Outline. Skeletal System. Tendons link the skeletal and the muscular systems.

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1 Outline Skeletal System Bio 105 I. Overview of the skeletal system II. Function of bones III. Bone structure IV. Bone cells V. Cartilage VI. Tendons and Ligaments VII. Joints VIII. Bone development IX. Hormonal regulation of bone growth X. Homeostasis XI. Disorders of the skeletal system Skeletal System The 4 main components of the skeletal system are different types of connective tissues: Bones rigid structure Cartilage soft, cushions the joints Ligaments attach bone to bone Tendons attach muscle to bone. Tendons link the skeletal and the muscular systems. 1

2 Functions of the Skeletal System 1. Supports and gives shape to the body. 2. Protects soft body parts. 3. Produces blood cells. 4. Stores minerals (calcium and phosphate). 5. Stores fat. 6. Along with the muscles, permits flexible body movement. Bone Bones have different types of tissue Calcified tissue = osseous tissue Blood vessels Nerves Contain collagen fibers that give flexibility The combination of calcified tissue and collagen fibers make the bone strong but flexible. Bone Structure All bones have two layers: Compact Bone Dense mineralized outer layer. Spongy Bone Inner layer with open network filled with marrow. Periosteum Periosteum Fibrous outer covering of the bone. Contains nerves, blood vessels, and lymphatic vessels. Functions in bone repair and growth. 2

3 Typical Long Bone Structure Epiphysis Rounded end of the typical long bone, composed mainly of red marrow where blood cells are made. Diaphysis Shaft of the typical long bone, has a cavity filled with yellow marrow where fat is stored. Typical Long Bone Structure Spongy bone (spaces contain red bone marrow) Compact bone on surface Yellow bone marrow Blood vessel Periosteum Central cavity (contains yellow bone marrow) (a) A long bone, such as the femur of the leg, consists of a shaft and two heads, or enlarged ends. Compact bone is located on the outer surface of the bone. Spongy bone is found in the heads. Figure 5.1a Spongy Bone Bone Is Living Tissue Osteon Blood vessels and nerve in central canal Periosteum Bone-forming cells (osteoblasts) Spongy bone Compact bone (b) The structural unit of compact bone is Figure 5.1e an osteon. Mature, living bone cells (osteocytes) are found in small spaces within the hard matrix. Figure 5.1b 3

4 Compact Bone Structure Osteon structural unit of the compact bone. Osteon Osteon Structure Central Canal (Haversian) Contain blood vessels and nerves. Osteocytes Mature bone cells. Maintain bone structure and density. Found in cavities called lacunae. Canaliculi - Canals that connect the lacunae to the central canal. Spongy bone Compact bone The Structure of Bone The Structure of Bone 4

5 Bone Cells Osteoblasts Osteocytes Osteoclasts Osteoblasts Osteoblasts = Bone forming cells. Immature cells that secrete material called bone ground substance = non-cellular matrix that surrounds the cells. Osteoblasts mature into osteocytes after they have secreted enough material. Osteoclasts The arrow is pointing to: Osteoclasts Bone removing cells. These are bone cells on the outer edge of bones. 1. Diaphysis 2. Epiphysis They release enzymes that eat away at the compact bone, releasing minerals. Diaphysis Epiphysis 5

6 The arrow is pointing to: Immature cells that secrete calcified material are: 1. Diaphysis 2. Epiphysis 1. Osteoclasts 2. Osteocytes 3. Osteoblasts Diaphysis Epiphysis Immature cells that secrete calcified material are: Osteocytes are found in cavities called 1. Osteoclasts 2. Osteocytes 3. Osteoblasts 1. Central canals 2. Collagen 3. Lacunae 4. Vellus 25% 25% 25% 25% Central canals Collagen Lacunae Vellus 6

7 Osteocytes are found in cavities called 1. Central canals 2. Collagen 3. Lacunae 4. Vellus 25% 25% 25% 25% Bone Development and Growth The skeleton begins to form at about 6 weeks. Most bones only grow through adolescence but some bones continue to grow through about age 25. Bones continue to change throughout life. Osteoclasts are removing the bone matrix. Osteoblasts are building the bone matrix. Central canals Collagen Lacunae Vellus Ossification formation of bones Figure 5.3 Steps of Bone Formation in Long and Short Bones 2 months Cartilage model Bone collar Fetal Development 3 months Deteriorating cartilage matrix 9 months Spongy bone formation Calcified cartilage Blood vessel Birth Cartilaginous surface Cartilaginous (epiphyseal) growth plate Childhood Spongy bone Compact bone Cartilage in Bones Two regions of cartilage remain at each end of the long bone. The cap that covers the surfaces that rub against other bones. A plate of cartilage called the epiphyseal plate, or growth plate. Step 1: A cartilaginous model of the future bone forms. Step 2: Osteoblasts form a collar of bone around the shaft of the model. Step 3: The shaft of the cartilage model begins to hollow out, and spongy bone fills the space. Blood vessels continue to penetrate the area, and the region of bone formation expands. Step 4: Secondary centers of bone formation develop in the ends of the bone. Step 5: Cartilage remains only on the surfaces that rub against other bones and in the cartilage growth plates. 7

