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J Appl Physiol after which time the athlete undergoes (A) Muscle glucose uptake decreases in 2000;88:774–787 discount biaxin 250mg amex gastritis diet . Genomics cheap biaxin 250mg with amex gastritis diet , genes, and environ- Immediately after rehabilitation begins, diabetes mental interaction: the role of exercise. Clin Sports Med during contraction at a fixed force increase only if endogenous or 2000;19:273–286. J Appl Physiol cells are required to perform the same insulin-independent glucose uptake 2001;90:2166–2171. Exer- (D) Oxidative energy-producing is reduced in active muscles cise training in coronary artery disease systems are up-regulated 16. N Engl J Med in the top five of her statewide high the following is a predictable effect of 2000;343:632–641. Role of exercise in preventing Encouraged, she redoubles her training pregnancy? Rheum Dis intensity, only to find that her (A) Increased average gestational Clin North Am 2001;27:131–141. After finally visiting her doctor, (B) Increased fetal weight at term and the immune system: regulation, in- her serum estrogen levels are found to (C) Decreased risk of maternal tegration, and adaptation. Potential benefits (A) Dynamic exercise endurance less (E) Decreased neonatal responsiveness and hazards of physical activity and ex- than an untrained person scores ercise on the gastrointestinal tract. CASE STUDIES FOR PART VIII • • • appears dazed, and his answers to questions are coherent CASE STUDY FOR CHAPTER 29 but slow. Blood sam- Heat Exhaustion with Dehydration ples are drawn, and an intravenous drip is started. The lab- oratory report shows serum [Na ] of 156 mmol/L (normal A Michigan National Guard infantry unit was sent at the end of May to Louisiana for a field training exercise. Two liters of normal saline in Michigan was cool, but during the exercise in Louisiana, (0. Well before the the temperature reached at least 30 C (86 F) every after- end of the infusion, the patient is alert, his nausea disap- noon. At 3:30 PM on the second day of the exercise, a 70-kg pears, and he asks for, and is given, water to drink. After infantryman became unsteady and, after a few more steps, the end of the infusion he is sent back to his unit with in- sat on the ground. He told his comrades that he was dizzy structions to consume salt with dinner, drink at least three and had a headache. When they urged him to drink from quarts of fluid before going to bed, and to return for fol- his canteen, he took a few swallows and said that he was low-up in the morning. What is the likely basis of the patient’s nausea, which also his rectal temperature is 38. If we assume that the patient’s total body water was 36 L CASE STUDY FOR CHAPTER 30 when he came for treatment, it can be shown that giving the patient 3 L of water without salt (by mouth and/or as an in- A Patient With Dyspnea During Exercise travenous infusion of glucose in water) would reduce serum A 56-year-old man complained of shortness of breath and [Na ] to 144 mmol/L. Such treatment would improve the pa- chest pain when climbing stairs or mowing the lawn. How might the medical offi- subjected to a stress test, with noninvasive monitoring of cer argue the case for giving 2 L of normal saline? What other (and relatively unusual) condition could produce and cardiac electrical activity. Did the medical officer rule this beats/min; blood pressure, 118/75 mm Hg; arterial blood possibility out by appropriate means? The patient’s nausea is probably a result of constriction of terminated because of the subject’s severe dyspnea. His the splanchnic vascular beds, which is part of the homeo- heart rate is 119 beats/min (his age and sex-adjusted pre- static cardiovascular response that helps maintain cardiac dicted maximal heart rate is 168 beats/min), blood pressure output and blood pressure when central blood volume is re- is 146/76 mm Hg, arterial blood oxygen saturation is 88%, duced. Central blood volume, in turn, was reduced by the and the ECG is normal (Fig. What are three lines of evidence for ventilatory limitation to constriction of the renal vascular beds, which, in turn, con- this subject’s exercise? Why did arterial blood oxygen saturation fall during exer- tion of the renin-angiotensin system) to scanty urine pro- cise?
