Chapter 6 The Skeletal System: Bone Tissue

what is a fracture hematoma?

blood vessels crossing the fracture line are broken. as blood leaks from the torn ends of the vessels, a mass of blood forms around the side of the fracture. swelling and inflammation occur in response to dead bone cells.

what does trabeculae consist of?

concentric lamellae, osteocytes that lie in lacunae, and canaliculi that radiate outward from lacunae.

what is intramembranous ossification?

process of bone formation where bone forms directly within mesenchyme, which is arrange in sheetlike layers that resemble membranes.

closed (simple) fracture?

does not break through the skin

what are spongy bone tissue?

does not contain osteons. always located in the interior of a bone and protected by covering of compact bone. It consists of lamellae that are arranged in an irregular pattern of thin columns called trabeculae. {it possesses bone trabeculae containing osteocytes in lacunae}

what is the bone extracellular matrix made of?

15% water, 30% collagen fibers, and 55% crystallized mineral salts. The most abundant mineral salt is calcium phosphate [Ca3(PO4)2]. It combines with calcium hydroxide [Ca(OH)2] to form crystals of hydroxyapatite [Ca10(PO4)6(OH)2]. As the crystals form, they combine with still other mineral salts such as calcium carbonate, and ions such as magnesium, fluoride, potassium, and sulfate. As these mineral salts are deposited in the framework formed by the collagen fibers of the extracellular matrix, they crystallize and the tissue hardens. This process, called calcification is initiated by bone-building cells called osteoblasts. {Collagen promotes bone mineralization}

what are perforating canals/Volkmann's canal?

Blood vessels, lymphatic vessels, and nerves from the periosteum penetrate the compact bone through transverse perforating canals/Volmann's canal. The vessels and nerves of these canals connect with those of the medullary cavity, periosteum, and central/haversian canals.

What are the six main functions of the skeletal system?

Bone tissue makes up about 18% of the weight of the human body. Six main functions are support, protection, assistance in movement, mineral homeostasis (storage and release), blood cell production, and triglyceride storage.

how does the skeletal system perform mineral homeostasis (storage and release)?

Bone tissue stores several mineral, especially calcium and phosphorus, which contribute to the strength of bone. Bone tissue stores about 99% of the body's calcium. On demand, bone releases mineral into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body.

what is the first step in intramembranous ossification?

Development of the ossification center. At the site where the bone will develop, specific chemical messages cause the mesenchymal cells to cluster and then into osteoblasts. The site of such a cluster is ossification center. osteoblasts secrete the organic extracellular matrix of bone until they are surrounded by it.

How many types of cells are in bone tissue and name them?

Four types of cells are in bone tissue: osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

what is compact bone tissue?

It contains few spaces and is the strongest form of bone tissue. It is found beneath the periosteum of all bones and makes up the bulk of the diaphysis of long bones. {makes up the shaft of long bone}. it provides protection and support and resists the stresses produced by weight and movement.

What is a long bone?

It is a bone with greater length than width. It has 7 parts: diaphysis, epiphyses, metaphyses, articular cartilage, periosteum, medullary cavity or marrow cavity, and endosteum.

How does the skeletal system give support?

The skeleton serves as the structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles.

how does the skeletal system store triglyceride?

Yellow bone marrow consists mainly of adipose cells, which store triglycerides. the stored triglycerides are a potential chemical energy reserve.

what is endochondral ossification?

bone forms within hyaline cartilage that develops from mesenchyme. The replacement of cartilage by bone.

what is nutrient foramen?

hole in compact bone for which nutrient artery passes through.

what are the two methods of bone formation?

intramembranous ossification and endochondral ossification

whats calcitonin?

a hormone that works to decrease blood calcium level. {it is produced in parafollicular cells in the thyroid. it inhibits osteoclast bone resorption and promotes calcium deposition in bone and bone formation}

greenstick fracture?

a partial fracture in which one side of the bone is broken and other side bends; similar to the way a green twig breaks on one side while the other side stays whole, but bends. occurs only in children.

what are metaphyseal arteries?

arteries that enter the metaphyses of long bone and together with the nutrient artery supply the red bone marrow and bone tissue of the metaphyses. (same for veins and nerves that accompany these arteries)

what are epiphyseal arteries?

arteries that enter the epiphyses of long bone supply the red bone marrow and bone tissue of the epiphyses. (same for veins and nerves that accompany these arteries)

whats fifth step in endochondral ossification?

development of the secondary ossification centers. when branches of the epiphyseal artery enter the epiphyses, secondary ossification centers develop, usually around the time of birth. Bone formation is similar to what occurs in primary ossification centers. however, in secondary ossification centers spongy bone remains in the interior of the epiphyses (no medullary cavities are formed here). in contrast to primary oss., secondary oss. proceeds outward from the center of the epiphysis toward the outer surface of the bone.