8 Bone Growth Bone growth is stimulated by growth hormone during childhood. Thyroid hormones ensure that the skeleton grows with the proper proportions. At puberty increasing levels of male or female sex hormones initially stimulate cartilage cells to divide. Eventually the hormones allow for the growth plates to fuse and bone can no longer increase in length. Hormonal Regulation of Bone Growth Growth hormone (GH) - Directly stimulates growth of the epiphyseal plate and bone growth in general. Vitamin D - Converted to a hormone (calcitrol) causing the intestines to absorb calcium. Sex hormones - Adolescents experience a growth spurt due to an increased level of sex hormones Hormonal Regulation of Bone Maintenance Parathyroid hormone (PTH) Produced by the parathyroid gland - accelerates bone recycling and increases blood calcium. Calcitonin Produced by the thyroid gland - a hormone that decreases blood calcium levels, deposits calcium into the bone. Homeostasis Maintaining a balance of calcium levels in blood and in bone. 8

9 Healing Broken Bones Broken bones and fractures are the same thing. Bone Fractures are Healed by Fibroblasts and Osteoblasts Formation of blood clot Formation of cartilaginous callus Bone fractures are healed by fibroblasts and osteoblasts. When a break occurs, there is bleeding followed by a clot. Fibroblasts secrete collagen fibers that form a callus linking the two parts of the bone. This is later replaced by bone. Step 1: Within hours after the fracture, a blood clot forms. Cartilaginous callus Blood clot (hematoma) Step 2: A cartilaginous callus is formed by invading fibroblasts. Spongy bone struts Figure 5.4 (1 of 2) Bone Fractures are Healed by Fibroblasts and Osteoblasts Formation of bony callus Bone remodeling This hormones accelerates bone recycling and increases blood calcium New blood vessels Bony callus Healed fracture 1. Growth hormone 2. Calcitonin 3. Parathyroid hormone 33% 33% 33% Step 3: Osteoblasts form new bone, converting the cartilaginous callus to a bony callus. Step 4: The fracture is healed and bone is remodeled, restoring bone to original shape. Growth hormone Calcitonin Parathyroid hormone Figure 5.4 (2 of 2) 9

10 This hormones accelerates bone recycling and increases blood calcium Calcitonin is produced by the gland 1. Growth hormone 2. Calcitonin 3. Parathyroid hormone 33% 33% 33% 1. Parathyroid 2. Thyroid 3. Anterior pituitary 4. Hypothalamus 25% 25% 25% 25% Growth hormone Calcitonin Parathyroid hormone Parathyroid Thyroid Anterior pituitary Hypothalamus Calcitonin is produced by the gland 1. Parathyroid 2. Thyroid 3. Anterior pituitary 4. Hypothalamus 25% 25% 25% 25% Cartilage Cartilage - Flexible connective tissue not as strong as bone tissue. Function: Cushion joints, provides flexibility. Found at the ends of long bones, nose, ends of ribs, larynx and trachea, disks between vertebrae and knee, ear flaps and epiglottis. Parathyroid Thyroid Anterior pituitary Hypothalamus Cartilage cells are chondrocytes. Cartilage lacks blood vessels, so slow to heal. 10

11 Tendons and Ligaments Ligaments Dense (white fibrous) Connective Tissue that connects bone to bone. Tendons Dense (white fibrous) Connective Tissue that connects muscle to bone Synovial Joints Freely movable joints held together by ligaments. Synovial membrane - Produces synovial fluid, an excellent lubricant for the joints. Bursae Fluid filled sacs, reduce friction. Meniscus Cartilage between the bones, acts as a cushion. Femur Synovial Joints A bursa is a fluid-filled sac that cushions certain joints and reduces friction between tendons and ligaments. A layer of cartilage on the articulating surfaces of the bones reduces friction as the bones move. The joint cavity is filled with synovial fluid, which serves as a shock absorber and lubricant. Fat pad The synovial membrane forms the inner surface of the joint cavity and secretes synovial fluid. Tibia (a) Synovial joints, such as the knee shown here, permit a great range of movement. Figure 5.13a 11

