The physiology of calcium and phosphate metabolism, formation of bone and teeth, and regulation of vitamin D, parathyroid hormone (PTH), and calcitonin are all closely intertwined. The extracellular calcium ion concentration, for example, is determined by the interplay of calcium absorption from the intestine, renal excretion of calcium, and bone uptake and release of calcium, each of which is regulated by the hormones just noted. Because…

The pancreas, in addition to its digestive functions, secretes two major hormones, insulin and glucagon , that are crucial for normal regulation of glucose, lipid, and protein metabolism. Although the pancreas secretes other hormones, such as amylin, somatostatin, and pancreatic polypeptide, their functions are not as well established. The main purpose of this chapter is to discuss the physiological roles of insulin and glucagon and the…

The two adrenal glands, each of which weighs about 4 grams, lie at the superior poles of the two kidneys. As shown in Figure 78-1 , each gland is composed of two major parts, the adrenal medulla and the adrenal cortex. The adrenal medulla, the central 20% of the gland, is functionally related to the sympathetic nervous system; it secretes the hormones epinephrine and norepinephrine in…

The thyroid gland, located immediately below the larynx on each side of and anterior to the trachea, is one of the largest of the endocrine glands, normally weighing 15 to 20 grams in adults. The thyroid secretes two major metabolic hormones, thyroxine and triiodothyronine, commonly called T 4 and T 3 , respectively. Both of these hormones profoundly increase the metabolic rate of the body. Complete…

Pituitary Gland and its Relation to the Hypothalamus Anterior and Posterior Lobes of The Pituitary Gland The pituitary gland ( Figure 76-1 ), also called the hypophysis, is a small gland—about 1 centimeter in diameter and 0.5 to 1 gram in weight—that lies in the sella turcica, a bony cavity at the base of the skull—and is connected to the hypothalamus by the pituitary (or hypophysial…

Coordination of Body Functions by Chemical Messengers The multiple activities of the cells, tissues, and organs of the body are coordinated by the interplay of several types of chemical messenger systems: 1. Neurotransmitters are released by axon terminals of neurons into the synaptic junctions and act locally to control nerve cell functions. 2. Endocrine hormones are released by glands or specialized cells into the circulating blood…

Normal Body Temperatures Body Core Temperature and Skin Temperature The temperature of the deep tissues of the body—the “core” of the body—usually remains very constant, within ±1°F (±0.6°C), except when a person has a febrile illness. Indeed, a nude person can be exposed to temperatures as low as 55°F or as high as 130°F in dry air and still maintain an almost constant core temperature. The…

Adenosine Triphosphate Functions as an “Energy Currency” in Metabolism Carbohydrates, fats, and proteins can all be used by cells to synthesize large quantities of adenosine triphosphate (ATP), which is used as an energy source for almost all other cellular functions. For this reason, ATP has been called an energy “currency” in cell metabolism. Indeed, the transfer of energy from foodstuffs to most functional systems of the…

Energy Intake And Output are Balanced Under Steady-State Conditions Proteins, carbohydrates, and fats in the diet provide energy for various body functions or for storage and later use. Stability of body weight and composition over long periods requires that a person’s energy intake and energy expenditure be balanced. When a person is overfed, and energy intake persistently exceeds expenditure, most of the excess energy is stored…

Although the liver is a discrete organ, it performs many different interrelating functions. The critical interrelated functions of the liver become especially evident when abnormalities of the liver occur. This chapter summarizes some of the major functions of the liver, including the following: (1) filtration and storage of blood; (2) metabolism of carbohydrates, proteins, fats, hormones, and foreign chemicals; (3) formation of bile; (4) storage of…

About three-quarters of the body solids are proteins. These proteins include structural proteins, enzymes, nucleoproteins, proteins that transport oxygen, proteins of the muscle that cause muscle contraction, and many other types that perform specific intracellular and extracellular functions throughout the body. The basic chemical properties that explain the diverse functions of proteins are so extensive that they constitute a major portion of the entire discipline of…

Several chemical compounds in food and in the body are classified as lipids, including the following: (1) neutral fat , also known as triglycerides; (2) phospholipids; (3) cholesterol; and (4) a few others of less importance. Chemically, the basic lipid moiety of triglycerides and phospholipids is fatty acids , which are long-chain hydrocarbon organic acids. A typical fatty acid, palmitic acid, is the following: CH 3…

The next few chapters deal with metabolism in the body—the chemical processes that make it possible for the cells to continue living. It is not the purpose of this text to present the chemical details of all the various cellular reactions, which lie in the discipline of biochemistry. Instead, these chapters are devoted to (1) a review of the principal chemical processes of the cell and…

Effective therapy for most gastrointestinal disorders depends on a basic knowledge of gastrointestinal physiology. The purpose of this chapter is to discuss a few representative types of gastrointestinal malfunction that have special physiological bases or consequences. Disorders of Swallowing and the Esophagus Paralysis of the Swallowing Mechanism Damage to the fifth, ninth, or tenth cerebral nerve can cause paralysis of significant portions of the swallowing mechanism.…

The major foods on which the body lives (with the exception of small quantities of substances such as vitamins and minerals) are carbohydrates, fats, and proteins. They generally cannot be absorbed in their natural forms through the gastrointestinal mucosa, and for this reason, they are useless as nutrients without preliminary digestion. This chapter discusses the processes by which carbohydrates, fats, and proteins are digested into small…

Throughout the gastrointestinal tract, secretory glands subserve two primary functions: (1) digestive enzymes are secreted in most areas of the alimentary tract, from the mouth to the distal end of the ileum; and (2) mucous glands located from the mouth to the anus provide mucus for lubrication and protection of all parts of the alimentary tract. Most digestive secretions are formed in response to the presence…

The time that food remains in each part of the alimentary tract is critical for optimal processing and absorption of nutrients. In addition, appropriate mixing must be provided. Because the requirements for mixing and propulsion are quite different at each stage of processing, multiple automatic nervous and hormonal mechanisms control the timing of each of these activities so they will occur optimally—not too rapidly and not…

The alimentary tract provides the body with a continual supply of water, electrolytes, vitamins, and nutrients, which requires the following: (1) movement of food through the alimentary tract; (2) secretion of digestive juices and digestion of the food; (3) absorption of water, various electrolytes, vitamins, and digestive products; (4) circulation of blood through the gastrointestinal organs to carry away the absorbed substances; and (5) control of…

Thus far, we have discussed the function of the brain as if it were independent of its blood flow, its metabolism, and its fluids. However, this is far from true because abnormalities of any of these aspects can profoundly affect brain function. For example, total cessation of blood flow to the brain causes unconsciousness within 5 to 10 seconds because lack of oxygen (O 2 )…

The autonomic nervous system is the portion of the nervous system that controls most visceral functions of the body . This system helps to control arterial pressure, gastrointestinal motility, gastrointestinal secretion, urinary bladder emptying, sweating, body temperature, and many other activities. Some of these activities are controlled almost entirely and some only partially by the autonomic nervous system. One of the most striking characteristics of the…