The Skeletal System

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Unit 4 The Skeletal System Lecture 1- Bone
Structure, Formation and Growth (Chapters 7 8)
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The Skeletal System- Overview

• The skeleton contains 206 bones
• Parts of the skeletal system
• Bones (skeleton)
• Joints
• Cartilages
• Ligaments (bone to bone)
• Divided into two divisions
• Axial skeleton
• Appendicular skeleton limbs and girdle

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Classification of Bones on the Basis of Shape
Figure 5.1
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Classification of Bones- Shape

• Long bones
• Typically longer than wide
• Have a shaft with heads at both ends
• Contain mostly compact bone
• Examples Femur, humerus

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Classification of Bones- Shape

• Short bones
• Generally cube-shape
• Contain mostly spongy bone
• Examples Carpals, tarsals
• Sesamoid bones
• Small, round
• Example patella

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Classification of Bones- Shape

• Flat bones
• Thin and flattened
• Usually curved
• Thin layers of compact bone around a layer of
  spongy bone
• Examples Skull, ribs, sternum

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Classification of Bones- Shape

• Irregular bones
• Irregular shape
• Do not fit into other bone classification
  categories
• Example Vertebrae and hip

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Classification of Bones on the Basis of Shape
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Classification of Bones- Markings

• Projections
• grow out from a bone surface
• site of muscle and ligament attachments
• help form joints
• Examples process, crest, facet, ramus, condyle

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Classification of Bones- Markings

• Openings
• Hollows, cavities or passageways
• allow blood vessels and nerves to pass through
• Examples sinus, meatus, foramen, groove,
  fissure
• Depressions
• Indentations
• articulates with a process
• Examples fossa

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Functions of Bones

• Support of the body
• Protection of soft organs
• Movement due to attached skeletal muscles
• Storage of minerals and fats
• Blood cell formation

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Mineral Storage

• Bone matrix is made of collagen and inorganic
  mineral salts
• Salt 70 of matrix weight
• Mostly calcium phosphate
• Calcium is vital in the body
• Muscle cell contraction
• Nerve impulse conduction
• Blood clot formation
• Low blood calcium osteoclasts break down bone
• High blood calcium osteoblasts form bone

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Blood Cell Formation

• Process of blood cell formation is called
  hematopoiesis
• Begins in yolk sac, outside of embryo
• Blood cells are later manufactured in the live
  and spleen
• Eventually form bone marrow
• Marrow is a soft mass of connective tissue

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Blood Cell Formation

• Types of Marrow
• Red Marrow
• Forms blood cells (red, white and platelets)
• Yellow Marrow
• Stores fat
• Does not produce blood cells
• Marrow distribution changes with age
• Infants- most marrow is red
• Over time yellow marrow replaces red marrow
• Adults- red marrow found in spongy bone of skull,
  ribs, sternum, clavicle, vertebrae and hips

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Bone Tissue

• Two basic types of bone tissue
• Compact bone
• Homogeneous
• Dense
• Outer bone
• Spongy bone
• Small needle-like pieces of bone
• Many open spaces, porous
• Inner bone

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Gross Anatomy of a Long Bone

• Diaphysis
• Shaft
• Composed of compact bone
• Epiphysis
• Ends of the bone
• Composed mostly of spongy bone
• Metaphysis
• Between diaphysis and epiphysis

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Structures of a Long Bone

• Periosteum
• Outside covering of the diaphysis
• Fibrous connective tissue membrane
• Endosteum
• Lines medullary cavity
• Sharpeys fibers
• Secure periosteum to underlying bone
• Arteries
• Supply bone cells with nutrients

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Structures of a Long Bone

• Medullary cavity
• Cavity of the shaft
• Contains yellow marrow (mostly fat) in adults
• Contains red marrow (for blood cell formation) in
  infants

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Structures of a Long Bone

• Articular cartilage
• Covers the external surface of the epiphyses
• Made of hyaline cartilage
• Decreases friction at joint surfaces

