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Chapter 7

Anatomy and Physiology #1 Dr.Days Class Chapter 7 Powerpoint Notes
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Functions of Bone: Support
Bones form the framework of the body and contribute to the shape, alignment, and positioning of body parts; ligaments help hold bones together
Functions of Bone: Protection
Bony "boxes" protect the delicate structures they enclose
Functions of Bone: Movement
Bones and their joints constitute levers that move as muscles contract
Functions of Bone: Mineral Storage
Bones are the major reservoir for calcium, phosphorus, and other minerals
Functions of Bone: Hematopoiesis
Blood cell formation is carried out by myeloid tissue
Functions of the Bone
Support, Protection, Movement, Mineral Storage, Hematopoiesis
5 Major Types of Structural Bones
Long bones, Short bones, Flat bones, Irregular bones, Sesamoid bones
Compact Bone
Is dense and solid in appearance
Cancellous Bone
Also known as spongy bone
Is characterized by open space partially filled with needlelike structures
Parts of a Long Bone: Diaphysis
*Main shaft of a long bone
*Hollow, cylindrical shape and thick compact bone
*Function is to provide strong support without cumbersome weight
Parts of a Long Bone:
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
Parts of a Long Bone:
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
Parts of a Long Bone:
Articular Cartilage
*Layer of hyaline cartilage that covers the articular surface of epiphyses
*Function is to cushion jolts and blows
Parts of a Long Bone:
Medullary (or Marrow) Cavity
*Tubelike, hollow space in the diaphysis
*Filled with yellow marrow in adults
Parts of a Long Bone:
Endosteum
thin, fibrous membrane that lines the medullary cavity
Parts of the Long Bone
Diaphysis, Epiphyses, Periosteum, Articular Cartilage, Medullary Cavity, Endosteum
Parts of a Flat Bone:
*Inner portion is cancellous bone covered on the outside with compact bone
-Cranial flat bones have an internal and external table of compact bone and an inner cancellous region called the diploë
-Bones are covered with periosteum and lined with endosteum, such as in a long bone
-Other flat bones, short bones, and irregular bones have features similar to the cranial bones
*Spaces inside the cancellous bone of short, flat, irregular and sesamoid bones are filled with red marrow
Bone Tissue
*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
Bone Tissue:
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 are also found in bone
Bone Tissue:
Composition of Bone Matrix-
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
Bone Tissue:
Composition of Bone Matrix-
Inorganic Salts and Organic Matrix
Microscopic Structure of Bone:
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 (Volkmann) 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
Structures that Make Up Each Osteon:
Lamellae
*Concentric: cylinder-shaped layers of calcified matrix around the central canal
*Interstitial: layers of bone matrix between the osteons; leftover from previous osteons
*Circumferential: 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
Structures that Make Up Each Osteon:
Lacunae
small spaces containing tissue fluid in which bone cells are located between hard layers of the lamella
Structures that Make Up Each Osteon:
Canaliculi
ultra-small canals radiating in all directions from the lacunae and connecting them to each other and to the central canal
Structures that Make Up Each Osteon:
Central Canal
extends lengthwise through the center of each osteon; contains blood vessels and lymphatic vessels
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
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
Types of Bone Cells:
Osteoclasts
*Giant multinucleated cells
*Responsible for the active erosion of bone minerals
*Contain large numbers of mitochondria and lysosomes
Types of Bone Cells:
Osteocytes
*Mature, nondividing osteoblasts surrounded by matrix and lying within lacunae
Bone Marrow
*Type of soft, diffuse connective tissue; called myeloid tissue
*Site for the production of blood cells
*Found in the medullary cavities of long bones and in the spaces of spongy bone
*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
Bone Marrow:
2 types of Marrow occur during a person's lifetime
-Red Marrow
-Yellow Marrow
Bone Marrow:
Red Marrow
*Found in virtually all bones in an infant's or child's body
*Produces red blood cells
Bone Marrow:
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
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
-Homeostasis of calcium ion concentration essential for the following:
+Bone formation, remodeling, and repair
+Blood clotting
+Transmission of nerve impulses
+Maintenance of skeletal and cardiac muscle contraction
Mechanisms of Calcium Homeostasis:
Parathyroid Hormone and Calcitonin
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
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
Development of Bone: Osteogenesis
Development of bone from small cartilage model to adult bone
Development of Bone:
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
*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
Development of Bone:
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
*Epiphyseal plate can be a site for bone fractures in young people
*Long bones grow in both length and diameter
Development of Bone:
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
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 Octedclasts and Osteoblasts
*Osteoclasts enlarge the diameter of the medullary cavity
*Osteoblasts from the periosteum build new bone around the outside of the bone
Note:
Mechanical Stress ( like Physical Activity) strengthens bones
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
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
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
Types of Cartilage:
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
Types of Cartilage:
Elastic Cartilage
*Forms external ear, epiglottis, and eustachian tubes
*Large number of elastic fibers confers elasticity and resiliency
Types of Cartilage:
Fibrocartilage
*Occurs in pubic symphysis and intervertebral disks
*Small quantities of matrix and abundant fibrous elements
*Strong and rigid
Types of Cartilage
Hyaline cartilage, Elastic Cartilage, Fibrocartilage
Functions of Cartilage
*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
Growth of Cartilage: Interstitial (or Endogenous) Growth
*Cartilage cells divide and secrete additional matrix
*Seen during childhood and early adolescence while cartilage is still soft and capable of expansion from within
Growth of Cartilage:
Appositional (or Exogenous) Growth
*Chondrocytes in the deep layer of the perichondrium divide and secrete matrix
*New matrix is deposited on the surface, thereby increasing its size
*Unusual in early childhood, but once initiated continues throughout life
Cycle of Life: Skeletal Tissue
*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
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