Chapter 6:

Bones & Skeletal Tissue

I. Skeletal Cartilage

A. Basic Structure, Types and Location 1. Skeletal cartilages are made from cartilage, surrounded by a layer

of dense irregular connective tissue called perichondrium

2. Hyaline cartilage is most abundant and includes: articular, costal, respiratory and nasal cartilage

3. Elastic Cartilages are most flexible and are located in the external ear and the epiglottis of the larnyx

4. Fibrocartilage is located in the areas where large amounts of pressure are exerted or stretch occurs ( knees and intervertbral discs)

B. Growth of Cartilage

1. Appositional growth results in outward expansion

due to the production of cartilage matrix on the

outer face of the tissue

2. Interstitial growth is the results in the expansion

from within the cartilage matrix due to the division

of the lacunae bound chondrocytes

II. Classification of Bone A. Divisions of the skeleton

1. Axial: Includes the rib cage and vertebral column,

2. Appendicular: Includes the bones of the upper limb, lower limb and the girdles that attach them to the axial skeleton

B. Shape 1. Long bones are longer than they are wide, have a definite shaft two

ends and consist of all the limb bones except the patella, carpals and tarsals

2. Short bones are somewhat cube shaped and include the the carpals, tarsals and patellas

3. Flat bones are thin, flattened, and often curve that include skull bones, sternum, scapulae and ribs

4. Irregular bones have complicated shapes the do not fit into any other class such as the vertebrae and coxae

III. Function of Bones A. Support

B. Protection for the soft organs

C. Movements

D. Nutrient storage

E. Produce hormones

IV: Bone Structure A. Gross Anatomy

1. Bones have projections, depressions and openings on the surface that function as sites for muscle, ligament and tendon attachment, serves as joint surfaces and opening for the passage of blood vessels

2. Bone Textures a. Spongy bone: Internal structure of the bone, looks like honeycomb, needle like

or flat pieces called trabeculae b. The bones dense out layer the is classified as compact and appears solid and

smooth c. Compact bone: Internal structure of the bone, looks like honeycomb, needle like

or flat pieces called trabeculae d. The bones dense outer layer the is classified as compact and appears solid and

smooth

3. Structure of short, irregular and flat bones a. Compact bone on outside and spongy bone on the inside, houses bone marrow

4. Structure of Typical Long Bone

a. Have a tubular diaphysis (shaft), consisting of a bone collar

surrounding a hollow medullary cavity with is filled with yellow

marrow in adults

b. Epiphysises are the ends of the bone and consist of internal spongy

bone covered by an outer layer of compact bone and articular

cartilage

c. Epiphyseal line is locacted between the epiphysises and diaphysis

which is a remnant of the epiphyseal plate, the hyaline cartilage that

provides lengthwise growth of the bone

d. The periosteum covers the bone and is the location of the osteogenic

cells (external surface)

e. The internal surface of the bone is lined with connective tissue called

endosteumand is the location of osteogenic cells in the bone.

5. Location of Hematopoietic Tissue in Bones

a. Red marrow is located in the trabecular cavities of the

spongy bone in long bones and in the diploe of flat bones

1. Red marrow is found only in inmature bone

2. Yellow marrow in found in MATURE bone

b. In long bones, red marrow is found in all medullary cavities

and all areas of spongy bone in infants, distribution is

restricted to the proximal epiphyses of the humerus and

femur in adults

B. Microscopic Anatomy 1. Bone tissue contains 5 types of cells: bone stem cells (osteogenic),

osteoblasts (secrete bone matrix), osteocytes & bone lining cells

(monitor and maintain bone matrix) and osteoclasts (bone

resorption)

2. Compact unit of bone structure is the osteon (Haversian System), a

series of concentric tubes or bone matrix (lamellae) surrounding

central Haversian canal and serves as a passageway for blood vessels

and nerves

a. Perforating (Volkman’s) canal lie at right angles to the long axis of the bone and

connect the blood and nerve supply of periosteum to the centeral canal and

medullary cavitiy

b. Lacunae, small holes housing the osteocytes, are junctions of the lamellae and are

connected to each other and the central canal via a series of hair like channels

called canaliculi.

