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Basic slides of skeletal system and its funtions
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The Skeletal System
Topics to be covered 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 Aging and Bone Tissue
Functions of Bone and Skeletal System4. Mineral Homeostasis:
Calcium balance: contribute to bone strength; stores 99% of body’s calcium;
Phosphorus balance: stored in bones and releases it on demand of the body
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, maintains bone tissues Exchange nutrients and wastes with the blood
Osteoclasts Release enzymes that digest the mineral
components of bone matrix (resorption) Regulate blood calcium level
Osteogenic cell
Osteoblast
Osteocytes
Osteoclast
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
1. Formation bone
1. 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.
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Development of ossification center
Collagen fiber
2. Calcification: Within a few days calcium and other mineral salts
are deposited and extracellular matrix becomes calcified.
1. Formation bone
Calcification2
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bonematrix
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 marrow
1. Formation bone
Mesenchymecondenses
Blood vessel
Spongy bonetrabeculae
Osteoblast
Formation of trabeculae3
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
Periosteum
Spongy bone tissue
Compact bone tissue
Development of the periosteum4
Bone Growth During Infancy, Childhood and Adolescence
Growth in Length The growth in length of long bones
involves four major events:
1. Growth of cartilage on the epiphyseal plate
2. Replacement of cartilage by bone tissue in the epiphyseal plate
3. The activity of the epiphyseal plate is the way bone can increase in length
4. 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
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 D helps build bone by increasing the absorption
of calcium from foods in the gastrointestinal tract into the blood
Vitamins K are also needed for synthesis of bone proteins
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 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