chapters 7 & 8: skeletal system and bone structure part 1

timeline of echondrondral ossification

- 8 to 12 weeks: Fetal hyaline cartilage model develops. - fetal period: Cartilage calcifies, and a periosteal bone collar forms around diaphysis and Primary ossification center forms in the diaphysis. -newborn to child: Secondary ossification centers form in epiphyses -child: Bone replaces cartilage, except the articular cartilage and epiphyseal plates. - Epiphyseal plates ossify and form epiphyseal lines.

spongy bone

-Cancellous or trabecular bone -Located internal to compact bone -Appears porous -20% of bone mass

Parallel lamellae of spongy bone

-Composted of bone matrix -Osteocytes resting between lamellae -Canaliculi radiating from lacunae - component of compact bone

osteoprogenitor cells

-stem cells derived from mesenchyme. -When they divide through the process of cellular division, another stem cell is produced along with a "committed cell" that matures to become an osteoblast Location: in both the periosteum and the endosteum.

what are the 4 steps for interstitial growth?

1. A chondrocyte within a lacuna begins to exhibit mitotic activity 2. Two cells (now called chondroblasts) are produced by mitosis from one chondrocyte and occupy one lacuna. 3. each cell produces new matrix and begins to separate from its neighbor. Each cell is now called a chondrocyte. 4. Cartilage continues to grow internally

how can bone fracture repair be described?

1. A fracture hematoma forms. 2. A fibrocartilaginous (soft) callus forms. 3. A hard (bony) callus forms 4. the bone is remodeled

steps of long endochondral bone growth

1. A hyaline cartilage model of bone forms. 2. Bone first replaces hyaline cartilage in the diaphysis. 3. Next, bone replaces hyaline cartilage in the epiphyses. 4. Eventually, bone replaces hyaline cartilage everywhere, except the epiphyseal plates and articular cartilage. 5. By a person's late 20s, all epiphyseal plates typically have ossified, and lengthwise bone growth is complete.

what are the 3 steps for appositional growth?

1. Mitotic activity occurs in stem cells within the perichondrium. 2. New undifferentiated stem cells and committed cells that differentiate into chondroblasts are formed. Chondroblasts produce new matrix at the periphery 3. As a result of matrix formation, the chondroblasts push apart and become chondrocytes. Chondrocytes continue to produce more matrix at the periphery.

3 steps of intramembraneous ossification

1. Ossification centers form within thickened regions of mesenchyme beginning at the eighth week of development. 2. Osteoid undergoes calcification. 3. Woven bone and its surrounding periosteum form. 4. Lamellar bone replaces woven bone, as compact and spongy bone form

5 microscopic zones in the epiphyseal plate

1. Zone of resting cartilage. (outermost) 2. Zone of proliferating cartilage 3. Zone of hypertrophic cartilage. 4. one of calcified cartilage. 5. Zone of ossification.(deepest)

what are the 3 steps of the activation of vitamin D to calcitriol?

1. the precursor molecule is converted to vitamin D3 (cholecalciferol). 2. Vitamin D3 is converted to calcidiol in the liver (when an —OH group is added). 3. Calcidiol is converted to calcitriol in the kidney (when another —OH group is added). HO Vitamin D3 (cholecalciferol)

Periosteum

A dense irregular connective membrane covering the surface of the bone shaft -protects bone from surrounding structures, anchors blood vessels and nerves to bone surface, attachment site for tendons and ligaments

what are the functions of bones?

Bones provide structural support and serve as a framework for the entire body. Bones also protect many delicate tissues and organs from injury and trauma. Bones serve as attachment sites for skeletal muscles, other soft tissues, and some organs example: The rib cage shields the heart and lungs; the cranial bones enclose and protect the brain

Articular acrtilage

Covering the joint surface of an epiphysis is a thin layer of hyaline cartilage

Perichondrium

Dense irregular connective tissue membrane covering cartilage and helps maintain its shape

transverse fracture

Fracture is at right angles to the long axis of the bone

Glucocorticoids

Increase bone loss and, in children, impair bone growth when there are chronically high levels of glucocorticoids

What two minerals are stored in bone, and what are their functions in the body?