This process is slower than the liberation of glucose CHAPTER 8 Contractile Properties of Muscle Cells 149 Energy produced Energy used Blood Muscle cell Creatine ADP phosphate 2 PCr ATP restored replenished A Actomyosin ATPase (contraction) 1 Creatine ATP B SR Ca2+ pump (relaxation) Glycogen C Other metabolic functions 36 (ion pumping cheap biaxin 500mg line chronic gastritis surgery, etc order 500mg biaxin free shipping gastritis symptoms causes treatments and more. The scheme shown here is typical for all types of of ATP for the actomyosin ATPase of the crossbridges. Energy muscle, although there are specific quantitative and qualitative sources are numbered in order of their proximity to the actual re- variations. Moderate activity, with brief rest Continue With an Inadequate Oxygen Supply periods, favors the consumption of fat as muscle fuel. Glycolytic (anaerobic) metabolism can provide energy Complete combustion of fat yields less ATP per mole of for sudden, rapid, and forceful contractions of some oxygen consumed than for glucose, but its high energy muscles. In such cases, the ready availability of gly- storage capacity (the equivalent of 138 moles of ATP per colytic ATP compensates for the relatively low yield of mole of a typical fatty acid) makes it an ideal energy store. The depletion of body fat reserves is almost never a limit- In most muscles, especially under conditions of rest or ing factor in muscle activity. However, protein is used by products of glycolysis) to supply the energy needs of the muscles for fuel mainly during dieting and starvation or contractile system. Under such conditions, proteins are several physiological mechanisms come into play to in- broken down into amino acids that provide energy for con- crease the blood supply (and, thus, the oxygen) to the traction and that can be resynthesized into glucose to meet working muscle. The gly- ing energy for contraction and the recycling of metabolites colytic pathway can continue to operate because the ex- (e. In addition to its oxygen- and formation of lactic acid, by preventing a buildup of pyru- carbon dioxide-carrying functions, the enhanced blood vic acid, also allows for the restoration of the enzyme supply to exercising muscle provides for a rapid exchange cofactor NAD , needed for a critical step in the gly- of essential metabolic materials and the removal of heat. Thus, ATP can continue to be produced under Those muscles adapted for mostly aerobic metabolism anaerobic conditions. This The accumulation of lactic acid is the largest contributor iron-containing molecule, essentially a monomeric form of (more than 60%) to oxygen deficit, which allows short-term the blood protein hemoglobin (see Chapter 11), gives aer- anaerobic metabolism to take place despite a relative lack of obic muscles their characteristic red color. Other depleted muscle oxygen stores have a smaller gen storage capacity of myoglobin is quite low, and it does capacity but can still participate in oxygen deficit. The largest not make a significant direct contribution to the cellular of these is the creatine phosphate pool (approximately 25%). Chapters 9 and 10 ATP levels return to normal, the energy stored in the crea- discuss metabolic adaptations that are specific to skeletal, tine phosphate energy pool is also replenished. REVIEW QUESTIONS DIRECTIONS: Each of the numbered (C) Maintain the separation of thick stretched beyond its optimal length items or incomplete statements in this and thin filaments when the muscle is (but not to the point where damage section is followed by answers or at rest occurs), the reduction in contractile completions of the statement. Select the (D) Promote the binding of calcium force is due to ONE lettered answer or completion that is ions to the regulatory proteins (A) Lengthening of the myofilaments so BEST in each case. Calcium ions are required for the that crossbridges become spaced farther normal activation of all muscle types. Skeletal, smooth, and cardiac muscle Which statement below most closely (B) Decreased overlap between thick all have which of the following in describes the role of calcium ions in and thin filaments, which reduces the common? During the shortening of skeletal filaments action potential muscle, (D) A high concentration of calcium (B) A rapid release of calcium from its (A) The distance between Z lines stays ions in the myofilament space is storage sites in the T tubules the same required to maintain muscle in a (C) A rapid release of calcium from the (B) The width of the I band changes relaxed state. The normal process of relaxation in reticulum (D) All internal spacings between skeletal muscle depends on (D) A release of calcium that is bound repeating structures change (A) A sudden reduction in the amount to cytoplasmic proteins in the region proportionately of ATP available for the crossbridge of the myofilaments 3. The relaxation of skeletal muscle is energy for muscle contraction during (B) Metabolically supported pumping associated with a reduction in free the crossbridge cycle. A second of calcium out of the cells when the intracellular calcium ion concentration. When an isolated skeletal muscle is molecules (continued) CHAPTER 8 Contractile Properties of Muscle Cells 151 (C) A change in the chemical nature of support contraction at a reduced rate (C) The muscle would continue to the myosin molecules, reducing their 11. In the face of insufficient oxygen to develop force, but its relaxation would enzymatic activity meet its current metabolic be slowed (D) Reduced contractile interaction by requirements, skeletal muscle (D) Activation of the muscle would no the binding of calcium to the active (A) Quickly loses its ability to contract longer be possible sites of the myosin molecules and relaxes until oxygen is again 9. The chemical energy source that most available SUGGESTED READING directly supports muscle contraction is (B) Maintains contraction by using Bagshaw CR. Muscle Physiology and Cardiac (C) ATP (C) Maintains contraction by using a Function. Carmel, IN: Biological Sci- (D) Free fatty acids large internal store of ATP that is kept ences Press-Cooper Group, 2000. Cellular Physiology of of ATP for skeletal muscle contraction, (D) Contracts more slowly at a given Nerve and Muscle. Boston: (A) Myofilament interaction ceases, force, resulting in a saving of energy Blackwell, 1991. Calcium in Muscle Contraction: (B) Actin and myosin filaments cannot sarcoplasmic reticulum were impaired Cellular and Molecular Physiology.
