Chapter 7 The Skeletal System

Objectives List and discuss the generalized functions of the skeletal system Identify the major anatomical structures found in a typical long bone Discuss the microscopic structure of bone and cartilage, including the identification of specific cell types and structural features Explain how bones are formed, how they grow, and how they are remodeled

Objectives Identify the two major subdivisions of the skeleton and list the bones found in each List and compare the major types of joints in the body and give an example of each Name and describe major disorders of bones and joints

Functions of Skeletal System Provides internal framework that supports the body Protects internal organs and helps fight disease by producing white blood cells Makes movement possible by working in concert with muscle contraction and relaxation Stores calcium, a vital resource Forms blood cells—process is called hematopoiesis What are the primary functions of bone? Bones form the body’s supporting framework. The hard structure of bones protect delicate structures enclosed within them. The skull protects the brain; the breastbone and ribs protect the heart and lungs. Muscles are anchored to bones. As muscles contract, they pull on bones and move them. What is the role of bone in maintaining homeostasis of blood calcium? Calcium storage: bones help maintain homeostasis of blood calcium, necessary for nerve and muscle function. Hematopoiesis: the process of blood cell formation is carried on in the red bone marrow.

Four major types, according to overall shape of the bone Types of Bones Four major types, according to overall shape of the bone Long—example: humerus (upper arm) Short—example: carpals (wrist) Flat—example: frontal (skull) Irregular—example: vertebrae (spinal bones) Some also recognize a sesamoid (round) bone category—example: patella (kneecap) Ask students to name other examples of the four different types of bones.

Types of Bones Structure of long bones Diaphysis, or shaft—hollow tube of hard compact bone Medullary cavity—hollow space inside the diaphysis that contains yellow marrow Epiphyses, or ends, of the bone—made of spongy bone that contains red bone marrow Articular cartilage—thin layer that covers each epiphysis; provides a cushion Periosteum—strong, fibrous membrane covering bone everywhere except at joint surfaces Endosteum—thin membrane that lines medullary cavity Diaphysis—hollow tube made of hard, compact bone. Rigid, strong, yet light enough to permit easy movement. Yellow bone marrow—inactive, fatty form of marrow found in adult skeletons. Articular cartilage covers the ends of bones where they form a joint. Discuss the significance of the epiphyseal line that divides the diaphysis from the epiphysis. Growth occurs at the epiphyseal line.

Longitudinal section of long bone.

Structure of flat bones Types of Bones Structure of flat bones Thin layer of compact bone surrounding cancellous (spongy or diploe) bone Open spaces within spongy bone are surrounded by boney trabeculae

Section of a flat bone. The outer layers of compact bone surround cancellous bone called diploe.

Microscopic Structure of Bone and Cartilage Two major types of connective tissue: bone and cartilage Bone types Spongy Texture from needlelike threads of bone called trabeculae surrounded by network of open spaces Found in epiphyses of bones Spaces contain red bone marrow

Microscopic structure of bone Microscopic structure of bone. The longitudinal section of a long bone (A) shows the location of themicroscopic section illustrated in B. Note that the compact bone forming the hard shell of the bone is constructed of cylindrical units called osteons. Spongy bone is constructed of bony projections calledtrabeculae. C, Photomicrograph shows osteon system of organization. The letter C shows the central canal and the arrow points to the lacunae or space that contains the mature osteocyte. (C, From Gartner LP, Hiatt JL: Color textbook of histology, ed 3, Philadelphia, 2007, Saunders.)

Microscopic Structure of Bone and Cartilage Bone types Compact Structural unit is an osteon-calcified matrix arranged in multiple layers or rings called concentric lamella Bone cells, called osteocytes, are found inside spaces called lacunae, which are connected by tiny tubes called canaliculi Covered by periosteum What are the two major types of connective tissue in the skeletal system? Bone and cartilage What are the two types of bone? Dense and compact bone

Microscopic Structure of Bone and Cartilage Structural unit called osteon or Haversian system composed of: Concentric lamella—circular layers of calcified matrix Lacunae—spaces in matrix between lamella containing osteocytes Canaliculi—canals/passageways that connect lacunae and all nutrients to reach osteocytes Central canal of osteon contains blood vessel Describe osteocytes, canaliculi, and lacunae. Osteocytes: mature bone cells that are made from the active bone building cells called osteoblasts. Canaliculi: small passageways or canals that contain cytoplasmic extensions of the osteocyte. Lacunae: little spaces between the hard layers of the lamellae.

