Chapter 6: Skeletal System Chapter 4: Skeletal Tissue

CHAPTER 6: SKELETAL SYSTEMCHAPTER 4: SKELETAL SYSTEM

TISSUE

Lesson Objectives Skeletal

Discuss the functions of the skeletal system. Classify bone in the basis of their shape and location. Describe parts of long bone. Describe the histological features of bone tissue. Explain the steps involved in bone formation. Describe the factors involved in bone growth and

maintenance. Compare the principal structural and functional

differences between male and female skeletons. Tissues

Explain how connective tissue is classified.

FUNCTIONS OF BONE AND THE SKELETAL SYSTEM

Support Framework of body; supports soft tissue; provides points of

attachment for skeletal muscles (most) Protection

Of internal organs Assisting in movement

How? Muscle to bone attachment; muscles contracts pulls on bone muscle + bone = movement

Mineral homeostasis Minerals stored in bone tissue (Ca and P); released on

demand when needed to other body parts via blood stream Production of blood cells Red Bone Marrow;

connective tissue

Red Bone Marrow Within connective tissue

Red bone marrow through hemopoiesis makes:

Red blood cells White blood cells Platelets

Fragment of cytoplasm enclosed in a cell membrane; lacks a nucleus

Found in circulating blood Plays role in hemostasis (stoppage of bleeding)

Red bone marrow consists of: Developing red blood cells Adipocytes (fat cells composed mainly of fat tissue adipose) Fibroblasts (large, flat cells that secrete matrix of extracellular

material of aerolar (collagen and elastic tissue) and dense connective tissue

Macrophages (white blood cells of immune system)

Location of Red Bone Marrow Developing bones of fetus and some

adult bones Pelvis Ribs Sternum Vertebrae Skull Ends of arm and thigh bones

FUNCTIONS OF BONE AND THE SKELETAL SYSTEM

Support Protection Assisting in movement Mineral homeostasis Production of blood cells Triglyceride storage

In adipose tissue or yellow bone marrow

Yellow Bone Marrow Yellow bone marrow consists of adipose

tissue and some blood cells Stores triglycerides in its adipose tissue

Potential energy reserve Adults most red bone marrow has

changed to yellow bone marrow Not found in newborns

TYPES OF BONES Four main types of bones of the body:

Long bones: have greater length and width, consists of a shaft and a variable number of ends, usually somewhat curved for strength.

Examples: thigh (femur), leg (tibia and fibula), arm (humerus), forearm (ulna and radius), and fingers and toes (phalanges)


Short bones: somewhat cube-shaped and nearly equal in length and width.

Examples: most wrist and ankle bones


Flat bones: generally thin, offer considerable protection, have extensive surface areas for muscle attachment.

Examples: cranial bones (protect the brain), sternum/breastbone and ribs (protect organs in thorax), pelvis (protects digestive and reproductive organs),and scapulae (shoulder blades)


Irregular bones: complex shapes Examples: vertebrae of the backbone and some facial bones

STRUCTURE OF BONE

Macroscopic Structure of Bone Microscopic Structure of Bone

Macroscopic Structure of Bone Parts as they relate to a long bone

with greater length than width Diaphysis: bone’s shaft or body; long,

cylindrical, main portion of bone Epiphyses: distal and proximal ends of

bones Metaphyses: regions in a mature bone

where diaphysis joins epiphyses; in growing bone each metaphyses includes an epiphyseal plate, layer of hyaline cartilage that allows the diaphysis of bone to grow in length; when bone growth in length stops, cartilage in epiphyseal plate replaced by bone and this bony structure is now known as the epiphyseal line

Macroscopic Structure of Bone

Articular cartilage: thin layer of hyaline cartilage covering part of the epiphysis where bone forms a joint (articulation) with another bone; it reduces friction and absorbs shock; lacks a perichondrium so repair of damage is limited


Periosteum: tough sheath of dense irregular connective tissue surrounding a bone’s surface wherever it lacks articular cartilage; consists of bone-forming cells enabling bone to grow in diameter or thickness; protects the bone, assists in fracture repair, helps nourish bone tissue, serves as attachment point for ligaments and tendons


Medullary cavity: marrow cavity; space within diaphysis containing yellow bone marrow in adults

