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Physiologically speaking penegra 50 mg on-line prostate cancer juice cure, acids fall into two groups: (1) right to left as strong acid is added discount 100 mg penegra prostate ultrasound procedure, H combines with the H2CO3 (carbonic acid), and (2) all other acids (noncar- bonic; also called “nonvolatile” or “fixed” acids). The dis- tinction between these groups occurs because H2CO3 is in equilibrium with the volatile gas CO2, which can leave the body via the lungs. The concentration of H2CO3 in arterial blood is, therefore, set by respiratory activity. By contrast, 9 HPO 2 noncarbonic acids in the body are not directly affected by 4 breathing. Metabolism Is a Constant Source 8 of Carbon Dioxide A normal adult produces about 300 L of CO2 daily from metabolism. CO2 from tissues enters the capillary blood, where it reacts with water to form H2CO3, which dissoci- ates instantly to yield H and HCO3 : CO2 H2O 7 H2CO3 H HCO3. Fortunately, H2CO3 produced from metabolic CO2 is only formed transiently in the transport of CO2 by the 6 blood and does not normally accumulate. Instead, it is con- verted to CO2 and water in the pulmonary capillaries and the CO2 is expired. In the lungs, the reactions reverse: H HCO3 H2CO3 H2O CO2 (12) 5 H PO As long as CO2 is expired as fast as it is produced, arte- 2 4 rial blood CO2 tension, H2CO3 concentration, and pH do not change. Amount of HCl added (mEq) Amount of NaOH added (mEq) Incomplete Carbohydrate and Fat Metabolism A titration curve for a phosphate buffer. A strong acid Normally, carbohydrates and fats are completely oxidized (HCl) (right to left) or strong base (NaOH) (left to right) was added and the resulting solution pH recorded (y-axis). Incomplete oxi- a given amount of acid or base is least) when the solution pH is dation of carbohydrates occurs when the tissues do not re- equal to the pKa of the buffer. In such states, glucose me- Food intake tabolism yields lactic acid (pKa 3. Incomplete fatty acid oxidation occurs in uncontrolled diabetes melli- tus, starvation, and alcoholism and produces ketone body Absorption acids (acetoacetic and -hydroxybutyric acids). At blood pH, they Cell metabolism buffering response response of food mostly dissociate into their anions and H , making the + + H H blood more acidic. Bound by Sulfate body buffer CO2 Phosphate bases Protein Metabolism Generates Strong Acids Chloride CO 2 The metabolism of dietary proteins is a major source of Extracellular H. The oxidation of proteins and amino acids produces New strong acids such as H SO , HCl, and H PO. The oxi- fluid HCO - 2 4 3 4 [HCO -] 3 3 dation of sulfur-containing amino acids (methionine, cys- teine, cystine) produces H2SO4, and the oxidation of cationic amino acids (arginine, lysine, and some histidine Extracellular residues) produces HCl. H3PO4 is produced by the oxi- fluid [HCO -] dation of phosphorus-containing proteins and phospho- 3 CO2 esters in nucleic acids. H+ Excreted (combined with urinary On a Mixed Diet, Net Acid Gain Threatens pH buffer bases) A diet containing both meat and vegetables results in a net Excreted production of acids, largely from protein oxidation. To Sulfate Sulfate some extent, acid-consuming metabolic reactions balance Phosphate Phosphate Chloride Chloride H production. When these are oxidized to CO2 and water, H ions are consumed (or, amounting to The maintenance of normal blood pH by FIGURE 25. The balance of acid- chemical buffers, the respiratory system, forming and acid-consuming metabolic reactions results in and the kidneys. On a mixed diet, pH is threatened by the pro- duction of strong acids (sulfuric, hydrochloric, and phosphoric) a net production of about 1 mEq H /kg body weight/day in an adult person who eats a mixed diet. These strong acids are vegetarians generally have less of a dietary acid burden and buffered in the body by chemical buffer bases, such as ECF HCO. The kidneys eliminate hydrogen ions (combined with a more alkaline urine pH than nonvegetarians because most 3 urinary buffers) and anions in the urine.

