Some of the most distressing types of heart malfunction occur because of abnormal rhythm of the heart. For example, sometimes the beat of the atria is not coordinated with the beat of the ventricles, so the atria no longer function to optimize ventricular filling. The purpose of this chapter is to discuss the physiology of common cardiac arrhythmias and their effects on heart pumping, as well…

From the discussion in Chapter 10 of impulse transmission through the heart, it is obvious that any change in the pattern of this transmission can cause abnormal electrical potentials around the heart and, consequently, alter the shapes of the waves in the electrocardiogram (ECG). For this reason, most serious abnormalities of the heart muscle can be diagnosed by analyzing the contours of the waves in the…

When a cardiac impulse passes through the heart, electrical current also spreads from the heart into the adjacent tissues surrounding the heart. A small portion of the current spreads all the way to the surface of the body. If electrodes are placed on the skin on opposite sides of the heart, electrical potentials generated by the current can be recorded; the recording is known as an…

The human heart has a special system for rhythmic self-excitation and repetitive contraction approximately 100,000 times each day or 3 billion times in the average human lifetime. This impressive feat is performed by a system that does the following: (1) generates electrical impulses to initiate rhythmical contraction of the heart muscle; and (2) conducts these impulses rapidly through the heart. When this system functions normally, the…

The heart, shown in Figure 9-1 , is actually two separate pumps, a right heart that pumps blood through the lungs and a left heart that pumps blood through the systemic circulation that provides blood flow to the other organs and tissues of the body. Each of these is a pulsatile, two-chamber pump composed of an atrium and a ventricle. Each atrium is a weak primer…

Contraction of Smooth Muscle Smooth muscle is composed of small fibers that are usually 1 to 5 micrometers in diameter and only 20 to 500 micrometers in length. In contrast, skeletal muscle fibers are as much as 30 times greater in diameter and hundreds of times as long. Many of the same principles of contraction apply to smooth muscle as to skeletal muscle. Most important, essentially…

Neuromuscular Junction and Transmission of Impulses from Nerve Endings to Skeletal Muscle Fibers Skeletal muscle fibers are innervated by large myelinated nerve fibers that originate from large motoneurons in the anterior horns of the spinal cord. As discussed in Chapter 6 , each nerve fiber, after entering the muscle belly, normally branches and stimulates from three to several hundred skeletal muscle fibers. Each nerve ending makes…

About 40% of the body is skeletal muscle, and perhaps another 10% is smooth and cardiac muscle. Some of the same basic principles of contraction apply to all these muscle types. In this chapter, we mainly consider skeletal muscle function; the specialized functions of smooth muscle are discussed in Chapter 8 , and cardiac muscle is discussed in Chapter 9 . Physiological Anatomy of Skeletal Muscle…

Electrical potentials exist across the membranes of virtually all cells of the body. Some cells, such as nerve and muscle cells, generate rapidly changing electrochemical impulses at their membranes, and these impulses are used to transmit signals along the nerve or muscle membranes. In other types of cells, such as glandular cells, macrophages, and ciliated cells, local changes in membrane potentials also activate many of the…

Figure 4-1 lists the approximate concentrations of important electrolytes and other substances in the extracellular fluid and intracellular fluid. Note that the extracellular fluid contains a large amount of sodium but only a small amount of potassium. The opposite is true of the intracellular fluid. Also, the extracellular fluid contains a large amount of chloride ions, whereas the intracellular fluid contains very little of these ions.…

Genes, which are located in the nuclei of all cells of the body, control heredity from parents to children, as well as the daily functioning of all the body’s cells. The genes control cell function by determining which structures, enzymes, and chemicals are synthesized within the cell. Figure 3-1 shows the general schema of genetic control. Each gene, which is composed of deoxyribonucleic acid (DNA), controls…

Each of the trillions of cells in a human being is a living structure that can survive for months or years, provided its surrounding fluids contain appropriate nutrients. Cells are the building blocks of the body, providing structure for the body’s tissues and organs, ingesting nutrients and converting them to energy, and performing specialized functions. Cells also contain the body’s hereditary code, which controls the substances…

Physiology is the science that seeks to explain the physical and chemical mechanisms that are responsible for the origin, development, and progression of life. Each type of life, from the simplest virus to the largest tree or the complicated human being, has its own functional characteristics. Therefore, the vast field of physiology can be divided into viral physiology, bacterial physiology, cellular physiology, plant physiology, invertebrate physiology,…