CHAPTER 6: Histology and Physiology of Bones

CARTILAGE: What I have learned?

Cartilage is a flexible connective tissue that is present in our body. It  has a lot of benefits, such as,  it provides  support, provides  a framework in which deposits of bones and can be equipped with smooth surfaces available to monitor the movement of articulation of the bones. There are three different types of cartilage:

Hyaline Cartilage, also called gristle. It is shiny, slippery, firm, translucent, and bluish-gray in color. It is simple in structure, with no nerves or blood vessels. It has high elasticity and helps cushion and protect bones. The word hyaline comes from the Greek for glassy, and refers to the translucence of the tissue. 

Fibrocartilage, A tough cartilage with a matrix consisting of dense bundles of fibers. Intervertebral discs and menisci are made of fibrocartilage, which has great tensile strength and is able to absorb considerable loads.

Elastic cartilage has a preponderance of dark-staining elastic fibers embedded in ground substance.  These fibers are clearly visible and this trait is the single, best identifier to be used for differentiating elastic cartilage from hyaline.  Perichondreum is also typically found around elastic cartilage.  Elastic cartilage is found in the pharyngotympanic(eusatachian) tubes, epiglottis, and ear lobes where needs dictate supportive tissues possess elasticity.artilage

BONES: What does it mean to me????? 

In this Chapter, I also learned the components of the skeletal system. 

BONE is the basic unit of the human skeletal system and provides the framework for and bears the weight Of the body, protects the vital organs, supports mechanical movement, and maintains iron homeostasis.

Classification of Bone

Bones can be classified based on their position, shape, size, and structure.

Based on location, bones can be classified as follows:

• Axial skeleton – Bones of the skull, vertebral column, sternum, and ribs

• Appendicular skeleton – Bones of the pectoral girdle, pelvis girdle, and limbs

o Acral skeleton – Part of the appendicular skeleton, including bones of the hands and feet

Based on shape, bones can be classified as follows:

• Flat bone – Bones of the skull, sternum, pelvis, and ribs

• Tubular bone –

o Long tubular bone, including bones of the limbs

o Short tubular bone, including bones of the hands and feet, such as the phalanges, metacarpals, and metatarsals

• Irregular bone – Bones of the face and vertebral column

• Sesamoid bone – Bones that develop in specific tendons, the largest example of which is the patella

• Accessory bone or supernumerary bone - Extra bones that develop in additional ossification centers or bones that failed to fuse with the main parts during development(Accessory bones are common in the foot and may be mistaken for bone chips or fractures.)

Based on size, bones can be classified as follows:

• Long bone – Tubular in shape, with a hollow shaft and 2 ends, including bones of the limbs

• Short bone – Cuboidal in shape, located only in the foot (tarsal bones) and wrist (carpal bones)

Gross Structures of Bone was also discussed here.

The gross structure of a long bone can be divided into several regions.

Epiphysis

In the long bones, the epiphysis is the region between the growth plate or growth plate scar and the expanded end of bone, covered by articular cartilage. An epiphysis in a skeletally mature person consists of abundant trabecular bone and a thin shell of cortical bone (see the image below). Although an epiphysis is present at each end of the long limb bones, it is found at only one end of the metacarpals (proximal first and distal second through the fifth metacarpals), metatarsals (proximal first and distal second through fifth metatarsals), phalanges (proximal ends), clavicles, and ribs.

Cortical bone is composed of haversian systems (osteons). Each osteon has a central haversian canal and peripheral concentric layers of lamellae.

The epiphysis is the location of secondary ossification centers during development. The structure of the epiphysis is more complex in bones that are fused from more than one part during development. Examples include the proximal and distal ends of the humerus, femur, and vertebrae. For instance, the proximal end of the humerus is developed from 3 separate ossification centers, which later coalesce to form a single epiphyseal mass. In the proximal humeral epiphysis, one of the centers forms the articular surface, and the other 2 become the greater and lesser tuberosities. Carpal bones, tarsal bones, and the patella are also called epiphysioid bones and are developmentally equivalent to the epiphyses of the long bones.

Knowledge of the location of the epiphysis and its equivalents in various bones aids clinicians in the recognition of the origin of bone lesions and further facilitates the diagnostic considerations, as some bone tumors such as chondroblastoma have a strong predilection for the epiphysis or epiphysioid bones.

