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The ECG shows QRS complexes that change of mean electrical axis buy femara 2.5 mg mastercard, and longer duration (ineffi- are not preceded by P waves buy 2.5 mg femara fast delivery. Atrial fibrillation is associated with nu- normal wave of excitation reached the AV node purchase 2.5 mg femara amex, retrograde CHAPTER 13 The Electrical Activity of the Heart 233 conduction usually dies out in the AV node cheap femara 2.5 mg without prescription. The next nor- tions are conducted by the AV node 2.5 mg femara for sale, it is second-degree mal atrial excitation (P wave) occurs but is hidden by the atrioventricular block. If atrial excitation never reaches the inverted T wave associated with the abnormal QRS com- ventricles, as in the example in Figure 13. This normal wave of atrial excitation does not result gree (complete) atrioventricular block. Ventricular excitation does not occur because, when the impulse arrives, a portion of the The ECG Provides Three Types of Information AV node is still refractory following excitation by the pre- About the Ventricular Myocardium mature complex. A prolonged interval following a The ECG provides information about the pattern of excita- premature ventricular beat is the compensatory pause. In this case, tive ventricular myocardium, and abnormal dipoles result- the P wave is abnormal but the QRS complex is normal. It provides Premature beats are often called extrasystoles, frequently a no direct information about the mechanical effectiveness of misnomer because there is no “extra” beat. However, in the heart; other tests are used to study the efficiency of the some cases, the premature beat is interpolated between two heart as a pump (see Chapter 14). Disease or injury present, but their timing is independent of each other. This can affect the pattern of ventricular depolarization and pro- is complete atrioventricular block in which the AV node duce an abnormality in the QRS complex. In this example, the distance right side of the heart is not conducting (i. The atrial pace- tivity coming from the normally depolarized left side of the maker is probably in the SA node, and the ventricular pace- heart. The resulting QRS complex has an abnormal shape maker is probably in a lower portion of the AV node or because of aberrant electrical conduction and is prolonged bundle of His. This is first-degree atrioven- bundle-branch block), also resulting in a wide, deformed tricular block. B, Altered QRS complex (leads V1 and V5) produced by left ventricular hypertrophy. Leads I, aVF, pertrophy rotates the direction of the major dipole associ- and V1 of a patient are shown. Abnormal Dipoles Resulting From Ventricular Myocar- Changes in the Mass of Electrically Active Ventricular My- dial Injury. In this case, the creased mass of right ventricular muscle changes the supply of ATP may decrease below the level required to direction of the major dipole during ventricular depolariza- maintain the active transport of ions across the cell mem- tion, resulting in large R waves in lead V1. The resulting alterations in the membrane potential waves in lead I and the large R waves in lead aVF are also in the ischemic region can affect the ECG. Normally, the characteristic of a shift in the dipole of ventricular depolar- ECG is at baseline (zero voltage) during ization to the right. This illustrates how a change in the • The interval between the completion of the T wave and mass of excited tissue can affect the amplitude and direc- the onset of the P wave (the TP interval), during which tion of the QRS complex. A, Dark shading depicts depolarized Because zero baseline is set arbitrarily (on the ECG recorder), a ventricular tissue. ST segment elevation can occur with myocar- depressed diastolic baseline (TP segment) and an elevated ST seg- dial injury. The apparent zero baseline of the ECG before depo- ment cannot be distinguished. Regardless of the mechanism, this larization is below zero because of partial depolarization of the is referred to as an elevated ST segment. After depolarization (during the action po- a patient with acute myocardial infarction. CHAPTER 13 The Electrical Activity of the Heart 235 With myocardial ischemia, the cells in the ischemic re- ST interval because depolarization is uniform and complete gion partially depolarize to a lower resting membrane po- in both injured and normal tissue (this is the plateau period tential because of a lowering of the potassium ion concen- of ventricular action potentials). Because the ECG is de- tration gradient, although they are still capable of action signed so that the TP interval is recorded as zero voltage, potentials. As a consequence, a dipole is present during the the true zero during the ST interval is recorded as a positive TP interval in injured hearts because of the voltage differ- or negative deflection (Fig. These deflections dur- ence between normal (polarized) and abnormal (partially ing the ST interval are of major clinical utility in the diag- polarized) tissue. REVIEW QUESTIONS DIRECTIONS: Each of the numbered (E) Pacemaker channels (C) Proceeds from the subendocardium items or incomplete statements in this 5.

