1. Lesson Overview
32.1 The Skeletal System

2. THINK ABOUT IT Broken bones can heal.
How does that happen? And what does that tell you about the nature of our skeleton?

3. The Skeleton The skeleton helps organisms retain their shape.
Skeletons include the external exoskeletons of arthropods (insects) and the internal endoskeletons of vertebrates.

4. Structure of the Skeleton
There are 206 bones in the adult human skeleton.
Divided into:
axial skeleton
appendicular skeleton.

5. Structure of the Skeleton
Axial skeleton
supports the central axis of the body
consists of the skull, the vertebral column, and the rib cage

6. Structure of the Skeleton
Appendicular skeleton
consists of the bones of the arms and legs, pelvis and shoulder

7. Functions of the Skeletal System
supports the body
protects internal organs
assists movement
stores minerals
a site of blood cell formation

8. Bones
What is the structure of a typical human bone?

9. Bones Bones are living tissue.
It consists of living cells and protein fibers that are surrounded by deposits of calcium and phosphorus salts.

10. Structure of Bones
The structure of a typical long bone is shown.

11. Structure of Bones
 The bone is surrounded by a tough layer of connective tissue called periosteum.

12. Structure of Bones
Beneath the periosteum is a thick layer of compact bone.

13. Structure of Bones
Nerves and blood vessels run through compact bone in channels called Haversian canals.

14. Structure of Bones
Spongy bone is a less dense tissue found under the outer layer of compact bone.

15. Structure of Bones
Spongy bone is found in the ends of long bones and in the middle of short, flat bones.
The latticework (lace) structure in spongy bone adds strength without adding excess mass.

16. Structure of Bones
Inside many bones are cavities that contain a soft tissue called bone marrow.

17. Structure of Bones
Yellow marrow consists primarily of cells that store fat.
Red marrow contains stem cells that produce most types of blood cells.

18. Development of Bones
The skeleton of a human embryo is composed mainly of a type of connective tissue called cartilage.
Cartilage is replaced by bone during the process of bone formation called ossification, which begins up to seven months before birth.

19. Development of Bones
Osteoblasts deposit minerals that replace the cartilage to form bones.
Most osteoblasts mature into osteocytes that maintain the minerals in bone tissue and strengthen the growing bone.

20. Development of Bones
Many long bones have growth plates at the ends.

21. Development of Bones
The growth of cartilage at these plates causes the bones to lengthen. The cartilage is gradually replaced by bone.
During late adolescence or early adulthood, growth plates become completely ossified, and the person “stops growing.”

22. Development of Bones
Cartilage remains in parts of the body that are flexible, such as the nose and ears.
 It also cushions the areas where bones meet (ex: knee).

23. Bone Remodeling and Repair
Osteoclasts are cells that break down old bone tissue and osteoblasts build new bone tissue so that bones do not become brittle and weak.
Both types of cells work together to repair broken and damaged bones.

24. Bone Remodeling and Repair
Osteoporosis
disorder in which bone is broken down faster that it is rebuilt
bones become less dense and weaker
more common in older adults, especially women 
consuming calcium and exercise can help with prevention

25. Joints
What is the role of joints?

26. Joints Joint where one or more bones meet
contain connective tissues that hold bones together
permit bones to move without damaging each other

27. Types of Joints
Type of joint depends on its type of movement
immovable
slightly movable
freely movable.

28. Immovable Joints
often called fixed joints
allow no movement
bones grow together until they are fused
example: the bones in the skull

29. Slightly Movable Joints
permit a small amount of movement
the bones of slightly movable joints are separated from each other
example: between the two bones of the lower leg and between vertebrae

30. Freely Movable Joints
permit movement in two or more directions
grouped according to the shapes of the surfaces of the adjacent bones
hinge joint
pivot joint
saddle joint
ball and socket joint

31. Types of Joints
Many freely movable joints are involved in the movements of a gymnast.

32. Structure of Joints
In freely movable joints, cartilage covers the surfaces where two bones come together.
The joints are surrounded by a fibrous joint capsule that helps hold the bones together while still allowing for movement.

33. Structure of Joints
Ligaments are strips of tough connective tissue that hold bones together in a joint.

34. Structure of Joints
The inner layer of the joint capsule, called the synovial cavity, produces a substance called synovial fluid.
 Synovial fluid reduces friction so the bones can slide over each other smoothly.

35. Structure of Joints
Small sacs of synovial fluid called bursae (singular: bursa) reduce the friction between the bones of a joint and act like tiny shock absorbers (example: knee)

36. Joint Injuries
A common injury among athletes is damage to the anterior cruciate ligament (ACL) of the knee. This ligament is found in the center of the knee between the femur and the tibia. It is common in sports like basketball and soccer.

37. Joint Injuries
Excessive strain on a joint can cause inflammation -a response in which excess fluid causes swelling, pain, heat, and redness.

38. Joint Injuries
Wear and tear over the years often leads to osteoarthritis, which develops as the cartilage begins to break down in joints that are used frequently (ex: fingers, knees, hips, and spine).
These joints become painful and stiff as the bones start to rub together.