QuadricepsThe quadriceps is a group of four muscles thatmake up the anterior portion of the thigh. The fourmuscles of this group are the rectus femoris thatoriginates at the ilium; and the vastus lateralis, v.medialis, v. intermedius (not shown), that originatealong the femur (fig. 1-28). All four are inserted intothe tuberosity of the tibia through a tendon passingover the knee joint. The quadriceps serves as a strongextensor of the leg at the knee and flexes the thigh.Additionally located in the quadriceps area is theadductor longus that adducts, rotates, and flexes thethigh.Biceps FemorisThe biceps femoris (often called the hamstringmuscle) originates at the tuberosity of the ischium (thelowest portion of the coxal bone, part of the pelvicgirdle) and the middle third of the femur (fig. 1-29). Itis inserted on the head of the fibula and the lateralcondyle of the tibia. It acts, along with other relatedmuscles, to flex the leg at the knee and to extend thethigh at the hip joint.GracilisThe gracilis is a long slender muscle located on theinner aspect of the thigh (figs. 1-28 and 1-29). Itadducts the thigh, and flexes and medially rotates theleg. Its origin is in the symphysis pubis, and itsinsertion is in the medial surface of the tibia, below thecondyle.SartoriusThe sartorius is the longest muscle in the body. Itextends diagonally across the front of the thigh from itsorigin at the ilium, down to its insertion near thetuberosity of the tibia (fig. 1-29). Its function is to flexthe thigh and rotate it laterally, and to flex the leg androtate it slightly medially.Gastrocnemius and SoleusT h e g a s t r o c n e m i u s a n d s o l e u s ( t o g e t h e rcommonly called the calf muscles) extend the foot atthe ankle (figs. 1-28 and 1-29). The gastrocnemiusoriginates at two points on the femur; the soleusoriginates at the head of the fibula and the medialborder of the tibia. Both are inserted in a commontendon called the calcaneus, or Achilles tendon.Tibialis AnteriorThe tibialis anterior originates at the upper half ofthe tibia and inserts at the first metatarsal andcuneiform bones (fig. 1-28). It flexes the foot.DiaphragmThe diaphragm (not shown) is an internal (asopposed to superficial) muscle that forms the floor ofthe thoracic cavity and the ceiling of the abdominalcavity. It is the primary muscle of respiration,modifying the size of the thorax and abdomenvertically. It has three openings for the passage ofnerves and blood vessels.THE INTEGUMENTARY SYSTEMLEARNING OBJECTIVE: Identify skin, itsfunctions, structure, and appendages.Organ systems are comprised of tissues groupedtogether to form organs, and groups of organs withspecialized functions. Since the skin acts with hairfollicles, sebaceous glands, and sweat glands, theseorgans together constitute the integumentary system.SKIN FUNCTIONThe skin covers almost every visible part of thehuman body. Even the hair and nails are outgrowthsfrom it. It protects the underlying structures frominjury and invasion by foreign organisms; it containsthe peripheral endings of many sensory nerves; and ithas limited excretory and absorbing powers. The skinalso plays an important part in regulating bodytemperature. In addition, the skin is a waterproofcovering that prevents excessive water loss, even invery dry climates.SKIN STRUCTUREThe skin, or integument, consists of two layers, theepidermis and the dermis, and supporting structuresand appendages (fig. 1-30).EpidermisThe epidermis is the outer skin layer (fig. 1-30). Itis made up of tough, flat, scalelike epithelial cells. Fivesublayers or strata of epidermal cells have beenidentified, and, listed from superficial to deep, they are1-22
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