Chapter 7 learning objectives

Explain the steps in endochondral ossification of a long bone.

1. BEGINS WITH A HYALINE CARTILAGE MODEL: fetal hyaline cartilage model develops 2.cartilage calcifies, and a periosteal bone collar forms around diaphysis, 3.primary ossification center forms in the diaphysis. 4. secondary ossification centers form in epiphyses 5. bone replaces cartilage, except the articular cartilage and epiphyseal plates 6. epiphyseal plate ossify and form epiphyseal lines.

Explain the four main steps in intramembranous ossification

1. BEGINS when mesenchyme becomes thickened with capillaries 2. Osteoid undergoes calcification 3.Woven bone and surrounding periosteum form 4. lamellar bone replaces woven bone, as compact and spongy bone form

explain the four steps by which fractures heal

1. FRACTURE HEMATOMA forms from clotted blood a.)blood vessels torn within periosteum 2. FIBROCARTILAGINOUS CALLUS FORMS a.)regenerated blood capillaries infiltrating hematoma b.)fracture hematoma reorganized into a connective tissue procallus c.)fibroblast producing collagen fibers d.)chondroblast forming dense regular connective tissue e.)procallus becoming fibrocartilagionous (soft) callus 3. HARD (BONY) CALLUS FORMS a.)osteoblast adjacent to callus producing trabeculae b.)callus replaced by this bone c,)forms a hard (bony) callus d.)continues to grow and thicken 4.THE BONE IS REMODELED a.)final phase of fracture repair b.)osteoclast removing excess bony material c.)compact bone replacing primary bone d.)usually leaves a slight thickening of bone

Explain the activation of vitamin D to calcitriol.

1. UV LIGHT COVERTS PRECURSOR MOLECULE IN BLOOD TO VITAMIN D3 a.)vitamin D3 also termed cholecalciferol b.)also absorbed from small intestines from the diet c.)the major source is milk 2. VITAMIN D3 CIRCULATES THROUGH THE BODY a.)converted to calcidiol by liver enzymes b.)occurs via addition of -OH group 3.CALCIDOL CIRCULATES IN BLOOD a.)converted to calcitriol by kidney b.)another -OH group added c.)becomes the active form of Vitamin D3, calcitriol d.)presence of parathyroid hormone increases rate of step e.)more calcitriol formed when PTH present

Compare and contrast the five zones of the epiphyseal plate, and describe how growth in length occurs there.

1. ZONE OF RESTING CARTILAGE: a.)nearest the epiphysis b.)composed of small chondrocytes distributed throughout the matrix c.) resembles mature hyaline cartilage d.)secure epiphysis to spiphyseal plate. 2. ZONE OF PROLIFERATING CARTILAGE: a.)chondrocytes undergo rapid mitotic division b.)become aligned into longitudinal columns of flattened lacunae c.)columns parallel to diaphysis. 3. ZONE OF HYPERTROPHIC CARTILAGE a.)chondrocytes cease to divide b.)chondrocytes begin to hypertrophy c.)walls of the lacunae become thin 4.ZONE OF CALCIFIED CARTILAGE: a.)composed of 2 to 3 layers of chodrocytes b.)minerals deposited between columbs of lacunae c.)destroys chondrocytes 5.ZONE OF OSSIFICATION: a.)walls break down between lacunae in columns b.)spaces invaded by capillaries and osteoprogenitor cells c.)new bone matrix deposited on the calcified cartilage matrix INTERSTITIAL GROWTH: BONE GROWTH IN LENGTH: a.)occurs specifically WITHIN ZONE 2 (proliferation cartilage) and ZONE 3 (hypertrophic cartilage) b.)pushes zone of resting cartilage towards the epiphysis c.)flexible hyaline ccartilage replaced by bone d.)new hyaline cartilage replaced by bone e.)similar to endochondral ossification during development EPIPHYSEAL PLATE: a.)maintains tickness during childhood b.)at maturity, shows slow rate of of cartilage production c.)also shows increased osteoblastic activity d.)narrows until it disappears (interstitial growth stops) e.)remnant in an internal thin line of compact bone (termed epipyseal line

Describe how aging influences bone structure

1.Decreases tensile strength of bone a.)reduce rate of protein synthesis by osteoblasts b.)relative amount of inorganic material increases c.)become brittle and susceptible to fractures 2. bone loss of calcium and other materials a.)bones thinner and weaker b.)insufficient ossification, termed osteopenia

Explain how parathyroid hormone and calcitriol function together to regulate blood calcium levels.