Complete disruption of the tendon fibers is seen in type III posterior tibial tendon tears 2.5 mg femara fast delivery. These are quite Achilles tendon injuries may be classified into non-in- rare and appear at MR imaging as tendon discontinuity buy discount femara 2.5 mg on line. The former group in- The gap may be filled with fluid or granulation tissue safe 2.5mg femara. Insertional Achilles disease in- cludes insertional tendinosis order femara 2.5 mg with amex, which may be associated Tears of the peroneal tendons are most commonly seen with a Haglund deformity of the calcaneus and insertion- along the lateral malleolus buy femara 2.5mg with amex, along the lateral calcaneal al tears. At the lateral At MR imaging, partial Achilles tendon tears demon- malleolus, tears may be associated with either superior strate heterogeneous signal intensity and thickening of peroneal retinacular tear or laxity secondary to a previous the tendon without complete interruption. Signal tenosynovitis include scarring around the tendons and changes tend to be along the posterior aspect of the ten- fluid within the common tendon sheath, respectively. Partial Care should be taken to differentiate physiologic fluid ac- tears, especially when acute, often depict edema and he- cumulation within the tendon sheath and tenosynovitis morrhage within Kager’s fat pad. Complete Achilles ten- from fluid within the common peroneal sheath secondary to a tear of the calcaneofibular ligament. Care should al- don rupture manifests as discontinuity with fraying and so be taken as well to differentiate between tendinosis retraction of the torn edges of the tendon. US is comparable to MR imaging for assessing Longitudinal intrasubstance tears of the peroneus bre- Achilles tendon injuries. In addition, US demonstrates vis tendon have a distinct appearance on axial MR im- neovascularization in painful Achilles tendons. The tendon assumes a C-shaped or boomerang con- while strongly associated with pain, is not predictable of figuration that partially envelops the peroneus longus an unfavorable outcome. Ultrasound may miss Achilles tendon lesions at frequently seen at the level of the peroneal tubercle or the muscle- tendon junction, while MR imaging at this cuboid tunnel. The imaging diagnosis of a tear of the per- site is associated with muscle edema, retraction of mus- oneus longus tendon at this location is clinically impor- cle fibers and hematoma. On An abnormal position of an os peroneum on conven- most follow-up MR imaging studies, intratendinous sig- tional radiographs may be a clue for possible tear of the nal intensity will decrease as the tendon heals. Hypertrophy of the peroneal tu- the tendon may remain thickened, simulating chronic bercle has also been implicated as a cause for tear of the tendinosis, even after normal signal intensity has been re- peroneus longus tendon at the midfoot. Imaging of the Foot and Ankle 43 Ligaments the ligament will allow the talar head to collapse result- ing in an acquired flat foot deformity. There is a high as- Lateral Collateral Ligaments sociation between rupture of the spring ligament and dys- function of the posterior tibial tendon. Ankle sprains are the most common musculoskeletal The spring ligament is composed of the inferior longi- cause for hospital emergency rooms and private practice tudinal calcaneonavicular and superomedial calcaneonav- visits. The anterior tibiofibular lig- oblique) of the spring ligament has been demonstrated. The posterior tibiofibular ligament, also visible on icular in the lower layer of the spring ligament complex, axial images at the tip of the fibula, is rarely torn. Early investigations have indicated that the calcane- Each of the three components can be visualized on MR ofibular ligament runs obliquely from the fibular tip pos- images. Therefore, oblique images have been considered to be superior in the Impingement Syndromes assessment of the ligament. In our experience, however, this plane is not clearly superior to coronal images in de- The role of impingement syndromes in producing chron- lineating the calcaneofibular ligament. This may be ex- ic ankle pain has been better appreciated in recent years. This is discussed more fully under the category of Among the four most common impingement syn- osseous injuries. Intra-articular synovial hypertrophy The tibiofibular syndesmosis is an important stabilizer of and fibrosis may occur in the lateral gutter secondary to the distal tibiofibular joint. It consists of the anteroinfe- capsular or ligamentous tears associated with inversion rior tibiofibular ligament, the posteroinferior tibiofibular injuries. This condition is optimally assessed with MR ligament, the transverse tibiofibular ligament, and the in- arthrography, although positive experience with this ap- terosseous tibiofibular ligament. Disruption or irregularities of the ligaments, ankle, excluding Morton’s neuroma, is tarsal tunnel syn- degenerative changes at the distal tibiofibular joint, and drome.