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It varies inversely with the distance the heat stances the subcutaneous fat layer penegra 100mg otc prostate cancer holistic treatment, which affects conduc- must travel discount penegra 50mg with visa prostate cancer metastasis to bone. Heat flow by convection depends on the rate of blood flow and the temperature difference between the tissue and Core Temperature Is Close to the blood supplying the tissue. Because the vessels of the mi- Central Blood Temperature crovasculature have thin walls and, collectively, a large total surface area, the blood comes to the temperature of the sur- Core temperature varies slightly from one site to another rounding tissue before it reaches the capillaries. Changes in depending on such local factors as metabolic rate, blood skin blood flow in a cool environment change the thickness supply, and the temperatures of neighboring tissues. When skin blood flow is reduced in the cold, the ever, temperatures at different places in the core are all affected skin becomes cooler, and the underlying tissues— close to the temperature of the central blood and tend to 530 PART VIII TEMPERATURE REGULATION AND EXERCISE PHYSIOLOGY change together. Infrared ear thermometers are convenient perature, although not strictly correct, is a useful approxi- and widely used in the clinic, but temperatures of the tym- mation. The effects of heavy exercise and fever are familiar; varia- Skin Temperature Is Important in Heat tion among individuals and such factors as time of day Exchange and Thermoregulatory Control (Fig. Temperature- vironmental factors such as air temperature, air move- sensitive neurons and nerve endings in the abdominal vis- ment, and thermal radiation. Skin temperature is one of cera, great veins, spinal cord, and, especially, the brain the major factors determining heat exchange with the en- provide this information. For these reasons, it provides the thermoregu- ulatory system processes and responds to this information latory system with important information about the need later in the chapter. Core temperature should be measured at a site whose Many bare nerve endings just under the skin are sensitive temperature is not biased by environmental temperature. Depending on the relation of discharge rate Sites used clinically include the rectum, the mouth and, oc- to temperature, they are classified as either warm or cold re- casionally, the axilla. Cold receptors are about 10 times environment; its temperature is independent of environ- more numerous than warm receptors. Furthermore, as the mental temperature and is a few tenths of 1 C warmer than skin is heated, warm receptors respond with a transient burst arterial blood and other core sites. The tongue is richly sup- of activity and cold receptors respond with a transient sup- plied with blood; oral temperature under the tongue is usu- pression; the reverse happens as the skin is cooled. If a patient diate information about changes in skin temperature and holds his or her upper arm firmly against the chest to close may explain, for example, the intense, brief sensation of be- the axilla, axillary temperature will eventually come rea- ing chilled that occurs during a plunge into cold water. However, as this may Since skin temperature usually is not uniform over the take 30 minutes or more, axillary temperature is infre- body surface, mean skin temperature (sk) is frequently cal- culated from temperatures at several skin sites, usually weighting each temperature according to the fraction of 37. Some 4:00 AM 8:00 AM Noon 4:00 PM 8:00 PM Midnight energy is exchanged as mechanical work, but most is ex- Time of day changed as heat (Fig. Heat is exchanged by conduc- tion, convection, and radiation and as latent heat through FIGURE 29. A criti- does not equal energy loss, the extra heat is “stored” in, or cal appraisal of 98. This relationship is summarized in the ture, and other legacies of Carl Reinhold August Wunderlich. JAMA 1992;268:1578–1580; and Stephenson LA, Wenger CB, heat balance equation: O’Donovan BH, et al. The calorie used in chemistry and physics is the quantity of heat that will raise the tem- perature of 1 g of pure water by 1 C; it is also called the small calorie or gram calorie. The Calorie (capital C) used in physiology and nutrition is the quantity of heat that will raise the temperature of 1 kg of pure water by 1 C; it is also called the large calorie, kilogram calorie, or (the usual prac- tice in thermal physiology) the kilocalorie (kcal). Because heat is a form of energy, it is now often measured in joules, the unit of work (1 kcal 4,186 J), and rate of heat pro- duction or heat flow in watts, the unit of power (1 W 1 J/sec). However, kilocalories are still used widely enough that it is necessary to be familiar with them, and there is a certain ad- vantage to a unit based on water because the body itself is mostly water.

