You’re Reading a Preview Become a Clinical Tree membership for Full access and enjoy Unlimited articles Become membership If you are a member. Log in here

Diuretics and Their Mechanisms of Action Diuretics increase the rate of urine volume output, as the name implies. Most diuretics also increase the urinary excretion of solutes, especially sodium and chloride. In fact, most diuretics that are used clinically act by decreasing renal tubular sodium reabsorption, which causes natriuresis (increased sodium output), in turn causing diuresis (increased water output). That is, in most cases, increased water…

The regulation of hydrogen ion (H + ) balance is similar in some ways to the regulation of other ions in the body. For example, there must be a balance between the intake or production of H + and the net removal of H + from the body to achieve homeostasis. And, as is true for other ions, the kidneys play a key role in regulating…

Regulation of Extracellular Fluid Potassium Concentration and Potassium Excretion The extracellular fluid potassium concentration normally is regulated at about 4.2 mEq/L, seldom rising or falling more than ±0.3 mEq This precise control is necessary because many cell functions are sensitive to changes in extracellular fluid potassium concentration. For example, an increase in plasma potassium concentration of only 3 to 4 mEq/L can cause cardiac arrhythmias, and…

For the cells of the body to function properly, they must be bathed in extracellular fluid with a relatively constant concentration of electrolytes. The total concentration of solutes in the extracellular fluid—and therefore the osmolarity—must also be precisely regulated to prevent the cells from shrinking or swelling. The osmolarity is determined by the amount of solute (mainly sodium chloride) divided by the volume of the extracellular…

As the glomerular filtrate enters the renal tubules, it flows sequentially through the successive parts of the tubule—the proximal tubule, loop of Henle, distal tubule, collecting tubule, and collecting duct— before it is excreted as urine. Along this course, some substances are selectively reabsorbed from the tubules back into the blood, whereas others are secreted from the blood into the tubular lumen. Eventually, the urine that…

Glomerular Filtration—The First Step in Urine Formation The first step in urine formation is filtration of large amounts of fluid through the glomerular capillaries into Bowman’s capsule—almost 180 L Most of this filtrate is reabsorbed, leaving only about 1 liter of fluid to be excreted each day, although the renal fluid excretion rate is highly variable, depending on fluid intake. The high rate of glomerular filtration…

Multiple Functions of the Kidneys Most people are familiar with one important function of the kidneys—to rid the body of waste materials that are ingested or produced by metabolism. A second function that is especially critical is to control the volume and electrolyte composition of the body fluids. For water and virtually all electrolytes in the body, the balance between intake (due to ingestion or metabolic…

The maintenance of a relatively constant volume and stable composition of the body fluids is essential for homeostasis. Some of the most common and important problems in clinical medicine arise because of abnormalities in the control systems that maintain this relative constancy of the body fluids. In this chapter and in the following chapters on the kidneys, we discuss overall regulation of body fluid volume, constituents…

Circulatory shock means generalized inadequate blood flow through the body to the extent that the body tissues are damaged, especially because too little oxygen and other nutrients are delivered to the tissue cells. Even the cardiovascular system itself—the heart musculature, walls of the blood vessels, vasomotor system, and other circulatory parts—begins to deteriorate, so the shock, once begun, is prone to become progressively worse. Physiological Causes…

Function of the heart valves was discussed in Chapter 9 , where we pointed out that closing of the valves causes audible sounds. Ordinarily, no audible sounds occur when the valves open. In this chapter, we first discuss the factors that cause the sounds in the heart under normal and abnormal conditions. Then we discuss the overall circulatory changes that occur when valvular or congenital heart…

One of the most important ailments treated by the physician is cardiac failure (heart failure). This ailment can result from any heart condition that reduces the ability of the heart to pump enough blood to meet the body’s needs. The cause is often decreased contractility of the myocardium resulting from diminished coronary blood flow. However, cardiac failure can also be caused by damaged heart valves, external…

In this chapter we consider the following: (1) blood flow to the skeletal muscles; and (2) coronary artery blood flow to the heart. Regulation of each of these types of blood flow is achieved mainly by local control of vascular resistance in response to muscle tissue metabolic needs. We also discuss the physiology of related subjects, including the following: (1) cardiac output control during exercise; (2)…

Cardiac output is the quantity of blood pumped into the aorta each minute by the heart. This is also the quantity of blood that flows through the circulation. Because cardiac output is the sum of the blood flow to all the tissues of the body, it is one of the most important factors to consider in relation to function of the cardiovascular system. Venous return is…

In addition to the rapidly acting mechanisms for regulation of arterial pressure discussed in Chapter 18 , the body also has powerful mechanisms for regulating arterial pressure week after week and month after month. This long-term control of arterial pressure is closely intertwined with homeostasis of body fluid volume, which is determined by the balance between fluid intake and output. For long-term survival, fluid intake and…

Nervous Regulation of the Circulation As discussed in Chapter 17 , adjustment of blood flow in the tissues and organs of the body is mainly the function of local tissue control mechanisms. In this chapter, we discuss how nervous control of the circulation has more global functions, such as redistributing blood flow to different areas of the body, increasing or decreasing pumping activity by the heart,…

Local Control of Blood Flow in Response to Tissue Needs A fundamental principle of circulatory function is that most tissues have the ability to control their own local blood flow in proportion to their specific metabolic needs. Some of the specific needs of the tissues for blood flow include the following: 1. Delivery of oxygen to the tissues 2. Delivery of other nutrients such as glucose,…

The most purposeful functions of the microcirculation are the transport of nutrients to the tissues and removal of cell excreta . The small arterioles control blood flow to each tissue, and local conditions in the tissues, in turn, control the diameters of the arterioles. Thus, each tissue, in most cases, controls its own blood flow in relationship to its individual needs as discussed in Chapter 17…

Vascular Distensibility A valuable characteristic of the vascular system is that all blood vessels are distensible. The distensible nature of the arteries allows them to accommodate the pulsatile output of the heart and to average out the pressure pulsations. This capability provides smooth continuous flow of blood through the very small blood vessels of the tissues. The most distensible of all the vessels are the veins.…

The function of the circulation is to serve the needs of the body tissues—to transport nutrients to the tissues, to transport waste products away, transport hormones from one part of the body to another and, in general, to maintain an appropriate environment in all the tissue fluids for survival and optimal function of the cells. The rate of blood flow through many tissues is controlled mainly…