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This structural arrangement plays a major role in stabi- lizing the shoulder joint cheap femara 2.5mg. When throwing a baseball generic femara 2.5 mg with visa, an abduction of the shoulder is followed by a rapid and forceful rotation and flexion of the shoulder joint 2.5mg femara fast delivery, which may strain the musculotendinous cuff discount 2.5mg femara fast delivery. Extension of the shoulder joint is in reference to brachii generic femara 2.5 mg on line, brachialis, brachioradialis, and triceps brachii (figs. In addition, a short triangular muscle, the anconeus, is ing the shoulder joint angle) movement of the arm. A transverse section through the brachium in impulses, will in time come to resemble cardiac muscle tissue figure 9. The procedure involves detaching the latissimus dorsi iar muscle of the arm, yet it has no attachments on the humerus. A pacemaker is required to long head originates on the superior tuberosity of the glenoid provide the continuous rhythmic contractions. Both heads of Scapular Muscles the biceps brachii muscle insert on the radial tuberosity. Although it has sev- prominent muscle positioned along the lateral (radial) surface of eral functions (table 9. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 268 Unit 4 Support and Movement FIGURE 9. The triceps brachii muscle, located on the posterior sur- joints—the elbow and wrist. Others act on the joints of the face of the brachium, extends the forearm at the elbow joint, in wrist, hand, and digits. Still others produce rotational movement opposition to the action of the biceps brachii. The triceps brachii has three heads, or fected at the hand and digits are: supination, pronation, flexion, origins. Two of the three, the lateral head and medial head, arise and extension. Other movements of the hand include adduction from the humerus, whereas the long head arises from the infra- and abduction. A common tendinous insertion attaches the triceps brachii muscle to the olecranon of the ulna. Two muscles are responsible for pronating the hand—the pronator teres and pronator quadratus. The pronator teres Muscles of the Forearm That Move the muscle is located on the upper medial side of the forearm, whereas the deep, anteriorly positioned pronator quadratus Joints of the Wrist, Hand, and Fingers muscle extends between the ulna and radius on the distal The muscles that cause most of the movements in the joints of fourth of the forearm. These two muscles work synergistically the wrist, hand, and fingers are positioned along the forearm to rotate the palm of the hand posteriorly and position the (figs. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 9 Muscular System 269 FIGURE 9. Flexion of the Wrist, Hand, and Fingers The palmaris longus is the most variable muscle in the body. It is totally absent in approximately 8% of all people, and in Six of the muscles that flex the joints of the wrist, hand, and fin- 4% it is absent in one or the other forearm. Furthermore, it is absent gers will be described from lateral to medial and from superficial more often in females than males, and on the left side in both sexes. Because of the superficial position of the palmaris longus muscle, to deep (figs. Although four of the six arise from you can readily determine whether it is present in your own forearm the medial epicondyle of the humerus (see table 9. The brachioradialis, al- and then examining for its tendon just proximal to the wrist (see ready described, is an obvious reference muscle for locating the figs. The flexor carpi ulnaris muscle is positioned on the me- The flexor carpi radialis muscle extends diagonally across dial anterior side of the forearm, where it assists in flexing the the anterior surface of the forearm, and its distal cordlike tendon wrist joints and adducting the hand. This muscle is an The broad superficial digital flexor (flexor digitorum super- important landmark for locating the radial artery, where the ficialis) muscle lies directly beneath the three flexor muscles just pulse is usually taken. It has an extensive origin, in- The narrow palmaris longus muscle is superficial in posi- volving the humerus, ulna, and radius (see table 9.

