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