Chapter 6: Bones and Skeletal Tissues

What is the human skeleton initially made up of?

cartilages and fibrous membranes

What is skeletal cartilage made of?

some variety of cartilage tissue sculpted to fit its body location and function

What does cartilage primarily consist of?

water

hyaline cartilage

fibrocartilage

elastic cartilage

How is cartilage resilient?

it has the ability to spring back to its original shape after being compressed

True or false: cartilage contains nerves and blood vessels

false

What is the perichondrium?

a layer of dense irregular connective tissue surrounding cartilage that contains the blood vessels that nourish the cartilage cells

What does the perichondrium do?

acts as reinforcement to resist outward expansion when the cartilage is compressed

What is the thickness of cartilage limited by?

the distance nutrients can diffuse through the matrix to reach the cells

What are the three types of cartilage tissue?

hyaline, elastic, and fibrocartilage

What components do all three types of cartilage have

chondrocytes enclosed in small cavities (lacunae) within an extracellular matrix containing a jellylike ground substance and fibers

What is the most abundant skeletal cartilage?

hyaline

What does hyaline cartilage look like when freshly exposed?

frosted glass

What is the function of hyaline cartilage?

to provide support with flexibility and resilience

What are the shape of chondrocytes in hyaline cartilage?

spherical

What is the only fiber type in hyaline cartilage?

fine collagen fibers

What are examples of hyaline cartilage?

• articular cartilage

• costal cartilage

• respiratory cartilage

• nasal cartilage

How are elastic cartilages different from hyaline cartilages?

they contain more stretchy elastic fibers and are better able to stand up to repeated bending

Where do fibrocartilages occur?

in sites that are subjected to both pressure and stretch, such as the padlike cartilages of the knee and the discs between vertebrae

Why does cartilage have a flexible matrix?

to accommodate mitosis; it is ideal to use to rapidly lay down the embryonic skeleton and to provide for new skeletal growth

What occurs in appositional growth?

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

What occurs in interstitial growth?

the lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within

When does cartilage growth typically end?

during adolescence, when the skeleton stops growing

What is cartilage surrounded by?

perichondrium

What is bone surrounded by?

periosteum

Where are blood vessels and nerves in cartilage?

only in perichondrium

Where are blood vessels and nerves in bone?

throughout the bone

What are in the lacunae of cartilage?

chondrocytes

What are in the osteocytes of bone?

osteocytes

What is the adaptability of the extracellular matrix in cartilage?

flexible

What is the adaptability of the extracellular matrix in bone?

rigid

What is cartilage’s extracellular matrix made by?

chondroblasts

What is bone’s extracellular matrix made by?

osteoblasts

What type of growth occurs in cartilage?

both appositional and interstitial

What type of growth occurs in bone?

only appositional

How does bone provide support?

it provides a framework that supports the body and cradles its soft organs

How does bone provide protection?

the fused bones of the skull protect the brain, the vertebrae surround the spinal cord, and the rib cage helps protect the vital organs of the thorax

How does bone provide anchorage?

by allowing skeletal muscles to use them as levels to move the body and its parts

How does bone provide mineral storage?

by serving as a reservoir for calcium and phosphate, which are released into the blood in their ionic form as needed for distribution to all parts of the body

How does bone serve as a site for blood cell formation?

hematopoiesis occurs in the red bone marrow of certain bones

How does bone serve as a site for fat storage?

fat is stored as yellow bone marrow in the cavities of long vones

How does bone produce hormones?

bones produce osteocalcin, a hormone that helps to regulate insulin secretion, glucose homeostasis, and energy expenditure

Axial skeleton

bones of the skull, vertebral column, and rib cage

What is the function of the axial skeleton’s bones?

to protect, support, or carry other body parts

Appendicular skeleton

bones of the upper and lower limbs and the girdles (shoulder bones and hip bones) that attach the limbs to the axial skeleton

What is the function of appendicular skeleton’s bones?

to help us to move from place to place (locomotion) and manipulate our environment

What is an example of how the unique shape of each bone fulfills a particular need?

the femur withstands great pressure, and its hollow-cylinder shape provides maximum strength with minimum weight to accommodate our upright pressure

Long bones

longer than they are wide; cylindrical shaft with two distinct and often expanded ends

Examples of long bones

all limb bones except the patella and the wrist and ankle bones

Short bones

roughly cube shaped

Examples of short bones

wrist and ankle bones

Sesamoid bones

sesame seed-shaped and form in a tendon

Example of sesamoid bones

patella

What do sesamoid bones do?

some act to alter the direction of pull of a tendon and others reduce friction and modify pressure on tendons to reduce abrasion or tearing

Flat bones

thin, flattened, and usually a bit curved

Examples of flat bones

sternum, ribs, and most cranial bones of the skull

Irregular bones

complicated shapes that fit none of the other categories

Examples of irregular bones

vertebrae and hip bones

Compact bone

the dense outer layer of the bone that looks smooth and solid to the naked eye

Spongy bone

the internal layer of the bone consisting of a honeycomb of small needle-like or flat pieces called trabeculae

What are the open spaces between trabeculae in living bone filled with?

red or yellow bone marrow

What characteristics do short, irregular and flat bones share?