Microscopic Structure of Bone and Cartilage Structural unit called osteon or Haversian system composed of: Spongy bone Found in epiphyses of bones Appears “porous” to naked eye with many open spaces in matrix Spaces contain red bone marrow Texture results from needlelike threads of bone called trabeculae Why is the end of the bone spongy rather than dense?

Bone cells. A, Osteoclasts are multinucleated cells that remove bone; B, osteoblasts are the bone-forming cells; and C, osteocytes are the mature bone cells that are located in the lacunae of compact bone. (Adapted from McCance K, Huether S: Pathophysiology, ed 4, St Louis, 2002, Mosby.)

Microscopic Structure of Bone and Cartilage Cell type called chondrocytes located in lacunae Matrix is flexible gel-like substance and lacks blood vessels Cartilage resembles bone in that it consists more of intercellular substance than of cells. In cartilage, the collagenous fibers that reinforce the matrix are embedded in a firm gel rather than the calcified cement substance in bone. Why does cartilage rebuild slowly after an injury? Because it lacks blood vessels.

Bone Formation and Growth New bone-forming cells are called osteoblasts and bone resorbing cells are called osteoclasts The ability of bone to ossify, grow, change shape, heal after injury, and respond to stress occurs because of continuous “sculpting” by osteoblasts and osteoclasts

Bone Formation and Growth Bone is formed by two processes Most bones develop from a process called endochondral ossification Some flat bones (e.g., skull bones) form in connective tissue membranes by another process Endochondral ossification is the process of forming bones from cartilage models.

Bone Formation and Growth Endochondral bone formation Bones develop from cartilage models Center of ossification first appears in diaphysis Centers of ossification then develop in epiphyses

Bone Formation and Growth Endochondral bone formation Epiphyseal plate of cartilage between epiphyses and diaphysis remains until skeletal maturity Epiphyseal line (bone) replaces epiphyseal plate (cartilage) when growth ceases What is the process of “remodeling” a bone? “Remodeling” a growing bone as it changes from a small cartilage model to an adult bone requires continuous activity by osteoblasts. What is responsible for “sculpting” bones? The process of “sculpting” by osteoblasts and osteoclasts allows bones to respond to stress and injury by changing size, shape, and density.

Cartilage tissue. Photomicrograph shows chondrocytes scattered around the tissue matrix in spaces called lacunae. (Dennis Strete.)

Bone Formation and Growth Early bone development (before birth) consists of cartilage and fibrous structures Cartilage models gradually replaced by calcified bone matrix—process called endochondral ossification Osteoblasts form new bone, and osteoclasts resorb bone

Endochondral ossification Endochondral ossification. A, Bone formation begins with a cartilage model. B and C, Invasion of the diaphysis (shaft) by blood vessels and the combined action of osteoblast and osteoclast cells results in cavity formation, calcification, and the appearance of bone tissue. D and E, Centers of ossification also appear in the epiphyses (ends) of the bone. F, Note the epiphyseal plate, an indication that this bone is not yet mature and that additional growth is possible. G, In a mature bone, only a faint epiphyseal line marks where the cartilage has disappeared and the centers of ossification have fused together.

Bone development in a newborn Bone development in a newborn. An infant’s skeleton has many bones that are not yet completelyossified. (Network Graphics.)

Divisions of Skeleton Axial skeleton (80 bones) Skull Spine, or vertebral column Thorax Appendicular skeleton (126 bones) Upper extremities, including shoulder (pectoral) girdle Lower extremities, including hip (pelvic) girdle Ask the students to identify the various parts of the axial skeleton and the appendicular skeleton. See Figure 7-8. Ask the students to identify the bones and sutures of the skull. See Table 7-2.

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Spine or vertebral column Four normal curves Three abnormal curves Lordosis or “swayback” Kyphosis or “hunchback” Scoliosis How many bones form the face? The skull consists of 8 bones that form the cranium, 14 bones that form the face, and 6 bones in the middle ear. The two parietal bones that give shape to the topside of the skull form immovable joints, called sutures, with several bones: the lambdoidal suture with the occipital bone, the squamous suture with the temporal bone, and the coronal suture with the frontal bone.

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Divisions Cervical (7 bones) Thoracic (12 bones) Lumbar (5 bones) Sacrum (1 bone) Coccyx (1 bone) The vertebral column consists of separate bones connected in a way that forms a flexible curved rod. Point out the cervical region, thoracic region, lumbar region, sacrum, and coccyx. Discuss the physiological reasons for the four curves of the spine. Strength to support the weight of the body; balance necessary to stand erect and walk on two feet.

