After the alveoli are ventilated with fresh air, the next step in respiration is diffusion of oxygen (O 2 ) from the alveoli into the pulmonary blood and diffusion of carbon dioxide (CO 2 ) in the opposite direction, out of the blood into the alveoli. The process of diffusion is simply the random motion of molecules in all directions through the respiratory membrane and adjacent…

The lung has two circulations, a high-pressure, low-flow circulation and a low-pressure, high-flow circulation . The high-pressure, low-flow circulation supplies systemic arterial blood to the trachea, bronchial tree (including the terminal bronchioles), supporting tissues of the lung, and outer coats (adventitia) of the pulmonary arteries and veins. The bronchial arteries , which are branches of the thoracic aorta, supply most of this systemic arterial blood at…

The main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide. The four major components of respiration are the following: (1) pulmonary ventilation , which means the inflow and outflow of air between the atmosphere and the lung alveoli; (2) diffusion of oxygen (O 2 ) and carbon dioxide (CO 2 ) between the alveoli and the blood ; (3) transport…

Hemostasis Events The term hemostasis means prevention of blood loss. Whenever a vessel is severed or ruptured, hemostasis is achieved by several mechanisms: (1) vascular constriction; (2) formation of a platelet plug; (3) formation of a blood clot as a result of blood coagulation; and (4) eventual growth of fibrous tissue into the blood clot to close the hole in the vessel permanently. Vascular Constriction Immediately…

Antigenicity Causes Immune Reactions of Blood When blood transfusions from one person to another were first attempted, immediate or delayed agglutination and hemolysis of the red blood cells (RBCs) often occurred, resulting in typical transfusion reactions that frequently led to death. Soon it was discovered that the blood types of different people have different antigenic and immune properties so that antibodies in the plasma of one…

The human body has the ability to resist almost all types of organisms or toxins that tend to damage the tissues and organs. This capability is called immunity . Much of the immunity is acquired immunity that does not develop until after the body is first attacked by a bacterium, virus, or toxin; often, weeks or months are required for the immunity to develop. An additional…

Our bodies are exposed continually to bacteria, viruses, fungi, and parasites, all of which occur normally and to varying degrees in the skin, mouth, respiratory passageways, intestinal tract, lining membranes of the eyes, and even the urinary tract. Many of these infectious agents are capable of causing serious abnormal physiological function or even death if they invade deeper tissues. We are also exposed intermittently to other…

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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)…