copyright 2009, john wiley & sons, inc. the skeletal system: bone tissue chapter 6

Copyright 2009, John Wiley & Sons, Inc.

The Skeletal System: Bone TissueChapter 6


The Skeletal System: Bone Tissue Functions of Bone and Skeletal System Structure of Bone Histology of Bone Tissue Blood and Nerve Supply of Bone Bone Formation Bone’s Role in Calcium Homeostasis Exercise and Bone Tissue Aging and Bone Tissue


Functions of Bone and Skeletal System1. Support: structural framework;

supporting soft tissues; attachment for muscles and tendons (fascia to periosteum

2. Protection: internal organs from injury; cranium/brain; vertebrae/spinal cord, ribs/heart and lungs

3. Assistance in Movement: chapter 11pp. 338 thru 342 “levers”; skeletal muscles pull bones


Functions of Bone and Skeletal System4. Mineral Homeostasis: calcium and

phosphorus contribute to bone strength; stores 99% of body’s calcium; releases it on demand (see PTH actions and calcium metabolism)

5. Blood Cell Production: red bone marrow produces RBC, WBC and platelets thru hemopoiesis; r.b.m. c/o of developing blood cells, adipocytes, fibroblasts and macrophages w/in a network of reticular fibers; found in hips, ribs, sternum, vertebrae, skull and ends of arm and thigh bones.


Functions of Bone and Skeletal System6. Triglyceride Storage: yellow bone

marrow c/o adipose tissue; chemical energy reserve and is involved in hemopoiesis; with increasing age red marrow changes to yellow


Structure of Bone

Diaphysis: shaft Epiphysis: proximal and distal ends Metaphysis: regions between diaphysis and

epiphysis Epiphyseal growth plate: layer of hyaline cartilage

that allow diaphysis to grow in length; ceases to grow between ages 18-21; replaced by bone then becomes epiphyseal line

Long Bone Anatomy (Humerus)


Structure of Bone

Articular cartilage: thin layer of hyaline cartilage where bone articulates (joint) with another; reduces friction and absorbs shock

Periosteum: composed of outer fibrous layer of dense irregular connective tissue and inner osteogenic layer; allows bone growth in thickness; protects bone, assists in fracture repair, bone nourishment and attachment point for ligaments and tendons



Structure of Bone

Periosteum (cont’d) Perforating fibers: Sharpey’s fibers, attachment to

underlying bone, c/o thick bundles of collagen extend into extracellular matrix of bone

Medullary cavity: hollow cylindrical space with diaphysis that contains fatty yellow marrow in adults

Endosteum: thin membrane that lines the internal surface facing the medullary cavity; made of single layers of cells and connective tissue



Histology of Bone Tissue Abundant extracellular matrix surrounding

widely separated cells Matrix

25% water 25% collagen fibers 50% crystallized mineral salts: calcium

phosphate combines with salt, calcium hydroxide to form crystals of hydroxyapatite then crystals combine with calcium carbonate and ions of magnesium, fluoride, potassium and sulfate.

The most abundant mineral salt is calcium phosphate


Histology of Bone Tissue A process called calcification is initiated

by bone-building cells called osteoblasts

Mineral salts are deposited and crystallize in the framework formed by the collagen fibers of the extracellular matrix

Bone’s flexibility depends on collagen fibers


Histology of Bone Tissue Four types of cells are present in bone tissue Osteogenic cells

Undergo cell division; the resulting cells develop into osteoblasts

Osteoblasts Bone-building cells Synthesize extracellular matrix of bone tissue

Osteocytes Mature bone cells Exchange nutrients and wastes with the blood

Osteoclasts Release enzymes that digest the mineral components of

bone matrix (resorption) Regulate blood calcium level


Histology of Bone Tissue Bone may be categorized as:

Compact Spongy


Histology of Bone Tissue Compact Bone

Resists the stresses produced by weight and movement

Components of compact bone are arranged into repeating structural units called osteons or Haversian systems

Osteons consist of a central (Haversian) canal with concentrically arranged lamellae, lacunae, osteocytes, and canaliculi


Histology of Bone Tissue Osteon

Central canals run longitudinally through bone Around the central canals are concentric

lamellae Rings of calcified matrix (like the rings of a tree

trunk) Between the lamellae are small spaces called

lacunae which contain osteocytes Radiating in all directions from the lacunae are

tiny canaliculi filled with extracellular fluid


Histology of Bone Tissue Osteon

Canaliculi connect lacunae, forming a system of interconnected canals Providing routes for nutrients and oxygen to

reach the osteocytes

The organization of osteons changes in response to the physical demands placed on the skeleton