The absorption of electrolytes and binding protein binds the free and methylated forms of minerals involves both passive and active processes effective biaxin 500 mg gastritis medicine cvs, result- folic acid in plasma order 500mg biaxin overnight delivery gastritis diet . Folic acid deficiency causes a fall in ing in the movement of electrolytes, water, and metabolic plasma and red cell folic acid content and, in its most severe substrates into the blood for distribution and use through- form, the development of megaloblastic anemia, dermato- out the body. The discovery of vitamin B12 (cobalamin) large amount of Na entering the GI lumen daily—on av- followed from the observation that patients with perni- erage, about 25 to 35 g of Na every day. Around 5 to 8 g cious anemia who ate large quantities of raw liver recov- are derived from the diet, and the rest from salivary, gastric, ered from the disease. Subsequent analysis of liver compo- biliary, pancreatic, and small intestinal secretions. The GI nents isolated the cobalt-containing vitamin, which plays tract is extremely efficient in conserving Na : only 0. The jejunum absorbs glycoprotein secreted by the parietal cells in the stomach more than half of the total Na , and the ileum and colon called the intrinsic factor binds strongly with vitamin B12 to absorb the remainder. The small intestine absorbs the bulk form a complex that is then absorbed in the terminal ileum of the Na presented to it, but the colon is most efficient in through a receptor-mediated process (Fig. B12 is transported in the portal blood bound to the protein Sodium is absorbed by several different mechanisms op- transcobalamin. Individuals who lack the intrinsic factor erating at varying degrees in different parts of the GI tract. When a meal that is hypotonic to plasma is ingested, con- siderable absorption of water from the lumen to the blood takes place, predominantly through tight junctions and in- tercellular spaces between the enterocytes, resulting in the ELECTROLYTE AND MINERAL ABSORPTION absorption of small solutes such as Na and Cl ions. This Nearly all of the dietary nutrients and approximately 95 to mode of absorption, called solvent drag, is responsible for 98% of the water and electrolytes that enter the upper small a significant amount of the Na absorption by the duode- 508 PART VII GASTROINTESTINAL PHYSIOLOGY Stomach most of the monosaccharides and amino acids have already Parietal cell been absorbed by the small intestine (Fig. Sodium chloride is transported via two exchangers located at the brush border membrane. The downhill move- Vitamin B12 ment of Na into the cell provides the energy required for the uphill movement of the H from the cell to the lumen. Similarly, the downhill movement of HCO3 out of the cell provides the energy for the uphill entry of Cl into the Intrinsic enterocytes. The Cl then leaves the cell through facili- factor Intrinsic factor/ tated transport. This mode of Na uptake is called vitamin B12 Na /H -Cl /HCO3 countertransport. There is no sugar- or amino acid–coupled Na transport because most Ileum Lumen sugars and amino acids have already been absorbed. Sodium is also absorbed here via Na -selective ion channels in the apical cell membrane (electrogenic Na absorption). Absorption takes place throughout the intestine by passive H+ + HCO - H CO CO + H O Blood Vitamin B released into blood 3 2 3 2 2 12 Cl- Transcobalamin/ Glucose, + Na+ + Na H Transcobalamin vitamin B amino 12 complex acids H2CO3 Cl- HCO - FIGURE 27. CO2 + H2O 3 Na+ Metabolism ATP K+ A num and jejunum, but it probably plays a minor role in Na absorption by the ileum and colon because more distal re- Blood gions of the intestine are lined by a “tight” epithelium (see Chapter 2). CO + H O H CO In the jejunum, Na is actively pumped out of the baso- 2 2 2 3 lateral surface of enterocytes by a Na /K -ATPase (Fig. The result is low intracellular Na concentration, and the luminal Na enters enterocytes down the electro- chemical gradient, providing energy for the extrusion of H into the lumen (via a Na /H exchanger). The H + + - - Cl- Na+ Na H HCO3 Cl then reacts with HCO3 in bile and pancreatic secretions in the intestinal lumen to form H2CO3. The CO2 readily diffuses H CO 2 3 across the small intestine into the blood. Another mode of Cl- Na uptake is via a carrier located in the enterocyte brush CO + H O 2 2 + + border membrane, which transports Na together with a Na Na monosaccharide (e. K+ K+ B In the ileum, the presence of a Na /K -ATPase at the basolateral membrane also creates a low intracellular Na Blood concentration, and luminal Na enters enterocytes down the electrochemical gradient. B, Na ab- coupled symporters is not as great as in the jejunum because sorption by the ileum. CHAPTER 27 Gastrointestinal Secretion, Digestion, and Absorption 509 diffusion through the tight junctions and lateral intercellu- increased by 1,25-dihydroxy vitamin D3. The driving force for K ab- cell, the Ca ions are sequestered in the ER and Golgi sorption is the difference between luminal and blood K membranes by binding to the CaBP in these organelles.