By E. Pavel. Strayer University.

Blood flow to an organ is regulated by the action of these precap- illary sphincters and by the degree of resistance to blood flow provided by the small arteries and arterioles in the organ cheap 100mg furosemide. Unlike the vessels of the arterial and venous systems generic furosemide 40mg free shipping, the walls of capillaries are composed of just one cell layer—a simple squamous epithelium buy discount furosemide 100mg, or endothelium furosemide 100mg on line. The absence of smooth muscle and connective tissue layers allows for exchange of mate- rials between the blood and the interstitial fluid order furosemide 100mg free shipping. Types of Capillaries There are several different types of capillaries, distinguished by sig- nificant differences in structure. In terms of their endothelial lin- ing, these capillary types include those that are continuous, those that are discontinuous, and those that are fenestrated (fig. Continuous capillaries are those in which adjacent en- dothelial cells are tightly joined together. These are found in muscles, lungs, adipose tissue, and in the central nervous system. The fact that continuous capillaries in the CNS lack intercellu- FIGURE 16. Continuous tinuous capillaries as they appear in the electron microscope. These capillaries are character- suggests that the intracellular transport of material may occur ized by wide intercellular pores (800–1,000Å) that are covered across the capillary walls. This type of transport appears to be the by a layer of mucoprotein, which may serve as a diaphragm. Dis- only available mechanism of capillary exchange within the cen- continuous capillaries are found in the bone marrow, liver, and tral nervous system and may account, in part, for the selective spleen. The space between endothelial cells is so great that these nature of the blood-brain barrier (see fig. Circulatory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 558 Unit 6 Maintenance of the Body FIGURE 16. When a person is more active, blood returns to the heart at a faster rate and less is left in the venous system. The accumulation of blood in the veins of the legs over a long FIGURE 16. The con- period of time, as may occur in people with occupations that traction of skeletal muscles helps pump blood toward the heart, but require standing still all day, can cause the veins to stretch to the the flow of blood away from the heart is prevented by closure of the point where the venous valves are no longer efficient. During walking, the movements of the foot acti- vate the soleus muscle pump. This effect can be produced in bedridden people by extending and flexing the ankle joints. Veins Veins are vessels that carry blood from capillaries back to the Blood Pressure heart. The blood is delivered from microscopic vessels called venules into progressively larger vessels that empty into the large Blood pressure is the force exerted by the blood against the veins. The average pressure in the veins is only 2 mmHg, inner walls of the vessels through which it flows. It plays its pri- compared to a much higher average arterial pressure of about mary role in the arteries and arterioles, where the pressure is by 100 mmHg. In capillaries and venules, blood pressure is con- that the blood exerts on the walls of the vessels. In the The low venous pressure is insufficient to return blood to veins, blood pressure plays only a minor role, because the action the heart, particularly from the lower limbs. Veins, however, pass of the valves and skeletal muscle pumps provides most of the between skeletal muscle groups that provide a massaging action force needed to move blood to the heart. As the veins are squeezed by con- ments of pulse rate, rate of breathing, and body temperature, tracting skeletal muscles, a one-way flow of blood to the heart is blood pressure is usually considered a vital sign. This in- nous blood flow is often described as the skeletal muscle pump. The strument has an inflatable cuff that is used to constrict an artery at rate of venous return to the heart is dependent, in large part, on a pressure point (see fig.

