Chapter 6 A&P Bones and Bone Structure

6-3: the two main functions of osteocytes

1 maintain the protein and mineral content of the surrounding matrix, and take part in the repair of damaged bone. 2 They can convert to a less specialized type of cell to assist in bone repair, like an osteoblast or osteogenic cell.

6-8: 3 major effects of parathyroid hormone to increase blood calcium ion level

1: stimulating osteoclast activity indirectly via PTH binding to receptors on osteoblasts adjacent to osteoclasts to receiev an osteoclast differentiation factor from the -blasts called RANKL, that activates receptors on pre -clast cells, triggering differentiation into mature -blasts. 2: increasing the amount of calcium ions absorbed by the intestines by enhancing calcitriol secretion by the kidneys. and 3: decreasing the amount of calcium ions excreted by the kidneys causing more calcium to remain in the bloodstream. Overall, more calcium ions enter body fluids and fewer are lost under these conditions to restore homeostasis.

6-7: vitamins A, K, and B12

A stimulates osteoblast activity and is necessary for normal bone growth in children. K and B12 are required for synthesis of proteins in normal bone.

6-1: skeletal system: leverage

Bones together can function as levers powered by skeletal muscles to move the body from precise, fine motor functions to large gross motor functions.

calcitonin

Calcitonin opposes the effects of parathyroid hormone (PTH), which acts to increase the blood calcium level. Calcitonin lowers blood calcium levels by suppressing osteoclast activity in the bones and increasing the amount of calcium excreted in the urine.

6-2: Bone are classified according to shape and structure, and they have a variety of bone markings

Classify bones according to shape and structure, giving examples of each type, and explain the functional significance of each of the major types of bone markings.

6-4: compact bone structure

Compact bone is thickest where stresses are applied from a limited number of directions. All osteons in compact bone are aligned the same, making such bones very strong when stressed along the axis of alignment. You might think of a single osteon as a drinking straw. Hard to compress or stretch lengthwise, but quite easy to bend width-wise. The osteons in the diaphysis of a long bone are parallel to the long axis of the shaft, f or this reason, the shaft does not bend, even when extreme forces are applied to either end. Vet a much smaller force applied to the side of the shaft can break the femur. A sudden sideways force, as in a fall or auto accident, causes the majority of breaks in this bone. The mature compact bone has specific qualities that will be analyzed in the following card.

6-5: Bones form through ossification and enlarge through interstitial and appositional growth

Compare the mechanisms of endochondral ossification and intramembranous ossification.

6-4: Compact bone contains parallel osteons, and spongy bone contains trabeculae

Compare the structures and functions of compact bone and spongy bone. They resist stress and store marrow. This section also covers the inner lining and outer covering of the bones (endosteum and periosteum)

6-1: The skeletal system has several major functions

Describe the major functions of the skeletal system.

6-6: Bone growth and development depend on bone remodeling, which is a balance between bone formation and bone resorption

Describe the remodeling and homeostatic mechanisms of the skeletal system.

6-9: A fracture is a crack or a break in the bone.

Describe the types of fractures, and explain how fractures heal. There are four categories, each with two groupings: 1 = position of bone ends (displaced or nondisplaced), 2 = completeness of break (complete or incomplete), 3 = orientation of break to the bones axis (linear or transverse) and 4 = whether or not the broken bone penetrates the skin (open or closed).

6-7: exercise, nutrition, and hormones affect bone development and the skeletal system.

Discuss the effects of exercise, nutrition, and hormones on bone development and on the skeletal system.

6-8: Calcium plays a critical role in bone physiology

Explain the role of calcium as it relates to the skeletal system.

6-3: osteoclasts

FUNCTION: cells that absorb and remove bone matrix. They tend to be larger cells with 50+ nuclei, and LOCATION: occur in shallow depressions called osteoclastic crypts that have eroded into the matrix (basically the pits of bone surfaces). They secrete acids and protein-digesting enzymes to dissolve the matrix and release its stored minerals. The ruffled boarder of fingerlike processes increase surface area for secretion into matrix. The erosion is called osteolysis or resorption. The released products are resorbed at the osteoclast's boarder. ORIGIN: They are derived from the same stem cells that make monocytes and macrophages that lie within the body's defense mechanisms.

