1. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 42 Structure and Function of the Skeletal System

2. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Connective Tissue Cells Extracellular matrix –Ground substance –Protein fibers Characteristics of the tissue depend on the extracellular matrix

3. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Cartilage Ground substance is a gel containing 65%–80% water Oxygen and food can diffuse through this gel Therefore, the tissue does not need blood vessels Different types of cartilage are distinguished by how many protein fibers are in the extracellular matrix –Hyaline cartilage: very few fibers –Fibrocartilage: some elastin fibers –Elastic cartilage: many elastin fibers

4. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Bone Ground substance contains crystals of calcium salts These make the bone rigid They block oxygen and food diffusion, so bone must contain blood vessels Types of bone are distinguished by the pattern the crystals are laid down in: –Cancellous bone: a lattice of tiny struts of bone, like a sponge –Compact bone: laid down in layers like an onion

5. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Bone Cells Osteogenic cells: divide to form the other bone cells Osteoblasts: lay down the extracellular matrix Osteocytes: live in the mature bone and maintain the extracellular matrix Osteoclasts: break down the extracellular matrix

6. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which type of bone cells remain in the extracellular matrix and function as strain sensors? a.Osteogenic b.Osteoblasts c.Osteoclasts d.Osteocytes

7. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer d.Osteocytes Osteocytes are osteoblasts that become trapped in the matrix as tissue is ossified. They live in lacunae, and function as strain sensors (stimulating or inhibiting other bone cells in response to stress).

8. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Bone Remodeling Osteoblasts and osteoclasts are formed when they are needed to remodel bone Osteoclasts remove damaged areas of bone Osteoblasts come after them and replace the extracellular matrix

9. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins PTH is released when blood calcium levels decrease Sustained PTH raises blood calcium levels three ways: ºFrom bone ºFrom kidneys ºFrom intestines Parathyroid Hormone

10. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario Two men have bone problems… One man developed a lung tumor that secreted constant high levels of parathyroid hormone; he became very weak and developed weak bones A second man suffered complete kidney failure; he also developed weak bones Question Why did these men both develop weak bones? Which of them is more likely to have increased blood calcium levels?

11. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Vitamin D Vitamin D is needed to absorb dietary calcium Created in skin cells under the influence of sunlight Absorbed from the diet as a fat-soluble vitamin Activated in a two-step process: –Liver –Kidneys

12. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Calcitonin Released by thyroids when blood calcium is too high Inhibits the release of calcium from bone Reduces osteoclast activity Inhibits vitamin D activation in the kidney Inhibits calcium reabsorption by the kidney

13. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. PTH is released as a result of hypocalcemia.

14. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True PTH is released by the parathyroid gland when serum calcium levels are low. PTH increases calcium levels by acting on bone (bone cells release more calcium), kidneys (more calcium is reabsorbed), and intestines (more calcium is reabsorbed).

15. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Skeletal Structures Epiphysis = end Diaphysis = shaft –Contains bone marrow ºRed marrow: makes blood cells ºYellow marrow: contains fat Metaphysis = widening before the end of the bone

16. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Tendons and Ligaments Extracellular matrix is filled with collagen fibers Strong and not elastic Tendons connect muscles to bone Ligaments connect bones to one another

17. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Joints Synarthroses: little mobility Diarthroses: highly mobile –Joint capsule connects the two bones –Synovial membrane lines joint capsule –Synovial fluid in the joint capsule lubricates joint –Menisci are protective smooth cartilage plates between the two bones –Bursae are small synovial sacs cushioning tendons

18. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which of the following is an example of a synarthrodial joint? a.Elbow b.Wrist c.Sutures of the skull d.Hip/coxal

19. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Sutures of the skull Synarthrodial joints have limited movement. The sutures of the skull do not move. All of the other joints are freely movable (diarthrodial) joints.