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The Skeletal System: Bone Tissue Chapter 6. The Skeletal System: Bone Tissue. 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 Exercise and Bone Tissue Aging and Bone Tissue.

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the skeletal system bone tissue
The Skeletal System: Bone Tissue
  • 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
  • Exercise and Bone Tissue
  • Aging and Bone Tissue
functions of bone and skeletal system
Functions of Bone and Skeletal System
  • Support
  • Protection
  • Assistance in Movement
  • Mineral Homeostasis
  • Blood Cell Production
  • Triglyceride Storage
functions of bone and skeletal system5
Functions of Bone and Skeletal System
  • Support
    • Structural framework of the body
      • Supports soft tissues
      • Provides attachment points for tendons of skeletal muscle
  • Protection
    • Protects important internal organs
      • Cranium protects brain
      • Vertebrae protects spinal cord
      • Ribs protect lungs and heart
functions of bone and skeletal system6
Functions of Bone and Skeletal System
  • Assistance in Movement
    • Skeletal muscle attaches to bone
      • Skeletal muscle contraction pulls on bone producing movement
  • Mineral Homeostasis
    • Bone tissue stores several minerals
      • Acts to serve as a reservoir of critical minerals
        • Calcium (99% of body’s content)
        • Phosphorus
functions of bone and skeletal system7
Functions of Bone and Skeletal System
  • Blood Cell Production
    • Red bone marrow produces (Hemopoiesis)
      • Red blood cells
      • White blood cells
      • Platelets
  • Triglyceride Storage
    • Yellow bone marrow
      • Triglycerides stored in adipose cells
        • Serves as a potential chemical energy reserve
structure of bone
Structure of Bone
  • Long Bone Anatomy (Humerus)
  • Diaphysis
  • Epiphysis
  • Metaphysis
    • Epiphyseal growth plate
  • Articular cartilage
    • Perforating fibers
  • Periosteum
  • Medullary cavity
  • Endosteum
histology of bone tissue
Histology of Bone Tissue
  • Extracellular matrix surrounding widely separated cells
    • Matrix
      • 15% water
      • 30% collagen fibers
      • 55% crystallized mineral salts
  • The most abundant mineral salt is calcium phosphate
histology of bone tissue12
Histology of Bone Tissue
  • A process called calcification is initiated by bone-building cells called osteoblasts
  • Mineral salts are deposited and crystallize in the framework formed by the collagen fibers of the extracellular matrix
  • Bone’s flexibilitydepends on collagen fibers
histology of bone tissue13
Histology of Bone Tissue
  • Four types of cells are present in bone tissue
  • Osteogenic cells
    • Undergo cell division (stem cells); the resulting cells develop into osteoblasts
  • Osteoblasts
    • Bone-building cells
    • Synthesize extracellular matrix of bone tissue
  • Osteocytes
    • Mature bone cells
    • Exchange nutrients and wastes with the blood
histology of bone tissue14
Histology of Bone Tissue
  • Osteoclasts
    • Release enzymes that digest the mineral components of bone matrix (resorption)
    • Regulate blood calcium level
histology of bone tissue15
Histology of Bone Tissue
  • Bone may be categorized as:
    • Compact
    • Spongy
histology of bone tissue16
Histology of Bone Tissue
  • Compact Bone
    • Resists the stresses produced by weight and movement
    • Components of compact bone are arranged into repeating structural units called osteons or Haversian systems
    • Osteons consist of a central (Haversian) canal with concentrically arranged lamellae, - lacunae, osteocytes, and canaliculi
histology of bone tissue20
Histology of Bone Tissue
  • Osteon
    • Central canals run longitudinally through bone
    • Around the central canals are concentric lamellae
      • Rings of calcified matrix (like the rings of a tree trunk)
    • Between the lamellae are small spaces called lacunae which contain osteocytes
    • Radiating in all directions from the lacunae are tiny canaliculi filled with extracellular fluid and the plasma membrane extensions of the osteocyte
histology of bone tissue21
Histology of Bone Tissue
  • Osteon
    • Canaliculi connect lacunae, forming a system of interconnected canals
      • Providing routes for nutrients and oxygen to reach the osteocytes
    • The organization of osteons changes in response to the physical demands placed on the skeleton
histology of bone tissue22
Histology of Bone Tissue
  • Spongy Bone
    • Lacks osteons
    • Lamellae are arranged in a lattice of thin columns called trabeculae
      • Spaces between the trabeculae make bones lighter
      • Trabeculae of spongy bone support and protect the red bone marrow
      • Hemopoiesis (blood cell production) occurs in red bone marrow of spongy bone
histology of bone tissue23
Histology of Bone Tissue
  • Spongy Bone
    • Within each trabecula are lacunae that contain osteocytes
    • Osteocytes are nourished from the blood circulating through the trabeculae within the red bone marrow.
    • Interior bone tissue is made up primarily of spongy bone
    • The trabeculae of spongy bone are oriented along lines of stress
      • helps bones resist stresses without breaking while keeping them light.
blood and nerve supply of bone
Blood and Nerve Supply of Bone
  • Bone is richly supplied with blood
    • Periosteal arteries accompanied by nerves supply the periosteum and compact bone