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Thorax Composed of: 12 pairs of ribs Sternum or breastbone Thoracic vertebrae Ribs True ribs—rib pairs 1 through 7 False ribs—rib pairs 8 through 10 Floating ribs—rib pairs 11 and 12 What is another name for the breastbone? Sternum What is the difference between “true ribs” and “false ribs”? The first seven pairs of ribs are called true ribs and are attached to the sternum. The eighth, ninth, and tenth ribs are attached to the cartilage of the seventh pair of ribs; they are called false ribs. The last two pairs of ribs are not attached to costal cartilage; they are called floating cartilage.

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Appendicular skeleton (126 bones) Bones in shoulder or pectoral girdle connect bones of upper extremity (arm, forearm, wrist, and hands) to axial skeleton Bones in hip or pelvic girdle connect bones of lower extremity (thigh, leg, ankle, and foot) to axial skeleton

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Upper extremity Shoulder or pectoral girdle formed by: Scapula Clavicle (frequently fractured) Arm—humerus Forearm—radius and ulna Wrist—8 carpal bones Hand—5 metacarpal bones Fingers—14 phalanges or finger bones In what part of the body is the humerus? Humerus is attached to the scapula at its proximal end and articulates with the two bones of the forearm at the elbow joint. In what part of the body are the radius and ulna? Bones of the forearm are the radius and ulna. Why is the anatomy of the elbow a good example of how structure is related to function? Bony process of the ulna, called olecranon process, fits into the olecranon fossa and makes movement possible.

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Lower extremity Hip or pelvic girdle formed by the two coxal or pelvic bones (one on each side) with sacrum and coccyx behind Each coxal bone in infant consists of separate ilium, ischium and pubic bones—bones are fused into a single coxal bone in the adult Acetabulum is cup-shaped socket—articulates with head of femur Coxal bone in infant consists of three separate bones: ilium, ischium, and pubis. The bones of the foot are comparable to the bones of the hand. Each foot contains five metatarsals (each hand contains five metacarpal bones) and seven tarsals (compared with the hand’s eight carpals). What is the name of the heel bone? Calcaneus

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Thigh bone—femur Patella or kneecap articulates with femur and tibia Lower leg—tibia (“shinbone”) and fibula

Divisions of Skeleton Skeleton composed of the following divisions and their subdivisions Foot 5 metatarsal bones 7 tarsal bones (calcaneus or heel bone is largest tarsal) 14 phalanges or toe bones 3 arches of foot—two longitudinal (medial and lateral) and a transverse or metatarsal arch—if weakened, result is “flat feet” Compare the names of the foot bones with the names of the hand bones. See Table 7-5. Notice the narrower width of the male pelvis, giving it a more funnel-like shape than the female pelvis.

Human skeleton. The axial skeleton is distinguished by a blue tint Human skeleton. The axial skeleton is distinguished by a blue tint. A, Anterior view. B, Posterior view.

Differences Between a Man’s and a Woman’s Skeleton Size—male skeleton generally larger Shape of pelvis—male pelvis deep and narrow; female pelvis broad and shallow Size of pelvic inlet—female pelvic inlet generally wider; normally large enough for baby’s head to pass through it Pubic angle—angle between pubic bones of female generally wider What are the primary differences between a male and female skeleton? In general, the female pelvis can accommodate the body of a fetus before birth and allow it to pass through it during birth. Male hipbones are generally larger and narrower than the female’s.

Comparison of the male and female pelvis Comparison of the male and female pelvis. Notice the narrower width of the male pelvis, giving it a more funnel-like shape than the female pelvis.

Joint (Articulations) Every bone except hyoid (which anchors the tongue) connects to at least one other bone Joint types classified by degree of movement Synarthrosis (no movement)—fibrous connective tissue grows between articulating bones (e.g., sutures of skull) Amphiarthrosis (slight movement)—cartilage connects articulating bones (e.g., symphysis pubis) Every bone in the body, except for one, connects to at least one other bone. What is the exception? The hyoid bone in the neck, to which the tongue anchors. In general, what functions do bone joints serve? Joints hold the bones together securely and at the same time make it possible for movement to occur between the bones. What are three classifications of joints? Synarthroses are joints in which fibrous connective tissue grows between the articulating bones, holding them close together. The joints between cranial bones are synarthroses. Amphiarthroses are joints in which cartilage connects the articulating bones. The joints between the bodies of the vertebrae are amphiarthroses. The joints make it possible to flex forward, sideways, and to rotate.

