Principles of Human Anatomy and Physiology, 11e 1 Chapter 6 The Skeletal System: Bone Tissue Lecture Outline

Principles of Human Anatomy and Physiology, 11e

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Chapter 6

The Skeletal System: Bone Tissue

Lecture Outline


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INTRODUCTION

Bone is made up of several different tissues working together: bone, cartilage, dense connective tissue, epithelium, various blood forming tissues, adipose tissue, and nervous tissue.

Each individual bone is an organ; the bones, along with their cartilages, make up the skeletal system.


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The Skeletal System:Bone Tissue

Dynamic and ever-changing throughout life Skeleton composed of many different tissues

cartilage, bone tissue, epithelium, nerve, blood forming tissue, adipose, and dense connective tissue


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Functions of Bone

Supporting & protecting soft tissues Attachment site for muscles making

movement possible Storage of the minerals, calcium &

phosphate -- mineral homeostasis Blood cell production occurs in red bone

marrow (hemopoiesis) Energy storage in yellow bone marrow


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Anatomy of a Long Bone diaphysis = shaft epiphysis = one end of a

long bone metaphyses are the

areas between the epiphysis and diaphysis and include the epiphyseal plate in growing bones.

Articular cartilage over joint surfaces acts as friction reducer & shock absorber

Medullary cavity = marrow cavity


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Anatomy of a Long Bone Endosteum = lining

of marrow cavity Periosteum = tough

membrane covering bone but not the cartilage fibrous layer =

dense irregular CT osteogenic layer =

bone cells & blood vessels that nourish or help with repairs


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Histology of Bone

A type of connective tissue as seen by widely spaced cells separated by matrix

Matrix of 25% water, 25% collagen fibers & 50% crystalized mineral salts

4 types of cells in bone tissue


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HISTOLOGY OF BONE TISSUE Bone (osseous) tissue consists of widely separated

cells surrounded by large amounts of matrix. The matrix of bone contains inorganic salts, primarily

hydroxyapatite and some calcium carbonate, and collagen fibers.

These and a few other salts are deposited in a framework of collagen fibers, a process called calcification or mineralization. The process of calcification occurs only in the

presence of collagen fibers. Mineral salts confer hardness on bone while

collagen fibers give bone its great tensile strength.


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bone cells.(Figure 6.2)

1. Osteogenic cells undergo cell division and develop into osteoblasts.

2. Osteoblasts are bone-building cells.

3. Osteocytes are mature bone cells and the principal cells of bone tissue.

4. Osteoclasts are derived from monocytes and serve to break down bone tissue.


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Cells of Bone

Osteoprogenitor cells ---- undifferentiated cells can divide to replace themselves & can become osteoblasts found in inner layer of periosteum and endosteum

Osteoblasts--form matrix & collagen fibers but can’t divide Osteocytes ---mature cells that no longer secrete matrix Osteoclasts---- huge cells from fused monocytes (WBC)

function in bone resorption at surfaces such as endosteum


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Cells of Bone

Osteoblasts Osteocytes Osteoclasts


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Matrix of Bone Inorganic mineral salts provide bone’s hardness

hydroxyapatite (calcium phosphate) & calcium carbonate

Organic collagen fibers provide bone’s flexibility their tensile strength resists being stretched or torn remove minerals with acid & rubbery structure results

Bone is not completely solid since it has small spaces for vessels and red bone marrow spongy bone has many such spaces compact bone has very few such spaces


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Compact Bone

Compact bone is arranged in units called osteons or Haversian systems (Figure 6.3a).

Osteons contain blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix.

Osteons are aligned in the same direction along lines of stress. These lines can slowly change as the stresses on the bone changes.


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Compact or Dense Bone

Looks like solid hard layer of bone Makes up the shaft of long bones and the

external layer of all bones Resists stresses produced by weight and

movement


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Histology of Compact Bone Osteon is concentric rings (lamellae) of calcified matrix

surrounding a vertically oriented blood vessel Osteocytes are found in spaces called lacunae Osteocytes communicate through canaliculi filled with

extracellular fluid that connect one cell to the next cell Interstitial lamellae represent older osteons that have

been partially removed during tissue remodeling


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Spongy Bone

Spongy (cancellous) bone does not contain osteons. It consists of trabeculae surrounding many red marrow filled spaces (Figure 6.3b).