Most of the body's reserves of the minerals calcium and phosphate are stored within and then released from bone. Calcium is an essential mineral for such body functions as muscle contraction

gross anatomy of long bones

One of the principal gross features of a long bone is its shaft, which is called the diaphysis. The elongated, usually cylindrical diaphysis provides for the leverage and major weight support of a long bone

what is the primary component of bone?

Osseous connective tissue (bone connective tissue)

Calcitonin

Promotes calcium deposition in bone , comes from the thyroid DECREASES calcium levels - protein hormone made in the thyroid gland -produced in response to HIGH blood calcium levels -stimulates bone deposition by osteoblasts -inhibits osteoclast activity *its such a blast to deposit bone*

gross anatomy

Study of structures that can be seen with the naked eye

TRUE/FALSE interstitial and appo- sitional cartilage growth occur simultaneously

True

resorption lacuna

a depression or pit on the bone surface

bone resorption

a process whereby bone matrix is destroyed by substances released from osteoclasts specially proteolytic enzymes released from lysosomes within osteoclasts - occur when blood calcium levels are low

Cartilage

a semirigid connective tissue that is more flexible than bone. Mature cartilage is avascular (lacks a blood supply).

stress fracture

a thin break caused by increased physical activity in which the bone experi- ences repetitive loads

how is Parathyroid hormone (PTH) used in the kidneys?

act synergistically to stimulate the kidneys to excrete less calcium in the urine - occurs by increasing calcium reabsorption in the tubules in the kidneys

medullary (marrow) cavity

along the length of the diaphysis are spicules (thin, needlelike structures) of spongy bone. The hollow, cylindrical space within the diaphysis - contains osteoclasts

endosteum (inner layer of periosteum)

an incomplete layer of cells that covers all internal surfaces of the bone within the medullary cavity -thin layer of CT - contains osteoprogenitor cells, osteoblasts, and osteoclasts.

interstitial lamellae

are either the components of compact bone that are between osteons or the leftover parts of osteons that have been partially resorbed, they often look like a "bite" has been taken out of them.

osteoblasts

are formed from osteoprogenitor stem cells. - synthesize and secrete osteoid which later becomes calcified -some but not all differentiate into osteocytes - Often, osteoblasts are positioned side by side on bone surface

long bones

are greater in length than width. These bones have an elongated, cylindrical shaft (diaphysis). This is the most common bone shape. Long bones are found in the upper limbs and lower limbs -longer than they are wide ex: small bones in the fingers and toes are long bones, as are the larger tibia and fibula of the lower limb.

osteoclasts

are large, multi-nuclear, phagocytic cells (eating). -They are derived from fused bone marrow cells similar to those that produce monocyte -involved in bone resorption (break down of bone)

Concentric lamella

are rings of bone connective tissue that surround the central canal and form the bulk of the osteon. The numbers of concentric lamellae vary among osteons

Circumferential lamella

are rings of bone immediately internal to the periosteum of the bone

Canaliculi

are tiny, interconnecting channels within the bone connective tissue that extend from each lacuna, travel through the lamellae, and connect to other lacunae and the central canal.

hyaline cartilage

attaches ribs to the sternum (costal cartilage), covers the ends of some bones (articular cartilage), and is the cartilage within growth plates (epiphyseal plates). Allows your bones to smoothly rub past each other. - contains a population of cells scattered throughout a glassy-appearing matrix of protein fibers (primarily collagen) embedded within a gel-like ground substance

why is it important for calcium concentration to be regulated?

because calcium is required for numerous physiologic processes such as initiation of muscle contraction, d for numerous physiologic processes such as initiation of muscle contraction, exocytosis of molecules from cells, including nerve cells; stimulation of the heart by pacemaker cells and blood clotting

when does cartilage growth start?

begins in the womb or after injury to the cartilage, yet this growth is limited due to the lack of blood vessels in the tissue.

bone formation of bone matrix

begins when osteoblasts secrete osteoid.

