1 - Bones can be classified by shape
Fig. 7.2 - Typical long bone: has compact and spongy bone
Fig. 7.4 - Compact bone.
Read TB, p. 186-189: Intramembranous Bones - Endochondral Bones Tab. 7.1 -
Major steps in Bone Development.
Give an example of Intramembranous Ossification. Fig. 7.6
Fig. 7.8 - Endochondral Ossification from hyaline cartilage.
Fig. 7.9 - Epiphyseal plate
Tab. 7.2 - Ossification Timetable.
You may want to try out the labeling exercises on the textbook
website: www.mhhe.com/shier11e
Click on ‘self-study’, scroll down to ‘chapter 7’, click on ‘more resources’ within
chapter 7, click on ‘labeling exercises’.
If the screen does not upload, ‘right click’ on the mouse and ‘open in new window’.

3. You are responsible for the following figures and tables:
Part II. Divisions and bones of the skeleton.
Tab. 7.3 - Bones of the adult skeleton. Read TB, p. 197. Differentiate between the
axial and the appendicular parts of the skeleton.
Fig. 7.16 – Sutural / wormian bones.
Fig. 7.21 - Cranial bones. Fig. 7.27 - Sinuses.
Read on the bones that make the face - facial bones - TB, p. 204.
Focus on the mandible and maxilla - Fig. 7.30, 7.31.
Fig. 7.33 - Fetal skull – note the fontanels and the split frontal plate.
Fig. 7.34 - Vertebral column –
Fig. 7.36 - Atlas and axis - vertebrae 1 and 2.
Fig. 7.39 - Sacrum and Coccyx –
Fig. 7.40 - Thoracic cage –
Fig. 7.43 - Parts of the pectoral girdle.
Fig. 7.44 - Upper limb. Note how the radius can be extended to the thumb.
Fig. 7.45 - Note the head of the humerus
Fig. 7.45 - Note the carpals, metacarpals and phalanges.
Fig. 7.49 - Pelvic girdle. Fig. 7.52 - Lower limb. Fig. 7.56 - Foot. Fig. 7.53 - Femur.
Tab. 7.13 - Effect of Aging. Geriatrics.

4. Bone Classification (Fig. 7.1)
Bones are classified according to shape
• Long bones are long with expanded ends,
Ex: forearm and thigh bone
• Short bones are cube like, Ex: wrist, ankle
• Flat bones are broad and plate like, Ex:
ribs, scapulae, and some skull bones
• Irregular bones vary in shape, Ex:
vertebrae
• Sesamoid or round bones are small bones
embedded in tendons, Ex: kneecap (patella)

5. Long Bone Structure (Figure 7.2)

6. Parts of Long Bone
• Epiphysis: end of the bone which articulates (forms
a joint) with another bone.
Epiphyses are composed of spongy bone and
covered with hyaline cartilage called articular
cartilage.
• Diaphysis: shaft of the bone between the epiphyses,
composed of compact bone with a medullary cavity
in the center.
• Periosteum: fibrous tissue covering of the bone.

7. Compact Bone (Fig. 7.4)
• Osteocytes and layers of intercellular material lie
in concentric rings around an osteonic canal.
• This unit is called an osteon or Haversian
system.
• Osteonic canals contain blood vessels and nerve
fibers and are interconnected by transverse
perforating (Volkmann’s) canals and even
smaller canaliculi.

8. Spongy Bone
• The spongy bone is found in the area
around the epiphyseal disk where cells
have high mitotic activity.
• Osteocytes lie within lacunae within
trabeculae or branching bony plates.
Canaliculi lead to the trabeculae.
• Nutrients needed for mitosis diffuse from a
blood vessel into the canaliculi.

9. Bone Growth and Development
Bone Development (Fig. 7.6 a):
The skeletal system begins to form during the
first weeks of prenatal development.
• Some bones originate within sheets of
connective tissue (intramembranous
bones).
• Some bones begin as models of hyaline
cartilage that are replaced by bone
(endochrondral bones).

10. Intramembranous Bones (Tab. 7.1)
• Broad, flat skull bones are intramembranous bones.
• During osteogenesis layers of primitive, connective tissue
supplied with blood vessels appear at the site of future
bone.
• Cells differentiate into osteoblasts (bone-building cells)
which deposit spongy bone.
• Osteoblasts become osteocytes when surrounded by bony
matrix in lacunae.
• Periosterum: Connective tissue on the surface of the bone
forms it.
• Osteoblasts on the inside of the periosteum deposit compact
bone over spongy bone. This process is called
intramembranous ossification.