Endosteum: thin membrane lining medullary cavity; contains single layer of bone-forming cells

Microscopic Structure of Bone

Composition of intracellular materials of the bone, or osseous tissue matrix: 25% water 25% collagen fibers (protein) 50% crystallized mineral salts

Calcification: mineral salts are deposited into a framework formed by collagen fibers they crystallize and tissue hardens Calcification is initiated by: osteoblasts; bone-building cells_ Hardness of bone depends on crystallized inorganic mineral salts Flexibility depends on collagen fibers Tensile strength is provided by collagen fibers and other organic molecules that offer resistance to being stretched or torn apart

Four Major Types of Bone Tissue Osteogenic cells=> producing =

unspecialized stem cells Osteoblasts=> blasts = buds or sprouts Osteocytes => cytes = cells Osteoclasts => clasts = break

Spaces between cells and matrix are for: channels for blood vessels (supply bone with

nutrients) storage for red blood marrow

Composition of skeleton: BASED ON SIZE AND DISTRIBUTION OF SPACES

80% compact bone20% spongy bone

Compact Bone Tissue Contains few spaces; forms external layer of all

bones; makes up bulk of diaphysis of long bone; provides protection and support; resists stress produced by weight and movement

Spongy Bone Tissue Makes up most of the bone tissue of short, flat, and

irregularly shaped bones; forms most of epiphyses of long bone and a narrow rim around the medullary cavity of the diaphysis of long bones.

Compact Bone Tissue Pages 127-129 explain how these

structures provide routes for nutrients and oxygen to reach osteocytes and for waste to diffuse away

Spongy Bone Tissue Trabeculae: little beams; irregular

latticework of thin columns of bone; spaces between filled with red bone marrow

Dense or Compact Bone Spongy or Cancellous BoneHardness Mostly solid

Bony structures with spaces filled with bone marrow

Consists of Osteocytes in lacunae Osteocytes in lacunae

Location Covers all bone surfaces; except where they could rub

Short, flat bones, inside ends of long bones

Functional units Osteons or haversian systems Trabeculae filled with red bone marrow

Stress tolerance High end to end; low from side

Not on heavy stress areas, can take stress from any direction- disperses it

Bone Scans Darker spots = ‘hotspots’

lighter spots = ‘coldspots’

OSSIFICATION: BONE FORMATION Ossification: process by which bone forms Site of ossification: loose fibrous connective

tissue membranes and pieces of hyaline cartilage, shaped like little bones in embryonic skeleton

Four Principle Situations (1) Initial formation of bones in embryo and

fetus(2) Growth of bones during infancy,

childhood, and adolescence until adult sizes are reached

(3) Remodeling of bone (replacement of old bone tissue by new bone tissue throughout life)

(4) Repair of fractures (breaks in bones) throughout life

Initial Bone Formation in an Embryo and Fetus

First composed of mesenchyme shaped liked bones, sites/templates where ossification will occur

Ossification begins during the sixth week of embryonic development and follows one of two patterns Intramembranous ossification Endochondral ossification

Two methods of bone formation Intramembranous Ossification

Bone forms directly in mesenchyme arranged in sheetlike layers resembling membranes; directly on or within loose fibrous connective tissue membranes

Endochondral Ossification Bone forms within hyaline cartilage that develop

from mesenchyme

Intramembranous OssificationSimplest of two methods-Forms flat bones of skull and mandible (lower jawbone) -Replaces ‘soft spot’ on fetal skull ______________

Endochondral Ossification Replacement of hyaline cartilage by

bone. Most bone in the body below the skull

except the clavicles are formed this way

Bone Growth in Length and Thickness

Long bones grow during infancy, childhood, and adolescense

Growth in Length Through the activity of the epiphyseal

plate Young chondrocytes divide in the

epiphyseal plate

Growth In Thickness As bones lengthen, they thicken Cells in perichondrium differentiate into

osteoblasts that secrete bone extracellular matrix

Osteoblasts develop into osteocytes, lamellae added to bone surface and new osteons of compact bone tissue

Bone Remodeling Remodeling: ongoing replacement of old bone

tissue by new bone tissue

COMMON DISORDERS---PAGE 133FRACTURES

fracture: any break in a bone

Four different types of fractures (1) partial: incomplete break across the bone;

i.e. a crack (2) complete: complete break across the bone;

bone broken in two or more pieces (3) closed (simple): fractured bone does not

break through skin (4) open (compound): broken ends of bone

protrude through skin

FRACTURE REPAIR

What happens when a bone breaks?