It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones.

Spongy bone tissue is light and supports and protects the red bone marrow.


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The Trabeculae of Spongy Bone Latticework of thin plates of bone called trabeculae oriented

along lines of stress Spaces in between these struts are filled with red marrow

where blood cells develop Found in ends of long bones and inside flat bones such as

the hipbones, sternum, sides of skull, and ribs.

No true Osteons.


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Blood and Nerve Supply of Bone Periosteal arteries

supply periosteum Nutrient arteries

enter through nutrient foramen

supplies compact bone of diaphysis & red marrow

Metaphyseal & epiphyseal aa. supply red marrow &

bone tissue of epiphyses


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BONE FORMATION All embryonic connective tissue begins as

mesenchyme. Bone formation is termed osteogenesis or

ossification and begins when mesenchymal cells provide the template for subsequent ossification.

Two types of ossification occur. Intramembranous ossification is the formation of

bone directly from or within fibrous connective tissue membranes.

Endochondrial ossification is the formation of bone from hyaline cartilage models.


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Intramembranous

Intramembranous ossification forms the flat bones of the skull and the mandible (Figure 6.5). An ossification center forms from mesenchymal

cells as they convert to osteoblasts and lay down osteoid matrix.

The matrix surrounds the cell and then calcifies as the osteoblast becomes an osteocyte.

The calcifying matrix centers join to form bridges of trabeculae that constitute spongy bone with red marrow between.

On the periphery the mesenchyme condenses and develops into the periosteum.


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Intramembranous Bone Formation

Mesenchymal cells become osteoprogenitor cells then osteoblasts.

Osteoblasts surround themselves with matrix to become osteocytes.


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Intramembranous Bone Formation (cont.)

Matrix calcifies into trabeculae with spaces holding red bone marrow.

Mesenchyme condenses as periosteum at the bone surface.

Superficial layers of spongy bone are replaced with compact bone.


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Intramembranous Bone Formation


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Endochondrial

Endochondrial ossification involves replacement of cartilage by bone and forms most of the bones of the body (Figure 6.6).

The first step in endochondrial ossification is the development of the cartilage model.


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Endochondral Bone Formation Development of Cartilage model

Mesenchymal cells form a cartilage model of the bone during development

Growth of Cartilage model in length by chondrocyte cell

division and matrix formation ( interstitial growth)

in width by formation of new matrix on the periphery by new chondroblasts from the perichondrium (appositional growth)

cells in midregion burst and change pH triggering calcification and chondrocyte death


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Endochondral Bone Formation Development of Primary

Ossification Center perichondrium lays down

periosteal bone collar nutrient artery penetrates

center of cartilage model periosteal bud brings

osteoblasts and osteoclasts to center of cartilage model

osteoblasts deposit bone matrix over calcified cartilage forming spongy bone trabeculae

osteoclasts form medullary cavity


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Endochondral Bone Formation

Development of Secondary Ossification Center blood vessels enter the epiphyses around time of birth spongy bone is formed but no medullary cavity

Formation of Articular Cartilage cartilage on ends of bone remains as articular cartilage.


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Bone Scan

Radioactive tracer is given intravenously Amount of uptake is related to amount of

blood flow to the bone “Hot spots” are areas of increased metabolic

activity that may indicate cancer, abnormal healing or growth

“Cold spots” indicate decreased metabolism of decalcified bone, fracture or bone infection


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BONE GROWTH


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Growth in Length To understand how a bone grows in length, one needs to

know details of the epiphyseal or growth plate (Figure 6.7). The epiphyseal plate consists of four zones: (Figure 6.7b)

zone of resting cartilage, zone of proliferation cartilage, zone of hypertrophic cartilage, and zone of calcified cartilage The activity of the epiphyseal

plate is the only means by which the diaphysis can increase in length.