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People of African ancestry also have the nar- rowest pelvic girdle for a given shoulder width order femara 2.5 mg visa. Define the terms puberty purchase 2.5mg femara fast delivery, pubescence buy 2.5mg femara, sexual dimorphism buy femara 2.5mg free shipping, ancestry have relatively short appendage lengths to sitting and menarche purchase femara 2.5mg without a prescription. These differences provide distinct advantages and disad- brings it about? Com- track events, particularly the sprints and high hurdles, whereas pare the body structure of an adult female to that of an whites are generally adapted to distance running. Developmental © The McGraw−Hill Anatomy, Sixth Edition Development Anatomy, Postnatal Companies, 2001 Growth, and Inheritance 782 Unit 7 Reproduction and Development (a) (b) FIGURE 22. The first 22 pairs of chromo- somes are called the autosomal chromosomes. The photographs of two Olympic 400-meter runners have been scaled so that both have the same sitting height. This does not produce 46 dif- ferent chromosomes; rather, it produces 23 pairs of homologous chromosomes. Each member of a homologous pair, with the im- INHERITANCE portant exception of the sex chromosomes, looks like the other and contains similar genes (such as those coding for eye color, Inheritance is the acquisition of characteristics or qualities by height, and so on). These homologous pairs of chromosomes can transmission from parent to offspring. Hereditary information is be karyotyped (photographed or illustrated) and identified, as transmitted by genes. The twenty-third pair of chromosomes are the sex Objective 20 Explain how probability is involved in chromosomes, which may lookdifferent and may carry different predicting inheritance and use a Punnett square to illustrate genes. In a female these consist of two X chromosomes, whereas selected probabilities. Genes and Alleles Genetics and inheritance are important in anatomy and physiol- A gene is the portion of the DNA of a chromosome that con- ogy because of the numerous developmental and functional dis- tains the information needed to synthesize a particular protein orders that have a genetic basis. Although each diploid cell has a pair of genes for each and diseases are inherited finds practical application in genetic characteristic, these genes may be present in variant forms. The genetic inheritance of an individual begins with Those alternative forms of a gene that affect the same character- conception. Developmental © The McGraw−Hill Anatomy, Sixth Edition Development Anatomy, Postnatal Companies, 2001 Growth, and Inheritance Chapter 22 Developmental Anatomy, Postnatal Growth, and Inheritance 783 TABLE 22. Homologous chromosomes contain genes for the same characteristic at the same locus. One allele of each pair originates from the female parent and the other from the male. The shape of a person’s ears, for example, is determined by the kind of allele re- ceived from each parent and how the alleles interact with one another. Alleles are always located on the same spot (called a locus) on homologous chromosomes (Fig. For any particular pair of alleles in a person, the two alleles are either identical or not identical. Two par- If the alleles for a particular trait are homozygous, the char- ents with unattached (free) earlobes can have a child with attached earlobes. If the alleles for a particular trait are heterozygous, phenotypes of the individuals would be free earlobes resulting from however, the allele that expresses itself and the way in which the the presence of a dominant allele in each genotype. A person who genes for that trait interact will determine the phenotype. The inherited two recessive alleles for earlobes would have the geno- allele that expresses itself is called the dominant allele, the one type ee and would have attached earlobes. The various combinations of Thus, three genotypes are possible when gene pairing in- dominant and recessive alleles are responsible for a person’s volves dominant and recessive alleles. Only In describing genotypes, it is traditional to use letter symbols two phenotypes are possible, however, because the dominant al- to refer to the alleles of an organism. The dominant alleles are sym- lele is expressed in both the homozygous dominant (EE) and bolized by uppercase letters, and the recessive alleles are symbolized the heterozygous (Ee) individuals. Thus, the genotype of a person who is homozygous for pressed only in the homozygous recessive (ee) condition.

