BIOL251 Exam 2

Chondr-

cartilage

Osteo-

bone

Functions of bones

support, protection, attachment point, storage, blood cell formation, hormone production

Support function of bones

Holds up the body and cradles organs.

Protection function of bones

Central nervous system protection: the skull protects the brain, vertebrae wrap around spinal cord

Visceral organ protection: rib cage wraps around organs in thorax & upper abdominal cavity.

Attachment point function of bones

Skeletal muscle attaches to bone via tendons. Allows for pushing and pulling of muscle

Tendon

thick band of dense regular connective tissue, attaches skeletal muscle to bone

Storage function of bones

Storing minerals and fat

Minerals: calcium phosphate salts to give bones rigidity and provide Ca2+ to CNS and muscle tissue

Yellow bone marrow

lipid based, can be used as an energy source

Blood cell formation function of bones

Hematopoiesis: formation of blood cells in red bone marrow.

Hormone production function of bones

Osteocalcin regulates insulin release, glucose homeostasis, & energy expenditure.

Cartilage and Skeleton formation

Before the osseous skeleton forms in an embryo, the skeleton is composed of cartilage and connective tissue fibers since cartilage grows much faster than bone

Characteristics of all cartilage types

1) Strength & resilience

2) High water content

3) No nerve supply & is avascular

4) Surrounded externally by fibrous connective tissue called perichondrium.

Strength and resilience of cartilage

Cartilage can be compressed and return to original shape; very difficult to break

High water content of cartilage

Contributes to flexibility, cartilage more abundant in parts of the body that need to be more flexible

No innervation and avascularity of cartilage

Lack of blood supply makes repair of cartilage very difficult

Perichondrium

fibrous connective tissue surrounding cartilage

3 types of cartilage

Hyaline, elastic, fibrocartilage

Hyaline cartilage

Most abundant type containing collagen fibers. Examples: Articular cartilage (prevents bone on bone rubbing at all joints), costal cartilage (ribs), respiratory cartilage (airways that lead into lungs, keeps pathways open), nasal cartilage (keeps nasal passages in nose open).

Elastic cartilage

Contains more elastic fibers. Much more flexible, found where bending is needed. Examples: External ear, epiglottis (helps with swallowing, prevents food and fluid being sucked down into lungs).

Fibrocartilage

Contains rows of chondrocytes alternating with thick collagen bands; most compressible & great tensile strength. Examples: Vertebral discs, knee (meniscus), pubic symphysis.

Types of cartilage growth

appositional growth and interstitial growth

Appositional growth

Laying down new cartilage on old cartilage; occurs at surface of cartilage tissue.

Cells just under perichondrium deposit new matrix on top of "old" cartilage

Causes cartilage to grow in width

Interstitial growth

Cells divide and secrete matrix within pre-existing cartilage; occurs deeper in cartilage tissue.

Causes cartilage to grow in length

How can bones be classified?

By location or shape

Classifications of bones by location

axial or appendicular skeleton

Axial skeleton

Long axis of body; includes skull, vertebral column, & ribs.

What is the primary function of the axial skeleton?

support and protect central organs (brain, spinal cord, heart, etc.)

Appendicular skeleton

Limbs (aka appendages) & the girdles; includes pectoral & pelvic girdles, arms & legs.

What is the primary function of appendicular skeleton bones?

Facilitate movement in the limbs

Classification of bones by shape

long bones, short bones, flat bones, irregular bones

Long bones

Longer than they are wide; example: almost all arm & leg bones.

Roughly column shaped

Short bones

Cube-shaped; examples: bones in wrists & ankles.

Sesamoid bones

Bone that forms in a tendon.

Flat bones

Thin, flat, curved; examples: sternum, scapulae, ribs, most cranial bones.

Irregular bones

Anything that does not fit in an above category; examples: vertebrae, os coxa (hip bones).

Oddly shaped

Gross anatomy of bone

all bones contain a outer layer of compact layer of spongy bon

Compact (lamellar) bone

Looks smooth and solid, outer bone

Spongy bone

Has open spaces with needle-like pieces of bone called trabeculae; open space is filled with red marrow or yellow marrow.