Joints of the skeleton. A, Synarthrotic joint. B, Amphiarthrotic joint.

Joint (Articulations) Joint types Diarthrosis (free movement)—most joints belong to this class Structures of freely movable joints—joint capsule and ligaments hold adjoining bones together but permit movement at joint Articular cartilage—covers joint ends of bones and absorbs jolts Synovial membrane—lines joint capsule and secretes lubricating fluid Joint cavity—space between joint ends of bones Diarthroses allow considerable movement; sometimes in many directions and sometimes in only one direction. What are the types of freely movable joints? Ball-and-socket, hinge, pivot, saddle, gliding, and condyloid.

Structure of a diathrotic joint Structure of a diathrotic joint. Each diarthrosis has a joint capsule, a joint cavity, and a layer of cartilage over the ends of the joined bones. (Barbara Cousins.)

Joint (Articulations) Freely movable joints Ball-and-socket Hinge Pivot Saddle Gliding Condyloid Ball-and-socket joints (shoulder and hip) permit the widest range of movement. Hinge joints (elbow) allow movement in only two directions: flexion and extension. Pivot joints (neck) allow rotation. Saddle joints (between thumb and wrist) allow great mobility. Gliding joints (between vertebrae) allow limited gliding movements. Condyloid joints fit into an elliptical socket (distal end of radius fits into depressions in carpal bones).

Types of diathrotic joints Types of diathrotic joints. Notice that the structure of each type indicates its function (movement).

Skeletal Disorders Tumors of bone and cartilage Osteosarcoma Most common and serious malignant bone neoplasm Frequent sites include distal femur and proximal tibia and humerus Chondrosarcoma Cancer of skeletal hyaline cartilage Second most common cancer of skeletal tissues Frequent sites include medullary cavity of humerus, femur, ribs, and pelvic bones Compare the differences between osteosarcoma and chondrosarcoma.

Tumors of bone and cartilage (surgical specimens sectioned longitudinally). A, Osteosarcoma of distal femur. The tumor has broken out of the medullary cavity and is growing on the surface of the bone. B, Chondrosarcoma of proximal humerus. Note the glistening appearance of the hyaline cartilage tumor in the medullary cavity. (From Damjanov I, Linder J: Anderson’s pathology, ed 10, St Louis, 1996, Mosby.)

Skeletal Disorders Metabolic bone diseases Osteoporosis Characterized by loss of calcified bone matrix and reduction in number of trabeculae in spongy bone Bones fracture easily, especially in wrists, hips, and vertebrae Treatment includes drug therapy, exercise, and dietary supplements of calcium and vitamin D What minerals are deficient with osteoporosis? Calcium, vitamin D What is the “dowager’s hump” that is associated with osteoporosis? Shortened stature and classic kyphosis of the thoracic spine.

Comparison of normal and osteoporotic spongy bone Comparison of normal and osteoporotic spongy bone. Scanning electron micrograph (SEM) of, A, normal bone and, B, bone with osteoporosis. Note the loss of trabeculae and appearance of enlarged pores in the osteoporotic bone.

Skeletal Disorders Metabolic bone diseases Rickets and osteomalacia—both diseases characterized by loss of bone minerals related to vitamins Rickets Loss of bone minerals occurs in infants and young children before skeletal maturity Lack of bone rigidity causes gross skeletal changes (bowing of legs) Treated with vitamin D

Rickets. Bowing of legs in this toddler is due to poorly mineralized bones. (From Kumar V, Abbas A, Fausto N: Robbins and Cotran pathologic basis of disease, ed 7, Philadelphia, 2005, Saunders.)

Skeletal Disorders Metabolic bone diseases Rickets and osteomalacia Mineral content is lost from bones that have already matured Increases susceptibility to fractures Treated with vitamin D

Skeletal Disorders Metabolic bone diseases Paget disease (osteitis deformans) Faulty remodeling results in deformed bones that fracture easily Cause may be genetic or triggered by viral infections

Paget disease (osteitis deformans) Paget disease (osteitis deformans). Note the weakened and irregular cancellous bone overgrowth in the femur. (From Browner B, Jupiter J, Trafton P: Skeletal trauma: basic science, management, and reconstruction, ed 3, Philadelphia, 2003, Saunders.)