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They the contact lens may develop an infection are prescribed by an ophthalmologist (a of the eye discount furosemide 40mg with visa, in which case contact lenses physician who specializes in the diagno- should not be worn purchase furosemide 100 mg on line. Refrac- hance the life of the individual generic furosemide 100 mg amex, not just to tive surgery may be used to treat myopia enhance the visual system cheap furosemide 100 mg on line. The types of de- (nearsightedness) cheap furosemide 100 mg online, hyperopia (farsighted- vices used should be based on individual ness), or astigmatism (irregularity in the needs as well as the willingness and abili- shape of the cornea or lens resulting in dis- ty to use them. Three primary ture, strengthen, and maintain individ- surgical techniques are used in refractory uals’ self-confidence for safe, independent eye surgery: radial keratotomy, photorefrac- functioning. These aids enhance remain- tive keratectomy, and laser-assisted in situ ing visual abilities through the use of indi- keratomileusis. Although refractive eye sur- vidually prescribed adaptive equipment ap- gery is often effective in correcting the propriate to individuals’ specific lifestyle. Low-tech- moval of the eyeball, or when there is a con- nology devices such as talking watches, genital absence of the eye (anophthal- raised dot markings for oven dials, or mia), a prosthetic eye may be constructed templates for check signing require little and worn by the individual. The prosthetic training and may require only simple eye, while not contributing to vision, serves adaptations. Additional devices, such as a cosmetic purpose and can enhance the talking clocks and timers, writing guides, individual’s body image and self-concept. Examples are video into the use of electrical stimulation to magnifiers and computer systems. Optical prostheses, magnifiers use closed-circuit television and which emulate functions of photorecep- can magnify a printed page on a television tors located in the retina, are an example screen for reading. Numerous computer of devices that have the potential for software programs and adaptive devices restoring rudimentary vision (Scarlatis, can be used to enlarge printed materials 2000). Although still in experimental or to convert print into synthetic speech stages, the development of optical pros- output. These devices include large-print theses is an important advance that may computer monitors, programs that enlarge make it possible for individuals with reti- print size on the screen, printers that mod- nal damage to have partial vision restored. Speech packages allow should be part of an overall program to en- for adjustments in the rate of speech and 136 CHAPTER 4 CONDITIONS OF THE EYE AND BLINDNESS the tone of voice to meet the needs of the 2002). Hard-copy Braille uses the familiar ronments and also provide training in the raised dot method, whereas soft-copy Braille use of public transportation, use of the is stored on electromagnetic tape and pre- cane, and use of mobility lights or elec- sented as patterns by a set of pins that rep- tronic travel aids. Individuals place their training, individuals with visual impair- fingers on display units through which the ments learn to orient themselves to their pins protrude. Another type of tactile aid environment by using compensatory is an electromechanical vibratory system. A strategies, including illumination tech- small camera is passed over a line of print, niques and the use of contrast, magnifi- and each printed letter is then displayed cation, memorization of location, and as a pattern of vibration that the individ- auditory and tactile feedback. The key to the successful use of any Various types of mobility aids, such as assistive or adaptive device is making sure sighted guides, guide dogs, canes, and that the individual using the device is electronic devices, are available to help in- involved in selecting it so that the device dividuals with a visual impairment move meets his or her requirements, capabilities, about the environment more freely (Cox and needs. Orientation and mobili- viduals view the device positively and use ty specialists can help the individual find it to best enhance their own functional the best system. Guide dogs not only increase the mobil- ity of the individual with a visual impair- Orientation and Mobility Training ment but can also provide protection and companionship. Guide dogs undergo in- The goal of orientation and mobility train- tensive training before being matched ing is to enable individuals with a visual with the individual to whom they are impairment to achieve as much mobility assigned. They are taught how to respond as possible according to their capabilities to various commands as well as how to and desires and to recapture, strengthen, respond to curbs, traffic, and other poten- and maintain self-reliance for safe and in- tial hazards in the environment. Orientation and mobil- vidual and dog train together for a ity (O&M) specialists provide training that number of weeks to become an effective helps individuals know where they are in team. Not all individuals are able to use a relation to their surroundings and how to guide dog, and some individuals prefer to safely navigate within their environment use other forms of mobility aids, such as (Turnbull, Turnbull, Shank, Smith, & Leal, a long cane. Psychosocial Issues in Conditions of the Eye and Blindness 137 The most common mobility aid is the with visual impairment (Vance, 2000). An viewed as malingerers by their families orientation and mobility specialist pre- and acquaintances because they can see scribes the cane according to the individ- some things but not others. The ed of denying their condition by those individual moves the cane rhythmically in who expect individuals with visual impair- an arc in front of the body to ensure a safe ments to be dependent and isolated. Although this pro- Adjustment to vision loss is not necessar- vides some protection, it does not account ily correlated with the degree of remain- for objects above the waist that are in the ing vision. In an attempt to com- do not have fewer adjustment issues than pensate for this type of obstacle, some those who are totally blind, and in fact canes have tone-emitting radar units that may have more adaptation difficulties be- give a differential pitch for the direction cause their partial sight presents an am- and height of obstacles in front of the biguous situation for others. Some individuals prefer col- individuals with partial sight may exhib- lapsible, folding, or telescopic canes, it high levels of anxiety because they may which are less obtrusive and can be col- be unsure about whether or when they lapsed and slipped into a purse or under will lose more of their residual vision.