Histology of Bone Tissue Spongy Bone

Lacks osteons Lamellae are arranged in a lattice of thin

columns called trabeculae Spaces between the trabeculae make bones

lighter Trabeculae of spongy bone support and protect

the red bone marrow Hemopoiesis (blood cell production) occurs in

spongy bone


Histology of Bone Tissue Spongy Bone

Within each trabecula are lacunae that contain osteocytes

Osteocytes are nourished from the blood circulating through the trabeculae

Interior bone tissue is made up primarily of spongy bone

The trabeculae of spongy bone are oriented along lines of stress helps bones resist stresses without breaking


Blood and Nerve Supply of Bone Bone is richly supplied with

blood Periosteal arteries

accompanied by nerves supply the periosteum and compact bone

Epiphyseal veins carry blood away from long bones

Nerves accompany the blood vessels that supply bones The periosteum is rich in

sensory nerves sensitive to tearing or tension


Bone Formation The process by which bone forms is

called ossification or osteogenesis Bone formation occurs in four situations:

1. Formation of bone in an embryo2. Growth of bones until adulthood3. Remodeling of bone4. Repair of fractures


Bone Formation Formation of Bone in an Embryo

Embryonic skeleton initially composed of mesenchyme (an embryonic connective tissue from which all other connective tissues arise) shaped like bones they become

Replacement of preexisting connective tissue with bone; basic structure and function of mature bone same even though there are 2 different means of formation

Cartilage formation and ossification occurs during the sixth week of embryonic development


Bone Formation Formation of Bone in an Embryo

Bone formation follows one of two patterns Intramembranous ossification

Simpler method of two Flat bones of the skull and mandible are formed in this

way “Soft spots” that help the fetal skull pass through the

birth canal later become ossified forming the skull Endochondral ossification

The replacement of cartilage by bone Most bones of the body are formed in this way including

long bones

1. Intramembranous ossification1. Development of the ossification center.

At site where bone develops specific chemical messages cause mesenchymal cells to aggregate and differentiate, first into osteogenic cells then osteoblasts.

Organic extracellular matrix secreted until bone surrounds cells.


1. Intramembranous ossification2. Calcification:

Within a few days calcium and other mineral salts are deposited and extracellular matrix becomes calcified.

3. Formation of trabeculae: Extracellular matrix develops into trabeculae that

fuse with each other to form spongy bone Blood vessels grow into the spaces Connective tissue associated with blood vessels

differentiates into red marrowCopyright 2009, John Wiley &

Sons, Inc.

1. Intramembranous ossification4. Development of the periosteum:

In conjunction with formation of trabeculae, the mesenchyme condenses at the periphery

Eventually a thin layer of compact bone replaces the spongy bone, but spongy bone remains in the center

Much of the new bone is remodeled as the bone is transformed into adult shape and size


1

Blood capillary

Ossification center

Mesenchymal cell

Osteoblast

Collagen fiber

Development of ossification center

Mandible

Flat boneof skull

1

Blood capillary

Ossification center

Mesenchymal cell

Osteoblast

Osteocyte in lacuna

Canaliculus

Osteoblast

Newly calcified bonematrix


Calcification

Mandible

Flat boneof skull

2

Collagen fiber

1

Blood capillary

Ossification center

Mesenchymal cell

Osteoblast


Calcification

Mandible

Flat boneof skull

2

Collagen fiber

Osteocyte in lacuna

Canaliculus

Osteoblast


Mesenchymecondenses

Blood vessel

Spongy bonetrabeculae

Osteoblast

Formation of trabeculae3

1

Blood capillary

Ossification center

Mesenchymal cell

Osteoblast

Mesenchymecondenses

Blood vessel

Spongy bonetrabeculae

Osteoblast

Periosteum

Spongy bone tissue

Compact bone tissue


Calcification Formation of trabeculae

Development of the periosteum

Mandible

Flat boneof skull

3

4

2

Collagen fiber

Osteocyte in lacuna

Canaliculus

Osteoblast


2. Endochondral ossification

Replacement of hyaline cartilage by bone

1. Development of the cartilage model: Specific chemical messages cause the

mesenchymal cells to crow together in the shape of the future bone and develop into chondroblasts

Chondroblasts secrete cartilage extracellular matrix producing the model

A covering called perichondrium develops around the model



2. Growth of the cartilage model: Once the chondroblasts are buried deep in

cartilage they become chondrocytes Interstitial growth: chondrocytes divide

accompanied by more cartilage matrix Appositional growth: More matrix is also laid

down at the periphery Matrix begins to calcify; chondrocytes

hypertrophy then die leaving lacunae which merge into small cavities



3. Development of the primary ossification center:

Nutrient artery penetrates perichondrium and calcifying cartilage model through a nutrient foramen

Stimulates cells in perichondrium to differentiate into osteoblasts

Perichondrium starts forming bone then becomes periosteum

Near the middle periosteal capillaries grow into the disintegrating calcified cartilage inducing the p.c.o.

