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…

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,…