A drawback of effective in homeothermy is that cheap 100mg penegra visa mens health 60 years old, in most homeotherms cheap penegra 50 mg mens health best, certain vital fever and Usual range processes cannot function at low levels of body tempera- health of normal at rest ture that poikilotherms tolerate easily. For example, ship- wreck victims immersed in cold water die of respiratory or circulatory failure (through disruption of the electrical ac- tivity of the brainstem or heart) at body temperatures of Temperature regulation about 25 C, even though such a temperature produces no impaired direct tissue injury and fish thrive in the same water. BODY TEMPERATURES AND HEAT TRANSFER Temperature IN THE BODY regulation lost The body is divided into a warm internal core and a cooler Lower limit outer shell (Fig. Temperature regulation and exposure to heat and outermost layer, the skin. Springfield, cm thick, but in a subject conserving heat in a cold envi- IL: CC Thomas, 1948. CHAPTER 29 The Regulation of Body Temperature 529 Thermal Conductivities and Rates TABLE 29. In this way, these un- derlying tissues, which in the heat were part of the body FIGURE 29. Since the temperatures of the surface and in the trunk and head, the core includes a greater or lesser the thickness of the shell depend on environmental temperature, amount of more superficial tissue—mostly skeletal muscle— the shell is thicker in the cold and thinner in the heat. Because the shell lies between the core and the environ- ment, all heat leaving the body core, except heat lost The internal body temperature that is regulated is the tem- through the respiratory tract, must pass through the shell perature of the vital organs inside the head and trunk, before being given up to the environment. Thus, the shell which, together with a variable amount of other tissue, insulates the core from the environment. We, therefore, need to Changes in skin blood flow, which directly affect core-to- consider heat transfer within the body, especially heat skin heat transfer by convection, also indirectly affect core- transfer (1) from major sites of heat production to the rest to-skin heat transfer by conduction by changing the thick- of the body, and (2) from the core to the skin. In a cool subject, the subcutaneous fat transported within the body by two means: conduction layer contributes to the insulation value of the shell because through the tissues and convection by the blood, a process the fat layer increases the thickness of the shell and because in which flowing blood carries heat from warmer tissues to fat has a conductivity about 0. Thus, fat is a correspondingly better Heat flow by conduction varies directly with the ther- insulator. In a warm subject, however, the shell is relatively mal conductivity of the tissues, the change in temperature thin, and provides little insulation. Furthermore, a warm over the distance the heat travels, and the area (perpendi- subject’s skin blood flow is high, so heat flow from the core cular to the direction of heat flow) through which the to the skin is dominated by convection. It varies inversely with the distance the heat stances the subcutaneous fat layer, which affects conduc- must travel. Heat flow by convection depends on the rate of blood flow and the temperature difference between the tissue and Core Temperature Is Close to the blood supplying the tissue. Because the vessels of the mi- Central Blood Temperature crovasculature have thin walls and, collectively, a large total surface area, the blood comes to the temperature of the sur- Core temperature varies slightly from one site to another rounding tissue before it reaches the capillaries. Changes in depending on such local factors as metabolic rate, blood skin blood flow in a cool environment change the thickness supply, and the temperatures of neighboring tissues. When skin blood flow is reduced in the cold, the ever, temperatures at different places in the core are all affected skin becomes cooler, and the underlying tissues— close to the temperature of the central blood and tend to 530 PART VIII TEMPERATURE REGULATION AND EXERCISE PHYSIOLOGY change together. Infrared ear thermometers are convenient perature, although not strictly correct, is a useful approxi- and widely used in the clinic, but temperatures of the tym- mation. The effects of heavy exercise and fever are familiar; varia- Skin Temperature Is Important in Heat tion among individuals and such factors as time of day Exchange and Thermoregulatory Control (Fig. Temperature- vironmental factors such as air temperature, air move- sensitive neurons and nerve endings in the abdominal vis- ment, and thermal radiation.