OUCH!!!

First step: phagocytes begin to remove dead bone tissue

Second step: chondrocytes form fibrocartilage at fracture site that bridges the broken ends of bones

Third step: fibrocartilage converted to spongy bone tissue by osteoblasts

Fourth step: bone remodeling occurs, dead portions are absorbed by osteoclasts and spongy bone converted to compact bone

Factors Affecting Bone Growth and Remodeling

Factors that control bone metabolism: Minerals: Ca, P, Mg need adequate amounts of each Vitamins: A, C, D Hormones: hGH, IGFs (insulin-like growth factors;

produced locally by bone and by the liver when stimulated by hGH ), insulin, thyroid hormones, parathyroid hormones, calcitonin hGH: _main hormone before puberty that stimulates

bone growth; produced by anterior lobe of pituitary gland over secretion of hGH: produces giantism, person becomes taller and heavier than normal

under secretion of hGH: _produces dwarfism, short stature

Stress (weight bearing exercise)

Mineral crystals generate : production of collagen fibers, bone mass

Osteoblasts are: bone-forming cells Heavily stressed bones are: notably thicker; builds &

retains bone mass Unstressed bones become: lose strength; loss of

bone mass Example: leg in cast up to ~30% of bone mass Examples of serious bone health risks:

bedridden or paralyzed patients people in weightless environments

Bone’s Role in Calcium Homeostasis

Bone stores 99% of the total amount of calcium in the body. Calcium become available to other tissues when broken down

during remodeling (replacement of old bone with new bone)

Effects of small changes in blood calcium levels: Too high: heart may stop Too low: breathing may cease

Bone’s Role in Calcium Homeostasis

Nerve cell functions depend on the right levels of Ca2+

Enzymes require Ca2+, as a cofactor (non-protein component of enzymes bound to proteins and required for biological functions).

Blood clotting requires Ca2+.

Function of bone in calcium homeostasis in blood calcium levels to “buffer” the blood calcium level, releasing Ca2+ to the blood

when blood calcium levels falls and depositing Ca2+ back in bone when blood level rises When levels falls in blood

parathyroid hormone (PTH) regulates Ca2+ and is produced by parathyroid glands

When levels rise in blood calcitonin (CT) produced by thyroid gland

Negative Feedback System Regulation of blood calcium

(Ca2+) levels

Exercise and Bone Tissue

Bone alters its strength in response to mechanical stress

HOW???? Increased deposition of mineral salts and

production of collagen fibers

Without mechanical stress bone does not remodel normally because resorption outpaces bone formation.

Comparison of Female and Male Skeletons

Aging and the Skeletal System Birth to adolescence=> more bone produced than

lost Young adults=> rate of production to loss about

equal Middle age=> decrease in bone mass

WHY??? Levels of sex steroids lowered

Greater problem for female; less bone mass to begin with = more osteoporosis in femalesFemales age 30 bone loss starts; about age 45 estrogen levels decrease; by age 70 -30% of bone calcium lostMales begins around age 60, then loss of about 3% of bone mass every 10 years

CHAPTER 4 TISSUES

Types of Tissues(1) Epithelial -covers body surfaces; body cavities, hollow organs, and ducts; forms glands(2) Connective -protects and supports the body and its organs, binds organs together, stores energy reserves as fat, provides immunity(3) Muscular -generates physical force to move body structures (4) Nervous -detects changes inside and outside the body, initiates and transmits nerve impulses that aid in homeostatic maintenance

Cell Junctions Point of contract between plasma

membranes of tissue cells As each osteocyte lays matrix, it gets

sealed into its own room and they reach out to the next osteocyte and communicate by gap junctions (type of cell junctions) called lacunae even though they are very isolated

Connective Tissue:General Features of Connective

Tissue Consists of two basic elements: cells and

extracellular matrix Highly vascular (have a rich blood supply) Has nerve cells; cartilage does not

Extracellular matrix materials between widely spaced cells composed of protein fibers and ground substance (materials between cell ands and fibers)

Cartilage and tendons are avascular…

Connective Tissue Cells Read through the types on pages 88-89;

which one(s) are found in bone connective tissue?