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Which portions of the aorta are exam generic furosemide 100 mg, the patient’s lungs are clear discount furosemide 40mg without a prescription, and heart involved? An electrocardiogram is also nor- difference in blood pressure between mal buy 100mg furosemide with mastercard. Because of his symptoms cheap furosemide 100 mg with visa, you suspect the left and right arm furosemide 40 mg free shipping, with the left arm an aortic dissection and order a CT scan. Her blood you request an angiogram of her abdominal pressure is markedly elevated today, and in arteries. How can the renal artery stenosis stethoscope, which corresponds to her heart- (narrowing) seen in the adjacent beat. Lab work shows very low serum potas- angiogram cause high blood pressure? Discuss the impact that this condition low potassium, so you start her on potassium may have on the opposite renal artery supplementation. Circulatory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 16 Circulatory System 599 Chapter Summary Functions and Major Components of the (c) The heart contains right and left (b) Veins have venous valves that direct Circulatory System (pp. The circulatory system transports oxygen and bicuspid valves, respectively); a compressed by the skeletal muscle and nutritive molecules to the tissue cells pulmonary semilunar valve; and an pumps. Capillaries are composed of endothelial from tissue cells; it also carries hormones 2. They are the basic functional and other regulatory molecules to their are the pulmonary and the systemic; in units of the circulatory system. Principal Arteries of the Body protect the body from infection, and (a) The pulmonary circulation includes (pp. The components of the circulatory system right ventricle through the lungs, and the brachiocephalic trunk, the left are the heart, blood vessels, and blood, from there to the left atrium. The brachiocephalic system, and the lymphatic vessels and other arteries, capillaries, and veins trunk divides into the right common lymphoid tissue and organs of the in the body. These vessels carry blood carotid artery and the right subclavian lymphatic system. Blood, a highly specialized connective (c) The myocardium of the heart is external carotid arteries and the vertebral tissue, consists of formed elements served by right and left coronary arteries. Erythrocytes are disc-shaped cells that coronary sinus collects and empties the paired vertebral arteries, which lack nuclei but contain hemoglobin. Contraction of the atria and ventricles is surrounding the pituitary gland. Leukocytes have nuclei and are classified the atria and then enter the 3. The upper extremity is served by the as granular (eosinophils, basophils, and atrioventricular (AV) node. Leukocytes defend the conducted by the atrioventricular the axillary artery and then the body against infections by bundle and conduction myofibers brachial artery as it enters the arm. During contraction of the ventricles, the the radial and ulnar arteries, which cytoplasmic fragments that assist in the intraventricular pressure rises and causes supply blood to the forearm and formation of clots to prevent blood loss. Erythrocytes are formed through a process the pulmonary and aortic valves close 4. The abdominal portion of the aorta has called erythropoiesis; leukocytes are because the pressure is greater in the the following branches: the inferior formed through leukopoiesis. Closing of the AV valves causes the first renal, suprarenal, testicular (or ovarian), sac, liver, and spleen. In the adult, red sound (lub); closing of the pulmonary and and inferior mesenteric arteries. Heart murmurs are commonly internal and external iliac arteries, which caused by abnormal valves or by septal supply branches to the pelvis and lower Heart (pp. The wall of the heart consists of the conduction is called an electrocardiogram Principal Veins of the Body epicardium, myocardium, and (ECG or EKG). Blood from the head and neck is drained (a) The right atrium receives blood from Blood Vessels (pp. Arteries and veins have a tunica externa, blood from the brain is drained by the and the right ventricle pumps blood tunica media, and tunica interna. Arteries ventricle pumps blood into the transport blood away from the heart. Circulatory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 600 Unit 6 Maintenance of the Body 3. In the thorax, the superior vena cava is oxygen and nutrients are obtained from 2.