When the epiphyseal plate closes, is replaced by bone, the epiphyseal line appears and indicates the bone has completed its growth in length.


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Bone Growth in Length Epiphyseal plate or cartilage growth

plate cartilage cells are produced by

mitosis on epiphyseal side of plate cartilage cells are destroyed and

replaced by bone on diaphyseal side of plate

Between ages 18 to 25, epiphyseal plates close. cartilage cells stop dividing and

bone replaces the cartilage (epiphyseal line)

Growth in length stops at age 25


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Zones of Growth in Epiphyseal Plate

Zone of resting cartilage anchors growth plate to bone

Zone of proliferating cartilage rapid cell division (stacked

coins) Zone of hypertrophic cartilage

cells enlarged & remain in columns

Zone of calcified cartilage thin zone, cells mostly dead

since matrix calcified osteoclasts removing matrix osteoblasts & capillaries move

in to create bone over calcified cartilage


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Growth in Thickness

Bone can grow in thickness or diameter only by appositional growth (Figure 6.8).

The steps in thes process are: Periosteal cells differentiate into osteoblasts which

secrete collagen fibers and organic molecules to form the matrix.

Ridges fuse and the periosteum becomes the endosteum.

New concentric lamellae are formed. Osetoblasts under the peritsteum form new

circumferential lamellae.


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Bone Growth in Width

Only by appositional growth at the bone’s surface Periosteal cells differentiate into osteoblasts and form bony ridges

and then a tunnel around periosteal blood vessel. Concentric lamellae fill in the tunnel to form an osteon.


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Factors Affecting Bone Growth Nutrition

adequate levels of minerals and vitamins calcium and phosphorus for bone growth vitamin C for collagen formation vitamins K and B12 for protein synthesis

Sufficient levels of specific hormones during childhood need insulinlike growth factor

promotes cell division at epiphyseal plate need hGH (growth), thyroid (T3 &T4) and insulin

sex steroids at puberty At puberty the sex hormones, estrogen and testosterone,

stimulate sudden growth and modifications of the skeleton to create the male and female forms.


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Hormonal Abnormalities

Oversecretion of hGH during childhood produces giantism

Undersecretion of hGH or thyroid hormone during childhood produces short stature

Both men or women that lack estrogen receptors on cells grow taller than normal estrogen is responsible for closure of growth

plate


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BONES AND HOMEOSTASIS


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Bone Remodeling

Remodeling is the ongoing replacement of old bone tissue by new bone tissue. Old bone is constantly destroyed by

osteoclasts, whereas new bone is constructed by osteoblasts.

In orthodontics teeth are moved by brraces. This places stress on bone in the sockets causing osteoclasts and osteablasts to remodel the sockets so that the teeth can be properly aligned (Figure 6.2)

Several hormones and calcitrol control bone growth and bone remodeling (Figure 6.11)


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Bone Remodeling

Ongoing since osteoclasts carve out small tunnels and osteoblasts rebuild osteons. osteoclasts form leak-proof seal around cell edges secrete enzymes and acids beneath themselves release calcium and phosphorus into interstitial

fluid osteoblasts take over bone rebuilding

Continual redistribution of bone matrix along lines of mechanical stress distal femur is fully remodeled every 4 months


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Fracture and Repair of Bone

A fracture is any break in a bone. Fracture repair (Figure 6.10)involves formation

of a clot called a fracture hematoma, organization of the fracture hematoma into granulation tissue called a procallus (subsequently transformed into a fibrocartilaginous [soft] callus), conversion of the fibrocartilaginous callus into the spongy bone of a bony (hard) callus, and, finally, remodeling of the callus to nearly original form.