what are haversian/central canals?

each osteon consists of concentric lamellae arranged around a central/haversian canal.

what are the three factors affecting bone growth and development?

minerals, vitamins and hormones

how does the skeletal system give assistance in movement?

most skeletal muscles attach to bones; when they contract, they pull on bones to produce movement.

what does nutrient artery do?

on entering the medullary cavity, it divides into proximal and distal branches that course toward each end of the bone. these branches supply both the inner part of compact bone tissue of the diaphysis and the spongy bone tissue and red bone marrow as far as the epiphyseal plates or lines.

impacted fracture?

one end of the fractured bone is forcefully driven into the interior of the other.

the spaces between the trabeculae inside the spongy bone are filled with what?

red bone marrow and yellow bone marrow.

what are periosteal arteries?

small arteries accompanied by nerves which enter the diaphysis through many perforating/Volkmann canals and supply the periosteum and outer part of the compact bone

what are lacunae?

they are small spaces between the concentric lamellae that contains osteocytes.

what is the epiphyses?

they are the proximal and distal ends of the bone.

How does the skeletal system give protection?

It protects the most important internal organs from injury. Example cranial bones protect the brain, vertebrae protect the spinal cord, and rib cage protects the heart and lungs.

what is the second step in intramembranous ossification?

calcification. the secretion of extracellular matrix stops, and the cells, now called osteocytes, lie in lacunae and extend their narrow cytoplasmic processes into canaliculi that radiate in all directions. within a few days, calcium and other mineral salts are deposited and the extracellular matrix hardens or calcifies.

what is the first step in endochondral ossification?

development of the cartilage model. at the site where the bone is going to form, specific chemical messages cause the mesenchyme cells to crowd together in the general shape of the future bone, and then develop into chondroblasts. the chondroblasts secrete cartilage extracellular matrix, producing a cartilage model consisting of hyaline cartilage. a covering called the perichondrium develops around the cartilage model.

whats fourth step in endochondral ossification?

development of the medullary (marrow) cavity. as the primary ossification center grows toward the ends of the bone, osteoclasts break down some of the newly formed spongy bone trabeculae. this activity leaves a cavity, the medullary (marrow) cavity, in the diaphysis. Eventually most of the wall of the diaphysis is replaced by compact bone.

what is the fourth step in intramembranous ossification?

development of the periosteum. in conjunction with the formation of trabeculae, the mesenchyme condenses at the periphery of the bone and develops into the periosteum. eventually a thin layer of compact bone replaces the surface layers of spongy bone, but spongy bone remains in the center. much of the newly formed bone is remodels (destroyed and reformed) as the bone is transforms into its adult size and shape.

whats third step in endochondral ossification?

development of the primary ossification center. primary ossification proceeds inward from the external surface of the bone. A nutrient artery penetrates the perichondrium and the calcifying cartilage model through a nutrient foramen in the midregion of the cartilage model, stimulating osteogenic cells in the perichondrium to differentiate into osteoblasts. once the perichondrium starts to form bone, it is known as the periosteum. near the middle of the model, periosteal capillaries grow into the disintegrating calcified cartilage, inducing growth of a primary ossification center, a region where bone tissue will replace most of the cartilage. Osteoblasts then begin to deposit bone extracellular matrix over the remnants of calcified cartilage, forming spongy bone trabeculae. Primary ossification spreads from this central location toward both ends of the cartilage model.

sixth step in endochondral oss?

formation of articular cartilage and the epiphyseal (growth) plate. the hyaline cartilage that covers the epiphyses becomes the articular cartilage. prior to adulthood, hyaline cartilage remains between the diaphysis and epiphysis and the epiphyseal plate, the region responsible for the lengthwise growth of long bones.

what is the third step in intramembranous ossification?

formation of trabeculae. as the bone extracellular matrix forms, it develops into trabeculae that fuse with one another to form spongy bone around the network of blood vessels in the tissue. connective tissue that is associated with the blood vessels in the trabeculae differentiates into red bone marrow.

colles fracture?

fracture of the distal end of the lateral forearm bone (radius) in which the distal fragment is displaced posteriorly.

pott fracture?

fracture of the distal end of the lateral leg bone (fibula), with serious injury of the distal tibial articulation.

what is the second step in endochondral ossification?