1.Elevate blood calcium 2.Return calcium within homeostatic range 3.Regulated by negative feedback a.)decreased blood calcium stimulating PTH release b.)PTH and calcitriol triggering increase in blood calcium c.)increase inhibiting further release of PTH

Explain the effect of mechanical stress on bone remodeling

1.Occurs in weight-bearing movement and exercise 2.Required for normal bone remodeling 3.Detected by osteocytes and communicated to osteoblasts (increased synthesis of osteoid) 4.Causes increase in bone strength 5.Results from skeletal contraction and gravitational forces 6.INCREASED BONE MASS a.)from lifting 7.DECREASED BONE MASS a.)from removal of mechanical stress

Describe the steps of appositional growth.

BONE GROWS IN DIAMETER 1. occurs within the periosteum 2. bone matrix deposited within layers parallel to surface 3. layers termed external circumferential lamellae a.)as they increase in number, structure increases in diameter 4. osteoclasts resorb bone matrix along medullary cavity 5. transforms infant bone into larger adult bone

Explain bone matrix formation and resorption

BONE MATRIX FORMATION: 1. Begins with secretion of osteoid 2. proceeds with CALCIFICATION. when hydroxapatite crystal deposited (calcium and phosphate ions precipitating out, forming crystals) 3. process requires vitamin D: enhances calcium absorption from gastrointestinal tract 4. requires vitamin C: needed for collagen formation. 5. requires calcium and phosphate for calcification BONE MATRIX RESORPTION: 1. bone matrix destroyed by substance released from osteoclast. 2. proteolytic enzymes released from lysosomes within osteoclasts: chemically digest organic matrix components 3.calcium and phosphate dissolved by hydrochloric acid 4. may occur when blood calcium levels low

Compare the structure of compact bone and spongy bone.

COMPACT BONE: Dense or cortical bone, solid. In long bones, compact bone forms the solid external walls of the bone SPONGY BONE: Cancellous or trabecular bone, porous, like a sponge, located internally within the epiphyses

Compare and contrast compact and spongy bone

COMPACT BONE: also called DENSE or CORTICAL bone, relatively dens connective bone tissue, appears white, smooth, and solid. SPONGY BONE: also called CANCELLOUS or TRABECULAR bone, located internal to compact bone, appears porous, 20% of bone mass.

Describe the general functions of bone.

FUNCTION: support and protection, movement, Hemopoiesis, storage of mineral and energy reserves.

Explain the structural components of a long bone.

GREATER IN LENGTH THAN WIDTH, have elongated, cylindrical shaft (diaphysis), MOST COMMON BONE SHAPE, found in UPPER LIMBS and LOWER LIMBS. (e.g., arm, forearm, fingers, thigh, leg, toes) VARY IN SIZE.

Identify the types and locations of cartilage within the skeletal system.

HYALINE CARTILAGE: end of sternum, ribs, and larynx. FIBROCARTILAGE: resists compression and tension, intermediate between elastic and hyaline location pads of some joints. ELASTIC CARTILAGE: allows great flexibility. external ear, epiglottis, Eustachian

Describe the composition of bone's matrix

INORGANIC COMPONENTS: made of salt crystal, primarily calcium phosphate, interacts with calcium hydroxide (forms crystals of hydroxyapatite) other substances incorporated into crystals (calcium carbonate, sodium magnesium ions) crystals deposited around collagen fibers, harden the matrix and account for relative rigidity of bones. PROPORTIONS OF ORGANIC AND INORGANIC SUBSTANCES: correct proportion allows optimal functioning, loss of protein resulting in brittle bone, insufficient calcium resulting in soft bone.

Differentiate between intramembranous ossification and endochondral ossification

INTRAMEMBRANOUS OSSIFICATION: also known as DERMAL OSSIFICATION, produces: flat bones of the skull, some of the facial bones, mandible, central part of the clavicle. ENDOCHONDRAL OSSIFICATION: produces MOST OF THE BONES OF THE SKELETON including: bones of the upper and lower limbs, pelvis, vertabrae, ends of the clavicle.

