Chapter 6: Skeletal Tissues:

Bones, Ligaments, Cartilage

FUNCTIONS OF skeletal tissues SUPPORT: Bones form the FRAMEWORK of the body

and contribute to the shape, alignment, and positioning of body parts;

LIGAMENTS help hold bones together,

CARTILAGE provides cushion and ‘shock-absorption ‘between bones

PROTECTION: bony “boxes” protect the delicate structures they enclose (ref; cranium, rib cage, pelvis)

MOVEMENT: bones and their joints constitute levers that move as muscles contract, and as sites of attachment for muscles

MINERAL STORAGE: bones are the major reservoir for

CALCIUM, PHOSPHORUS, and other minerals

HEMATOPOIESIS: blood cell formation is carried out by Myeloid tissue, which is located

in the bone marrow

Bones are the ‘organs’ of the skeletal system.

All bones have: outer “dense” layer of

compact bone Inner, honeycombed

region of spongy (cancellous) bone

Spaces between trabeculae filled with red or yellow marrow

trabeculae

TYPES OF BONES Five major types of structural bones

Long bones Short bones Flat bones Irregular bones Sesamoid bones develops within a tendon ( ex.: patella)

Bones serve various needs, and their size, shape, and appearance vary to meet those needs

Bones vary in the proportion of compact and cancellous (spongy)

bone; COMPACT BONE is dense and solid in

appearance, whereas CANCELLOUS BONE is characterized by open space partially filled with needle-like structures,

called spicules, or trabeculae

Most of the bones of the skull are ‘flat bones’

Long

short

Irregular

flat

sesamoid

The 6 ‘long’ bones:

Humerus

Radius Ulna

Femur

Tibia Fibula

Upperextremity

Lowerextremity

Parts of a long bone

DIAPHYSIS Main SHAFT of a long bone Hollow, cylindrical shape and thick compact bone on

the perimeter, with marrow in the middle, (MEDULLARY cavity)

Function is to provide strong support without cumbersome weight. (like an architechural column)

EPIPHYSES Both ends of a long bone; made of

CANCELLOUS BONE filled with marrow Bulbous shape Function is to provide attachments for muscles and

give stability to joints

Long bone diaphysis – shaft epiphyses – bone ends

Articular cartilage covers joint surface

Epiphyseal line located between diaphysis and each epiphysis

(in young, growing bones, this can be seen as a METAPHYSIS - an ‘area’

of cartilage between the epiphysis and the diaphysis)

In a youngster, this is seen as the epiphyseal plate;Once the bone is mature, it is simply an epiphyseal

‘line’

Epiphysis

Diaphysis

Articular cartilage

Periosteum

Medullary cavity

Endosteum

Compact bone

Cancellous (spongy)bone

membranes periosteum – covers surface of

bone (attachment site for tendons & ligaments)

endosteum – lines marrow cavityBoth membranes contain:

• osteogenic cells – stem cells; which give rise to osteoblasts &

osteoclasts•

• OSTEOBLASTS – cells that secrete bone matrix

• OSTEOCLASTS – cells that break down bone matrix

(Pls. remember this concept: perimysium, perineurium)

More on the components of bones Articular cartilage

Layer of hyaline cartilage that covers the articular surface of epiphyses

Function is to cushion jolts and blows

Periosteum Dense, white fibrous membrane that

covers bone Attaches tendons firmly to bones Contains cells that form and destroy bone Contains blood vessels important in

growth and repair Contains blood vessels that send branches

into bone Essential for bone cell survival and bone

formation

Components of bone

Medullary (or marrow) cavityTubelike, hollow space in the diaphysis

Filled with yellow marrow in adults . (Yellow marrow is fatty, can be called upon to become active hematopoietic tissue if needed)

Endosteum: thin, fibrous membrane that lines the medullary cavity

Short, irregular & flat bones do NOT have shaft, epiphyses, or

medullary cavity thin layer of compact bone

surrounds spongy bone center (contains red marrow)

• periosteum covers compact bone

• endosteum encloses trabeculae

Spongy bone of flat bones is called diploe

Frontal sinuses

GLOSSARY OF TERMS: SKELETAL SYSTEM Term: Definition (with one example):analagous to geographic terms such as peak mount hill cape bluff isle cove condyle a rounded process that articulates

with another bone eg. occipital condyle

crest a narrow, ridge-like projection; eg. iliac crest

epicondyle a projection situated above a condyle

eg. medial epicondyle of humerus

facet a small smooth surface eg. rib facet of a thoracic

vertebra

foramen an opening for the passage of b.v. &/or nerves

eg. foramen magnum

fossa a relatively deep pit or depression; eg. olecranon

fossa

fovea a tiny pit or depression; eg. fovea capitis

head an enlargement at the end of a bone;