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Progres- sive occlusion of coronary arteries by atherosclerotic plaques and acute occlusion as a result of the formation of blood clots in damaged coronary arteries are life-threaten- ing because the metabolic needs of the cardiac muscle can no longer be met by the blood flow buy discount penegra 100mg man health 4 u. Because the plaque or clot partially occludes the vessel lumen 100mg penegra free shipping androgen hormone x cocktail, vascular resistance is increased, and blood flow would decrease if smaller coro- nary vessels did not dilate to restore a relatively normal blood flow at rest. In doing so, the reserve for dilation of 0 these vessels is compromised. While this usually has no ef- fect at rest, when cardiac metabolism is increased, the de- 50 creased ability to increase blood flow can limit cardiac per- formance. In many cases, inadequate blood flow is first noticed as chest pain—known as angina pectoris—origi- nating from the heart, and a feeling of shortness of breath during exercise or work. The vascular occlusion can cause 0 conditions ranging from impaired contractile ability of the 0. Note that left coronary artery blood flow decreases dramati- be used to cause coronary vasodilation or decreased car- cally during the isovolumetric phase of systole, prior to opening diac work, or both. Left coronary artery blood flow remains lower normal, various approaches are used to lower the blood during systole than during diastole because of compression of the pressure, decreasing the heart’s workload and oxygen coronary blood vessels in the contracting myocardium. The left ventricle receives most of its arterial blood inflow during diastole. In addition to pharmacological treatment, mild to Right coronary artery blood flow tends to be sustained during moderate exercise, depending on the status of the coro- both systole and diastole because lower intraventricular pressures nary disease, is often advised. Aerobic exercise stimulates are developed by the contracting right ventricle, resulting in less the development of collateral vessels in the heart, im- compression of coronary blood vessels. Systemic and coronary energetics in the tem, and increases the efficiency of the body during work resting unanesthetized dog. Phasic right coronary artery blood flow in output needed for a given task, thereby decreasing the conscious dogs with normal and elevated right ventricular pres- heart’s metabolic energy requirement. This, in turn, leads to dilatory stimuli that po- have been shown to greatly slow and even slightly reverse tentially could overcome vasoconstriction. The goal is to lower blood lev- The overall concept evolving from both human and els of low-density lipoproteins (LDLs), which are known animal studies is that the sympathetic nervous system to accelerate the formation of cholesterol-containing ar- suppresses the decrease in coronary vascular resistance terial plaques. The LDL concentration should typically be during exercise despite the metabolic effects of epineph- lowered below 120 mg/dL, but some cardiologists favor rine mentioned. The partial constriction of large coro- lowering levels below 100 mg/dL. For most people, re- nary arterioles and most arteries by norepinephrine ap- ductions in LDL below 120 mg/dL are not attainable with pears to limit the retrograde flow of blood during diet and exercise. In those persons, drugs, known as ventricular systole and, in doing so, prevents part of the statins, which block the formation of cholesterol in the decreased flow in the deep layers of the heart wall. In ef- liver, appear to be highly effective in decreasing the risk fect, the body trades a small decrease in flow, relative to and severity of coronary artery disease. Simultaneous CHAPTER 17 Special Circulations 279 treatment with an aerobic exercise program and large CEREBRAL CIRCULATION amounts of niacin, to increase high-density lipoproteins The ultimate organ of life is the brain. Even the determina- (HDLs), may help the body remove cholesterol for pro- tion of death often depends upon whether or not the brain cessing in the liver. The most common cause of brain injury is some form of impaired brain blood flow. Such problems can de- Collateral Vessels Interconnect Sections velop as a result of accidents to arteries in the neck or brain, of the Cardiac Microvasculature occlusion of vessels secondary to atherosclerotic processes, and, surprisingly frequently, aneurysms that occur as a re- One of the likely contributing factors to compensate for sult of vessel wall tearing. Fortunately, treatment of these slowly developing coronary vascular disease is the enlarge- problems is constantly improving. In the healthy heart of a sedentary person, collateral arterial Brain Blood Flow Is Virtually Constant vessels are rare, but arteriolar collaterals (internal diameter, Despite Changes in Arterial Blood Pressure 100 m) do occur in small numbers.

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