tailieunhanh - Ebook Ganong’s review of medical physiology (23/E): Part 2

Part 2 book ““Ganong’s review of medical physiology” has contents: Gastrointestinal physiology, cardiovascular physiology, respiratory physiology, renal physiology. Invite reference you. | SECTION V GASTROINTESTINAL PHYSIOLOGY Overview of Gastrointestinal Function & Regulation 26 C H A P T E R O B JE C TIVE S After studying this chapter, you should be able to: ■ ■ ■ ■ ■ ■ Understand the functional significance of the gastrointestinal system, and in particular, its roles in nutrient assimilation, excretion, and immunity. Describe the structure of the gastrointestinal tract, the glands that drain into it, and its subdivision into functional segments. List the major gastrointestinal secretions, their components, and the stimuli that regulate their production. Describe water balance in the gastrointestinal tract and explain how the level of luminal fluidity is adjusted to allow for digestion and absorption. Identify the major hormones, other peptides, and key neurotransmitters of the gastrointestinal system. Describe the special features of the enteric nervous system and the splanchnic circulation. INTRODUCTION The gastrointestinal tract is a continuous tube that stretches from the mouth to the anus. Its primary function is to serve as a portal whereby nutrients and water can be absorbed into the body. In fulfilling this function, the meal is mixed with a variety of secretions that arise from both the gastrointestinal tract itself and organs that drain into it, such as the pancreas, gallbladder, and salivary glands. Likewise, the intestine displays a variety of motility patterns that serve to mix the meal with digestive secretions and move it along the length of the gastrointestinal tract. Ultimately, residues of the meal that cannot be absorbed, along with cellular debris and lipid-soluble metabolic end products that are excreted in the bile rather than the urine, are expelled from the body. All of these functions are tightly regulated in concert with the ingestion of meals. Thus, the gastrointestinal system has evolved a large number of regulatory mechanisms that act both locally and to coordinate the function of the gut, and the organs that