Porth's Essentials of Pathophysiology, 4e

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Musculoskeletal Function

U N I T 1 2

Such conditions occur when tendons are deflected over bone or where skin must move freely over bony tissue. Bursae may become injured or inflamed, causing dis- comfort, swelling, and limitation in movement of the involved area. In addition to bursae, structures called tendon sheaths also reduce friction at joints. Tendon sheaths are tubelike bursae that wrap around tendons where there is considerable friction. This occurs where ten- dons pass through synovial cavities, such as the ten- don of the biceps brachi muscle at the shoulder joint. Similar areas of friction are found at the wrist and ankle, where many tendons come together in a con- fined space and may be torn as the result of an injury (see Chapter 44). ■■ Joints (or articulations) are areas where two or more bones are joined together by fibrous tissue, cartilage, or bone. In fibrous joints, or synarthroses, such as those of the skull, the bones are joined by fibrous tissue. In cartilaginous joints, or amphiarthoses, bones are jointed by hyaline cartilage (as in the epiphyseal plate during childhood and early adolescence). In fibrocartilaginous joints (as in those that join the vertebrae and intervertebral disks) the articular surface is covered with hyaline cartilage, which in turn is fused to an intervening pad of fibrocartilage. ■■ Synovial joints or diarthroses are freely moveable joints in which the surfaces of the articulating ends of bones are enclosed in a fibrous joint capsule.The joint capsule consists of two layers: an outer fibrous layer and an inner synovial membrane (or synovium).The synovial fluid, which is secreted by the synovium into the joint capsule, acts as a lubricant and facilitates movement of the joint’s articulating surfaces.The articulating surfaces of synovial joints are covered with a layer of avascular cartilage that relies on oxygen and nutrients contained in the synovial fluid. ■■ Tendons and ligaments are dense connective tissue structures that connect the muscles and bones of diarthroidal joints. Bursae, which are closed sacs containing synovial fluid, prevent friction in areas where tendons are deflected over bone or where skin must move freely over bony tissue. SUMMARY CONCEPTS

R E V I EW E X E R C I S E S

1. Hyaline cartilage degenerates when the chondrocytes become metabolically inactive and die, causing the matrix to calcify and be replaced by bone. A. Explain how this process can contribute to normal skeletal growth during childhood and adolescence, but cause joint pain and immobility when it occurs during adulthood. 2. Persons with end-stage kidney disease have a deficiency of activated vitamin D. A. Explain why this occurs, and what effect it would have on the persons’ bones. B. How might this deficiency be treated? 3. Recent studies have revealed that estrogen deficiency as well as normal aging may produce a decrease in osteoblast activity. A. Explain how this would contribute to a disruption in bone remodeling and the development of osteoporosis. 4. Often pain from injury to the knee is experienced as pain in the hip. A. Explain why this might occur. Cohen S. Role of RANK ligand in normal and pathologic bone remodeling and therapeutic potential of novel inhibitory molecules in musculoskeletal disease. Arthritis Rheum. 2006;55(1):15–18. Garcia RA, Klein MJ, Schiller AL. Bones and joints. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine . 6th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2012:1199–1218, 1250–1254. Hall JE. Guyton and Hall Textbook of Medical Physiology . 12th ed. Philadelphia, PA: Saunders Elsevier; 2011:955–966. Hofbauer LC, Schoppet M. Clinical implications of osteoprotegrin/ RANKL/RANK system for bone and vascular disease. JAMA. 2004;292(4):490–495. Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266–281. Marsall R, Einhorn TA. The biology of fracture healing. Injury. 2011;42(6):551–555. Moore KL, Dalley AF, Agur AM. Clinically Oriented Anatomy . 6th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2010:19–29. Moore KL, Persaud TVN. The Developing Human: Clinically Oriented Embryology . 7th ed. Philadelphia, PA: Saunders; 2003:381–399. Neve A, Corrado A, Cantatore FP. Osteocytes: central conductors of bone biology in normal and pathological conditions. Acta Physiol (Oxf). 2011;204:317–330. B I B L I O G R A P H Y