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Fracture & Repair of Bone Healing is faster in bone than in

cartilage due to lack of blood vessels in cartilage

Healing of bone is still slow process due to vessel damage

Clinical treatment closed reduction = restore pieces to

normal position by manipulation open reduction = realignment during

surgery


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Fractures

Named for shape or position of fracture line

Common types of fracture greenstick -- partial fracture impacted -- one side of fracture driven into

the interior of other side


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Fractures

Named for shape or position of fracture line Common types of fracture

closed -- no break in skin open fracture --skin broken comminuted -- broken ends of bones are

fragmented


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Fractures

Named for shape or position of fracture line Common types of fracture

Pott’s -- distal fibular fracture Colles’s -- distal radial fracture stress fracture -- microscopic fissures from

repeated strenuous activities


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Repair of a Fracture


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Formation of fracture hematoma damaged blood vessels produce clot in 6-8 hours, bone cells die inflammation brings in phagocytic cells for clean-up duty new capillaries grow into damaged area

Formation of fibrocartilagenous callus formation fibroblasts invade the procallus & lay down collagen fibers chondroblasts produce fibrocartilage to span the broken ends of the bone


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Formation of bony callus osteoblasts secrete spongy bone that joins 2 broken

ends of bone lasts 3-4 months

Bone remodeling compact bone replaces the spongy in the bony callus surface is remodeled back to normal shape


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Calcium Homeostasis & Bone Tissue

Skeleton is a reservoir of Calcium & Phosphate Calcium ions involved with many body systems

nerve & muscle cell function blood clotting enzyme function in many biochemical reactions

Small changes in blood levels of Ca+2 can be deadly (plasma level maintained 9-11mg/100mL) cardiac arrest if too high respiratory arrest if too low


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Hormonal Influences Parathyroid hormone (PTH) is

secreted if Ca+2 levels falls PTH gene is turned on & more PTH

is secreted from gland osteoclast activity increased,

kidney retains Ca+2 and produces calcitriol

Calcitonin hormone is secreted from parafollicular cells in thyroid if Ca+2 blood levels get too high inhibits osteoclast activity increases bone formation by

osteoblasts


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EXERCISE AND BONE TISSUE

Within limits, bone has the ability to alter its strength in response to mechanical stress by increasing deposition of mineral salts and production of collagen fibers. Removal of mechanical stress leads to weakening of

bone through demineralization (loss of bone minerals) and collagen reduction.

reduced activity while in a cast astronauts in weightless environment bedridden person

Weight-bearing activities, such as walking or moderate weightlifting, help build and retain bone mass.


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Development of Bone Tissue

Both types of bone formation begin with mesenchymal cells

Mesenchymal cells transform into chondroblasts which form cartilage

OR Mesenchymal cells become

osteoblasts which form boneMesenchymal Cells


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Developmental Anatomy

5th Week =limb bud appears as mesoderm covered with ectoderm

6th Week = constriction produces hand or foot plate

and skeleton now totally cartilaginous

7th Week = endochondral ossification begins

8th Week = upper & lower limbs appropriately named


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AGING AND BONE TISSUE

Of two principal effects of aging on bone, the first is the loss of calcium and other minerals from bone matrix (demineralization), which may result in osteoporosis. very rapid in women 40-45 as estrogens levels decrease in males, begins after age 60

The second principal effect of aging on the skeletal system is a decreased rate of protein synthesis decrease in collagen production which gives bone its

tensile strength decrease in growth hormone bone becomes brittle & susceptible to fracture


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Osteoporosis Decreased bone mass resulting in porous bones Those at risk

white, thin menopausal, smoking, drinking female with family history

athletes who are not menstruating due to decreased body fat & decreased estrogen levels

people allergic to milk or with eating disorders whose intake of calcium is too low

Prevention or decrease in severity adequate diet, weight-bearing exercise, & estrogen

replacement therapy (for menopausal women) behavior when young may be most important factor


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Disorders of Bone Ossification

Rickets calcium salts are not deposited properly bones of growing children are soft bowed legs, skull, rib cage, and pelvic

deformities result

Osteomalacia new adult bone produced during remodeling

fails to ossify hip fractures are common


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Principles of Human Anatomy and Physiology, 11e 1 Chapter 6 The Skeletal System: Bone Tissue Lecture Outline