SKELETAL SYSTEM OUTLINE 6.1 Cartilage 147 6.1a Functions of Cartilage 147 6 6.1b Growth Patterns of Cartilage 148 6.2 Bone 148 6.2a Functions of Bone 148 6.3 Classification and Anatomy of Bones 150 Cartilage 6.3a General Structure and Gross Anatomy of Long Bones 150 6.4 Ossification 157 6.4a Intramembranous Ossification 157 and Bone 6.4b Endochondral Ossification 157 6.4c Epiphyseal Plate Morphology 160 6.4d Growth of Bone 161 6.4e Blood Supply and Innervation 162 6.5 Maintaining Homeostasis and Promoting Bone Growth 163 6.5a Effects of Hormones 163 6.5b Effects of Vitamins 164 6.5c Effects of Exercise 165 6.5d Fracture Repair 165 6.6 Bone Markings 167 6.7 Aging of the Skeletal System 168 MODULE 5: SKELETAL SYSTEM mck78097_ch06_146-172.indd 146 2/14/11 3:40 PM Chapter Six Cartilage and Bone 147 entionentionn ofof thethe skeletalskeletal systemsystem conjuresconjures up imagesimages ofof dry, lifelesslifeless Cartilage is found throughout the human body (figure 6.1). Mbobonesnes in vvariousarious sizsizeses and shashapes.pes. BButut thethe sskeletonkeleton ((skelskel ́ĕ́ĕ --ton;ton; Cartilage is a semirigid connective tissue that is weaker than bone, skskeletoseletos = dridried)ed) is mmuchuch momorere thathann a supportingsupporting framework for the but more flexible and resilient (see chapter 4). As with all connec- sosoftft tistissuessues ooff ththee bobody.dy. ThThee skeletal ssystemystem is comcomposedposed ooff ddynamicynamic tive tissue types, cartilage contains a population of cells scattered lilivingving ttissues;issues; it interactsinteracts witwithh all of the other ororgangan systems and throughout a matrix of protein fibers embedded within a gel-like cocontinuallyntinually rebuildsrebuilds and remodels itself. Our skeletal systemsystem includes ground substance. Chondroblasts (kon ́drō -blast; chondros = grit the boneboness of the skeleton as well as cartilage,cartilage, ligaments,ligaments, and other or gristle, blastos = germ) are the cells that produce the matrix coconnectivennective tissues thatthat stabilizestabilize or connect thethe bones.bones. Bones supportsupport of cartilage. Once they become encased within the matrix they ouourr weightweight and interact with muscles to produce precisely controlled have produced and secreted, the cells are called chondrocytes movements. This interaction ppermitsermits us to sit, stand, walk, and run. (kon ́drō -sı̄ t; cyte = cell) and occupy small spaces called lacunae. Further, our bones serve as vital reservoirs forfor calcium and phospho-phospho- These mature cartilage cells maintain the matrix and ensure that rus. BeBeforefore concentratinconcentratingg on bone connective tissue, we firstfirst examine it remains healthy and viable. Mature cartilage is avascular (not the cartilage components of the skeleton. penetrated by blood vessels) so nutrients must diffuse through the matrix. The three different types of cartilage—hyaline, elastic, and fibrocartilage—are described in detail in chapter 4, so only cartilage 6.1 Cartilage functions, locations, and growth will be discussed in this chapter. Learning Objectives: 6.1a Functions of Cartilage 1. Explain the functions of cartilage. Cartilage has three major functions in the body: 2. Describe the function and distribution of hyaline cartilage, fibrocartilage, and elastic cartilage. ■ Supporting soft tissues. For example, C -shaped hyaline 3. Explain both the interstitial and appositional growth of cartilage rings in the trachea support the connective cartilage. tissue and musculature of the tracheal wall, fibrocartilage Cartilage in external ear Extracellular matrix Epiglottis Cartilages in nose Lacuna Larynx (with chondrocyte) Trachea Lung Articular cartilage of a joint Costal cartilage LM 180x (b) Hyaline cartilage Cartilage of intervertebral disc Respiratory tract cartilages Lacunae in the lungs, trachea, (with chondrocytes) and larynx Pubic symphysis Extracellular matrix Collagen fibers LM 80x (c) Fibrocartilage Meniscus (padlike Elastic fibers cartilage in knee joint) Lacunae (with chondrocytes) Extracellular matrix Articular cartilage Hyaline cartilage of a joint Fibrocartilage Elastic cartilage LM 200x (a) (d) Elastic cartilage Figure 6.1 Distribution of Cartilage in an Adult. (a) Three types of cartilage are found within an adult. Photomicrographs show (b) hyaline cartilage, (c) fibrocartilage, and (d ) elastic cartilage. mck78097_ch06_146-172.indd 147 2/14/11 2:36 PM 148 Chapter Six Cartilage and Bone provides both toughness and flexibility to the pubic symphysis and intervertebral discs, and flexible elastic 6.2 Bone cartilage supports the fleshy, external part of the ear called the auricle (aw ri-kl;́ auris = ear). Learning Objective: ■ Providing a gliding surface at articulations (joints), where 