6-3: osteogenic cells aka osteoprogenitor cells

FUNCTION: mesenchymal cells (aka stem cells) that ; to produce daughter cells that differentiate into osteoblasts to maintain populations of osteoblasts and so are important in the repair of a fracture. ORIGIN: deep layers of the periosteum and the marrow. LOCATION: They are found in inner, cellular layer of the periosteum, and are also found in a cellular layer, or endosteum that lines medullary cavities and passageways for blood vessels that penetrate the matrix of compact bone.

6-3: osteoblasts

FUNCTION: produce new bone matrix in a process called osteogenesis aka ossification. Osteoblasts make and release the proteins and other organic components of the matrix. Osteoblasts also help increase local concentrations of calcium phosphate above its solubility limit, triggering the deposition of calcium salts in the organic matrix, converting osteoid into bone. ORIGIN: bone marrow. LOCATION: periosteum and endosteum

6-3: Bone is composed of matrix and several types of cells: osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

Identify the cell types in bone and list their major functions

6-8: hormones and calcium ion balance

If calcium ion concentration in body fluids increases by 30 percent, neurons and muscle cells become unresponsive. If they decrease by 35%, neurons become so excitable that convulsions occur. 50% cut causes death. Two hormones with opposing effects maintain this important homeostasis; the parathyroid hormone and calcitronin coordinate storage (bones), absorption (digestive tract), and excretion (kidneys) of calcium ions.

6-2: spongy bone

Layer of bone tissue having many small spaces and found just inside the layer of compact bone. aka trabecular bone. consists of red bone marrow and a medullary cavity (EXCEPT CRANIUM) and an open network of strugs and plates that resembles a three dimensional garden lattice.

6-3: osteoid

ORIGIN: Osteoblasts secrete it. FUNCTION: Before calcium salts are deposited by osteoblasts, this organic matrix is called osteoid. Gets converted into bone when osteoblasts increase calcium phosphate above solubility limit, triggering calcium salt deposit into matrix. See figure 6-5.

6-3: canaliculi

The matrix contains canaliculi that contain cytoplasmic extensions of osteocytes to aid in osteocyte to osteocyte communication between different lacunae via access to nutrients of blood vessels in central canal, by creating gap junctions between the osteocytes.

Parathyroid hormone (PTH)

acts to increase the blood calcium level. enhances the release of calcium from the large reservoir contained in the bones. Bone resorption is the normal destruction of bone by osteoclasts, which are indirectly stimulated by PTH.

androgens

aid in producing bone faster than epiphyseal cartilage can expand, causing epiphyseal closure during puberty. stimulation of androgen receptors in osteoblastic bone marrow stromal cells inhibits the differentiation of osteoclasts in the bone marrow cavity.

6-2: sutural bones

aka wormian bones. small/flat/irregularly shaped bones between flat bones of the skull. Range in size from grain of sand to a quarter. their boarders look like an odd jigsaw puzzle piece.

estrogens

also aid in epiphyseal closure during puberty. causes epiphyseal closure faster than testosterone making women shorter usually than men. With estrogen deficiency, the osteoclasts live longer and are therefore able to resorb more bone.

6-4: endosteum

an incomplete cellular layer. lines the medullary cavity. active during bone growth, repair, and remodeling. It covers the trabeculae of spongy bone and lines the inner surfaces of the central canals of compact bone. consists of a simple flattened layer of osteogenic cells that covers the bone generally without any intervening connective tissue fibers. cellular layer isn't compete in some places, leaving matrix exposed for osteoclasts and osteoblasts to remove or deposit matrix components.

6-7: sex hormones

at puberty, estrogen in femals and testosterone in males stimulate osteoblasts to produce bones faster than the rate at which epiphyseal cartilage expands, leading to epiphyseal closure. Estrogen causes epiphyseal closure faster than testosterone, making women shorter on average than men at matruity.

6-4: osteon

basic functional unit of mature compact bone. contains osteocytes arranged in concentric layers around a central canal containing 1 or more blood vessels, usually a capillary and a venule, which carry blood to and from the osteon, and run parallel to the surface of the bone. perforating canals run perpendicular to the surface and supply blood to both osteons deeper in the bone andto tissues of medullary cavity.

