Minocin

By O. Yespas. Albright College.

The suppressed insulin response develops after pulmonary artery to the left heart is obstructed (i buy 50mg minocin with mastercard. The peripheral sensory nerves of the body are nourished by causes distension of the artery buy 50 mg minocin mastercard, which may contribute to the microscopic blood vessels, and the loss of even a few ves- sensation of chest discomfort. An altered sensory pressure (pulmonary hypertension) leads to right heart fail- nerve may fire too frequently, causing odd sensations, or ure. Because left atrial (and left ventricular) filling is reduced not fire at all, causing numbness. Neuropathy or nerve im- (as a result of lack of blood flow from the lungs), left-side pairment of the lower body is one of the most common cardiac output also falls. Even though this patient would likely have a high insulin right- and left-side heart failure, producing the signs and concentration, additional insulin is required to stimulate the symptoms seen in this patient. The right ventricular pressure is likely to be increased be- ment could gradually be decreased or discontinued with a cause the blood clot in the pulmonary artery acts as a form major change in diet, amount of body fat, and exercise of obstruction that raises the pulmonary artery resistance. The problem here is increased afterload of the right ventri- provement in glucose metabolism. Exercise improves the cle caused by partial obstruction of the outflow tract. Be- ability of skeletal muscle cells to take up and burn glucose cause of this obstructed outflow, the diastolic volume of the without the presence of insulin or at reduced insulin con- right ventricle is already high. Handbook of Venous Disorders: Coronary Artery Disease Guidelines of the American Venous Forum. London: Chapman A 57-year-old man experienced several months of vague & Hall, 1996;274. During a touch football game at a family picnic, he had CASE STUDY FOR CHAPTER 16 much more intense pain and had to rest. After about 45 minutes of intermittent pain, his family brought him to Diabetic Microvascular Disease the emergency department. A 48-year-old man went for a vision examination be- His heart rate is 105 beats/min, his blood pressure is cause his eyesight had been blurry for the past several 105/85 mm Hg, and his hands and feet are cool to touch months. He is sweating and is short of cian after seeing a few areas of dense clumps of capillar- breath. An electrocardiogram indicates an elevated ST ies over the retinas of both eyes. The family physician finds fasting blood plasma glu- The attending cardiologist administers streptokinase in- cose of 297 mg/dL. CHAPTER 18 Control Mechanisms in Circulatory Function 307 One hour later, the ST segment abnormality is less limiting clot formation in areas of vessels with damaged en- noticeable. The production of prostaglandins by blood pressure is 120/85 mm Hg, and the patient’s hands platelets is part of the clotting process. The patient is alert, not released by activated platelets will cause constriction of sweating, and does not complain of chest pain or short- coronary arteries and arterioles, lowering blood flow in an ness of breath. Although regression of plaques is not dramatic when low- gioplasty was performed to open several partially density lipoproteins are reduced, continued growth of the blocked coronary arteries. The patient is told to take half plaque is decreased and, in some cases, virtually stopped. In addition, he ing the formation of a new clot that will occlude the artery. Baltimore: Williams ing predict some abnormality of coronary artery function? Why was a 45-minute delay before going for medical inter- vention after intense pain started inappropriate for the CASE STUDY FOR CHAPTER 18 man’s health? How does the lower than normal arterial pressure, smaller than normal arterial pulse pressure, and decreased blood During a routine health assessment, a 52-year-old man flow to the hands and feet indicate impairment of the con- was found to have a blood pressure of 180/95 mm Hg. How did the streptokinase improve performance of the blood pressure has always been a little high. How is aspirin useful to protect the coronary vasculature the heart, eyes (including the blood vessels of the from occlusions by blood clots? How might lowering the low-density lipoproteins and rais- resting heart rate is 87 beats/min. Explain how drugs might lower the blood pressure by af- oxygen for the heart cells. Partially occluded arteries did not fecting 1-adrenergic receptors, 1-adrenergic receptors, in- provide sufficient blood flow to provide the needed oxygen travascular fluid volume, the renin-angiotensin-aldosterone and hypoxia resulted.