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Microscopic Anatomy of Bone

• Osteon
• A unit of bone
• Central (Haversian) Canal
• Opening in the center of an osteon
• Carries blood vessels and nerves

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Microscopic Anatomy of Bone

• Lacunae
• Cavities containing bone cells (osteocytes)
• Arranged in concentric rings
• Lamellae
• Rings around the central canal
• Sites of lacunae
• Canaliculi
• Tiny canals
• Connect lacunae

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Microscopic Anatomy of Bone
Figure 5.3
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Types of Bone Cells

• Osteocytes
• Mature bone cells
• Osteoblasts
• Bone-forming cells
• Osteoclasts
• Bone-destroying cells
• Break down bone matrix for remodeling and release
  of calcium
• Bone remodeling is a process by both osteoblasts
  and osteoclasts

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Builds new bone
Osteoblast
Mature bone cell
Osteocyte
Osteoclast
Eats bone
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Bone Development and Growth

• Osteogenesis- development of bone
• Intramembranous bones
• originate within layers of connective tissue
• Flat bones of skull, clavicles, sternum and some
  facial bones
• Endochondral bones
• Develop from hyaline cartilage
• Shaped like future bones
• Initial growth is rapid

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Endochondral Bone Formation

1. Perichondrium becomes a periosteum and a bone
   collar forms around the cartilage model.
2. Cavity begins to form within cartilage.
3. Periosteal bud invades marrow cavity.
4. Osteoblasts lay down spongy bone in the bone
   interior.
5. Osteoclast eventually remove the spongy bone and
   leave a cavity to house fat.

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Endochondral Bone Formation
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Bone Development and Growth- Fetus

• The skeleton begins to form during the first few
  weeks of prenatal development
• In embryos, the skeleton is primarily hyaline
  cartilage
• Cartilage remains in isolated areas
• Bridge of the nose
• Parts of ribs
• Joints
• Bone structures continue to develop into adulthood

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Fetal Skeleton
275 bones12 weeks (6-9 inches long)
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Bone Growth in Childhood

• Epiphyseal plates allow for growth of long bone
  during childhood
• New cartilage is continuously formed
• Older cartilage becomes ossified
• Cartilage is broken down
• Bone replaces cartilage

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Long Bone Formation and Growth
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Bone Growth in Adulthood

• Bone formation and growth stops between 23-25
  years of age
• Bone remodeling continues throughout life
• Osteoclasts resorb bone tissue
• Osteoblasts replace/deposit new bone
• 10-20 of the skeleton is replaced annually

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Factors Affecting Bone Development, Growth and
Repair

• Nutrition
• Vitamin D
• Needed for calcium absorption
• Lack of calcium softens and deforms bones
• Vitamin A and C
• A is needed for osteoblast and osteoclast
  activity
• Deficiency slows bones development
• C is needed for collagen formation
• Deficiency leads to slender, fragile bones

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Factors Affecting Bone Development, Growth and
Repair

• Hormones
• Pituitary gland secretes growth hormone
• Stimulates division of cartilage cells
• Pituitary dwarfism
• Absence of growth hormone
• Very short, normal body proportions
• Pituitary gigantism
• Excess growth hormone
• Height over 8 feet
• In adults, enlarged hands, feet or jaw

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Factors Affecting Bone Development, Growth and
Repair

• (Hormones cont.)
• Sex hormones promote bone formation
• Abundant during puberty, so long bone growth
  increases
• Also stimulate ossification and eventually stop
  bone growth
• Estrogen is stronger, so females reach maximum
  height sooner
• Physical Stress

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Factors Affecting Bone Development, Growth and
Repair

• Physical Stress
• Contraction of skeletal muscles cause bone tissue
  to thicken and strengthen
• Hypertrophy
• Bones of athletes are stronger and heavier
• Lack of exercise cause bone tissue to waste
• Atrophy
• Fractures can cause shortening of bones
• Astronauts experience a 1 loss of bone mass per
  month in space