6-3: Bone cells

bone contains four types of cells: osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

6-5: intramembranous ossification

bone develops directly from mesenchyme or fibrous connective tissue. occurs mostly in flat bones. begins i osteoblasts differentiate within a mesenchymal or fibrous connective tissue. normally takes place in the deeper of tine dermis, resulting in dermal bones like the flat bones of the skull, the mandible and the clavicle. ALL STEPS IN 6-13. First the stem cells cluster and secrete organic components into matrix for mineralization with calcium salts to form bone matrix. Then some osteoblasts are trapped to differentiate into osteocytes, growing the bone outward from these ossification centers called spicules. After that the blood vessels branch within the region and grow between spicules, and as they interconnect, they trap blood vessels within the bone. Following that third step, continued deposition of bone by osteoblasts located close to blood vessels makes a plate of spongy bone with vessels weaved throughout. Finally, the subsequent remodeling around blood vessels makes osteons typical of compact bone that together with the connective tissue form the periosteum.

6-5: ossification aka osteogenesis

bone growth that refers specifically to the formation of bone. Occurs in two ways; endochondral ossification and intramembraneous ossification. Bones start forming 6 weeks after fertilization, when the embryo is around .5 inches. during fetal development (embryo is greater than 8 weeks old) the cartilages are replaced by bone either via endochondral or intramembranous ossification. Bone growth continues and generally doesn't stop until age 25.

6-3: overall strength of bones

bone is on par with the best steel-reinforced concrete. In fact, bone is far superior to concrete, because it can undergo remodeling (cycles of bone formation and resorption) as needed and can repair itself after injury.

6-4: lamellae of the osteon

bone matrix forms layers called ______. These thin plates of each osteon form a series of nested cylinders around the entral canal. There are three types: concentric, interstitial, and circumferential.

6-5: endochondral ossification

bone replaces existing cartilage in to grow bone in length via interstitial growth, and in width via appositional growth. occurs mostly in long bones. The primary ossification center is developed inside the cartilage. begins with the formation of a hyaline cartilage model. This model serves as the pattern for almost all bone development. Limb bone development is a good example of this process, by the time an embryo is six weeks old, the proximal bones of the limbs, the humerus (upper limb) and femur (lower limb), have formed, but they are composed entirely of cartilage. These cartilage models continue to grow by expansion of the cartilage matrix (interstitial growth) and the production of more cartilage at the outer surface (appositional growth)

6-3: osteogenesis/ossification

bone tissue formation, created by osteoblasts. Opposite = osteolysis, enacted by osteoclasts.

6-2: short bones

boxy, with approximately equal dimensions. includes carpal bones and tarsal bones.

6-7: calcitriol and vitamin D3

calcitriol is synthesized in the kidneys for the purpose of normal calcium and phosphate ion absorption in the digestive tract.

6-8: the skeleton as a calcium reserve

calcium is the most abundant mineral in the body, 99% of which lies in the skeleton. As such, the skeleton is most important role in homeostatic regulation of calcium ion concentration in body fluids necessary for muscle contraction, nerve impulses, blood clotting, stability of cell membranes and cell metabolism. The more calcium released from the bone, the weaker it becomes. The more calcium salts are deposited, the stronger and denser they become.

6-3: bone matrix

calcium phosphate (Ca3(PO4)2) makes up almost two thirds of the weight of bone (the other 1/3rd is mostly collagen) and interacts with calcium hydroxide to form crystals of hydroxyapatite, which incorporate other calcium salts and ions. The matrix of a bone makes it incredibly strong. Without the matrix, it would be flexible.

6-10: osteoclast-activating factor

cancers of bone marrow, breast, or other tissues releases this factor that increases both the number and activity of osteoclasts and produces severe osteoporosis.

6-9: simple (closed) fractures

completely internal fractures.

6-7: minerals

constant dietary source of calcium, phosphorus and lesser minerals like magnesium, fluoride, iron and manganese are needed for normal bone growth and maintenance.

6-3: osteocytes

develop from osteoblasts that have become completely surrounded by bone matrix. the mature bone cells make up most of the cell population. Each osteocyte occupies a lacuna, a pocket sandwiched between layers of matrix Osteocytes cannot divide, and a lacuna never contains more than one osteocyte. Neighboring ones are linked by gap junctions to allow for rapid exchange ions and small molecules to pass through.