Where is trabeculae found in greatest concentration?

Found in greatest concentration along lines of stress.

Why is trabeculae found along lines of stress?

Bones are frequently being pushed along these lines. Adds to skeletal strength.

Structure of flat, irregular, and short bone

Thin plate of spongy bone covered by compact bone.

No large cavities for bone marrow, all bone marrow found around trabeculae of spongy bone

Features of all long bones

Diaphysis, epiphysis, membranes, innervation and vascularization

Diaphysis

Bone shaft composed of compact bone 'collar' with internal medullary cavity containing bone marrow

Epiphysis

Bone ends composed of compact bone externally & spongy bone internally.

Found where one bone articulate with another bone at a joint and/or allows for attachment of ligaments and tendons

Articular Cartilage

Covers the epiphysis and allows for articulation with another bone at a joint.

Two membranes of long bone

Periosteum and endosteum

Periosteum

Covers external bone surface except at epiphysis; very well vascularized and innervated.

Causes pain when damaged

Endosteum

Covers internal bone surfaces including trabeculae in spongy bone and cavities in compact bone.

What vascularization and innervation serves the diaphysis?

Nutrient Vein and Nutrient Artery

What vascularization and innervation serves the epiphyses?

Epiphyseal artery and epiphyseal vein

Microscopic anatomy of long bone

Osteon, central canals, perforating canals, interstitial lamellae, circumferential lamellae

Osteon

Structural unit of compact bone that helps bone withstand pressure/stress.

Made of lamella

Bone salts found on and in between fibers

Lamella

Several layers packed closely together in a single osteon.

Collagen fibers run in one direction for a single lamella, fibers always run in opposite directions in adjacent lamella

Why is the direction collagen fibers run in lamella important?

Direction allows fibers to resist twisting and torsional force

Central Canals

Run through the center of each osteon and contain nerve and blood vessels.

Perforating Canals

Extend from central canal to connect neighboring osteons and medullary cavity.

Helps with blood supply exchange

Interstitial Lamellae

Incomplete lamellae found in between complete osteons that fill gaps between osteons (there should not be empty space in compact bone)

Circumferential Lamellae

Found just deep to periosteum and extend completely around the circumference of the diaphysis.

Helps resist twisting of long bone, as fibers still run in opposite directions adjacent to one another

Types of hematopoietic tissue

red bone marrow and yellow bone marrow

Red Bone Marrow

Hematopoietic tissue responsible for the production of blood cells.

Found in adults in the skull, hips, ribs, sternum, clavicles, scapula, vertebrae, the head of the femur, and the head of the humerus

Found in infants in flat bones, short bones, irregular bones, the head of the humerus, and the head of the femur

Yellow Marrow

Found in the medullary cavity of long bones in adults, contains more fat and less blood supply than red marrow.

Can be converted back to red marrow

Cell types responsible for bone growth

Osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

Osteoprogenitor Cells

Stem cells that are mitotically active and can differentiate to form osteoblasts.

Can also remain as osteogenic cells

Osteoblasts

Bone-forming cells that secrete unmineralized matrix (osteoid) that forms bone tissue.

Will secrete matrix until surrounded

What does it mean that the osteoid is unmineralized?

The fibers of the matrix have no calcium phosphate salts

Osteocytes

Mature bone cells that monitor and maintain bone matrix.

