1. Ch. 6 The Skeletal System

2. Introduction Skeletal System Bones Structures that make up the joints
Tissues
Bone
Cartilage
Fibrous conn. tissue – forms ligaments that connect bone to bone

3. Functions of the Skeleton
Supports the body
Protects some internal organs
Contains & protects red bone marrow
Stores excess calcium

4. Types of Bone Tissue Bone cells – osteocytes
Matrix – calcium salts, collagen
In normal circumstances, calcium removed = calcium deposited
Regulated by osteocytes
Fig. 6-1 shows 2 types of bone tissue
Compact (ground)
Cancellous (spongy)

6. Types of Bone Tissue (cont.)
Compact
Made of osteons (haversian systems)
Microscopic cylinders of bone matrix with osteocytes in concentric rings around central haversian canals
Microscopic channels (canaliculi) connect osteocytes with blood vessels and other osteocytes

7. Types of Bone Tissue (cont.)
Spongy
No haversian system
Contains osteocytes, matrix, blood vessels
Cavities often contain red bone marrow, which produce RBCs, platelets, WBCs

8. Classification of Bones
Long
Short
Bones of wrists, ankles
Flat
Ribs, shoulder blades, hip bones, cranial bones
Irregular
Vertebrae, facial bones

9. Classification of Bones (cont.)
Long Bones
Bones of arms, legs, hands, feet
Shaft (diaphysis)
Made of compact bone; hollow, forming a canal within the shaft
Marrow canal (medullary cavity) contains yellow bone marrow (adipose tissue)
Ends (epiphyses) (Fig. 6-1)
Made of spongy bone covered with thin layer of compact bone
Red bone marrow replaced by yellow in adult bones

11. Classification of Bones (cont.)
Short, flat, irregular bones made of spongy bone covered with thin layer of compact bone
Red bone marrow within spongy bone
Joint surfaces covered with articular cartilage
Periosteum covers remainder of bone
Fibrous conn. tissue membrane; its collagen fibers merge with tendons & ligaments attached to bone
Anchors aforementioned structures and contains blood vessels & osteoblasts

12. Embryonic Growth of Bone
Skeleton is first made of cartilage & fibrous connective tissue; gradually replaced by bone
Bone matrix produced by osteoblasts
Process called ossification
Baby has fibrous connective tissue between skull bones (fontanels); Fig. 6-2
Permit compression during birth, growth of brain after birth
These “soft spots” are ossified by the age of 2

14. Embryonic Growth of Bone (cont.)
Rest of embryonic skeleton
First made of cartilage
ossification begins in 3rd month of gestation in long bones
Osteoblasts produce bone matrix in center of diaphyses of long bones and in center of short, flat, irregular bones (Fig. 6-3)

16. Embryonic Growth of Bone (cont.)
Long bones develop centers of ossification in epiphyses
Growth occurs in epiphyseal discs (cartilage) at jxn of diaphysis with epiphysis
Bone grows in length as more cartilage is produced on epiphysis side (Fig. 6-3)
On diaphysis side, osteoblasts produce bone matrix to replace cartilage
B/w ages 16-25, all cartilage of epiphyseal disc is replaced by bone; bone lengthening stops

17. Embryonic Growth of Bone (cont.)
Osteoclasts dissolve & reabsorb minerals of bone matrix (resorption)
Very active in embryonic long bones
Reabsorb bone matrix in center of diaphysis to form marrow canal
Blood vessels grow into marrow canals of embryonic long bones, establishing red bone marrow
After birth, red marrow replaced by yellow
Red marrow remains in spongy bone of short, flat, irregular bones

18. Factors that Affect Bone Growth & Maintenance
Heredity – polygenic inheritance
Nutrition – Ca, P, protein, vitamin A, C, D
Hormones – growth hormone, thyroxine, parathyroid hormone, insulin, estrogen, testosterone (Table 6-1)
Exercise or “stress” – bearing weight
As simple as everyday walking

19. The Skeleton 2 divisions 206 bones in body (Fig. 6-4)
Axial – forms body’s axis
Skull, vertebral column, rib cage
Appendicular – supports appendages or limbs
Bones of arms, legs, shoulder, pelvic girdles
206 bones in body (Fig. 6-4)

20. The Skeleton
Study Fig. 6-4 thru 6-16
Study Tables 6-2 thru 6-5

21. Joints - Articulations
Joint – where 2 bones meet or articulate
See Table 6-5 & Fig. 6-15
Classification of joints
Synarthrosis – immovable joint (suture b/w 2 cranial bones)
Amphiarthrosis – slightly movable joint (symphysis joint b/w adjacent vertebrae)
Diarthrosis – freely movable joint; largest category
Ball & socket
Pivot
Hinge, etc.

23. Synovial Joints All diarthroses are synovial joints (Fig. 6-16)
On the joint surface of each bone is articular cartilage, providing a smooth surface
Joint capsule of fibrous connective tissue encloses joint in a strong sheath
Synovial membrane lines joint capsule, secreting synovial fluid into joint cavity
Fluid is thick & slippery, preventing friction

24. Synovial Joints Many have bursae Bursitis
Small sacs of synovial fluid b/w joint & tendons that cross over the joint
Permit tendons to slide easily as bones are moved
Bursitis
Excessive use of a joint, causing inflammation & pain

25. Aging & The Skeletal System
Bone tissue loses Ca
Bone matrix thins
Bones become brittle
Fractures are more likely to occur
Erosion of articular cartilage
Knees, fingers
What can you do?
Exercise
Diet high in Ca, Vitamin D