Metaphysis

The metaphysis is the junctional region between the growth plate (see the image below) and the diaphysis. The metaphysis contains abundant trabecular bone, but the cortical bone thins here relative to the diaphysis. This region is a common site for many primary bone tumors and similar lesions. The relative predilection of osteosarcoma for the metaphyseal region of long bones in children has been attributed to the rapid bone turnover due to extensive bone remodeling during growth spurts (see Growth, Modeling, and Remodeling of Bone, below).

 Growth plate.

Osteosarcoma is a malignant primary bone tumor that is characterized by neoplastic osteoblasts that produce osteoid. Because of increased osteoblastic activity, the serum level of alkaline phosphatase is often significantly increased in this disease; however, acid phosphatase is synthesized by osteoclasts and will not be significantly increased in this disease, although scattered osteoclasts can also be present. The Codman triangle is a pattern of periosteal reaction that is often associated with osteosarcoma, although this pattern may also be seen with other aggressive processes, including osteomyelitis.

Diaphysis

The diaphysis is the shaft of long bones and is located in the region between metaphyses, composed mainly of compact cortical bone. The medullary canal contains marrow and a small amount of trabecular bone.

Physis (epiphyseal plate, growth plate)

The physis is the region that separates the epiphysis from the metaphysis. It is the zone of endochondral ossification in an actively growing bone or the epiphyseal scar in a fully grown bone.

WHAT ARE THE CELLS FOUND IN OUR BONE???

The cells found in the bone are the OSTEOBLAST, OSTEOCYTES and OSTEOCLAST.

osteblast- Osteoblasts are also responsible for mineralization of this matrix. Zinc, copper and sodium are some of the minerals required in this process. Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, in charge of production of matrix and mineral, and osteoclasts, which remodel the tissue. Osteoblast cells tend to decrease with age, affecting the balance of formation and resorption in the bone tissue. 

OSTEOCYTES-it is the most abundant cell found in compact bone.  It is responsible for the breakdown of bones.

   

OSTEOCLAST- is a type of bone cell that removes bone tissue by removing its mineralized matrix and breaking up the organic bone (organic dry weight is 90% collagen).

WHAT IS CANCELLOUS AND COMPACT BONE?

Cancellous bone- is the meshwork of spongy tissue (trabeculae) of mature adult bone typically found at the core of vertebral bones in the spine and the ends of the long bones (such as the femur or thigh bone).

Compact Bone- is what is found on the outside of bones. It is the hard outer layer that gives bones their smooth white appearance.

 

WHAT IS THE CENTER OF OSSIFICATION

the center of ossification is the site where bone begins to form in a specific bone or part of bone as a result of the accumulation of osteoblasts in the connective tissue. It is where bone begins to form in the shaft of a long bone or the body of an irregular bone; primary ossification center. Bone formation continues after beginning in the long shaft or body of the bone, usually in an epiphysis; secondary ossification center.

What is FONTANELS???

It is one of the membrane-covered spaces remaining at the junction of the sutures in the incompletely ossified skull of the fetus or infant. Actually there are two soft spots close together, representing gaps in the bone structure which will be filled in by bone during the normal process of growth. The anterior fontanelle is diamond shaped and lies at the junction of the frontal and parietal bones. This fontanelle usually fills in and closes between the eighth and fifteenth months of life. The posterior fontanelle lies at the junction of the occipital and parietal bones, is triangular in shape, and usually closes by the third or fourth month of life. Though these “soft spots” may appear very vulnerable, they may be touched gently without harm. Care should be exercised that they be protected from strong pressure or direct injury.

BONE GROWTH: unlike cartilage, bones cannot grow by interstitial growth. Bones increase in size only by APPOSITIONAL GROWTH, the formation of new bone on the surface of older bone or cartilage.

watch this:

BONE REPAIR

bone is a living tissue that can undergo repair following damage to it.

THE IMPORTANCE OF CALCIUM IN OUR BONES

Calcium as most of us know is an important part of our bones. Calcium gives our bones the necessary strength to carry our body weight. Calcium is also required for functioning of all the muscles and the most important muscle being the heart of course. Without calcium, muscles would not contract normally, blood would not clot and nerves would be unable to carry messages. Calcium and bone health go hand-in-hand. Increasing scientific evidence indicates that adequate calcium intake reduces the risk of several major chronic diseases, most notably osteoporosis, a potentially crippling disease of thin and fragile bones. Calcium also helps protect against colon cancer, high blood pressure and recurring premenstrual syndrome, and possibly cardiovascular disease and kidney stones (well most think it causes stones)