Lesson 2 Chapter 5 – Skeletal System

LESSON 2 Chapter 5 – Skeletal System Unit 2 Study Guide Excluded from study: Bone development and growth page 122-126 Skeletal System The skeletal structure is strong, yet light and is almost perfectly adapted for the protective, locomotor, and manipulative functions it performs. The skeleton is composed of bones, cartilage, joints, and ligaments. There are 206 bones in the human skeleton and they are divided into the axial and appendicular skeleton. The axial skeleton forms the long axis of the body and includes the bones of the skull, vertebral column, and rib cage. The appendicular skeleton consists of the bones of the upper and lower limbs and the girdles that attach the limbs to the axial skeleton Classification Almost all the bones of the body may be classified into four principal types on the basis of shape: long bones, short bones, flat bones, and irregular bones 1 LESSON 2 Chapter 5 – Skeletal System 2 Long bones: Longer than they are wide. Reflects the elongated shape rather than the overall size. Consist of a shaft plus two ends and are constructed primarily of compact bone, but may contain substantial amounts of spongy bone. All bones of the limbs, except the patella, wrist and ankle bones, are long bones. Short bones: Roughly cubelike, containing mostly spongy bone. Comprise bones of the wrist and ankle. Vary in size and number in different individuals. Flat bones: Thin, flattened, and usually a bit curved, they have two roughly parallel compact bone surfaces, with a layer of spongy bone between. Examples include the sternum, ribs, and most of the skull bones. Irregular bones: Fit none of the previous classes. Include some skull bones, vertebrae, and hip bones. Have complicated shapes and consist mainly of spongy bone enclosed by thin layers of compact bone. Functions of bones: 1. Support: provides framework that supports and anchors all soft organs. Leg bones act as pillars to support the body trunk, and the ribs support the thorax wall. 2. Protection: skull and vertebrae surround soft tissue of the nervous system, and the rib cage protects vital thoracic organs. 3. Movement: skeletal muscles use the bones as levers to move the body. 4. Storage: fat stored in the interior of the bones. Bone matrix serves as a storehouse for various minerals. 5. Blood Cell Formation: hematopoiesis occurs within the marrow cavities of the bones. Cells: - Ending in –blasts = immature cells Ending in –cytes = mature cells LESSON 2 Chapter 5 – Skeletal System Cells of Mature Bones (Osteo- = bones) a) Osteoprogenitor cells: 1) Found on inner and outer surfaces of a bone. 2) Divide and differentiate to form new osteoblasts. b) Osteoblasts immature, active cells: 1) Found on inner and outer surfaces of a bone. 2) Responsible for the process of making new bone, which is called osteogenesis. c) Osteocytes (mature cells) maintain bone tissue d) Osteoclasts are giant multinucleated cells: 1) Perform osteolysis (breakdown of bone matrix) Bone matrix The intercellular substance of bone tissue consisting of collagen fibers, ground substance, and inorganic bone salts. - Osteoclasts synthesize matrix fibers. - Ground substance (hardened, calcified – calcium and PO4) Q: If there is too much calcium in the blood. A: Osteoblast will be busy building new bone. Q: If there is not enough calcium in the blood. A: Osteoclast will be busy breaking down bones so calcium is released. Therefore, osteoblasts (under) and osteoclasts (excessive) 3 LESSON 2 Chapter 5 – Skeletal System 4 Bones can be classified by the two types of osseous tissue. Bones of different shapes contain different proportions of the two basic types of osseous tissue (compact & spongy bone). Compact bone is dense and looks smooth and homogeneous. Spongy bone is composed of small needlelike or flat pieces of bone called trabeculae and has much open space. The trabeculae form an open network which is filled with bone marrow. Diaphysis: "shaft" which constitutes the long axis of the bone. Constructed of a thick collar of compact bone that surrounds a cavity. The medulla cavity in adults contains fat (yellow marrow). Epiphyses: "ends" or extremities. They are usually more expanded than the diaphyses. A thin layer of compact bone forms the exterior and the interior contains spongy bone. Epiphyseal plate: In young bones, cartilage is present at the junction of the diaphysis and epiphysis. This is the growth area that allows bones to lengthen. Epiphyseal