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The choice of additional imaging plane or Information on tumor enhancement is not without a planes varies with the involved body part order furosemide 100 mg with mastercard, the lesion loca- price discount furosemide 40mg online. The use of intravenous contrast substantially in- tion order furosemide 40mg with amex, and the relation of the lesion to crucial structures purchase 100mg furosemide fast delivery. One specific circumstance in which gadolin- recovery (STIR) imaging discount 40 mg furosemide, as the case requires. In such cases, contrast-enhanced imaging may times, decreased motion artifact, increased patient toler- reveal a small tumor nodule that may have been inappar- ance, and higher patient throughput [12, 13], although they ent within the hemorrhage on conventional MRI [19, 20]. Gradient- Caution is required, however, in that the fibrovascular tis- echo imaging may be a useful supplement in demonstrat- sue in organizing hematomas may show enhancement. STIR imaging produces fat suppression and these necrotic or cystic areas show no enhancement. This technique fluid show high signal intensity, well-defined margins, and increases lesion conspicuity [14, 15], but typically has a homogeneous signal intensity, and is particularly important lower signal-to-noise ratio than does spin-echo imaging; it when guiding biopsy to areas that harbor diagnostic tissue. Lesions are generally well seen on standard imaging, and Magnetic Resonance Diagnosis STIR imaging tends to reduce the variations in signal in- tensities identified on conventional spin-echo MRI, which Despite the superiority of MRI in delineating soft-tissue is most helpful in tissue characterization. Murphey terize them, with most lesions demonstrating prolonged T1 study has suggested that MR can differentiate benign from and T2 relaxation times. The majority of lesions remain malignant masses in greater than 90% of cases based on nonspecific, with a correct histologic diagnosis reached on the morphology of the lesion. Criteria used for benign the basis of imaging studies alone in only approximately lesions included smooth, well-defined margins, small size, 25-35% of cases [22-24]. There are instances, however, in and homogeneous signal intensity, particularly on T2- which a specific diagnosis may be made or strongly sus- weighted images. Other studies, however, note that malig- pected on the basis of MRI features (Table 1). This is usu- nant lesions may appear as smoothly marginated, homoge- ally done on the basis of lesion signal intensity, pattern of neous masses and MR cannot reliably distinguish benign growth, location and associated “signs” and findings. This discrepancy MRI appearance of these lesions has been well reported likely reflects differences within the studied populations. More commonly, MRI may re- When the MR images of a lesion are not sufficiently veal a nonspecific appearance. In such cases, it is often not characteristic to suggest a specific diagnosis, a conserva- possible to establish a meaningful differential diagnosis or tive approach is warranted. Malignancies, by virtue of reliably determine whether a lesion is benign or malignant. Consequently, the larger a mass is, of MR in many cases, the issue of whether it can reliably and the greater its heterogeneity, the greater is the concern distinguish benign from malignant is much less clear. Only 5% of benign soft-tissue tumors ex- ceed 5 cm in diameter [25, 26]. In addition, most malig- nancies are deep lesions, whereas only about 1% of all be- Table 1. Specific diagnoses that may be made or suspected on the basis of magnetic resonance imaging nign soft-tissue tumors are deep [25, 26] Although these figures are based on surgical, not imaging, series, these Vascular lesions Hemangioma trends likely remain valid for radiologists. Hemangiomatosis (angiomatosis) When sarcomas are superficial, they generally have a less Arteriovenous hemangioma (arteriovenous malformation) aggressive biologic behavior than do deep lesions. As a Lymphangioma rule, most malignancies grow as deep space-occupying le- Lymphangiomatosis sions, enlarging in a centripetal fashion, pushing, rather Bone and cartilage Myositis ossificans than infiltrating adjacent structures (although clearly there forming lesions Panniculitis ossificans are exceptions to this general rule). As sarcomas enlarge, a Fibrous lesions Elastofibroma pseudocapsule of fibrous connective tissue is formed around Fibrous hamartoma of infancy them by compression and layering of normal tissue, associ- Musculoaponeurotic fibromatosis ated inflammatory reaction, and vascularization. Superficial fibromatosis (plantar fibromatosis/Dupuytren contracture) Generally, they respect fascial borders and remain within Lipomatous lesions Lipoma anatomic compartments until late in their course. It is this Lipomatosis pattern of growth which gives most sarcomas relatively Hibernoma well-defined margins, in distinction to the general concepts Intramuscular lipoma of margins used in the evaluation of osseous tumors. Neural fibrolipoma Increased signal intensity in the skeletal muscle sur- Lipoblastoma Lipoblastomatosis rounding a musculoskeletal mass on T2-weighted SE MR Liposarcoma images or other fluid-sensitive sequences (i. These results are based on studies in which both lesions MPNST (malignant peripheral nerve bone and soft-tissue lesions were evaluated. Although sheath tumors) this increased signal intensity may be seen with malig- Synovial lesions Pigmented villonodular synovitis nancy, in our experience this finding is quite nonspecif- Giant cell tumor of tendon sheath Synovial chondromatosis ic.

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