1. Explain the functions of bone. two bones meet. The bones of the skeleton are complex, dynamic organs ■ Providing a model for the formation of most of the bones containing all tissue types. Their primary component is bone con- in the body. Beginning in the embryonic period, cartilage nective tissue, also called osseous (os ḗ -ŭ s) connective tissue (see serves as a “rough draft” form that is later replaced by chapter 4). In addition, they contain connective tissue proper (peri- bone tissue. osteum), cartilage connective tissue (articular cartilage), smooth muscle tissue (forming the walls of blood vessels that supply bone), 6.1b Growth Patterns of Cartilage fluid connective tissue (blood), epithelial tissue (lining the inside Cartilage grows in two ways. Growth from within the cartilage opening of blood vessels), and nervous tissue (nerves that supply itself is termed interstitial (in-ter-stish ắ l) growth. Growth along bone). The matrix of bone connective tissue is sturdy and rigid due the cartilage’s outside edge, or periphery, is called appositional to deposition of minerals in the matrix, a process called calcifica- (ap-ō -zish ́ŭ n-ă l) growth (figure 6.2). tion (kal si-fi-ḱ ā sh́ ŭ n), or mineralization. Interstitial Growth Interstitial growth occurs through a series of steps: Study Tip! You can do a quick overnight experiment to demonstrate what 1. Chondrocytes housed in lacunae undergo mitotic cell would happen to our body shape if the composition of our bones division. changed. Obtain the “wishbone” (fused clavicles) from a chicken or game 2. Following cell division, the two new cells occupy a single hen and observe its physical characteristics. Next, place the bone in lacuna. a glass container of vinegar. Let it stand overnight, and then examine 3. As the cells begin to synthesize and secrete new cartilage the bone. You should see the following changes: (1) The bone is darker matrix, they are pushed apart and now reside in their own because the acid in the vinegar has dissolved the calcium phosphate in lacunae. the bone, and (2) the bone is somewhat limp like a wet noodle because 4. The new individual cells within their own lacunae are it has lost its strength due to the removal of the calcium phosphate called chondrocytes. New matrix has been produced from the bone. internally, and thus interstitial growth has occurred. Appositional Growth Appositional growth also occurs through a series of defined steps: 6.2a Functions of Bone Bone connective tissue and the bones that compose the skeletal 1. Stem cells at the internal edge of the perichondrium system perform several basic functions: support and protection, begin to divide, forming new stem cells and movement, hemopoiesis, and storage of mineral and energy committed cells. reserves. 2. The committed cells differentiate into chondroblasts. 3. These chondroblasts, located at the periphery of the old Support and Protection cartilage, begin to produce and secrete new cartilage Bones provide structural support and serve as a framework for the matrix. As a result, they push apart and become entire body. Bones also protect many delicate tissues and organs chondrocytes, each occupying its own lacuna. from injury and trauma. The rib cage protects the heart and lungs, 4. The new matrix has been produced peripherally, and thus the cranial bones enclose and protect the brain, the vertebrae appositional growth has occurred. enclose the spinal cord, and the pelvis cradles some digestive, uri- During early embryonic development, both interstitial nary, and reproductive organs. and appositional cartilage growth occur simultaneously. Movement However, interstitial growth declines rapidly as the carti- lage matures because the cartilage becomes semirigid as it Individual groups of bones serve as attachment sites for skeletal matures, and the matrix is no longer able to expand. Further muscles, other soft tissues, and some organs. Bones of the skeleton growth can occur only at the periphery of the tissue, so later function as levers that are pulled when skeletal muscles contract. growth is primarily appositional. Once the cartilage is fully The direction and magnitude of the forces generated by the skeletal mature, new cartilage growth typically stops entirely. From muscles can be altered by bones. Potential movements range from this point on, cartilage growth usually occurs only after injury powerful contractions needed for running and jumping to delicate, to the cartilage. precise movements required to remove a splinter from the finger. Hemopoiesis WHATW DID YOU LEARN? The process of blood cell production is called hemopoiesis ●1 How do the three cartilage types differ with respect to their (hē ḿ ō -poy-ē sis;́ haima = blood, poiesi = making). Blood cells are locations