chapter 6 Bone tissue

How do hormones act on bone to regulate calcium homeostasis?

PTH secreted by the PT glands increases blood Ca+. Calcitonin from the thyroid has potential to decrease Ca+. Vit. D enhances absorption of CA+ and phosphate and raise blood levels of these substances.

Describe the role of bones in blood cell production

Red marrow produces RBCs, WBCs, and platelets. (hemopoises). Red Marrow consists of developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers.

Define remodeling, and describe the roles of osteoblasts and osteoclasts in the process.

The ongoing replacement of old bone tissue by new bone tissue. See Osteoblast, osteoclast

epiphyseal arteries

enters the epiphyses of a long bone and supplies red marrow and bone tissue of the epiphysis.

Which bones of the body develop by intramembranous ossification?

flat bones of the skull, most facial bones, mandible, and medial part of the clavicle.

Zone of resting cartilage

layer of small, scattered chondrocytes near the epiphysis. Anchor E.P. to epiphysis but does not function in bone growth

zone of proliferating cartilage

Chondrocytes arranged like stacks of coins that divide and secrete ECM to replace dead chondrocytes at the diaphyseal side of the E.P.

What factors contribute to the hardness and tensile strength of bone?

Hardness depends on crystallized inorganic mineral salts.Collagen fibers and organic molecules provide tensile strength.

How does the skeletal system function in movement ?

Most skeletal muscles attach to bones. Muscles contract and pull on bones to produce movement.

Explain why bone tissue is classified as a connective tissue

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How are intramembranous ossification and endochondral ossification different?

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How could the metaphyseal area of a bone help determine the age of a skeleton?

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See fig. 6.1

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Describe the cellular composition of bone tissue and the functions of each type of cell

...Bone tissue consists of widely separated cells surrounded by large amounts of extracellular matrix. The ECM of bone contains abundant mineral salts and collagen fibers, while the four principal types of cells are osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

What is the composition of extracellular matrix of bone tissue?

15% Water, 30% collagen fibers, and 55% crystalized mineral salts. Most abundant mineral salt is calcium phosphate, which comines with calcium hydroxide to form crystals of hydroxyapatite.

What is a bone scan, and how is it used clinically?

A diagnostic in which radioactive material is injected, and reuptake is monitored to determine the blood flow to various parts of the bone. It's the standard test for bone density screening, particularly for osteoporosis in females.

Why does it sometimes take months for a fracture to heal?

Ca2+ and phosphorus deposition is a slow process, and bone cells generally grow and reproduce slowly.

Compare the structural differences between compact and spongy bone tissue

Compact bone contains osteons with little space between them, and spongy bone does not contain osteons, but rather trabeculae surrounding many red bone marrow filled spaces.

How are compact and spongy bones different in microscopic apprearance, location, and function?

Compact bone is organized in concentric lamellae around a central haversian canal with little space between them. Spongy bone contains irregularly arranged lamellae in the trabeculae, which surround red bone marrow filled spaces.

Compare the functional differences between compact and spongy bone tissue

Compact bone tissue is the strongest form of bone and protects, supports and resists stress. Spongy bone tissue trabeculae offer resistance along lines of stress, support and protect red bone marrow, and make bones lighter for easier movement.

What changes occur in the organic part of bone extracellular matrix with aging?

Decreased production of ECM proteins which make bones more brittle and thus more susceptible to fracture.

Which bones contain red bone marrow?

Developing bones of the fetus in addition to the adult pelvic bones, ribs, sternum, vertbrae and femur.

Describe the structure and function of each part of a long bone

Diaphysis (shaft), proximal and distal epiphyses (connect at joints), metaphyses (between D and E, contains epiphyseal plate), articular cartilage (hyaline cartlige that reduces friction and absorbs shock at joints), periosteum, medullary cavity (contains yellow bone marrow and minimizes bone weight), and endosteum.

Describe the zones of the epiphyseal plate and their functions, and the significance of the epiphyseal line.

E.P. is a layer of hyaline cartligein the metaphysis of a growing bone that consists of four zones. Diaphysis increases in length due to cell division in E.P. When E.P. fades, it leaves behind a bony structure called the E. line.

What is the functional significance of the periosteum?

Essential for growth in bone thickness, bone repair, and bone nutrition. Also serves as point of attachment for ligaments and tendons.

outline the four steps involved in fracture repair.

Formation of a fracture hematoma, Fibrocartilaginous callus formation, Bony Callus formation and bone remodeling.

What body functions depend on proper levels of Ca2+

Heartbeat, respiration, nerve cell functioning, enzyme functioning and blood clotting.

Osteoclasts

Huge cells derrived from fusion of 50 monocytes. Concentrated in endosteum. Releases enzymes that digest protein and minderal components of underlying ECM.

Explain calcification

Hydroxyapatite combines w/ other mineral salts , which are deposited into the collagen fiber framework of the ECM where they crystallize and harden.

