A&P Chapter 7 Skeletal system: Bone Structure & Function

Osteoblasts

Osteoid is produced by?

Low blood calcium levels

Parathyroid hormone and calcitriol are secreted in response to what?

yellow, adult

Potential energy in the form of lipids is stored in _____ bone marrow in shafts of some ____ bones

Calcitonin

Promotes calcium deposition in bone and inhibits osteoclast activity

Nutrient foramen

Small opening or hole in the bone where one nutrient artery enters and on nutrient vein exits.

diploë

Spongy bone is also called _____ in flat skull bones.

Bone remodeling

The constant, dynamic process of continual addition of new bone tissue (bone deposition) and removal of old bone tissue (bone resorption) is a process called?

optimally

The correct proportion of organic & inorganic substances in the matrix of bone allows it to function _______.

Hormone

The decrease in _____ levels contributes to reduction in bone mass.

4-6 months

The distal part of the femur (thigh bone) is replaced every __ to __ months, whereas the diaphysis of this bone may not be completely replaced during an individuals lifetime.

Perforating fibers

The periosteum is anchored to the bone by numerous collagen fibers called _______ fibers, which run perpendicular to the diaphysis.

faster

The rate of bone formation occurs at a _____ rate than the rate of cartilage growth

Epiphyseal line

The remnant of the epiphyseal plate in adults is a thin, defined area of compact bone caked the?

harden, inflexibility

The salt crystals _____ the bone matrix and account for the rigidity or relative _______ of bone that provide its compressional strength.

Bone marrow

The soft connective tissue of bone

thicker

Typically bones become ______ due to repetitive and stressful exercise.

osteons, trabeculae

Unlike compact bone, spongy bone contains no ______, but contains _______.

Some alter rates of chondrocyte, osteoblast, and osteoclast activity which influences bone composition and growth patterns

What activity can hormones alter?

1.) Decreased tensile strength of bone -reduced rate of protein synthesis by osteoblasts -relative amount of inorganic material increases -become brittle and susceptible to fracture 2.) Bone loss of calcium and other minerals -bones thinner and weaker -insufficient ossification, termed osteopenia

What are the 2 ways aging affects bone?

Long bones Short bones Flat bones Irregular bones

What are the 4 classes of bone determined by shape?

-Support and protection -Movement -Hemopoiesis -Storage of mineral and energy reserves

What are the basic functions of bone?

The central (Haversian) canal Concentric lamallae Osteocytes Lacunae Canaliculi Perforating canals Circumferential lamallae Interstitial lamallae

What are the components of an osteon?

1. Fracture hematoma forms, 2. fibrocartilaginous (soft) callus forms, 3. hard (bony) callus forms. 4. bone is remodeled

What are the four basic steps in fracture repair?

Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts

What are the four types of cells found in bone connective tissue?

located in the spongy bone and medullary cavity of long bones

What are the locations of Red bone marrow in children?

1. Mitotic activity occurs in stem cells within the perichondrium. 2. New undifferentiated stem cells and new chondroblasts are formed. Chondroblasts produce new matrix at the periphery of old cartilage. 3. Chondroblasts push apart and become chondrocytes.

What are the steps of appositional growth in hyaline cartilage?

1. A chondrocyte within a lacuna is stimulated to mitotically divide. 2. Two cells, now called chondroblasts, occupy a single lacuna. 3. Chondroblasts secrete new material and are pushed apart. 4. Each is now called a chondrocyte. Cartilage continues to grow internally.

What are the steps of interstitial growth in hyaline cartilage?

1.) Ossification centers form within thickened regions of mesenchyme -Some cells becoming osteoprogenitor cells -Some cells becoming osteoblasts secreting osteoid 2.) Osteoid undergoes calcification -Calcium salts deposited onto osteoid and crystallize -Entrapped cells becoming osteocytes 3.) Woven bone and surrounding periosteum form -At first, bone immature and poorly organized -Termed woven bone (primary bone) -Mesenchyme surrounding woven bone beginning to form periosteum 4.) Lamellar bone (secondary bone) replaces woven bone -Compact and spongy bone formed from trabeculae -Typical structure of a flat cranial bone -composed of two external layers of compact bone -layer of spongy bone in between

What are the steps of intramembranous ossification?

