Chapter 7

Skeletal System

PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 10th edition, edited by S.C. Wache for Biol2064.01

Falsely colored radiograph of the human skull.

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 shapeFig. 7.2 - Typical long bone: has compact and spongy boneFig. 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. 7.6Fig. 7.8 - Endochondral Ossification from hyaline cartilage.Fig. 7.9 - Epiphyseal plate Tab. 7.2 - Ossification Timetable.

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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 humerusFig. 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.

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)

Long Bone Structure (Figure 7.2)

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.

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.

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.

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).

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.

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.

Bone Growth and Development

Bone Growth (Fig. 7.9; Fig. 7.11):

Growth of long bones occurs along four layers ofcartilage 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.

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.

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.

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.

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.

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).

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

Body MovementTo move downward, the triceps contracts.

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.

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.

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:

Figure 7.17 – red portion of the figure

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.

Figure 7.17 – yellow portion of the figure

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

Figure 7.21

Frontal bone

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

Figure 7.22 – Note the location of the sphenoid bone.

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

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.

Figure 7.33

Vertebral ColumnNote: 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

Vertebral Column (Fig. 7.34)

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.

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.

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

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

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.

Fig. 7.47

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.

Fig. 7.49 – Anterior view.

Fig. 7.49 – Posterior view.

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.

Fig. 7.51

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

Fig. 7.52

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.

Fig. 7.55

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

Life-Span Changes

• By age 35, everyone loses bone mass.

• Trabecular bone is lost before compact bone.