components of the skeletal system

bone, cartilage, other connective tissue, ligaments

osteopenia

bones of the skeleton become thinner and weaker, resulting in insufficient ossification

what is bone composed of?

both cells and extracellular matrix, like all connective tissue.

how do hormones effect bone growth and maintenance?

by altering the rates of chondrocyte, osteoblast, and osteoclast activity

Chondroblasts

cartilage forming cells derived from mesenchymal cells and they produce the cartilage matrix.

chondrocytes

chondroblasts become encased within the matrix they have produced and secreted, the cells -maintains the matrix

types of bone

compact and spongy

does a simple or compound feature take longer to heal?

compound fracture

severe anemia

condition in which erythrocyte (red blood cell) numbers are lower than normal, resulting in insufficient oxygen reaching the cells of the body may trigger conversion of yellow bone marrow back to red bone marrow, a change that facilitates the production of additional erythrocytes.

perforating fibers

consisting of bundles of strong predominantly type I collagen fibres connecting periosteum to bone. run perpendicular to the diaphysis.

the central canal

cylindrical channel that lies in the center of the osteon and runs parallel to it. Extending through the central canal are the blood vessels and nerves that supply the bone.

compact bone

dense or cortical bone -80% of bone mass

what is the spongy bone in the flat bone of the skull called?

dipole

bone remodeling

dynamic process of continual addition of new bone tissue (bone deposition) and removal of old bone tissue

yellow bone marrow

fatty tissue found in the medullary cavity of most adult long bones - can concert back to red bone marrow -product of red bone marrow degeneration as children mature - facilitates the production of additional erythrocytes.

flat bones

flat, thin surfaces that may be slightly curved. They provide extensive surface areas for muscle attachment and protect underlying soft tissues. - form the roof of the skull

short bones

have a length nearly equal to their width. Examples of short bones include the carpals (wrist bones) and tarsals (bones in the foot). -length is nearly equal to width more examples: Sesamoid bones, which are small, sesame seed-shaped bones along the tendons of some muscles, are also classified as short bones.

irregular bones

have elaborate, sometimes complex shapes and do not fit into any of the preceding categories. examples: the vertebrae; the ossa coxae (hip bones), several bones in the skull

what is the location of osteoprogenitor cells?

in both the periosteum and the endosteum.

osteoid

initial semisolid organic form of bone matrix

rickets

is a disease caused by a vitamin D deficiency in childhood and characterized by overproduction and deficient calcification of osteoid tissue.

Fibrocartilage

is a weight-bearing cartilage that withstands compression. It forms the intervertebral discs, the pubic symphysis (cartilage between bones of the pelvis

intersitial growth

is an increase in length that occurs within the internal regions of cartilage grows be length

red bone marrow

is hemopoietic ( blood cell-forming) and contains reticular connective tissue, developing blood cells, and adipocytes.

calcitonin

is released from the thyroid gland to DECREASE blood calcium levels—specifically, from its parafollicular cells in response to high blood calcium levels; it is also secreted in response to stress from exercise. - seems to have the greatest effect under conditions where there is the greatest turnover of bone, such as in growing children.

thyroid hormone

is secreted by the thyroid gland and stimu- lates bone growth by influencing the basal metabolic rate of bone cells

hemopoiesis

is the process of blood cell production. It occurs in red bone marrow connective tissue, which contains stem cells that form blood cells and platelets

locations of red bone marrow in adults

lat bones of the skull, the vertebrae, the ribs, the sternum, and the ossa coxae (hip bones), and in the proximal epiphyses of each humerus and femur.

intramembranous ossification

literally means "bone growth within a membrane." It is so named because the thin layer of mesenchyme in these areas is sometimes referred to as a membrane. - produces the flat bones of the skull (e.g., frontal bone), some of the facial bones (e.g., zygomatic bone, maxilla), the mandible (lower jaw), and the central part of the clavicle (collarbone).

osteocytes

mature bone cells derived from osteoblasts that have lost their bone-forming ability when enveloped by calcified osteoid -detects stress in bones; trigger new bone formation

hormones

molecules that are released from one cell into the blood and are transported throughout the body to affect other cells