1. Outer fibrous layer of dense irregular connective tissue -protects bone from surrounding structures -anchors blood vessels and nerves to bone surface -attachment site for ligaments and tendons 2. Inner cellular layer -includes osteoprogenitor cells, osteoblasts, and osteoclasts

What are the two layers of the periosteum? What are the functions of the outer layer? What does the inner layer consist of?

Calcitrol (an active form of Vitamin D) & Parathyroid hormone

What are the two primary hormones that regulate blood calcium?

Thigh bone

What bone is the femur?

Flat bones of the skull, some of the facial bones, the mandible, the central part of the clavicle

What bones are formed from intramembranous ossification?

Chondroblasts secrete the cartilage matrix. Mature chondroblasts trapped in the matrix are known as chondrocytes. They maintain the matrix.

What cells secrete the cartilage matrix? What cells maintain the matrix?

Osteopenia

What condition displays a reduction in bone mass by loss of calcium and other minerals, but without yet compromising normal function?

They give bone tensile strength by resisting stretching and twisting & contribute to bone flexibility.

What does an osteoid and its organic components do for bone?

Vitamin D (which enhances calcium absorption from the gastrointestinal tract: Vitamin C (which is required for collagen formation) Calcium & phosphate for calcification

What does the process of bone formation require?

Growth hormone

What hormone stimulates the liver to produce somatomedin, causing cartilage proliferation at the epiphyseal plate?

The coordinated activities of osteoblasts, osteocytes, and osteoclasts.

What is bone remodeling dependent upon?

-initiation of muscle contraction -exocytosis of molecules from cells, including neurons -stimulation of the heart by pacemaker cells -blood clotting

What is calcium required for?

ATP utilization the plasma membrane

What is phosphate required for? Where is it an important component?

Osteoblasts secrete osteoid and build bone. Osteoclasts break down (resorb) bone.

What is the function of an osteoblast? An osteoclast?

It is made up of salt crystals -primarily calcium phosphate Ca3(PO4)2

What is the inorganic portion of the matrix of bone connective tissue?

Osteoid

What is the organic component of the matrix of bone connective tissue?

-Population of cells scattered through matrix of protein fibers -Embedded in a gel-like ground substance -includes proteoglycans but not calcium -Resilient and flexible -High percentage of water -Highly compressible and a good shock absorber -Avascular and contains no nerves

What is the structure of hyaline cartilage?

Appositional growth Interstitial growth

What is the term for bone growth in width? For bone growth in length?

The organic component is osteoid, composed of collagen, proteoglycans, and glycoproteins. The inorganic component is formed from hydroxyapatite, which includes calcium phosphate. Other salts and ions are also incorporated, e.g., calcium carbonate and sodium and magnesium ions.

What organic substances compose bone matrix? What inorganic substances?

Kidney (which coverts vitamin D3 to calcidiol); liver (which converts calcidiol to calcitriol)

What organs are involved in activating vitamin D3 to calcitriol?

The metaphysis

What portion of bone contains the epiphyseal plate?

Short bones

What type of bones have a length nearly equal to their width?

-in selected portions of the axial skeleton e.g., flat bones of the skull, vertebrae, ribs, sternum, ossa coxae -in proximal epiphyses of humerus and femur

Where do adults have red bone marrow?

Within the periosteum

Where does appositional growth occur in bone?

in red bone marrow connective tissue that contains stem cells that form blood cells and platelets.

Where does hemopoiesis occur?

Interstitial growth occurs within the internal regions of cartilage. Appositional growth occurs along the cartilage's outside edge.

Where does interstitial growth of cartilage occur? Appositional growth?

Occurs at both the periosteal and endosteal surfaces of bone.

Where does the ongoing process of bone remodeling occur?

Stored in bone and released into blood as needed

Where is Calcium & Phosphate stored and then released?