eg. femoral head

linea a narrow line-like ridge; eg. linea aspera of femur

meatus a tube-like passageway within a bone

eg. external auditory meatus

process a prominent projection of a bone

eg. mastoid process of temporal bone

ramus a branch-like process; eg. ramus of mandible

sinus a cavity within a bone; eg. frontal sinus

Spine a sharp projection; eg. spine of scapula

styloid a pen-like projection; eg. styloid process of ulna

suture interlocking junction between cranial bones;

eg. coronal suture

trochanter a relatively large process;

eg. Greater trochanter of femur

tubercle a small knob-like process; eg. tubercle of rib

tuberosity a knob-like process larger than a tubercle; eg. tibial tuberosity

condyle a rounded process that articulates with another bone eg. occipital condyle

crest a narrow, ridge-like projection; eg. iliac crest epicondyle a projection situated above a

condyle eg. medial epicondyle of

humerus facet a small smooth surface eg. rib facet of a thoracic

vertebra

foramen an opening for the passage of b.v. &/or nerves

eg. foramen magnum

fossa a relatively deep pit or depression; eg. Olecranon fossa

fovea a tiny pit or depression; eg. fovea capitis

head an enlargement at the end of a bone;

eg. femoral head

linea a narrow line-like ridge; eg. linea aspera of

femur meatus a tube-like passageway

within a bone eg. external auditory meatus

process a prominent projection of a bone

eg. mastoid process of temporal bone

ramus a branch-like process; eg. ramus of mandible,

Pubic ramus sinus a cavity within a bone; eg.

frontal sinus spine a sharp projection; eg. spine

of scapula

styloid a pen-like projection; eg. styloid process of ulna suture interlocking junction between

cranial bones; eg. coronal suture

TROCHANTER a relatively large process;

eg. Greater trochanter of femur

TUBERCLE a small knob-like process; eg. tubercle of rib TUBEROSITY a knob-like process

larger than a tubercle; eg. tibial tuberosity

Important points re: the makeup of BONE TISSUE Bone is Most distinctive form of

connective tissue Extracellular components are hard and

calcified

Rigidity of bone gives it supportive and protective functions

Tensile strength nearly equal to that of cast iron at less than one third the weight:

It takes: GRIT and GLUE TO

MAKE BONE:, MINERAL and MATRIX >>>>>>>

see next slide

BONE TISSUE , grit and glue, calcium and collagen !!! Composition of bone matrix

INORGANIC SALTS Hydroxyapatite: crystals of CALCIUM AND PHOSPHATE contribute to bone hardness

Slender, needlelike crystals are oriented to most effectively resist stress and mechanical deformation

Magnesium, sodium, sulfate, and fluoride also found in bone

ORGANIC MATRIX Composite of COLLAGENOUS fibers and an

amorphous mixture of protein and polysaccharides called ground substance

Ground substance is secreted by connective tissue cells

Adds to overall strength of bone and gives some degree of resilience to bone

Collagen provides flexibility & tensile strength (ability to endure stretching forces)

Bones break easily if collagen is inadequate

Hydroxyapatites (calcium and phosphate) provide compression strength (ability to endure squeezing forces)

Inadequate mineralization = “soft bones” ie osteoporosisBottom line: ya gotta have the GRIT and the GLUE !

MICROSCOPIC STRUCTURE OF Compact bone -- OSTEONS

Compact bone contains many cylinder-shaped structural units called osteons, or haversian systems

Osteons surround central (osteonal or haversian) canals that run lengthwise through bone and are connected by transverse canals

Living bone cells are located in these units, which constitute the structural framework of compact bone

Osteons permit delivery of nutrients and removal of waste products

2. Microscopic Anatomy (compact bone)

Osteon

osteon (Haversian system) – structural unit of compact bone; runs parallel to long axis of bone; consists of: concentric lamellae - rings of matrix that

surround the central canal - like ‘wrappings’

Represents a single osteon (Singular: Lamella)

ref.: ‘ laminate ‘

osteocytes – mature bone cells; embedded in lacunae (cavities within matrix)

canaliculi – tiny channels; connect osteocytes to central canal

Circumferential lamellae surround diaphysis

Interstitial lamellae

Concentric lamellae

Flat bones also have both compact and cancellous bone tissue

MICROSCOPIC STRUCTURE OF BONE (cont.)

Structures that make up each osteonLamellae

Concentric Lamellae: cylinder-shaped layers of calcified matrix around the central canal

Interstitial Lamellae: layers of bone matrix between the osteons; leftover from previous osteons

Circumferential Lamellae: few layers of bone matrix that surround all the osteons; run along the outer circumference of a bone and inner circumference (boundary of medullary cavity) of a bone

MICROSCOPIC STRUCTURE OF BONE (cont.) Structures that make up each osteon (cont.)