Calcitriol

most active form of vitamin D -Stimulates absorption of calcium ions from the small intestine into the blood

bone matrix

nonliving, structural part of bone -organic components include: collagen protein inorganic components include salt crystals, calcium phosphate -gives bone tensile strength by resisting stretching and contributes to bone flexibility

locations of red bone marrow in children

ocated in the spongy bone of most of the bones of the body as well as the medullary cavity of long bones

mechanical stress

occurs in the form of weight-bearing move- ment and exercise, and it is required for normal bone remodeling. Stress is detected by osteocytes and communicated to osteoblasts. Osteoblasts increase the synthesis of osteoid, and this is followed by deposition of mineral salts.

appositional growth of bone

occurs within the periosteum. Grows by width. In this process, osteoblasts in the inner cellular layer of the periosteum produce and deposit bone matrix within layers parallel to the surface, called external circumferential lamellae. ** continues throughout an individual's lifetime.

compound fracture

one or both ends of the broken bone pierce the overlying skin

how is fusion of epiphyseal plates scored?

open: no bony fusion or union between the epiphysis and the other bone end partial union: some fusion between the epiphysis and the rest of the bone, but a distinct line of separation may be seen complete union: all visible aspects of the epiphysis are united to the rest of the bone

what are the 4 cells of bone?

osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

how does bone strength increase?

over a period of time in response to mechanical stress.

serotonin

play a role in the rate and regulation of normal bone remodeling because it affects osteoblast differen- tiation

bones

primary organs of the skeletal system, rigid framework of body

growth hormone

produced by the anterior pituitary gland. It affects bone growth by stimulating the liver to form another hormone called insulin-like growth factor (IGF). Both growth hormone and IGF directly stimulate growth of cartilage in the epiphyseal plate.

Osteoporosis

reduction in bone mass sufficient to compromise normal function

ossification

refers to the formation and development of bone connective tissue. - process requires vitamin D, C, Calcium, and phosphate

epiphyseal line

remnant of the epiphyseal plate (growth plate) in adults is a thin, defined area of compact bone

Parathyroid hormone

secreted and released by the parathyroid glands *****primary regulator of calcium homeostasis***** - detects LOW blood calcium levels and releases this hormone through parathyroid glands -stimulates vitamin D synthesis - increase renal absorption of calcium from urine -stimulates osteoclasts to initiate breakdown of bone matrix and increase blood calcium levels

lacunae

small cavities in bone that contain osteocytes

what is the function of vitamin D in its active form of calcitriol hormone in the small intestine?

stimulating absorption of calcium ions (Ca2+) from the small intestine into the blood.

calcification of bone matrix

subsequently occurs to the osteoid when hydroxyapatite crystals deposit in the bone matrix.

trabeculae

supporting bundles of bony fibers in spongy bone, it's an open lattice of narrow rods and plates of bone, second compost of compact bond - often form a meshwork of crisscrossing bars and plates of small bone pieces. -structure provides great resistance to stresses applied in many directions by distributing the stress throughout the entire framework.

what function do osteoblasts perform?

synthesizing and secreting the initial semisolid organic form of bone matrix called osteoid

simple fracture

the broken bone does not penetrate the skin

how is Parathyroid hormone (PTH) used in bone?

to increase the release of calcium from the bone into the blood, by increasing osteoclast activity.

TRUE/FALSE Compact bone and spongy bone have unique microscopic architecture

true

pathologic fracture

usually occurs in bone that has been weakened by disease.

what are the effects of significant decrease of mechanical stress?

weakens bone through both reduction of collagen formation and demineralization. example: When a person has a fractured bone and wears a cast or is bedridden, the strength of the unstressed bone decreases in the immobilized limb

when is calcification initiated?

when the concentration of calcium ions and phosphate ions reaches critical levels and precipitate out of solution, thus forming the hydroxyapatite crystals that deposit in and around the collagen fibers.

sex hormones

which begin to be secreted in relatively large amounts at puberty, dramatically accelerate bone growth. Sex hormones increase the rate of both cartilage growth and bone formation within the epiphyseal plate.