The higher the decibel level re- ther testing to determine whether hearing quired for either threshold buy 50mg minocin with visa, the greater the loss is sensorineural minocin 50 mg low cost, conductive, or mixed. A speech reception threshold Tests used for this purpose include bone or average pure-tone threshold of 25 deci- conduction tests. The procedure for bone bels (dBHL) (HL = hearing level), for in- conduction audiometry consists of placing stance, is considered borderline normal a vibrator on the individual’s mastoid hearing for adults. A tones from the vibrator go directly into threshold of 26 to 40 decibels is considered the inner ear, bypassing the external and a mild hearing loss. The individual’s In addition to measuring how loud responses to the thresholds are plotted on speech has to be to be heard, testing also the audiogram and contrasted with the air determines how well individuals under- conduction test results. Speech discrimination tests (sometimes thresholds for air and bone conduction are called word recognition tests) help to pro- compared. During the test, between the two thresholds, hearing loss words from standardized lists of phon- is classified as sensorineural, conductive, or etically balanced one-syllable words are mixed. Words are Speech Audiometry presented at a suprathreshold level, and the individual must identify and repeat Whereas pure-tone audiometry is used to words back to the examiner. The test is determine individuals’ ability to hear scored as the percentage of correctly specific tones, speech audiometry may indi- repeated words. The lower the percentage, cate individuals’ ability to understand the greater the problem in understanding. Two meas- Individuals with speech discrimination ures are speech reception threshold and hearing loss may be able to recognize speech discrimination threshold. The individuals wear headphones and listen to speech discrimination score provides a words being transmitted through the measure of the ability to understand words headphones without any visual cues. It assesses the Diagnostic Procedures 155 ability to judge acoustic information and Acoustic immittance testing requires no to distinguish between similar speech voluntary responses from the individual. Acoustic immittance measurement in- Electrocochleography cludes a battery of tests that evaluate mid- dle ear status. Tympanometry is a test of Electrocochleography is a procedure in acoustic immittance in which the mobility which stimulus-related electrical activity or flexibility of the tympanic membrane generated in the cochlea and auditory is assessed by measuring how much sound nerve is recorded. For the test, the individ- energy is admitted into the ear as air pres- ual reclines with electrodes placed in the sure is varied in the external auditory external auditory canal. The by altering the air pressure in the ear canal test is useful in evaluating inner ear fluid and measuring the response of the ear- disorders such as Meniere’s syndrome. Auditory Brain Stem Response As sound energy strikes the eardrum, some (ABR) Testing is transmitted to the middle and inner ear, but some is reflected back into the ear The ABR records electrical activity gen- canal. If the tympanic membrane is stiff, erated as sound travels from the auditory much of the sound energy is reflected back nerve through the auditory brain stem into the external ear canal. The individual reclines with pedance, the more sound energy is admit- electrodes placed on the mastoid or on the ted to the middle and inner ear. A stimulus is then presented increased level of resistance is diagnostic through earphones, and electroencephalo- of middle ear pathology. The results are gram activity is evaluated and the audito- plotted on a graph called a tympanogram. The ABR The ear’s response is plotted on the verti- is useful in ruling out auditory diseases cal dimension of the graph, and air pres- such as diseases of the cochlea; degener- sures are plotted on the horizontal ative or demyelinating diseases of the dimension. Acoustic immittance testing auditory system, such as multiple sclero- may also be used to measure the acoustic sis; or tumors of the auditory system. It should occur in both ears in response to a loud Otoacoustic emissions are measured sound, even if only one ear is stimulated. Otoacoustic emis- diagnosing conditions or problems that sions testing allows one to measure hear- involve the cochlea or auditory nervous ing in infants, young children, and difficult- system. The technology ed structures) provides medical evaluation has enhanced the ability to detect hearing and treatment of hearing loss. The audiologist reviews hearing test results and consults with indi- Individuals who experience vertigo viduals about their listening needs before (dizziness) or who have problems with recommending which style or type of balance are frequently tested for inner ear hearing aid would be most beneficial. These tests are per- speech production difficulties because of formed either by an audiologist or physi- lack of auditory feedback. In one test of vestibular nerve guage pathologists often work with individ- function, the caloric test, either cold or hot uals to help them with particular aspects water is introduced into the external audi- of speech, language, or both in order to tory canal. The introduction of dividuals with special problems in commun- the water into the ear creates a reflex ication. Such training may be included in response of the eye called nystagmus hearing aid orientation and/or special pro- (involuntary horizontal eye movement).