The capillary loops into creased blood temperature as it enters the skin femara 2.5 mg line. During mild to moderate exercise in a warm envi- ronment cheap femara 2.5 mg without a prescription, skin blood flow can equal or exceed blood flow to Sweat glands derive virtually all sweat water from blood the skeletal muscles discount femara 2.5mg online. Exercise tolerance can purchase 2.5 mg femara amex, therefore cheap femara 2.5mg on line, be plasma and are surrounded by a dense capillary network in lower in a warm environment because the vascular resist- the deeper layers of the dermis. As explained in Chapter 29, ance of the skin and muscle is too low to maintain an ap- neural regulation of the sweating mechanism not only propriate arterial blood pressure, even at maximum cardiac causes the formation of sweat but also substantially in- output. One of the adaptations to exercise is an ability to creases skin blood flow. All the capillaries from the superfi- increase blood flow in skin and dissipate more heat. In ad- cial skin layers are drained by venules, which form a venous dition, aerobically trained humans are capable of higher plexus in the superficial dermis and eventually drain into sweat production rates; this increases heat loss and induces many large venules and small veins beneath the dermis. The vascular pattern just described is modified in the tis- The vast majority of humans live in cool to cold regions, sues of the hand, feet, ears, nose, and some areas of the face where body heat conservation is imperative. The sensation in that direct vascular connections between arterioles and of cool or cold skin, or a lowered body core temperature, venules, known as arteriovenous anastomoses, occur pri- elicits a reflex increase in sympathetic nerve activity, which marily in the superficial dermal tissues (see Fig. Heat loss contrast, relatively few arteriovenous anastomoses exist in is minimized because the skin becomes a poorly perfused in- the major portion of human skin over the limbs and torso. As long as the skin tem- If a great amount of heat must be dissipated, dilation of the perature is higher than about 10 to 13 C (50 to 55 F), the arteriovenous anastomoses allows substantially increased neurally induced vasoconstriction is sustained. However, at skin blood flow to warm the skin, thereby increasing heat lower tissue temperatures, the vascular smooth muscle cells loss to the environment. This allows vasculatures of the progressively lose their contractile ability, and the vessels 286 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY passively dilate to various extents. The reddish color of the plied by two umbilical arteries, which branch from the in- hands, face, and ears on a cold day demonstrates increased ternal iliac arteries, and is drained by a single umbilical vein blood flow and vasodilation as a result of low temperatures. The umbilical vein of the fetus returns oxygen To some extent, this cold-mediated vasodilation is useful be- and nutrients from the mother’s body to the fetal cardio- cause it lessens the chance of cold injury to exposed skin. Although many liters of oxy- inadequate clothing is worn, heat loss would be rapid and hy- gen and carbon dioxide, together with hundreds of grams pothermia would result. This large chemical exchange without cellular exchange is possible because the fetal and FETAL AND PLACENTAL CIRCULATIONS maternal blood are kept completely separate, or nearly so. The Placenta Has Maternal and Fetal The fundamental anatomical and physiological structure Circulations That Allow Exchange Between for exchange is the placental villus. As the umbilical arter- ies enter the fetal placenta, they divide into many branches the Mother and Fetus that penetrate the placenta toward the maternal system. The development of a human fetus depends on nutrient, These small arteries divide in a pattern similar to a fir tree, gas, water, and waste exchange in the maternal and fetal the placental villi being the small branches. The human fetal placenta is sup- laries bring in the fetal blood from the umbilical arteries Fetal lung Arteries to upper body High-resistance pulmonary vessels Ductus Pulmonary arteriosus artery Foramen 31 ovale Superior FIGURE 17. Schematic representation of the left and right sides of the fe- tal heart are separated to empha- 52 62 size the right-to-left shunt of blood through the open foramen ovale in Right Left ventricle ventricle 58 the atrial septum and the right-to- Inferior left shunt through the ductus arte- vena cava 67 Abdominal riosus. The numbers 27 Portal represent the percentage of satura- vein tion of blood hemoglobin with oxygen in the fetal circulation. Iliac Closure of the ductus venosus, 26 arteries Liver 80 foramen ovale, ductus arteriosus, 58 Umbilical Umbilical artery and placental vessels at birth and Syncytiotrophoblast vein the dilation of the pulmonary vas- Cytotrophoblast culature establish the adult circula- tion pattern. The insert is a cross- sectional view of a fetal placental villus, one of the branches of the Intervillous tree-like fetal vascular system in space the placenta. The fetal capillaries Fetal provide incoming blood, and the placenta sinusoidal capillaries act as the ve- Maternal nous drainage. The villus is com- placenta pletely surrounded by the maternal blood, and the exchange of nutri- Fetal Syncytial Spiral artery Endometrial vein ents and wastes occurs across the capillary knot fetal syncytiotrophoblast. CHAPTER 17 Special Circulations 287 and then blood leaves through sinusoidal capillaries to the pinocytosis and exocytosis. Exchange occurs in the fetal cap- through the lipid bilayer of cell membranes. For example, illaries and probably to some extent in the sinusoidal capil- lipid-soluble anesthetic agents in the mother’s blood do en- laries. The mother’s vascular system forms a reservoir ter and depress the fetus.

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