The lungs and the kidneys are largely responsible for regulating the acid-base balance of the blood (see Chapter 28 ). They do so by independently controlling the two major components of the body's major buffering system: CO 2 and ( Fig. 39-1 ). Chapter 31 focuses on how the lungs control plasma [CO 2 ]. In this chapter we see how the kidneys control plasma […
Water Balance and the Overall Renal Handling of Water The kidney can generate a urine as dilute as 40 mOsm (one seventh of plasma osmolality) or as concentrated as 1200 mOsm (four times plasma osmolality) In the steady state, water intake and output must be equal ( Table 38-1 ). The body's three major sources of water are (1) ingested water, (2) water contained in the foods eaten,…
Potassium Balance and the Overall Renal Handling of Potassium Changes in K + concentrations can have major effects on cell and organ function The distribution of K + in the body differs strikingly from that of Na + . Whereas Na + is largely extracellular, K + is the most abundant intracellular cation. Some 98% of the total-body K + content (~50 mmol/kg body weight) is inside…
The kidney plays a central role in controlling the plasma levels of a wide range of solutes that are present at low concentrations in the body. The renal excretion of a solute depends on three processes—filtration, reabsorption, and secretion (see pp. 732–733 ). The kidney filters and then totally reabsorbs some of the substances we discuss in this chapter (e.g., glucose). Others, it filters and also…
The kidneys help to maintain the body's extracellular fluid (ECF) volume by regulating the amount of Na + in the urine. Sodium salts (predominantly NaCl) are the most important contributor to the osmolality of the ECF; hence, where Na + goes, water follows. This chapter focuses on how the kidneys maintain the ECF volume by regulating excretion of Na + and its most prevalent anion, Cl…
Glomerular Filtration A high glomerular filtration rate is essential for maintaining stable and optimal extracellular levels of solutes and water Qualitatively, the filtration of blood plasma by the renal glomeruli is the same as the filtration of blood plasma across capillaries in other vascular beds (see pp. 467–468 ). Glomerular ultrafiltration results in the formation of a fluid—the glomerular filtrate —with solute concentrations that are similar…
The kidneys serve three essential functions. First, they act as filters, removing metabolic products and toxins from the blood and excreting them through the urine. Second, they regulate the body's fluid status, electrolyte balance, and acid-base balance. Third, the kidneys produce or activate hormones that are involved in erythrogenesis, Ca 2+ metabolism, and the regulation of blood pressure and blood flow. Functional Anatomy of the Kidney…
Overview of the Respiratory Control System Breathing is one of those things in life that you almost never think about until something goes wrong with it. However, those with pulmonary disease become intensely aware of breathing, as do people who overexert themselves, especially at high altitude. The feeling of dyspnea that they experience (see p. 701 ) is one of the most unpleasant sensations in life…
Although diffusion is at the very heart of the gas exchange, as we discussed in Chapter 30 , two other parameters are also extremely important. Ventilation and perfusion—both of which require energy—are critical because they set up the partial-pressure gradients along which O 2 and CO 2 diffuse. Ventilation is the convective movement of air that exchanges gases between the atmosphere and the alveoli. In Chapter…
The complex anatomy of the pulmonary tree, the mechanics of the respiratory system, and the sophisticated carriage mechanisms for O 2 and CO 2 combine to serve two essential purposes: the ready diffusion of O 2 from the alveoli to the pulmonary-capillary blood, and the movement of CO 2 in the opposite direction. In this chapter, we consider principles that govern these diffusive events and factors…
Carriage of O 2 The amount of O 2 dissolved in blood is far too small to meet the metabolic demands of the body Blood carries oxygen in two forms. More than 98% of the O 2 normally binds to hemoglobin within the erythrocytes, also known as red blood cells or RBCs (see pp. 434–435 ). A tiny fraction physically dissolves in the aqueous phases of…
Acid-base physiology is really the study of the proton, or hydrogen ion (H + ). Although they are present in exceedingly low concentrations in most intracellular and extracellular fluids, protons nevertheless have a major impact on biochemical reactions and on a variety of physiological processes that are critical for the homeostasis of the entire body and individual cells. Not surprisingly, the body has evolved sophisticated systems…
The field of pulmonary mechanics —the physics of the lungs, airways, and chest wall—deals with how the body moves air in and out of the lungs, producing a change in lung volume (V L ). When we examine these mechanical properties while no air is flowing, we are studying static properties. The situation becomes more complicated under dynamic conditions, when the lungs are changing volume and…
Comparative Physiology of Respiration External respiration is the exchange of O 2 and CO 2 between the atmosphere and the mitochondria For millennia, people have regarded breathing as being synonymous with life. Life begins and ends with breathing. The Bible states that God “breathed into [Adam's] nostrils the breath of life” and then later used part of Adam's ventilatory apparatus—a rib—to give life to Eve. In…
In the preceding chapters, we examined cardiovascular regulation at several different levels. Powerful systemic mechanisms operate over both the short term and the long term to control mean arterial pressure and cardiac output. Operating independently of these are local mechanisms of control that regulate blood flow at the microcirculatory level. In addition, individual organs have their own unique tools for managing specific circulatory requirements. In this…
In the preceding chapters, we considered blood flow to peripheral capillary beds as if the “periphery” were a single entity. In this chapter, we break that entity down into some of its component parts. Because each organ in the body has its own unique set of requirements, special circulations within each organ have evolved with their own particular features and regulatory mechanisms. Especially for times of…
When faced with a patient who appears seriously ill, clinicians focus their immediate attention on the patient's vital signs: temperature, respiratory rate, pulse, and blood pressure. These parameters are aptly named vital because they reflect the most fundamental aspects of health and even survival; a significant abnormality in any of these components indicates that emergent care is required. In this chapter, we focus on blood pressure,…
The Cardiac Cycle The sequence of mechanical and electrical events that repeats with every heartbeat is called the cardiac cycle. The duration of the cardiac cycle is the reciprocal of the heart rate: For example, for a heart rate of 75 beats/min, the cardiac cycle lasts 0.8 s or 800 ms. The closing and opening of the cardiac valves define four phases of the cardiac cycle The cardiac…
Different cardiac cells serve different and very specialized functions, but all are electrically active. The heart's electrical signal normally originates in a group of cells high in the right atrium that depolarize spontaneously; it then spreads throughout the heart from cell to cell ( Fig. 21-1 ). As this action potential propagates through the heart—sometimes carried by cells that form specialized conducting pathways and sometimes by…
The microcirculation serves both nutritional and non-nutritional roles The primary function of the cardiovascular system is to maintain a suitable environment for the tissues. The microcirculation is the “business end” of the system. The capillary is the principal site for exchange of gases, water, nutrients, and waste products. In most tissues, capillary flow exclusively serves these nutritional needs. In a few tissues, however, a large portion…