Spongy bone is formed spreading from center to the ends



4. Development of the medullary cavity (marrow): Osteoclasts resorb some spongy bone leaving a cavity in

the diaphysis the wall of the diaphysis is eventually replaced by

compact bone

5. Development of the secondary ossification centers:

Branches of epiphyseal artery enter around the time of birth

Develops similar to primary center Spongy bone remains w/o formation of medullary cavity



6. Formation of articular cartilage and the epiphyseal growth plate:

Hyaline cartilage covers the epiphyses Prior to adulthood, hyaline cartilage remains in

metaphysis


1 Development ofcartilage model

Hyalinecartilage

Perichondrium

Proximalepiphysis

Distalepiphysis

Diaphysis


Growth ofcartilage model

2

Hyalinecartilage

Uncalcifiedmatrix

Calcifiedmatrix

Perichondrium

Proximalepiphysis

Distalepiphysis

Diaphysis


Development ofprimary ossificationcenter


2 3

Hyalinecartilage

Uncalcifiedmatrix

Calcifiedmatrix

Nutrientartery

Perichondrium

Proximalepiphysis

Distalepiphysis

Diaphysis

Periosteum

Primaryossificationcenter

Spongybone

1

Hyalinecartilage

CalcifiedmatrixPeriosteum(covering compact bone)

Uncalcifiedmatrix

Calcifiedmatrix

Medullarycavity

Nutrientartery and vein

Nutrientartery

Perichondrium

Proximalepiphysis

Distalepiphysis

Diaphysis

Development ofcartilage model


Development ofthe medullarycavity


Periosteum


2 3 4

Spongybone

Uncalcifiedmatrix





2 3 4

Hyalinecartilage


Uncalcifiedmatrix

Calcifiedmatrix

Medullarycavity


Nutrientartery

Perichondrium

Proximalepiphysis

Distalepiphysis

Diaphysis

Periosteum


Secondaryossificationcenter


Uncalcifiedmatrix

Epiphysealartery andvein

Development of secondaryossification center

5

Spongybone

Uncalcifiedmatrix

1

Articular cartilage

Spongy bone

Epiphyseal plate

Secondaryossificationcenter


Uncalcifiedmatrix

Epiphysealartery andvein

Formation of articular cartilageand epiphyseal plate

Development of secondaryossification center

Development ofcartilage model




2 3 4

5 6

Hyalinecartilage

Uncalcifiedmatrix


Uncalcifiedmatrix

Calcifiedmatrix

Medullarycavity


Nutrientartery

Perichondrium

Proximalepiphysis

Distalepiphysis

Diaphysis

Periosteum


Spongybone


Bone Growth During Infancy, Childhood and Adolescence

Growth in Length The growth in length of

long bones involves two major events:1. Growth of cartilage

on the epiphyseal plate

2. Replacement of cartilage by bone tissue in the epiphyseal plate


Bone Growth During Infancy, Childhood and Adolescence

Osteoclasts dissolve the calcified cartilage, and osteoblasts invade the area laying down bone matrix

The activity of the epiphyseal plate is the way bone can increase in length

At adulthood, the epiphyseal plates close and bone replaces all the cartilage leaving a bony structure called the epiphyseal line


Bone Growth During Infancy, Childhood and Adolescence Growth in Thickness

Bones grow in thickness at the outer surface Remodeling of Bone

Bone forms before birth and continually renews itself

The ongoing replacement of old bone tissue by new bone tissue

Old bone is continually destroyed and new bone is formed in its place throughout an individual’s life


Bone Growth During Infancy, Childhood and Adolescence A balance must exist between the actions of

osteoclasts and osteoblasts

If too much new tissue is formed, the bones become abnormally thick and heavy

Excessive loss of calcium weakens the bones, as occurs in osteoporosis

Or they may become too flexible, as in rickets and osteomalacia


Factors Affecting Bone Growth and Bone Remodeling Normal bone metabolism depends on several factors Minerals

Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling

Vitamins Vitamin A stimulates activity of osteoblasts Vitamin C is needed for synthesis of collagen Vitamin D helps build bone by increasing the

absorption of calcium from foods in the gastrointestinal tract into the blood

Vitamins K and B12 are also needed for synthesis of bone proteins


Factors Affecting Bone Growth and Bone Remodeling Hormones

During childhood, the hormones most important to bone growth are growth factors (IGFs), produced by the liver IGFs stimulate osteoblasts, promote cell division at the

epiphyseal plate, and enhance protein synthesis

Thyroid hormones also promote bone growth by stimulating osteoblasts

Insulin promotes bone growth by increasing the synthesis of bone proteins


Factors Affecting Bone Growth and Bone Remodeling Hormones

Estrogen and testosterone cause a dramatic effect on bone growth Cause of the sudden “growth spurt” that occurs

during the teenage year Promote changes in females, such as widening of

the pelvis Shut down growth at epiphyseal plates

Parathyroid hormone, calcitriol, and calcitonin are other hormones that can affect bone remodeling