    • Epiphyseal veins carry blood away from long bones
  • Nerves accompany the blood vessels that supply bones
    • The periosteum is rich in sensory nerves sensitive to tearing or tension
bone formation
Bone Formation
  • The process by which bone forms is called ossification
  • Bone formation occurs in four situations:
    • 1) Formation of bone in an embryo
    • 2) Growth of bones until adulthood
    • 3) Remodeling of bone
    • 4) Repair of fractures
bone formation27
Bone Formation
  • Formation of Bone in an Embryo
    • Bone formation follows one of two patterns
      • Intramembranous ossification
        • Flat bones of the skull and mandible are formed in this way
        • “Soft spots” that help the fetal skull pass through the birth canal later become ossified forming the skull
      • Endochondral ossification
        • The replacement of cartilage by bone
        • Most bones of the body are formed in this way including long bones
bone formation28
Bone Formation
  • Formation of Bone in an Embryo
    • Cartilage formation and ossification occurs during the sixth week of embryonic development
bone growth during infancy childhood and adolescence
Bone Growth During Infancy, Childhood and Adolescence
  • Growth in Length
  • The growth in length of long bones involves two major events:
    • 1) Growth of cartilage on the epiphyseal plate
    • 2) Replacement of cartilage by bone tissue in the epiphyseal plate
bone growth during infancy childhood and adolescence41
Bone Growth During Infancy, Childhood and Adolescence
  • Osteoclasts dissolve the calcified cartilage, and osteoblasts invade the area laying down bone matrix
  • The activity of the epiphyseal plate is the way bone can increase in length
  • 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 adolescence43
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
bone growth during infancy childhood and adolescence44
Bone Growth During Infancy, Childhood and Adolescence
  • A balance must exist between the actions of osteoclasts and osteoblasts
    • If too much new tissue is formed, the bones become abnormally thick and heavy
    • Excessive loss of calcium weakens the bones, as occurs in osteoporosis
    • Or they may become too flexible, as in rickets and osteomalacia
factors affecting bone growth and bone remodeling
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 A stimulates activity of osteoblasts
    • Vitamin C is needed for synthesis of collagen
    • Vitamin D helps build bone by increasing the absorption of calcium from foods in the gastrointestinal tract into the blood
    • Vitamins K and B12 are also needed for synthesis of bone proteins
factors affecting bone growth and bone remodeling46
Factors Affecting Bone Growth and Bone Remodeling
  • Hormones
    • During childhood, the hormones most important to bone growth are growth factors (IGFs), produced by the liver and bone tissue (under influence of hGH)
      • IGFs stimulate osteoblasts, promote cell division at the epiphyseal plate, and enhance protein synthesis
    • Thyroid hormones (T3 and T4) also promote bone growth by stimulating osteoblasts
    • Insulin promotes bone growth by increasing the synthesis of bone proteins
factors affecting bone growth and bone remodeling47
Factors Affecting Bone Growth and Bone Remodeling
  • Hormones
    • Estrogen and testosterone cause a dramatic effect on bone growth
      • Cause of the sudden “growth spurt” that occurs during the teenage year
      • Promote changes in females, such as widening of the pelvis
      • Ultimately-Shut down growth at epiphyseal plates
    • Parathyroid hormone, calcitriol, and calcitonin are other hormones that can affect bone remodeling
bone s role in calcium homeostasis
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 homeostasis49
Bone’s Role in Calcium Homeostasis
  • Actions that help elevate blood Ca2+ level
    • Parathyroid hormone (PTH) regulatesCa2+ exchange between blood and bone tissue
      • PTH increases the number and activity of osteoclasts (i.e., resorption)
      • PTH acts on the kidneys to decrease loss of Ca2+ in the urine
      • PTH stimulates formation of calcitriol (active form of Vitamin D) a hormone that promotes absorption of calcium from foods in the gastrointestinal tract
bone s role in calcium homeostasis51
Bone’s Role in Calcium Homeostasis
  • Actions that work to decrease blood Ca2+ level
    • The thyroid gland (i.e., parafollicular cells) secretes calcitonin (CT) whichinhibits activity of osteoclasts
    • The result is that CT promotes bone formation and decreases blood Ca2+ level
    • See Table 6.2
fracture and repair of bone
Fracture and Repair of Bone
  • Fracture Types
    • Open (compound) fracture
      • The broken ends of the bone protrude through the skin
    • Closed (simple) fracture
      • Does not break the skin
    • Comminuted fracture
      • The bone is splintered, crushed, or broken into pieces
    • Greenstick fracture
      • A partial fracture in which one side of the bone is broken and the other side bends
    • Impacted fracture
      • One end of the fractured bone is forcefully driven into another
    • Pott’s fracture
      • Fracture of the fibula, with injury of the tibial articulation
    • Colles’ fracture
      • A fracture of the radius in which the distal fragment is displaced
    • Stress fracture
      • A series of microscopic fissures in bone
fracture and repair
Fracture and Repair
  • Anatomical appearance – like breaking a green twig