line: remnant of the epiphyseal plate. After puberty the cartilage of the epiphyseal plate is converted to bone and no further growth is possible. Periosteum: the outer surface of the diaphysis which is covered and protected by a double layered membrane. Connective tissue consisting primarily of bone-forming cells (osteoblasts). Provides an insertion or anchoring point for tendons and ligaments. LESSON 2 Chapter 5 – Skeletal System 5 Endosteum: internal bone surfaces are covered with a delicate connective tissue membrane. Covers the trabeculae of spongy bone in the narrow cavities and lines the canals that pass through the compact bone. Articular Cartilage: where long bones articulate at epiphyseal surfaces, the bony surfaces are covered with articular (hyaline) cartilage which cushions the bone ends and absorbs stress during joint movement. Periosteum - covers outer layer - articular cartilages not covered by periosteum Endosteum - covers inner later (medullary cavity) - active in bone growth and repair Compact bone Microscopically, compact bone is riddled with canals and passageways that serve as conduits for nerves, blood vessels, and lymphatic vessels. The structural unit of compact bone is called the osteon or Haversian system. Each osteon is an elongated cylinder oriented along the long axis of the bone. Osteons appear as tiny weight-bearing pillars composed of a group of hollow tubes of bone matrix, one placed inside the next. Running through the core of each osteon is a canal (central or Haversian canal) which contains small blood vessels and nerve fibers. Running a right angles to the long axis are canals (perforating or Volkmann's canals) which connect the vascular and nerve supplies of the periosteum to those in the central canals and medullary cavity. Spongy Bone Consists of trabeculae which are positioned where the bone is stressed. Only a few layers thick, the trabeculae contain irregularly arranged lamellae and osteocytes interconnected by canaliculi. No osteons are present. Projections that are sites of muscle and ligament attachment: Tuberosity: large rounded projection Crest: narrow ridge of bone, usually prominent Trochanter: very large, blunt, irregularly shaped process LESSON 2 Chapter 5 – Skeletal System Tubercle: small rounded projection or process Epicondyle: raised area on or above a condyle Spine: sharp, slender, often pointed projection Projections that help form joints: Head: bony expansion carried on a narrow neck Condyle: rounded articular projection Ramus: armlike bar of bone Depressions and openings: Meatus: canal-like passageway Sinus: cavity within a bone, filled with air and lined with mucous membrane Fossa: shallow basinlike depression in a bone often serving as an articular surface Fissure: narrow, slitlike opening Foramen: round or oval opening through a bone Types of fractures: simple - bone breaks cleanly, does not penetrate the skin compound - broken ends of bone protrude through skin 6 LESSON 2 Chapter 5 – Skeletal System comminuted - bone fragments into many pieces compression - bone is crushed depressed - broken bone portion is pressed inward impacted - broken bone ends are forced into each other spiral - ragged break occurring when excessive twisting forces are applied to bone greenstick - bone breaks incompletely similar to a green twig Bone Repair of a Simple Fracture: 1. Hematoma formation - A mass of clotted blood forms at fracture site. Bone cells begin to die and tissue becomes swollen, painful, and inflamed. 2. Fibrocartilaginous callus formation - Capillaries grow into the area and macrophages clean up debris. Fibroblasts and osteoblasts migrate to the area and begin reconstructing bone. Fibroblasts produce collagen fibers that begin to connect broken ends. Some fibroblasts become chondroblasts which make cartilage. Osteoblasts begin forming spongy bone. All of the repair tissue at this stage is called the fibrocartilage callus. 3. Bony callus formation - The fibrocartilage callus is converted to a hard bony callus of spongy bone by the action of the osteoblasts and osteoclasts. This begins 3-4 weeks post injury and continues until a firm union forms 2-3 months later. 4. Remodeling - During bony callus formation and the following several months remodeling occurs. Excess material outside the shaft is removed and compact bone is laid down to reconstruct the shaft. The final structure will resemble unbroken bone because it is under the same set of mechanical stimuli. 7