Whole Chapter 6

Three types of cartilage

hyaline, elastic, fibrocartilage

hyaline cartilage

most abundant skeletal cartilage, their chondrocytes are spherical and their fibers are fine collagen fiber. found in articular (joint), costal (breastbone), respiratory, and nasal cartilages.

elastic cartilage

resemble hyaline cartilage but are more stretchy, only found at external ear and epiglottis

Fibrocartilage

highly compressible, consist of roughly parallel rows of chondrocytes with thick collagen fibers. found in places of pressure and stretch such as knee and back.

appositional growth

cartilage-forming cells in the surrounding perichondrium secrete new matrix against the external face of the existing cartilage tissue

interstitual growth

chondrocytes divide to grow cartilage from within

functions of bone

support, protection, anchorage (movement), mineral storage, blood cell formation, triglyceride (fat) storage, hormone production

axial skeleton

forms the long axis of the body and includes the bones of the skull, vertebral column, and rib cage

appendicular skeleton

bones of the limbs

long bones

elongated shape

short bones

roughly cube shaped (sesamoid: type of short bone), ex: wrist

flat bones

thin, flattened, curved

irregular bones

Complicated shapes, ex: vertebrae and hip bones

bone structure at 3 levels

gross, microscopic, chemical

Structure of short, irregular, and flat bones (gross)

Consist of thin plates of spongy bone covered by compact bone

structure of long bones

diaphysis, epiphysis, membranes

Diaphysis

tubular shaft that forms long axis of bone

Consists of compact bone surrounding central medullary cavity that is filled with yellow marrow in adults

membranes

white, double layered membrane called periosteum covers surface of bones, minus joint surfaces. Outer layer of periosteum is dense irregular tissue while inner layer contains osteoprogenitor cells. Periosteum richly supplied with nerve fibers and blood vessels.

hematopoietic tissue in bones (gross)

red marrow in adults is found in flat bones of skull, ribs, hips, vertebrae, and also in thigh bone and long bone of arm

bone markings

bones display projections, depressions, and openings that serve as sites of muscle, ligament, and tendon attachment, as joint surfaces, or as conduits for blood vessels

microscopic anatomy of bones

cells of bone tissue, anatomy of compact bone, anatomy of spongy bone

osteoprogenitor cells

bone stem cells

Osteoblasts

bone forming cells

osteocytes

mature bone cells

bone lining cells

flat cells found on bone surfaces where bone remodeling is not going on, maintain bone matrix

Osteclasts

break down bone

Osteon

elongated cylinder, tiny weight bearing pillars

canals of compact bone

central canals run through core of each osteon, while perforating canals connect blood and nerve supply

Canaliculi (compact bone)

small channels that connect lacunae; allow for nutrient exchange and cellular communication between osteocytes

interstitial lamellae

fill spaces between osteons

circumferential lamellae

located deep to periosteum and superficial to endosteum and extend around entire circumference of the diaphysis and resist twisting of long bone

microscopic anatomy of spongy bone

may look unorganized, but they align precisely along lines of stress and help the bone resist stress

chemical composition of bone

organic (bone cells and osteoid to resist tension) and inorganic components (mineral salts to resist compression)

Ossification (osteogenesis)

process of bone tissue formation

endochondral ossification

process in which bone forms by replacing hyaline cartilage (forms essentially all bones below base of the skull)

1. bone collar forms around diaphysis of the hyaline cartilage model

2. cartilage calcifies in the center of the diaphysis and then develops cavities

3. the periosteal bud invades the internal cavities and spongy bone forms

4. the diaphysis elongates and a medullary cavity forms

5. the epiphysis ossify

intramembranous ossification

bone develops from a fibrous membrane (how bones of the skull are formed)

1. ossification centers develop in the fibrous connective tissue membrane

2. osteoid is secreted and calcifies

3. immature spongy bone and periosteum forms

4. compact bone replaces immature spongy bone, just deep to the periosteum, red marrow develops

postnatal bone growth

During infancy and, youth, long bones lengthen by interstitial growth and all bones grow in thickness by appositional growth.

Growth in length of long bones

1. proliferation zone - cartilage cells undergo mitosis

2. hypertrophic zone - older cartilage cells enlarge

3. calcification zone - matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity

4. ossification zone - new bone forms

bone remodeling

Process involving bone formation and destruction in response to hormonal and mechanical factors

bone resorption

the removal of osseous tissue. osteoclasts move along a bone surface, digging depressions/grooves as they break down the bone matrix, and undergo apoptosis when complete.

bone deposition

osteoblasts deposit new bone matrix, begins as an osteoid seam. osteoid becomes calcified when concentrations of Ca 2+ and Pi are high enough

control of remodeling

continuous remodeling regulated by two control loops

1. maintaining Ca 2+ homeostasis - primarily involves parathyroid hormone (PTH). when blood levels of Ca2+ decline, PTH are released into the blood. if calcium levels are low for an extended time, the bones become so demineralized that they develop large holes.

2. keeping bone strong - Wolff's law holds that a bone grows or remodels in response to the demands placed on it.

fracture classification

1. Position of bone ends after fracture

-Nondisplaced—ends retain normal position

-Displaced—ends out of normal alignment

2. Completeness of break

-Complete—broken all the way through

-Incomplete—not broken all the way through

3. Whether skin is penetrated

-Open (compound) - skin is penetrated

-Closed (simple) - skin is not penetrated

Addition classifications of fractures

Comminuted: bone fragments into 3 or more pieces

Compression: bone is crushed

Spiral: ragged break occurs when excessive twisting forces are applied to a bone

Epiphyseal: epiphysis separates from the diaphysis along the epiphysial plate

Depressed: broken bone portion is pressed inward

Greenstick: bone breaks incompletely

Stages in healing of a bone fracture

1. Hematoma forms

2. Fibrocartilaginous callus forms

3. Bony callus formation

4. Bone remodeling

osteomalacia

disorders in which bones are poorly mineralized. osteoid is produced, but calcium salts are not adequately deposited, so bones are soft and weak. Caused by insufficient calcium or vitamin D.

Rickets

the softening and weakening of bones in children, caused by insufficient calcium or vitamin D.

osteoporosis

group of diseases in which bone resorption outpaces bone deposit, decreased density and strength of bone. factors that may contribute include decreased sex hormones, insufficient bone stress, poor diet, etc.

Paget's disease

disorder characterized by excessive bone breakdown and abnormal bone formation. the newly formed bone, pagetic bone, is hastily made and has an abnormally high ratio of spongy bone to compact bone, usually localized condition, cause unknown.

Cranial bones

enclose and protect brain, attachment site for head and neck muscles

Facial bones

-Form framework of the face

-Form cavities for the sense organs of sight, taste, and smell

-Provide openings for the passage of air and food

-Hold the teeth in place

-Anchor muscles of the face

vault of cranium

superior, lateral and posterior bones of the skull (includes forehead)

base of cranium

inferior part of the cranium

Frontal Bone of the Cranium

forms the anterior part of the skull and the forehead