Explain how bone growth in length differs from bone growth in thickness.

In length, E. Plate cartlige is replaced by bone on diaphyseal side, which lengthens diapysis. Addition of new bone tissue by periosteal osteoblasts (appositional growth) causes growth in thickness.

How does the epiphiyseal plate account for the lengthwise growth of the diaphysis?

LW growth of diaphysis is caused by cell divisions in the zone of proliferating cartilage and replacement of the zone of calcified cartilage with bone. (new diaphysis)

Osteocytes.

Main cells in bone tissue. Maintians daily metabolism and exchange of nutrients and wastes with blood. Does not undergo cell division.

What factors affect bone growth and bone remodeling

Minerals, Vitamins and hormones.

How is a bone marrow needle biopsy performed? What conditions are diagnosed through this procedure?

Needle is inserted into bone to withdraw a sample of red marrow to examine for laukemias, metastatic neoplasms, lymphoma, hodgkin's disease, and aplastic anemia. Pain is felt as needle passes through periosteum, but little pain after that.

Would children raised in space ever be able to return to earth?

No. Removal of mechanical stress weakens bone through demineralization and collagen fiber reduction.

List the types of fractures

Open (compound), Comminuted, Greenstick, Impacted, Pott, and Colles.

How does the skeletal system function in support ?

S: provides structural framework for body by supporting soft tissues and providing attachement points for the tendons of most skeletal muscles.

Periosteal arteries

Small arteries accompanied by nerves that enterdiaphysis through volkmann's canals and supply the periosteum and outer part of compact bone.

Why is it important to engage in weight bearing exercises before the epiphyseal plates close?

To help build total mass before the mass reduction that accompanies aging.

How do red bone marrow and yellow bone marrow differ in composition and function?

Yellow bone marrow consists mainly of adipose cells, which store tryglicerides as a potential energy reserve, whereas red marrow consists of developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers which produce RBCs, WBCs and platelets (hemopoises).

How does the skeletal system function in storage of materials?

Yellow bone marrow consists of adipose cells, which store triglicerides, which are a potential chemical energy reserve.

Osteoblasts

bone building cells that synthesize and secrete collagen fibers, and initiate calcification.They surround themselves with ECM and become trapped in their secretions and become osteocytes.

What are the major events of endochondral ossification?

bone foms with hyaline cartilage that develops from mesenchyme.

zone of hypertrophic cartilage

large, maturing chondrocytes arranged in columns.

As people age, some central canals may become blocked. What effect would this have on the surrounding osteocytes?

haversian canals are main blood supply to osteocytes of an osteon (haversian system) so their blockage would lead to death of the osteocytes.

Nutrient foramina

large hole in compact bone near the center of the dyaphysis.

What are the major events of intramembranous ossification?

bone forms directly within mesenchyme, which is arranged in sheetlike layers that resemble membranes.

How does the medullary cavity enlarge during growth in thisckness?

by activity of osteoclasts in the endosteum.

How do mechanical stresses strengthen bone tissue?

by increasing deposition of mineral salts and production of collagen fibers.

zone of calcified cartilage

mostly dead chondrocytes, only a few cells thick. ECM around them has calcified. Becomes ossified and then becomes new diaphysis.

Why is bone resorption important?

necessary for development, maintenance and repair of bone.

If you wanted to develop a drug to lessen the effects of osteoporosis, would you look for a chemical that inhibits the activity of osteoblasts or that of osteoclasts?

osteoclasts, since they are responsible for bone resorption.

nutrient arteries

pass through nutrient foramen and divides into branches which supply inner compact bone of diaphysys, spongy bone, and red marrow as far as the epiphyseal plates.

Where do periosteal arteries enter bone tissue?

perforating (Volkmann's) canals.

Which part of a bone contains sensory nerves associated with pain?

periosteum

How does the skeletal system function in protection ?

protects most important internal oragns from injury. Ex: cranial bones protect brain, bertebrae protect spinal cord, and rib cage protects heart and lungs.

Where in the cartilage model do secondary ossification centers develop during endochondral ossification?

regions of the cartilage model that will give rise to the epiphyses.

blast=

secretes ECM

Describe the 6 main functions of the skeletal system

support, protection, movement, mineral homoestasis, blood cell production and triglyceride storage.

List the four types of cells in bone tissue and explain their functions

the four principal types of cells are osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

What is demineralization, and how does it affect the functioning of bone?

the loss of calcium and other minerals from ECM due to reduced osteoblast activity. This leads to loss of bone mass.

Describe one situation in which these sensory neurons are important

they are especially sensitive to tearing or tension, which explains the severe pain resulting from a fracture or a bone tumor.

osteogonic cells

unspecialized stem cells derived from mesenchyme. Only bone cells to undergo cell division and then develop into osteoblasts. Found along inner portion of periosteum, in endosteumand in canalswithin bone that contain blood vessles.