11. Endochondral Bones (Tab. 7.1; Fig. 7.8)
• Hyaline cartilage forms models of future bones.
• Cartilage degenerates, periosteum forms.
• Periosteal blood vessels and osteoblasts invade the bone
forming a primary ossification center in the diaphysis.
• Secondary ossification centers develop in the epiphyses.
• Osteoblasts form spongy bone in the space occupied by
cartilage.
• Osteoblasts become osteocytes when bony matrix
surrounds them.
• Osteoblasts beneath the periosteum deposit compact bone
around spongy bone.
• A band of cartilage remains between the diaphysis and
epiphyses as the epiphyseal disk.

12. Bone Growth and Development
Bone Growth (Fig. 7.9; Fig. 7.11):
Growth of long bones occurs along four layers of
cartilage in the epiphyseal disk.
• First Layer: resting cells that do not grow.
• Second Layer: young cells that are actively
dividing by mitosis.
• Third Layer: older cells that enlarge.
• Fourth Layer: dead cells and calcified
intercellular substances.

13. Bone Homeostasis -Remodeling
• After bone formation, osteoclasts and
osteoblasts continue to remodel the bone.
• Resorption and deposition are hormonally
regulated to keep bone mass constant (textbook
p. 194).
• The hormone controlling bone resorption is
PTH or parathyroid hormone. The hormone of
bone synthesis is calcitonin.

14. Nutrition and Bone Development
• Vitamin D is necessary to absorb calcium
in the small intestine.
Vitamin D deficiency leads in rickets in
children and osteomalacia in adults.
• Vitamin A is necessary for osteoblast and
osteoclast activity.
• Vitamin C is necessary for collagen
synthesis.

15. Hormonal Control of Bone Growth
• Growth Hormone (GH) stimulates cell
division in epiphyseal cartilage.
• Deficiency of GH: pituitary dwarfism.
Excess GH: pituitary gigantism in children
and acromegaly in adults.
• Thyroid hormone stimulates cartilage
replacement in the epiphyseal disks.
• Sex steroids promote formation of bone
tissue close the epiphyseal disk.

16. Physical Factors Affecting Bone
• Physical stress stimulates bone growth.
• Weight bearing exercise stimulates bone
tissue to thicken and strengthen
(hypertrophy).
• Lack of exercise leads to bone wasting
(atrophy) especially noted in the field of
geriatrics.

17. Bone Function
• Bones shape, support, and protect the body
structures.
• They act as levers to create body movement with
muscles.
• They house blood cell producing tissue such as red
bone marrow (textbook pp. 183, 194).
• They store fatty / lipidic nutrients in yellow bone
marrow.
• They store inorganic salts like calcium phosphates
also called hydroxyapatite in their matrix (textbook
pp. 183, 194).

18. Body Movement (Figure 7.14)
For the lower arm to move upward, the biceps contracts.

19. Body Movement
To move downward, the triceps contracts.

20. Fracture Repair (Clin. Appl. 7.1, p. 193)
• Blood escapes from damaged blood vessels
and forms a hematoma.
• Spongy bone forms in regions near blood
vessels and fibrocartilage forms farther away.
• A bony callus replaces the fibrocartilage.
• Osteoclasts remove excess bony tissue and
new bone is restored much like the original
involving osteoblasts.

21. Blood Cell Formation
• In embryonic development, blood cell
formation (hematopoeisis) occurs in yolk
sac outside of the embryo.
• Later, it occurs in the liver and spleen of the
fetus .
• In the adult, red and white blood cell
precursor cells or stem cells are formed in
the red bone marrow.
Note: Erythropoesis is the synthesis of Red Blood Cells.

22. Skeletal Organization (Tab. 7.3):
Axial and Appendicular Skeleton
It consists of bones that support organs of the
head, neck, and trunk.
• Skull: cranium and facial bones.
• Hyoid bone.
• Vertebral column.
• Thoracic cage: ribs and sternum.
Axial Skeleton:

23. Figure 7.17 – red portion of the figure

24. Appendicular Skeleton:
It consists of the bones of limbs and bones
that anchor the limbs to the axial skeleton.
• Pectoral girdle: scapula, clavicle.
• Upper limbs: humerus, radius, ulna, carpals,
metacarpals, phalanges.
• Pelvic girdle: coxal bones.
• Lower limbs: femur, tibia, fibula, patella,
tarsals, metatarsals, phalanges.