Respond to mechanical stress on bone (bone loading) and chemical signals (calcium levels in bone)

Often have several projections of cell membrane surface

Osteoclasts

bone-degrading cells that maintain, repair, and remodel bones

important for blood calcium homeostasis

Collagenase

enzyme produced by osteoclast cells

Organic composition of bone

cells and osteoid

Inorganic composition of bone

mineral salts, mostly calcium phosphate packed around collagen fibers

Homeostatic imbalance of chemical composition of bone

Osteomalacia and Ricket's

Osteomalacia

condition in adults characterized by less mineral salts deposited in bone than normal, resulting in weak/soft bones

Ricket's

condition in children characterized by less mineral salts deposited in bone than normal, resulting in weak/soft bones

Extra concern for Ricket's

Skeleton is not done growing yet, which could cause skeletal deformity

Causes of Osteomalacia and Ricket's

insufficient calcium in diet and/or vitamin D deficiency

calcium could be given to other organ systems when intake is low

Endochondral ossification

formation of ossified bone by replacement of cartilage with bone

occurs in most bones below the skull

hyaline cartilage used as a blue print to form ossified bone (as ossified bone is laid down, hyaline cartilage is broken down)

Step 1 of endochondral ossification

formation of a bone collar

osteoblasts lay down bone matrix against cartilage surface

formation of primary ossification center after bone collar

Primary ossification center

formed after bone collar formation, rigid and tough on outside, filled with cartilage on inside

cells in diaphysis will hypertrophy

bone formation actually begins here

Step two of endochondral ossification

Cavity forms in diaphysis center

cells inside ossification center die off and cartilage inside POC breaks down, creating cavity

cartilage outside cavity continues to grow which elongates bone

Why is the bone collar important for cavity formation?

The bone collar prevents diaphysis from being crushed by growing cartilage

Step 3 of endochondral ossification

Initial spongy bone formation

occurs when periosteal bud invades cavity and osteoblasts secrete matrix around calcified cartilage

initial formation of spongy bone is bone covered cartilage trabeculae

Periosteal bud

contains a nutrient artery and vein, nerve fibers, red marrow elements, osteogenic cells, and osteoclasts

osteogenic cells differentiate into osteoblasts to lay down new bone tissue

Step 4 of endochondral ossification

Formation of medullary cavity and elongation of diaphysis

Initial spongy bone from step 3 broken down by osteoclasts forming medullary cavity

Cartilage in remaining diaphysis is calcified, broken down, replaced with bone

Secondary ossification center

forms in epiphyses during endochondral ossification

Step 5 of endochondral ossification

Secondary ossification continues in epiphyses

similar to primary ossification except spongy bone is retained

there are still some areas with actively growing cartilage

Growth in Length

accomplished by interstitial growth at the epiphyseal plate

Epiphyseal plate

cartilage plate that is found between the epiphysis and diaphysis

Overall process of growth in length

1) New cartilage laid down at top of epiphyseal plate

2) Cartilage cells at the center of the epiphyseal plate enlarge, cartilage is calcified

3) Calcified cartilage is broken down by osteoclasts and osteoblasts lay down new bone tissue at the bottom of the plate closer to the diaphysis

Pushing epiphysis away from diaphysis

Cartilage production in epiphyseal plate

slows and stops at the end of adolescence (contingent partially on hormone activity)

existing cartilage in plate is calcified and completely replaced by bone, causing bone of diaphysis to fuse with bone of epiphysis

Growth in Width

accomplished by appositional growth occurring at the same time as bone lengthening

Why is it important that growth in width occurs at the same time as growth in length?

growth imbalances can impact, shape, size, and toughness of bone

Overall process of growth in width

1. Osteoblasts secrete new matrix at the periosteum

2. Osteoclasts break down bone tissue at the endosteum

What difference in activity rate between the cells must there be for growth in width to occur?

Osteoblasts must be faster than osteoclasts

Growth hormone

controls activity at the epiphyseal plate and is released by the anterior pituitary gland

controls growth in length

What effect does growth hormone have on the epiphyseal plate?

Cells exposed to GH lay cartilage down faster

Not enough GH= lower activity, can cause people to be shorter

Sex hormones

estrogen and testosterone

Estrogens

cause growth spurt at puberty and induce epiphyseal plate closure in high levels

causes feminization of certain parts of skeleton (influences shape of pelvic girdle: makes it wider for child birth)

What is the typical age at which a female stops growing?

Earlier, normally around 18 years old

Testosterone

causes 'masculinization' of certain parts of the skeleton