Skeletal Disorders Metabolic bone diseases Osteogenesis imperfecta (also called brittle bone disease) Bones are brittle because of lack of organic matrix Treatment may include splinting to reduce fracture and drugs that decrease cell activity

Osteogenesis imperfecta treatment of femurs Osteogenesis imperfecta treatment of femurs. These x-ray films show the progression of treatment in the same individual with “brittle bone disease.” A telescoping medullary rod is inserted and expanded while the individual grows. A, Shows original x-ray _ lm; B, same individual with the rods in place; C, x-ray film of the same person 4 years later. (From Canale ST: Campbell’s operative orthopaedics, ed 9, St Louis, 1998, Mosby.)

Skeletal Disorders Bone infection Osteomyelitis General term for bacterial (usually staphylococcal) infection of bone Treatment may involve surgery, drainage of pus, and IV antibiotic treatment—often over prolonged periods

Osteomyelitis. Segment of the femur from a patient with chronic osteomyelitis. (From Kumar V, Abbas A, Fausto N: Robbins and Cotran pathologic basis of disease, ed 7, Philadelphia, 2005, Saunders.)

Skeletal Disorders Bone fractures Open (compound) fractures pierce the skin and closed (simple) fractures do not Fracture types include complete and incomplete, linear, transverse and oblique Ask students to recall any fractures that they or their family members have had in the past. What type of fracture was it? What was the treatment? Did it require a cast or surgery? What type of fracture usually requires surgery? Open What type of fracture can most often be treated by casting? Closed

Bone fractures. A, Open. B, Closed. C, Incomplete and complete Bone fractures. A, Open. B, Closed. C, Incomplete and complete. D, Linear, transverse, and oblique.

Skeletal Disorders Joint disorders Noninflammatory joint disorders—do not usually involve inflammation of the synovial membrane; symptoms tend to be local and not systemic Osteoarthritis, or degenerative joint disease (DJD) Most common noninflammatory disorder of movable joints—often called “wear and tear” arthritis Symptoms: joint pain, morning stiffness, Bouchard nodes (at proximal interphalangeal joints), Heberden nodes (at distal interphalangeal joints) of the fingers Most common cause for partial and total hip and knee replacements

Types of arthritis. A, Osteoarthritis Types of arthritis. A, Osteoarthritis. Note the presence of nodes in the proximal interphalangeal joints (Bouchard nodes) and distal interphalangeal joints (Heberden nodes). (From Swartz MH: Textbook of physical diagnosis, ed 4, Philadelphia, 2002, Saunders.)

Skeletal Disorders Joint disorders Noninflammatory joint disorders Traumatic injury Dislocation or subluxation—articular surfaces of bones in joint are no longer in proper contact Sprain—acute injury to ligaments around joints (e.g., whiplash type injuries) Strain—acute injury to any part of the “musculotendinous unit” (muscle, tendon, junction between the two, and attachments to bone)

Skeletal Disorders Joint disorders Inflammatory joint disorders Arthritis: general name for several inflammatory joint diseases that may be caused by infection, injury, genetic factors, and autoimmunity Inflammation of the synovial membrane occurs, often with systemic signs and symptoms After reviewing the keys points of this slide, ask students to name some forms of arthritis that they are familiar with and to provide some distinguishing characteristics or symptoms of each one named. There are approximately 25 forms of arthritis.

Skeletal Disorders Joint disorders Inflammatory joint disorders Rheumatoid arthritis Systemic autoimmune disease—chronic inflammation of synovial membrane with involvement of other tissues such as blood vessels, eyes, heart, and lungs Gouty arthritis—synovial inflammation caused by gout, a condition in which sodium urate crystals form in joints and other tissues Infectious arthritis—arthritis resulting from infection by a pathogen, as in Lyme arthritis and ehrlichiosis, caused by two different bacteria that are transmitted to humans by tick bites

Types of arthritis. B, Rheumatoid arthritis Types of arthritis. B, Rheumatoid arthritis. Note themarked ulnar deviation of the wrists. (From Swartz MH: Textbook of physical diagnosis, ed 4, Philadelphia, 2002, Saunders.)

Types of arthritis. C, Gouty arthritis Types of arthritis. C, Gouty arthritis. Note tophi filled with sodium urate crystals. (From Swartz MH: Textbook of physical diagnosis, ed 4, Philadelphia, 2002, Saunders.)