The Skeletal System: Bone Tissue

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Chapter 6

• The Skeletal System Bone Tissue
• Lecture Outline

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INTRODUCTION

• Bone is made up of several different tissues
  working together.
• Each individual bone is an organ the bones,
  along with their cartilages, make up the skeletal
  system.
• The study of bone structure and the treatment of
  bone disorders is called osteology.

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Functions of Bone

• Supporting soft tissues, providing an attachment
  site for tendons and muscles
• Protects internal organs from injury
• Work with muscles to produce movement
• Storage of minerals like calcium phosphate
• Blood cell production occurs in red bone marrow
• Energy storage (triglycerides) in yellow bone
  marrow

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Bone Anatomy

• A long bone is one that has greater length than
  width.

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Anatomy of a Long Bone

• Diaphysis shaft the long, cylindrical main
  portion of the bone
• Epiphysis either end of a long bone
• Metaphyses are the areas between the epiphysis
  and diaphysis

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Anatomy of a Long Bone

• Articular cartilage is a thin layer of cartilage
  that forms a joint where two bones connect.
• Periosteum is a tough connective tissue covering
  that surrounds a bone.

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Anatomy of a Long Bone

• The medullary cavity or marrow cavity is the
  space in the diaphysis that stores yellow bone
  marrow.
• The endosteum is a thin membrane that lines the
  medullary cavity.

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HISTOLOGY OF BONE TISSUE

• Bone (osseous) tissue consists of widely
  separated cells surrounded by large amounts of
  matrix.
• The matrix of bone is made up of water, collagen,
  and salts.
• These salts are used to form new bone tissue,
  which is called calcification.

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Bone Marrow

• Red bone marrow produces red blood cells, white
  blood cells, and platelets
• Yellow bone marrow stores triglycerides (fats)
  which are used for energy

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Bone Cells (4)

1. Osteogenic cells are stem cells that can undergo
   cell division and become other bone cells.
2. Osteoblasts are bone-building cells.
3. Osteocytes are mature bone cells and the
   principal cells of bone tissue. They maintain
   bone metabolism, and exchange nutrients and
   wastes with the blood.
4. Osteoclasts are large cells that are used for
   bone development, growth, maintenance, and repair

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Types of Bone

• 80 of your skeleton is made of compact bone.
• 20 is spongy bone.

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Compact Bone

• Compact bone contains few spaces and is the
  strongest type of bone.
• It makes up the bulk of long bones
• It provides protection and support, and resists
  the stresses of weight and movement
• It is made of osteons, hard rings of material

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Spongy Bone

• Spongy bone does not contain osteons. It consists
  of thin columns of bone with many red marrow
  filled spaces.
• It forms most of the structure of short, flat,
  and irregular bones, and the epiphyses of long
  bones.
• Spongy bone tissue is light and supports and
  protects the red bone marrow.
• Hip bones, rib bones, the breastbone, vertebrae
  are types of spongy bones

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Blood and Nerve Supply of Bone

• Periosteal arteries
• supply periosteum (outer part of bone)
• Nutrient arteries
• Supplies inner bone and red marrow
• Veins carry blood away from the bone and back to
  the heart.
• All bones have sensory nerves attached to them.

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BONE FORMATION

• Bone formation is termed osteogenesis or
  ossification
• 1. Formation of the bony skeleton. (embryonic
  development)
• 2. Bone Growth (childhood into early adulthood)
• 3. Bone Remodeling and Repair (adulthood)
• Two types of ossification occur.
• Intramembranous ossification
• Endochondrial ossification

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Intramembranous Ossification

• The flat bones of the skull and the jaw are
  formed this way.
• These bones develop from fibrous membranes.
• 1. A cluster of cells, called the ossification
  center, and form osteoblasts.
• 2. Osteoblasts become osteocytes, and harden
  (calcify)
• 3. Blood vessels grow into place.
• 4. The periosteum (membrane) grows over the bone.

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Endochondral Ossification

• Endochondral ossification is the replacement of
  cartilage by bone. Most bones in the body form
  this way.
• 1. Cartilage forms in the shape of the bone.
• 2. An ossification center forms, and begins to
  grow osteoblasts.
• 3. The marrow cavity forms.
• 4. New ossification centers form at each
  epiphysis, so bones can continue to elongate.

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Growth in Length

• Bones grow only at the epiphyseal plate which is
  located in the metaphysis of a growing bone.
• Between ages 18 to 25, epiphyseal plates close.
• Growth in length stops at age 25

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Growth in Thickness

• Bone can increase in diameter through
  appositional growth.
• Osteoblasts grow outward and form hardened ridges
• These ridges fold over and become osteons (rings)
• The marrow cavity enlarges.

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Bone Remodeling

• Remodeling is the ongoing replacement of old bone
  tissue by new bone tissue.
• Old bone is constantly destroyed by osteoclasts
  (bone resorption), whereas new bone is
  constructed by osteoblasts (bone deposition).
• 20 of spongy bone and 4 of compact bone is
  remodeled each year!
• This can be triggered by exercise, diet, or lack
  of exercise.