Lacunae: small spaces containing tissue fluid in which bone cells are located between hard layers of the lamella

Canaliculi: ultra-small canals radiating in all directions from the lacunae and connecting them to each other and to the central canal

Central (osteonal or Haversian) canal: extends lengthwise through the center of each osteon; contains blood vessels and lymphatic vessels

MICROSCOPIC STRUCTURE OF BONE (cont.)

Cancellous bone No osteons in cancellous bone; it has trabeculae

instead Nutrients are delivered and waste products

removed by diffusion through tiny canaliculi Bony branches (trabeculae) are arranged along

lines of stress to enhance the bone’s strength Blood supply

Bone cells are metabolically active and need a blood supply, which comes from the bone marrow in the internal medullary cavity of cancellous bone

Compact bone, in addition to bone marrow and blood vessels from the periosteum, penetrates the bone and then, by way of transverse (Volkmann) canals, connects with vessels in the central canals of osteons

MICROSCOPIC STRUCTURE OF BONE (cont.)

Types of bone cells Osteoblasts

Bone-forming cells found in all bone surfaces

Small cells synthesize and secrete osteoid, an important part of the ground substance

Collagen fibrils line up in osteoid and form a framework for the deposition of calcium and phosphate

MICROSCOPIC STRUCTURE OF BONE (cont.)

Types of bone cells Osteoclasts

Giant multinucleated cells Responsible for the active erosion of bone

minerals Contain large numbers of mitochondria

and lysosomes

Osteocytes: mature, nondividing osteoblasts surrounded by matrix and lying within lacunae

((retirees of the bone, - alive, but relativley inactive, except for ‘maintenance’ - they maintain the

matrix surrounding them)

So,Osteoblasts MAKE bone,

Osteoclasts BREAK DOWN bone, and Osteocytes MAINTAIN bone.

question:

What is a ‘GIGABYTE’?

Slide 40

Answer:

AGGIE FAST FOOD DIET

(GIG A BITE)

Slide 41

More functions of the skeletal system, bone tissue:

Blood formation, calcium storage / regulation

BONE MARROW

Type of soft, diffuse connective tissue; called myeloid tissue

(it is the primary HEMATOPOIETIC tissue - producing BLOOD CELLS)

Site for the production of blood cells

Found in the medullary cavities of long bones and in the spaces of spongy bone

BONE MARROW (cont.)

Two types of marrow occur during a person’s lifetime RED MARROW

Found in virtually all bones in an infant’s or child’s body

Produces red blood cells

YELLOW MARROW As an individual ages, red marrow is replaced

by yellow marrow Marrow cells become saturated with fat and

are no longer active in blood cell production

BONE MARROW (cont.)

The main bones in an adult that still contain red marrow include the ribs, bodies of the vertebrae, humerus, pelvis, and femur

Yellow marrow can change to red marrow during times of decreased blood supply, such as anemia, exposure to radiation, and certain diseases

REGULATION OF BLOOD CALCIUM LEVELS Skeletal system is a storehouse for about

98% of body calcium reserves

Helps maintain constancy of blood calcium levels Calcium is mobilized and moves in and out of

blood during bone remodeling

During bone formation, OSTEOBLASTS REMOVE CALCIUM from blood and lower circulating levels

During breakdown of bone, OSTEOCLASTS RELEASE CALCIUM into blood and increase circulating levels

REGULATION OF BLOOD CALCIUM LEVELS (cont.)

Homeostasis of calcium ion concentration

is essential for the following:

Transmission of nerve impulses

Blood clotting

Bone formation, remodeling, and repair

Maintenance of skeletal and cardiac muscle contraction

REGULATION OF BLOOD CALCIUM LEVELS (cont.)

Mechanisms of calcium homeostasis Parathyroid hormone

Primary regulator of calcium homeostasis

Stimulates osteoclasts to initiate breakdown of bone matrix and increase blood calcium levels

Increases renal absorption of calcium from urine

Stimulates vitamin D synthesis

REGULATION OF BLOOD CALCIUM LEVELS (cont.)