Proximal epiphyses of humerus and femur and portions of axial skeleton: skull, vertebrae, ribs, sternum, ossa coxae

Where is red bone marrow found in the adult skeleton?

Spongy

____ bone within the epiphysis resists stress that is applied from many directions.

Compact, spongy

_____ bone in our skeleton is replaced at a slower rate than the ____ bone.

Proteolytic enzymes, Hydrochloric acid (HCL), calcium & phosphate ions

________ enzymes released from lysosomes within the osteoclasts chemically digest the organic components (collagen fibers and proteoglycans) of the matrix, while ____________ dissolves the mineral parts (calcium & phosphate) of the bone matrix. The liberated ______ and ______ ions enter the blood. ((during bone resorption))

Achondroplasia

________ is characterized by abnormal conversion of hyaline cartilage to bone.

Bone resorption

a process whereby bone matrix is destroyed by substances released from osteoclasts into the extracellular space adjacent to the bone.

Stress fracture

a thin break caused by increased physical activity in which the bone experiences repetitive loads (e.g., as seen in some runners)

Chondroblasts

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

Osteoid

composed of: -collagen protein -a semisolid ground substance of proteoglycans -glycoproteins that suspends and supports the collagen fibers.

Ligaments

dense regular connective tissue that anchors bone to bone

Tendons

dense regular connective tissue that anchors muscle to bone

Calcitonin

is released from the thyroid gland in response to HIGH blood calcium levels; it is also secreted in response to stress from exercise.

Parathyroid hormone (PTH)

is secreted & released by the parathyroid glands in response to reduced blood calcium levels

Red bone marrow transplant

may be necessary if bone marrow was destroyed by radiation or chemotherapy, or abnormally functioning (as is the case in an individual with leukemia, where the marrow produces abnormal blood cells)

Osteopenia

- insufficient ossification (decreased calcification or density of bone) -Occurs slightly in all people with age -Begins as early as age 35-40 -Osteoblast activity declining; osteoclast activity at previous levels -Vertebrae, jaw bones, epiphyses losing large amount of mass -Women losing more of their skeletal mass every decade than men

Intramembranous Ossification

-Also known as dermal ossification -Produces: flat bones of the skull some of the facial bones mandible central part of the clavicle -Begins when mesenchyme becomes thickened with capillaires

Red bone marrow

-Also known as myeloid tissue -Hemopoietic (blood cell forming) -Contains reticular connective tissue, immature blood cells, and fat

Ossification

-Also known as osteogenesis -The formation and development of bone connective tissue -Begins in the embryo -Continues through childhood and adolescence as the skeleton grows -Begins by the eighth through twelfth weeks of embryonic development -Occurs through intramenbrous ossification or endochondral ossification

Endochondral ossification

-Begins with a hyaline cartilage model -Produces most bones of the skeleton, including: -bones of the upper and lower limbs -pelvis -vertebrae -ends of the clavicle

Long bones

-Bones greater in length than width -Have elongated, cylindrical shaft (diaphysis) -Most common bone shape -Found in upper and lower limbs e.g., arm, forearm, fingers, thigh, leg, toes -Vary in size

Irregular bones

-Bones that have elaborate shapes -E.g., vertebrae, ossa coxae (hip bones) -E.g., several bones in the skull (ethmoid, sphenoid)

Flat bones

-Bones that have flat, thin surfaces, may be slightly curved -Provide surfaces for muscle attachment -Protect underlying soft tissues -Form: the roof of the skull the scapulae (shoulder blades) the sternum (breastbone) the ribs

Short bones

-Bones with a length nearly equal to width -E.g., carpal bones (wrist bones) -E.g., sesamoid bones, bones along tendons of muscles -E.g., patella (kneecap), largest sesamoid bone

Rickets

-Disease caused by vitamin D deficiency in childhood -Characterized by deficient calcification of osteoid tissue -Acquire bowlegged appearance -Disturbances in growth, hypocalcemia, and tetany (cramps and twitches) -caused by low blood calcium -Continues to occur in some developing nations -Incidence increasing in urban U.S. children