Greenstick

fracture and repair54
Fracture and Repair
  • Anatomical appearance – the distal part is shoved up into the proximal part.

Impacted

fracture and repair55
Fracture and Repair
  • Anatomical appearance – though not seen here, one or both bones are “open” to the outside.

Open (compound)

fracture and repair56
Fracture and Repair
  • Eponyms – Colles’ is a fracture of the distal radius ± ulna.

Colles’

fracture and repair of bone57
Fracture and Repair of Bone
  • Calcium and phosphorus needed to strengthen and harden new bone after a fracture are deposited only gradually and may take several months
  • The repair of a bone fracture involves the following steps
    • 1) Formation of fracture hematoma
      • Blood leaks from the torn ends of blood vessels, a clotted mass of blood forms around the site of the fracture
    • 2) Fibrocartilaginous callus formation
      • Fibroblasts invade the fracture site and produce collagen fibers bridging the broken ends of the bone
    • 3) Bony callus formation
      • Osteoblasts begin to produce spongy bone trabeculae joining portions of the original bone fragments
    • 4) Bone remodeling
      • Compact bone replaces spongy bone
slide58

Osteon

Osteon

Osteon

Osteon

Periosteum

Periosteum

Periosteum

Periosteum

Compact bone

Compact bone

Compact bone

Compact bone

Spongy bone

Spongy bone

Spongy bone

Spongy bone

Fracture hematoma

Fracture hematoma

Fracture hematoma

Fracture hematoma

Blood vessel

Blood vessel

Blood vessel

Blood vessel

Fibroblast

Fibroblast

Fibroblast

Phagocyte

Phagocyte

Phagocyte

Phagocyte

Phagocyte

Phagocyte

Phagocyte

Fibrocartilaginous

callus

Fibrocartilaginous

callus

Fibrocartilaginous

callus

Fracture

hematoma

Fracture

hematoma

Fracture

hematoma

Fracture

hematoma

Osteoblast

Osteoblast

Osteoblast

Red blood

cell

Red blood

cell

Red blood

cell

Red blood

cell

Collagen fiber

Collagen fiber

Collagen fiber

Chondroblast

Chondroblast

Chondroblast

Bone

fragment

Bone

fragment

Bone

fragment

Bone

fragment

Cartilage

Cartilage

Cartilage

Osteocyte

Osteocyte

Osteocyte

Osteocyte

1

1

1

1

2

2

2

Formation of fracture hematoma

Formation of fracture hematoma

Formation of fracture hematoma

Formation of fracture hematoma

Fibrocartilaginous callus formation

Fibrocartilaginous callus formation

Fibrocartilaginous callus formation

Bony callus

Bony callus

New compact

bone

Osteoblast

Osteoblast

Osteoclast

Spongy bone

Spongy bone

Osteocyte

Osteocyte

3

3

4

Bony callus formation

Bony callus formation

Bone remodeling

fracture and repair59
Fracture and Repair

Once a bone is fractured, repair proceeds in

a predictable pattern:

  • The first step, which occurs 6-8 hours after injury, is the formation of a fracture

hematoma, as a result of

blood vessels breaking in

the periosteum and

in osteons.

fracture and repair60
Fracture and Repair
  • The second and third steps involve the formation of a callus (takes a few weeks, to as many as six months).
    • Phagocytes remove cellular debris and fibroblasts

deposit collagen to

form a fibro-

cartilaginous callus...

fracture and repair61
Fracture and Repair
  • ... which is followed by osteoblasts forming a bony

callus of spongy bone.

fracture and repair62
Fracture and Repair
  • The final step takes several months and is called remodeling :
    • Spongy bone is replaced by

compact bone.

    • The fracture line

disappears, but

evidence of the break

remains.

exercise and bone tissue
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 and fibroblasts
    • 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
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 tissue65
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