1. Skeletal Tissues

2. Compact vs. Spongy Compact bone is dense and solid in appearance.
Cancellous, or spongy, bone is characterized by open space partially filled by an assemblage of needle-like structures.

3. Compact and Spongy Bone

4. Four Bone Types
Long bones – extended longitudinal axis and expanded and often uniquely shaped articular ends.
Examples are the femur and humerus
Short Bones – cube- or box-shaped structure, which are about as broad as they are long.
Examples include the wrist (carpals) and ankle (tarsal) bones

5. Flat bones – generally broad and thin with a flattened and often curved surface.
Examples include some skull bones, scapulae, ribs, and sternum
Irregular Bones – often clustered in groups and come in various shapes and sizes.
Examples include the vertebral bones that form the spine and facial bones

7. Parts of a Long Bone Diaphysis – main shaftlike portion
Epiphyses – both ends of a long bone have a bulbous shape that provides generous space near the joints for stability and muscle attachment.
Articular Cartilage – thin layer of hyaline cartilage that covers joint epiphyses and acts as a cushion.

8. Periosteum – Dense, white fibrous membrane that covers bone except at joint surfaces
Medullary (marrow) cavity – tubelike hollow space in the diaphysis of a long bone. In adults it is filled with fatty yellow marrow.
Endosteum – thin epithelial membrane that lines the medullary cavity of long bones.

10. Bone (Osseous) Tissue Connective tissue
Consists of cells, fibers, and extracellular matrix
Extracellular components are hard and calcified
Matrix is more abundant that the bone cells

11. Composition of Bone Matrix
Inorganic Salt are responsible for the hardness of bone.
Hydroxyapatite – composed of calcium and phosphate
Organic Matrix – composite of collagenous fibers and a mixture of protein and polysaccharides called ground substance.

12. Osteoporosis
Age related skeletal disease that is characterized by loss of bone mineral density, increased bone fragility, and susceptibility to fractures
More common in women
May lose 4% - 8% of their bone density on a yearly basis

14. Microscopic Structure of Bone
Compact bone contains many cylinder-shaped structural units called osteons, or Haversian systems.
Each osteon surrounds a canal that runs lengthwise through the bone.

15. Main Structures of the Osteon
Lamellae – concentric, cylinder shaped layers of calcified matrix.
Lacunae – small spaces containing fluid and bone cells
Canaliculi – ultrasmall canals radiating in all directions from the lacunae that connects them to each other and the Haversian canal

16. Haversian canal – Extends lengthwise through the center of each Haversian system; contains blood vessels, lymph vessels and nerves
Volkmann’s canals – run perpendicular to Haversian canals

17. Structure of Compact and Cancellous Bone

18. Section of Flat Bone

19. Cancellous Bone There are no osteons in cancellous bone
Consists of needle-like bony spicules called trabeculae.
Bone cells are found within the trabaculae
Nutrients are delivered and wastes removed by diffusion

20. Orientation of Trabeculae

21. Types of Bone Cells
Osteoblasts – synthesize and secrete a specialized organic matrix called osteoid, that is an important part of the ground substance of bone. (bone forming cells)
Osteoclasts – giant multinucleate cells that are responsible for the active erosion of bone minerals. (bone reabsorbing cells)

22. Osteocytes – mature, non-dividing osteoblasts that have become surrounded by matrix and now within a lacunae.

23. Osteoblasts and Osteocytes

24. Osteoclast

25. Bone Marrow Soft, diffuse connective tissue called myeloid tissue.
Site of blood cell production
Found in medullary cavities of certain long bones and in the spaces of some spongy bones.

26. Red Marrow & Yellow Marrow
In a child’s body, virtually all of the bones contain red marrow.
Red marrow produces red blood cells.
As an individual ages red marrow is replaced by yellow marrow.
Yellow marrow has become saturated with fat and is no longer active in blood cell production.

27. Active Marrow in Adults

28. Functions of Bone Support – supporting framework of body
Protection – protect delicate structures such as the brain
Movement – joints act as levers and allow movement in conjuction with muscular system
Mineral Storage – major reservoir for calcium, phosphorus, and certain other minerals
Hematopoiesis – blood cell formation

29. Regulation of Blood Calcium Levels
98% of body calcium is stored in bone
Osteoblasts remove calcium from blood
Osteoclasts break down bone and calcium levels in the blood increases
Calcium is important for normal blood clotting, nerve impulses, and muscle contraction

30. Calcium in the Body
Calcium that is consumed is absorbed through the intestines
Calcium is stored and released from bone tissue
The kidneys eliminate extra calcium and absorb calcium from urine if blood calcium levels get too low.

31. Parathyroid Hormone
When calcium levels fall below their “set point,” osteoclasts are stimulated to increase the rate of bone matrix breakdown.
Calcium is released into the blood until the level returns to normal.

32. Vitamin D (Calcitriol)
Acts to increase blood calcium levels
Facilitates the absorption of calcium in the small intestines

33. Calcitonin Functions to reduce blood calcium levels
Enhances excretion of calcium in urine
Inhibits osteoclasts

34. Calcium Deprivation

35. Development of Bone
Before birth, the skeleton consists of cartilage and fibrous structures shaped like bones.
Cartilage is replaced with calcified bone matrix
The combined action of osteoblast and osteoclasts to make bone is known as osteogenesis

37. Intramembranous Ossification
Takes place within a connective tissue membrane

38. Endochondral Ossification
Bone forms from cartilage models
Forms from the center to the ends

39. Endochondral Ossification

44. Epiphyseal Fracture

45. Bone Growth and Resorption
Bone growth is from the combined action of osteoclasts and osteoblasts
Osteoclasts break down bone to enlarge the diameter of the medullary cavity.
Osteoblasts from the periosteum build new bone around the outside of the bone

47. Bone Fracture Repair