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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)
TYPES OF BONES Four main types of bones of the body:
Short bones: somewhat cube-shaped and nearly equal in length and width.
Examples: most wrist and ankle bones
TYPES OF BONES Four main types of bones of the body:
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)
TYPES OF BONES Four main types of bones of the body:
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
Macroscopic Structure of Bone
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
Macroscopic Structure of Bone
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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