growth of the cartilage model. once chondroblasts become deeply buried in the cartilage extracellular matrix, they are called chondrocytes. the cartilage model grows in length by continual cell division of chondrocytes, accompanied by further secretion of the cartilage extracellular matrix. this type of cartilaginous growth, called interstitial (endogenous) growth, results in an increase in length. in contrast, growth of the cartilage in thickness is due mainly to the deposition of the extracellular matrix material on the cartilage surface of the model by new chondroblasts that develop from the perichondrium. this process is called appositional (exogenous) growth, meaning growth at the outer surface. as the cartilage model continues to grow, chondrocytes in its mid-region hypertrophy (increase in size) and the surrounding cartilage extracellular matrix begins to calcify. other chondrocytes within the calcifying cartilage die because nutrients can no longer diffuse quickly enough through the extracellular matrix. as these chondrocytes die, the spaces left behind by dead chondrocytes merge into small cavities called lacunae.

how does bone regulate calcium blood level?

help "buffer" the blood calcium level by releasing calcium into blood plasma using osteoclasts when level decreases and absorbing calcium using osteoblasts when the level rises. calcium exchange is regulated by hormones which most important is parathyroid hormone (PTH) secreted by parathyroid glands.

whats bony callus?

in areas closer to well vascularized healthy bone tissue, osteogenic cells develop into osteoblasts, which begin to produce spongy bone trabeculae. the trabeculae join living and dead portions of the original bone fragments. fibrocartilage is converted to spongy bone, and the callus is called bony callus. {normal alignment of broken bones reduces swelling. its called reduction. can be via external manipulation or by internal means-surgery.

what does the canaliculi do?

it connects lacunae with one another and with the central canals, forming an intricate, miniature system of interconnected canals throughout the bone. This system provides many routes for nutrients and oxygen to reach the osteocytes and for the removal of wastes.

waht is parathyroid hormone (PTH)?

it increases blood calcium level. PTH secretion operates via a negative feedback system. when calcium level decreases, parathyroid glands (receptors) detect the change and increase production of a molecule known as cyclic adenosine monophosphate (cAMP). the gene for PTH detects the intracellular increase of cAMP. as a result, PTH synthesis speeds up and more PTH is released into blood. more PTH increase the number and activity of osteoclasts which step up the pace of bone resorption. the resulting release of calcium from bone into blood returns the blood calcium level to normal. {PTH inhibits calcium loss in urine and stimulates cacitriol production which increases calcium absorption in the intestine}

what is the medullary/marrow cavity?

it is a hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults. The cavity minimizes the weight of the bone by reducing the dense bony material where it is least needed. The long bones' tubular design provides maximum strength with minimum weight.

what is the articular cartilage?

it is a thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone. Articular cartilage reduces friction and absorbs shock at freely movable joints. Because articular cartilage lacks a perichondrium and lacks blood vessels, repair of damage is limited.

what is the endosteum?

it is a thin membrane that lines the medullary cavity. It contains a single layer of bone-forming cells and a small amount of connective tissue.

what is the periosteum?

it is a tough connective tissue sheath and its associated blood supply that surrounds the bone surface wherever it is not covered by articular cartilage. It is composed of an outer fibrous layer of dense irregular connective tissue and an inner osteogenic layer that consists of cells. Some of the cells enable bone to grow in thickness, but not in length. The periosteum also protects the bone, assists in fracture repair, helps nourish bone tissue, and serves as an attachment point for ligaments and tendons. The periosteum is attaches to the underlying bone by perforating (Sharpey's) fibers, thick bundles of collagen that extend from the periosteum into the bone extracellular matrix.

what is nutrient artery?

its a large artery near the center of the diaphysis that passes through a hole in compact bone.

what are circumferential lamellae?

lamellae that are arranged around the entire outer and inner circumference of the shaft of a long bone. They develop during initial bone formation.

how does minerals affect bone growth?

large amounts of calcium and phosphorus are needed while bones are growing, as are smaller amounts of magnesium, fluoride, and manganese. These minerals are also necessary during bone remodeling.

what are concentric lamellae?

resembling growth rings of a tree, they are circular plates of mineralized extracellular matrix of increasing diameter, surround a small network of blood vessels, lymphatics, and nerves located in the central canal.

where is spongy bone found?

spongy bone tissue makes up most of the interior bone tissue of short, flat, sesamoid, and irregularly shaped bones. In long bones it forms the core of the epiphysis beneath the paper-thin layer of compact bone and forms a variable narrow rim bordering the medullary cavity of diaphysis. {is found in epiphyses of long bones, and is adjacent to marrow cavities of long bones and inside short and flat bones. It supports and protects bone marrow.

what are interstitial lamellae?

the areas between neighboring osteons which contain lamellae, lacunae with osteocytes, and canaliculi. they are fragments of older osteons that have been partially destroyed during bone rebuilding or growth. {fill in spaces between haversian canals}.

comminuted fracture?

the bone is splintered, crushed, or broken into pieces at the site of impact, and smaller bone fragments lie between the two main fragments.