6-3: characteristics of a bone: periosteum

except at joints, this covers the outer surface of the bones and consists of an outer fibrous layer and an inner cellular layer.

6-8: rickets

form of osteomalacia affecting children resulting from a vitamin D3 deficiency caused by inadequate exposure to sunlight/lack of dietary D3, causing bones to become flexible and bent laterally, creating bowlegged appearance from lack of resistance to tension and compression of body weight on bones.

6-9: compound (open) fractures

fractures that project through the skin. Higher risk of infection or uncontrolled bleeding.

6-2: metaphysis

growth zone between the epiphysis and the diaphysis during development of a long bone

6-2: irregular bones

have complex shapes with short, flat, notched, or ridged surfaces, like the vertebrae, pelvis, and certain skull bones.

6-2: flat bones

have thin, parallel surfaces which produce a flattened shape. Include the roof of the skull, the sternum, the ribs, and the scapulae. They provide protection for underlying soft tissues and offer extensive surface area for the attachment of skeletal muscles.

6-2: medullary cavity

hollow area inside the diaphysis of the bone that contains yellow bone marrow

6-10: osteopenia

inadequate ossification, normal in everyone as we age and lose bone mass. most often begins between 30-40 years of age. Women lose 8% of bone mass a decade. Men lose 3% a decade. Women's bones are protected by estrogen, which decreases after menopause, increasing susceptibility to this condition.

6-1: skeletal system

includes bones, cartilages, ligaments, and other connective tissues that stabilize or interconnect the bones. It has 5 major functions; support, storage of minerals and lipids, blood cell production, protection, and leverage.

6-2: bone structure

includes the diaphysis, epiphysis, metaphysis, compact bone, medullary cavity, and spongy bone

6-1: skeletal system: storage of minerals and lipids

inorganic ions known as minerals take part in maintaining osmosis in body fluids, and are also important cofactors for enzymes. Calcium is the most abundant mineral in the human body an its salts are a valuable mineral reserve for maintaining calcium and phosphate ion concentrations in body fluid. Lipids in the bones are known as yellow bone marrow. This adipose tissue is found in internal bone cavities, and stores energy.

6-4: spongy bone structure

lamellae are not arranged in osteons, and no osteons are present. the matrix forms a meshwork of trabeculae, the supporting bundles of fibers that branch to make an open network, oriented along the stress lines and extensively cross braced. This bone structure is less dense and reduces the weight of the skeleton. There are no capillaries or venules in this matrix. Instead, the spongy bone within the epiphyses of long bones like the femur contain red bone marrow, that forms blood cells. Blood vessels close by this tissue deliver nutrients to osteocytes via diffusion into canaliculi of the trabeculae, which remove wastes. Other sites of spongy bone have yellow bone marrow, which contains adipose tissue for energy reserves.

scurvy

loss of bone mass and strength due to vitamin c deficiency

6-3: characteristics of a bone: canaliculi

narrow passageways through the matrix, extending between the lacunae and nearby blood vessels, forming a branching network through which osteocytes exchange nutrients, wastes, and gases.

6-7: Nutritional and hormonal effects on the bone

nutritional bone growth and maintenance depend on a combination of nutritional and hormonal factors like minerals, calcitriol and vitamin D3, vitamin C, vitamins A, K, and B12, growth hormone and thyroxine, sex hormones, parathyroid hormone and calcitonin. major hormones affecting growth and maintenance are on table 6-1.

6-6: bone remodeling

occurs throughout life as osteoclasts resorb bone tissue and osteoblasts replace the bone. As quickly as osteoclasts remove the matrix, osteoblasts add to it. When osteoclasts remove the calcium salts faster than osteoblasts deposit them, the bones weaken. When osteoblasts dominate, the bones strengthen. To keep bones strong, subject them to muscular stress through weight training and avoid immobility. Any heavy metels in blood steram will be deposited inot bone matrix and will eventually be released into circulation again. Radiation can be released from your own bones in this way after nuclear reactor tragedies.