• thin plates of spongy bone covered by compact bone

• compact bone is covered outside and inside by connective tissue membranes, respectively the periosteum and endosteum

• not cylindrical so they have no shafts or expanded ends

• contain bone marrow, but no well-defined marrow cavity

• hyaline cartilage covers surfaces of movable joints

Diaphysis

the shaft that forms the long axis of long bone, constructed of a relatively thick collar of compact bone

Medullary cavity

central cavity of a long bone containing yellow or red bone marrow

What is often between the medullary cavity and the compact bone?

a thin layer of spongy bone

Epiphyses

bone ends with a compact bone outer shell and spongy bone inner shell

What covers the joint surface of each epiphysis?

a thin layer of articular (hyaline) cartilage, which cushions the opposing bone ends during movement and absorbs stress

What is between the diaphysis and each epiphysis of an adult long bone?

an epiphyseal line

What is the epiphyseal line a remnant of?

the epiphyseal plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone

What is the metaphysis?

the flared portion of the bone where the diaphysis and epiphysis meet

What is the periosteum?

a glistening white, double-layered membrane that covers the external surface of the entire bone expect the join surfaces

What is the outer fibrous layer of the periosteum made of?

dense irregular connective tissue

What is the inner osteogenic layer of the periosteum made of?

osteoprogenitor cells, osteoclasts, and osteoblasts

osteoprogenitor cell

osteoblast

osteocyte

osteoclast

Why are broken bones painful and bloody?

because the periosteum is richly supplied with nerve fibers and blood vessels

What are perforating fibers?

bundles of collagen fibers that extend into the bone matrix and secure the periosteum to the underlying bone

What is the endosteum?

a delicate connective tissue membrane that covers internal bone surfaces and the trabeculae of spongy

What are the main vessels serving the diaphysis?

a nutrient artery and a nutrient vein

What is the nutrient foramen?

a hole in the wall of the diaphysis through with the nutrient artery and vein run, with the nutrient artery running inward to supply the bone marrow and the spongy bone, and branches then outward to supply the compact bone

Where is red bone marrow found in infants?

in the medullary cavity of the diaphysis and all areas of spongy bone

Where is red bone marrow found in adults?

in the flat bones of the skull, sternum, ribs, clavicles, scapulae, hip bones, and vertebrae and in the heads of the femur and humerus

How does the red marrow found in flat bones and some irregular bones differ from that of long bones?

it is much more active in hematopoiesis

What do clinicians do when they suspect problems with the blood-forming tissue?

they obtain red marrow samples from these sites

What can happen to yellow marrow in the medullary cavity if a person becomes very anemic?

it can revert to red marrow

What are bone markings?

features on the external surface of a bone that provide a wealth of information about how that bone and its attached muscles and ligaments work together

Osteoprogenitor (osteogenic) cells

mitotically active stem cells found in the membranous periosteum and endosteum

What shape are osteoprogenitor cells in growing bones?

flattened or squamous

What happens when osteoprogenitor cells are stimulated?

they differentiate into osteoblasts, while others persist as osteoprogenitor cells

Osteoblasts

actively mitotic bone-forming cells that secrete the bone matrix

What does the bone matrix secreted by osteoblasts include?

collagen and calcium-binding proteins that make up the initial unmineralized bone, or osteoid

What shape are actively depositing osteoblasts?

cubed

What do inactive osteoblasts look like?

they resemble the flattened osteoprogenitor cells or may differentiate into bone linings

What do osteoblasts become once they are completely surrounded by the matrix being secreted?

osteocytes

Osteocytes

spidery mature bone cells that occupy spaces (lacunae) that conform to their shape

What do osteocytes do?

• monitor and maintain the bone matrix

• act as stress or strain “sensors”

• respond to mechanical stimuli, communicating the information to the cell responsible for bone modeling so that bone matrix can be made or degraded as mechanical stresses dictate

• can trigger bone remodeling to maintain calcium homeostasis