What is the diaphysis?

the bone's shaft of body--the long, cylindrical, main portion of the bone.

whats open (compound) fracture?

the broken ends of bone protrude through the skin

what are inner circumferential lamellae?

the circumferential lamellae that line the medullary cavity.

what are outer circumferential lamellae?

the circumferential lamellae thats directly deep to the periosteum. They are connected to the periosteum by perforating fibers (Sharpey's).

how does hormones affect bone growth?

the hormones most important for growth during childhood are the insulinlike growth factors (IGFs), which are produced by liver and bone tissue. IGFs stimulate osteoblasts, promote cell division at the epiphyseal plate and in the periosteum, and enhance synthesis of the proteins needed to build new bone. thyroid hormones (T3 and T4) from the thyroid gland also promote bone growth by stimulating osteoblasts. In addition, the hormone insulin from the pancreas promotes bone growth by increasing the synthesis of bone proteins. {high estrogen inhibits long bone elongation. estrogen promotes osteoclast apoptosis and works against osteoporosis.

how does teeth align straight by using braces?

the movement of teeth by braces places a stress on the bone that forms the sockets that anchor the teeth. In response to this artificial stress, osteoclasts and osteoblasts remodel the sockets so that the teeth align properly.

what are osteoblasts?

they are bone-building cells. they synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue, and they initiate calcification. As osteoblasts surround themselves with extracellular matrix, they become trapped in their secretions and become osteocytes. (the ending -blast in the name of a bone cell or any other connective tissue cell means that the cell secretes extracellular matrix.) {Bone matrix first secreted is called osteoid. osteoid becomes bone matrix after calcium hydroxyapatite crystals infiltrate osteoid. Osteoblasts secrete alkaline phospatase needed for mineralization of bone}

what are osteoclasts?

they are huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell) and are concentrated in the endosteum. On the side of the ell that faces the the bone surface, the osteoclast's plasma membrane is deeply folded into a ruffled border. Here the cell releases powerful lysosomal enzymes and acids {HCL} that digest the protein and mineral components of the underlying extracellular bone matrix. this breakdown of bone extracellular matrix (resorption) is part of the normal development, maintenance, and repair of bone. In response to certain hormones, osteoclasts help regulate blood calcium level. they are also target cells for drug therapy used to treat osteoporosis. (ending -clast means the cell breaks down extracellular matrix)

what are haversian systems/osteons?

they are repeating structural units that makes up the compact bone tissue.

what are canaliculi?

they are small channels that radiate from in all directions from the lacunae, which are filled with extracellular fluid.

what are osteocytes?

they are the mature bone cells and the main cells in bone tissue. They maintain its daily metabolism, such as the exchange of nutrients and wastes with the blood. like osteoblasts, osteocytes do not undergo cell division. (the ending -cyte in the name of a bone cell or any other tissue cell means that the cell maintains the tissue) {found in bone lacunae}

what is the metaphyses?

they are the regions between the diaphysis and the epiphyses. in a growing bone, each metaphysis contains an epiphyseal (growth) plate, a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length. when bone ceases to grow in length about ages 18-21, the cartilage in the epiphyseal plate is replaced by bone; the resulting bony structure is known as epiphyseal line.

what are osteogenic cells?

they are unspecialized bone stem cells derived from mesenchyme, the tissue from which almost all connective tissues are formed. they are the only bone cells to undergo cell division; the resulting cells develop into osteoblasts. osteogenic cells are found along the inner portion of the periosteum, the endosteum, and in the canals within the bone that contain blood vessels.

whats fibroblasts?

they invade the fracture site and produce collagen fibers. in addition cells from the periosteum develop into chondroblasts and begin to produce fibrocartilage in this region. these events lead to the development of a fibrocartilaginous callus, a mass of repair tissue consisting of collagen fibers and cartilage that bridges the broken ends of the bone.

how does vitamins affect bone growth?

vit A stimulates activity of osteoblasts. vit C is needed for synthesis of collagen, the main bone protein. vit D helps build bone by increasing the absorption of calcium from foods in the gastrointestinal tract into the blood. vit K and B12 are needed for synthesis of bone proteins.

How does the skeletal system produce blood cell?

within certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells, and platelets, a process called hemopoiesis. Red bone marrow consists of developing blood cells, adipocytes, fibroblasts, and macrophages within network of reticular fibers. It is present in developing bones of the fetus and in some adult bones, such as the hip (pelvic) bones, ribs, sternum, vertebrae, skull, and ends of bones of the humerus and femur. in a newborn, all bone marrow is red and is involves in hemopoiesis. with increasing age, much of the bone marrow changes from red to yellow.