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Lecture 1- Bone Structure, Formation and Growth

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

2 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

3 Classification of Bones on the Basis of Shape
Figure 5.1

4 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

5 Classification of Bones- Shape
Short bones Generally cube-shape Contain mostly spongy bone Examples: Carpals, tarsals Sesamoid bones Small, round Example: patella

6 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

7 Classification of Bones- Shape
Irregular bones Irregular shape Do not fit into other bone classification categories Example: Vertebrae and hip

8 Classification of Bones on the Basis of Shape

9 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 a

10 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 a

11 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

12 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

13 Blood Cell Formation Marrow is a soft mass of connective tissue
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

14 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

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

16 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


18 Structures of a Long Bone
Periosteum Outside covering of the diaphysis Fibrous connective tissue membrane Endosteum Lines medullary cavity Sharpey’s fibers Secure periosteum to underlying bone Arteries Supply bone cells with nutrients

19 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

20 Structures of a Long Bone
Articular cartilage Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces

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

22 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

23 Microscopic Anatomy of Bone
Figure 5.3

24 Types of Bone Cells Osteocytes Osteoblasts Osteoclasts
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

25 Osteoblast Osteocyte Osteoclast Builds new bone Mature bone cell
OsteoblastsOsteoblasts are responsible for building new bone and lie at the centre of bone physiology. Their functions include the synthesis of collagen and the control of mineralisation. OsteoclastsOsteoclasts are specialised cells that resorb bone. They work by sealing off an area of bone surface then, when activated, they pump out hydrogen ions to produce a very acid environment, which dissolves the hydroxyapatite. OsteocytesBone adapts to applied forces by growing stronger in order to withstand them; it is known that exercise can help to improve bone strength. Osteocytes are thought to be part of the cellular feed-back mechanism which directs bone to form in the places where it is most needed. They lie within mineralised bone and it is thought that they may detect mechanical deformation and mediate the response of the osteoblasts. Osteoclast Eats bone


27 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

28 Endochondral Bone Formation
Perichondrium becomes a periosteum and a bone collar forms around the cartilage model. Cavity begins to form within cartilage. Periosteal bud invades marrow cavity. Osteoblasts lay down spongy bone in the bone interior. Osteoclast eventually remove the spongy bone and leave a cavity to house fat.

29 Endochondral Bone Formation

30 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

31 275 bones 12 weeks (6-9 inches long)
Fetal Skeleton 275 bones 12 weeks (6-9 inches long)

32 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

33 Long Bone Formation and Growth

34 Bone Growth in Adulthood
Bone formation and growth stops between 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

35 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

36 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

37 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

38 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

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