12 Synovial Joints Cartilage cells are: Femur Quadriceps tendon 1. fibrocytes 2. osteocytes 33% 33% 33% Lateral collateral ligament Posterior cruciate ligament Anterior cruciate ligament 3. chondrocytes Medial collateral ligament Fibula Tibia Patellar ligament Patella (kneecap) (b) Ligaments hold bones together, support the joint, and direct the movement of the bones. Figure 5.13b fibrocytes osteocytes chondrocytes Cartilage cells are: This type of connective tissue connects bone to bone 1. fibrocytes 2. osteocytes 3. chondrocytes 33% 33% 33% 1. Ligaments 2. Tendons fibrocytes osteocytes chondrocytes Ligaments Tendons 12

13 This type of connective tissue connects bone to bone Fluid filled sacs are called: 1. Ligaments 2. Tendons 1. Synovia 2. Menisci 3. Bursae 33% 33% 33% Ligaments Tendons Synovia Menisci Bursae Fluid filled sacs are called: 1. Synovia 2. Menisci 3. Bursae 33% 33% 33% Osteoarthritis - Deterioration of cartilage at joints. Rheumatoid Arthritis Chronic inflammation of the joints due to an autoimmune disorder. Sprain When ligaments are stretched or torn. Bursitis Inflammation of a bursa. Tendonitis Inflammation of tendon sheath. Fracture Broken bone. Simple = Bone breaks but does not penetrate the skin. Compound = Bone breaks and protrudes through the skin. Disorders of the Skeletal System Synovia Menisci Bursae

14 Osteoporosis When more bone is reabsorbed than is formed. This is when homeostasis is not maintained and more calcium is taken out of the bones than is replaced. Estrogen and Testosterone help maintain the bone density. After menopause women produce less estrogen and this can lead to less bone density. Risk Factors for Osteoporosis Post menopausal Not enough exercise Poor diet, not enough calcium in the diet Smoking Low vitamin D levels Certain hormonal disorders Treatment for Osteoporosis Exercise. Increased Calcium in the diet, calcium supplements if needed, the type of calcium supplement is important. Estrogen replacement therapy. Prescription drugs. 14

15 Recommended Calcium Intakes* Ages Amount mg/day Birth - 6 months months - 1 year or older 1200 Food Calcium (mg) % DV* Yogurt, plain, low fat, 8 oz % Yogurt, fruit, low fat, 8 oz %-38% Sardines, canned in oil, with bones, 3 oz % Cheddar cheese, 1 ½ oz shredded % Milk, non-fat, 8 fl oz % Tofu, firm, ½ cup % Mozzarella, part skim 1 ½ oz % Orange juice, calcium fortified, 6 fl oz % Turnip greens, boiled, ½ cup 99 10% Kale, cooked, 1 cup 94 9% Turnip greens, boiled, ½ cup 99 10% Ready to eat cereal, calcium fortified, 1 cup %-100% Cottage cheese, 1% milk fat, 1 cup unpacked % Decreased Calcium Absorption Oxalic acid potent inhibitor of calcium absorption, and is found in high concentrations in spinach and rhubarb and in somewhat lower concentrations in sweet potato and dried beans. Sodium Increased sodium intake results in increased loss of calcium in the urine. Protein As dietary protein intake increases, the urinary excretion of calcium also increases. Caffeine Caffeine in large amounts increases urinary calcium content for a short time. 15

16 Fractured bones are the same thing as broken bones Fractured bones are the same thing as broken bones 1. True 2. False 1. True 2. False True False True False Important Concepts Read Ch 7 What are the four components of the skeletal system, and their functions What are the functions of bone What are the two layers of bone What is the periosteum and what is its function What is the structure of the osteon, what are the features found in the osteon Important Concepts What are the three types of bone cells and their functions What are the functions of cartilage, tendons, and ligaments. What are the parts of synovial joints and their functions What are the hormones involved in bone growth and homeostasis, what glands produce calcitonin and parathyroid hormones 16

17 Important Concepts What are the disorders of the skeletal system How do bones heal What is osteoporosis, what are the risk factors, what can you do to prevent it. Definitions Compact bone, osteon, central canal (haversian canal), Spongy bone, Epiphysis, Diaphysis, Periosteum, lacunae, callus, fibroblasts, Osteoblasts, Osteocytes, Osteoclasts, Chondrocytes, growth hormone, Parathyroid hormone (PTH), Calcitonin, Vitamin D, epiphyseal plate, growth plate 17