When a SR buy minocin 50 mg on line, and the calcium then diffuses the short distance to the 184 PART III MUSCLE PHYSIOLOGY CLINICAL FOCUS BOX 10 generic 50 mg minocin otc. Because the muscle cannot be Heart failure is evident when the heart is unable to main- sufficiently lengthened during its rest period (diastole), it tain sufficient output to meet the body’s normal metabolic begins its contraction at too short a length. The term congestive heart failure refers to fluid length-dependent, the speed at which the muscle can congestion of the lungs that often accompanies heart fail- shorten is also reduced. Treatment of heart failure involves approaches that af- Patients suffering from heart failure may be unable to fect several areas of muscle mechanics. Drugs that in- perform simple everyday tasks without fatigue or short- crease the contractility of cardiac muscle, such as digitalis ness of breath. In later stages, there may be significant dis- and its derivatives, may be used to cause more effective tress even while resting. While many intrinsic and extrinsic contraction and allow the muscle to operate along an im- factors contribute to the condition, this discussion will fo- proved force-velocity curve. Most contractility-increasing cus on those closely related to the mechanical properties drugs work by increasing the amount of intracellular cal- of the heart muscle. The most important aspects the heart to the excitatory action of the sympathetic nerv- of the mechanical behavior are described by the length- ous system (which affects both heart rate and muscle con- tension and force-velocity curves, which, together with tractility) can protect against an increased workload. Drugs knowledge of the current state of contractility, can provide that lower blood pressure by their effects on the arterial a complete picture of the muscle function. If the heart cle must contract, and the muscle can operate on a more has been damaged by a myocardial infarction (heart at- efficient portion of the force-velocity curve. Drugs or di- tack) or ischemia (impaired blood supply to the heart etary regimens that reduce blood volume (via increased re- muscle) or by chronic overload (as with untreated high nal excretion of salt and water) can also lower the load blood pressure), the muscle may become weakened and against which the muscle must contract; the same is true have reduced contractility. In this case, the load pre- of drugs that cause relaxation of the muscle in the walls of sented to the heart by the blood pressure is too high (rel- the venous system. Lowering the blood volume also acts ative to the weakened condition of the muscle), and (as to decrease the over-distension of the heart during dias- the force-velocity curve describes) the rate of shortening tole. While it would seem that an increase in the resting (velocity) of the muscle will be reduced. The length-ten- muscle length would have a beneficial effect on the sion curve indicates that the larger the load, the less the strength of contraction, geometric factors in the intact shortening (see Fig. Therefore, less blood will be heart place the overstretched muscle at a mechanical dis- pumped with each beat. Therapy for this type of failure in- advantage that the length-tension curve cannot ade- volves improving the contractility of the muscle and/or re- quately overcome. Heart failure involves numerous interacting organ sys- Heart failure can also be of the diastolic type (and may tems. The mechanical behavior of the heart muscle, as un- occur along with systolic failure). Here the relaxation is derstood in the context of the length-tension and force-ve- impaired, and the muscle is resistant to the stretch that locity curves, is only a part of the problem. Some types of therapy must also consider factors external to the heart hypertrophy or connective tissue fibrosis also may con- muscle itself. The amount of cal- This mechanism is part of a coupled transport system in which cium in the cytoplasm, the cytosolic calcium pool, deter- three sodium ions, entering the cell down their electrochemi- mines the magnitude of the myofilament activation and, cal gradient, are exchanged for the ejection of one calcium ion. Proper function of this exchange mechanism requires a steep During relaxation, the cytoplasmic calcium concentration sodium concentration gradient, maintained by the membrane is rapidly lowered through several pathways. Because the 2 2 brane contains a vigorous Ca -ATPase (8) that runs continu- Na /Ca exchange mechanism derives its energy from the ously and is further activated, through a protein phosphoryla- sodium gradient, any reduction in the pumping action of the tion mechanism, by high levels of cytoplasmic calcium. Under level of the sarcolemma, two additional mechanisms work to normal conditions, these mechanisms can maintain a 10,000- 2 rid the cell of the calcium that entered via previous action po- fold Ca concentration difference between the inside and 2 tentials. Since a cardiac cell contracts repeatedly cium, ejecting one calcium ion for each ATP molecule con- many times per minute with each beat being accompanied by 2 sumed. Additional calcium is removed by a Na /Ca an influx of calcium, the extrusion mechanisms must also work exchange mechanism (10), also located in the cell membrane. The mito- CHAPTER 10 Cardiac Muscle 185 indicators of contractility) increases.

