Unit 3 Part 1 Notes


Unit 3 Part 1 – Skeletal System


  1. Bone Formation and Growth

 Image result for bone formation and growth


  1. Endochondral Ossification (Initial Bone Formation)


  • Masses of hyaline cartilage form blueprint of future bones.
  • Cartilage tissue breaks down and disappears.
  • Blood vessels and osteoblasts invade disintegrating tissue.
  • Osteoblasts form spongy bone in place of original cartilage.


  1. Bone Growth


  • Bones grow (wider and longer) from small openings in distal ends of bone (epiphyses) and from a larger opening in the middle of bone (diaphysis).
  • If an epiphyseal plate is present, bone is still growing.
  • Growth ceases when epiphyseal cartilage in the plate becomes bone (ossifies).


  1. Ossification Timetable


  • Third month (Prenatal) – Long bone ossification begins.
  • Fourth month (Prenatal) – Ossification centers appear in diaphysis.
  • Birth to age 5 – Ossification centers appear in epiphyses.
  • 5 – 12 (Female) Ossification occurring in head,
  • 5 – 14 (Male)     hands, and feet.
  • 17 – 20 Upper limbs and scapulae ossify.
  • 18 – 23 Lower limbs and coxal (hip) bones ossify.
  • 23 – 25 Sternum, clavicle, and vertebrae ossify.
  • By 25   All bones ossify.


  1. Factors Affecting Bone Growth


  • 1 – Nutrition
    1. Vitamin D – Absorption of calcium in intestines
      1. Lack of results in rickets (children) and osteomalacia (adults).


    1. Vitamin A – Bone Resorption
      1. Lack of results in bone retardation.
    2. Vitamin C – Synthesis of collagen
      1. Lack of results in thin and fragile bones.
      2. Scurvy


  • 2 – Physical Exercise
    1. Increased physical stress - Hypertrophy (thick and strong).


    1. Lack of physical stress - Atrophy (thin and weak)
    2. Image result for thin legs wheelchair


  • 3 – Hormonal Secretions (Growth Hormone) 
    1. Too much - Gigantisism (Robert Wadlow 8’11” tallest man in recorded history)
    2. Related image


    1. Too little - Dwarfism


  1. Microscopic Structure of Bone and Cartilage


  • Bone (Diagram below is the Tibia)
      1. Thin outer covering of the entire bone is called the periosteum. (only the articular cartilage at epiphyses is not covered)
      2. Outer layer hard and dense (Dense or Compact Bone).
      3. Ends of bone have numerous spaces and marrow (Spongy Bone/Cancellous Bone).
      • Threads of spongy bone contain spaces – Trabeculae (Red Marrow Cavities in the above diagram)
      1. Cartilage found between the Epiphysis and the Diaphysis is called the Epiphyseal/Growth Plate.  When completely turned to bone it is called the Epiphyseal Line.
      2. Hollowed diaphysis is called the Medullary Cavity.
      3. Marrow found in the Medullary Cavity of a young long bone is Red Marrow (hemopoeisis); Adult Bone is Yellow Marrow (fat storage).


  • Haversian Systems  (the picture below is microscope slide of an actual Haversian System found in Compact Bone of a Long Bone
  • Compact bone made up of Haversian Systems.
    1. Haversian systems made up of circular rings – Concentric Lamella
    2. Lamella surround Haversian canal which contains blood vessel.
    3. Osteocytes (Bone cells) lie in spaces between lamella – Lacunae
    4. Canaliculi – Canals that connect lamella: Nutrients --> Blood Vessel in Haversian Canal --> Canaliculi --> Osteocytes in Lacunae


  • Cartilage
    • Image result for cartilage
    1. Made up of collagen (flexibility)
    2. Chondrocytes  - Cartilage cells (instead of osteocytes) occupy lacunae.


  1. Functions of Bone (Them Dry Bones Link)
  • Support – Supporting framework and attachment point for skeletal muscles.


  • Protection of internal organs (ribs, skull and vertebrae)
    •     Related image


  • Movement – Muscles pull on bones at joints.


  • Storage of calcium and phosphorus.
    • Calcitonin
      • Hormone released by Throid Gland
      • Causes calcium to be directed to the bone from the blood
      • Activates Osteoblast activity
    • PTH/Parathyroid Hormone
      • Hormone released by Parathyroid Glands
      • Causes calcium to be directed to the blood from the bone
      • Activates Osteoclast activity




  • Hemopoeisis – Blood cell formation in red bone marrow.
  • Image result for hematopoiesis


  1. Differences in Male and Female Skeleton
  • Male skeleton typically larger.
  • Image result for male vs female skeleton differences


  • Female arm and leg bones are typically lighter.


  • Angle of elbow joint is different.


  • Female pelvis is broader and has larger opening.
  • Image result for male vs female skeleton differences


  1. Types of Bone


  • Long – Humerus, radius, ulna, femur, tibia, fibula 

Image result for long bones

  • Short – Metacarpals, Metetarsals, Phalanges

  • Flat – Skull bones, scapula, ribs & sternum

           Image result for scapula      Related image

  • Irregular – Vertebrae, hip, facial bones

Related image      Image result for facial bones

  • Sesamoid /Round – Patella, Carpals, Tarsals

 Image result for patella    Image result for carpals tarsals


  1. Structure of Long Bones


  • Diaphysis – Hollow shaft of bone made up of compact bone.
  • Medullary cavity – Space within diaphysis filled with  yellow bone marrow.
  • Epiphyses – Ends of bone filled with red bone marrow.
  • Articular Cartilage – Thin layer of cartilage covering each epiphysis which forms a cushion between joints.
  • Periosteum – Strong covering surface of long bones (except at joints).
  • Endosteum – Membrane that lines medullary cavity.
  • Red Marrow -- Marrow mainly found in the spongy bone of adults and it makes new blood cells
  • Yellow Marrow -- Mainly found in the shafts of long bone in adults and is made up of fatty tissue



  1. Hematopoetic Tissue


  • Red Bone Marrow (the picture below shows where active red marrow is found in adults)


    1. Also called “myeloid” tissue
    2. Mainly found in flat bones and cancellous areas of long bones
    3. Red Blood cells, platelets and white blood cells are made here
    4. At birth, nearly all marrow in body is red
      1. Image result for red bone marrow


  • Yellow Bone Marrow

    Image result for red bone marrow

    1. Has a yellow color due to high ratio of fat cells found here
    2. Can convert into red marrow during times of severe blood loss
    3. Can make some white blood cells “leukocytes”


  1. Stem Cells found in Marrow


  • Hematopoetic Stem Cells in Red Bone Marrow
    1. Give rise to the three classes of blood cell that are found in the circulation
      1. Red Blood Cells “erythrocytes”
      2. White Blood Cells “leukocytes”
      3. Platelets “thrombocytes” (clotting cells)


  1. Bone Marrow Diseases
  • Tuberculosis – infections of the bone marrow that lead to decreased blood cell formation (rarer form of bacterial infection)


  • Leukemia – cancer of the bone marrow cells

  • Cures or treatment?
    • Chemotherapy – radiation that kills rapidly dividing cancer cells (also greatly reduces immune system)


  • Marrow Transplants – Compatible donor tissue is taken from the ileum and transplanted into marrow deficient patient