Short, flat, & irregular bones

-External surface generally composed of compact bone -Interior composed entirely of spongy bone -Lack a medullary cavity

Osteoblasts

-Formed from osteoprogenitor stem cells -Often positioned side by side on bone surfaces -Synthesize and secrete osteoid -initial semisolid form of bone matrix -later calcifies -Become entrapped within the matrix they produce -differentiate into osteocytes

Decreased bone mass

-From removal of mechanical stress -Reduced collagen formation -Demineralization e.g., decreased strength of unstressed bone in immobilized fracture

Endosteum

-Incomplete layer of cells that covers all internal surfaces of the bone within the medullary cavity -Contains osteoprogenitor cells, osteoblasts, and osteoclasts

Osteoclasts

-Large, multinuclear, phagocytic cells -Derived from fused bone marrow cells -Exhibit a ruffled border where they contact the bone, to increase surface area exposed to bone -Often located within or adjacent to a depression or pit on bone surface -termed resorption lacuna -Involved in breaking down bone in a process called bone resorption

Osteocytes

-Mature bone cells derived from osteoblasts -Have lost bone forming ability when enveloped by calcified osteoid -Maintain bone matrix -Detect mechanical stress on bone -May trigger deposition of new bone matrix at the surface if stress is detected

Mechanical stress

-Occurs in the form of weight-bearing movement and exercise -Required for normal bone remodeling

Bone connective tissue

-Primary component of bone -Also called osseous connective tissue -Composed of cells and extracellular matrix

Bones

-Primary organs of the skeletal system -Form the rigid framework of the body

Osteoporosis

-Reduced bone mass sufficient to compromise normal function -Occurs in a significant percentage of older women -Occurs in a smaller percentage of older men

Osteitis Deformans

-Results from disruption between osteoclast and osteoblast function -Characterized by excessive bone resorption followed by excessive bone deposition -Larger osteoclasts resorbing bone at higher rate -Newly deposited bone poorly formed -Most commonly affected bones: -pelvis, skull, vertebrae, femur, tibia -Symptoms of bone deformity and pain

Increased bone mass

-Results from weight-bearing activities -e.g., weight lifting, walking, or running -Can ______ total ____ ____ throughout the lifetime

Osteoprogenitor cells

-Stem cells derived from mesenchyme -When they divide through mitosis, another stem cell is produced along with a "committed cell" that matures to become an osteoblast -Located in periosteum and endosteum

Calcification

-Subsequently occurs to osteoid formation when hydroxyapatite crystals deposit in the bone matrix. -Occurs when the concentration of calcium ions and phosphate ions reach critical levels and precipitate out of solution, thus forming the hydroxyapatite crystals that deposit in and around the collagen fibers -also known as mineralization

Serotonin

-a chemical signaling molecule called a neurotransmitter for the nervous system -also acts like a hormone in other body systems -inhibits osteoprogenitor cells from differentiating into osteoblasts when there are chronically high levels of ______.

Glucocorticoids

-a group of steroid hormones that are released from the adrenal cortex and regulate blood glucose levels -cortisol is the primary ________ - increase bone loss, and in children, impair bone growth when there are chronically high levels of _______ (e.g., cortisol, cortisone)

Spongy bone

-also called cancellous or trabecular bone -located internal to compact bone -appears porous -makes up approximately 30% of the total bone mass -interior cavity of bone contains a connective tissue that is either red bone marrow or yellow bone marrow

Compact bone

-also called dense or cortical bone -a relatively dense connective bone tissue that appears white, smooth, and solid -makes up approximately 80% of the total bone mass

Growth hormone (somatotropin)

-also called insulin-like growth factor -is produced by the anterior pituitary gland -affects bone growth by stimulating the liver to form another hormone called somatomedin -both directly stimulate growth of cartilage in the epiphyseal plate

Interstitial lamellae

-are either the components of compact bone between osteons or are the leftover parts of osteons that have been partially resorbed -look like a "bite" taken out of them -incomplete and typically have no central canal