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Factors Affecting Bone Growth

• Nutrition
• adequate levels of minerals and vitamins
• calcium and phosphorus for bone growth
• vitamin C for collagen formation, Vitamin A for
  osteoblasts
• vitamins K and B12 for protein synthesis

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Factors affecting Bone Growth

• Sufficient levels of specific hormones
• during childhood need insulin like growth factor
  (IGF)
• Human Growth Hormone (too muchgigantism, not
  enoughpituitary dwarfism)
• sex steroids at puberty
• At puberty the sex hormones, estrogen and
  testosterone, stimulate sudden growth and
  modifications of the skeleton to create the male
  and female forms (wider pelvis).

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Bone Scan

• A bone scan is a diagnostic technique for viewing
  bones.
• A radioactive tracer is injected through an IV
• A scanner measures blood flow to areas of the
  bone
• Dark areas (more blood flow) may indicate cancer
• Light areas (less blood) may indicate arthritis
  or bone loss.

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Braces

• In orthodontics teeth are moved by braces.
• This places stress on bone in the sockets causing
  osteoclasts and osteoblasts to remodel the
  sockets so that the teeth can be properly
  aligned.

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Fracture and Repair of Bone

• A fracture is any break in a bone.
• Fractures are named according to their severity,
  the shape of the fracture, or the physician who
  first described fractures.

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Common Fractures

• Open/Compound Fracture Broken bones protrude
  through skin
• Closed Fracture Broken bones do NOT show through
• Comminuted fracture Bone splinters at site of
  impact
• Greenstick Fracture One side of the bone breaks,
  the other bends (only occurs in children)
• Impacted fracture One bone is driven into another

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Common Fractures

• Potts fracture fracture of the fibula (leg
  bone)
• Colles fracture fracture of the forearm bone
• Stress fracture Microscopic fissures but no
  broken bones
• Results from repeated, strenuous activity like
  running, jumping, or dancing

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Fracture Repair of Bone

• Healing is faster in bone than in cartilage since
  bones have better blood supplies
• Healing of bone is still slow process due to
  vessel damage
• Clinical treatment
• closed reduction restore pieces to normal
  position by manipulation
• open reduction realignment during surgery
• Both are followed by immobilization in a cast,
  sling, or bandage

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Repair of a Fracture

• 1. Formation of fracture hematoma
• Damaged blood vessels produce a clot
• 2. Formation of fibrocartilagenous callus
• Collagen and cartilage fibers span the break

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Repair of a Fracture

• 3. Formation of bony callus
• osteoblasts secrete spongy bone
• lasts 3-4 months
• 4. Bone remodeling
• compact bone replaces the spongy in the bony
  callus
• surface is remodeled back to normal shape

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Calcium Homeostasis Bone Tissue

• Skeleton is a reservoir of Calcium Phosphate
• Calcium ions involved with many body systems
• nerve muscle cell function
• blood clotting
• enzyme function in many biochemical reactions
• Small changes in blood levels of Ca2 can be
  deadly
• cardiac arrest if too high
• respiratory arrest if too low

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EXERCISE AND BONE TISSUE

• Within limits, bone has the ability to alter its
  strength in response to mechanical stress by
  increasing deposition of mineral salts and
  production of collagen fibers.
• Removal of mechanical stress leads to weakening
  of bone through demineralization (loss of bone
  minerals) and collagen reduction.
• reduced activity while in a cast
• astronauts in weightless environment
• bedridden person
• Weight-bearing activities, such as walking or
  moderate weightlifting, help build and retain
  bone mass.

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AGING AND BONE TISSUE

• Loss of calcium which may result in osteoporosis.
• very rapid in women 40-45 as estrogens levels
  decrease
• in males, begins after age 60
• Decreased rate of protein synthesis
• decrease in collagen production which gives bone
  its tensile strength
• decrease in growth hormone
• bone becomes brittle susceptible to fracture

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Osteoporosis

• Decreased bone mass resulting in porous bones
• Those at risk
• white, thin menopausal, smoking, drinking female
  with family history
• athletes who are not menstruating due to
  decreased body fat decreased estrogen levels
• people allergic to milk or with eating disorders
  whose intake of calcium is too low
• Prevention or decrease in severity
• adequate diet, weight-bearing exercise,
  estrogen replacement therapy (for menopausal
  women)
• behavior when young may be most important factor

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• Osteoarthritis
• degenerative arthritis or degenerative joint
  disease
• caused by 'wear and tear' on a joint
• Cartilage breaks down and wears away then the
  bones rub together, causing pain, swelling, and
  stiffness.
• Factors age, weight, sports, previous injuries.
• Rheumatoid Arthritis
• A disease that leads to inflammation of the
  joints and surrounding tissues.

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Disorders of Bone Ossification

• Rickets
• calcium salts are not deposited properly
• bones of growing children are soft
• bowed legs, skull, rib cage, and pelvic
  deformities result
• Osteomalacia
• new adult bone produced during remodeling fails
  to ossify
• hip fractures are common

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Diseases and Disorders of the Bone

• Submit a 1-2 page, TYPED report, due Monday
  10/29.
• 1. Describe the disease/disorder.
• 2. What causes this to happen?
• 3. Are there certain groups more at risk than
  others?
• 4. What are some treatments? Cures?
• 5. Describe the impact on the life of someone
  affected.
• 6. Are there support groups?
• 7. REFERENCES!!!!