Fracture and Repair of Bone Calcium and phosphorus needed to strengthen and

harden new bone after a fracture are deposited only gradually and may take several months

The repair of a bone fracture involves the following steps1) Formation of fracture hematoma

Blood leaks from the torn ends of blood vessels, a clotted mass of blood forms around the site of the fracture

2) Fibrocartilaginous callus formation Fibroblasts invade the fracture site and produce collagen

fibers bridging the broken ends of the bone3) Bony callus formation

Osteoblasts begin to produce spongy bone trabeculae joining portions of the original bone fragments

4) Bone remodeling Compact bone replaces spongy bone

Compact boneSpongy bone

Periosteum

Fracture hematoma

Fracturehematoma

BonefragmentOsteocyte

Red bloodcell

Blood vessel

Formation of fracture hematoma

Phagocyte

Osteon

1

Phagocyte

Osteoblast

Fibroblast

Fibrocartilaginouscallus

Collagen fiberChondroblastCartilage

Fibrocartilaginous callus formation2


Periosteum

Fracture hematoma

Fracturehematoma


Red bloodcell

Blood vessel


Phagocyte

Osteon

1

Bony callus

Spongy bone

Osteoblast

Bony callus formation

Osteocyte

3


Periosteum

Fracture hematoma

Fracturehematoma


Red bloodcell

Blood vessel


Phagocyte

Osteon

1

Phagocyte

Osteoblast

Fibroblast




Spongy bone

OsteoblastOsteoclast

New compactbone

Bony callus formation Bone remodeling

Osteocyte

3 4


Periosteum

Fracture hematoma

Fracturehematoma


Red bloodcell

Blood vessel


Phagocyte

Osteon

1

Phagocyte

Osteoblast

Fibroblast




Bony callus


Bone’s Role in Calcium Homeostasis Bone is the body’s major calcium reservoir Levels of calcium in the blood are maintained

by controlling the rates of calcium resorption from bone into blood and of calcium deposition from blood into bone Both nerve and muscle cells depend on

calcium ions (Ca2+) to function properly Blood clotting also requires Ca2+

Many enzymes require Ca2+ as a cofactor


Bone’s Role in Calcium Homeostasis Actions that help elevate blood Ca2+ level

Parathyroid hormone (PTH) regulates Ca2+ exchange between blood and bone tissue PTH increases the number and activity of

osteoclasts PTH acts on the kidneys to decrease loss of

Ca2+ in the urine PTH stimulates formation of calcitriol a

hormone that promotes absorption of calcium from foods in the gastrointestinal tract


Bone’s Role in Calcium Homeostasis


Bone’s Role in Calcium Homeostasis Actions that work to decrease blood Ca2+

level

The thyroid gland secretes calcitonin (CT) which inhibits activity of osteoclasts

The result is that CT promotes bone formation and decreases blood Ca2+ level

Accelerates uptake of calcium and phosphate into bone matrix


Exercise and Bone Tissue Bone tissue alters its strength in response to

changes in mechanical stress Under stress, bone tissue becomes stronger through

deposition of mineral salts and production of collagen fibers by osteoblasts

Unstressed bones diminishes because of the loss of bone minerals and decreased numbers of collagen fibers

The main mechanical stresses on bone are those that result from the pull of skeletal muscles and the pull of gravity

Weight-bearing activities help build and retain bone mass


Aging and Bone Tissue The level of sex hormones diminishes during

middle age, especially in women after menopause A decrease in bone mass occurs Bone resorption by osteoclasts outpaces bone

deposition by osteoblasts Female bones generally are smaller and less

massive than males Loss of bone mass in old age has a greater

adverse effect in females


Aging and Bone Tissue There are two principal effects of aging on bone tissue:

1) Loss of bone mass Results from the loss of calcium from bone matrix The loss of calcium from bones is one of the symptoms in

osteoporosis

2) Brittleness Results from a decreased rate of protein synthesis Collagen fibers gives bone its tensile strength The loss of tensile strength causes the bones to become very brittle

and susceptible to fracture


End of Chapter 6

Copyright 2009 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.

copyright 2009, john wiley & sons, inc. the skeletal system: bone tissue chapter 6

Documents

bone tissue functions

bone tissue slide

bone growth

bone nourishment

bone tissue chapter

bone tissue aging

structure of bone diaphysis

yellow bone marrow