Skeletal System- Part II (PDF) - Abu Dhabi University Fall 2023

Skeletal System- Part II Nermin Eissa, Ph.D. College of Health Sciences Abu Dhabi University Fall-2023  Learning Outcomes: List the three types of joints. Describe the structure and operation of a synovial joint. Summarize the process of...

Skeletal System- Part II Nermin Eissa, Ph.D. College of Health Sciences Abu Dhabi University Fall-2023  Learning Outcomes: List the three types of joints. Describe the structure and operation of a synovial joint. Summarize the process of ossification and list the types of cells involved. Describe the process of bone remodeling. Explain the steps in the repair of bone. 2 ©2020 McGraw-Hill Education  Articulations 2 Articulations (joints) Where bones come together. Are classified as fibrous, cartilaginous, or synovial. Fibrous joints are immovable. Cartilaginous joints are Slightly movable. Synovial joints are freely movable. 3 ©2020 McGraw-Hill Education  Types of Synovial Joints Types of synovial joints: Ball-and-socket joints—allow movement in all planes, even rotational movement. That is, the hips and shoulders. Hinge joints—permit movement in only one direction. That is, the elbow and knee. 52 ©2020 McGraw-Hill Education  Synovial Joints Allow for a Variety of Movement Access the text alternative for these images 53 ©2020 McGraw-Hill Education  Check Your Progress List the three major types of joints. Describe the different movements of synovial joints, and give an example of each in the body. 6 ©2020 McGraw-Hill Education  Bone Growth and Homeostasis 2 Cells involved in bone growth, remodeling, and repair: Osteoblasts—bone-forming cells. Secrete the organic matrix of bone and promote the deposition of calcium salts into the matrix. Osteocytes—mature bone cells. When osteoblasts surround themselves with calcified matrix, they become osteocytes within lacunae. Osteoclasts—bone-absorbing cells. Break down bone; return calcium and phosphate to the blood. Throughout life, osteoclasts remove the matrix of bone and osteoblasts build it up. 7 ©2020 McGraw-Hill Education  Intramembranous Ossification Ossification—the formation of bone. Bones form during embryonic development in two distinctive ways: 1. Intramembranous ossification—forms flat bones (that is, bones of the skull). Bones develop between sheets of fibrous connective tissue. Osteoblasts in the periosteum carry out further ossification. Trabeculae form and fuse into compact bone, which surrounds the spongy bone inside. 8 ©2020 McGraw-Hill Education  Endochondral Ossification 2. Endochondral ossification—forms most bones (that is, long bones like the tibia). Calcified bone matrix replaces the hyaline cartilage models of the bones. Bone formation spreads from the center of the bone to the ends. Bone Growth by Endochondral Ossification 9 ©2020 McGraw-Hill Education  Steps of Endochondral Ossification 1 The steps of endochondral ossification: The cartilage model: in the embryo, chondrocytes form cartilage models (hyaline cartilage shaped like the future bones). The bone collar: osteoblasts secrete the matrix, which then calcifies. The result is a bone collar made of compact bone, which covers the diaphysis. 10 ©2020 McGraw-Hill Education  Steps of Endochondral Ossification 2 The primary ossification center: blood vessels bring osteoblasts to a region called a primary ossification center—the first center for bone formation. The medullary cavity and secondary ossification sites: spongy bone in the diaphysis is absorbed by osteoclasts, forming the medullary cavity. Shortly after birth, secondary ossification centers form in the epiphyses. 11 ©2020 McGraw-Hill Education  Steps of Endochondral Ossification 3 The epiphyseal (growth) plate: a band of cartilage remains between the primary ossification center and each secondary center. The limbs keep increasing in length as long as the epiphyseal plates are present. Cartilage is now present at two locations: the epiphyseal (growth) plate and articular cartilage, which covers the ends of long bones. 