6-5: growth in length; interstitial growth.

on figure 6-11, it's steps 5-7. 5: capillaries and osteoblasts migrate into the epiphyses, creating secondary ossification centers. 6. The epiphyses eventually become filled iwth spongy bone. The metaphysis (a relatively narrow cartilaginous region called the epiphyseal cartilage aka epiphyseal plate) now sepeartes the epiphysis from the diaphysis. On the shaft dise of the metaphysis, osteoblasts continually invade the cartilage and replace it with bone. new cartilage is produced at the same rate on the epiphyseal side. 7. At puberty, the rate of epiphyseal cartilage production slows and the of osteoblast activity accelerates. As a result, the epiphyseal cartilage gets narrower and narrower, until it ultimately disappears. This event is called epiphyseal closure. The former location of the epiphyseal cartilage becomes a distinct epiphyseal line that remains after epiphyseal growth has ended.

6-5: Blood and nerve supply to bones

osseous tissue is highly vascular. In a typical bone such as the humerus, three major sets of blood vessels develop; Nutrient Artery and Vein, the Metaphyseal Vessels and the periosteal Vessels. Following the closure of the epiphyses, all three sets of vessels become extensively interconnected. The periosteum also contains a network of lymphatic vessels (lymphatics, collect from branches that enter the bone and reach individual osteons by the perforating canals) and sensory nerves (penetrate the compact bone with the nutrient artery to innervate the endosteum, medullary cavity, and epiphyses).

6-3: characteristics of a bone: osteocytes and lacunae

osteocytes are bone cells with pockets in them called lacunae, which are organized around blood vessels that branch through the bony matrix.

6-7: parathyroid hormone and calcitonin

parathyroid hormone from the parathyroid glands stimulates osteoclast and osteoblast activity and increases blood calcium ion level. calcitonin from the C cells of the thyroid gland is used to decrease this blood calcium ion level and in pregnant and nursing women, as well as aid in transfer calcium ions to the fetus.

6-4: surface coverings of bone

periosteum (outside) and endosteum (inside)

6-4: periosteum at synovial joints

periosteum is continuous with the lOint capsule. The fibers of the periosteum are also interwoven those of the tendons attached to the bone. As the bone grows, these tendon fibers are cemented into the circumferential lamellae by osteoblasts from the cellular layer of the periosteum. Collagen fibers incorporated into bone tissue from tendons and ligaments, as well as from the superficial periosteum, are called perforating fibers.

6-1: skeletal system: support

provides a structural framework for the body's soft tissues and organs

6-1: skeletal system: blood cell production

red blood cells, white blood cells, and other blood elements are made in the red bone marrow in the internal cavities of many bones.

6-2: long bones

relatively long and slender consisting of a shaft with two ends wider than the shaft. Arm, forearm, thigh, leg, palms, soles, fingers, and toes. femur = longest one, and is the largest and heaviest bone in the body.

6-3: collagen in the bone matrix

remarkably strong, stronger than steel when subjected to the pull of tension, while still staying flexible with bending. Useless as a force of resistance against compression

6-2: diaphysis

shaft of a long bone

6-1: skeletal system: protection

skeletal structures protect soft tissues and organs. The ribs protect the heart and lungs, the skull protects the brain, the vertebrae protects the spinal cord, and the pelvis cradles the digestive and reproductive organs.

6-2: diploë

spongy bone inside the cranium. Includes red bone marrow, but does not include the medullary cavity.

6-10: osteopenia has widespread affects on aging bones

summarize the effects of the aging process on the skeletal system.

6-5: growth in width: appositional growth

superficial layer of bone, or bone collar, forms early in endochondral ossification. After that, the developing bone increases in diameter through appositional growth at the outer surface. In this process. cells of the inner layer of the periosteum differentiate into osteoblasts and deposit superficial layers of bone matrix. Eventually, these osteoblasts become surrounded by matrix and differentiate into osteocytes. this adds series of layers that form circumferential lamellae In time, the deepest circumferential lamellae are recycled and replaced by osteons typical of compact bone. While bone matrix is being added to the outer surface of the growing bone, osteoclasts are removing bone matrix at the inner surface, but at a lower rate. As a result, the medullary cavity gradually enlarges as the bone gets larger in diameter. step 2 of 6-11.