The openings created in this The increasing numbers of vessels through successive process allow tissue fluid and molecules carried in the fluid branches dramatically increases the surface area of the mi- to easily enter the lymphatic vessels purchase minocin 50 mg with amex. The surface area is determined by the length discount minocin 50 mg amex, The movement of fluid from tissue to the lymphatic ves- diameter, and number of vessels. When compressed or actively con- example, the total surface area of the capillaries and smallest tracted lymphatic vessels are allowed to passively relax, the 2 3 venules is more than 10 cm for one cm of tissue. The large pressure in the lumen becomes slightly lower than in the in- surface area of the capillaries and smallest venules is impor- terstitial space, and tissue fluid enters the lymphatic vessel. When the lymphatic bulb or vessel again actively contracts or is compressed, the overlapped cells are me- chanically sealed to hold the lymph. The pressure devel- The Large Number of Microvessels Minimizes the oped inside the lymphatic vessel forces the lymph into the Diffusion Distance Between Cells and Blood next downstream segment of the lymphatic system. Be- cause the anchoring filaments are stretched during this The spacing of microvessels in the tissues determines the process, the overlapped cells can again be parted during re- distance molecules must diffuse from the blood to the inte- laxation of the lymphatic vessel. The arteriolar dila- A tion during exercise allows arterioles to supply blood flow to nearly all of the available capillaries in muscle. Regular exercise induces the growth of new capillaries in skeletal muscle. However, decreasing the number of capillaries perfused with blood Capillary by constricting arterioles or obliterating capillaries, as in di- abetes mellitus, can lengthen diffusion distances and de- crease exchange. B The Interstitial Space Between Cells Is a Complex Environment of Water- and Gel-Filled Areas As molecules diffuse from the microvessels to the cells or from the cells to the microvessels, they must pass through the interstitial space that forms the extracellular environ- Capillary ment between cells. This space contains strands of collagen and elastin together with hyaluronic acid (a high-molecu- lar-weight unbranched polysaccharide) and proteoglycans C (complex polysaccharides bound to polypeptides). To some extent, the large molecules and water may cause the interstitial space to behave as alternating regions of gel- like consistency and water-filled regions. The gel-like areas may restrict the diffusion of water-soluble solutes and may exclude solutes from their water. An implication of the gel and water properties of the in- terstitial space is that the effective concentration of mole- cules in the free interstitial water is higher than expected Capillary because the molecules are restricted to readily accessible Effect of the number of perfused capillaries water-filled areas. A, With one capillary, the left side of the cell has a spaces slows the diffusion of water-soluble molecules. B, The concentration can be substantially in- also possible that the relative amounts of gel and water creased if a second capillary is perfused. C, The perfusion of three phases can be altered in a way that diffusion in the extra- capillaries around the cell increases concentrations of bloodborne cellular space is changed. The Rate of Diffusion Depends on Permeability single capillary provides all the nutrients to the cell. The and Concentration Differences concentration of bloodborne molecules across the cell in- Diffusion is by far the most important means for moving terior is represented by the density of dots at various loca- solutes across capillary walls. Diffusion distances are important; as molecules travel solute between blood and tissue is given by Fick’s law (see farther from the capillary, their concentration decreases Chapter 2): substantially because the volume into which diffusion pro- Js P (Cb C )t ceeds increases as the square of the distance. In addition, some of the molecules may be consumed by different cellu- Js is the net movement of solute (often expressed in lar components, which further reduces the concentration. Therefore, increasing the The permeability coefficient is usually measured under number of microvessels reduces diffusion distances from a conditions in which neither the surface area of the vascula- given point inside a cell to the nearest capillary. Doing so ture nor the diffusion distance is known, but the tissue mass minimizes the dilution of molecules within the cells caused can be determined. At any given moment during related to the diffusion coefficient of the solute in the capil- resting conditions, only about 40 to 60% of the capillaries lary wall and the vascular surface area available for exchange are perfused by red blood cells in most organs. Ex- area and diffusion distance are determined, in part, by the ercise results in an increase in the number of perfused cap- number of microvessels with active blood flow. The diffusion 268 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY coefficient is relatively constant unless the capillaries are If the blood loses material to the tissue, the value of E is damaged because it depends on the anatomical properties of positive and has a maximum value of 1 if all material is re- the vessel wall (e. A negative E The number of perfused capillaries and blood and tissue value (Cv Ca) indicates that the tissue added material to concentrations of solutes are constantly changing, and the blood.