Connective Tissue Extracellular Matrix

Ground substance Between the cells and fibers Supports cells, binds them together, provides

medium through which substances are exchanged between the blood and cells

Chondroitin sulfate ground substance is found in bone and cartilage Provides support and adhesiveness in bone

connective tissues Fibers

Strengthen and support connective tissues Read page 90 for rest of information…

Classification of Connective Tissues

1. Loose Connective Tissue a. areolar connective tissue---not applicable to bones note: only truly found in joint areas b. adipose tissue---yellow bone marrow, padding around joints function: serves as energy reserve; support c. reticular connective tissue---red bone marrow (gives rise to RBCs); cells that make the reticular fibers are fibroblasts function: filters and removes worn-out blood cells; forms a scaffolding for bone marrow

Three Types of Fibers Loose connective tissue is composed of loosely

woven collagen and elastic fibers. The fibers and other components of the connective tissue matrix are secreted by fibroblasts (i.e.: reticular fiber).

Continued…2. Dense Connective Tissue a. dense regular connective tissue---forms tendons (attach muscle to bone), most ligaments (attach bone to bone), and aponeuroses (sheet-like tendons attach muscle to muscle or muscle to bone) function: provides strong attachment between structures, allows them to resist pulling (tension) b. dense irregular connective tissue---periosteum of bone, periosteum of cartilage, joint capsules function: provides tensile (pulling) strength c. elastic connective tissue---not applicable to bones *****NOTE: FOUND IN SOME LIGAMENTS BETWEEN VERTEBRAE

Continued… 3. Cartilage Consists of: dense network of collagen fibers embedded in chondroitin sulfate

Strength is due to: collagen fibers Resilience due to: chondroitin sulfate (rubbery component of ground substance)

Cells called chondrocytes (mature cartilage) are found in lacunae lacunae like little lakes within extracellular matrix

Perichondrium (dense irregular connective tissue) surrounds the surface of cartilage

Cartilage is different from other types of connective tissue because it does not have a blood supply or nerves and it secretes antiangiogenesis factor (substance that prevents blood vessel growth

Three Types of Cartilage(1) hyaline cartilage (most common; weakest)

Consists of: resilient gel as its ground substance; appears in body as bluish-white shiny substance

Properties: compressible, flexible, insensitive Locations: ribs to sternum; supporting

larynx, trachea, and bronchia; bone ends at synovial joints; part of large septum

Three Types of Cartilage(2) fibrocartilage (strongest)

Consists of: chondrocytes scattered among bundles of collagen fibers

Lacks: perichondrium Properties: strength and rigidity Location: discs between vertebrae, pads of knee

joints

Three Types of Cartilage(3) elastic cartilage

Consists of: chondrocytes within threadlike network of elastic fibers

Properties: strength and elasticity; maintains shape of certain structures; i.e. external ear

Locations: auricle of external ear; epiglottis and part of larynx; auditory canal

Bone Tissue SHOULD READ COMPOSED

OF… bone or osseous tissue periosteum red and yellow bone marrow endosteum

Main component of compact bone: Osteon of Haversian system

Main component of spongy bone: Trabeculae

Bone Tissue Functions Supports soft tissue Protects delicate structures Works with skeletal muscles to generate

movement Stores calcium and phosphorus Stores red bone marrow Storage site for triglycerides

Membranes

Synovial membranes (flat sheets of pliable tissue) line the cavities of some joints

Location: joints areas of bone Types of tissue: composed of areolar

connective tissue and adipose tissue with collagen fibers

Function: secretes synovial fluid from its synoviocytes that lubricates ends of bones as they move at the joints, nourishes cartilage, removes microbes and debris from joint cavity

Muscular Tissue- page 98Tissue Repairing: Restoring Homeostasis- pages 98-99

Aging and Tissues- page 100

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Chapter 6: Skeletal System Chapter 4: Skeletal Tissue

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