3. Spongy bone lacks osteons but has trabeculae that align along lines

of stress, which contain irregular lamellae and osteocytes connected

with the canaliculi

C. Chemical Composition

1. Organic components of the bone include cells and osteoid (ground

substance and collagen fibers), which contribute to the flexibility

and tensile strength of the bone

2. Inorganic components make up 65% of the bone by mass and

consist of hydroxyapatites, mineral salts (largely calcium

phosphates), that account for the hardness and compression

resistance of bones

V. Bone Development A. Formation of Bony Skeleton (embryonic development)

1. In endochrondral ossification, bone tissue replaces hyaline cartilage, forming all bones below the skull except for the clavicles

a. Initially, osteoblasts secrete osteoid, creating a bone collar around the diaphysis of the hyaling cartilage model

b. Cartilage in the center of the diaphysis calcifies and deteriorates forming cavities

c. The periosteal bud invades the internal cavities and spongy pne forms around the remaining fragments of hyaline cartilage

d. The diaphysis elongates as the cartilage in the epiphysis continues to lengthen and a medullary cavity forms through the action of osteoclasts within the center of the diaphysis

e. The epiphyses ossify shortly after birth through the development of secondary ossification centers

1. Itramembranous ossification forms membrane bone from fibrous connective tissue membranes and result in the cranial bones and clavical

B. Postnatal Bone Growth 1. Growth in length of long bones occurs at the ossification zone

through the rapid division of the upper cells in the columns of chondrocytes, calcification and deterioration of cartilage at the bottom of the columns and subsequent replacement of bone tissue

2. Growth is width or thickness occurs through appositional growth due to deposition of bone matrix by osteoblasts beneath the periosteum

3. Hormonal Regulation of bone growth

a. During infancy and childhood, the most important stimulus of epiphyseal plate activity is the growth hormone from the anterior pituitary gland whose effects are modulated by thyroid hormone

b. At puberty, testosterone and estrogen promote a growth spurt, ultimately resulting in the closure of the epiphyseal plate

VI. Bone Homeostasis: Remodeling &

Repair A. Bone Remodeling 1. In adult skeletons, done deposit and resorption occur beneath

the periosteum and endosteum

2. Is balanced bone deposit and resorption

3. Control of Remodeling

a. Hormonal control is mostly used to maintain blood calcium homeostasis and balances activity of parathyroid hormone and calcitonin

b. In response to mechanical stress and gravity, bone grows or remodels in what that allow it to withstand the stresses it experiences

B. Bone Repair

1. Fractures or breaks in bones are classified by:

a. The position of the bones ends after the fracture

b. Completeness of the break

c. Whether the bone penetrates the skin

2. The repair of fractures involves 4 stages

a. Formation of Hematoma

b. Fibrocartilagous callus formation (about a week after

damage)

c. Bony callus formation

d. Remodeling of the bony callus (takes months)

VII: Homeostatic Imbalance

A. Osteomalacia and Rickets

1. Osteomalacia is a disorder in adults in

which the bone is inadequately mineralized

resulting in soft bones

2. Rickets is the inadequate mineralization of

bones in children caused by insufficient

calcium in the diet or by Vitamin D deficiency

B. Osteoporosis

1. A group of disorders in adults by which the rate of bone resorption exceeds rate of formation (decays faster than replaced)

2. Bones have normal matrix but the mass is reduced and bones become more porous and lighter (fracture easier)

3. Elderly women are more vulnerable due to the decline of estrogen hormone caused by menopause

4. Contributing factors are: Petite stature, lack of exercise, poor calcium and Vitamin D diet, and smoking

C. Paget’s Disease

1. Excessive bone deposition and resorption

2. Results in abnormally high amounts of spongy bone

3. Localized condition (varies in location), deformation

of affected bone is common

VIII. Developmental Aspects of Bone

A. Bones begin with the embryonic mesenchyme cells, ossification occurs at precise times. Most long bones have primary ossification centers 12 weeks after conception

B. At birth most bones are well ossified except for the epiphyses which are secondary ossifications points

C. Throughout childhood bone growth exceeds resorption (bone gain), young adult equal process, old age resorption exceeds formation (bone loss)