25. Figure 7.17 – yellow portion of the figure

26. Cranium – Memorize the eight cranial plates.
• Frontal bone: forehead
• 2 Parietal bones: top of the skull
• Occipital bone: back of the skull
• 2 Temporal bones: side of skull, near ears
• Sphenoid bone:base of the cranium
• Ethmoid bone: roof of the nasal cavity

27. Figure 7.21
Frontal bone

28. Figure 7.21- Note the location of the sphenoid and ethmoid bones.

29. Figure 7.22 – Note the location of the sphenoid bone.

30. Facial Skeleton
* Note: We will not focus on the facial skeleton except to
know the locations of the jaw bones and their names.
• Maxillary bones: upper jaw, hard palate
• Palatine bones: hard palate, nasal cavity
• Zygomatic bones: cheek bones
• Lacrimal bones: orbit of the eye
• Nasal bones: bridge of the nose
• Vomer bone: nasal septum
• Nasal conchae: walls of the nasal cavity
• Mandible: lower jaw

31. Infantile Skull (Fig. 7.33)
• The skull at birth is not fully developed.
• Fibrous membranes, fontanels, connect the
cranial bones.
• They allow movement of the bones to enable the
skull to pass through the birth canal.
• The fontanels close as cranial bones grow.
• The posterior fontanel closes within two
months after birth. All others close within two
years after birth.

32. Figure 7.33

33. Vertebral Column
Note: You are responsible for memorizing the names of the regions of the
vertebral column.
• Cervical vertebrae: seven vertebrae of the
neck, includes atlas and axis
• Thoracic vertebrae: twelve vertebrae that
articulate with the ribs
• Lumbar vertebrae: five vertebrae that make up
the small of the back
• Sacrum: five vertebrae that fuse in early
adulthood, part of the pelvis
• Coccyx: four small fused vertebrae

34. Vertebral Column (Fig. 7.34)

35. Thoracic Cage (Fig. 7.40)
• Ribs: twelve pair of ribs attached to each
thoracic vertebrae.
• Seven pairs: true ribs and attach to the
sternum by costal cartilage.
• Two pairs: false ribs that attach to
cartilage.
• Two pairs: floating ribs that do not attach
to the sternum or its cartilage.
• Sternum: the manubrium, the body, and the
xyphoid process.

36. Pectoral Girdle (Fig. 7.42)
• Clavicles: collar bones that attach the sternum
to the shoulder anteriorly.
• Scapulae: shoulder blades with two processes.
• Acromion process: tip of the shoulder.
• Coracoid process: attaches to the clavicle and
provides attachments for muscles.
• Glenoid fossa: It articulates with the humerus.

37. Fig. 7.42 – Pectoral girdle, thoracic cage and upper limb.

38. Upper limb (Fig. 7.44)
• Humerus: upper arm bone, articulates with
the glenoid fossa of the scapula
• Radius: thumb side of the forearm,
articulates with the capitulum of the
humerus and the radial notch of the ulna
• Ulna: longer bone of the forearm, olecranon
and coronoid processes articulate with the
humerus

39. Hand (Fig. 7.47)
* Note: We will not focus on the eight separate carpals,
but you need to know that they are named carpals.
• Carpal bones: eight small bones of the
wrist, a total of sixteen carpals.
• Metacarpal bones: five bones, the
framework of the palm.
• Phalanges: finger bones, three in each
finger (proximal, middle, distal phalanx),
two in the thumb.

40. Fig. 7.47

41. Pelvic Girdle (Fig. 7.49)
Two Coxal bones or coxae:
two hip bones composed of three fused bones.
• Ilium: superior part of the coxal bone.
• Ischium: lowest portion of the coxal bone.
• Pubis: anterior part of the coxal bone. The two
pubic bones joint at the symphysis pubis.

42. Fig. 7.49 – Anterior view.

43. Fig. 7.49 – Posterior view.

44. Male and Female Pelvis
Differences are due to birthing necessitating a
wider area for carrying the fetus:
• Female iliac bones are more flared.
• The female pubic arch angle is greater.
• There is a greater distance between the
ischial spines and tuberosities in the female.
• The sacral curvature is shorter and flatter.
• The differences create a wider pelvic cavity.

45. Fig. 7.51

46. Lower Limb (Figure 7.52)
• Femur: thigh bone, longest bone
• Patella: kneecap, located in a tendon,
femur, tibia, and patella form the knee joint
• Tibia: shinbone, lateral malleolus forms the
ankle
• Fibula: slender bone lateral to the tibia, not
part of the knee joint

47. Fig. 7.52

48. Foot (Fig. 7.55)
• Tarsal bones: seven small bones in the
ankle. The calcaneus (heel bone) is the
largest, located below the talus, a total of
fourteen bones.
• Metatarsal bones: elongated bones that
form the arch of the foot.
• Phalanges: each toe has three except the
great tow which has two.

49. Fig. 7.55

50. Life-Span Changes
• Calcium levels fall throughout life and the skeleton loses strength.
• Osteoclasts eventually outnumber osteoblasts.

51. Life-Span Changes
• By age 35,
everyone
loses bone
mass.
• Trabecular
bone is lost
before
compact
bone.