Bone formation

-begins when osteoblasts secrete the initial semisolid organic form of bone matrix (osteoid) -proceeds with calcification -requires: Vitamin D, Vitamin C, Calcium, & Phosphate

Chondrocytes

-chondroblasts that have become encased within the matrix -occupy small spaces called lacunae -maintain the matrix

Perforating canals

-component of an osteon -contain blood vessels and nerves -run perpendicular to the central canals -help connect multiple central canals within different osteons, thus creating a vascular and innervation connection among the multiple osteons

The central canal

-component of an osteon -cylindrical channel -lies in the center of the osteon and runs parallel to it -blood vessels and nerves that supply the bone travel within

Osteocytes

-component of an osteon -mature bone cells -found in small spaces between adjacent concentric lamellae (lacunae) -maintain bone matrix

Concentric lamellae

-component of an osteon -rings of bone connective tissue -surround the central canal & form the bulk of the osteon -contain collagen fibers -oriented at an angle 90 degrees from previous and next lamellae -The alternating pattern of collagen fiber direction gives bone part of its strength and resilience

(External & Internal) Circumferential lamellae

-component of an osteon -rings of bone immediately internal to the periosteum of the bone (external ____ ______) or internal to the endosteum (internal ______ ______) -run the entire circumference of bone

Canaliculi

-component of an osteon -tiny interconnecting channels within bone connective tissue that extend from each lacuna -travel through lamellae -connect to other lacunae and the central canal -house osteocyte projections permitting intercellular contact & communication -allow travel of nutrients, minerals, gases, and wastes through the cytoplasmic extensions within these passageways between blood vessels of the central canal and the osteocytes

Trabeculae

-component of spongy bone -open lattice of narrow rods and plates of bones -bone marrow (when present) fills spaces between _____ -form a meshwork of crisscrossing bars and plates of small bone pieces -provide great resistance to stresses

Perichondrium

-dense irregular connective tissue sheet -covers cartilage and helps maintain its shape

Diaphysis

-elongated, usually cylindrical shaft of a long bone -provides for leverage and major weight support -compact bone has thin spicules of spongy bone extending inward

Medullary cavity

-hollow, cylindrical space within the diaphysis -contains red bone marrow in children -contains yellow bone marrow in adults

Thyroid hormone

-hormone secreted by the thyroid gland -stimulates bone growth by influencing the basal metabolic rate of bone cells -helps maintain normal activity at the epiphyseal plates until puberty -Hypothyroidism that results from low thyroid hormone levels leads to impaired skeletal growth and other problems in children

Epiphyseal (growth) plate

-in metaphysis -thin layer of hyaline cartilage -provides for the continued lengthwise growth of the bone -remnant in adults termed the epiphyseal line

Estrogen & testosterone

-sex hormones -begin to be secreted in relatively large amounts at puberty -dramatically accelerate bone growth -increase rate of cartilage growth and bone formation in epiphyseal plate -results in increased length of long bones & height -high levels of these hormones at puberty signal the beginning of the end for growth at the epiphyseal plate

Osteon

-the basic functional and structural unit of mature compact bone -oriented parallel to the diaphysis of the long bone -when viewed in a cross section, it has the appearance of a bull's-eye target

Hyaline cartilage

-type of cartilage -attaches ribs to the sternum -covers the ends of some bones -cartilage within growth plates -model for formation of most bones

Fibrocartilage

-type of cartilage -weight-bearing cartilage that withstands compression -forms intervertebral discs -forms pubic symphysis (cartilage between bones of the pelvis) -forms cartilage pads of the knee joints

Hormone

A _____ binds to cellular receptors of specific cells to initiate cellular change.

Fracture hematoma

A bone fracture tears blood vessels inside the bone and within the periosteum, causing bleeding. This bleeding results in a _____ ______ that forms from the clotted blood.

Resorption lacuna

A depression or pit on the bone surface

brittle bones

A loss of protein, or the presence of abnormal protein, results in?