Mechanisms of calcium homeostasis CALCITONIN

Protein hormone produced in the thyroid gland

Produced in response to high blood calcium levels

Stimulates bone deposition by osteoblasts

Inhibits osteoclast activity

Far less important in homeostasis of blood calcium levels than is parathyroid hormone

CARTILAGE

CARTILAGE Characteristics

Avascular connective tissue Fibers of cartilage are embedded in a firm

gel Has the flexibility of firm plastic

No canal system or blood vessels Chondrocytes receive oxygen and nutrients

by diffusion

Perichondrium: fibrous covering of the cartilage

Cartilage types differ because of the amount of matrix present and the amounts of elastic and collagenous fibers

CARTILAGE (cont.) Types of cartilage (Figure 7-21)

HYALINE CARTILAGE

Most common type

Covers the articular surfaces of bones

Forms the costal cartilages, cartilage rings in the trachea, bronchi of the lungs, and the tip of the nose

Forms from special cells in chondrification centers, which secrete matrix material

Chondrocytes are isolated into lacunae

CARTILAGE (cont.) Types of cartilage

Elastic cartilage Forms external ear, epiglottis, and eustachian

tubes Large number of elastic fibers confers elasticity

and resiliency

Fibrocartilage Occurs in pubic symphysis and intervertebral disks, and the meniscii of the knee joints

Small quantities of matrix and abundant fibrous elements

Strong and rigid

CARTILAGE (cont.)

Functions

Tough, rubberlike nature permits cartilage to sustain great weight or serve as a shock absorber

Strong yet pliable support structure

Permits growth in length of long bones

Next few slides are of INTEREST - not to be tested upon, sit back and relax , watch, listen.

Bone development, fractures and repair:

DEVELOPMENT OF BONES Osteogenesis: development of bone

from small cartilage model to adult bone (Figure 7-11)

Intramembranous ossification, (some)

Endochondral ossification (most)

Intramembranous ossification: Occurs within a connective tissue membrane Flat bones begin when groups of cells

differentiate into osteoblasts Osteoblasts are clustered together in

ossification center Osteoblasts secrete matrix material and

collagenous fibrils

. Bone Development (osteogenesis)1. Formation of the skeleton

Initial embryonic skeleton made ofa. fibrous membranes (cranial bones &

clavicles) &b. hyaline cartilage (all other bones)

At birth, osseous

development, (shows

LargeAreas still are

cartilagenous)

DEVELOPMENT OF BONES (cont.) Intramembranous ossification

Large amounts of ground substance accumulate around each osteoblast

Collagenous fibers become embedded in the ground substance and constitute the bone matrix

Bone matrix calcifies when calcium salts are deposited

Trabeculae appear and join in a network to form spongy bone

Appositional growth occurs by adding osseous tissue

(like a tree grows in diameter)

DEVELOPMENT OF BONES (cont.) Endochondral ossification

Most bones begin as a cartilage model with bone formation spreading essentially from the center to the ends

Periosteum develops and enlarges to produce a collar of bone

Primary ossification center forms

Blood vessel enters the cartilage model at the midpoint of the diaphysis

Bone grows in length as endochondral ossification progresses from the diaphysis toward each epiphysis

Secondary ossification centers appear in the epiphysis, and bone growth proceeds toward the diaphysis

Epiphyseal plate remains between the diaphysis and each epiphysis until bone growth in length is complete

DEVELOPMENT OF BONES (cont.) Epiphyseal plate is composed of four layers

“Resting” cartilage cells: point of attachment joining the epiphysis to the shaft

Zone of proliferation: cartilage cells undergoing active mitosis, which causes the layer to thicken and the plate to increase in length

Zone of hypertrophy: older, enlarged cells undergoing degenerative changes associated with calcium deposition

Zone of calcification: dead or dying cartilage cells undergoing rapid calcification

DEVELOPMENT OF BONES (cont.)

Epiphyseal plate can be a site for bone fractures in young people

Long bones grow in both length and diameter

BONE REMODELING Primary osteons develop within early

woven bone

Conelike or tubelike space is hollowed out by osteoclasts

Osteoblasts in the endosteum that lines the tube begin forming layers (lamellae) that trap osteocytes between layers

A central canal is left for the blood and lymphatic vessels and nerves

Primary osteons can be replaced later by secondary osteons in a similar manner

Bones grow in length and diameter by the combined action of osteoclasts and

osteoblasts

Osteoclasts enlarge the diameter of the medullary cavity

Osteoblasts from the periosteum build new bone around the outside of the bone

Mechanical stress, such as physical activity, strengthens bone

Fractures and Repairs

Slide 76

REPAIR OF BONE FRACTURES Fracture: break in the continuity of a bone

Fracture healing Fracture tears and destroys blood vessels

that carry nutrients to osteocytes

Vascular damage initiates repair sequence

Callus: special repair tissue that binds the broken ends of the fracture together

Fracture hematoma: blood clot occurring immediately after the fracture, which is then resorbed and replaced by callus

CYCLE OF LIFE: SKELETAL ISSUES Skeleton fully ossified by mid-20s

Soft tissue may continue to grow; ossifies more slowly

Adults: changes occur from specific conditions Increased density and strength from

exercise Decreased density and strength from

pregnancy, nutritional deficiencies, and illness

Advanced adulthood: apparent degeneration Hard bone matrix replaced by softer

connective tissue Exercise can counteract degeneration