12 ©2020 McGraw-Hill Education  The Epiphyseal Plate The epiphyseal plate contains four layers: The layer nearest the epiphysis is the resting zone, where cartilage remains. The next layer is the proliferating zone, in which chondrocytes are producing new cartilage cells. In the third layer, the degenerating zone, the cartilage cells are dying off. In the fourth layer, the ossification zone, bone is forming, which increases the length of the bone. 13 ©2020 McGraw-Hill Education  Increasing Bone Length Access the text alternative for these images 14 ©2020 McGraw-Hill Education  Final Size of the Bones Final size of the bones. When the epiphyseal plates close, bone lengthening can no longer occur. Several hormones play an important role in bone growth: vitamin D, growth hormone, thyroid hormone, and sex hormones. 15 ©2020 McGraw-Hill Education  Hormones Affect Bone Growth 1 Vitamin D—formed in the skin when exposed to sunlight. Is converted to a hormone that is necessary for absorption of calcium from food. Low vitamin D levels in children causes rickets. Bone deformities 16 ©2020 McGraw-Hill Education  Hormones Affect Bone Growth 2 Growth hormone (GH)—stimulates bone growth. Need concurrent action of thyroid hormone to stimulate metabolism. Dwarfism—too little GH in childhood. Gigantism—excess GH in childhood. Acromegaly—excess GH in adults. Excessive growth of bones in the hands and face. Sex hormones—increase growth during adolescence. 17 ©2020 McGraw-Hill Education  Bone Remodeling and Calcium Homeostasis 1 Bone remodeling—osteoclasts break bone down, osteoblasts build it up. Recycles 18% of bone each year. Paget disease—new bone is generated at a faster-than-normal rate. Produces softer and weaker bones. Can cause bone pain, deformities, and fractures. 18 ©2020 McGraw-Hill Education  Bone Remodeling and Calcium Homeostasis 2 Calcium homeostasis. If blood calcium rises, some of the excess is deposited in bones. If blood calcium drops, calcium is removed from bones to bring it up to normal. 19 ©2020 McGraw-Hill Education  Calcium Homeostasis 1 Parathyroid hormone (PTH). Stimulates osteoclasts to dissolve bone. Promotes calcium absorption in the small intestine and kidney, increasing blood calcium levels. Vitamin D. Needed for the absorption of Ca2+ from the digestive tract. 20 ©2020 McGraw-Hill Education  Calcium Homeostasis 2 Calcitonin. Has opposite effects as PTH. Estrogen. Increases the number of osteoblasts. The reduction of estrogen in older women can cause osteoporosis. 21 ©2020 McGraw-Hill Education  Osteoporosis. Bones are weakened due to decreased bone mass. Skeletal mass increases until age 30. After that, there is an equal rate of formation and breakdown of bone mass until age 50. Then, reabsorption begins to exceed formation, and the total bone mass slowly decreases. Risk factors include: women, family history, early menopause, smoking, diet low in calcium, excessive caffeine or alcohol consumption. 22 ©2020 McGraw-Hill Education  Bone Repair 1 Steps of bone repair: Hematoma—forms 6 to 8 hours after the fracture. Blood clot between broken bones. Fibrocartilaginous callus—forms in 3 weeks. Fibrocartilage callus between broken bones. Bony callus—forms in 3 to 4 months. Cartilaginous callus turns into bone. Remodeling. Osteoblasts build new compact bone at the periphery, osteoclasts absorb the spongy bone, creating a new medullary cavity. 23 ©2020 McGraw-Hill Education  Bone Repair Following a Fracture 24 ©2020 McGraw-Hill Education  Bone Repair 2 Types of bone fractures: Complete—the bone is broken clear through. Incomplete—the bone is not separated into two parts. Simple—it does not pierce the skin. Compound—it does pierce the skin. Impacted—the broken ends are wedged into each other. Spiral—the break is ragged due to twisting of the bone. 25 ©2020 McGraw-Hill Education  Blood Cells Are Produced in Bones There are two types of marrow: yellow and red. Fat is stored in yellow bone marrow. Red bone marrow is the site of blood cell production. 26 ©2020 McGraw-Hill Education  Check Your Progress Summarize the stages in the repair of bone. Explain how the skeletal system is involved in calcium homeostasis. 27 ©2020 McGraw-Hill Education