2 to 3 months

A simple fracture takes about __ to __ months to heal while a compound fracture takes longer.

Periosteum

A tough sheath covering the outer surface of bone except for the areas covered by articular cartilage.

compact, spongy

An epiphysis is composed of an outer thin layer of _____ bone and an inner, more extensive region of ____ bone.

Periosteum

Blood vessels enter bones from the _______.

nutrients & oxygen

Blood vessels supply _____ & _____ required by cells & remove waste products from bone cells.

overcomes

Bone growth eventually ______ the region of cartilage, replacing all cartilage with bone.

Vascularized

Bone is highly ______ (meaning it is supplied by many blood vessels) especially in regions containing spongy bone.

blood calcium

Bone resorption may occur when _____ ______ levels are low.

-skeletal muscles -soft tissues -some organs

Bones serve as attachment sites for?

Fractures

Breaks in bone are termed?

-muscle contraction -blood clotting -nerve signal transmission

Calcium is one of the minerals stored and released from bone. What are some of its functions within the body?

Hydroxyapatite, which is Ca10(PO4)6(OH)2

Calcium phosphate and calcium hydroxide interact to form crystals of __________.

Osteons

Compact bone is composed of small cylindrical structures called _____.

Articular cartilage

Covering the joint surface of an epiphysis covered by a thin layer of hyaline cartilage, called the ______ cartilage, that helps reduce friction and absorb shock in moveable joints.

simultaneously

During early embryonic development interstitial and appositional growth occur ___________.

Cortisol

High amounts of ______ (which is a glucocorticoid) increase bone loss and, in children, impairs growth at the epiphyseal plate. It is because of this that a child's growth is monitored if receiving high doses of glucocorticoids as an anti-inflammatory such as a treatment for children with severe asthma.

- Inhibits osteoclast activity (less calcium released from bone into blood); - stimulates kidneys to increase the loss of calcium in the urine (reducing calcium blood levels)

How does calcitonin work on bone connective tissue and the kidneys to regulate blood calcium levels?

The diaphysis The epiphyses

In what portion of a long bone do primary ossification centers form? Secondary ossification centers?

The intervertebral discs, the pubic symphysis, and the cartilage pads of the knee joints

In what three locations of the body do you find fibrocartilage?

Parathyroid hormone

Increases blood calcium levels by encouraging bone resorption by osteoclasts

soft bones

Insufficient calcium results in?

20%

It is estimated that about __% of the adult human bone is replaced yearly.

Sensory

It is mainly ____ nerves that accompany blood vessels that signal injuries of the skeleton.

Yes, it may occur during severe anemia - a condition with reduced erythrocytes (red blood cells), resulting in insufficient oxygen reaching blood cells of the body - When it converts back, it is a change that facilitates the production of additional erythrocytes

May yellow bone marrow convert back into red bone marrow? If so, when?

osteocytes, osteoblasts

Mechanical stress is detected by _______ and communicated to ______.

Hormones

Molecules released from one cell into the blood, and travel throughout the body to affect other cells are defined as?

calcium & phosphate

Most of the body's reserves for the minerals _____ & _____ are stored within and then released from bone.

Yellow bone marrow

Much of the red bone marrow degenerates and turns into a fatty substance called ______________ as children mature into adults.

Nutrient foramen

Nerves that supply bones accompany blood vessels through the ______ ______ and innervate the bone as well as its periosteum, endosteum, and marrow cavity.

Compound fracture

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

Cartilage

semi-rigid connective tissue that is more flexible than bone

Simple fracture

the broken bone does not penetrate the skin

Proximal epiphysis

the end of the long bone closest to the body trunk

Distal epiphysis

the end of the long bone farthest from the trunk

Epiphysis

the expanded knobby region at the end of a long bone

Hemopoiesis

the process of blood cell production

Metaphysis

the region in a mature bone sandwiched between the diaphysis and epiphysis

Lacunae

the small spaces that house an osteocyte

Pathologic fracture

usually occurs in bone that has been weakened by disease