Compare the gross anatomy of other bones to that of a long bone.

LONG BONE- Contains the shaft (diaphysis) which holds yellow marrow. Bone ends (epiphyses) which are covered with articular cartilage. Membranes (periosteum) coves the external surface of the entire bone. SHORT, FLAT, AND IRREGULAR BONES- Thin plates of spongy bone (dipole) covered by compact bone. Covered inside and outside by connective tissue membrane called periosteum and endosteum. Red Marrow found within trabecular cavity (spongy bone) of LONG BONES and in the dipole of SHORT BONES.

Describe the four major classes of bones as determined by shape.

LONG bone, SHORT bone, FLAT bone, IRREGULAR bone.

Explain the general function of blood vessels and nerves that serve a bone.

NERVES THAT SUPPLY BONE: accompany blood vessels through foramen, innervate bone, periosteum, endosteum, and marrow cavity, mainly sensory nerves

Name the four types of bone cells and their functions.

OSTEOPROGENITOR CELLS: stem cells dervied from mesenchyme, PRODUCE CELLS THAT MATURE TO BECOME OSTEOBLASTS, located in periodsteum and endosteum. OSTEOBLAST: often positioned side by side on bone surfaces, SYNTHESIZE AND SECRETE OSTEOID (intital semisolid form of bone matrix, later calcifies) becomes entrapped withing the matrix they produce. OSTEOCYTES: mature bone cells derived from osteoblasts, have lost bone forming ability, maintin bone matrix, detect mechanical stress on bone, may trigger deposition of new bone matrix. OSTERCLASTS: Large, multinuclear phagocytic cells, derived from fused bone marrow cells, ruffled border to increase surface area exposed to bone, INVOLVED IN BREAKING DOWN BONE.

Identify bones that are produced by intramembranous ossification.

PRODUCES: flat bones of the skull some of the facial bones mandible central part of the clavicle

Compare and contrast the structure and location of the two types of bone marrow

RED MARROW: is HEMOPOIETIC (blood cell forming) found mainly in the flat bones hip bone, breast bone, skull, ribs, vertebrae and shoulder blades YELLOW MARROW: is PRODUCT OF RED BONE MARROW DEGENERATION, FATTY SUBSTANCE, found in the medullary cavity the hollow interior of the middle portion of long bones.

Identify the hormones that influence bone growth and bone remodeling, and describe their effects.

Sex hormones (estrogen and testosterone) ---> Begin to secrete in relatively large amoounts at puberty. These hormones dramatically accelerate bone growth; they increase the rate of cartilage growth and bone formation within the epiphyseal plate. Growth hormone (insulin-like growth factor) ---> Produced by the anterior pituitary gland. It affects bone growth by stimulating the liver to form another hormone called somatomedin. Thyroid hormone ---> Secreted by the thyroid gland and stimulates bone growth by stimulating metaboliic rate of osteoblasts. Glucocorticoids ---> Increase bone loss and, in children, impair bone growth when there are chronnically high levels of glucocorticoids. Serotonin ---> Inhibits osteoprogenitor cells from differentiating into osteoblasts when there are chronically high levels of serotonin.

Define bone remodeling, and give examples of how it varies in different bones and different portions of the same bone

a.)Continual process of bone deposition and resorption. b.)continues through adulthood c.)occurs at periosteal and endosteal surfaces of a bone d.)occurs at different rates: (e.g, distal part of femur replace every 4 to 6 months/ diaphysis of femur not completely replaced over a lifetime) e.)20% of skeleton replaced yearly f.)dependent on the coordinates activities of osteoblast, osteocytes, and osteoclasts.

Discuss the homeostatic system involving the hormone calcitonin and its effect on blood calcium levels.

a.)aids in regulating blood calcium levels b.)less significant than PTH or calcitrol c.)inhibits osteoclast activity in bone connective tissue (less calcium release from bone into blood) d.)stimulates kidneys to increase loss of calcium in the unrine (reducing blood calcium levels)

Discuss the release of parathyroid hormone.

a.)secreted and released by parathyroid glands b.)secreted in response to reduced blood calcium levels c. calcitriol formed more readily in the presence of PTH