6-5: Blood and nerve supply to bones: Metaphyseal vessels

supply blood to diaphyseal (inner) surface of each epiphyseal cartilage where it will be replaced by bone.

6-3: bone tissue

supporting connective tissue. contains specialized cells and a matrix of extracellular protein fibers and a ground substance.

6-2: bone markings

surface features. includes, prjections, openings, and depressions. Openings and depressions are sites where blood vessels or nerves lie alongside or penetrate the bone.

calcitriol

synthesized in kidneys for normal calcium and phosphate ion absorption in digestive tract.

6-3: hydroxyapatite in the bone matrix

the chief crystal of bone, formed from calcium and phosphorus. they can withstand compression but are more likely to shatter with twisting, bending, or sudden impacts.

6-5: calcification

the deposition of calcium salts that take place during ossification, but also take place in other tissues like calcified cartilage.

6-3: characteristics of a bone: dense matrix

the deposits of calcium salts around the protein fibers makes the matrix very dense.

6-7: The effects of exercise on the bone

theory: osteoblasts are sensitive to electrical events, which is used as a mechanism to control the internal organization and structure of bone. When the bone is stressed, the minerals generate tiny electrical fields that attract osteoblasts to begin producing bone. Bone shapes reflect forces applied to them. the larger bumps and ridges are where tendons attach, and the bumps enlarge on the bone as the muscles grow and increase the tendon's pull on the bone. This is why regular exercise is important for maintaining strong bones. Without activity, bones degenerate, explaining why a broken leg can lose up to a third of its mass when unstressed.

6-2: bone shapes

there are 206 major bones that can be divided into 6 categories based on shapes; sutural, irregular, short, flat, long, and sesamoid.

6-4: circumferential lamellae

these are found at the outer and inner surfaces of the bone where they are covered by the periosteum and endosteum, respectively. They are produced during growth of the bone.

6-4: concentric lamellae

these can be seen in a cross section, and look like a target with the canal as a bulls eye.

6-4: interstitial lamellae

these fill in the spaces bewteen the osteons in the compact bone.

6-5: Blood and nerve supply to bones: Periosteal vessels

these vessels from the periostium give blood to superficial osteons of shaft. During endochondral bone formation, branches of these enter the epiphysis to bring blood to secondary ossification centers.

6-5: Blood and nerve supply to bones: The nutrient artery and vein

these vessels supply diaphysis and are formed by invading the cartilage model as endochondral ossification begins. They enter the bone through nutrient foramina and then branch with its canals throughout the shaft into the osteons of surrounding compact bone.

6-7: vitamin C

this must be present for key enzymatic reactions in collagen synthesis and stimulates osteoblast differentiation.

6-7: growth hormone and thyroxine

thyroxine from the thyroid gland stimulates bone growth. It also stimulates cell metabolism and increases rates of osteoblast activity.growth hormone from the pituitary gland stimulates protein synthesis and rates of cell division and cell growth throughout the body. Both of these hormones work in balance to maintain normal activity at epiphyseal cartilages until puberty.

6-2: compact bone

tightly solid bone tissue that forms the exterior of bones

6-4: periosteum

tough, fibrous tissue that forms the outermost covering of bone and contains a cellular inner layer. Near joints, the periosteum becomes continuous with the connective tissues that hold the bones in place. Has three major functions: 1 ) isolates the bone i surrounding tissues, (2 ) provides a route for the blood vessels and nerves, and (3) takes part in bone growth and repair.

6-2: sesamoid bones

usually round, small and flat shaped like a sesame seed, and tend to develop with the tendons. Examples include the patella.

6-8: osteomalacia

vitamin D deficiency causes this. bones appear normal but are weak and flexible due to poor mineralization. Proof that changes in mineral content don't always affect bone shape.

6-10: osteoporosis

when reduction in bone mass is sufficient to compromise normal function, becoming brittle and fragile, causing 90 year olds to break a hip by standing. The loss of spongy and compact bone mass are equally severe. sex hormones contribute to this. As hormone levels decline, bone mass diminishes. Women's bones are protected by estrogen, which decreases after menopause, increasing susceptibility to this condition.

6-2: epiphysis

wide ends of a long bone